AIR TO WATER HEAT PUMPS Energy efficient Heating & Hot Water
What is an air to water heatpump?
An air to water heatpump is a device which extracts naturally produced energy from the air around us and converts it into useful energy, warm enough to heat your central heating and domestic hot water.
How does it work?
Outside air is drawn through a set of fins at the rear of the heatpump. This is called an evaporator. Heat is extracted from the air and used to heat a refrigerant circuit which has a very low boiling point. The heated refrigerant is then compressed producing a superheated refrigerant gas, and this is then passed through a second heat exchanger called a condenser. On the other side of the condenser is the central heating water. The heat produced from the compressed refrigerant gas is transferred through the condenser into the central heating water, heating it to a high enough temperature to be able to run your radiators or underfloor and provide your domestic hot water.
As the heat transfer takes place, the refrigerant is cooled and then passes through an expansion valve which changes its state back to a vapour and the pressure is reduced. The process can then begin again. Excess used air is pushed back to the atmosphere by means on a fan at the front of the unit.
An example adjacent shows the typical operation cylcle for an air to water heatpump.
Air to Water Heatpump Options
There are two styles of air to water heatpump most commonly installed, the Monobloc type and the Split type. Both will provide the central heating and domestic hot water and the principals in operation as detailed above, remain the same.
The main difference comes when deciding the outdoor unit location plus space availability inside the building.
An air to water heatpump with the refrigeration cycle contained within the outdoor unit is called “monobloc”. This means that no refrigeration flows beyond the outdoor unit, just pipework carrying the heated water to the heating and hot water systems.
A “split” air to water heatpump, will consist of a smaller outdoor unit and a separate indoor unit (similar in size to a wall mounted boiler) called a Hydrobox. The main difference from the monobloc unit is that the refrigeration circuit is split between the outdoor unit and Hydrobox. Refrigeration pipework installed by F GAS Registered personnel links the two units together. The hot water produced from the unit is distributed to the central heating and hot water systems from the Hydrobox.
Although most split heatpump systems are low temperature types, there are some manufacturers who produce a high temperature split unit. This follows the same installation principals as detailed above however has two refrigerant circuit installed. The first circuit heats the second circuit producing even greater water temperatures. The high temperature unit tends to be used in retrofit jobs where the levels of insulation required for a standard unit is hard to achieve. They generally are more costly to run and have a lower efficiency.
COP (Co-efficient of Performance)
The heatpumps design efficiency is usually stated as the Co-efficient of Performance or COP and is calculated at a specific operating condition. The industry standard condition is, outside air temperature at 7 Deg c and the output water temperature at 35Degc. Typically at these conditions, an air to water heatpump would normally have a COP of around 3.4 (340% efficient). This means that for every kilowatt used to power the heatpump 3.4 kilowatts is delivered into the building. This figure will vary depending upon the heatloss of the property and the position of the outdoor unit.
Other Changes to Factor into Your Decision
For an air to water heatpump to work efficiently and for it to live up to expectations, it is essential that the buildings fabric insulation is taken into consideration. As a minimum, the property ideally needs to be double glazed with a decent level of roof insulation, cavity wall / internal/external wall insulation and if possible floor insulation.
When in heating mode, the heatpump will work on low water temperature ideally around 40 - 45Deg c and therefore all heat emitters need to be sized accordingly.
This generally does not present too much of an issue where underfloor heating is concerned, however if the property had existing radiators and was previously fed from a gas or oil boiler, the chances are they will need to be replaced and upsized to cope with the heatpumps lower water temperature.
The same is required where the hot water cylinder is concerned. If existing hot water cylinder was previously heated by a gas or oil boiler, the cylinder will also need upgrading to one with a larger internal coil suitable for the heatpumps lower water temperature. The heatpump will naturally heat the water in the cylinder to around 55Deg c with no additional back up.
Please Note: Most air to water heatpumps are fitted with a 3kw element (like an immersion heater). This is generally used for pasteurisation (Legionella protection) whereby the water in the cylinder is taken up to 60Deg c and held for a period of time (generally up to an hour) before switching off. The exception to this is the high temperature split system detailed above.
Positioning of the outdoor is important. Ideally the best location for the heatpumps outdoor unit is facing due south (warmer air currents), in front of an unobstructed wall, with no obstacles in front of the fan. If this cannot be achieved, please don’t worry. Most outdoor units are designed to operate down to air temperatures of -25Deg c.
The siting of the outdoor unit will have to comply with local planning regulations relating to positioning and sound. Although most installations can be fitted under permitted development rights, planning permission will be required if your property is listed or falls within the boundary of a conservation area.
So Why Purchase an Air to Water Heatpump?
If you are building or renovating a property and are looking for a fossil fuel alternative, then an air to water heatpump is the perfect solution.
Its High Efficiency (compared to gas / oil boilers)
Low on Energy Consumption
Lower Running Costs
Less costly to install compared to a ground source
Low Carbon Emissions
Government Financial Incentives
Air Management Solutions also offer a competitively priced maintenance package which covers your annual service (Please contact the office for more details). We will automatically contact you when due to arrange a suitable time and date to attend.
We also offer a standard and emergency breakdown service for all types of heatpump, installed by us and also by others.
Our fully certified and qualified team are committed to ensuring all our customers needs are met offering a highly skilled, professional, efficient and cost effective service tailored to your individual needs. And you can rest assured that all work is fully guaranteed.