How Do Air Source Heat Pumps Work? April 04, 2025 Air source heat pumps are not merely another heating appliance; they are intelligent energy transfer mechanisms that can extract thermal energy from external air, even in seemingly inhospitable temperatures. By leveraging fundamental principles of thermodynamics, these systems can provide heating in winter and cooling in summer with remarkable efficiency. Understanding how air source heat pumps operate is crucial for homeowners and energy professionals alike. This technology isn't just about comfort—it's about making informed, sustainable choices that reduce carbon footprint and minimise long-term energy expenditure. Whether you're considering a residential upgrade or seeking to comprehend the mechanics of modern climate control, this detailed exploration will demystify the inner workings of air source heat pumps. What is an Air Source Heat Pump? An air source heat pump is a highly efficient heating and cooling system that transfers heat between the outdoor air and indoor space. It operates on the principle of vapour compression, similar to a refrigerator, but with the ability to reverse its cycle. There are two main types of heat pumps: air-source and ground-source. Air-source heat pumps extract heat from the outdoor air, while ground-source heat pumps utilise heat from the ground. This article focuses on air-source heat pumps. Components of an Air Source Heat Pump The system comprises two primary units: outdoor and indoor. Outdoor unit (condensing unit): Compressor: Pressurises the refrigerant Reversing valve: Changes refrigerant flow direction Expansion valve: Controls refrigerant flow and pressure Condenser coil: Facilitates heat exchange Refrigerant: Absorbs and releases heat Fan motor: Moves air across the coil Indoor unit (evaporator coil or indoor air handler unit): Coil: Enables heat transfer with indoor air Fan motor: Circulates air through the system How Does an Air Source Heat Pump Work? A. Heating Cycle 1. The outdoor unit extracts heat from ambient air, even in cold temperatures. 2. Refrigerant flow process: Expansion device: Liquid refrigerant expands, cooling significantlyOutdoor coil (evaporator): Cold refrigerant absorbs heat from outdoor airReversing valve: Directs hot gas to indoor unitCompressor: Pressurises and heats the refrigerant furtherIndoor coil (condenser): Hot refrigerant releases heat to indoor air 3. The system transfers heat to indoor spaces via the air handler. The heating efficiency depends on outdoor temperature. As temperatures drop, the heat pump works harder to extract heat, reaching a thermal balance point where supplementary heating may be required. B. Cooling Cycle 1. The indoor unit absorbs heat from indoor air. 2. Refrigerant flow process: Expansion device: Liquid refrigerant expands and coolsIndoor coil (evaporator): Cold refrigerant absorbs indoor heatCompressor: Pressurises and heats the refrigerantOutdoor coil (condenser): Hot refrigerant releases heat to outdoor air 3. The system expels heat to the outdoor environment. C. Defrost Cycle In cold, humid conditions, frost can accumulate on the outdoor coil, reducing efficiency. The defrost cycle reverses the heating process briefly to melt frost: 1. Reversing valve switches to cooling mode 2. Hot refrigerant flows through outdoor coil, melting frost 3. System returns to heating mode This cycle is crucial for maintaining efficiency and preventing damage to the outdoor unit. Efficiency and Performance Several factors influence heat pump performance: 1. Outdoor temperature: Efficiency decreases as temperatures drop 2. Proper sizing: Oversized or undersized units operate inefficiently 3. Installation quality: Poor installation can reduce efficiency by up to 30% 4. Maintenance: Regular servicing ensures optimal performance In extremely cold climates, heat pumps may struggle to extract sufficient heat from the air. Most systems have a minimum operating temperature, below which supplementary heating is necessary. This can be provided by electric resistance heaters or a hybrid system with a gas furnace. Despite these limitations, air source heat pumps are highly energy-efficient. They can deliver up to three times more heat energy than the electrical energy they consume, resulting in significant cost savings compared to traditional heating systems. FAQs How does a heat pump provide both heating and cooling? Air source heat pumps can provide both heating and cooling by using a reversing valve to change the direction of the refrigerant flow. In the heating mode, the heat pump extracts heat from the outdoor air and transfers it to the indoor air. In the cooling mode, the process is reversed, and the heat pump absorbs heat from the indoor air and releases it to the outdoor air. What are the main components of an air source heat pump? The main components of an air source heat pump include: a compressor, a reversing valve, an expansion valve, a condenser coil, refrigerant, and fan motors for both the indoor and outdoor units. Can an air source heat pump operate in very cold temperatures? Air source heat pumps can operate in cold temperatures, but their efficiency and heating capacity decreases as the outdoor temperature drops. At very low temperatures, a supplementary heating source, such as a furnace or electric heater, may be required to maintain the desired indoor comfort level. How efficient are air source heat pumps compared to other HVAC systems? Air source heat pumps are generally more energy-efficient than traditional HVAC systems, such as furnaces and air conditioners. They can provide up to 300% efficiency, meaning they can deliver 3 units of heat for every 1 unit of electricity consumed. This can result in significant cost savings on energy bills compared to other heating and cooling systems. Do air source heat pumps require regular maintenance? Yes, air source heat pumps require regular maintenance to ensure optimal performance and longevity. This typically includes cleaning or replacing air filters, checking and cleaning the outdoor coil, and inspecting the refrigerant levels and other components. Regular maintenance can help improve energy efficiency, extend the lifespan of the system, and prevent potential issues. Can I use my heat pump as the primary source of heat if propane gets expensive? You can use your air source heat pump as the primary source of heat, even if propane prices are high. However, it's important to consider the minimum operating temperatures of the heat pump and the need for a supplementary heating source when the outdoor temperature drops below the heat pump's efficient operating range. Consulting with a professional HVAC contractor can help you determine the best approach for your specific heating needs and climate. Why might I need to replace my heat pump along with my furnace? You may need to replace your heat pump along with your furnace if the two systems are not compatible or if upgrading to a more efficient system. Newer, high-efficiency heat pumps may not be compatible with older furnaces, and replacing both components can improve the overall efficiency and performance of your HVAC system. How long do air source heat pumps typically last? With proper maintenance, air source heat pumps can typically last 15 to 20 years or more. However, factors such as usage, climate, and quality of installation can affect the lifespan of the system. Regular maintenance and prompt repairs can help extend the lifespan of an air source heat pump. Can I manually switch between my heat pump and furnace for heat? Yes, you can typically switch between your heat pump and furnace for heating manually. This is often done using a thermostat or control system that allows you to select the desired heating source. However, it's important to consult with a professional contractor to ensure that the systems are compatible and that the manual switching process is performed correctly to avoid any potential issues. Get in Touch Interested in finding out more about air source heat pumps? Get in touch with our team based across Liverpool, St Helens and Warrington.
