Air-to-water heat pumps: how they work, the pros and cons
Carrier air-to-water heat pumps utilise free environmental energy to provide your home with sufficient warmth. This is made possible by an innovative process that requires electrical energy. But how does the technology work? What are its pros and cons and when is such a system an option? We answer the most important questions about Carrier heat pumps here.
How does a heat pump work? Principle explained simple
Carrier air-to-water heat pumps are heating appliances that provide heat for central and DHW heating. They can be installed indoors or outdoors and continuously draw in outdoor air. A special process is required to utilise free environmental energy in homes.
Refrigerant circuit utilises thermal energy from the environment for heating
The operating principle of a Carrier heat pump is based on the refrigerant circuit. This runs inside the heating system and can be described in four simple steps:
- Step 1 – Refrigerant absorbs environmental energy: Firstly, the refrigerant in the air-to-water heat pump absorbs thermal energy from the air. The medium vaporises in the process.
- Step 2 – Compressor compresses the refrigerant vapour: In the next step, a compressor raises the temperature of the medium along with the pressure.
- Step 3 – Refrigerant releases heat to the heating system: Once the refrigerant is warm enough, it transfers thermal energy to the heating water. The medium cools down and condenses back into a liquid.
- Step 4 – Return of the refrigerant to its initial state: In the final step, the medium flows through a pressure release valve. The pressure is released here so that the cycle can begin again.
The principle behind air source heat pumps is therefore similar to that of refrigerators. The biggest difference: while a refrigerator releases heat into the ambient air, a Carrier air-to-water heat pump transfers thermal energy to the heating system.
The heating system efficiency depends on the temperature difference
How efficiently an air source heat pump heats the water in a building depends on what is known as the temperature rise. This describes the difference between the temperature of the environmental energy source and the heating water temperature. In practice: the greater the temperature rise, the more power the compressor requires. An air-to-water heat pump operates most efficiently with the highest possible air temperature and the lowest possible heating water temperature.
Good to know: The efficiency of an air source heat pump can be measured using the COP. This indicates how much heat can be generated from one kilowatt hour of electricity. With a COP of three, for example, the system requires one kilowatt hour of electricity to provide three kilowatt hours of heat. However, please note: the COP only applies under specific operating conditions. The seasonal performance factor (SPF) is therefore more important for operating efficiency. This indicates the ratio of heat generated to electricity consumed over the course of a year.
Different designs: monoblock and split heat pumps
If you're thinking about using the air as a heat source with a Carrier heat pump, there are various designs to consider. You can choose between monoblock and split units.
- Monoblock units consist of one appliance that contains all the important components. It can be installed inside or outside the building and connected directly to the heating system. If you install an air source heat pump indoors, sufficiently large ventilation openings are required in the façade in order to be able to draw in and blow out the outdoor air.
- Split units consist of an outdoor and an indoor unit. Both can be set up to save space and are connected to refrigerant lines. In addition to the flexibility of installation, split systems also have the advantage that the noise-generating components are housed outside.
Regardless of whether you opt for an air-to-water heat pump as a monoblock or split version, the principle is always the same. As the split unit components come from air conditioning production, they are generally cheaper to buy.
Air-to-water heat pumps: pros and cons at glance
Carrier air source heat pumps utilise air as a renewable and inexhaustible source of energy. They do not emit any flue gases themselves and are easy to install and commission.
If the conditions are favourable, the systems generate low heating costs. They are considered to be low-maintenance and very reliable. The disadvantage, however, is the higher investment costs, which can be significantly reduced with a state subsidy of up to 70 percent.
It should also be noted that the outdoor units can emit disturbing noises if they are positioned incorrectly and that the heating costs depend heavily on the temperature conditions. The following table summarises the most important benefits and drawbacks:
Use and technical requirements of environmental heating
Carrier air source heat pumps are suitable for both new and older buildings. To achieve low heating costs, the heating system has to operate at the lowest possible flow temperature. If this is below 50 to 55 degrees Celsius, this environmental heating system can generally be used economically. If you lower the flow temperature further, the heating costs per degree Celsius will be around two to three percent lower. This can be achieved with large radiators, area heating systems and/or effective building insulation.
Tip: Read our guide to setting up your heat pump correctly to find out how to set up your system for particularly efficient operation.
Hybrid heating as an alternative to pure air-to-water heat pumps
Even if the conditions for a standalone heat pump are not ideal, a Carrier air source heat pump may still be a good option for you. In this case, a combination with an existing heating system, such as gas or oil, is recommended. The fossil fuel heating system then only kicks in when temperatures are very low in winter, while the environmental heating system alone ensures cosy, warm rooms and hot water for most of the year. It also makes sense to combine this setup with a photovoltaic system so that part of the heat pump electricity can be harvested directly from your own roof.
Important to know: If the heating costs of the air-to-water heat pump are only slightly higher than those of a hybrid heating system, it is generally worth doing without the fossil fuel component. This eliminates maintenance, connection and flue gas inspection costs.
