What is A Good COP Value For Air Source Heat Pump
The Coefficient of Performance (COP) refers to the ratio of the heat or cooling produced by a heat pump to the specific energy input. The ideal COP value for heat pump systems starts at 2.0. The ideal COP value for an air-source heat pump is 2.0, while for a ground-source heat pump, it is 3.1. However, the COP of heat pumps can also exceed 4.0. In the following guide, we will discuss the ideal COP for different heat pump units and the practical significance of COP.
What is the ideal COP for an air-source heat pump?
If you are using a closed-loop heat pump, the ideal COP value ranges from 3.5 to 4.2. The maximum COP should be above 4.7.
Finally, the ideal COP value for a direct exchange geothermal heat pump is 4.1, with a maximum value of 5.0+.
COP should not be mistaken for the efficiency rating of an air-source heat pump. The SEER (Seasonal Energy Efficiency Ratio) for air-source heat pumps is 13 in the northern region of the United States and 14 in the southern region. Their minimum HSPF (Heating Seasonal Performance Factor) for heating efficiency is 8.5.
In addition, ground-source heat pumps can be classified into different categories based on their loop type and water-to-air or water-to-water configurations. You can find information about their efficiency on the Energy.gov website. Furthermore, as efficiency improves over the years, the most efficient figures will always have a “+” sign.
Can heat pumps be compared based on their COP?
Since environmental conditions can vary significantly during operation (and also change throughout the year), COP is not a suitable basis for comparing different types of heat pumps. For this purpose, you should refer to the SPF (Seasonal Performance Factor). However, when directly comparing similar heat pumps under the same operating conditions, COP is a very good benchmark for comparing efficiency.
Why is the Coefficient of Performance important when buying a heat pump?
Since heat pumps utilize free environmental heat, you only need to pay for the electricity used during operation (if you don’t generate your own electricity through photovoltaic systems).
Understanding the COP is crucial as it helps you assess its operational efficiency. This value also serves as an indicator of the environmental friendliness of your heating system. The higher the COP, the less electricity the heat pump consumes. This saves energy and reduces CO2 emissions. Last but not least, it also translates to lower heating costs.
How is the COP of an air-source heat pump calculated?
The heat output of an air-source heat pump is divided by the energy input to calculate the COP.
COP = Heat Output / Energy Input
Understanding the Coefficient of Performance
As mentioned earlier, the COP is a performance rating. It shows the effectiveness of an air-source heat pump in transferring heat by dividing the heat output by the energy input. Keep in mind that air-source heat pumps move heat from a low-temperature area to a high-temperature area.
This goes against the laws of thermodynamics, as heat is supposed to flow from high-temperature areas to low-temperature areas. In this regard, the “uphill” heat transfer against the thermodynamic law requires work. Therefore, the COP shows the efficiency of the air-source heat pump in doing this work. It indicates the power required for the equipment to move a fixed amount of heat at a fixed temperature.
If you want to know how much heat a heat pump can transfer with a certain amount of energy input, then COP is what you’re looking for. For example, an air-source heat pump with a COP value of 2.5 delivers heat that is 2.5 times the energy it consumes.
So, how do you determine the COP value of an air-source heat pump?
Simply put, you can determine the COP of a unit using the formula where COP is equal to the heat output divided by the energy input. The unit of measuring heat transferred is BTU (British Thermal Units) per hour, while energy is measured in watts. 1 BTU is equal to 0.293 watts.
For example, if the heat output of an air-source heat pump is approximately 60,000 BTUs, and its operating power is 42,000 watts, you can calculate the COP as follows:
Heat output in watts: 60,000 BTU * 0.293 = 17,580 watts
COP = 17,580 watts / 4,200 watts ≈ 4.18
How to maximize the COP of an air-source heat pump
While the COP will be set by the manufacturer and model of the air-source heat pump through its efficiency design, there are measures you can take to help ensure the heat pump runs as efficiently as possible (achieving its highest potential COP):
Insulate your home: Properly insulating your home can help retain heat inside for a longer period, reducing the demand on the heat pump to provide the desired indoor temperature and using less energy.
Use a programmable thermostat: A programmable thermostat can also help improve the COP of an air-source heat pump. You can set heating times and temperatures, so the heat pump doesn’t have to work hard to meet high user demands when you’re away or asleep.
Regularly maintain your heat pump: Having qualified technicians service your air-source heat pump is essential, typically at least once a year. This will help ensure it operates at peak efficiency and doesn’t use unnecessary energy.
Opt for a more efficient heating system: The indoor heating unit is as important as the heat pump in terms of efficiency and COP. As ASHP systems operate at lower temperatures compared to other heating systems, it becomes especially important for the internal heating unit to release heat as efficiently as possible. For air-source heat pumps, using underfloor heating and modern radiators with larger surface areas can help improve overall efficiency.
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Methods to increase heat release efficiency
The COP of an air-source heat pump can be increased by reducing the cold-to-hot temperature difference during the unit’s operation. Since the air-source heat pump operates in both heating and cooling modes, the output temperature must be lowered. The new reading should be around 30 °C. Oversized pipes, piped floors, walls, or ceilings should be used to reduce noise. On the other hand, the input temperature should be raised. In this regard, groundwater should be used instead of air.
By increasing the size of the internal heat exchanger, the heat pump can be improved. This will increase efficiency while reducing the energy consumption of the compressor, as it reduces the temperature difference between the equipment’s interior and the compressor.
Compared to single-effect coolers, double-effect and triple-effect coolers have super high efficiency, with a COP of more than 1. They require high-pressure and superheated steam, but the steam consumption for cooling one ton for 60 minutes is still relatively low.
Factors affecting the coefficient of performance (COP) performance
Air-water heat pumps absorb heat in the summer and discharge it into the soil or water. Air source also works in the same way in outdoor air. Air-water heat pumps are easy to extract and release heat. This is because the ground temperature is higher in winter and lower in summer.
Nevertheless, some factors may hinder their performance, such as:
Type of air-water loop
Open-loop heat pumps usually have the highest COP. On the other hand, the COP of closed-loop heat pumps is relatively higher but not as high as open-loop heat pumps.
Usage
Like many ground-source heat pumps, their optimal mode of operation is cooling rather than heating.
Operating at a higher or lower stage?
Ground-source heat pumps have dual compressor capabilities. Using the lower stage only consumes less energy. Therefore, the COP of the heat pump will be higher when operating in the lower stage.
Outdoor temperature
The outdoor temperature has a significant impact. For instance, if the heat pump is conditioning indoor air, and the outdoor temperatures are 80°F and 70°F, respectively, there will be a temperature difference of 10 degrees indoors. At 80°F, heat dissipation is straightforward. However, if the outdoor temperature reaches 110°F, the heat pump will have to exert more pressure, consume more energy, and thus lower the COP.
In summary, looking back, the ideal COP for an air-source heat pump should be above 4.0. What is the load type of the air-source heat pump? Is it operating in cooling mode or heating mode? Are you using the higher or lower stage? In general, the COP of a heat pump can reach 4.7 or higher under optimal operating conditions.
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