# Tracer Summit User’s Group 5/22/2012

## Presentation on theme: "Tracer Summit User’s Group 5/22/2012"— Presentation transcript:

Tracer Summit User’s Group 5/22/2012
[LEE] Okay, Don. Thanks for that physics review. We’ll refer to it more than once to make sure we’re not breaking these laws as we discuss drive applications. The first application of a drive we will examine will be for a “free discharge” fan. The example we’ll use for this type of fan is a draw through cooling tower. Another example of a system with free discharge fans is fan coil units Later Don will come back and discuss different types of fans and their control characteristics. VSDs and their effect on HVAC system components

e = mc² speed of light 299,792,458 m/s water 2 m/s air 10–20 m/s [SLIDE] This famous formula reminds us energy is proportional to velocity squared. [CLICK] The speed of light is slightly less than 300 million meters per second. In our field, we move things a little slower. [CLICK] As plumbers we pump water at a snail’s pace of about 2 meters per second. [CLICK] When it comes to moving air we step on the accelerator a little and race around the duct work at speeds approaching 20 meters per second. © 2006 American Standard Inc.

500,000 lbs/hr air [SLIDE] While we don’t move air and water with great velocity, we do move large quantities of air and large quantities water. Consider this cooling tower serving a 600 ton chiller; In one hour it moves half a million pounds of air and receives 600,000 pounds of water. Some want to pump even more! [DON] The science of air-conditioning is the art of designing air distribution systems and water distribution systems to move massive amounts of air and water with as little energy as possible. It is appropriate that we investigate methods of providing comfort with smaller indoor fans, smaller cooling tower fans, and smaller pumps for both chilled water and cooling water. We can also improve system efficiency by exploiting load diversity to greatest extent possible. At times when the air-conditioning load is less we should move less air. When cooling loads are less we should move less water. When ambient wet-bulb temperature is lower, we should move less air through the cooling tower; variable air volume, variable primary flow of chilled water, and chiller/tower optimization are clear examples of reducing mass flow to match the current need. All of these energy saving techniques require some means of reducing flow. Variable frequency drives are prime candidates for this assignment. 600,000 lbs/hr water © 2006 American Standard Inc.

work = mass × resistance [SLIDE] The work of a fan, pump, compressor, or any device to move mass is a function of how much mass is moved and and how hard we have to push to move that mass, or resistance. [DON] Remember, our primary task is to air-condition the space or cool the process. Moving air and pumping water is method of transporting the heat we wish to remove. Of course we hope each unit of mass carries as much heat as possible. This is accomplished by increasing the temperature rise of air and water. Two Engineers Newsletters, “Cold Air Makes Good Cents” and “How Low-flow Systems Can Help You Give Your Customers What They Want,” are included in the bibliography. © 2006 American Standard Inc.

Darcy-Weisbach Equation
path diameter path length velocity fluid density L r V² D 2 gc Dp = f friction factor gravitational constant [SLIDE] So how do we measure this resistance? Sometimes engineering is the feat of making the simple seem complex. This is the Darcy-Weisbach equation that quantifies the resistance to flow measured in units of pressure. It looks complicated, but that’s only because the versatility of this equation. It works for any “well behaved” fluid, including air and water. [CLICK] It also works any place. For example as soon as we know what planet we’re on we know the gravitational constant gc. [CLICK] When we know the roughness of the pipe and the viscosity of the fluid we can determine the friction factor. [CLICK] Knowing the fluid, we know the density of what we wish to move. [CLICK] And to make the fluid go where we want it to go, we need a pathway, duct work for air and pipe for water. Once the air distribution system or water distribution system is defined we know length and diameter of the conduit. [CLICK] The only variable left is velocity.

Darcy-Weisbach Equation
resistance a velocity² [SLIDE] Resistance is proportional to velocity squared.

System Resistance return duct dampers supply duct
[DON] Now that the resistance, or static-pressure loss, we must overcome to move a given quantity of air through the air distribution system can be determined, [SLIDE] Let’s turn our attention to the device that moves the air … the fan. diffusers and grilles coil

cfm a rpm Dp a rpm² a cfm² hp a rpm³ Fan Laws
Fans obey a list of rules we call “Fan Laws.” [CLICK] First rule. The faster we shovel, the more stuff we move. The volume of air moved is proportional to rotational fan speed, or revolutions per minute. [CLICK] Second rule. Pump head or fan static is proportional to rpm squared. [CLICK] If cfm and rpm are proportional, this means static pressure produced by the fan is proportional to the velocity of air moved by the fan squared. Note how this matches the resistance to velocity predicted by the Darcy-Weisbach equation which reminds us resistance is also proportional to velocity squared. How fortuitous, we should find a way to exploit this. [CLICK] And it gets even better. Third rule. The energy required to move air or pump water is proportional to rpm cubed. [DON] Everybody wants to save energy. The fan laws also apply to pumps. Fan laws, pump laws, or affinity laws as we sometimes call them; are different names for the same set of relationships.

resistance a velocity²
Chiller Laws? resistance a velocity² [DON] How come we don’t have chiller laws? Chillers do have to obey the same rules of physics. [SLIDE] However, in a refrigeration system resistance to mass flow is not a function of refrigerant velocity. The resistance a compressor must work against is the pressure difference between condenser pressure and evaporator pressure. [CLICK] We call this pressure difference lift. Ryan will will tell us more about lift and compressor work later in the broadcast. [DON, LEE] Lee, how about applying these fan laws to cooling tower fans? resistance a “lift”

Practical Application: Free Discharge Fans
[LEE] Okay, Don. Thanks for that physics review. We’ll refer to it more than once to make sure we’re not breaking these laws as we discuss drive applications. The first application of a drive we will examine will be for a “free discharge” fan. The example we’ll use for this type of fan is a draw through cooling tower. Another example of a system with free discharge fans is fan coil units Later Don will come back and discuss different types of fans and their control characteristics. VSDs and their effect on system components

Free Discharge System Draw-through cooling tower Propeller fan
louvers I’m sure most of you are familiar with a draw through cooling tower. [SLIDE] The one shown here uses a propeller type fan mounted on the top which pulls air through the tower louvers, fill and falling water. The tower cooling effect is caused by the evaporation of some fraction of the water as it falls from the distribution pans on the top to the collection sump at the bottom. [LEE] For the purpose of exploring the performance of a free discharge fan system we are going to ignore the impact of changes in air density at different tower loads. So, what do the fan laws tell us about the performance of this system? outdoor air fill sump

General Fan Performance
cfm a rpm Dp a rpm² hp a rpm³ [SLIDE] As Don discussed, the total pressure the fan must work against at various loads is related to approximately the square of the airflow rate. But this is really only true for free discharge fan systems.

system performance Static Pressure
100 system resistance 80 60 static pressure, % 40 friction pressure [SLIDE] Many fan system applications require a fixed static pressure component, as shown on this system/pressure flow diagram. [CLICK] This actually pushes the system curve up and causes a deviation from the fan law prediction. [LEE] But we’ll let Don worry about the effect of this. 20 fixed pressure 20 40 60 80 100 airflow, %

system performance Free Discharge System
100 80 60 system resistance static pressure, % 40 The good news with a cooling tower is that there is no fixed static pressure component. So the fan law equation describes the system performance pretty well. [SLIDE] For our purposes this will be the definition of a Free Discharge System—one in which the static pressure component is equal to zero. The result is that the system curve intersects the chart’s origin, and the pressure rises per the square of the flow to the system design point. Now that we understand the system curve, we need to look at the fan curve for a propeller-type fan and see how it interacts with the system curve. 20 20 40 60 80 100 airflow, %

fan performance curves Fan Speed (N)
100 80 N2 60 N1 static pressure, % 40 [SLIDE] The basic fan curve at a specific speed might look similar to this. It rises somewhat from the blocked tight, no flow condition, then at higher flows falls to the final design volume and pressure. [CLICK] When you slow the fan speed, the whole curve shifts downward. At a given static pressure—at a lower speed—the fan moves less volume. [LEE] What about the fan’s mechanical efficiency at different loads and speeds? As fan speed varies … 20 so does airflow volume 20 40 60 80 100 airflow, %

fan performance curves Speed N vs. Efficiency h
100 h2 80 h1 N2 60 h2' N1 static pressure, % h1' 40 If you were to draw lines of equal fan mechanical efficiency between the different speed curves, they would lay in something like this. [SLIDE] The exact efficiency curves are dependent on the fan design. The important question we must answer is how does all of this interact with the system curve? Let’s add the system curve back and see what observations we can make. 20 20 40 60 80 100 airflow, %

performance curves Fan and System
100 80 h1 N2 60 N1 static pressure, % h1' 40 [SLIDE] When we add the free-discharge system curve, we see one characteristic that makes it a great application for variable speed capacity control. The system curve typically tracks relatively closely to the fan constant efficiency lines. [LEE] So if an efficient fan is chosen at design conditions, it will maintain its mechanical efficiency as the capacity is reduced via speed reduction. 20 20 40 60 80 100 airflow, %

fan performance curves Cooling Tower
100 80 60 fan power, % 40 Let’s look at some fan energy curves using a few different capacity control methods. [SLIDE] If the towers capacity is modulated by varying the fan speed so that the fan curve tracks the system curve, the fan’s energy use would follow this orange curve. The fan energy use is proportional to approximately the “cube of the speed.” How else might the airflow be modulated? 20 20 40 60 80 100 airflow, %

