Seasonal Energy Efficiency Ratio (SEER)

Seasonal Energy Efficiency Ratio (SEER)

 

As with EER, the SEER is the ratio of output cooling energy (in BTU) to electrical input energy (in Watt-hour). However the SEER is a representative measurement of how the system behaves over a season where the outdoor temperature varies:

The US DoE defined the formula to be used to calculate SEER values for residential air conditioning systems of less than 65,000 BTU/h (19 kW). The manufacturer makes EER or COP measurements at various values for indoor and outdoor temperature and then computes the SEER. The result is one number that may guide a prospective purchaser or owner of a system to compare one unit with another unit.6
As an example, consider a five ton unit (60,000 BTU/h) that runs on average eight hours a day during the cooling season. 7 At the ends of the season, the system may run only four hours a day but at the peak of the season, it is running 14 hours a day. Assume the cooling season is 180 days (about six months). Again, assume that on average throughout the season, the unit runs at two thirds of its capacity. The cooling energy is:

If the system has a SEER of 13, the total electrical energy used is:

If the cost of electricity is 17 ¢ per kWh, the cost to run this air conditioning unit during the season is:

The EER is usually specified under the conditions shown in table 1. The SEER is averaged over a range of temperatures that are less than or equal to this, including one test where the outside temperature is 82°F (28°C) and the inside temperature is 80°F (27°C). We know that as the delta temperature goes down, the efficiency goes up, so therefore the SEER is greater than the EER (typically by about 15% to 35%). One formula, to convert between the two was proposed by a student in a master’s thesis as follows:8

This implies SEER is 20% more, but in practice the value may be larger. 9 Also, because the conditions to calculate the SEER are fixed, they may differ widely from where the air conditioning unit is actually installed where temperatures and operating parameters vary significantly. Therefore, the actual ratio observed in practice may differ widely from the published SEER, making it difficult to accurately estimate the energy to run the system during a season.
In the US, the DoE specifies the minimum values for SEER as shown in table 2. The law was changed in January 2006 and the table lists the old and new standards.

A split system is one where the evaporator and condenser are in physically different places. The compressor is usually housed with the condenser and these are in one package that is usually installed outside or on a roof. The metering device (expansion device) is adjacent to the evaporator and installed inside the space where the air used to cool the space can flow.
A packaged system has all four major components (evaporator, condenser, metering device, and evaporator) in a single unit that is usually placed outside. Air ducts transport the supply and return air to the unit.
Using equation 9, we see that a unit that is rated at SEER of 13 is 30% more efficient than a unit rated at SEER 10.