Chilled Water, in the Air Conditioning Business

A chiller is a machine that removes heat from water via a vapor-compression refrigeration cycle. These machines can utilize a variety of refrigerants. Most often, water is the liquid chilled by the refrigerant. The water may also contain a percentage of and/or corrosion inhibitors.

CHW air conditioners are found in some very large residential applications. They are common in large and multistory commercial applications. Applications include buildings where space is not available for lower cost systems. CHW is also used in many industrial applications.

In air conditioning systems, chilled water is typically distributed to, located in air handling units, or fan coil units. The chilled water is re-circulated back to the chiller to be cooled again. These cooling coils transfer sensible heat and latent heat from the air to the chilled water, thus cooling and usually dehumidifying the air stream. A typical chiller for air conditioning applications is rated between 15 to 3000 tons in cooling capacity. Chilled water temperatures range from 40 to 45 degrees Fahrenheit .

The heat rejection side of water chillers can be either water cooled or air-cooled. Water cooled chillers incorporate the use of cooling towers which improve the chillers’ thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air’s wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature.

Water cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere.

Air Cooled chillers are intended for outdoor installation and operation. Air cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine’s condenser coil to expel heat to the atmosphere.

Chillers can be field constructed but most are installed as factory assembled units. Systems contain the following components to produce cooled or heated air:

Package Water Chiller (air cooled):

•Compressors
•Evaporator
•Metering device
•Air cooled condenser coils
•Condenser fans
Package Water Chiller (water cooled):

•Compressors
•Evaporator
•Metering device
•Water cooled condenser
•Condenser Water Pumps (CWP)
•Evaporative Cooling Tower
Chill Water Pumps (CHWP)

Air Handling Units (AHU), Fan Coil Units

•Chill water coils
•Supply air fan
Air Distribution System

•Ductwork
Advantages

The advantages Chill Water Systems:

•Typically long life heavy duty components.
•Versatility in zoning and design. Number of zones is unlimited. Multiple zones with different heat gain characteristics such as east, west building exposures, people, and different floors.
•Unlimited size. 50 tons to 3000+ tons.
•Multiple compressor technologies, screw, and centrifigul.
•Energy efficient units utilizing multiple compressors and variable speed compressors are available at additional cost.•Air cooled or water cooled condensers.•Supply fans are available in the standard constant volume, or more efficient variable speed variable air volume. Disadvantages

•Higher cost.
•Part load efficiency is important
Vapor-Compression Chiller Technology

There are basically four different types of compressors used in vapor compression chillers: Reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical machines that can be powered by electric motors or gas turbines. They produce their cooling effect via the cycle, also known as ‘vapor-compression’. With evaporative cooling heat rejection, their coefficients-of-performance (COPs) are very high and typically 4.0 or more.

In recent years, application of Variable Speed Drive (VSD) technology has increased efficiencies of vapor compression chillers. VSDs are being applied to rotary screw and scroll technology compressors.

Cost

Cost is about $4,500 per ton (12,000 Btu/h) of cooling capacity.

HVAV Business