fan performance curves Cooling Tower
100 1-speed motor 80 60 fan and motor power, % 40 potential energy savings [SLIDE] Simple on/off control could be used to achieve an AVERAGE fan volume based on the time weighted average of full on and full off airflow. In this case the theoretical fan energy use would follow a straight line between the full on and off energy values. It’s obvious that at any fan airflow other than zero and 100 percent this control strategy’s energy use is significantly greater than that for variable speed. [CLICK] The area between the orange curve and the black line represents the potential energy savings between the two forms of control. 20 20 40 60 80 100 airflow, %

fan performance curves Cooling Tower
100 80 1-speed motor 60 fan and motor power, % 40 2- speed motor [SLIDE] The other historically common method for varying cooling tower fan capacity is the application of a two-speed motor, or two different motors, a large motor for design conditions and a smaller pony motor that operates at a lower speed. In this application, the fan cycles between high, medium and off. The energy used in achieving a specific AVERAGE fan volume is based on the time weighted average of the run time at these three speeds. [LEE] It’s really interesting that just by using a two-speed fan, you can come VERY close to achieving the fan energy of variable speed control. However this comes at the cost and complexity of a two-speed motor or two motors and the accompanying electrical switch gear. In the past the cost of the motor and switch gear was less than the cost of a VFD. But with the continued drop in the cost of VFDs, we understand that in a number of cases VFD cost is the same or even less than a two-speed motor and switch gear. 20 20 40 60 80 100 airflow, %

fan performance curves Cooling Tower
100 80 VSD 60 fan and motor power, % 40 So let’s talk about the VFD application. The FAN energy drops with the cube of the speed. But what does the customer’s utility meter see? [SLIDE] If we plot the electrical energy use of the tower fan MOTOR we see that it tracks above the fan energy curve. The motor and VFD efficiency ratings must applied to get the actual electrical energy used. Depending on the motor and VFD selected this would be between 3-6% at full load and greater at part load. [LEE] What does this all mean in terms of actual energy savings? 20 20 40 60 80 100 airflow, %

cooling tower application Fan Energy Comparison
Control strategy Energy use factor 1-speed fan cycling (base) 100% kWh 2-speed fan cycling 39% kWh Here’s an example that tells it all. [SLIDE] When controlling a cooling tower to a fixed setpoint, a two speed motor draws less than half of a single-speed application. A VFD application could save close to 80 percent. Both very impressive percentages. variable-speed control 19% kWh source: Marley Technical Report H-001A

fan/tower performance curves Free Cooling at Low Load
100 100 tower capacity 80 80 60 60 fan and motor power, % tower capacity, % 40 40 [SLIDE] There is some other good news when it comes to draw-thru cooling tower operation. It has nothing to do with fan operation and results in significant “free cooling.” Because of its open construction, a draw-thru cooling tower can provide between 5 and 15 percent of its rated capacity with its fan off. Therefore, at low system loads the tower can provide true free cooling! [LEE] This is good news no matter what type of fan modulation you use. It’s one of the few times you get something for nothing—as long as you ignore the condenser water pump energy, anyway. 20 20 “free” cooling 20 40 60 80 100 airflow, %

free discharge fans Summary
Performance approximates the “cube of the speed” Variable-speed drives (VSDs) are a great option for modulating capacity When considering VSDs for chilled water plants, start at the cooling tower [LEE] As we’ve seen in this discussion free discharge fan applications benefit greatly from variable speed control. [SLIDE] With little or no fixed static pressure they can take full advantage of the fan law relationships. We’re often asked if variable speed drives should be applied in building HVAC systems. When it comes to cooling tower control I would suggest the answer is a resounding - YES - almost always. [LEE & DON] Don, I got the easy fan type. How about you do some hard work and discuss the operation of other fan applications?

Practical Application: Ducted Indoor Fans
[HIDDEN SLIDE] VSDs and their effect on system components

System Resistance 3,500 cfm 2.0 in. wg static pressure airflow
[DON] Let’s turn our attention to an indoor fan and associated duct work to deliver the air. [SLIDE] Assume that a system is designed to deliver 3,500 cfm and that to overcome the system pressure losses, the fan must generate 2.0 in. of water static pressure. airflow

L r V² Dp = f D 2 gc System Resistance
[SLIDE] The Darcy-Weisbach equation tells us the static-pressure loss varies with the square of airflow.

system resistance curve
3,500 cfm 2.0 in. wg system resistance curve static pressure This system resistance curve represents the static pressure that the fan must generate, at various airflows, to overcome the resistance—or static-pressure loss—within this particular system. This curve is true only if all elements of the duct system obey the Darcy- Weisbach equation. [DON] We have found devices in the air distribution system that don’t follow Darcy- Weisbach. 2,000 cfm 0.65 in. wg airflow

some devices don’t obey the rules for System Resistance
Valves. Actually valves seems to do just the opposite of Darcy-Weisbach. [SLIDE] Air valves and water valves appear to produce the highest pressure loss when flow is low and produce a lower pressure drop when mass flow is high. Valves are the devices we employ to regulate mass flow. [DON] Valves regulate mass flow consuming energy … energy produced by the fan or pump.

system resistance curve
valves closed valves open system resistance curve static pressure [SLIDE] Air valves in a VAV system and water valves in a variable primary system alter the system resistance curve by creating more or less resistance to mass flow. airflow

VAV System system resistance actual design surge region
static pressure modulation range [SLIDE] This modulation causes the actual system resistance curve to shift. In a VAV system, therefore, the fan no longer operates at a single point on its performance curve but must operate over a range of such points. airflow

Fan Performance 1,100 rpm blocked-tight static pressure
[DON] Fans create the pressure necessary to overcome resistance to flow imposed by ductwork. The geometry of the fan will influence fan efficiency as well as the relationship between airflow, static pressure, and power. [SLIDE] For example, many of you in the audience recognize this curve as typical of a forward curved fan. This curve graphically illustrates the performance of this fan when it is operated at a constant speed. The curve extends from blocked-tight static pressure, with a corresponding zero airflow, to wide-open airflow, with a corresponding zero static pressure. wide-open airflow airflow

Fan Speed static pressure 1100 rpm 900 rpm 700 rpm 500 rpm airflow
[DON] The fan laws predict performance characteristics of the fan at other rotational speeds. Air flow is proportional to rpm and static pressure is proportional to rpm squared. [SLIDE] The result is a family of curves that represent airflow capacity and static pressure at various fan speeds. 700 rpm 500 rpm airflow

VAV System system resistance static pressure 1100 rpm 900 rpm 700 rpm
[SLIDE] The fan is compelled to obey the fan laws. Resistance imposed by ductwork is predicted by the system resistance curve. Fan and ductwork both operate at the same point: That point where the system curve and fan curve intersect. [DON] But variable air volume is a dynamic system, with an ever changing system resistance curve, and a large family of fan curves at various speeds. 700 rpm 500 rpm fan speed airflow

VAV System System resistance changes as valves modulate … T T
In a VAV system, the quantity of air being delivered to each space is controlled by an air valve. [SLIDE] This device is controlled by a thermostat to provide only the quantity of conditioned air needed to balance the space load. [CLICK] As the air valves modulate, the overall system resistance changes as well as the desired air flow. [DON] We need some type control system to alter the cfm moved by the fan as well as changing the static pressure produced by the fan. air valves 900 cfm 500 cfm T T

comparison of methods Fan Modulation
100 1 BI fan with discharge dampers 80 1 2 AF fan with inlet vanes 60 2 3 FC fan with discharge dampers 40 4 FC fan with inlet vanes design power, % 3 [SLIDE] These curves describe the performance characteristics of various methods of fan capacity control. Many methods of fan control have been employed. Fan speed control can be applied to any fan type and practically all fan applications. [DON] What is it we want the fan modulation system to do? Is it more than just save energy? 4 5 fan-speed control 20 5 vaneaxial fan with variable-pitch blades 6 6 20 40 60 80 100 design airflow, %

fan modulation Objectives
Produce adequate static pressure Eliminate excess static pressure Exploit diversity Maximize energy savings at fan Provide stable control Keep everyone comfortable [DON] There are a number of assignments given to a capable fan capacity control system. [SLIDE] First, the capacity control system must keep fan static pressure within the desired range; but we also want the control to be stable, we want to save a lot of energy, and of course we want everyone to be comfortable.

