1. Energy Saving DDC Control Strategies

2. DDC Controls Architecture
Operator Interface
Level
SQL
Server
BACnet
Ethernet LAN
Building Control
Level
BCU
BCU
MP581
AH541
ZN521
CH530
Unit Control
Level
VV550
LonTalk

3. Energy Saving Control Strategies for VAV Systems
Optimum Start/Stop
Fan Pressure Optimization
Supply Air Temperature Reset
Demand Controlled Ventilation
4 Major strategies were discussed in the Engineers Newsletter broadcast they were:
1) Optimum start and optimum stop
2) Fan pressure optimization
3) Supply air temperature reset
4) Demand controlled ventilation

4. Optimum Start/Stop Lowers system run time Increases occupancy comfort
Tracer Summit Optimal Start
Advantages of optimum start/stop
Lowers system run time by calculating actual time needed to reach setpoint instead of only working off of a schedule
Increases occupancy comfort when compared to not starting the system before occupants arrive.
The way Tracer Summit does optimal start is that the user defines an acceptable time limit as to how early the heating and cooling can begin for morning warm-up, then it calculates based off of past experience and external factors how long it will take the system to heat up or cool down today and then only starts running when it needs to in order to reach desired setpoints at occupied time.

5. Optimum Start/Stop

6. Fan Pressure Optimization
Fan Outlet Static Control (Good)
Supply Duct Static Control (Better)
Critical Zone Reset (Best)
ASHRAE 90.1 Prescriptive Path
There are three methods to achieve fan pressure optimization which include:
Fan outlet static control
Supply duct static control
Critical zone reset
The graph shows the pressure profile of an elementary one zone VAV air deliver system (illustration only as you would never do a one zone VAV system)
Fan pressure optimization is actually one of the prescriptive paths for ASHRAE standard

7. Fan Outlet Static Control
sensor located at fan outlet
static pressure sensor
VAV
terminal units
Fan outlet static control uses a duct pressure sensor mounted at the supply fan (always best when factory mounted) to control supply air to design static pressure.
When the duct static pressure sensor is located at the outlet of the fan, the static pressure controller, SPC in our system example, must be set to 1.40 in. wg so that the pressure at the inlet of the VAV terminal unit is 0.80 in. wg at design airflow. Figure 4A shows the system resistance curves, fan modulation curve, and the new fan curve at part-load flow. They indicate that at zero airflow, fan static pressure is the duct static pressure set point, SPC = 1.40 in. wg. At our part-load airflow, the inlet guide vanes are repositioned and a new fan curve is created so that 18,000 cfm is delivered and the duct static pressure at the fan outlet is constant at 1.40 in. wg.
The fan now operates at the intersection of the fan modulation curve and new fan curve, Point C. As the pressure gradient curve in Figure 4B shows, fan static pressure drops to 2.13 in. wg, duct static pressure is constant at 1.40 in. wg, and the static pressure at the inlet to the terminal unit rises to 1.06 in. wg. The terminal unit must close to introduce a 0.78 in. wg pressure drop, but fan brake horsepower is reduced to 13 bhp.
supply
fan

8. Fan Outlet Static Control
Sample Case
Fan outlet static control uses a duct pressure sensor mounted at the supply fan (always best when factory mounted) to control supply air to design static pressure.
When the duct static pressure sensor is located at the outlet of the fan, the static pressure controller, SPC in our system example, must be set to 1.40 in. wg so that the pressure at the inlet of the VAV terminal unit is 0.80 in. wg at design airflow. Figure 4A shows the system resistance curves, fan modulation curve, and the new fan curve at part-load flow. They indicate that at zero airflow, fan static pressure is the duct static pressure set point, SPC = 1.40 in. wg. At our part-load airflow, the inlet guide vanes are repositioned and a new fan curve is created so that 18,000 cfm is delivered and the duct static pressure at the fan outlet is constant at 1.40 in. wg.
The fan now operates at the intersection of the fan modulation curve and new fan curve, Point C. As the pressure gradient curve in Figure 4B shows, fan static pressure drops to 2.13 in. wg, duct static pressure is constant at 1.40 in. wg, and the static pressure at the inlet to the terminal unit rises to 1.06 in. wg. The terminal unit must close to introduce a 0.78 in. wg pressure drop, but fan brake horsepower is reduced to 13 bhp.

