The energy efficiency of air conditioners and chillers is commonly represented in either COP, SEER or EER. Sometimes, people like to use kW/Ton and windows air conditioners use CEER to indicate energy efficiency value. But, what are these efficiency values mean? So, this is a complete guide to HVAC efficiency ratings.
Generally, industrial and commercial chillers use COP to represent their energy efficiency. Next, SEER is used to represent the energy efficiency of residential air conditioners, mostly in the United States.
As for EER, it has been long used by all kinds of air conditioning equipment around the world based on preferences. Meanwhile, window air conditioners always use CEER to represent their energy efficiency, also mostly in the United States.
Only certain countries practice the use of kW/Ton to compare energy efficiency. It's mostly used for medium to large capacity air conditioners and chillers by people who actually work in the HVAC industry. The country where I live, Malaysia, likes to use kW/Ton.
|Primary Unit||Conversion Unit|
|1 COP||3.5 EER|
|1 kW/Ton||3.5 COP|
|12 EER||1 kW/Ton|
Now, let's take a step back and ask what is energy efficiency? Basically, energy efficiency is about the result of a given input. The smaller the input and the greater the output, the better the resulting energy efficiency.
However, the reason why air conditioners don't use a simple input to output ratio to represent their energy efficiency is that the input and output are always changing based on the operating condition.
So, if we use a simple input/output ratio, the energy efficiency rating will not be accurate.
Contrarily, equipment like instantaneous water heaters can use a simple power input to heating capacity ratio to represent their energy efficiency because they use resistive heating which always yields a one-to-one ratio.
Hence, for air conditioners, government bodies and organizations came out with different ways to better represent their actual energy efficiency value.
So, let's dive into each energy efficiency rating standard to see what are they and how can we relate each of them for comparison and selection purposes.
Common HVAC Energy Efficiency Value
Let's take a look at the big picture. Following is a table showing the common energy efficiency value across different types of air conditioning systems sorted by efficiency:
|Air Conditioning System||COP||SEER||EER||CEER||kW/Ton|
|Water-Cooled Chiller (Commercial)||6.4||–||22.0||–||0.55|
|Evaporative Hybrid Chiller (Commercial)||4.6||–||16.0||–||0.75|
|Air-Cooled Chiller (Commercial)||3.7||–||12.5||–||0.96|
|Single-Zone Mini Split (Residential)||3.7||20.0||12.5||–||0.96|
|Window Air Conditioner (Residential)||3.5||–||12.0||12.0||1.00|
|VRF System (Residential)||3.5||14.0||12.0||–||1.00|
|Central Split (Residential)||3.5||14.5||12.0||–||1.00|
|Multi-Zone Mini Split (Residential)||2.9||16.0||10.0||–||1.20|
|Portable Air Conditioner (Residential)||2.9||–||10.0||6.5||1.20|
Take note that the above energy efficiency values are NOT averaged or calculated based on an acceptable amount of data. These values are derived based on my experience. However, I do believe they are more or less there.
With that said, it is a fact that most single-zone mini splits have a higher energy efficiency value than other types of residential air conditioners. For commercial applications, the most energy-efficient air conditioner is a water-cooled chiller.
Relevant post: 5 Types of Chillers in HVAC (Capacity & Efficiency).
However, there are other air conditioning systems such as geothermal and radiant cooling which can be more efficient than water-cooled chillers. But, they are less common.
What is COP in HVAC?
Although COP can be used for all kinds of air conditioners, it is more commonly used for large-capacity chillers. So, what exactly is COP in HVAC?
COP stands for coefficient of performance. The unit of measurement for COP is kW/kW. To calculate the COP of an air conditioner, divide the cooling output (in kW) by the power input (in kW). The higher the COP value, the higher the efficiency of the air conditioner.
The formula to calculate COP is as follow:
COP = Cooling Capacity / Power Consumption
COP = Coefficient of performance, kW/kW
Cooling Capacity = Cooling Output, kW
Power Consumption = Power Input, kW
Since the cooling capacity of air conditioners is often rated in BTU (British Thermal Unit), you need to divide it by 3412 to convert the cooling capacity to kW (kilowatt).