Static Pressure Control
Insufficient static pressure? [DON] When the static pressure upstream of the air valve, or damper, is too low the VAV unit is unable to delivered the desired airflow. [SLIDE] Comfortable conditions cannot be maintained no matter how low we set the thermostat. We better give the maintenance department a call. VAV box delivers too little airflow

Static Pressure Control
Excessive static pressure? Excessively high upstream static pressure can cause more problems than just wasting energy. High duct pressures make air flow control difficult and can increase damper generated noise. [DON]“Why is MY desk located under noisy duct work?” Wasted energy Poor comfort control Poor acoustics

Fan Control Loop static pressure sensor supply fan S controller
In order to ensure adequate static pressure at the VAV terminal units, a simple control loop is used. [SLIDE] First, the static pressure is sensed from a location in the system. Next, a controller compares this static-pressure reading to the system’s set point. Finally, the fan capacity is varied to deliver the required airflow at a static pressure that maintains this set point at the location of the system’s sensor. [DON] That seems simple. “Where do I locate the sensor?” controller

VAV System Modulation system resistance actual design static pressure
VAV modulation curve A better understanding of how fan capacity is controlled will help answer that question. [SLIDE] Assume that the air conditioning load decreases, causing all or some of the VAV dampers to modulate closed. [CLICK] This causes the system resistance curve to shift upwards. In response, the fan begins to “ride up” its performance curve. As a result, the fan delivers a lower airflow at a higher static pressure. The system static-pressure controller senses this higher static pressure and sends a signal to the supply fan controller to reduce fan speed. [CLICK] A lower fan speed results in a new fan-system balance point, bringing the system static pressure down to the sensor’s set point. [CLICK] This action results in the fan unloading along a curve called the VAV system modulation curve. This curve represents the fan modulation needed to balance the static pressure produced by the fan with the static pressure required by the system. The fan operating point will always be on the VAV system modulation curve because fan speed is control by the static pressure sensor, not the velocity squared value predicted by Darcy- Weisbach. [DON] The sensor needs some non zero measurable setpoint. Substantial energy is saved. However, some of the dampers will be throttling flow and consuming energy. It is the need for fan control that causes energy saved to be less than rpm cubed. Notice we control system static pressure, not system cfm. 1100 rpm 800 rpm airflow

static pressure control Sensor at Fan Outlet
supply fan S [SLIDE] One possible location for the static pressure sensor is near the outlet of the supply fan. The controller is set to maintain the static pressure required at design flow. The appeal of this method is that the sensor can be factory-installed and tested, resulting in greater reliability and no field installation cost. If fire dampers are included in the supply duct, this method ensures that the sensor is on the fan side of the damper so that the duct is protected from high pressures. Also, depending on the layout of the duct system, this method may eliminate the need for multiple duct-mounted sensors. It is not, however, as energy efficient as the other methods. [DON] This concept requires all the dampers to throttle back increasing fan static to a level above design. Sensing this over pressure, the fan controller will reduce fan rpm. However the savings presented by the form of speed control are limited because all the dampers are throttled to an energy wasting position. VAV boxes controller

static pressure control Sensor Down 2/3 of Duct
supply fan S [SLIDE] In the most common method for sensing and controlling system static pressure, the static-pressure sensor is located in the supply duct system. Determining the best sensor location for all load conditions can be difficult—often determined by trial and error or by using multiple sensors. [CLICK] A typical starting point is two-thirds of the distance between the supply fan and the end of the supply duct. [DON]“Why two thirds?” Notice that dampers located downstream of the static pressure sensor have no vote. [SLIDE-CLICK] Because the controller maintains a fixed static pressure upstream of these zones, these dampers must close, wasting fan energy, in order to deliver the desired airflow in those zones. VAV boxes controller

static pressure control Sensor Down 3/4 of Duct
supply fan S [SLIDE] Fan energy savings can be increased by moving the sensor further down the air distribution system. This will increase the amount of load diversity sensed above the static pressure sensor. [DON] In essence more dampers are allowed to move to a more open position. Less fan energy is wasted by dampers throttled closed. VAV boxes controller

static pressure control Sensor Down 3/4 of Duct
supply fan S [SLIDE] There is a possibility that this far location in not sensitive to all upstream damper conditions. [CLICK] Some dampers upstream of the sensor may be starved for air. The simple solution is a higher setpoint at the static sensor. This defeats the the gain of moving the sensor downstream. [DON] In the end static pressure sensor setpoint may be more critical the actual sensor location. ASHRAE Standard 90.1 requires static pressure setpoint to be no greater than one-third the total design fan static pressure, if this control method is used. VAV boxes controller

optimized static pressure control Sensor at Fan Outlet
VAV damper positions supply fan speed or inlet vane position static pressure S static pressure setpoint An optimized static-pressure control method combines the location-related benefits of fan outlet control with operating cost savings that exceed those of supply duct static-pressure control. [SLIDE] A single static-pressure sensor is located at the fan outlet, and the controller dynamically adjusts the static-pressure set point based on damper position in the VAV units. The DDC/VAV controllers know damper position and, because they are pressure independent, they modulate damper position to maintain required airflow. The building automation system continually polls the VAV units looking for the most-open damper. The controller resets the static-pressure set point so that at least one damper, the one requiring the highest inlet pressure, is nearly wide open. The result is that the supply fan generates only enough static pressure to get the required flow through this “critical” vav damper. [DON] This method allows the sensor to be factory-installed and tested. If the vav units use DDC control, the system-level communications are already in place, making this the lowest-cost, highest energy savings strategy. ASHRAE Standard 90.1 requires VAV systems with direct digital control of individual zone boxes reporting to the central control panel, to reset static pressure setpoint based on the zone requiring the most pressure. communicating BAS

static pressure control methods Performance Comparison
Fan static pressure 2.7 in. wg 2.1 in. wg 1.9 in. wg 1.5 in. wg Fan input power 13 hp 22 hp 12 hp 9.5 hp Full-load power 60% 100% 55% 43% Airflow 24,000 cfm (full load) 18,000 cfm Fan outlet [SLIDE] A comparison of these static-pressure control methods demonstrates the energy savings potential. At this representative part-load condition, using the optimized static- pressure control method allows the supply fan to use only 43% of its full-load power versus 55% for the supply duct static-pressure control method. [DON] In addition to the supply fan energy savings, because the optimized static-pressure control method allows the system to operate as if the static pressure sensor was at each individual terminal unit, it ensures that no spaces are “starved” for air. There are also acoustical benefits at part load by operating the supply fan and VAV terminal units at the lowest possible duct static pressure. Supply duct Optimized

VSDs and their effect on system components
System Demonstration [HIDDEN SLIDE] [LEE & DON] Wow - so much for the thought that “a fan is a fan is a fan.” Don, that’s a great reminder that the application and control really does impact the benefit of the modulation technology applied. Let's now turn to pumps, variable flow and variable speed. VSDs and their effect on system components

Practical Application: Pumping Water
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Practical Application: Pumping Water [HIDDEN SLIDE] [LEE & DON] Wow - so much for the thought that “a fan is a fan is a fan.” Don, that’s a great reminder that the application and control really does impact the benefit of the modulation technology applied. Let's now turn to pumps, variable flow and variable speed. VSDs and their effect on system components

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 why care about Pump Energy According to the DOE ... Pumps represent 5% of industrial energy consumption Total cost of owning a pump is 90% energy consumption Pump energy consumption generally can be reduced by as much as 20% Of course we’re interested in pumps because they consume a significant amount of global energy. [SLIDE] According to the DOE, better pumping system design and control could save up to one fifth of the total pumping energy used world wide. Also the use of variable water flow in HVAC systems is an exploding trend. One reason is because of its energy saving potential and a second is that many codes require it.

pumping chilled water ASHRAE 90.1-2001
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pumping chilled water ASHRAE Requires variable chilled water flow if: Total pump power exceeds 75 hp AND System includes > 3 control valves ASHRAE 90.1 for example requires that any heating or cooling water system that has a total pump power that exceeds 75 horsepower and has more than three control valves be variable flow.

pumping chilled water ASHRAE 90.1-2001
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pumping chilled water ASHRAE Requires 30% design wattage at 50% flow if: Any variable-flow pump motor > 50 hp AND Design head pressure > 100 ft [LEE] In addition, once any system pump that must overcome 100 feet of pressure difference has at least a 50 horsepower motor, [SLIDE] it must have the capability to greatly reduce its energy consumption at system part load conditions. [CLICK] This is almost always achieved by using a variable speed drive on the pump motor. Typical solution: Variable-speed drive

chilled water system Variable Primary Flow
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Variable Primary Flow 1 2 750 gpm [LEE] Okay, so we’ll assume we have a variable flow chilled water system. Let’s look at an example system and see how it reacts to variable flow and how different pump control options impact pump energy use. [SLIDE] Shown here is a flow diagram for a simple two chiller variable primary flow system. Lets take this system and examine its pressure drop profile at full and part load flows using different pump control techniques.

chilled water system Full-Load Pressure Drop
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Full-Load Pressure Drop 1 2 750 gpm control valve [SLIDE] We are going to plot the system pressure profile on a chart below the system diagram. We’ll start at one point and plot the fluid pressure variation as it flows around the system. This will help us to visualize the impact of different pump control strategies on system components. [CLICK] For the full load plot, we will start at the inlet to the pump. We see that the pump must raise the pressure from its inlet to its discharge equal to the total pressure drop of the system. [CLICK] The pressure of the water leaving the pump drops in proportion to the supply piping friction until it reaches the air-handler coil control valves. [CLICK] The valve’s job is to control the flow to the coil by devouring, or wasting, as much pressure as required so the coil flow just meets the cooling load demanded by the space. It will be important to observe how the valve pressure drop changes under different load conditions and with different pump control strategies. [CLICK] The water leaves the control valve and flows through the coil. Finally doing the work for which it was chilled. [CLICK] The water pressure continues to drop as the water flows back to the inlet of the pump via the return piping. The pressure drop in this chart ignores the fact that there might be a triple duty valve or balancing valve on the outlet of the pump reducing its flow to the desired design value. DP tP © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Full-Load Pressure Drop 1 2 750 gpm [SLIDE] If we were to include the triple duty valve for balancing flow in the system its pressure drop would appear something like this. This is another case where we waste pressure, and therefore energy, to control the system flow. [LEE] A balancing valve should only be required on a constant volume system if the pumps are oversized. Because we are working with a variable flow system, an energy consuming system balancing valve is a unneeded device. triple-duty valve © 2006 American Standard Inc.

