1. Jim Chmielewski – HVAC Sales Manager Emerson Control Techniques
Chilled Water Systems
Jim Chmielewski – HVAC Sales Manager Emerson Control Techniques

2. Energy Opportunity Areas
Steam Generation
Steam Distribution
and Return
Chilled Water
Compressed Air
Electric
Generation
Electrical Distribution

3. CW Systems – General Info
In typical commercial buildings, water-cooled chilled water plants use a significant amount of energy.
They account for between 10% and 20% of the overall facilities usage and serve roughly one third of the commercial floor space.
Can consume more than 50% of electrical usage
Use approximately 20% of total electrical power generated in USA
US DOE estimates chillers expend up to 30% more energy through inefficiency

4. Chilled Water Systems
Chilled Water Systems are present in cooling applications for air conditioning in commercial buildings and process cooling for industrial processes.

5. Chilled Water Systems
Chilled water is used in a variety of cooling requirements:
Air conditioning
Refrigeration Systems
Process Cooling for manufacturing processes
Dehumidification systems

6. Chilled Water Systems
Proper control of the production and the distribution of that chilled water presents large opportunities for savings
A large chilled water system introduces several components that are involved in the production and distribution of chilled water. Pumps distribute the water to the areas requiring cooling. Cooling Towers reject some of the heat that is picked up by the chilled water to the atmosphere through evaporation of some of the water. And finally chillers which compress a refrigerant and through the use of a heat exchanger take heat out of the water that was picked up by the load.

7. Chilled Water Systems Why use water and not cool directly?
Water is an efficient medium to collect heat and is a liquid from 32 F to 212 F (lower if mixed with a glycol solution).
Water is an inexpensive medium to use.
Water can be transported from place to place under relatively low pressures.
Water is non-toxic and does not destroy the environment

8. Chilled Water Systems
Chilled water is distributed by pumps which follow the Affinity Laws:
Pump capacity is proportional to Pump speed
Pump head is proportional to the speed squared
Pump bhp is proportional to the speed cubed
The distribution of chilled water is accomplished with pumps. Pumps provide the opportunity for savings in that due to changing loads the full capability provided by the pump is rarely required. Systems are designed for worse case. Worst case is when the most amount of cooling is required. Due to changing environmental conditions and some over-sizing to provide safety factors within the design it becomes rare that the full capacity of the pump is required. Varying the speed of the pump provides tremendous opportunities for savings. Many times pump capacity is varied by introducing a valve which throttles the output of pump . This is a very inefficient way to control a pumps capacity.
Pump Application Desk Book
Second Edition (Paul N. Garay, PE)

9. Chilled Water Systems
Energy is wasted when a pump is run at full speed and its output is modulated by using a valve.
Modulating the amount of water produced by a pump is important in the proper control of any cooling process. Valves are the traditional method of pump control. They will reduce the amount of flow (gpm) as shown above by falling back on the fixed speed pump curve shown above. The extra pressure created when the flow is reduced shows up as an energy loss across the valve (or obstruction to flow) that is introduced to control the flow. A more efficient form of control is to control the speed of that pump. The energy consumed by both methods is shown in the shaded areas above.

10. Chilled Water Systems Provide significant energy savings when:
Pumps are operated at low flow rates
System has low static head
Local electricity costs are high
Building codes (ASHRAE 90.1) require variable speed chilled water pumps to meet the part load efficiency requirements

11. A VSD is the BEST way to regulate flow to save energy
Chilled Water Systems
Elimination of expensive valves and valve controls
Reduces power surges and stress associated with across the line starting
Provides accurate flow control
Longer Pump and seal life
Reduced wear
Less noise
A VSD is the BEST way to regulate flow to save energy
There are additional benefits with operating a chilled water pump at variable speed. The primary benefit is the increased efficiency but these other side benefits do exist.

12. Chilled Water
Air Conditioning in large commercial buildings is accomplished through the use of chilled water distributed throughout the building by pumping systems .
The most efficient way and in some cases the only practical way to provide air conditioning in large commercial building is through the use of chilled water.

13. Air Conditioning: Chilled Water
In large commercial buildings the chilled water passes through a coil that has air flowing across it and the air is cooled as it moves across the chilled coil. Much like heat is rejected through the radiator in your car
Chilled water is pumped out to a space and it passes through a coil which has air flowing across it. The chilled water picks up the heat from that air as the air passes across the coil.

14. Chilled Water Pump CTA HVAC Overview
April 19, 2017
Chilled Water Pump
The amount of air that is chilled by the chilled water that is required in each controlled space is determined the temperature of that space compared to setpoint. The setpoint is the setting on the thermostat that sets the desired room temperature. When more air flows across the coil and into the space there is greater amount of heat rejected to the chilled water thereby increasing the need for more chilled water. Likewise as the spaces become satisfied and demand decreases the amount of air and chilled water can be decreased.

