Air Source Heat Pumps
Why Air Source Heat Pumps?
Air Source Heat Pump (ASHP) are a less expensive alternative to the Ground Source Heat Pump. They are much easier to install and only require a small space at the side of a building.
The performance from an ASHP will vary according to the actual conditions on any given day.
That is to say the amount of energy (output) is not constant. However, they still maintain their output in very cold weather.
How they work
An ASHP uses the variable energy found in the ambient air temperature. Typical average UK winter air temperatures tend to be around 4 or 5º C with only limited periods of very cold weather.
The heat pump boosts this low energy via its refrigeration circuit to a usable level for the provision of heating and hot water for the home.
This works by taking advantage of the energy created when a refrigerant gas is compressed to a liquid. The refrigerant is first passed through a heat exchanger where it is warmed by the air.
This heat exchanger is called the evaporator. The now slightly warmed refrigerant gas is compressed to a liquid which dramatically increases the temperature of the refrigerant.
The hot refrigerant liquid is then passed through another heat exchanger which is then used to warm the system water (Underfloor Heating or Radiators).
This second heat exchanger is called the condenser.
In order to start the cycle again, the refrigerant liquid must be converted back to a gas and this is done by the expansion valve.
How varying air and water temperatures affect the performance, Buyer Beware!
The output from some ASHPs is not fixed and it will vary depending on certain conditions.
Radiant has noted some manufacturers appear to be misleading consumers about the power delivery of their Heat Pumps. It's not just as easy as seeing a product can deliver 20KW of power, a lot of factors will need to be considered during the design process.
Here are some points.
The certified output of an ASHP is measured for an air temperature of -2ºC and a heated water temperature of 35ºC
However, if the air temperature falls or the water temperature rises then the output of the ASHP will fall.
The variation in output is approximately 250 watts for every degree Celsius change in air temperature.
However, the rate of variation is not constant and will vary depending on the actual air temperature and the actual water temperature.
Depending on your requirements, heating/hot water we will source the appropriate heat pump to suit you.
Why our Air Source Heat Pumps?
Over 25 years we have built up a wealth of knowledge on energy efficient heating systems. We know how to correctly size a heat pump in order to give the right amount of heat for any building, throughout the year.
We know how to make a heat pump work with any type of heating system, Plus we know how to link a Heat Pump in with other heating plant for complete system integration schemes.
Right for our climate
Radiant Heating Solutions Ltd partners range of heat only air source Heat Pumps are specifically suited for the UK climate. All of these Heat Pumps use the very latest refrigeration technologies. They work effectively in temperatures as low as -20 degrees C.
Our partner's single phase units have output ranges from 5KW to 16KW with single compressors.
Our partners 3 phase units range from 10KW to 60KW in a single unit.
All of them can do heating and hot water and some can also be specified to do cooling if required.
What you get at a glance
All our partners heat pumps use scroll inverter compressors, R410a refrigerant gas, 316 grade stainless steel heat exchangers and micro-processor controls.
Also fitted to some are auxiliary heaters to boost the performance in very cold weather and tray heaters to assist in clearing water in the defrost cycle.
The smaller models fit as standard the water circulation pump. Our partners heat pumps are easy to install by competent engineers. We offer our own installation team to ensure full MCS compliance.
It is very important to size the heat pump correctly for the job it is going to do. From our comprehensive range will be the correct sized unit for your project.
The outputs from our partner's machines are based on an air temperature of -2º C and a heated water flow of 35º C.
This is the European standard measurement for heat pumps and will normally be displayed as A-2/W35.
When comparing different heat pumps it is important to make sure that the stated output always relates to this standard.
The performance of a heat pump is referred to as the co-efficiency of performance (COP). This in simple terms is the relationship to the amount of energy used to the amount generated. If the heat pump uses 1KW of electricity and produces 3KW of heating water the COP would be 3.
How to specify Air Source Heat Pumps? and integration
Sizing of the ASHP
There are a lot of misunderstandings when it comes to sizing a heat pump. Many suppliers will have you believe that for some magical reason the heat pump only needs a small output.
This may be because they only produce small heat pumps or more likely, they just don’t understand how to correctly size the unit.
Sizing the heat pump starts in just the same way as sizing a boiler; you have to work out the true heat loss of the building.
There are many ways to do this and if you need help we can quote you for this. Once you know the heat loss you can then look to match this to a heat pump.
However, there is the additional factor of defrosting that must be added to correctly size the heat pump.
An ASHP will automatically switch to defrost mode during normal operation. This happens because the air will contain varying degrees of moisture. As this ‘moist’ air is drawn across the evaporator by the fan, the moisture begins to freeze on contact.
This result is a slow build-up of frosting or ice on the evaporator that must be removed to prevent a loss of performance. The reason this happens is because the refrigerant gas inside the evaporator is many times colder than the air temperature.
The defrosting of the evaporator can take quite a while depending on the air temperature. Whilst the heat pump is in defrost mode there will be no heat going in to the building.
To compensate for this defrost cycle an additional capacity is required from the heat pump. Radiant Heating Solutions partners heat pumps take into account the defrost cycle in accordance with EN 14511.
For those who are unsure and don’t want to get it wrong, we can quote you for this.
Guide note and example
The best form of heat emitter for a heat pump is a low temperature delivery system such as underfloor heating, wall heating or fan assisted radiators.
For areas with high ceilings that are not using underfloor or wall heating then the total volume of the space needs to be factored in which will add extra kW capacity.
Underfloor or wall heating should always be installed with the pipes embedded in screed/plaster or a Fermacel type board to give high thermal mass.
The underfloor or wall heating pipework must be spaced at the correct centre's for designed output and U values of the building.
This can be a complicated process and we would urge you to get a full quote from us for this.