Heat pumps are an emerging and economical solution for heating, cooling, and in some cases for producing domestic hot water in an apartment, a detached house, or a commercial space.

The technology they use is similar to that of an air conditioner or refrigerator. They consume a small amount of electricity from the grid and draw the rest of the energy from the environment. This results in saving energy and money, since there is no longer a need to buy oil or wood, while electricity consumption is also lower.

Heat pumps in brief!

Depending on the technology they use, they are divided into 2 main categories: air-cooled units, which are divided into air-to-air and air-to-water, and water-cooled units, which are divided into: water-to-air, ground-to-water, and water-to-water.

In terms of their construction, they are divided into monoblock (single unit) systems and split (split type) systems. Their power supply can be either single-phase or three-phase. For selecting the appropriate heat pump, it is recommended to consult a specialized professional who will assess all the data and then be able to suggest the best possible solution.

Why choose a heat pump?

+ Heat pumps, in addition to electricity, can also be connected to renewable energy sources, such as solar panels and natural gas.

+ They can provide heat to a space even when the ambient temperature is low, unlike oil or gas boilers.

+ They have a long lifespan with minimal maintenance (cleaning is required every few months) and low maintenance costs (by a technician, annually).

+ They are classified as renewable forms of heat/cooling production, offering a low environmental footprint (i.e., carbon dioxide emissions into the environment).

What are their disadvantages?

• They perform better when combined with underfloor heating or fan coil units, compared to conventional radiators (Akan type).
• The outdoor unit produces considerable noise (similar to that of an air conditioner).
• The initial purchase cost is high.

Selecting and then installing the appropriate heat pump, while taking into account the needs of each building, is a complex and multifactorial process, with many factors that need to be considered.

Skroutz Tip: Attention! Before choosing a pump, consult a specialist to conduct a mechanical study, which is based on many parameters and various measurements, such as: the location of the building, the type of window frames, possible thermal losses in each space, and the output of each unit (if already installed), in relation to the supply temperatures.

How do they work?

To produce heat, pumps transfer heat from the environment to the desired space. They consume a small amount of electrical energy from the grid and draw the rest of the energy for free from the environment. For cooling a space, the operation is reversed. Thus, they extract heat from the interior, which is then released into the environment.

The ratio of energy required for the pump's operation is approximately ¾ from the environment and ¼ from electricity. For example, this means that for every 3kWh drawn from the environment, combined with 1kWh of electricity required for its operation, we get a total of 4kWh of useful thermal energy.

Do you want to learn more and become an expert in heat pumps? Below you will find detailed information you need, such as: their technology, operating systems, power supply, additional features, COP and EER performance ratings, as well as information about the "Home Energy Saving" program.

1. Technology

Depending on how they extract heat from the environment, they are divided into two main categories:

I) Air-cooled units, which extract heat from the air, and

II) Water-cooled (geothermal) units, which extract heat from water or the ground

I. Air-cooled units

These include two types of categories: air-to-air heat pumps and air-to-water heat pumps.

Air-to-air heat pumps use air as a source of heat and as a transfer medium, to deliver cooling or heating to the space (like air conditioners). Their installation is easy and quick, while they offer immediate heating or cooling to the area. However, during winter, when the ambient temperature is at low levels, their efficiency is significantly reduced.

On the other hand, air-to-water heat pumps use air as a source of heat and water as a transfer medium. In other words, they heat or cool the water, which is then distributed inside the residence. They can be easily adapted to an existing system and maintain the quality of heating they provide. However, their efficiency can vary depending on the external temperatures of the given environment.

Skroutz Tip: The majority of heat pumps belong to the air-to-water category, which are connected to the radiators that are already installed or will be installed in the spaces. In contrast, air-to-air heat pumps are not connected to central heating, as they include the indoor unit that distributes warm or cool air, such as a floor or cabinet air conditioner.

II. Water-cooled units

There are three types of water-cooled units: water-to-air heat pumps, ground-to-water heat pumps, and water-to-water heat pumps.

