When it comes to air conditioner efficiency acronyms like COP and IEER, are you a sufferer of TMATKUW (Too Many Acronyms To Keep Up With) syndrome like me? Have you also noticed that even when you do know what an acronym stands for, there are often nuances in definition depending the source or scenario? If so, hopefully this article will assist with the management of your condition.

Here you will find formal acronym definitions as outlined by prominent HVAC authorities, guidelines and standards from Australia and around the world, as well as informal definitions that are often used in general contexts. By having a clearer understanding of air conditioner efficiency and the different ways it can be quantified, anyone involved in the HVAC industry can more effectively contribute to lowering the energy consumption of today’s energy-hungry buildings.

**General Definition**

COP is probably the most commonly used air conditioner efficiency acronym. The exact definition can vary (as you will learn in this article), however it is basically the ratio of useful heat transfer between a heat source and a heat sink, to the work required for the transfer to happen.

Generally speaking, COP can be expressed in relation to either useful cooling done (room air conditioning scenario) or the useful heating done (reverse cycle room heating scenario), with the equations below.

As per the above equations, the higher the COP figure, the greater the heat transfer is with respect to the energy input and therefore the greater the efficiency. Typically COP figures of well over 1 are achievable because refrigeration systems use energy to transfer heat from one place to another, as opposed to something like an electric element heater which transfers electrical energy directly into thermal energy (and therefore efficiency cannot be more than 100%).

Additionally, the COP of a refrigeration system is higher in heating mode because the heat generated by the compressor gets absorbed by the refrigerant and adds to the useful heat transfer.

**COP according to – AS NZS 3823.1.2 [1]**

Often formal definitions of COP only refer to heating mode scenarios, like below:

“ratio of the heating capacity to the effective power input of the device at any given set of rating conditions. NOTE where COP is stated without an indication of units, it shall be understood that it is derived from watts/watts.”

**COP according to – ASHREA Terminology [2]**

-Coefficient of performance:

“(1) ratio of the rate of net heat output to the total energy input expressed in consistent units and under designated rating conditions. (2) ratio of the refrigerating capacity to the work absorbed by the compressor per unit time.”

-Coefficient of performance, heat pump heating:

“the ratio of the rate of heat delivered to the rate of energy input, in consistent units, for a complete heat pump system, including the compressor and, if applicable, auxiliary heat, under designated operating conditions.”

**COP according to – AHRI Standard 210/240 [3]**

“A ratio of the cooling/heating capacity in watts to the power input values in watts at any given set of Rating Conditions expressed in watt/watt (a dimensionless quantity). For heating COP, supplementary resistance heat shall be excluded.”

COSP is an acronym that I have come across in academic papers and industry journals. It is a term that has arisen because the energy/power input component of COP and what it consists of exactly is sometimes a bit ambiguous or inconsistently defined. By some definitions the energy input refers to an air conditioning unit as a whole, with the compressor and all ancillary power consumers like fans and condenser water pumps being taken into account. While on the other hand, some definitions only seem to make reference to the power requirement of the compressor alone. This nuance could obviously result in quite a significant difference in calculated COP figures.

By including the word “system” in COSP, it is made clear that the power consumption of the whole air conditioning unit is taken into account with efficiency calculations.

**ACOP according to – AS/NZS 3823.2 [4]**

ACOP is a metric that attempts to quantify air conditioner heating mode efficiency in a more real-world manner. It takes into account a general heating mode run-time of 2000 hours per year, along with the standby power consumption of a unit (which can be considerable with compressor crankcase heaters). Refer to AS/NZS 3823.2 for the equation and a detailed explanation.

**HSPF according to – AS/NZS 3823.4.2 [5]**

As air conditioner efficiency varies with ambient condition and load, AS/NZS 3823.4.2 outlines a metric that considers a range of operating temperatures and capacities in order to better reflect the real world heating mode efficiency. It produces a seasonal efficiency figure calculated from a weighted equation that is based on a climate file for a particular location. This provides a much more substantial means of assessing and comparing air conditioner performance than ACOP or other more basic efficiency metrics.

