Manual S OEM Performance Data

Original Equipment Manufacturer (OEM) performance data describes how an HVAC system performs under different operating conditions. It may include heating capacity, total cooling capacity, sensible cooling capacity, airflow, and the effects of outdoor and indoor temperatures.

Expanded performance tables provide information beyond the equipment's nominal capacity or published AHRI rating. For example, a nominal 3-ton air conditioner does not necessarily deliver 36,000 Btu/h of cooling at the home's outdoor design temperature.

Performance data must correspond to the actual equipment combination being evaluated, including the outdoor unit and applicable indoor coil or air handler.

Manual S begins with the heating and cooling loads calculated using Manual J. The designer then evaluates equipment performance at the project's design conditions using applicable manufacturer data.

For cooling, this includes total and sensible capacity at the applicable indoor entering-air conditions, outdoor temperature, and airflow. Latent capacity is the difference between total and sensible cooling capacity.

For heating, the designer evaluates the equipment's available heating output at the outdoor heating design temperature. Heat pumps require particular attention because their heating capacity can change significantly as outdoor temperatures decrease.

AHRI ratings provide standardized performance information that allows HVAC equipment to be compared under consistent test conditions. For typical residential unitary air-conditioning equipment, standard full-load cooling rating conditions include 80°F indoor dry-bulb, 67°F indoor wet-bulb, and 95°F outdoor dry-bulb.

These standardized conditions are intended for consistent equipment ratings, not to represent every home's actual design conditions. Even where the outdoor design temperature is 95°F, the homeowner's indoor design temperature and humidity conditions may differ.

For example, equipment evaluated at 75°F indoor dry-bulb, approximately 63°F indoor wet-bulb, and 95°F outdoor dry-bulb may deliver a different total and sensible cooling capacity than at the AHRI rating conditions.

Because capacity changes with temperature, humidity, airflow, and equipment combination, AHRI-rated capacity does not necessarily represent the capacity available at the home's design conditions.

Manual S therefore uses applicable manufacturer performance information and the procedures of the relevant standard edition to evaluate equipment at the project's conditions.

The performance of an HVAC system depends on the specific equipment combination, not simply the model number or nominal capacity of the outdoor unit.

Different indoor coils, air handlers, blower settings, and matched components can affect available capacity and airflow. Multi-zone equipment introduces additional considerations because performance depends on the connected indoor units and applicable operating conditions.

A defensible Manual S selection identifies the equipment being evaluated and uses performance information appropriate to that configuration.