For example, given that a central split air conditioner has a cooling capacity of 48000 BTU with a power consumption of 4000 Watt, its COP can be calculated as follow:
COP = Cooling Capacity / Power Consumption
COP = (48000/3412) / (4000/1000)
COP = 14 / 4
COP = 3.5
Normally, we don't really put down the unit of measurement for COP. So, COP is usually unitless.
Just like any other type of energy efficiency value, COP is not a constant. In fact, COP changes based on the operating condition. A very common example is the part-load efficiency of a water-cooled chiller as illustrated in the following graph:
From the above graph, we can see that the chiller is most efficient when running at 80% load. Hence, running multiple chillers at part-load sometimes is more efficient than running a few chillers at full load.
In commercial chilled water systems, the part-load efficiency curve of chillers is one of the most important elements to study in order for the system to operate at the most optimal energy efficiency value.
In other words, we are trying to determine at what operating condition, the chiller will run at maximum COP so that we can have the most savings.
Although residential and small capacity air conditioners also experience COP fluctuations, we don't really study it as much because the impact is relatively insignificant.
What is SEER in HVAC?
SEER is the most important energy efficiency value to compare for residential air conditioners. But, what is SEER rating and why do we use SEER?
SEER stands for seasonal energy efficiency ratio. The unit of measurement for SEER is BTU/Watt. The SEER value of an air conditioner is calculated based on different outdoor conditions. The higher the SEER value, the higher the efficiency of the air conditioner.
SEER rating is determined based on different outdoor conditions. As we now know that the power consumption and cooling capacity vary based on the operating condition, SEER rating takes into account that factor.
One of the most impactful factors that affect the energy efficiency of an air conditioner is the outdoor air temperature. Basically, for cooling, the higher the outdoor temperature, the lower the efficiency.
Hence, in order for consumers to better expect the power consumption of an air conditioner, SEER rating isolates the outdoor temperature condition to just the summer where cooling demand is the highest.
In other words, SEER indicates the average energy efficiency of an air conditioner across the entire cooling season (summer) rather than based on a fixed operating condition.
Normally, the energy efficiency of air conditioners is required to be tested based on a fixed outdoor temperature. However, SEER uses a range of different outdoor temperatures to try to produce a more relevant and targeted efficiency value.
Hence, this type of energy efficiency rating system is geographical-dependent. Different regions of the world have different cooling-season outdoor temperatures. So, other countries may have their own version of SEER rating.
What is EER in HVAC?
EER is an energy efficiency rating that can be found in almost all kinds of air conditioners regardless of whether it is for residential or commercial applications.
EER stands for energy efficiency ratio. The unit of measurement for EER is also BTU/Watt. To calculate the EER value of an air conditioner, divide the cooling output (in BTU) by the power input (in Watt). The higher the EER value, the higher the efficiency of the air conditioner.
The formula to calculate EER value is as follow:
EER = Cooling Capacity / Power Consumption
EER = Energy efficiency ratio, BTU/Watt
Cooling Capacity = Cooling output, BTU
Power Consumption = Power input, W
The difference between EER and SEER is that EER doesn't account for different outdoor temperatures. Instead, it is based on a fixed outdoor temperature, usually at 35°C (95°F).
If an air conditioner is tested based on the same operating condition, we can compare one from different regions of the world and it'll be a fair and square, direct apple-to-apple comparison.
Furthermore, COP has the same characteristic as EER. In fact, they both represent the same thing but in different units of measurement. Usually, people prefer to use COP more than EER because COP is unitless.
In the HVAC industry, we rarely use EER for the energy efficiency of air conditioners. We prefer to use COP. To convert from EER to COP, simply divide the EER value by 3.5.
What is kW/Ton in HVAC?
Alongside COP, another frequently used efficiency rating by people working in the HVAC industry for the energy efficiency of commercial air conditioners is kW/Ton.
