Air Source Heat Pump Efficiency: A Comprehensive Guide

Discover the efficiency of air source heat pumps (ASHPs) in providing low-carbon heating. Learn about COP, factors affecting efficiency, and tips for optimisation.

Key Takeaways

 

  • Air source heat pumps (ASHP’s) are typically 200-400% efficient which means that you get 2-4kWh of heat output for every 1kWh of electricity to run the pump.
  • Air source heat pumps are highly efficient heating systems that extract heat from the outside air and transfer it into a building.
  • Several factors contribute to the efficiency of an air source heat pump system, including heat pump design, insulation and weatherisation of the building, proper sizing and installation, and regular maintenance and servicing.
  • The efficiency of an air source heat pump is crucial for energy savings, reduced carbon emissions, and long-term investment. Any heating system that transports heat via water can further improve efficiency by using EndoTherm.

How Does an Air Source Heat Pump Work?

An air source heat pump (ASHP) is a renewable heating technology that extracts heat from the outside air and transfers it into a building to provide space heating and hot water. It operates on the principle of refrigeration, similar to a refrigerator but in reverse. An air source heat pump consists of three main components: an outdoor unit, an indoor unit, and a refrigerant.

 

  1. The outdoor unit contains a fan that draws in air from the surroundings.
  2. The air passes over an evaporator coil containing a refrigerant, which absorbs the heat from the air and evaporates becoming a gas.
  3. The evaporated refrigerant is then compressed by a compressor, which increases its temperature.
  4. The hot gas then passes through a heat exchanger where it transfers it’s heat to water that circulates throughout a building via piping and ductwork, releasing the heat into the building.
  5. The cooled gas then passes through another heat exchanger where it absorbs heat from the indoor circulating ductwork returning to the evaporator coil where the cycle repeats.
Air Source Heat Pump Efficiency

How Efficient Is an Air Source Heat Pump?

Air source heat pumps are highly efficient heating systems, capable of producing more energy than they consume. The efficiency of an ASHP can be measured by its Coefficient of Performance (COP), which is the ratio of heat output to electrical input. A higher COP indicates a more efficient system.

Depending on conditions, ASHPs can achieve COPs of 2 to 4, meaning they produce 2 to 4 units of heat for every unit of electricity consumed. This high efficiency is due to the fact that the majority of the heat generated comes from the ambient air, a free and renewable energy source.


How Important Is the Efficiency of an Air Heat Pump?

The efficiency of an air source heat pump is of utmost importance for several reasons:

  1. Energy Savings: An efficient heat pump consumes less electricity, resulting in lower energy bills. The higher the COP, the more energy-efficient the system, leading to significant cost savings over time.
  2. Reduced Carbon Emissions: Air source heat pumps are a low-carbon heating technology, and their efficiency contributes to further reducing carbon emissions. By utilizing renewable energy from the air, ASHPs help combat climate change and reduce environmental impact.
  3. Long-Term Investment: Investing in an efficient ASHP ensures long-term reliability and performance. A well-maintained and efficient system can provide heating and hot water for many years, offering a return on investment and enhancing property value.

 

EndoTherm can improve the efficiency of Air Source Heat Pumps even further. Get in touch to find out more...

What Factors Affect the Efficiency of an Air Source Heat Pump?

Several factors can influence the efficiency of an air source heat pump:

Ambient Temperature and Climate Conditions

The ambient air temperature affects the efficiency of an ASHP. As the temperature drops, the heat pump’s ability to extract heat from the air decreases, reducing its efficiency. However, modern heat pumps are designed to operate efficiently even in colder climates, with some models capable of extracting heat at temperatures as low as -15°C (5°F).

Sizing and Installation Considerations

Proper sizing and installation are crucial for maximising air source heat pump efficiency. Undersized heat pumps may struggle to meet heating demands, leading to reduced efficiency. Oversized units can short cycle, turning on and off frequently, which decreases efficiency and increases wear and tear on the system.

Insulation and Weatherisation of the Building

Well-insulated buildings retain heat more effectively, reducing the workload on the heat pump. Proper insulation and weatherisation prevent heat loss through walls, roofs, and windows, allowing the heat pump to operate more efficiently.

