All heat pumps work based upon the fact that heat can be extracted from one place and transferred to another for use in providing domestic hot water or central heating. Some of the most environmentally friendly home heating systems around, there are three kinds of heat pump, and each works differently from the rest.
The 3 Kinds of Heat Pump
The three kinds of heat pump extract their heat from air, ground, or water, and are capable of taking heat from temperatures as low as -15C.
1. Air Source
Air source heat pumps work by extracting heat from the air using an evaporator coil. Installing an air source heat pump is simple compared to a ground source heat pump (GSHP) as no ground works involved. An air source heat pump (ASHP) is able to operate at a varying temperature range -15 °C to +25 °C. It also has Coefficient of Performance (COP) of 3 and therefore for every input of 1KW of electricity there is an output of 3KW worth of heat.
The benefits of air source heat pumps:
- Can heat energy from the air in temperatures as low as 15°C.
- An air source system will significantly lower your heating bills (compared to a standard heating system).
- You will lower your carbon emissions.
- Installation is simple as no groundwork involved.
- Able to operate at a varying temperature range -15 °C to +25 °C.
- Coefficient of Performance (COP) of 3 (every 1Kw of electricity input gives 3Kw of heat as output).
The drawbacks of air source heat pumps:
- Air source is not suitable for all properties (only if your house is well insulated).
- They are noisy when running (from a fan and a compressor).
- Not ideal for coastal regions (salt in the air can corrode the heat pump).
- Air temperatures vary throughout the year, resulting in a lower COP during the cold winter months when the heating is required.
- Electricity is needed to run it (not emission free).
2. Ground Source
Ground source heat pumps work when a loop of pipe is filled with a mixture of water and antifreeze (also known as a brine solution) and is buried beneath the ground. This can be done in a trench around 1.5 meters deep or down a bore-hole up to 100m deep. The water and antifreeze absorbs the heat from the ground. The ground is a constant temperature of 8C-12C throughout the year. The brine solution is returned to the heat pump and passes over the evaporator, which transfers the heat absorbed from the ground into the refrigeration cycle.
The benefits of ground source heat pumps:
- The system can heat your home and provide hot water.
- Requires very little maintenance.
- Generates less CO2 than standard heating systems.
- Great for projects with low environmental impact.
- Safe, silent and out of sight.
- Has a longer lifespan than an air source heat pump.
- The ground temperature is fairly constant all year round, offering a stable performance of the heat pump
The drawbacks of ground source heat pumps:
- Installation can be expensive and prices can range from £9,000 – £17,000.
- Planning permission may be necessary.
- Recommended for newer buildings with good insulation.
- Electricity is needed to run it (not emission free)
3. Water Source
A water source heat pump (WSHP) functions in a similar way to the ground source heat pump (GSHP). These are available in either an open loop or closed loop system. A closed loop system involves pipes which are submerged in lakes or rivers as temperatures remain at a fairly constant level between 7C – 12C. The solution within the pipes is known as the brine solution, it circulates through the pipes to extract the energy to heat buildings. An open loop system extracts water from the source, which is passed directly into the evaporator.
4. Natural Gas
There is one last kind of heat pump which is largely unknown. Otherwise known as absorption pumps, natural gas heat pumps work similarly to air source pumps, but rely on natural gas rather than electricity. Natural gas has the lowest carbon content of any fossil fuel, and it is both readily available and cost effective. Whilst the gas is non-renewable, it is less harmful to the environment than other fossil fuels and contains no refrigerants which can harm the ozone layer. However, the downside of these systems is the cost. Whilst they are cost-effective in comparison to other heating systems, natural gas heat pumps are more expensive than the three previously mentioned, although they are far less wasteful and provide your home with efficient warmth.
Cost Savings: Dependent upon Replaced Fuel
As with any energy-saving measure, the amount of money you cut your bills by will depend upon how much you were spending in the first place.
The amount that you save will depend on the fuel that you are replacing and also the installation. Some companies will suggest that savings of up to 50% can be achieved; however this is not always the case.
