If someone mentions heat pumps, it is the air source heat pump that often springs to mind. And that for good reasons – these systems are widely deployed, they are suitable for both new build and modernising energy systems in existing buildings, and can be installed easily and at low cost. In order to ensure efficient and reliable operation of air source heat pumps, several conditions must be met which are explained in more detail below.
The basic principles of an air source heat pump can be explained quickly and simply:
A fan draws in outdoor air, which then passes through a heat exchanger, causing the refrigerant in the heat pump to evaporate. Within the heat pump circuit, this is then brought up to a higher temperature by compression, making energy available for space heating and domestic hot water heating. For more information, please read the section on Heat pump operating principles. Air is available in unlimited amounts, everywhere and at all times. With our sophisticated and highly efficient OCHSNER systems, air as the heat source can also be used efficiently at sub-zero outdoor temperatures. The outdoor temperature must be only slightly higher than the boiling point of the refrigerant used.
BUT VERY INEXPENSIVE TO INSTALL
In winter, at low air temperatures, air source heat pumps operate somewhat less efficiently than systems with ground or groundwater heat sources. This is mainly down to the fact that more drive energy is required for heat pump operation at lower outdoor temperatures. But, since neither drilling nor collectors are required, the installation of an air source heat pump is significantly less expensive than the installation of alternative systems. Special permits are also not required.
WITH OUTDOOR FAN
Generally, air source heat pumps are designed as split systems. This means that the fan unit and the actual heat pump are separated and linked by a suitable line. In this case, the fan is installed outdoors and the actual heat pump inside your house. One advantage over complete outdoor installation is that no pipework is required for outdoor areas prone to frost. Inlet and outlet pipes for the refrigerant are all that is required. The refrigerant reaches boiling point at minus temperatures and therefore cannot freeze. Simpler entry-level models work with less expensive vertical fans; high end systems from OCHSNER with bench evaporators feature fans that are installed horizontally.
Fans generate noise.
How loud this is depends very much on the technology used. Inexpensive appliances, in particular, can be exceedingly noisy and create a nuisance for neighbours. The OCHSNER bench evaporators with their horizontally mounted fans run extremely quietly. In addition to this, the OCHSNER Air Eagle air source heat pump with bench evaporator is equipped with inverter technology. This means that the compressor output as well as the speed of fans can be variably adjusted to the current heat demand. This results in significantly more efficient heat pumps which are at the same time quieter. With a special silent mode, the output can be reduced still further, at specific times, to keep the noise level as low as possible. Sound attenuating panelling for the outdoor sections is also available. Before installing an air source heat pump, it is advisable to gather detailed information on permissible noise emissions, minimum distance from neighbours, etc. from an OCHSNER system partner, for example.
FOR RELIABLE OPERATION
At temperatures of between -10 and +5 °C and with high humidity, icing can occur on the heat exchanger of the evaporator due to condensing moisture. This would result in the heat transfer to the refrigerant dropping or being interrupted. To prevent this, OCHSNER bench evaporators are equipped with hot gas defrosting. This works on the principle of hot gas from the compressor being fed back briefly to the evaporator to melt the ice and ensure full performance at all times.
FLEXIBLE AND EASY TO HANDLE
Regardless of which version the owner or moderniser decides on, a significant benefit of air source heat pumps is their simple and economic installation. When it comes to location and installation, these systems are designed to be flexible and easy to handle. The indoor units are not much bigger than a refrigerator and can therefore be easily located in a cellar. The outdoor units can be installed in the garden but also, for example, on top of a garage, carport or flat roof. Apart from observing minimum clearances and noise protection regulations, special planning permission is not required. Air source heat pumps are an economically interesting alternative, particularly for modern houses with low heat demand, modernisation projects on sites with a mature garden which should not be disturbed, or if ground and groundwater cannot be accessed efficiently. Many systems can be used not just for heating, but also for cooling in summer. For this, the heat pump process is simply reversed – the heat pump draws heat from the house and expels it to the outdoors via the evaporator.
THE EFFICIENCY OF THE AIR SOURCE HEAT PUMP CAREFULLY IN ADVANCE
Extensive consultation with an expert should always take place before deciding on an air source heat pump. How efficiently the system will operate in practice depends on many factors, about which an OCHSNER system partner can give you detailed information. One crucial variable is the Seasonal Performance Factor (SPF) which must be calculated individually in each case. In general, OCHSNER systems are characterised by high operational reliability and low noise emissions. Air source heat pumps regularly achieve best marks in tests carried out by the Buchs heat pump centre in Switzerland. Currently, the OCHSNER Air Eagle is the most efficient variable speed air source heat pump in the world. It is, therefore, an environmentally sound and reliable all rounder that can be employed in a wide range of applications.