Environmental Engineering Reference
In-Depth Information
In a typical air-cooled condenser, only sensitive heat is used to extract heat from the refrigerant.
When water evaporates on the surface of the condenser, the extra latent heat allows the
refrigerant to condensate at temperatures below the ambient temperature.
Often noncondensable gases accumulate in the refrigeration system and decrease its
overall efficiency. Typically, these gases are air (introduced during maintenance operations
or due to leaks in areas of the system with negative pressure) and by-products of lubricant oil
breakdown. Automatic purge systems can be installed to continuously eliminate nonconden-
sable gases from the system and avoid a drop in efficiency due to contamination of the
refrigerant in the long run.
Reducing cooling load consists of a series of actions that decreases the amount of heat the
refrigeration system needs to remove. This is accomplished by insulating pipes carrying cold
refrigerant, minimizing sources of heat in cold rooms, such as lights, forklifts, motors, and
personnel, and by reducing air infiltration from outside by using tight door seals (Masanet et
al., 2008).
All measures previously described have significant improvements in the efficiency of
refrigeration systems; however, that efficiency can be maintained only if adequate preventive
maintenance is in place. Relatively simple tasks such as maintaining clean heat transfer
surfaces, clean filters, an adequate load of refrigerant, and a leak-free system assure not only
efficiency but also increase the reliability of the refrigeration system.
Off-peak cooling
Off-peak cooling is the process of generating “cold” at night, storing the cold (“charging”),
and using it during the day when needed. The main incentive to use off-peak cooling is a lower
price of energy at off-peak night hours. In addition, when base load electricity at off-peak
hours is generated by nuclear or large hydroplants, then the consumer uses electricity with
virtually zero carbon dioxide emissions. A third advantage is that refrigeration equipment is
more efficient during night hours because the ambient temperature is lower, which makes the
condensers work more efficiently. In contrast, the main disadvantages of off-peak cooling are
the need for a thermal energy storage unit and additional equipment to circulate a heat transfer
fluid. The preferred medium for energy storage is ice because it is inexpensive and has a high
latent heat of fusion.
Off-peak cooling has been used mainly in air-conditioning applications, but the food-
processing industry needs to take a serious look at this technology. In installations that require
refrigeration during 24 hours, off-peak cooling probably would be impractical. However,
when large volumes of chilled water for processing are needed (e.g., the poultry industry) then
it could be a good option to consider. Another application to contemplate is the use of
cold water obtained at off-peak hours as a cooling medium for condensers in refrigeration
equipments during the day.
Energy monitoring and management
The first step is conducting an energy assessment, which consists of analyzing a facility's
energy end uses and performance at different levels of complexity. It can be as simple as a walk
through the plant and the review of utility bills and historical energy consumption to monitor-
ing individual equipment. The main objective of an energy assessment is to identify where
energy is wasted in the current system and to uncover new opportunities of energy savings
through changes in the process (EPA, 2007b).
In any energy-efficiency improvement, data will show whether the efforts are heading in
the right direction. Consumption data can be generated by constantly monitoring energy used
