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14 Sept 2023

Air source VS ground source heat pump: what's the difference?

Anna Dearden
Home Sector Specialist
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Heating and cooling your home efficiently and sustainably has become a top priority for homeowners looking to reduce energy consumption and environmental impact. Two popular options for achieving this goal are air source heat pumps (ASHPs) and ground source heat pumps (GSHPs). 


These systems offer significant benefits over traditional heating and cooling methods, but they operate differently and come with distinct advantages and disadvantages. Before you invest in heat pumps, it’s important to explore the differences between air source heat pumps and ground source heat pumps. It’s also a good idea to understand how they work, their installation process, costs, and the role of home insulation in optimising their performance.


What is a heat pump?


Before delving into the specifics of air source and ground source heat pumps, let's first understand what a heat pump is and how it functions. A heat pump is a device that transfers heat from one location to another, using a refrigeration cycle to move heat from a colder area to a warmer one, or vice versa, depending on the season.


Heat pumps have two primary components: an indoor unit (evaporator) and an outdoor unit (condenser). They rely on a refrigerant to absorb heat from the source (either the air, ground, or water) and release it into your home or vice versa. By reversing the flow of refrigerant, heat pumps can provide both heating and cooling capabilities, making them versatile and energy-efficient solutions for maintaining indoor comfort.


How does an air source heat pump work?


An air source heat pump, as the name suggests, extracts heat from the outdoor air and uses it to heat your home during the colder months. This process can seem counterintuitive, as even cold air contains some heat energy. Here's a simplified overview of how an ASHP works:


Evaporation: The refrigerant inside the outdoor unit evaporates, absorbing heat from the surrounding air.


Compression: The compressor then increases the pressure and temperature of the refrigerant.


Condensation: The hot, high-pressure refrigerant is condensed inside the indoor unit, releasing the absorbed heat into your home.


Expansion valve: The refrigerant is expanded through a valve, which lowers its temperature and prepares it to repeat the cycle.


Advantages of air source heat pumps


Why consider installing an air source heat pump?


Lower installation costs: ASHPs are generally more affordable to install than GSHPs due to their simpler setup, requiring less excavation and fewer groundworks.


Versatility: You can install them in a variety of locations, including on the side of your house or even on the roof.


Less space required: ASHPs are more space-efficient than their ground-source counterparts, making them a great choice for smaller properties.


Drawbacks of air source heat pumps


We can see that air source heat pumps bring an array of benefits — but what are the drawbacks?


Efficiency variation: It’s important to note that an ASHP’s efficiency can decrease in extremely cold weather, as there's less heat energy in the air to extract.


Noise: Outdoor units of ASHPs can produce some noise, which may be a concern if you live in a noise-sensitive area.


How does a ground source heat pump work?


In contrast to air source heat pumps, ground source heat pumps utilise the relatively stable temperature of the ground below the frost line to provide heating and cooling. Here's an overview of how a GSHP operates:


Ground loop: A network of pipes, known as a ground loop, is buried in the ground around your property. This loop contains a heat-transfer fluid, typically a water and antifreeze mixture.


Heat exchange: During the heating cycle, the heat pump extracts heat from the ground loop by circulating the fluid through it. The heat is absorbed from the relatively warm ground and transferred to the refrigerant.


Compression and release: The refrigerant is then compressed, and the heat is released into your home through the indoor unit.


Reversal for cooling: In the cooling mode, the process is reversed, with heat from your home being transferred into the ground loop to cool your living space.


Advantages of ground source heat pumps


There are many advantages of ground source heat pumps due to their durability.


Steady performance: GSHPs are not affected by outdoor temperature variations, making them highly efficient all year-round.


Quiet operation: Ground source heat pumps are quieter than ASHPs since most of the equipment is located underground.


Longevity: GSHPs typically have a longer lifespan than ASHPs due to their lower maintenance requirements.