Guidelines are provided for fixed capacity, two-stage, multi-stage and variable capacity units. This is important as it makes the efficiency advantages of variable capacity inverter units clear when other metrics fail to do so. Further, by adding a “T” to the acronym and making Total Heating Seasonal Performance Factor, requires that active, inactive and disconnected modes are considered in the efficiency calculations.

Refer to the AS/NZS 3823.4.2 for a full explanation on this efficiency metric.

**HSPF according to – AHRI Standard 210/240 [3]**

According to AHRI, HSPF is the heating mode equivalent of SEER (covered later in this article) with its definition being:

“The total space heating required during the space heating season, Btu, divided by the total electrical energy, W∙h, consumed by the heat pump system during the same season, Btu/(Wh). HSPF will vary depending on the region and Design Heating Requirement”.

**General definition**

EER only refers to efficiency in cooling mode. Where definitions are based in imperial units, EER is a dimensioned figure (with Btu/Wh), alternate to cooling mode COP which is a dimensionless figure (with W/W or J/J).

**EER according to – AHRI Standard 210/240 [3]**

“A ratio of the cooling capacity in Btu/h to the Total Power in watts at any given set of Rating Conditions expressed in

Btu/(W x h)”

**EER according to – AS/NZS 3823.1.2 [1]**

“ratio of the total cooling capacity to the effective power input to the device at any given set of rating conditions. NOTE Where the EER is stated without an indication of units, it is understood that it is derived from watts/watts.”

**EER according to – ASHREA Terminology [2]**

“(1) ratio of net cooling capacity in Btu/h to total rate of electric input in watts under designated operating conditions. (2) ratio of the net total cooling capacity to the effective power input at any given set of rating conditions, in watts per watt.”

**AEER according to – AS/NZS 3823.2 [4]**

According to AUS/NZS 3832.2, AEER is the cooling mode equivalent of ACOP. It takes into account a general cooling mode run-time of 2000 hours per year, along with the standby power consumption of a unit (which can be considerable with compressor crankcase heaters). Refer to AS/NZS 3823.2 for the equation and a detailed explanation.

**CSPF according to – AS/NZS 3823.4.1 [6]**

CSPF is the cooling mode equivalent of HSPF according to AS/NZS 3823.4.2

As air conditioner efficiency varies with ambient condition and load, AS/NZS 3823.4.1 outlines a metric that considers a range of operating temperatures and capacities in order to better reflect the real world cooling mode efficiency. It produces a seasonal efficiency figure calculated from a weighted equation that is based on a climate file for a particular location. This provides a much more substantial means of assessing and comparing air conditioner performance than AEER or other more basic efficiency metrics.

Guidelines are provided for fixed capacity, two-stage, multi-stage and variable capacity units. This is important as it makes the efficiency advantages of variable capacity inverter units clear when other metrics fail to do so. Further, by adding a “T” to the acronym and making Total Cooling Seasonal Performance Factor, requires that active, inactive and disconnected modes are considered in the efficiency calculations.

Refer to the AS/NZS 3823.4.1 for a full explanation on this efficiency metric.

**SEER according to – Greenhouse and Energy Minimum Standards Determination 2019 [7]**

Realising the downfalls of current regulations, the GEMS Determination 2019 draws heavily upon AS/NZS 3823.4 to provide more substantial requirements with regards to quantifying the efficiency of certain types of air conditioning equipment. It defines SEER as per below:

“A single air conditioner will have a number of different SEER ratings. A single reverse-cycle air conditioner could have:

– a Total Cooling Seasonal Performance Factor (TCSPF);

– a Heating Seasonal Performance Factor (HSPF);

– a Cooling Season Total Energy Consumption;

– a Heating Season Total Energy Consumption”

**SEER according to – ASHREA Terminology [2]**

-seasonal energy efficiency ratio – air-source combined appliance (SEERca)

“for the cooling season, the ratio of the total heat removed from the conditioned space to the total electrical energy input required to remove that heat, evaluated over all appliance operating modes. The quantity is expressed in units of Btu/Wh.”

-seasonal energy efficiency ratio – cooling only (SEER)

“for the cooling season, the ratio of the total heat removed from the conditioned space to the total electrical energy input if the combined appliance operated exclusively in a space-cooling-only (COOL) mode. The quantity is expressed in units of Btu/Wh.”