9. Supply Duct Static Control
sensor located 2/3 down supply duct
static pressure sensor
VAV
terminal units
Supply duct static control uses a duct pressure sensor mounted 2/3 down the duct to control supply air to design static pressure. The main issue in this case is it is often difficult to determine what the 2/3 point in the duct is. It is not always easy to determine what the most “critical” terminal unit is so this method does not always work out as well as conceptualized, and adding numerous pressure sensors can become expensive as each one has to be field mounted.
In our simple example system, since we only have one terminal unit, supply-duct static-pressure control is best implemented by locating the supply-duct static- pressure sensor in the inlet to the terminal unit itself, rather than “two-thirds down the duct.” This is the “critical terminal unit,” that is, the terminal unit that always requires the highest pressure. With the sensor at the terminal unit inlet, the controller must be set to 0.80 in. wg (SPC = 0.80 in. wg), the required terminal inlet pressure at design airflow. Figure 5A shows the system resistance curves, fan modulation curve, and fan curves. At our part-load airflow, the inlet guide vanes are repositioned, creating another new fan curve. The fan operates at the intersection of the new fan curve and the fan modulation curve, Point D, to deliver part-load airflow of 18,000 cfm.
As the pressure gradient in Figure 5B shows, fan static pressure at this point is reduced to 1.85 in. wg, duct static pressure is reduced to 1.12 in. wg, and the static pressure at the terminal unit inlet is held constant at 0.80 in. wg. The terminal unit must close to introduce a 0.50 in. wg pressure drop. The fan now requires only 12 bhp (approximately) to deliver 18,000 cfm at 1.85 in. wg.
supply
fan

10. Supply Duct Static Control
Sample Case
Supply duct static control uses a duct pressure sensor mounted 2/3 down the duct to control supply air to design static pressure. The main issue in this case is it is often difficult to determine what the 2/3 point in the duct is. It is not always easy to determine what the most “critical” terminal unit is so this method does not always work out as well as conceptualized, and adding numerous pressure sensors can become expensive as each one has to be field mounted.
In our simple example system, since we only have one terminal unit, supply-duct static-pressure control is best implemented by locating the supply-duct static- pressure sensor in the inlet to the terminal unit itself, rather than “two-thirds down the duct.” This is the “critical terminal unit,” that is, the terminal unit that always requires the highest pressure. With the sensor at the terminal unit inlet, the controller must be set to 0.80 in. wg (SPC = 0.80 in. wg), the required terminal inlet pressure at design airflow. Figure 5A shows the system resistance curves, fan modulation curve, and fan curves. At our part-load airflow, the inlet guide vanes are repositioned, creating another new fan curve. The fan operates at the intersection of the new fan curve and the fan modulation curve, Point D, to deliver part-load airflow of 18,000 cfm.
As the pressure gradient in Figure 5B shows, fan static pressure at this point is reduced to 1.85 in. wg, duct static pressure is reduced to 1.12 in. wg, and the static pressure at the terminal unit inlet is held constant at 0.80 in. wg. The terminal unit must close to introduce a 0.50 in. wg pressure drop. The fan now requires only 12 bhp (approximately) to deliver 18,000 cfm at 1.85 in. wg.

11. Critical Zone Reset sensor located at fan outlet
static pressure sensor
supply
fan
VAV
terminal
units
communicating BAS
The critical zone reset method combines the location-related benefits of fan outlet static control with operating cost savings that exceed those possible with supply-duct-static-pressure control. The single static-pressure sensor is located at the fan outlet, and the static-pressure controller is set to control the design flow static pressure. But the actual static pressure set point is continually adjusted (reset) so that at least one terminal unit in the system—the terminal unit serving the critical zone—is wide open.
Figure 6A shows the fan curves and system resistance curve for our simple system with critical zone reset. At 18,000 cfm, the vanes are repositioned so that the new fan curve intersects the original design flow system curve, Point E, at the lowest fan static pressure possible. As Figure 6B shows, fan static pressure is reduced to 1.52 in. wg, duct static pressure is reduced to 0.79 in. wg, and the pressure at the inlet to the terminal unit is reduced to 0.45 in. wg. The pressure drop across the wide-open terminal unit is only 0.17 in. wg, and the required fan brake horsepower is only 9.5 bhp. (Note: Although the duct static sensor is located at the fan outlet, critical zone reset has the effect of moving the sensor to the critical zone itself.) Fan static pressure and horsepower requirements for the different control methods discussed, as applied to our simple example system at various flow rates, are summarized in Figure 7. It demonstrates that critical zone reset is the most energy-efficient fan-capacity control method for our system.
damper positions
fan speed

