Chilled water
Encyclopedia
Chilled water is a commodity often used to cool a building's air and equipment, especially in situations where many individual rooms must be controlled separately, such as a hotel. The chilled water can be supplied by a vendor, such as a public utility
or created at the location of the building that will use it, which has been the norm.
is pumped through an air handler to cool the air.
Regardless of who provides it, the chilled water (between 4° and 7°C) is pumped through an air handler
, which captures the heat from the air, then disperses the air throughout the area to be cooled.
, which is a heat exchange
device used to transfer waste heat to the atmosphere
. The extent to which the cooling tower decreases the temperature depends upon the outside temperature, the relative humidity
and the atmospheric pressure
. The water in the chilled water circuit will be lowered to the Wet-bulb temperature
or dry-bulb temperature
before proceeding to the water chiller
, where it is cooled to between 4° and 7°C and pumped to the air handler, where the cycle is repeated. The equipment required includes chillers, cooling towers, pump
s and electrical control equipment. The initial capital outlay for these is substantial and maintenance costs can fluctuate. Adequate space must be included in building design for the physical plant and access to equipment.
Utility supplied chilled water has been used successfully since the 1960’s in many cities, and technological advances in the equipment, controls and trenchless installation have increased efficiency and lowered costs.
The advantage of utility-supplied chilled water is based on economy of scale. A utility can operate one large system more economically than a customer can operate the individual system in one building. The utility's system also has back-up capacity to protect against sudden outages. The cost of such "insurance" is also markedly lower than what it would be for an individual structure.
The use of utility supplied chilled water is most cost effective when it is designed into the building’s infrastructure or when chiller/cooling tower equipment must be replaced. Commercial customers often lower their air conditioning costs from 10-20% by purchasing chilled water.
Public utility
A public utility is an organization that maintains the infrastructure for a public service . Public utilities are subject to forms of public control and regulation ranging from local community-based groups to state-wide government monopolies...
or created at the location of the building that will use it, which has been the norm.
Use
Chilled water cooling is very different from typical residential air conditioning where a refrigerantRefrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...
is pumped through an air handler to cool the air.
Regardless of who provides it, the chilled water (between 4° and 7°C) is pumped through an air handler
Air handler
An air handler, or air handling unit , is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning system. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and...
, which captures the heat from the air, then disperses the air throughout the area to be cooled.
Site generated
The condenser water absorbs heat from the refrigerant in the condenser barrel of the water chiller, and is then sent via return lines to a cooling towerCooling tower
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
, which is a heat exchange
Heat exchange
Heat exchange may refer to:*Heat transfer, an area of engineering concerned with the transfer of thermal energy *Heat exchanger, a device built for heat transfer from one medium to another...
device used to transfer waste heat to the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
. The extent to which the cooling tower decreases the temperature depends upon the outside temperature, the relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
and the atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
. The water in the chilled water circuit will be lowered to the Wet-bulb temperature
Wet-bulb temperature
The wet-bulb temperature is a type of temperature measurement that reflects the physical properties of a system with a mixture of a gas and a vapor, usually air and water vapor. Wet bulb temperature is the lowest temperature that can be reached by the evaporation of water only. It is the...
or dry-bulb temperature
Dry-bulb temperature
The dry-bulb temperature is the temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. Dry bulb temperature is the temperature that is usually thought of as air temperature, and it is the true thermodynamic temperature. It is the...
before proceeding to the water chiller
Water chiller
A water chiller is a mechanical device used to facilitate heat exchange from water to a refrigerant in a closed loop system. The refrigerant is then pumped to a location where the waste heat is transferred to the atmosphere....
, where it is cooled to between 4° and 7°C and pumped to the air handler, where the cycle is repeated. The equipment required includes chillers, cooling towers, pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s and electrical control equipment. The initial capital outlay for these is substantial and maintenance costs can fluctuate. Adequate space must be included in building design for the physical plant and access to equipment.
Utility generated
The chilled water, which absorbed heat from the air, is sent via return lines back to the utility facility, where the process described in the previous section occurs. Utility generated chilled water eliminates the need for chillers and cooling towers at the property, reduces capital outlays and eliminates ongoing maintenance costs. The physical space saved can also become rentable, increasing revenue.Utility supplied chilled water has been used successfully since the 1960’s in many cities, and technological advances in the equipment, controls and trenchless installation have increased efficiency and lowered costs.
The advantage of utility-supplied chilled water is based on economy of scale. A utility can operate one large system more economically than a customer can operate the individual system in one building. The utility's system also has back-up capacity to protect against sudden outages. The cost of such "insurance" is also markedly lower than what it would be for an individual structure.
The use of utility supplied chilled water is most cost effective when it is designed into the building’s infrastructure or when chiller/cooling tower equipment must be replaced. Commercial customers often lower their air conditioning costs from 10-20% by purchasing chilled water.