Proper Maintenance and Regular Servicing

Regular maintenance and servicing ensure the heat pump operates at its optimal efficiency. Cleaning or replacing filters, checking refrigerant levels, and inspecting components prevent issues that could reduce efficiency. Additionally, professional servicing can identify any potential problems and address them promptly.


Improving Air Source Heat Pump Efficiency with EndoTherm

The efficiency of a heating system powered by an air source heat pump (ASHP) can be further improved by optimising the performance of the fluid within the heating system. This is where EndoTherm comes in.

EndoTherm is an additive that can be added to any wet heating system that changes the properties of the system fluid to perform better.

Independent tests have shown that EndoTherm can save up to 15% on heating energy consumption.

By improving the performance of the heating system, EndoTherm can help already highly efficient systems that feature air source heat pumps to operate even more efficiently, further reducing energy consumption and carbon emissions.

EndoTherm is a cost-effective and easy-to-install solution for improving the efficiency of wet heating systems. It can be added to any wet heating system, regardless of heat source.

By optimizing the performance of the heating system, EndoTherm can help to maximise the energy savings and carbon reductions of low carbon heating systems.

Low Carbon Heating Systems can further improve efficiency with EndoTherm

How Is the Efficiency of an Air Source Heat Pump Measured?

The efficiency of an air source heat pump can be determined via a number of measures including Coefficient of Performance (COP), Energy Efficiency Ratio (EER) and Seasonal Performance Factor.

What is the Coefficient of Performance?

The Coefficient of Performance (COP) is a measure of the efficiency of an air source heat pump. It represents the ratio of useful heat output to electrical input. A COP of 3, for example, means that the heat pump produces three units of heat for every unit of electricity consumed.

COP can vary depending on the operating conditions of the heat pump. Manufacturers typically provide COP values for specific temperature ranges, allowing users to assess the system’s efficiency in various climates.

 

How Can You Measure Air Source Heat Pump Efficiency Through Coefficient of Performance?

To measure the efficiency of an air source heat pump, you can calculate its Coefficient of Performance (COP) using the following formula:

COP = Heat Output (kW) / Electrical Input (kW)

The heat output is the amount of heat the heat pump provides to the building, measured in kilowatts (kW). The electrical input is the amount of electricity the heat pump consumes, also measured in kilowatts (kW). By dividing the heat output by the electrical input, you can determine the COP and assess the system’s efficiency. The COP can be different for heating and cooling modes since the heat pump works in reverse during the cooling mode. It is important to note that higher COP values indicate better efficiency, as they represent greater heat output per unit of energy input.

COP is closely related to energy efficiency. The higher the COP, the more energy-efficient the heat pump, resulting in reduced energy consumption and lower utility bills. However, it is essential to consider other efficiency metrics in conjunction with COP to obtain a comprehensive understanding of the system’s overall performance.

 

Factors Affecting Coefficient of Performance

 

Impact of Temperature Differences on COP

COP is influenced by the temperature difference between the heat source (outdoor air) and the heat sink (indoor air). This relationship can be understood through Carnot’s theorem, which states that the maximum possible efficiency of a heat engine is determined by the temperature difference.

The outdoor temperature affects the heat pump’s ability to absorb heat from the air, while the indoor temperature determines the desired heat output. As the temperature difference increases, the heat pump’s COP decreases. Therefore, it is crucial to consider climate conditions and insulation levels when sizing and selecting an air source heat pump.

 

Importance of Proper Sizing and Installation

Proper sizing and installation of air source heat pumps are vital for achieving optimal COP. Undersized or oversized systems can lead to reduced efficiency and increased energy consumption. Proper airflow, refrigerant charge, and ductwork design are essential factors to consider during installation. Inadequate airflow or improper refrigerant levels can negatively impact the COP, reducing the overall efficiency of the system.

 

Impact of Refrigerant Choice and System Configuration

The choice of refrigerant and the design of the heat pump system also influence the COP. Different refrigerants have varying thermodynamic properties, affecting the heat transfer capabilities and efficiency of the heat pump.

Refrigerants with low ozone depletion potential (ODP) and global warming potential (GWP) can contribute to higher COP values, reducing the environmental impact of the heat pump system. Additionally, the configuration of the system, such as the type of compressor and heat exchanger, can affect the overall efficiency and COP.

 

What Is the Coefficient of Performance of an Air Source Heat Pump?

