APPENDIX A (Continued)
Direct Exhaust Systems. Direct exhaust systems may
reduce the cooling load in a space requiring high ventilation
rates to remove high heat loads of a source. Evaluate the energy
required for the extra makeup air.
Heat Recovery Systems (Cascading Energies). Consider
the following economic factors when evaluating heat recovery
Higher first costs,
Higher maintenance costs,
Additional building space requirements, and
Added complication to HVAC equipment.
Exhaust Air Heat Recovery. With the air exhaust heat
recovery system in the heating mode, heat from exhaust air is
recovered and used to preheat the outdoor air supply, domestic
hot water, boiler combustion air, and boiler makeup water. In
the cooling mode, exhaust air is used to pre-cool outdoor air.
In addition to the economic factors cited above, system pressure
is increased. The five methods available for exhaust air heat
recovery air are as follows:
Rotary air wheel method,
Static heat exchanger method,
Heat pipe method,
Runaround system/closed loop method, and
Runaround system/open loop method.
The rotary air wheel, static heat exchanger, and heat
pipe methods require supply and exhaust ducts to be adjacent
ducts. Therefore, duct design should ensure that the outside air
and exhaust air louvers are adequately separated to prevent cross
information, refer to ASHRAE Equipment Handbook, the chapter
entitled "Air-to-Air Energy Recovery Equipment."