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Heating, ventilation and air conditioning (HVAC) chillers are refrigeration systems that provide cooling for industrial and commercial applications. They use water, oils or other fluids as refrigerants.
HVAC chillers include a compressor, condenser, thermal expansion valve, evaporator, reservoir, and stabilization assembly. Compressing the refrigerant creates a high pressure, superheated gas that the condenser air-cools to a warm liquid. The thermal expansion valve (TXV) releases refrigerant into the evaporator, converting the warm liquid to a cool, dry gas. Often, a hot gas bypass is used to stabilize the cooling output by allowing the hot gas to warm up the evaporator. This causes a reduction in cooling efficiency, but stabilizes the chilled water temperatures. When water is pumped from the reservoir to the compressor, the chilling cycle begins again.
Condenser Cooling Specifications
HVAC chillers vary in terms of condenser cooling method, cooling specifications and process pump specifications.
There are several condenser cooling methods.
Air-cooled devices use a fan to force air over the condenser coils.
Water-cooled devices fill the condenser coils with circulating water.
Remote air or slit systems locate the main part of the chiller in the application area and position the condenser remotely, usually outdoors. The cooling air is supplied remotely to the chiller system.
Cooling specifications for HVAC chillers include cooling capacity, fluid discharge temperature, and compressor motor horsepower.
Cooling capacity - Total capacity of the chiller to remove heat from the process fluid. Cooling capacity is measured in kilowatts or tons of refrigeration.
Fluid discharge temperature - The required temperature of fluid discharge.
Compressor motor horsepower - This is a nominal value by which chillers can be approximately specified. True differentiating specifications are capacity and discharge temperature.
Process pump specifications include process flow, process pressure, and pump rating.
Process flow is the required flow capacity of the pump.
Process pressure is the required developed pressure of the pump.
Pump rating is the horsepower rating of the pump.
HVAC chillers are available with additional features to ensure best fit for the desired application.
Microprocessor controls - Computerized controller available for more precise programming of chiller performance.
Emergency alarms - Signals or alarms for emergency events such as over temperature, low coolant, etc.
Integral pump - Chiller contains integral pumping capacity.
Outdoor chillers- Constructed and rated for installation on the outside of a building with available rooftop mounting.
Modular systems - Modular systems can be configured in different ways based on application requirements. For example, in air conditioning systems, HVAC chillers are used to pump water to coils in different parts of a building.
Applications for HVAC chillers include the cooling of plastics, printing equipment, laser cutting machines, and large-scale medical devices such as magnetic resonance imaging (MRI) equipment.
HVAC chillers must adhere to certain standards to ensure proper design and functionality. Additional standards can be found at the IHS standards store.
H-08-4 VOL 3 613.0 - Standard for water cooled chiller unit and cooling tower.
MIL-C-22014 - Standard for chiller units, liquid, packaged, and electric motor driven.
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Industrial chillers cool water using refrigeration cycles to provide a constant stream of coolant for manufacturing and laboratory processes.