15. Chilled Water In a primary/secondary chilled water pumping system:
CTA HVAC Overview
April 19, 2017
Chilled Water
In a primary/secondary chilled water pumping system:
Refrigerant is used to cool water in a chiller. The flow of water through the chiller is kept constant. Balancing valves are used to optimize the flow and compensate for build up of scale on the inside of piping and the tubes inside of the chiller.
The primary pumps produce a continuous flow and the secondary pumps are speed controlled as space conditions call for more or less cooling. Valves open and close to allow more or less water to flow through cooling coils. As space temperatures become satisfied the valves close causing the pressure to rise and the pumps can be slowed down.
A chilled water loop in larger commercial building consists of both a primary loop and secondary loop. The primary loop provides a constant flow through the chiller and the secondary loop draws chilled water from the primary loop as required by the space.

16. Chilled Water HVAC primary/secondary chilled water system
CTA HVAC Overview
April 19, 2017
Chilled Water
A chiller requires continuous flow through chiller. Too low of a flow will can cause freezing of the water flowing through it. The ability to draw from the loop and provide chilled water to the individual spaces is the job of the secondary loop.
HVAC primary/secondary chilled water system

17. Cooling Tower CTA HVAC Overview
April 19, 2017
Cooling Tower
Cooling Towers are a device that is used to lower the temperature of water that is used in a chilled water loop. A cooling tower has hot water that flows from the top of the tower across a medium (fill) where the heat is rejected by the flow of cooler air across the medium. The rejection of this heat is aided by a cooling tower fan which draws air across the medium. Much the same way that you can feel cooling on your skin when you put water on it and blow on your skin causing some of the water to evaporate.

18. Cooling Tower CTA HVAC Overview
April 19, 2017
Cooling Tower
Control of the cooling tower is also possible since the temperature of the water entering the tower can vary and since the tower sits outside the amount of cooling the tower will provide varies based on the environmental conditions of that day. The most cost effective form of capacity control of the cooling tower is speed control.

19. CTA HVAC Overview
April 19, 2017
Chilled Water
Chilled water is used in the production of a variety of foods, many of which we couldn’t do without. Control of temperature is critical to the proper fermentation of malt beverages.
Control of temperature in a process is important to the perfection of the product (Beer!)

20. Chilled Water Refrigeration (food processing & cold storage)
CTA HVAC Overview
April 19, 2017
Chilled Water
Refrigeration (food processing & cold storage)
Water or mixture of water and glycol is used to provide cooling
Some refrigerants used in food processing (such as ammonia) are toxic and it is desirable to contain their use to non-occupied spaces. Water is chilled by a compressor using this refrigerant to extract heat from the water and then the water is transmitted to the space requiring refrigeration.
Newer refrigerants that are more environmentally friendly operate but they operate under very high pressures making it important that they need not be transmitted all over a facility.
Providing direct cooling through the use of compressors and a refrigerant is possible in some cases, but there are continuing issues with refrigerants and their use. Some of the more efficient and easier to use refrigerants that can operate at lower pressures are either toxic or not environmentally friendly. The refrigerants that are non-toxic and environmentally friendly are not as efficient and must operate under much higher pressures.

21. CTA HVAC Overview
April 19, 2017
Chilled Water
Process Cooling for manufacturing processes – plastic molds, die castings, semi-conductor manufacturing
Cooling is required to control the rate of heating or cooling (accelerating it or decelerating it) in a manufacturing process to maintain the integrity of the finished product and/or to accelerate the process.
Chilled water produced and distributed the same way that an air conditioning system works is used in a variety of industrial applications. We will take a closer look at one of those applications.

22. CTA HVAC Overview
April 19, 2017
Chilled Water
Like many other processes, plastic extrusion requires a substantial amount of cooling capacity. During processing, the plastic is heated, melted and extruded through the die. It then must be cooled so that it will solidify into its new shape. The faster the heat can be removed, the faster the extrusion line can run. For this reason, rapid heat transfer is crucial to plant efficiency and profitability.
Plastic extrusion is one such process. A chilled water system can provide water to many extrusion lines. Do to change in product and the number of extruders operating at any given time, the need for chilled water varies.

23. A Typical Plant Operating Situation
Chilled Water Systems
A Typical Plant Operating Situation
A plastic container manufacturer has 9 plastic extrusion lines.
Chilled water is provided to each extruder from 1-75 pump.
The pressure at the extruder, the longest distance from the pump must be maintained at 65 psi for proper operation.
The chilled water system is design for all extruders to be able to operate.
Flow rate at each extruder is optimized to maximize production
This is a typical example of a plastics extrusion plant.

24. A Typical Plant Operating Situation
Chilled Water Systems
A Typical Plant Operating Situation
This system is similar to an air conditioning system with the exception of that in this case no cooling provided by a compressor and refrigerant is being used. The cooling is provided solely by a cooling tower. A large cooling pond (if available) is another way to provide the cooling for the water. If the water temperature does not have to be lowered below what the outside air temperature is this could prove to be an effective way to provide the cooling. But in any case delivery of the chilled water is still provided for by a pump which delivers it out to the machines as required. The valves show serve to control the flow and isolate any given machine if required for maintenance.