12. Critical Zone Reset Sample Case
The critical zone reset method combines the location-related benefits of fan outlet static control with operating cost savings that exceed those possible with supply-duct-static-pressure control. The single static-pressure sensor is located at the fan outlet, and the static-pressure controller is set to control the design flow static pressure. But the actual static pressure set point is continually adjusted (reset) so that at least one terminal unit in the system—the terminal unit serving the critical zone—is wide open.
Figure 6A shows the fan curves and system resistance curve for our simple system with critical zone reset. At 18,000 cfm, the vanes are repositioned so that the new fan curve intersects the original design flow system curve, Point E, at the lowest fan static pressure possible. As Figure 6B shows, fan static pressure is reduced to 1.52 in. wg, duct static pressure is reduced to 0.79 in. wg, and the pressure at the inlet to the terminal unit is reduced to 0.45 in. wg. The pressure drop across the wide-open terminal unit is only 0.17 in. wg, and the required fan brake horsepower is only 9.5 bhp. (Note: Although the duct static sensor is located at the fan outlet, critical zone reset has the effect of moving the sensor to the critical zone itself.) Fan static pressure and horsepower requirements for the different control methods discussed, as applied to our simple example system at various flow rates, are summarized in Figure 7. It demonstrates that critical zone reset is the most energy-efficient fan-capacity control method for our system.

13. Fan Pressure Optimization
control
method
fan static
pressure
fan input
power
% full-load
power
airflow
full load
24,000 cfm
[11.3 m3/s]
2.7 in. H2O
[672.5 Pa]
22 hp
[16.4 kW]
100%
part load
fan outlet
18,000 cfm
[8.5 m3/s]
2.1 in. H2O
[523.1 Pa]
13 hp
[9.7 kW]
60%
supply duct
18,000 cfm
[8.5 m3/s]
1.9 in. H2O
[473.3 Pa]
12 hp
[8.9 kW]
55%
optimized
18,000 cfm
[8.5 m3/s]
1.5 in. H2O
[373.6 Pa]
9.5 hp
[7.1 kW]
43%

14. Fan Pressure Optimization
surge
duct static pressure control
static pressure
1000 rpm
900 rpm
potential savings
800 rpm
fan-pressure optimization
airflow

15. Fan Pressure Optimization
Advantages
Reduced supply fan energy
Lower sound levels
Reduced risk of fan surge
Where does this show up in Summit? Is there a good way to illustrate this as it applies to Trane?

16. Supply Air Temperature Reset
Advantages
Lower compressor and reheat energy
Increased economizing time
Disadvantages
May increase fan energy
Increased humidity level
Key to success:
Combine as a balanced approach with fan pressure optimization
This is generally a good strategy in our area since we don’t usually have too humid of air and we are economizing frequently anyways.
Have we ever calculated greatest savings, SAT reset vs. Fan pressure optimization?
The Oregon energy code requires the use of supply air temperature reset in our area. They decided this was a better strategy than Fan pressure optimization (which ASHRAE requires in 90.1) due to our mild climate and a greater potential for energy savings in this area. However the problem with this is that a compressor cannot maintain tight temperature control due to its large variance in temperature difference between each stage. This is where Trane’s experience in combining the strategies of Fan Pressure Optimization and Supply Air Temperature Reset can insure maximum energy savings. It can be difficult to determine the best way to combine these strategies however through the years we have created custom programming that is flexible for different jobs, but takes advantage of the experience of past jobs to ensure a proper working program.

17. Basic Control Model Example
SAT Reset, Pressure Optimization, Opt Start
Total Energy Savings %: 12 building energy savings

18. Demand-Controlled Ventilation
Methods of Ventilation:
Fixed Damper position
OA method (min at design)
ASHRAE method (min at worst case)
Flow Control
Ventilation Reset
Methods of DCV:
Using a fixed damper we can choose a position the damper should be open at design to meet ventilation requirements. Unfortunately this method no longer meets ASHRAE 62 due to the wide use of VFD’s and the fact that different spaces require different ventilation rates. Sticking with the fixed damper idea we can use ASHRAE’s method of keeping the damper at a minimum position that represents worst case scenario. As you can see this causes extreme over ventilation at design load.
Another method is using Flow control through a Trane Traq Damper or airflow station to determine the amount of outside air coming into the unit and then adjusting that value based on load conditions. We see that this greatly reduces the over ventilation but there is still one step more to take to have complete optimization.
Using ventilation reset we can dynamically determine the amount of outside air required at each different load condition, and then adjust the damper position to meet that requirement. This is the most energy efficient strategy that can be used while still maintaining compliance with ASHRAE 62