Drawbacks of ground source heat pumps


We’ve discussed the advantages of ground source heat pumps, but they also have a few disadvantages that you may wish to consider.


Higher installation costs: GSHPs are more expensive to install due to the need for excavation and the ground loop installation. Use our price comparison search tool to find the best deal for your heat pumps.


Space requirements: They require ample space for the ground loop, which might not be suitable for smaller properties or urban areas.


Heat pump costs: The cost of installing an air source or ground source heat pump can vary widely depending on factors such as system size, location, and existing infrastructure. Here's a breakdown of the cost considerations for both types of heat pumps:


Air source heat pump costs


Initial installation: On average, an ASHP installation costs between £7,000 and £15,000. This cost includes the unit, labour, and any necessary modifications to your existing heating system, but it’s best to shop around and compare prices from various providers first.


Operating costs: ASHPs are generally more cost-effective to operate than traditional heating systems, but their efficiency may decrease in extremely cold conditions, slightly increasing energy consumption.


Maintenance: Maintenance costs are relatively low for ASHPs, primarily involving regular filter cleaning or replacement and occasional professional check-ups.


Ground source heat pump costs


Initial installation:: GSHP installations are more expensive, ranging from £17,000 to £35,000 or more, but you can find the best deal by comparing prices with SpotDif. The high upfront cost is mainly due to the ground loop installation and excavation expenses. 


Operating costs: GSHPs are highly efficient and cost-effective to operate, as they are not affected by outdoor temperature fluctuations.


Maintenance: GSHPs have lower maintenance costs compared to ASHPs, with the ground loop typically requiring minimal maintenance once installed.



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Heat pump installation


Air source heat pump installation


Installing an air source heat pump is generally less invasive and quicker than installing a ground source heat pump. Here's an overview of the installation process:


Site assessment: A technician assesses your property to determine the best location for the outdoor unit and evaluates your existing heating system.


Unit placement: The outdoor unit is installed on a concrete pad or mounted on a wall, and refrigerant lines are run to the indoor unit.


Indoor unit: The indoor unit is typically installed in your basement or utility room, connected to your existing ductwork or installed with a ductless system.


Electrical connections: Electrical wiring is run to connect the heat pump to your home's electrical system.


The role of home insulation


Whether you choose an air source or ground source heat pump, the efficiency of your heating and cooling system is closely tied to the insulation of your home. Proper insulation is essential for maintaining a comfortable indoor temperature and minimising heat loss or gain. Here's how home insulation contributes to the performance of both types of heat pumps:


Reducing heat loss: Adequate insulation in walls, ceilings, and floors helps prevent heat loss during the winter and heat gain during the summer. This means your heat pump doesn't have to work as hard to maintain a consistent indoor temperature, saving energy and reducing operating costs.


Even temperature distribution: Good insulation ensures that the heated or cooled air remains inside your living spaces, leading to more even temperature distribution throughout your home.


Optimising heat pump performance: Proper insulation maximises the effectiveness of your heat pump by minimising the temperature differential between indoor and outdoor environments. This allows the heat pump to operate at its most efficient level.


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Find heat pump suppliers with SpotDif


Both air source heat pumps and ground source heat pumps offer energy-efficient and eco-friendly solutions for heating and cooling your home. The choice between the two largely depends on factors such as your budget, available space, and your climate. 


While air source heat pumps are generally more affordable and easier to install, ground source heat pumps provide consistent efficiency and longevity. To maximise the performance of your chosen heat pump, invest in proper home insulation, ensuring that your home remains comfortable year-round while minimising energy consumption and costs. 


Ultimately, both options represent significant steps toward a more sustainable and comfortable home environment. If you’re looking at investing in heat pumps for your property or business, find your supplier with SpotDif. Start today. 

author
Anna Dearden
Home Sector Specialist
Combining in-depth research with an interest in all things home improvement, I aim to keep SpotDif readers up to date with interior design trends, renewable energy options, and more.
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