Air Source Heat Pumps

What are Air Source Heat Pumps?

Heat pumps are effective and environmentally friendly solutions for heating and cooling all types of buildings, households and commercial premises. They effectively harvest energy from one medium, enhance it and transfer to another in a very efficient manner using relatively small amounts of energy. In most UK applications, air source heat pumps are used for heating purposes, with the medium that they harvest the energy from being free and abundant; the air.

The atmospheric air is heated by the sun on a daily basis, effectively creating a vast, universally available source of free low-grade heat. The heat pump can extract this heat from the air and concentrate it from low-grade heat to temperatures that are high enough to be used for heating water, homes and commercial premises. The systems can also be reversed which makes them ideally suited to heating and cooling, providing the perfect temperature in all seasons.

Air source heat pumps don't just work in temperate climates. In fact, even at temperatures as low as -20C, air source heat pumps yield sufficient heat from the outside air. This means they can be installed in most UK properties and are rapidly growing in popularity in the UK as people are realising the financial and environmental benefits of these systems.

How Does it Work?

Unlike traditional boilers, air source heat pumps do not use energy to generate heat directly through combustion. Instead the systems use relatively small amounts of electricity to circulate and compress fluid with an electric pump. This system extracts and upgrades the temperature of the free energy drawn from the outside air sufficiently for space and hot water heating; as a result, they are a very energy efficient method for heating.

There are different types of air source heat pumps, but the principle on which they operate is similar. All Green Energy Doctor systems consist of two main components:

Fan Unit with Heat Exchangers
The main unit comprises of a box that is usually placed outside the property. The box contains a fan that draws large volumes of air into the unit and across a heat exchanger. This heat exchanger (evaporator) extracts free low temperature heat from the outside air, which is transferred from to a refrigerant that runs through it. The refrigerant has a low boiling point (-10C) and as it absorbing the heat it evaporates into a gaseous state. The gaseous refrigerant is then increased in pressure by a compressor. As the gas is compressed it increases in temperature. The refrigerant gas passes to the condenser (a second heat exchanger) where it cools and condenses as the expansion valve allows the pressure to drop. As it condenses, this enhanced energy is transferred from the refrigerant to the heating system.

Using compression technology similar to that found in your fridge, air source heat pumps capture and upgrade heat which is found in the air and transfer it to be used for space heating (and cooling) and water heating. 1: Fan draws air into unit, 2: Evaporator Heat exchanger (heat from air to refrigerant) , 3: Compressor, 4: Condenser Heat Exchanger (refrigerant to heating system), 5: Expansion Valve that releases pressure.

Heating System & Hot Water Cylinder
You've probably got one of those already in the form of radiators. The condenser heat exchanger transfers the heat in the refrigerant to the water circulated in the central heating system that runs through your radiators, underfloor heating and sanitary hot water tank. Ideally, for maximum benefit and efficiency, a heat pump is best used with under-floor heating, but industry standard low temperature radiators can prove to be a very efficient option.

What Are The Benefits?

Reduce Your Energy Bills By Up to 40% (or more)
With a properly sized and installed air source heat pump you may typically cut your heating bills by up to 40% if you are using a traditional gas boiler, which will mean yearly savings of many hundreds of pounds. They can be particularly cost effective in areas where mains gas is not available, as an oil-fired boiler would cost considerably more to run, and electric heating would be at least three times as expensive.

Improved Efficiency
Unlike traditional boilers that generally create heat through the inefficient combustion of fossil fuels, modern heat pumps are extremely efficient. Heat pump efficiencies are normally quoted as the 'coefficient of performance' of the system; these are typically in the range 3 to 5. In other words, extracting heat from renewable sources requires just 1kW of electrical input in order to generate 3kW to 5kW of heating output. Heat pump systems therefore, are 3 to 5 times more efficient than fossil fuel boilers and are more than capable of warming a house completely, even during the lowest winter temperatures.

Reduce Your Impact On The Environment
Fossil fuel use has a particular detrimental effect to the environment as when these fuels are burned, carbon dioxide is released into the atmosphere contributing significantly to global warming. Heat pumps can extract around 75% of usable heating energy from the environment and can generally reduce carbon emissions compared to gas central heating systems by approximately 50%. These savings are even greater when compared to other fuels such as oil or gas. For a particularly environmental solution, you can purchase a green electricity tariff to power the compressor and pump.

Reduce Your Dependency On Fossil Fuel Imports:
Security of energy supply is a recurrent concern for fossil fuels; geopolitical instabilities in oil and gas producing regions can threaten availability and lead to unexpected price changes. With the majority of your heating and cooling being derived from the air, any price changes are likely to be less extreme than can occur with fossil fuels and may also be more manageable/predictable.

Lower Maintenance Cost
The technology inside a heat pump works on similar principles to those of a domestic fridge, but in reverse. The technology is proven technology and like most fridges, there is no need for regular servicing or annual safety checks and maintenance is minimal.