pumping system Pump & System Curves
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pumping system Pump & System Curves 100 pump 80 design point 60 pump head, % system 40 Let’s plot the system and pump curves on a flow verses pressure chart. [SLIDE] As the system flow increases the pressure drop rises up [CLICK] in accordance with the pump affinity laws. [CLICK] The pump pressure falls following that particular pump’s flow verses pressure curve. [CLICK] The intersection of the curves represents the design flow and pressure drop operating point for the system. 20 20 40 60 80 100 water flow, %

pump characteristics Power
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Power 100 pump 80 design point 60 pump head, % system 40 [SLIDE] If we add the pumping power to this chart we can find the corresponding pump power for the system. We also see that the power drops per the pump affinity laws. [LEE] Its drop is proportional to the change in flow and pressure drop. 20 100 pump power 50 power 20 40 60 80 100 water flow, %

variable-flow water system How Does It Unload?
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-flow water system How Does It Unload? Depends on: Chilled-water system curve Pump curve Pump control method Ride the curve Different pump sizes Vary the speed [SLIDE] The key question that we want to answer is how does the system unload with various load control techniques? [CLICK] We’ll start by examining a system that varies its capacity simply by throttling the control valves and RIDING the pump curve. [LEE] Let’s see what this looks like on the system and pump curve and then on a system diagram.

pump characteristics Ride the Curve
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Ride the Curve 100 pump 80 part-load point design point 60 pump head, % system 40 [SLIDE] The pump in this case is operating at a constant speed and its curve is fixed. If we want to reduce the system flow and therefore capacity we must add resistance to the system to push the system curve back up the pump curve. This is what is known as riding the pump curve. The way resistance is added to the system is simply by modulating the control valves more closed. Note that the lower the flow the higher the pump pressure and the more pressure the control valves must close off against. [LEE] The pump energy saved is PROPORTIONAL to the reduction in flow and INVERSELY proportional to the increase in pump pressure. Therefore the actual energy saved is a function of the shape of the pump curve. If the pump curve is flat then the savings will be significant. If the curve is steep and the pressure rises quickly then the savings will be smaller. That is why on this type of system, pumps with a flat curve should always be selected. 20 100 pump power 50 power 20 40 60 80 100 water flow, %

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Part Load: Ride the Curve 1 2 750 gpm Let’s view this capacity reduction strategy on the system pressure profile. The gray lines you see are the original full load pressure profile we plotted a few slides ago. [SLIDE] We’ll superimpose the part load lines over top of these for reference [CLICK] Remember the goal is to lower the flow through the coil to reduce its capacity. So this time we’ll start the plot with it. [CLICK] Who or what is it in the system that accomplishes this flow reduction? Obviously it’s the control valve. But wait - this shows the control valve’s parasitic pressure drop went way up - much more than the coil’s pressure drop went down. Why is that? [CLICK] Since the flow is down the frictional pressure drop of the supply and return piping is less. So the valve must compensate. [CLICK] But also remember that the pump is riding up its flow / pressure curve. So at this lower flow the pressure it produces is greater. From a pressure point of view the pump works harder at part load. The situation looks pretty bleak doesn’t it? [LEE] Not really. Systems have been designed and operated like this for many years. As long as you pick a pump with a flat curve to minimize pump pressure rise, the flow based energy savings will be dominant. Don’t forget another key element in making the system work is to specify control valves with sufficient close off pressure rating. control valve tP coil flow © 2006 American Standard Inc.

variable-flow water system How Does It Unload?
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-flow water system How Does It Unload? safe zone Depends on: Chilled water system curve Pump curve Pump control method Ride the curve Different pump sizes Vary the speed [LEE] Rather than ride a single pump curve lets try applying multiple pumps of different sizes.

Pump Characteristics pump pump head, % design point system pump power
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Pump Characteristics 100 pump 80 design point 60 pump head, % system 40 pump power [SLIDE] Here again we see our design-condition system/pump curve. 20 100 50 power 20 40 60 80 100 water flow, %

pump characteristics Different Pump Sizes
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Different Pump Sizes 100 system pump 80 design point 60 pump head, % part-load point 40 pump power [SLIDE] If we have available a second smaller pump selected for a lower flow at a lower pressure drop for part load not only will the system pressure go down, rather than up, but that pump’s power curve will be lower also. 20 100 50 power 20 40 60 80 100 water flow, %

pump characteristics Different Pump Sizes
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Different Pump Sizes 100 system pump 80 60 pump head, % 40 pump power [SLIDE] Add a third even smaller pump for even lower loads and it gets even better. MAYBE we’re on to something here? [LEE] But the complexity of selecting and operating all these different pumps would be daunting. Well, this is really just a bait and switch on my part. 20 100 50 power 20 40 60 80 100 water flow, %

pump characteristics VFD = Different Pumps
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics VFD = Different Pumps 100 system 80 1750 rpm 1488 rpm 60 pump head, % 1225 rpm 40 [SLIDE] Having a variable speed pump is really just like having an infinite number of different size pumps. Excellent! We can have the perfectly sized pump at every load point IF we can control the PUMP speed to slide down the SYSTEM curve rather than riding up the PUMP curve. [LEE] Now this is a neat concept but the actual energy use can vary greatly depending on how the pump speed is actually controlled. If we don’t control the pump speed to ride the system curve we will not achieve the potential energy savings. Again, lets examine a few examples and see the impact of different control methods. 20 100 50 power 20 40 60 80 100 water flow, %

variable-speed pump Control Methods
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-speed pump Control Methods Pressure control (DP) at pump Pressure control (DP) at end of system Critical-valve pressure reset [SLIDE] We’ll look at these three pump control methods and graphically evaluate their impact on system energy use.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Part Load: DP at Pump 1 DP 750 gpm 2 750 gpm [SLIDE] Let’s start with a strategy that controls the pump speed to maintain the design pressure at the pump at all loads. We’ll start plotting at the pump again since its pressure is our controlled variable [CLICK] The pump’s pressure rise is controlled to the design value, it does not change with load. [CLICK] Because of the lower flow, the frictional pressure drop through the supply and return piping is less. [CLICK] The control valve must again devour the amount of pressure required to lower the coil flow. Because of the pump pressure control it wastes less than would have been the case if we were riding the pump curve. [CLICK] The decreased flow through the coil shows itself in the form of lower pressure drop. [LEE] It’s interesting to note that the total pressure drop through the control valve and coil is still greater at part load than it was at design. tP © 2006 American Standard Inc.

variable-speed pump Control Methods
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-speed pump Control Methods Pressure control (DP) at pump Pressure control (DP) at end of system Critical-valve pressure reset [LEE] But if we’ve gone as far as putting in a variable speed pump and DDC control can’t we do better with our controls strategy? The answer is absolutely! Let’s try controlling the pump speed to a pressure that we measure at the end of the system ...

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Part Load: DP at End of System 1 DP 750 gpm 2 750 gpm [SLIDE] A pressure differential transducer is typically installed at the furthermost point in the system. [CLICK] Since we’re controlling the pressure across the control valve and coil lets start our pressure plot there. [CLICK] The pressure here stays constant at reduced flows. The control valve only has to waste the amount of pressure drop the coil gives up - much less than in other cases. [CLICK] As we’ve seen before, the lower flow through the supply and return piping results in less pressure drop. [CLICK] Ultimately the pump pressure is significantly less then the design condition. This results in much lower pump energy as well as better pump operation. DP tP © 2006 American Standard Inc.

variable-speed pump Control Methods
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-speed pump Control Methods Pressure control at pump Pressure control at end of system Critical valve pressure reset [LEE] [Hidden Slide] Let’s examine one more strategy to see if we can squeeze just a little more energy savings out of our system. Maybe it won’t be so little.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chilled water system Part Load: Critical Valve Reset 1 P 750 gpm 2 750 gpm [LEE] What if, instead of controlling to a fixed pressure somewhere in the system, we controlled based on the actual air-handler cooling demand? If the HVAC control system is integrated enough, we can monitor the air-handler load via the control valve position. [SLIDE] This is sometimes called critical valve pump pressure control. [CLICK] Here’s this control strategy pressure profile starting at the control valve. [CLICK] By monitoring the valve’s position and reducing the pump pressure to keeping the most demanding valve almost wide open the pressure drop through that valve will DROP with reduced flow rather than rise. The pressure drop through all the other control valves will drop also. [CLICK] The coil… and supply and return piping pressure drop is lower due to reduced flow. [CLICK] The resulting pressure at the pump is as low as possible at every load condition. This results in the lowest possible pump operating energy. Critical valve pressure reset virtually eliminates the system fixed pressure component and therefore it allows the pump savings to approach the pure pump affinity laws prediction. [LEE] From an operational point of view it just does not get any better than this. Now, just to reinforce the different strategy’s impact on pump energy lets quickly view each on a pressure - flow diagram. valve position tP © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Part Load: Ride the Pump Curve 120 100 80 excess pump pressure pump head part load 60 full load 40 [SLIDE] If we examine the “ride the pump curve” strategy we see that as the system unloads the gpm drops but the pump pressure rises. The area in pink represents the pressure the valve must devour at part load. [LEE] However, there ARE energy savings compared to a constant flow system. dynamic pressure 20 fixed pressure 20 40 60 80 100 © 2006 American Standard Inc. water flow, %

