How do you determine what the SEER is for a unit?
The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB and 67°F wB indoor entering air temperature by the Part Load Factor (PLF) of the system. (The PLF is supplied by the government.)
Add to this the Part Load Factor (PLF):
The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB/ 67°F wb 50% RH indoor entering air temperature by the “Part Load Factor” (PLF) of the system.
The PLF is a measure of the cyclic performance (CD) of a system and is calculated as follows: CD is Cyclical Data
PLF = 1.00 - (CD X’s 0.5)
“The cyclic performance (CD) value in the above equation has been determined by the government to be 0.25.” The government contends that the PLF should equal:
[1.00 - (.25 x .5)] = .125
1.00 - .125 = 0.875, which yields: PLF of 0.875
The SEER rating is at only one set of conditions that are NOT typical of what we design for. Summer Outdoor Design varies however, we usually design for 75-F indoors NOT 80-F, also when systems’ are downsized properly to achieve long runtimes the Part Load Factor becomes far less of a factor. Always go by the EER Rating NOT the SEER rating because as the SEER goes higher the EER ratio to it drops. Therefore, when the system is sized properly you have have a lot more steady-state continuous runtime cycles & the PLF will be minimized.
Proper system sizing for long runtimes along with a computerized variable speed blower motor to keep the evaporator’s heatload capacity rating optimized, would help to achieve more of the BTUH, EER, & SEER Ratings of the unit!
When selecting and installing a new unit. First, make all the changes you can to reduce the heat load/heat loss, --more insulation, etc. Then have a complete room-by-room Manual J. It was jointly developed by the Air Conditioning Contractors of America (ACCA) and the Air-Conditioning and Refrigeration Institute (ARI) heat load/loss calculation done on the house to insure correct sizing of the unit, then a Manual S for selecting the correct sized A/C equipment to meet the design load. Then use the Manual D for correct sizing of the Main and Branch Ducts. Manuals S and D were established by the ACCA. Use design outdoor conditions and daily temperature range exactly for your location per Manual J or ASHRAE Handbook of Fundamentals.