The full form of kW/Ton is kilowatt per refrigerant tonnages (RT). To calculate the kW/Ton of an air conditioner, divide the power input (in kW) by the cooling output (in RT). The LOWER the kW/Ton value, the higher the efficiency of the air conditioner.
The formula to calculate kW/Ton is as follow:
kW/Ton = Power Consumption / Cooling Capacity
kW/Ton = kilowatt per tons, kW/Ton
Power Consumption = Power input, kW
Cooling Capacity = Cooling output, RT
One refrigerant ton (RT) is equivalent to 12000 BTU. One refrigerant ton (RT) is also equivalent to about 3.5 kW of cooling capacity because 1 kW of cooling capacity is equivalent to 3412 BTU.
Relevant post: BTU to HP | BTU to Ton | BTU to kW | Conversion Tables.
kW/Ton is easier to use than COP. Although both are essentially the same thing, maintaining the use of refrigerant tons (RT) makes the calculation of kW/Ton much easier than COP.
Usually, large capacity air conditioners use refrigerant tons (RT) as the unit of measurement for their cooling capacity because BTU simply has too many digits.
For instance, a 200 RT chiller is also a 2.4 million BTU chiller. People will say: “I need a 200 RT chiller”. Nobody will say: “I need a 2 million BTU chiller”.
Using kW for the cooling capacity of a 200 RT chiller is inconvenient too. 200 RT is equivalent to about 700 kW. I rarely heard people say: “I need a 700 kW chiller”.
All and all, people tend to use RT here and there. Therefore, they simply divide the power consumption (always in kW) by the RT to get the kW/Ton efficiency; there is no need for them to convert from RT to kW for COP.
Nevertheless, kW/Ton is kinda like an informal / unofficial / not so professional way to say the energy efficiency of an air conditioner. If you ever read HVAC handbooks, they always use COP instead of kW/Ton.
What is CEER in HVAC?
Only window air conditioners are using CEER as the rating system for their energy efficiency. Now, what is CEER and how it is different from other ratings?
CEER stands for combined energy efficiency ratio. The unit of measurement for CEER is BTU/Watt. To calculate the CEER value of a window air conditioner, divide the cooling output of an air conditioner (in BTU) by the total power input including standby power (in kW). The higher the CEER value, the higher the efficiency of the window air conditioner.
Sometimes, we don't use the air conditioner 24/7. Hence, there are times when the air conditioner is in standby mode. However, it does consume some power while idling. So, CEER accounts for ALL of the power consumptions to better reflect the actual efficiency of window air conditioners.
What is HSPF in HVAC?
Mini splits not only use SEER value to represent their energy efficiency, but they also use HSPF value to represent the energy efficiency of their heating performance.
HSPF stands for heating seasonal performance factor. HSPF is the opposite of SEER. HSPF accounts for different outdoor conditions. Hence, the higher the HSPF value, the higher the energy efficiency of an air conditioner.
Most of the time, the SEER and HSPF of a mini split are almost proportional. Meaning, mini splits with high SEER values will also have high HSPF values.
Relevant post: 7 Best Mini Split Air Conditioners (2022 Buyer’s Guide).
On a side note, only mini splits with a heating function (also known as mini split heat pumps) have an HSPF value. Without heating, mini splits only have a SEER value.
COP is a more formal way to represent the energy efficiency of air conditioners and chillers. It is more commonly used for commercial chillers as well as residential central split units. The higher the better.
SEER is a better energy efficiency indicator for air conditioners in the United States and some other countries. HSPF is the opposite of SEER. The higher the better.
EER is sort of like a universal energy efficiency rating. It is the same as COP but with a different unit of measurement. For the people working in the HVAC industry, EER is less preferred than COP. The higher the better.
CEER so far is only applicable for window air conditioners in the United States and perhaps, some other countries. It accounts for total power consumption including standby power. The higher the better.
kW/Ton is a convenient way to represent the energy efficiency of large-capacity air conditioners and chillers because the unit of measurement for cooling capacity is refrigerant tons. The LOWER the better.
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