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Part Load: DP Control at Pump What the pump needs to produce the required system pressure determines minimum pump pressure, motor speed 100 80 excess pump pressure 60 all loads pump head 40 [SLIDE] For a system with pressure controlled at the pump we see is that the pump makes its design pressure at all loads. The gpm drops and the pump pressure does not rise. The pumps speed reduction is limited because it gets no head relief from this control scheme. [LEE] Still it results in energy savings compared to simply riding the pump curve. dynamic pressure 20 fixed pressure 20 40 60 80 100 © 2006 American Standard Inc. water flow, %

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Part Load: DP Control at End of System Pump DP “slides” down the system curve … 100 80 60 pump head 40 [SLIDE] If we control the pump at the most distant point in the system we provide only the static pressure the control valve and coil require at design conditions. At full load this will result in the pump producing the full design pressure but at part load much less. [CLICK] At part load the system pressure slides down the system curve. This allows the pump to slow down more enabling significant energy savings. dynamic pressure 20 DP fixed pressure 20 40 60 80 100 © 2006 American Standard Inc. water flow, %

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 pump characteristics Part Load: Critical Valve Reset Pump DP constantly reset to lowest possible value … almost all pressure drop is dynamic 100 80 previous system curve 60 pump head 40 [LEE] Critical valve pump pressure reset reduces control valve pressure drop, which lowers the whole system curve. The pump benefits from a lower system curve at all loads. [SLIDE] By monitoring the air hander control valve positions and controlling the pump pressure such that it is the minimum that will satisfy the most demanding air handler we can basically convert the fixed static pressure to dynamic pressure [LEE] Let’s summarize what we seen with pressure regulated closed pumping systems. pump pressure 20 20 40 60 80 100 © 2006 American Standard Inc. water flow, %

variable-flow pumping Summary
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-flow pumping Summary Energy savings depends on: Pump selections Fixed vs. frictional pressure components Control strategy Energy savings can approach “cube of speed” Great application for variable-speed drives [LEE] The potential amount of energy saved with variable flow is a function of a number of system design criteria - control strategy being a key one. [SLIDE] Depending on the design, the energy savings can approach that predicted by the pump affinity laws. And finally, over all, this is a great application for VFD-based speed control. This is born out by the overwhelming use we see for VFDs in this application. [LEE] Well, that’s my time. Mick, your turn. Take us through variable flow on condenser water systems.

variable-flow condenser water Pump Speed
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable-flow condenser water Pump Speed Determining minimum speed How variable flow affects: Pump Cooling tower Chiller Controlling flow to improve system performance [MICK] Thanks for covering the chilled water pump portion of the system, Lee. Now let’s move over to the condenser water side. [SLIDE] There are three topics we’ll cover: Determining minimum pump speed The effect of variable condenser water flow on the pump, cooling tower and chiller, and Controlling the condenser water pump to give better system performance.

condenser water pump Minimum Speed
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 condenser water pump Minimum Speed Determinants: Minimum condenser flow Tower static lift Minimum tower flow Nozzle selection Performance Compare curve with cubic [SLIDE] The minimum pump speed depends on a number of variables. The first is the minimum flow rate allowed through the chiller’s condenser. This information can be gotten directly from the chiller manufacturer. Next, when we consider the condenser water loop, a portion of that loop is closed and a portion of the loop is open.

cooling tower Static Lift
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 cooling tower Static Lift static lift [SLIDE] Within the closed portion of the loop the water elevation difference doesn’t add pressure the pump must push against. However, the pump must always overcome any elevation difference in the open portion of the loop. This open portion is at the cooling tower. The elevation difference between the cooling tower’s sump and the top of the cooling tower is known as “static lift” and must always be overcome. So in this case, the minimum for the pump is not a flow rate, but a speed at which the pump can still produce the pressure required to overcome the system pressure drop plus the tower static lift.

cooling tower Water Distribution
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 cooling tower Water Distribution The third possible limit for minimum condenser water flow is the minimum flow rate the tower manufacturer will allow. In order to maintain effective heat transfer the tower fill must remain wetted. If the flow rate drops too far portions of the tower can become dry – obviously affecting heat transfer. So, if you’re considering variable condenser water flow, make sure you work closely with the cooling tower provider. That way, they can provide the tower that can maintain good heat transfer as flow is reduced.

VSDs and Their Effect on System Components • 1 Feb 2006 Example 1500 gpm system, 1770 rpm Minimum flows: Chiller 658 gpm Tower 750 gpm Tower static lift 12.2 ft Pump: Speed 974 rpm Pump flow 875 gpm [SLIDE] Here’s an example system that has 1500 gpm as its design and the minimum flow rates on the slide. The limiting factor in this case is the tower static lift. To meet that lift requirement we need to maintain a flow rate of at least 875 gpm.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser-water flow Effect on Pump 100 60% 80 75% 81% 83% 60 75% pump head, ft 1770 rpm 40 1505 rpm [SLIDE] So a condenser water pump with a VFD reduces its energy consumption until it reaches 875 gpm, then runs at a constant flow rate and power draw. Next, we’ll look at how flow affects the rest of the system. 1239 rpm 20 974 rpm 400 800 1200 1600 2000 2400 capacity, gpm © 2006 American Standard Inc.

operating dependencies Full Flow
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 operating dependencies Full Flow [SLIDE] The chiller and tower work “together” in that they are “connected” by condenser water temperature and flow. As we’ll see in Ryan’s portion this sets the “lift” or pressure difference the chiller must work against. The chiller power is also dependent on its design and the load its producing at this point in time. The tower operation is dependent on its design as well as the ambient conditions and heat rejection load, [CLICK] Both the chiller and the tower are affected when the condenser water flow rate is reduced. Let’s look at an example to see how much. Tower design Condenser water temperature & flow Heat rejection Wet bulb Chiller design Condenser water temperature & flow Load

variable condenser water flow Effect on Tower
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser water flow Effect on Tower 110 100 100% fan 90 tower entering water, °F 80 [SLIDE] Cooling towers can reject heat at many conditions. Shown here is the performance of the cooling tower, with a chiller load of 70% and an ambient wet bulb temperature of 70 F. We’ve charted the temperature of water entering the cooling tower. On the right side of the chart we see that the water temperature entering the tower is about 84 degrees. If we reduce the water flow rate, the temperature entering the tower goes up. Since we are rejecting the same amount of heat with lower water flow, the water temperature entering the tower rises. For example at 50% flow it’s 96 degrees. Now, since the tower entering water temperature is the same as the chiller leaving condenser water temperature, we can look at the chiller power at each of these conditions. 70 60 50 60 70 80 90 100 condenser water flow, %

variable condenser water flow Effect on Chiller
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser water flow Effect on Chiller 300 96°F LCWT 250 200 84°F LCWT chiller power, kW 150 [SLIDE] At the same chiller load, as the water temperature leaving its condenser rises, so does chiller kW. Ryan will talk about the chiller change in a few minutes. If we just looked at chiller kW, we’d never reduce the condenser water flow rate. But we need to add the cooling tower fan kW, the pump kW and the chiller kW so we can see how the system operates. Remember, this is a snapshot in time – 70% load and 70 degree wet bulb. 100 Conditions: 70% load 70°F WB Full-speed tower fan 50 50 60 70 80 90 100 condenser water flow, %

variable condenser water flow Effect on System
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser water flow Effect on System 300 system 250 chiller 200 component/system power, kW 150 [SLIDE] The minimum chiller plus condenser water pump plus cooling tower kW occurs between 80 and 90% of the condenser water flow rate. However, it’s not that easy. So far we’ve assumed that the cooling tower fans are operating at full speed all the time. Since ASHRAE 90.1 requires speed control on cooling tower fans in many applications, a lot of people put VFD’s on their cooling tower fans. 100 50 tower pump 50 60 70 80 90 100 condenser water flow, %

reducing flow & fan speed Effect on Tower
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 reducing flow & fan speed Effect on Tower fan speed 110 50% 60% 100 80% 100% 90 tower entering water, °F 80 conditions: 70% load 70°F WB [SLIDE] So, we need to examine how the entering tower water temperature changes when we reduce the flow rate AND tower fan speed. Since reducing tower fan speed reduces airflow – and heat rejection capability, the tower entering water temperature rises at reduced tower airflows as shown in this chart. So, let’s look at all of these flow rates and tower fan speeds and see how the system kW compares. 70 60 50 60 70 80 90 100 condenser water flow, %