19. Demand-Controlled Ventilation
What kind of energy saving should you expect?
Model:
This bar graph was created by doing an energy study on a 3-story 60,000 sq ft office space. 24 zones, FC fan, vfd, comparative enthalpy economizing, and series-fan powered VAV’s

20. Demand-Controlled Ventilation
How do I save more energy?
The right tools
CO2 sensors
Occupancy sensors
TOD schedule
Advantages
Ensures compliance with ASHRAE 62.1
Reduce outside air during low occupancy
Decreases reheat energy
LEED EQ Credit 1: Outdoor Air delivery monitoring
An important factor when considering DCV is cost. It is not very cost efficient to put 100’s of CO2 sensors in a building to check every area. It is however a good idea to place sensors in the most critical areas while using other strategies such as TOD schedules and occupancy sensors for non-critical areas. It is also not very cost efficient to pump more outside air than necessary into an area that is not occupied. This is especially important when going for LEED credit EQ 2. Since this credit could potentially increase energy costs and take points away from EA credit 1 it is important to take measures to cut these energy losses with occupancy sensors and accurate TOD schedules.

21. LEED Credit Possibilities
EA Prereq 1 – Commissioning
EA Prereq 2 – Minimum Energy performance
EQ Prereq 1 – Minimum IAQ performance
EA Credit 1 – Optimize Energy Performance through energy simulation
EQ Credit 1 – Outdoor air delivery monitoring
EQ Credit 2 – Increased Ventilation
EQ Credit 6.2 – Controllability of systems: Thermal Comfort
EQ Credit 7.1 – Thermal Comfort: Design
Prereqs: EA Prereq 1- From equipment, to construction, to controls sequencing; commissioning is something that ensures engineered design is implemented during the build process. We will work with commissioning agents to help them understand our system and our sequences to make sure that the buildings runs as efficiently as possible.
EA Prereq 2- Controls strategies and sequences are crucial in ensuring compliance with ASHRAE standard 90.1 as well as reducing energy usage in HVAC. Through proper install and programming you can be sure that Trane controls will meet this standard.
EQ Prereq 1- Controls strategies and sequences are also crucial in complying with ASHRAE Where Trane can really shine in this area is in helping to make this process cost efficient by making the system as effective as possible without putting CO2 sensors in every room.
Credits: EA Credit 1- Optimizing energy performance is one of the most tangible LEED credit for an owner to understand. Decreasing energy bills is something that everyone can understand. This credit is also worth the most points in the LEED rating system. There are many ways to decrease energy usage such as higher efficiency equipment but controls is one of the few areas where there isn’t a huge cost associated with improved energy performance, but much like design it is an are that requires thought and a complete understanding of the applications.
EQ Credit 1- To help achieve the point in this credit Summit will monitor, trend, and alarm air quality for all spaces with high occupant density by using CO2 sensors in these critical locations.
EQ Credit 2- Taking it one step further, Summit through correct use of Supply-Air-Temperature reset and demand controlled ventilation the Trane control system can help with increasing outdoor air by 30% above minimum rates without making too large of an impact on the need for extraneous reheating or cooling.
EQ Credit This credit is pretty simple, just provide thermostats/temp sensors with adjustable setpoint wheels in at least 50% of the building occupants as well as providing comfort systems for all shared multi-occupant spaces.
EQ Credit Summit can help check the air temperature, radiant temperature, air speed, and relative humidity in spaces to ensure compliance with ASHRAE as well as provide thermal comfort to create productivity and well-being of building occupants.

22. Chiller Plant Optimization
Chilled Water Reset
Increasing chilled water temp to reduce compressor energy
Increases pumping energy
Plant optimization
Weighing the energy use of CT vs. Chiller vs. Pumps
COP Weight
COP of chiller vs. cooling tower and pumps
Size of cooling tower and temp

23. Chiller Plant Optimization
Modeled Example
COP of chiller vs. cooling tower and pumps
Size of cooling tower and temp

24. Energy Management “Intelligent Building” Building Dashboards
Demand Control

25. Energy Management

26. Energy Management

27. Retro-Commissioning The Easiest Energy Saver
Building Operators Changes
How To Stay On Top Of This

28. Constant Reporting

29. Thank You! References: Trane Engineering Newsletters
Intelligent Buildings Roadmap (CABA)
BuildingLogiX Images