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Air Handler Operation for Equipment Removal
This section is available as background to clarify why an increase in utility energy consumption will occur with the
removal of internal loads from an operating room (OR). As seen in Figure A6-1 each air handler services a number of
Operating Rooms. Due to the codes dictating operating room airflow, each OR must be supplied with a minimum
outdoor air supply, and thus is a Constant Volume 100% outdoor air assembly. These ORs all require a certain heat
load to be removed, signified by the Q’s. Q is dictated by the internal load from equipment, lighting, occupancy, and
other heat gain. In the example below OR 2 requires 7,560 BTUH to be removed. With the supplied air, an air
temperature differential of 7° F between the supply and return is required to meet that load. Therefore, operating
rooms 1 and 3 will require the supplied air to be reheated by the specified amount in order to meeting that room’s set
point. If equipment is removed from either OR 1 or 3 their respective internal loads (Q) will be reduced, but the drop in
cooling load will be picked up by the reheat coils.
Figure A6-1: Air Handler Airflow Diagram
OTHER AHU TYPES
This is a different in single zone, multizone or VAV assemblies. For these scenarios an equipment load reduction is a
direct decrease in HVAC load, and in the case of variable airflow system a decrease in fan energy. The reheat required
to maintain setpoint will only occur under heating conditions
Salas O’Brien Engineers | expect a difference | Project No. 09104
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