reducing flow & fan speed Effect on System
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 reducing flow & fan speed Effect on System 300 80% 60% 50% fan speed 250 100% 200 system power, kW 150 conditions: 70% load 70°F WB [SLIDE] When we look at all the possible operating points we see that the system kW is at its minimum when the fans and pumps are at about 90% flow rate. But this graphic also shows another important fact. Take the top, red line where the cooling tower fan is operated at 50% speed. Once the water flow rate drops below 80%, the temperature of water produced by the cooling tower rises so much that it sends the chiller’s compressor into a surge region – again Ryan will cover this. If you’re going to reduce flow rates and tower fan speeds, do so in a manner that keeps the chiller from surging. Okay, what we just looked at was the chiller operating at 70% load when the wet bulb is 70 degrees. 100 50 50 60 70 80 90 100 condenser water flow, %

reducing flow & fan speed Effect on System
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 reducing flow & fan speed Effect on System fan speed 300 250 50% 60% 80% 200 100% system power, kW 150 conditions: 70% load 50°F WB [SLIDE] What if the chiller is at 70% load, but the ambient wet bulb is 50 degrees? This might occur in a multiple chiller plant when only one chiller is operating. Here, a tower fan speed of about 80% and a water flow rate of 80-90% is the best. Note that if the water flow gets turned down too far, the total system kW rises significantly. A piece good news is that since the ambient wet bulb is low enough, the chiller doesn’t surge. 100 50 50 60 70 80 90 100 condenser water flow, %

reducing flow & fan speed Effect on System
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 reducing flow & fan speed Effect on System fan speed 300 250 conditions: 30% load 50°F WB 200 system power, kW 150 100% 80% [SLIDE] Our final example examines the same system at 30% load, and a wet bulb of 50 degrees. The system power consumption is fairly flat. The one thing I’ll note is that reducing the tower fan speed makes sense at all water flow rates. Said another way, while chillers can operate with entering condenser water temperatures of 55 degrees, don’t try to drive the tower water temperature as cold as possible. Back off on tower fan speed and save some system energy consumption. 100 50 60% 50% 50 60 70 80 90 100 condenser water flow, %

variable condenser water flow Summary
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser water flow Summary Determine what savings, if any, are possible Are pumps already low power? Can reducing tower-fan speed achieve most of the savings? [MICK] Remember that the charts you saw here were for one specific application of a chiller, pump and cooling tower. Depending on the efficiency and power draw of each, the results can vary significantly. Nevertheless, sometimes we’re asked for guidance when people are considering variable condenser water flow. [SLIDE] First, you need to determine whether or not reducing condenser water flow rates should even be considered. If you’ve already minimized the condenser water pump kW, for example by its reducing design flow rate to 1.5 or 2 gpm/ton, it may not even make sense to take the time to look further. [MICK] Also, reducing just the tower fan speed may give you most of the energy savings, and it’s simpler.

variable condenser water flow Summary
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser water flow Summary If you decide to reduce flow: Find minimum condenser- water flow rate Examine system at various loads and wet-bulbs … keep chiller out of surge Document the sequence of operation Help commission the system [SLIDE] If you do decide to reduce condenser water flow rates during operation, [CLICK] know the minimum condenser water flow rate for your system. Then, to find efficient operating points at various loads and ambient conditions, [CLICK] take the time to examine the system at all those loads and ambient wet bulb temperatures. What occurs in real life is quite different than what the ARI chiller rating standard assumes. One reason to study the system is to keep the chiller out of its surge region and allow it to meet the cooling load. This is especially important at wet bulb temperatures closer to design. Once you’ve done this work, [CLICK] write a detailed sequence of operation. Finally, there is no replacement for being out at the job site with the system operator and seeing what happens during operation. [CLICK] Consider being part of the commissioning team.

variable condenser water flow Guidance
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 variable condenser water flow Guidance Can provide savings … Finding proper operating points requires more time, more fine-tuning Two-step process: 1 Reduce design pump power 2 Is variable condenser-water flow still warranted? The bottom line is that variable condenser water flow allows some systems savings, but it takes more design examination and on-site fine tuning to achieve those savings. We suggest that you first reduce condenser water pump power at design – you can easily do this by reducing the design flow rate. Then determine if variable flow is warranted.

Practical Application: How VSDs Affect Chillers
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Practical Application: How VSDs Affect Chillers [HIDDEN SLIDE] [MICK] Okay, I touched on how a chiller is impacted by external variables in a system. For example condenser water entering and leaving temperatures, and condenser water flow rate. Ryan is now going to take us inside the chiller so we can understand their impact, and more specifically how a variable speed drive affects chiller performance as these external parameters change. We’ll see that it’s quite different than the pump or fan effects we’ve seen so far. VSDs and their effect on system components

VSDs and Chiller Laws resistance a velocity² resistance a “lift”
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and Chiller Laws Variable-speed drives benefit centrifugal compressors in water chillers Review “chiller laws” Explore scientific cause-and-effect relationships Maximize benefits [RYAN] Thanks, Mick. Clearly, drive technology offers tangible energy-saving opportunities … and, the same CAN hold true for chillers. [SLIDE] [CLICK] As Don pointed out earlier, the centrifugal chiller laws remind us that “resistance” to mass flow is not a function of refrigerant velocity. Rather, the “resistance” correlates to the pressure difference, or “lift,” the compressor must generate between the condenser and the evaporator. Therefore, resistance is not proportional to velocity squared; instead, it is proportional to “lift.” [RYAN] I will explore these ideas in detail, but before I do, I’d like to share an often-told story on this topic, as many believe the following analogy formulates a better understanding. resistance a velocity² resistance a “lift”

VSD and centrifugal chillers A Simple Analogy
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSD and centrifugal chillers A Simple Analogy brake (inlet guide vanes for unloading) accelerator (speed control of chiller motor) [SLIDE] It goes like this … [CLICK] Think of your vehicle's accelerator as the chiller’s electric motor speed control. [CLICK] You can also think of the vehicle's brake as the inlet guide vanes, or the unloading device.

a simple analogy Constant-Speed Chiller
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 a simple analogy Constant-Speed Chiller Motor runs at constant speed, regardless of load [RYAN] If you have a constant-speed chiller, the electric motor runs at a constant speed regardless of load. If the chiller needs to operate at off-design conditions, inlet guide vanes restrict the amount of refrigerant allowed in the compressor. [SLIDE] Applying this concept to the story, then, [CLICK] one might think of the accelerator being pegged to the floor, and [CLICK] to slow down, you press the brake. Inlet guide vanes restrict refrigerant at off-design conditions

a simple analogy Variable-Speed Chiller
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 a simple analogy Variable-Speed Chiller Based on load, motor speeds up or slows down [SLIDE] If you have a variable speed chiller, the analogy implies the electric motor slows down or speeds up depending on the load, just as the accelerator on an automobile.

VSDs and centrifugal chillers An Analogy
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and centrifugal chillers An Analogy In each case: Energy is wasted Mechanical wear-and-tear is increased [RYAN] Common sense tells you that pegging the accelerator to the floor and using the brake to slow down is a terrible waste of fuel and can lead to added wear and tear. The analogy implies the same conclusions, that is without a VSD on the chiller, electricity is wasted and mechanical wear and tear increases. Simple, and easily understood. Let’s “test” this accuracy by looking into the science.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Typical Centrifugal Chiller capacity- modulating device compressor condenser controller [RYAN] First, as a reminder, centrifugal chillers convert kinetic energy into static energy by increasing the pressure and temperature of the refrigerant; [SLIDE] and, the six main components contained on every centrifugal chiller, are the evaporator, the condenser, the compressor, a pressure-reducing device, a capacity modulation device, and an integrated unit-mounted controller. not shown: pressure-reducing device evaporator © 2006 American Standard Inc.

