CH-77-09-3 -- Central Plant Heat Recovery--Guidelines and Economics PDF

The use of central plant heat recovery systems, although not new, are becoming an increasingly popular means of conserving energy. And with the cost of energy continuing to rise coupled with energy shortages, it promises to be even more popular in the years to come.

Beyond this ASHRAE Standard 90-75 strongly encourages the use of heat recovery provided that the new energy expended in the recovery process is less than the amount recovered. More specifically, ASHRAE Standard 90-75 discourages the use of simultaneous heating and cooling systems unless recovered energy is utilized for reheating or mixing.

Conversely, systems such as terminal reheat or multizone may be utilized as long as the energy expended in reheating or mixing is recovered energy.

One of the more popular ways to design heat recovery systems is to build the water cooled condenser of a water chiller with two separate water circuits. One circuit rejects heat to the cooling tower during the cooling cycle of the building and the other circuit of the condenser on the heating cycle of the building rejects heat to the heating loop usually feeding the coils of a variable temperature constant volume system or, in some cases, a fin tube radiation system.

However, the lower temperature levels available off of the heating bundle of the condenser usually rule out the direct use of this recovered energy with radiation products to handle skin heating loads unless supplemental heat is provided to the condenser water prior to circulation through the fin tube radiation system.

The heat rejected from the condenser bundle may also be used in the form of reheat energy for coils in conventional terminal reheat systems or variable air volume reheat systems or it may be used to heat domestic hot water for buildings.

Because of this, you can see that the use of heat recovery really has no geographical limitations. The acid test for heat recovery application is do I have a source of heat and do I have a place to use it which are reasonably coincident in time.