# Air Conditioner Efficiency

## The ratio between heat removed and power (watt) used - *EER* and *SEER*.

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*