cold refrigerant vapor
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Impeller hot refrigerant vapor cold refrigerant vapor [SLIDE] At the core of the chiller’s centrifugal compressor is a rotating impeller, fit with blades, that draws refrigerant vapor into radial passages. blade © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Multistage Compressor inlet vanes [RYAN] Capacity modulation is done utilizing a mechanical device commonly referred to as inlet guide vanes. Centrifugal chillers run at a fixed speed, or RPM; and because the speed is fixed, at reduced capacity conditions, the chiller needs a means to unload. [SLIDE] Inlet guide vanes control the refrigerant flow by modulating the vapor prior to entering the impeller. Also, enabled by the unique characteristics of centrifugal compression, inlet guide vanes pre-whirl the vapor, optimizing the chiller’s efficiency at a reduced load. So, even though the chiller remains at constant speed, less refrigerant gas is processed, reducing the compressor’s work and resulting in less power drawn. [RYAN] So, returning to the analogy, even on a constant-speed chiller, you ease off the accelerator at part load. inlet vanes impellers © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Centrifugal Compressor volute diffuser passage impeller passage [SLIDE] Looking closer at the compressor, the impeller rotates -- accelerating the refrigerant vapor, increasing its velocity and consequently its kinetic energy. [CLICK] Then, as the area increases in the diffuser passages, static pressure is generated as the velocity of the refrigerant decreases and is converted to static energy. [CLICK] Finally, the high pressure refrigerant collects in the volute around the perimeter of the compressor, where the final energy conversion to static pressure is completed. [RYAN] The now elevated temperature and pressure refrigerant travels to the condenser completing the compression cycle. © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Lift versus Load lvg evaporator water lvg condenser water 56°F 41°F 85°F 99°F 800 gpm load = 500 tons 2 gpm/ton 58°F lift (DT) The compressor, then, generates a pressure differential, or head. [SLIDE] The conventional reference to compressor “Lift” was adopted simply because [CLICK] the compressor “elevates” the refrigerant’s pressure from the evaporator to the condenser. Because of the direct correlation between the refrigerant pressures and their associated leaving water temperatures, for convenience, [CLICK] “Lift” is often communicated as the difference in leaving evaporator and leaving condenser water temperatures. [CLICK] Load, by contrast, is independent of vessel pressures and dependent upon the flow rate and the temperature difference of the water across only the chiller’s evaporator. [CLICK] Applying some numbers, these concepts become clear. Here, a chiller operating at full load produces 800 GPM of 41 degree water with a 15 degree delta T across the evaporator and receives [RYAN] 2 GPM/ton of 85 degree condenser water resulting in a leaving condenser temperature of 99 degrees. The “load” on this chiller is defined as 500 tons, and the required compressor head, while is dependent on pressures, is simply referred to as 58 degrees of LIFT. lift a Pcnd – Pevp lift a Tlvg cnd – Tlvg evp load a gpm × (Tent evp – Tlvg evp) © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Compressor Work and Chiller Efficiency lvg cond water head/“lift” 58°F compressor work Unmistakably, load and lift are related to total compressor work, ultimately corresponding to the amount of potential energy savings. [SLIDE] This graphic, referred to as the “compressor work rectangle,” illustrates this distinct relationship. [CLICK] The width of the rectangle represents the mass flow of refrigerant through the compressor and translates into chiller cooling capacity, or load, and measured in tons. [CLICK] The height of the rectangle represents compressor head, or LIFT, required of the compressor. [CLICK] So, referring to the previous example, the load is 500 tons and the “lift” is 58 degrees. [RYAN] Now, let’s take a look at the origin of the work rectangle. cooling capacity/“load” lvg evap water 500 tons © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Impeller Dynamics Vr a refrig flow rate Vt a rpm × diameter Vt R tangential velocity LIFT resultant velocity LOAD compressor work diameter Vr refrigerant flow rate [As referred to earlier, the refrigerant leaving the impeller and work done by the compressor is kinetic, as represented by the resultant velocity vector. [SLIDE] This refrigerant velocity vector is broken down by two key components, a radial vector and a tangential vector. The radial vector moves the refrigerant away from the impeller, and the tangential vector acts to move the refrigerant in the direction of the impeller’s rotation. [CLICK] Radial velocity for a given compressor is directly proportional to the flow rate of refrigerant vapor through the compressor, and [CLICK] tangential velocity is proportional to tip speed. [CLICK] Applying the compressor work rectangle, then, we can see how it functions to represent these concepts. Centrifugal compression is correlated closely with: Refrigerant mass flow rate, determined by the building’s load and out of our direct control. [RYAN] Impeller diameter, determined by the chiller’s full-load design conditions and fixed upon final selection configuration. And, impeller tip speed, also determined by the chiller’s final full-load design selection, but can change if the chiller is equipped with a variable-speed drive. How do the variables of refrigerant mass flow rate and impeller tip speed affect compressor work? radial velocity rotational speed © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Compressor Response to Load Vr Vt R Vt R Vr [SLIDE] First, consider a given-diameter compressor impeller that rotates at a constant speed. As the load on the chiller decreases, [CLICK] the inlet vanes partially close and the flow rate of refrigerant through the compressor drops. Radial velocity, which is proportional to refrigerant flow, decreases as well. [RYAN] Even though the speed of rotation and diameter of the impeller are constant, the radial velocity drops due to the additional pressure drop caused by the inlet vanes reducing the flow of refrigerant. As a result, less static pressure is produced, and less power is drawn from the compressor motor. Because centrifugal compression is variable volume, as the system load decreases and the chiller operates at a part-load condition, the chiller will draw less power, whether it is a constant-speed or variable-speed chiller. In this application, applying variable-speed drives and slowing the impeller’s tip speed may reveal some benefit; however, slowing the impeller too much will result in surge. full load part load © 2006 American Standard Inc.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Compressor Response to Lift R Vt Vr Vt R Vr [RYAN] Now, let's move our attention from Part Load to Part Lift. [SLIDE] Consider the same given-diameter compressor impeller that rotates at a constant speed. Even though the speed of rotation and diameter of the impeller are constant, [CLICK] the tangential velocity drops due to the additional pressure drop imparted on the refrigerant by the inlet vanes. This reduces compressor work at part-lift conditions, thus reducing the power draw of the compressor. Once again, this reduction in power occurs without a reduction in the impeller’s tip speed. [RYAN] The efficiency of the compressor could be further improved by eliminating the losses imparted by the inlet guide vanes, and this can be done by reducing the impeller’s tip speed… Enter variable-speed drives! Now, while the tangential vector and radial vectors remain the same, reducing tip speed more effectively repositions and matches the chiller’s operational requirements when a part-lift condition occurs, resulting in a further reduction in energy drawn. Bottom line, while applying variable-speed drives to centrifugal compressors may gain minimal benefit at part load, the real savings tie directly to a reduction in LIFT. full load part load © 2006 American Standard Inc.

Lessons Learned To reduce lift:
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Lessons Learned lvg cond water To reduce lift: Decrease condenser pressure by reducing leaving-tower water temperature Increase evaporator pressure by raising chilled water setpoint VSDs optimize chiller lift efficiency 99°F 75°F compressor work [SLIDE] Applying these concepts to the compressor work rectangle will graphically demonstrate that LIFT is reduced only through 2 means: 1. [CLICK] Lowering the condensing temperature by delivering colder condenser water than design. Or, 2. [CLICK] Increasing the evaporator temperature by resetting the chilled water setpoint warmer. Understanding the differences between load and lift is critical to ensure the benefits of drive technology are attainable and balance the higher first cost with potential energy savings. [RYAN] As discussed, centrifugal compressors are variable volume; therefore, either inlet guide vanes alone or the combination of inlet guide vanes and a variable-speed drive will respond to a change in load and result in reduced power consumption. All types of centrifugal chillers benefit from lower condensing temperatures. Variable-speed drives simply allow more benefit by improving the part lift efficiency of chillers. [MICK] Ryan, let me take a shot at showing how chiller savings compares to fan and pump savings we’ve already looked at. [RYAN] Okay. 45°F 41°F lvg evap water

various system components Energy Use
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 various system components Energy Use free discharge fan 100 chilled water pump (DP at end of loop) 80 condenser water pump (stopped at 875 gpm) 60 chiller w/low lift energy use, % 40 [MICK] I think of the “static lift” of the cooling tower as comparable to the compressor “lift.” A condenser pump must always overcome the water elevation difference between the cooling tower’s sump and the top of the cooling tower, and the chiller’s compressor must overcome the difference in pressures between the evaporator and the condenser. [RYAN] I like the comparison. [SLIDE][MICK] So, from a comparison standpoint we can look at the energy consumption of: [CLICK] A free discharge cooling tower fan [CLICK] A chilled water pump using a DP sensor at the end of the loop, [CLICK] A condenser water pump that had to stop at 875 gpm, and [CLICK] A chiller running with reduced condenser water temperature – and thus lower lift. [RYAN] So this shows that chillers do not benefit from the “cube of the savings” rule of thumb. [MICK] Exactly. The chiller evaporator and condenser water temperatures make what might be thought of as a “DP setpoint” for the chiller. Okay, with that said, let’s look back at that analogy you began with … it seemed pretty simple. Maybe too simple? static lift 20 20 40 60 80 100 load, %

VSDs and centrifugal chillers A Simple Analogy
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and centrifugal chillers A Simple Analogy brake (inlet guide vanes for unloading) But misleading and technically incorrect accelerator (speed control of chiller motor) [SLIDE] [RYAN] Yes. I think of it as simply misleading and technically wrong. As we’ve seen, it misrepresents how a VSD integrates with the fundamentals of centrifugal compression leading people to incorrect conclusions and misapplication of drives. [RYAN] Simply stated, variable-speed-drive chillers do not follow the “cubic savings” rule of thumb. Now let me take a few minutes to discuss how chillers are rated.

chiller efficiency at part load IPLV and NPLV Conditions
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 chiller efficiency at part load IPLV and NPLV Conditions 100% 85°F ECWT 75% 75°F ECWT 50% 65°F ECWT lift [RYAN] Because there is a clear need to establish minimum efficiency standards, ARI, the Air-conditioning & Refrigeration Institute, created Standard 550/590 as an attempt to identify a single variable or unit of measure to represent a chiller’s performance rating. IPLV, or integrated part-load value is defined as a weighted average of compressor work by combining both part load and associated part lift into four arbitrary, predefined conditions. Now, remember, part load and part lift are different, so the assumptions made are critical. Unrealistic assumptions will lead to incorrect performance conclusions. NPLV, or non-standard part-load value was also established to allow the chiller’s design operating conditions to vary while re-using the same IPLV formulas and associated load and lift predefined buckets. [SLIDE] Symbolically, applying the compressor work rectangle to the IPLV/NPLV variable might look something like this … [CLICK] the assumption is all hours of operation would fit into these 4 fixed conditions. That is to say, all the hours operating at certain part load conditions would simultaneously be operating at reduced lift conditions. This model might provide a means by which to compare one chiller’s performance to another, but it will not, nor was it intended to, be representative of how a chiller will operate within a system. [RYAN] The ARI standard simply cannot accurately represent a chiller’s energy use in a system, nor can the IPLV/NPLV value predict the savings that can be associated with the additional investment of a drive. As the standard suggests in its Appendix D, careful analysis is the only real method to reach fiscally responsible decisions. 25% load

