Air Source Heat Pumps (ASHP) use the ambient temperature of air, drawn through a fan unit to extract the heat from the atmosphere to expand the compressed refrigerant gas. They can be a ‘monobloc’ in that the heat pump and fan evaporator are housed in single unit, or a split system where the compressor and heat exchange is in an inside unit and the fan unit outside.
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Ground Source heat pumps (GSHP) use the more stable temperature of the earth at around 1m depth to extract the heat from. Pipes, usually containing the glycol are sunk horizontally underground and extract the heat from the soil. As the earth 1m below ground rarely falls below 8°C the performance is more stable and predictable all year round. They require a lot of land to be effective.
Often confused with GSHP because they too use the earth as the heat source, but in this case a series of bore holes are sunk vertically to much greater depths; sometimes as much as 100m. Much higher temperatures can be found the deeper you go, but the installation costs can be much greater then either ASHP or GSHP.
Similar in principle to an ASHP but extract heat from the air and use it to heat the air (or cool if reverse cycled). Usually found in smaller properties and often in hotels and apartments for example. They are effective but it does look like you have an A3 printer on the wall of each room...
WILL A HEAT PUMP SUIT YOUR NEEDS AND YOUR PROPERTY...
However, in reality, a Heat Pump cannot replace a gas boiler in every instance, and the gas energy suppliers and boiler manufacturers are starting to push back highlighting some of the practical difficulties of the Governments position. Hydrogen and bio-gas are just some of the alternative technologies being proposed to supplement or replace methane or natural gas in the network. The result is likely to be a mix of technologies (known in Political speak as a ‘Fudge’) and so you should consider what’s best for you and your property. Here are some examples for you to consider:
In essence, this is the holy grail of heat pump applications and where the technology first found a foothold. If the options are between oil, LPG , biomass or direct electric heating, the convenience as well as the grants and RHI (Renewable Heat Incentive) available to a new build home owner for heat pumps make this a ‘no-brainer’.
A more nuanced decision given the availability and cost of gas. The higher insulation levels of a new build will make a heat pump £ for £ on a par with a gas boiler, although servicing and maintenance might be higher. If you have any grants or RHI available to you, this will tip the balance in an ASHP or GSHP’s favour
This will depend on a) the level of insulation that can practically be achieved and b) the availability of mains gas. Older properties do not have the inherent insulation levels to make a heat pump a viable and economical proposition without remediation. Long abandoned building techniques such as solid outer walls, uninsulated solid asphalt or suspended timber ground floors, single pane glazing all need attention if the target heat losses of under 50w/m2 are to be achieved. Other considerations such as existing pipework means that a careful costing should be undertaken first – especially if a gas boiler is a viable option.
Even ASHP require some outside space and good air circulation to facilitate the fan unit, and an internal cylinder to store the hot water. Not all small properties have been designed with this is mind, and other considerations such as access for maintenance, noise pollution and routing pipework into and through the property may be problematic.
most suited to semi-detached and detached properties as they will require some external space to locate the fan unit and be ground or lowly wall mounted for ease of access and servicing. They require at least a metre of clearance and should not be within 1 metre of a boundary or under trees or plants as this can affect their performance
Typical installed cost: £10~£14K
Requires at least 250m2 of garden area for the coils of pipes to absorb enough heat from the ground, and often 500m2 for larger properties. It is important that there is sufficient earth to provide enough heat for the property. If too much heat is extracted from too small an area, then the ground can actually develop a permafrost which will severely deteriorate the performance until the ground thaws out.
Typical installed cost £12~£18K
Generally for a single room or small dwelling they extract the air from within the property and induct air from outside. These can often provide a heating and cooling function (like an air-con unit) and can substitute for a mechanical ventilation and heat recovery unit (MVHR). Often combined on top of water cylinder, they can remove warm stale air from bathrooms and kitchens, extract the heat through the heat pump cycle and then reintroduce fresh air into the property.