The Coefficient of Performance (COP) of an air source heat pump indicates its efficiency in converting electrical energy into heat. COP values typically range from 2 to 4, meaning that for every unit of electricity consumed, the heat pump produces two to four units of heat. The higher the COP, the more efficient the heat pump.

It’s important to note that COP can vary depending on the operating conditions of the heat pump. Manufacturers often provide COP values for specific temperature ranges, allowing users to assess the system’s efficiency in different climates.

 

Practical Implications and Benefits of COP

 

Importance of Considering COP when Selecting an Air Source Heat Pump

When selecting an air source heat pump, COP is a valuable metric to consider. A higher COP signifies improved energy efficiency and lower operating costs. By choosing a heat pump with a higher COP, homeowners and businesses can benefit from reduced energy bills and a smaller environmental footprint.

 

Financial Benefits of Energy-Efficient Air Source Heat Pumps

Investing in energy-efficient heat pumps with higher COP can provide significant long-term financial benefits. The reduced energy consumption leads to lower utility bills, offsetting the initial investment over time. Additionally, energy-efficient systems may qualify for government incentives or rebates, further enhancing the financial advantages.

 

Environmental Impact and Emissions Reduction

Air source heat pumps with high COP contribute to reducing greenhouse gas emissions and combating climate change. By efficiently utilising renewable energy from the surrounding air, these systems minimise reliance on fossil fuels, resulting in lower carbon dioxide emissions. Increased adoption of heat pumps with high COP can play a crucial role in achieving sustainability goals and a greener future.


What is Energy Efficiency Ratio (EER)?

When looking at the efficiency of air source heat pumps, one key metric to consider is the Energy Efficiency Ratio (EER). The EER measures how efficiently a heat pump converts electrical energy into cooling power. Specifically, it is calculated by dividing the heat pump’s cooling output, measured in British Thermal Units (BTUs), by the electrical energy input, measured in watt-hours.

The EER calculation takes into account important factors like the outdoor and indoor temperatures and humidity levels. Heat pumps operating under more extreme temperature or moisture conditions require more electrical input to achieve the same cooling output.

As a general rule, a higher EER indicates a more efficient air source heat pump system. Industry experts often recommend selecting units with an EER of 12 or greater. The EER is comparable to the Seasonal Energy Efficiency Ratio (SEER) used for rating the cooling efficiency of air conditioners.

The EER is an important metric for evaluating the cooling efficiency and energy savings of an air source heat pump. Focusing on systems with a higher EER will lead to lower electricity bills and more environmentally friendly operation. When making purchasing decisions, be sure to compare EER ratings to pick the most energy efficient heat pump.


What is Seasonal Performance Factor (SPF)?

When evaluating the efficiency of air source heat pumps for heating, an important metric to consider is the Seasonal Performance Factor (SPF) or Heating Seasonal Performance Factor (HSPF). Unlike the Coefficient of Performance (COP) which measures efficiency at a single point in time, the SPF takes into account performance across an entire heating season.

The SPF is calculated by dividing the total heat energy supplied to the building over a season by the electricity consumed by the heat pump system during that same period. A higher SPF indicates greater efficiency, as more heat is being produced per unit of electrical energy.

Since the SPF factors in a heat pump’s operation at both high and low outdoor temperatures, it provides a more realistic measure of efficiency than the COP alone. The actual SPF is influenced by variables like the heating system’s flow/return temperatures, the heat source, the building’s insulation and heat losses, and owner heating habits.

The Seasonal Performance Factor gives a good annual snapshot of an air source heat pump’s heating efficiency under real-world conditions. Along with the COP, it is an important metric to examine when comparing different systems and making purchase decisions. Focusing on heat pumps with higher SPF ratings will lead to lower heating bills and more environmentally sustainable operation.


How to Make an Air Source Heat Pump More Efficient?

