Cooling and Heating - Performance and Efficiency Terminology

Commonly used performance and efficient terminology in connection with cooling and heating systems:

SEER - Seasonal Energy Efficiency Ratio

The term SEER is used to define the average annual cooling efficiency of an air-conditioning or heat pump system. The term SEER is similar to the term EER but is related to a typical (hypothetical) season rather than for a single rated condition. The SEER is a weighted average of EERs over a range of rated outside air conditions following a specific standard test method. The term is generally applied to systems less than 60,000 Btu/h. The units of SEER are Btu/Wh. It is important to note that this efficiency term typically includes the energy requirements of auxiliary systems such as the indoor and outdoor fans. For purposes of comparison, the higher the SEER the more efficient the system. Although SEERs and EERs cannot be directly compared, the SEERs usually range from 0.5 to 1.0 higher than corresponding EERs.

COP - Coefficient of Performance

COP - Coefficient of Performance is the ratio of cooling or heating to energy consumption and can be expressed as

COP = useful energy transferred to the system per hour / energy applied to the system per hour

A refrigerator with a COP of 2 moves 2 Watts of heat for every Watt of electricity consumed. An air conditioner with a COP of 4 moves 4 Watts of heat for every watt consumed.

COP may also be used for domestic heating. An electric heater has a COP of 1. Each watt of power consumed produces 1 Watt of heat. Conventional heat pumps have COP of 2 - 5, delivering 2 to 5 times the energy they consume.

Example - Hot Water Radiator System

COP = 500 q dt / 3143 P                                                  (1)

where

q = hot water flow (gal/min)

dt = temperature difference between supply and return water (^oF)

P = input power to pump (kW)

EER - Energy Efficiency Ratio

Room air conditioners in general range from 5,000 Btu per hour to 15,000 Btu per hour. Select room air conditioners with EER of at least 9.0 for mild climates. In a hot climates, select air conditioners with EER over 10.

kW/t

IPLV - Integrated Part-Load Value

The term IPLV is used to signify the cooling efficiency related to a typical (hypothetical) season rather than a single rated condition. The IPLV is calculated by determining the weighted average efficiency at part-load capacities specified by an accepted standard. It is also important to note that IPLVs are typically calculated using the same condensing temperature for each part-load condition and IPLVs do not include cycling or load/unload losses. The units of IPLV are not consistent in the literature; therefore, it is important to confirm which units are implied when the term IPLV is used. ASHRAE Standard 90.1 (using ARI reference standards) uses the term IPLV to report seasonal cooling efficiency for both seasonal COPs (unit-less) and seasonal EERs (Btu/Wh), depending on the equipment capacity category; and most chillers manufacturers report seasonal efficiency for large chillers as IPLV using units of kW/ton. Depending on how a cooling system loads and unloads (or cycles), the IPLV can be between 5 and 50% higher than the EER at the standard rated condition.

IPLV can be expressed as:

IPLV = 1 / (0.01 / A + 0.42 / B + 0.45 / C + 0.12 / D)                                               (2)

where 

A = kW/ton at 100%

B = kW/ton at 75%

C = kW/ton at 50%

D = kW/ton at 25% 

n_c or E_c - Combustion Efficiency

For fuel-fired systems, this efficiency term is defined as the ratio of the fuel energy input minus the flue gas losses (dry flue gas, incomplete combustion and moisture formed by combustion of hydrogen) to the fuel energy input. In the U.S., fuel-fired efficiency are reported based on the higher heating value of the fuel. Other countries report fuel-fired efficiency based on the lower heating value of the fuel. The combustion efficiency is calculated by determining the fuel gas losses as a percent of fuel burned. [E_c = 1 - flue gas losses]

Thermal Efficiency (n_t or E_t)

This efficiency term is generally defined as the ratio of the heat absorbed by the water (or the water and steam) to the heat value of the energy consumed. The combustion efficiency of a fuel-fired system will be higher than its thermal efficiency. See ASME Power Test Code 4.1 for more details on determining the thermal efficiency of boilers and other fuel-fired systems. In the U.S., fuel-fired efficiency are typically reported based on the higher heating value of the fuel. Other countries typically report fuel-fired efficiency based on the fuel′s lower heating value. The difference between a fuel′s higher heating value and its lower heating value is the latent energy contained in the water vapor (in the exhaust gas) which results when hydrogen (from the fuel) is burned. The efficiency of a system based on a fuel′s lower heating value can be 10 to 15% higher than its efficiency based on a fuel′s higher heating value.

HSPF - Heating Seasonal Performance Factor

The term HSPF is similar to the term SEER, except it is used to signify the seasonal heating efficiency of heat pumps. The HSPF is a weighted average efficiency over a range of outside air conditions following a specific standard test method. The term is generally applied to heat pump systems less than 60000 Btu/h (rated cooling capacity.) The units of HSPF are Btu/w-h. It is important to note that this efficiency term typically includes the energy requirement of auxiliary systems such as the indoor and outdoor fans. For purposes of comparison, the higher the HSPF the more efficient the system.