Ease of Installation & Use
The compact outdoor unit can be located where convenient and requires no drilling or excavation work to collect heat. The installation is just as easy as a standard oil or gas boiler and does not require a dedicated technical room, or additional infrastructure, such as chimneys, fuel tanks or gas connections. The system can be connected to industry standard low temperature radiators and underfloor heating systems and can be configured for use in both new and refurbishment applications.

Low capital cost of Installation
Payback of the small extra capital cost of the heat pump over fossil fuel boiler is relatively short giving significant savings on running costs.

Types of System

There are two primary system configurations that can be used to ensure optimum efficiency of the system:

Monovalent systems:
This solution is ideal for new build, very well insulated properties or existing properties with low temperature space heating requirements. The heat pump is used on its own and is sized to provide 100% of the heating requirement even on the coldest day of the year as well as the direct hot water requirement. The initial investment costs may be higher but energy consumption is the lowest of all systems.

Bivalent and integrated systems:
This solution is ideal for retro fitting into existing properties where the heat pump is combined with a secondary heat source or an existing fossil fuel boiler, allowing the user to retain their existing boiler for additional heating capacity. As the ambient air temperature is at its coldest when the highest heat demand is required, the efficiency of the heat pump is reduced inline with the outside temperature. Therefore, the heat pump would provide the largest proportion of the annual heating requirement with existing boiler topping up on the coldest days.

Is It Suitable For My Requirements?

Because air is an abundant resource that is freely available throughout the UK, air source heat pumps can be effectively used almost anywhere. However, which system is most suitable for your property or project depends on a number of factors that Green Energy Doctor will take into account prior to designing a solution.

In the meantime, the following gives a good indication of some general principles that should be taken into account when deciding if the technology is suitable, and if so, designing a cost effective system:

Insulation of the property and heating requirement
Air source heat pump efficiency demands a properly insulated and draught proofed house: insufficient insulated walls, floors, ceilings or attics and basements may turn the system less effective. The cost of a system is directly related to its size based on your heat demand. Most new build properties will be sufficiently insulated, but for existing properties, money spent on upgrading insulation levels can save a considerable amount on the system cost. Although rare, some buildings can never be made sufficiently energy efficient to use a low temperature heating distribution system.

Heating System
Air source heat pumps work best with heating systems that are optimised to run at a lower water temperature than is commonly used in UK boiler and radiator systems. As such, they make an ideal partner for underfloor heating systems or oversized radiators sized for the typical temperatures obtained from air source heat pump systems. For homes without such modern additions, radiators can still prove to be an effective option, without the need for replacing or modifying the existing system. Green Energy Doctor will be able to advise on the suitability of your current system and any potential changes that would be required to make the system suitable.

Buffer Cylinder
Although not essential, a buffer cylinder is generally recommended to ensure a trouble-free heat pump operation. Heat pumps require a minimum flow rate of heating water for a smooth operation and buffer cylinders provide a separation between the flow rate in heat pumps and that in the heating circuits to ensure the flow rate in the heat pump circuit remains constant. They are also required for the defrost operation when temperatures drop to a level that can freeze key components. Their installation does not require any significant modification of the existing system, but it is important to consider additional space required for the small cylinder to be located.

Air source or Ground Source Heat Pump
Air source heat pumps work on a similar basis to ground source heat pumps (see separate fact sheet), but instead of harvesting heat from the ground they harvest from the atmospheric air. One particular benefit of air source heat pumps is the ease of installation, as no extensive groundwork or well drilling is required. However, the ambient air temperature is less consistent and is at its coldest when the highest heat demand is required the heat pump coefficient of performance or efficiency of the system is reduced inline with the outside temperature. It is for that reason, that in most cases a combination with a second heat source is desired (or included) that boosts the heating system, particularly during the colder season.

Space & Location
Air source systems can be fitted using very little space and are therefore are very suitable for an urban home with limited space. All that is required is a small footprint of approximately 1m2 on an external wall outside. The units can also be placed inside as long as the fan vent can draw air from outside and expel it freely.

There are very few projects where we are not able to come up with a satisfactory solution. That is why the Green Energy Doctor is on hand to help and advise you on the best course.

Please feel free to call us, send us an email or send us a drawing of your specific project.

How Much Does It Cost To Install?

As a general rule it costs between £900 and ¶1300 per 1 kW of heat output. So the typical cost for a professionally designed and installed domestic 9kW system would cost between £8,000-£12,000.

Even though the installation price of a air source heat pump can be several times that of conventional heating systems of equal capacity, it is more efficient, thereby saving money every month. Savings will vary depending on the fuel replaced.

When included in a mortgage, your air source heat pump will have a positive cash flow from the beginning, as the energy cost savings will easily exceed that added mortgage amount over the course of each year. With a system life is estimated at 25 years or more, you will continue to make savings long into the future.

Once the technical survey has been carried out, all Green Energy Doctor prices will be given as fixed prices.

Government grants are available for these technologies; please contact us to find out more information.

How to Get Started...

To organise a no obligation site visit or to start moving your project forward contact the Green Energy Doctor today on:

T: 0845 009 5652
E: info@greenenergydoctor.co.uk