Typical installed cost; £4~£6k each.
The formula for calculating the volume of hot water required to heat a room is Q = M x C x (dT)
where Q is the heat load of the room (in Kw), M is the mass/volume of the water,
C is the specific heat capacity of water (4.2) and dT is the difference between the
room temperature and the average water temperature of the heating system
(and thus the radiators).
If a room has a heat load of 1kw (1,000w), a desired room temperature of 20°C, and the water temperature is 70°C for a boiler and 45°C for a heat pump you can soon see that the dT is halved (70°-20° = 50°, and 45° – 25° = 25°). Therefore, it is easy to see that the Mass/Volume of the water must double to achieve the same output of 1kw.
This means that whilst a boiler heated property can comfortably deliver enough heat using 22mm main feed pipes and 15mm or 10mm tails to each radiator, when using a heat pump, the pipe sizes need to increase to 28mm (or even 35mm) for the main feed and return and 22mm for as far as practically possible to the radiators or heat emitters (the last ½ metre could be reduced to 15mm for ease of final connection).
The alternative is to double the flow rate through the existing pipes by using additional pumps or a low loss header (don’t ask!) which can introduce other issues such as noise and vibration as well as additional cost.
In summary its not always necessary to change the pipework in your home if retrofitting a heat pump, but it must be considered and calculated.
This may mean the radiators increasing in size by as much as double, although many radiators are already oversized by up to 25% (the typical plumbers’ factor of safety) so it’s worth doing the maths first. It is of course possible to save some money on replacement radiators by moving larger radiators from, say, the living room into a bedroom and then only replacing the living room with a larger one etc. As radiators are really convectors and thus rely on hot air rising, it might be beneficial to fit 2 normal sized radiators rather than one large one to compensate for the reduced heat distribution caused by operating at low surface temperatures.
These include an internal fan unit to extract more heat from the hot water by blowing air across a heat exchanger. They will require a new and separate electrical connection to provide the power (they should not really be plugged into a socket outlet as they are a fixed heating appliance for Building Control purposes) and a suitable sturdy wall to fix to.
This is often installed with heat pumps as it naturally operates at lower flow temperature and has a large surface area. Retrofitting to existing properties can be difficult and often new floors are required to provide the necessary insulation underneath and the choice of floor coverings can be limited to tiles and hard surfaces if performance is not to be degraded by carpets and wood. Overlaid systems may require doors to be planed down and skirting boards to be removed in any event and so larger radiators or skirting heating may prove to be more cost effective.
As heat pumps often have to operate 24/7 during the colder months to keep a house warm, it is important that heat is preserved wherever possible to avoid unnecessary expense. Ideally, smart heating controls with time and temperature and heat pump interface should be employed to ensure that only the rooms that require heat are heated and at the appropriate time (for example bedrooms OFF in the daytime).
Your system needs to be properly pressurised to work efficiently. This is
typically 1.5~ 2.2 bar on the boiler pressure gauge (usually indicated by the
green section on the gauge).
If your system continuously needs topping up then you may have a leak
somewhere on the system, although it will usually go into fault mode if the
pressure drops below 0.5bar.
If you have a leak on a radiator or skirting heater, these are very easy to
find and remedy- usually it will be where the pipework connects onto the
radiator panel and simple to get at.
It is common in areas with high levels of calcium carbonate dissolved into the water, to use a water filter or softener to reduce limescale and improve the taste. Under no circumstances should chemically softened water be plumbed into the central heating system. Whilst limescale can build up in appliances that are constantly being refilled (such as kettles, baths etc) the water in the central heating is a ‘closed’ system and apart from the occasional top up (see above) the calcium carbonate levels are static. As such limescale build up is minimal in closed loop systems especially if plastic pipe has been used. Introducing chemically softened water can damage boilers, heat exchangers, aluminium radiators etc. and should be avoided at all costs. Mechanical or centrifugal filters do not present such a hazard, but double check the suitability of your heating system to accept softened water. If in doubt, treat only the domestic potable water.