25. CTA HVAC Overview
April 19, 2017
Chilled Water
This shows the comparison of providing direct cooling for each of the plastics extrusion lines versus a central chiller and a chilled water loop. A lower initial cost and operating cost in this particular case show that a central chilled water system comes out ahead.
The above is an example of a facility having 16 plastic extruders and the initial cost and operating costs of a chilled water system versus a small portable chiller for each extruder

26. CTA HVAC Overview
April 19, 2017
Chilled Water
Dehumidification systems use chilled water to extract moisture from the air in a conditioned space.
Control of humidity is important to prevent static build up, prevent mold, maintain the integrity of the product being stored.
Swimming pools
Libraries
Plastic webs
Control of humidification is also important in conditioning of many spaces. Passing warm moist air over a coil that has chilled water running through it will act not only to lower the temperature of that air but it will also extract moisture from the air.

27. CTA HVAC Overview
April 19, 2017
Chilled Water
In high humidity environments such as swimming pools, control of humidity is important .
First high humidity results in condensation in or on the
structure, which can lead to rapid deterioration of structural elements
and finish materials and the way humidity is controlled can affect the amount of energy your facility uses.
Secondly, high humidity
can result in uncomfortable conditions.
Humidity control is important not only for comfort levels but to control the growth of mold and the control of condensation that can affect stored materials as well as degrade construction materials.

28. Efficiency Improvements (Cooling Tower)
CTA HVAC Overview
April 19, 2017
Efficiency Improvements (Cooling Tower)
Cycling
Two Speed Motors and Controls
Variable Speed
Example:
Annual Operating Cost (50 HP Cooling Tower $0.10 kwhr, 365 days per year)
cycled on and off – 20 hrs on 4 hrs off – $28,752
Two speed hrs full speed, 12 hrs ½ speed – $19,714
Variable Speed (24 hrs over continuous load profile) – $7,580
Cooling towers rarely see the peak loads that they are designed for. To compensate for a lighter they can be cycled on and off which must allow for some temperature drift since rapid cycling on and off of the cooling tower fan will result in failures. Alternately multiple smaller towers can be staged on and off or a two speed motor and starter can provide different levels of cooling. The optimal method is to control the speed of the cooling tower fan since it provides for the widest range of cooling, smallest power consumption and the best level of control of water temperature.

29. Efficiency Improvements (Pumps)
CTA HVAC Overview
April 19, 2017
Efficiency Improvements (Pumps)
Pump Cycling
Pump Throttling
Variable Speed
Example:
Annual Operating Cost (50 HP $0.10 kwhr, 365 days per year)
Pump Cycling 20 hrs on 4 hrs off - $28,752
Pump Throttling - $24,997
Variable Speed (24 hrs over continuous load profile) - $7,580
Pumps that distribute chilled water to the process whether it is conditioning the air in a space or providing cooling to an industrial process will have varying requirements. They can be cycled on and off but cooling requirements typically do not allow this. The normal method of controlling the output of the pump is through the use of a throttling valve or by using more and smaller pumps and staging them on as additional flow is required. The most efficient form of control of the amount of water that is required is by running the pump at variable speed.

30. Efficiency Improvements (Chillers)
CTA HVAC Overview
April 19, 2017
Efficiency Improvements (Chillers)
Compressor Cycling
Compressor Modulation with a slide valve
Variable Speed Compressor
Example:
Annual Operating Cost (50 HP $0.10 kwhr, 365 days per year)
Compressor cycled (on 20 hrs – off 4 hrs) - $28,752
Constant speed compressor with slide valve 24 hrs on - $27,505
Variable Speed (24 hrs over continuous load profile averaging 75% speed) – $25,786
*Variable Speed Energy Savings are minimal but optimal control of temperature and reduced maintenance and wear due to less frequent starting and stopping are benefits
Compressor control is slightly more difficult that fan or pump control in a chilled water system. One issue is that compressors do not exhibit the same large savings when their speed is reduced. The HP required and capacity produced by a compressor varies directly with speed. (ie half speed=half capacity and half the hp), versus the cube with a fan or pump. Another issue is that many compressors require at least 50% speed for proper lubrication. Cycling of compressors, multiple staging of compressors (2-25 HP compressors or 5-10 HP compressors, etc..rather than on 50 HP compressor) or a mechanical form of modulation are more commonly employed but compressors specifically designed for variable speed operation are becoming more popular since some compressors can also be run at higher than speeds to gain additional capacity (30-90 Hz results in a 50 HP compressor putting out half of its capacity at 30 Hz and 1.5 times its normal capacity at 90 Hz).

31. Cliff Notes for CW Energy Savings
Operate Chillers, Cooling Towers and Pumps at their peak efficiencies
Optimize temperatures and flow rates to operate equipment at peak efficiencies.
Check refrigerant pressures to minimize leaks.
Clean chiller tubes, cooling towers and keep water free of contaminants. Scale, corrosion and deposits can impede heat transfer and create resistance to flow.
Consider:
Variable Speed Drives to operate equipment at lower speeds when requirements are less than peak to optimize overall efficiencies.
Using power during off peak times if rate structures allow. Ice storage can sometimes be justified if off peak rates are favorable.

32. Questions?