**SEER according to – AHRI Standard 210/240 [3]**

“The total heat removed from the conditioned space during the annual cooling season, Btu, divided by the total electrical energy, W·h, consumed by the air-conditioner or heat pump during the same season, Btu/(Wh)”.

**IEER according to – AHRI Standard 340/360 [8]**

IEER is another efficiency metric designed to better quantify annual performance and allow for a more comprehensive comparison between equipment. It considers the efficiency of equipment at different loading scenarios with a weighted equation producing the IEER figure. In principle it is similar to CSPF of AS/NZS 3823.4.1 but with standardised conditions and weightings (as opposed to having location specific climate files). The IEER equation is as follows:

EER = (0.02 x A) + (0.617 x B) + (0.238 x C) + (0.125 x D)

Where,

A = EER at 100% Capacity at AHRI Standard Rating Conditions

B = EER at 75% Capacity and reduced condenser temperature

C = EER at 50% Capacity and reduced condenser temperature

D = EER at 25% Capacity and reduced condenser temperature

IEER is the air conditioning equivalent of IPLV which is used with chillers.

AHRI Standard 340/360 outlines test procedures for fixed capacity units, staged capacity units, and variable capacity units. It is not designed to estimate the actual efficiency of a particular installation, instead it is just a means of equipment comparison. Refer to this standard for a full explanation of this metric.

**ESEER according to – Eurovent Certification [9]**

ESEER is a very similar metric to IEER as defined by AHRI, but with different capacity weightings and test conditions. The equation is as follows:

ESEER = (0.03 x A) + (0.33 x B) + (0.41 x C) + (0.23 x D)

Where,

A = EER at 100% Capacity at standard rating condition

B = EER at 75% Capacity and reduced condenser temperature

C = EER at 50% Capacity and reduced condenser temperature

D = EER at 25% Capacity and reduced condenser temperature

Refer to Eurovent Certification standards for a detailed explanation of this metric.

Hopefully all these air conditioner efficiency acronyms will now make a bit more sense to anyone who has previously been a bit confused. Note that there are likely many more acronyms in use around the world, and even more variations in definition. However, if this article has at least helped highlight that efficiency metrics can be quite nuanced and that considerations need to be made for proper comparisons between equipment, then it has served its purpose.

This article was written by Matthew Gellert who is a Business Development Engineer at Air Change.

[1] AS/NZS 3823.1.2:2012. Performance of electrical appliances – Airconditioners and heat pumps. Part 1.2: Ducted airconditioners and air-to-air heat pumps – Testing and rating for performance (ISO 13253:2011, MOD)

[2] ASHREA Terminology. https://www.ashrae.org/technical-resources/free-resources/ashrae-terminology

[3] AHRI Standard 210/240. 2017 Standard for Performance Rating of Unitary Air-conditioning & Air-source Heat Pump Equipment.

[4] AS/NZS 3823.2:2013. Performance of electrical appliances – Airconditioners and heat pumps. Part 2: Energy labelling and minimum energy performance standards (MEPS) requirements

[5] AS/NZS 3823.4.2:2014. Performance of electrical appliances – Airconditioners and heat pumps. Part 4.2: Air-cooled air conditioners and air-to-air heat pumps – Testing and calculating methods for seasonal performance factors – Heating seasonal performance factor (ISO 16358-2:2013, (MOD))

[6] AS/NZS 3823.4.1:2014. Performance of electrical appliances – Airconditioners and heat pumps. Part 4.2: Air-cooled air conditioners and air-to-air heat pumps – Testing and calculating methods for seasonal performance factors – Cooling seasonal performance factor (ISO 16358-1:2013, (MOD))

[7] Greenhouse and Energy Minimum Standards (Air Conditioners up to 65kW) Determination 2019, Commonwealth of Australia, Dated 25th March 2019

[8] AHRI Standard 340/360. 2015 Standard for Performance Rating of Commercial and Industrial Unitary Air-conditioning and Heat Pump Equipment.

[9] https://en.wikipedia.org/wiki/European_seasonal_energy_efficiency_ratio

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