Chilled Water Systems

Jim Chmielewski – HVAC Sales Manager Emerson Control Techniques

Energy Opportunity Areas

Chilled Water

Electrical Distribution

Compressed Air

Steam Generation

Electric Generation

Steam Distributionand Return

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

Chilled Water Systems

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

Chilled Water Systems

Chilled water is used in a variety of cooling requirements:

Air conditioning

Refrigeration Systems

Process Cooling for manufacturing processes

Dehumidification systems

Proper control of the production and the distribution of that chilled water presents large opportunities for savings

Chilled Water Systems

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

-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

Pump Application Desk BookSecond Edition (Paul N. Garay, PE)

Chilled Water Systems

Energy is wasted when a pump is run at full speed and its output is modulated by using a valve.

Chilled Water Systems

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

Elimination of expensive valves and valve controlsReduces power surges and stress associated with across the line startingProvides accurate flow controlLonger Pump and seal lifeReduced wear Less noiseA VSD is the BEST way to regulate flow to save

energy

Chilled Water Systems

Air Conditioning in large commercial buildings is accomplished through the use of chilled water distributed throughout the building by pumping systems .

Chilled Water

• Air Conditioning:

• 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

Chilled Water Pump

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.

Chilled Water

HVAC primary/secondary chilled water system

Cooling Tower

Cooling Tower

Chilled Water

Control of temperature in a process is important to the perfection of the product (Beer!)

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.

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

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.

Chilled Water Systems

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

A Typical Plant Operating Situation

Chilled Water SystemsA Typical Plant Operating Situation

Chilled Water

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

-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

Chilled Water

Chilled Water

In high humidity environments such as swimming pools, control of humidity is important .

First high humidity results in condensation in or on thestructure, which can lead to rapid deterioration of structural elementsand finish materials and the way humidity is controlled can affect the amount of energy your facility uses.

Secondly, high humiditycan result in uncomfortable conditions.

Efficiency Improvements (Cooling Tower)

CyclingTwo Speed Motors and ControlsVariable Speed

Example:

Annual Operating Cost (50 HP Cooling Tower Fan @ $0.10 kwhr, 365 days per year)cycled on and off – 20 hrs on 4 hrs off – $28,752Two speed - 12 hrs full speed, 12 hrs ½ speed – $19,714Variable Speed (24 hrs over continuous load profile) – $7,580

Efficiency Improvements (Pumps)

Pump Cycling Pump Throttling

Variable Speed

Example:

Annual Operating Cost (50 HP Pump @ $0.10 kwhr, 365 days per year)Pump Cycling 20 hrs on 4 hrs off - $28,752Pump Throttling - $24,997Variable Speed (24 hrs over continuous load profile) - $7,580

Efficiency Improvements (Chillers)

Compressor Cycling Compressor Modulation with a slide valve

Variable Speed Compressor

Example:

Annual Operating Cost (50 HP Compressor @ $0.10 kwhr, 365 days per year)Compressor cycled (on 20 hrs – off 4 hrs) - $28,752Constant speed compressor with slide valve 24 hrs on - $27,505Variable 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

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.

Questions?