VSDs and centrifugal chillers A Closer Look at IPLV
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and centrifugal chillers A Closer Look at IPLV Load Weighting ECWT kW/Ton 100% 0.01 85°F 0.572 75% 0.42 75°F 0.429 50% 0.45 65°F 0.324 [SLIDE] Looking closer, and combining representative chiller performance values with the four arbitrarily chosen conditions for IPLV/NPLV highlights another controversial industry issue. That is, the recent claims that running two chillers with variable-speed drives at part load is more efficient than one chiller fulfilling the same load… Of course, if attention is focused on these numbers, the assertion seems authentic. Here the 50% load value of kW/ton has a commanding efficiency advantage over the full load value of [CLICK] But, the 50% load number has condenser water that is 20 degrees colder than the full load number! Of course it looks more efficient – its lift has been reduced! Again, variable-speed-drive chillers are part-lift devices. [RYAN] We need to compare the chillers at the same condenser water temperature. Let’s do that. 50% 0.45 65°F 0.393 VSDs improve part-lift performance, so running two chillers with VSDs at part load seems more efficient than one chiller at double the same load, but …

VSDs and centrifugal chillers Performance at 90% Load
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and centrifugal chillers Performance at 90% Load ECWT 85°F 80°F 75°F 70°F 65°F 2 Chillers* 306.4 268.0 230.8 195.2 160.3 1 Chiller 268.0 238.0 210.6 185.7 164.3 Difference –38.4 –30.0 –20.2 –9.5 +4.3 [SLIDE] The results, for a system load of 90% and with the condenser water temperatures shown, are represented here in the table. Unmistakably, in all but the most reduced “LIFT” condition, 1 variable-speed chiller operating at 90% load consumes less power than 2 equally loaded variable-speed chillers. [RYAN] It’s worth emphasizing that this comparison does what IPLV cannot – compare “like chillers" in a “like condition.” … Apples to apples, if you will. Note: Data shows only chiller power. *Load equally divided

VSDs and centrifugal chillers Performance at 90% Load
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and centrifugal chillers Performance at 90% Load 350 2 chillers: 45% load each 1 chiller: 90% load 300 250 chiller power, kW 200 150 [SLIDE] Representing the same data in a graphical format, punctuates that running 1 chiller consumes less power than running 2 at all but the coldest of condenser water temperatures. [RYAN] Remember, as Mick discussed, these cold condenser water conditions may not be economically attained. Also, pump and tower energy are not included in these numbers; only the chiller energy is shown here. When a chiller is brought on line, the associated ancillary equipment consumes power, too. If we leave a chiller off, there is no ancillary consumption. After all, there is no substitute for “OFF” when trying to maximize energy savings! 100 50 65 70 75 80 85 entering condenser water, °F Conclusion: 1 chiller uses less power than 2 chillers

Analyze the System Model: Building use Local weather Economizers
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Analyze the System Model: Building use Local weather Economizers Utility rates System design Use programs like TRACE™, DOE 2.x, Chiller Plant Analyzer, HAP [RYAN] We’ve found that VSD chillers can often be justified when: There are lots of run hours at low lift conditions, and with high energy rates during those run hours. One example where a VSD chiller often pays back is a chiller that operates during the winter. It has a lot of hours at low lift conditions. But, it’s imperative to analyze the system to make proper life-cycle decisions. [SLIDE] Only a system study that incorporates all aspects of location dependant weather, building diversity, and chiller performance characteristics will be able to determine if applying variable-speed drives to chillers is economical, such as a comprehensive hour-by- hour analysis tool. Bin methods can’t do this. Programs like TRACE, DOE, Chiller Plant Analyzer or HAP help you give the owner the information to make life-cycle cost decisions.

VSDs and centrifugal chillers Summary
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VSDs and centrifugal chillers Summary VSDs improve chiller part-lift performance Lots of operational hours Reduced condenser water temperatures Higher costs of electricity IPLV is not an economic tool [RYAN] The science of variable speed technology and its application to centrifugal chillers is similar, but discernibly different from pumps and fans. I leave you with these thoughts: First, there are many analogies and misconceptions surrounding this topic, and hopefully the discussion exposes the need for concern and a word of caution. [SLIDE] Perhaps the use of the compressor work rectangle may better serve the industry to best represent drives on chillers. Also, remember that variable-speed drives impact centrifugal chillers part-lift efficiency, not part load. As such, the combination does not follow the often referenced “cubic savings” rule of thumb. And, only an analysis, not a single number like IPLV/NPLV, can adequately represent how drives will perform. [RYAN] Bottom line, variable-speed drives are viable and effective, and should be applied to centrifugal chillers to maximize energy savings … in the right application.

a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 Answers to Your Questions [HIDDEN SLIDE] [MICK] You know, it always comes back to using the proper technology in the proper application. Now, it’s time to move to our question and answer session. Thanks for faxing yours in today. If we can’t get to yours while we’re on the air, we’ll get back to you within 4 weeks. VSDs and their effect on system components

wrap-up VSD Effect Differs
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 wrap-up VSD Effect Differs Cubic relationship to speed only occurs in “free discharge” systems Control parameters affect savings In chillers, external parameters define lift (pressure difference) [MICK] To summarize what the team covered today, all drive effects are not created equal. While we know what the fan laws say about the cubic relationship, this very rarely occurs in HVAC systems. [SLIDE] Fan and pump savings are affected extensively by the control method chosen. And in chillers, the pressure difference the compressor must overcome is defined by external parameters – most often chilled and condenser water temperature.

wrap-up VSD Effect Differs
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 wrap-up VSD Effect Differs Cooling towers: Nearly cubic HVAC fans: Not cubic Depends on control strategy Fan pressure optimization is best Chilled water pumps: Not cubic Affected by valves and control method Consider pump pressure optimization based on critical valve [RYAN] Lee showed us that the closest we come to the cubic relationship is at the cooling tower – [SLIDE] [CLICK] and that reducing cooling tower fan speed can increase system efficiency – even though the chiller uses more power. [CLICK] Don covered how VFD’s on fans work within the system – and showed us that the savings are predicated on the control strategy. Fan pressure optimization is the best – and remember that ASHRAE 90.1 requires this on DDC/VAV systems. [CLICK] Chilled water pumps work in a similar manner to HVAC supply fans in that the control method is also critical. Pump pressure optimization is being used as a more common system control method.

wrap-up VSD Effect Differs
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 wrap-up VSD Effect Differs Condenser water pumps: Not cubic Must meet minimum flow or pressure Tower static lift Minimum condenser water flow Minimum tower flow Reduced flow affects chiller and tower performance Before applying a VSD, reduce pump design power (CW flow rate) [SLIDE] [CLICK] On the condenser water side you have to keep the pump speed high enough to meet the minimum flow rate or pressure – and you really need to understand how the reduced condenser water flow rate affects the chiller and tower performance. [MICK] We suggest that before taking the time to investigate that relationship for your particular job, that you reduce the condenser water pump design power, by selecting it at lower flow rate.

wrap-up VSD Effect Differs
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 wrap-up VSD Effect Differs Power for any chiller is reduced at part load and lift Chiller savings? Not even close to cubic VSD helps more at part-lift conditions MUST reduce lift for VSD to slow down and give benefit Use same condenser water temperature to compare constant- and variable-speed chillers [SLIDE] Next, no matter how a chiller is controlled, power is reduced at part load and part lift. The present rating standard makes inaccurate assumptions about lift. A better analysis is warranted, and the tools are available. Having a VFD on a chiller can work very well – as long as it’s in the proper application – that is, reduced lift conditions. In order for the drive to save energy it must be able to slow down. For the drive to slow down the pressure difference or lift must be reduced. [MICK] So, remember that a VFD on the chiller helps part lift operation – and this needs to be analyzed properly.

VFDs and Gensets Trane Engineers Newsletter volume 35-1
a Trane Engineers Newsletter Live satellite broadcast VSDs and Their Effect on System Components • 1 Feb 2006 VFDs and Gensets Trane Engineers Newsletter volume 35-1 “How VFDs Affect Genset Sizing” by Court Nebuda location.aspx?item=5 [MICK] Another aspect of drives we didn’t have time to cover today is that engine generators – or gensets – are being used in more facilities today to provide backup for critical loads, such as hospitals or data processing. A myth sometimes heard today is that the genset can be downsized when variable-speed drives are used. [SLIDE] This is not true across the board – in fact there are times when the genset actually has to be oversized! In February of 2005 the national ASHRAE meetings held a very clear discussion on this topic. Please take a look at the newsletter written by Court Nebuda to help you understand genset issues if that application arises.