Air to water heat pump: operation and advantages

The heat pump is a machine that, using different forms of energy, is able to extract and transfer thermal energy. Among the different types of heat pumps, there is the air to water heat pump that can perform both heating and cooling functions in the indoor environment, depending on the seasons and external temperatures.

It is a high-efficiency technology that allows for energy savings while ensuring optimal performance in every season.

To evaluate the actual efficiency of an air to water heat pump, in addition to the COP (Coefficient of Performance), which is purely indicative, the SCOP index (Seasonal Coefficient of Performance) should be considered. It evaluates the operation based on different outdoor air temperatures and indicates the ratio between the annual energy requirement and the annual electrical consumption dedicated to heating.

The SCOP index can only be measured after installation, but it can also be estimated by a designer using thermal software that correlates the design data of the building, the climatic conditions of the installation location, and the heat pump performance under different operating conditions.

Let’s analyze in detail how an air to water heat pump works and the advantages of its installation.

What is a heat pump

Before analyzing the characteristics of an air to water heat pump, it is necessary to first provide a definition of a heat pump. The heat pump is a machine capable of transferring energy from a lower temperature environment to a higher temperature one.

Heat pumps are available in 3 types:

• water-to-water heat pumps;
• geothermal heat pumps;
• air source heat pumps.

Air source heat pumps, in turn, are divided into: air to air heat pumps and air to water heat pumps.

Air to water heat pump: what is it

The air to water heat pump is a heat generator that produces thermal energy by utilizing the external air around the building. This system allows for generating heat for heating during winter and cooling the spaces during summer.

It is an ecological alternative to traditional heating systems as it uses renewable energies by extracting the heat already present in nature.

The efficiency of this type of heat pump is influenced by the external temperature and the characteristics of the building in which it is used. Unlike air to air heat pumps, air to water heat pumps maintain good performance even in low external temperatures.

How does an air to water heat pump work

The operation of an air to water heat pump is similar to air to air systems, with the significant difference that the heat is transferred to the water in the heating system. This is a key point as it allows these systems to work with radiators or underfloor heating.

These systems require hot water to function, and air to water heat pumps are designed to produce it and be compatible with these types of systems.

The operation of an air to water heat pump for cooling is based on 4 main phases:

• heat is extracted from the air through an external unit to the building and absorbed by a heat exchanger by a heat transfer fluid capable of vaporizing even at low temperatures;
• the generated vapor is further compressed by a compressor, increasing its temperature. The compressor and other system components are powered by electricity;
• in the condenser, the fluid returns to a liquid state, releasing the heat it had collected to the water circuit, which will enter the water system to be used for domestic hot water and/or heating.
• the fluid is cooled by the expansion valve to restart the cycle.

The cycle repeats continuously as long as the heat pump remains operational.

For heating, the air to water heat pump uses the same processes as for cooling. However, in this case, the heat pump extracts thermal energy from the external environment through the refrigerant, which, in condensing, transfers it to the heating system and/or domestic hot water production.

Air to water heat pump system diagram

Below is a diagram of how an air to water heat pump works.

Air to water heat pump

What are the advantages of an air to water heat pump

The advantages of using an air to water heat pump are numerous:

• versatility: air to water heat pumps are very versatile and can be used for both heating and cooling buildings of various sizes;
• energy saving: air to water heat pumps mainly exploit thermal energy for their operation, so the consumption of electrical energy is only partial. The energy efficiency of an air to water heat pump depends on various factors, including the coefficient of performance (COP), the energy class to which the device belongs, and the characteristics of the house (heating type, insulation, exposure, etc.);
• environmental friendliness: air to water heat pumps are a sustainable and environmentally friendly solution, as their operation is based on transferring heat from a clean and renewable energy source, namely the outside air. In this way, it is possible to minimize the environmental impact;
• incentives: air to water heat pumps can benefit from incentives.

Air to water heat pumps have some disadvantages to consider before making a purchase. Among these, the initial cost and the installation cost are certainly relevant. However, it is important to bear in mind that these costs can be offset in the short term thanks to the energy savings that these pumps offer.

Another limitation of air to water heat pumps is their lower efficiency in extreme climatic conditions, which may require the use of backup heating systems. However, in Italy, thanks to the predominantly mild climate, this issue is less significant.

Finally, regular maintenance of air to water heat pumps may entail additional costs. It is important to note, however, that regular maintenance is essential to ensure the correct operation and longevity of any system.