To improve the efficiency of an air source heat pump, consider the following tips: 

  • Optimise heat pump settings: Adjust the heat pump’s settings to maximise efficiency. Consult the manufacturer’s guidelines to ensure the system operates at its optimal performance. Avoid setting the thermostat too high or too low. Each degree increase or decrease can impact energy consumption. Optimal temperatures for comfort and efficiency are typically around 18-21°C (64-70°F).
  • Use smart controls: Utilise programmable or smart thermostats to schedule heating according to your needs. This allows you to reduce energy consumption during periods when the building is unoccupied.
  • Ensure proper insulation: Insulate your building properly to minimise heat loss. Insulation in walls, roofs, and floors helps to retain heat to create a more energy-efficient and comfortable environment while reducing the workload on the heat pump.
  • Seal air leaks: Identify and seal any air leaks in windows, doors, and other areas where drafts may occur. This prevents cold air from entering and warm air from escaping, improving efficiency.
  • Regularly maintain the heat pump: Clean or replace filters regularly to ensure optimal airflow. Schedule professional maintenance to check refrigerant levels, inspect components, and address any issues promptly. This ensures that the system operates at its best efficiency.
  • Consider zoning: Implementing zoning systems allows you to heat specific areas of your building as needed, reducing energy consumption and increasing efficiency.
  • Maximise natural sunlight: Utilise natural sunlight to heat your building during the day. Keep curtains and blinds open to allow sunlight in, reducing the reliance on the heat pump.
  • Avoid blocking airflow: Ensure that the outdoor unit has adequate space around it for proper airflow. Clear any debris or obstructions that may hinder the heat pump’s performance.
  • Monitor and optimise performance: Keep track of the heat pump’s performance and energy consumption. Monitor the COP and energy usage to identify any changes or inefficiencies and take appropriate action. Install EndoTherm energy saving additive into the system fluid to optimise transfer of heat around the building.
  • Consider renewable electricity: If possible, generate electricity from renewable sources to power your heat pump. This further reduces carbon emissions and enhances the overall sustainability of the system.
  • Stay informed: Keep up-to-date with the latest advancements in heat pump technology and efficiency measures. New innovations and improvements can help further enhance the efficiency of your system.
Low Carbon Heating Systems - Electric Combi Boiler

How Does the Efficiency of an Air Source Heat Pump Compare to Other Heating Systems?

When comparing the efficiency of air source heat pumps to other heating systems, two main comparisons can be made: traditional gas boilers and other renewable heating technologies.

Comparison to Traditional Gas Boilers

Air source heat pumps are significantly more efficient than traditional gas boilers. While gas boilers typically have an efficiency rating of around 90%, air source heat pumps can achieve COPs of 2 to 4, resulting in an efficiency of 200% to 400%. This means that for every unit of electricity consumed, the heat pump produces two to four units of heat.

Comparison to Other Renewable Heating Technologies

Air source heat pumps are also more efficient than many other renewable heating technologies. For example, biomass boilers have an efficiency of around 70% to 90%, while ground source heat pumps can achieve COPs of 4 to 5, similar to air source heat pumps. However, ground source heat pumps require more extensive installation and higher upfront costs compared to air source heat pumps.


How Efficient Are Air Source Heat Pumps in Winter?

Air source heat pumps can still operate efficiently in winter, even in colder climates. While extreme temperatures can affect the heat pump’s efficiency, modern models are designed to handle cold weather conditions.

In winter, the Coefficient of Performance (COP) may decrease due to the lower ambient air temperature. However, advanced heat pumps can still achieve COPs of 2 to 3 in temperatures as low as -15°C (5°F).

It’s important to choose a heat pump specifically designed for cold climates and ensure proper installation, insulation, and maintenance to maximise efficiency during winter months.


At What Temperature Do Heat Pumps Stop Being Efficient?

Heat pumps do not stop being efficient at any specific temperature. However, as the ambient air temperature drops, the efficiency of the heat pump decreases. The Coefficient of Performance (COP) of the heat pump may decline as the temperature approaches its lower operating limit.

Most air source heat pumps are designed to operate efficiently in temperatures as low as -15°C (5°F) or even lower. While the COP may decrease in extremely cold temperatures, the heat pump can still provide heating, albeit with reduced efficiency.

It’s important to note that advancements in heat pump technology continue to improve their performance in colder climates, allowing for increased efficiency even at lower temperatures.


Overall, air source heat pumps offer a sustainable way to provide heat and hot water to a property while reducing carbon emissions. With the right system and support, homeowners, businesses, and organizations can make a positive impact on the environment while enjoying the benefits of low carbon heating. 

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EndoTherm is independently proven to save up to 15% on heating bills.