The price will depend on the type of fuel used and the performance of the heat pump. Gas is the cheapest fuel and the most expensive is direct electricity. Heat pumps do require electricity in order to work but if you are currently heating with electricity then your cost per kWh can be quartered.
If your home requires mains gas then the running cost of a heat pump is similar. However, if you decide to add radiators to the property it will pay to stay with gas as your fuel.
Heat pumps would not suit all properties; an older building with very little insulation would not be the best candidate. Installing a heat pump in a poorly insulated building is unwise. However, when the property is well insulated and all other aspects are covered a heat pump can significantly reduce the carbon emissions and heating costs.
The Coefficient of Performance (CoP)
This is a term you are definitely going to come across when looking into heat pumps, and although it may look a little daunting, it really just relates to the efficiency of the heat pump. The CoP is the ratio of electrical input to heating powered gained. This can be found once the once the useful heat output has been divided by the energy input. e.g. If a heat pump produces 4kw of heat for 1kw of input power it will have a CoP of 4.
Take a look at our helpful Heat Pump Key Words to help you navigate your way to a heat-pumped home.
Passive and Active Cooling
Heat pumps are a versatile kind of technology, and can be used in more ways than one. Whilst pumping heat into the home is the equipment’s main job, it can also pump heat out to keep the house cool in the summertime.
Passive cooling occurs when only the circulation pump and control unit are left working. The heat pump itself is switched off. You may also hear passive cooling as ‘natural cooling’. The passive method is beneficial in two ways: whilst at first you benefit from the cooling effects of the heat being removed from the house, you will later benefit from all that extra heat stored in the ground outside (assuming you are using a ground-source heat pump). This kind of cooling is much better suited to domestic settings.
Most of the time, active cooling is not necessary and passive cooling will do the job well. Active cooling is achieved by the heat pump reversing its function and the compressors acting like those in a fridge, therefore cooling your home ‘actively’. Active cooling is not as cheap as passive cooling, as it uses greater amounts of energy. However, it is capable of cooling your home much more efficiently than standard air conditioning.
Solar Powered Heat Pumps
For those of us interested in keeping our bills down and the air clean, combining energy-saving measures can be a brilliant way of achieving our eco goals. Heat pumps and solar power can work very well together.
Where solar panels can be useful in recharging the ground to temperature is during the early springtime and autumn. At these times of the year, energy is deposited in the ground whilst the sun is shining in the daytime. The energy that is deposited is held around the ground array pipes, and so as the sun sets and the heating system is required, this deposited energy from the ground is still held nearby and therefore is absorbed back into the system. This improves the Coefficient of Performance (CoP) and, therefore, the ground source heat pump efficiency.
Heat Pumps Uses
Heat pumps are not solely for use in providing domestic hot water and central heating; and can actually be used in various different ways.
A heat pump is simply the most efficient way of heating a swimming pool. With a CoP of 5.0, and very little maintenance to deal with, there is no doubt that a heat pump is the way to go for your pool-warming needs.
For those who have underfloor heating installed, the idea of installing a heat pump is not one to be passed up. This will increase the efficiency of your heating system. A ground source heat pump running at 60 degrees (required for most radiators) will have a coefficient of performance (COP) of just 2.5.The COP for a heat pump running at 35 degrees will be 4.5.What does this mean for you? When used with radiators the running cost of a heat pump increases by 81%.The solution would be to install oversized radiators to ensure more heat is released throughout your home. To negate the running cost of the scenario above, you would have to oversize your radiators by a factor of 6.
Commissioning Your Heat Pump
Before you can go ahead and beginning reaping the rewards of having installed a heat pump, the system will need to be commissioned by a trained professional.
The Importance of Insulation
Heat pumps are a low temperature heating system. That means your home will have to be well insulated.
Poorly insulated homes mean the heating system requires a higher flow temperature (to compensate for the high heat loss). The maximum temperature that a standard heat pump could provide is 55C.
If your home would require this temperature the efficiency of the heat pump would drastically fall. This is because the compressor has to work harder to produce the higher temperatures.
Image by Matt E
If your home is not well insulated then installing a heat pump is not cost effective. It would be far better for you to reduce your heating demand.