Monobloc heat pumps are single unit heat pumps that contain all of the parts; like the heat exchanger, main pump, evaporator, condenser and compression valves in a single system. The single unit normally sits outside of your home.
Monobloc heat pumps are quite large and require outdoor space against an external wall so they can be installed correctly.
Monobloc heat pumps need professional installation but are simpler to install than air conditioning or ground or water source heat pumps.
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The monobloc heat pumps outdoor unit will connect directly with your home’s conventional heating systems to provide heat through radiators or underfloor heating from external air.
Here’s What is a heat pump which explains the basics of heat pumps.
The pros and cons of a monobloc heat pump system include;
Some of the benefits of a monobloc heat pump system include;
Here are the disadvantages of monobloc heat pumps;
Monobloc heat pumps only heat water to pump around your central heating system which goes directly to your radiators or underfloor heating.
To get running hot water you will also need to install a separate hot water storage tank. The only element of a monobloc heat pump that will be located within your home is the connected hot water cylinder.
Split heat pumps conversely are different to monobloc heat pumps because they have two separate units. The split system usually has an internal unit and an outdoor unit which works as a heat exchanger and compressor.
Split heat pumps are better for situations where more complex installations are necessary or when there’s no obvious place for a monobloc heat pump unit and they can also be very quiet.
They can be preferable if you only have a small outside space as the outside unit is generally smaller.
Split systems are often referred to as HVACs. Find out more about split HVAC heat pump systems.
Monobloc air source heat pumps include all of their essential parts and equipment within a single unit that can be installed outside your home.
The majority of monobloc air source heat pumps, don’t require traditional gas to work instead they use refrigerants so monobloc heat pumps do not require F gas qualifications (fluorinated gas) to install.
This makes many monobloc heat pump systems cheaper and easier to install than air conditioning units or ventilation systems.
Most monobloc heat pump systems will need to be installed by professional heating installers.
Air source monobloc heat pumps will need external air so the majority of systems are designed as a single outdoor unit that is installed outside the property.
The external unit will need to be installed at ground floor level and somewhere that is easy to access for ongoing maintenance and servicing.
Many people choose to have their heat pump unit situated outside their utility or boiler room is a popular choice because it is easy to connect the heat pump to the heating system.
The outside unit is generally reasonably large due to housing all of the components necessary to get your home’s heating up and running.
Monobloc heat pumps can work well on large properties where you have plenty of outdoor space to house the system and let it operate successfully.
You can get monobloc ground source heat pumps and water source heat pumps. However, they will need to connect to a suitable heat source, through boreholes, aquifers, lakes, rivers or waste heat through a series of pipes.
A monobloc ground source heat pump can still be considered a split system because ground and water source systems require underground or underwater pumps in boreholes to access heat from the ground or a body of water to generate heat.
You will also need an internal hot water tank to store hot water from your heat pump to feed hot water taps in your home.
Most monobloc heat pumps can work effectively in temperatures as low as -25° C. Many heat pumps designed for lower temperatures feature enhanced vapour injection (EVI) technology that helps to maintain the pressures of the refrigerant even at low temperatures.
In a much colder climate, a ground source monobloc heat pump could be a better option as ground temperatures are more stable throughout the year than air temperatures.
Air sealing and insulation, as well as correctly sizing the heat pump for your home are also important considerations.
If you’re replacing a traditional boiler with a heat pump, you shouldn’t have too many changes to make. However, you may wish to;
Improve your home’s insulation; this will help your home retain more heat so your heat pump won’t have to work so hard to keep your home at a comfortable temperature. Many UK homes are currently poorly insulated.
Upgrade your radiators; heat pumps work best when they have a larger surface area to distribute heat. So upgrading your radiators can help your home feel warmer more quickly. Replacing existing radiators with aluminium radiators can also help distribute heat from your heat pump quickly and efficiently as aluminium is an effective conductor.