Science Energy Recovery System
In early 2007, an energy recovery loop was installed in the science complex to reclaim heating and cooling energy from the building exhaust. Year round, the system is expected to save $53,000 in heating and cooling costs.
The laboratory exhaust hoods in Carr and Kendade labs are served by four 100-hp fans that exhaust the air, and two 150-hp air handlers that provide conditioned outside air to replace the exhaust. All these systems are variable speed, varying the airflow to accommodate the number of hoods in use.
These fans move roughly 50,000 cubic feet per minute through the space. That's a lot of air, enough to serve all the bathrooms in all the dorms on campus. And to heat and cool all that air takes a lot of energy, which costs about $85,000 a year. The original system's state-of-the-air variable volume controls did, in fact, save a lot of energy and money, a 50% operating savings over a constant-volume system, but additional opportunity existed. A heat recovery system takes some of the energy being thrown away in the exhaust stream, and uses it to pre-heat or pre-cool the incoming outdoor air. For the science complex, a "runaround loop" heat recovery system was selected. This system uses an intermediate fluid, in this case an antifreeze solution, to transfer heat between the exhaust and incoming makeup air streams. This system does not require that the incoming and makeup air streams be in close proximity, and does not run the risk of cross-contamination should a component fail.
Coils were placed in the exhaust and supply air streams, connected by pipes that contain the pumped antifreeze. In peak winter conditions, 74ºF exhaust air passes over the coil and warms the antifreeze from 34ºF to 41ºF. The warm fluid is pumped to coils in the air handlers, where it is cooled by incoming air at -5ºF. This air is warmed to 27ºF, which now requires less than half the heating energy to bring it to room temperature. In summer, the opposite happens where heat is transferred out of the hot incoming air into the conditioned exhaust air, dropping the load on cooling equipment. Operation of the system will be quite invisible as service to the labs will be unchanged. However,very significant loads will be removed for the central heating and cooling systems. The peak loads are approximately equal to those that will be added by the new residence hall, meaning that Mount Holyoke College can construct an entire new building with no net increase on the central campus heating and cooling systems.