# Air Conditioner Efficiency

Equipment used in cooling systems in residential and small commercial buildings often express the cooling system efficiency in terms like

*EER - Energy Efficiency Ratio and/or**SEER - Seasonal Energy Efficiency Ratio*

For air conditioners in rooms it is common to use * EER - Energy Efficiency Ratio *.

For central air conditioner systems it is more common to use * SEER - Seasonal Energy Efficiency Ratio. *

These ratings are normally posted on the ** Energy Guide Label ** attached to all new air conditioners.

Some air conditioner manufacturers participates in the voluntary ** Energy Star ** labeling program where the Energy Star label indicates higher

*EER*and

*SEER*ratings.

* EER * - ** Energy Efficiency Ratio **

* EER * is a measure of how efficient a cooling system operates in steady state (over time) when the outdoor temperature is at a specific level (outdoor conditions commonly used are * 95 ^{o}F (35 ^{o}C) * ).

- the higher
*EER*- the more energy efficient is the system

* EER * can be calculated

EER = q_{ c }/ E (1)

where

q_{ c }= output coolingenergy(Btu)

E = input electricalenergyconsumption (watt-hours, Wh)

* EER * is common for room air conditioners ranging * 5000 - 15000 Btu per hour (1.5 kW - 4.5 kW) *.

*1 Btu/h = 2.931x10*^{-4}kW = 0.0299 kpm/s = 0.252 kcal/h = 3.986x10^{-4}hk = 3.939x10^{-4}hp = 0.2163 ft lb/s

In mild climates air conditioners with EER of at least * 9.0 * should be selected. In hotter climates air conditioners with EER above * 10 * should be selected.

Note that EER is sometimes erroneous based on cooling power and electrical power consumption as

* EER _{ power } = P _{ c } / P _{ w } (1b) *

* where *

* P _{ c } = output cooling power (Btu/h) *

* P _{ w } = input electrical power consumption (W) *

### SEER - Seasonal Energy Efficiency Ratio

SEER - Seasonal Energy Efficiency Ratio - can be calculated

SEER = Q_{ c }/ E (2)

where

Q_{ c }= seasonal coolingenergy(Btu)

E = seasonal electricalenergyconsumption (Wh)

* SEER * should be at least * 10 * - there are units where SEER reach at least * 17 *.

### Example - * EER *_{ power } vs. COP _{ }

_{ power }vs. COP

_{ }

A cooling unit operates at * 1 ton cooling (1 ton/kW) * - or * 12000 Btu/h *.

The Energy Efficiendy Ratio EER _{ power } can be calculated as

* EER _{ power } = (12000 Btu/h) / (1000 W) *

* = 12 *

Coefficient of Performance - COP - can be calculated as

* COP = P _{ c } / P _{ w } (3) *

* where *

* COP = Coefficient of Performance *

* P _{ c } = output cooling power (Btu/h, W) *

* P _{ w } = input electrical power consumption (Btu/h, W) *

Since * 1 kW = 3412 Btu/h * - COP for * 1 ton cooling * can be calculated as

* COP = (12000 Btu/h) / ((1 kW) (3412 Btu/h / kW) *

* = 3.52 *

A small cooling unit operating at * 1 ton per kW (1000 watts) * is equivalent to a * COP * of * 3.52 * or an * EER _{ power } * of

*12*.

The relationship between * EER * _{ power } and * COP * can be expressed as

* EER _{ power } * =

*12 / 3.52 COP*

* = 3.41 COP *

## Related Topics

### • Air Conditioning Systems

Design of Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.

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Calculating chiller and cooling tower refrigeration loads - in tons.

### Cooling and Heating - Performance and Efficiency Terminology

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### Cooling Load - Convert between kW/ton to COP or EER

Convert between cooling load units like kW/ton, COP and EER.

### Efficiency

The measure of usefulness.

### Efficiency

Efficiency is the ratio useful energy output to energy input.