1. The first category uses water from the ground as a heat source and air as a transfer medium, to deliver cooling or heating to the space.
2. The second category uses the stored energy in the ground as a heat source and water as a transfer medium.
3. While the third uses water from the ground as both a heat source and a transfer medium, to deliver cooling or heating to the space. These heat pumps have a high degree of efficiency, since the heat source is the ground, which provides a stable temperature all year round. Their only drawback is that they have a high installation cost, as special (vertical or horizontal) placement of the exchangers in the ground is required.

2. Types of Heat Pumps

Depending on the needs and requirements of each building, there are three types of pumps that can be installed. They are classified according to the maximum temperature of the water that exits the pump towards the installed heating units and are as follows:

• Low temperature heat pumps
• Medium temperature heat pumps
• High temperature heat pumps

Low Temperature Heat Pumps

The majority of low temperature heat pumps also offer a cooling function. They produce hot water with a temperature of up to 55°C and are suitable for installation in new buildings. They can be connected to underfloor heating systems or fan coils.

Skroutz Tip: The ideal combination for a low temperature heat pump is with underfloor heating, as it offers the highest efficiency for heating or cooling the space, with the lowest electricity consumption cost. The underfloor heating circuit provides uniform heat distribution in the room during winter, maintaining a stable room temperature. Additionally, in summer it offers gentle cooling, thanks to the cold water circulating through the floor pipes.

Medium Temperature Heat Pumps

Medium temperature heat pumps can also offer a cooling function, just like low temperature ones. The maximum water temperature they can produce reaches up to 65°C and they can be combined with underfloor heating or fan coils for heating or cooling the building.

Skroutz Tip: Medium temperature heat pumps can be combined and are equally efficient with both underfloor heating and fan coils!

High Temperature Heat Pumps

Finally, high temperature heat pumps only produce hot water at high temperatures, reaching up to 80°C. This means they do not offer a cooling function, making them suitable for applications where the production of high temperature hot water is necessary.

Skroutz Tip The ideal combination is with classic radiators, which are already installed as a heating system in the building, as there is no need to replace them with new ones. They are an ideal solution when replacing an old boiler, since they produce high temperature water just like the boiler. They can be easily integrated into the existing pipes and radiators, without the need to replace the entire system.

3. Operating Systems

In terms of system construction, heat pumps are divided into the following two types:

I. Monoblock System (single unit type)

In the monoblock system, all its individual structural components (such as the compressor, heat exchanger, fans, etc.) are integrated into a single unit, which is placed outdoors, offering easy installation and direct connection to the water system. However, because the pipes and the heat exchanger are located outside, there is heat loss or, in worse cases, due to extreme weather conditions (such as frost), there is a possibility that the heat exchanger or the pipes may break.

II. Split system (divided type)

The split system consists of two independent units: the indoor unit (which contains the circulator, the heat exchanger, etc.) and the outdoor unit (which houses the compressor, the exchanger, the fan, etc.), which are connected to each other with copper pipes. This system offers many possibilities for customization in separate areas (e.g. creating different zones according to the requirements of each space) and there is no risk of the unit freezing, since there is an independent exchanger inside the building. However, this also acts as a disadvantage, because there are limitations regarding the distance at which the outdoor unit can be installed in relation to the exchanger.

Skroutz Tip: Don't know what to choose? The answer mainly depends on the available space for their installation, as there is no significant difference in their performance and energy characteristics.

4. Additional Features

Domestic Hot Water

Regardless of heating or cooling a building, a heat pump can also have the capability for domestic hot water production throughout the year. This can be achieved in two ways: either the heat pump has a built-in boiler (that is, the water storage tank), or the connection with the boiler is optional. In the second case, the choice can be made based on the needs of the building, and the installation of the tank can also be done at a later time.

Skroutz Tip: Alternatively, it is possible to install a heat pump that only produces domestic hot water, thus offering up to ⅓ reduction in electricity consumption compared to an electric water heater.

5. Power Supply

In terms of voltage, heat pumps are divided into two categories: single-phase and three-phase.

I. Single-phase heat pump

A single-phase heat pump can be connected to a single-phase or three-phase power supply. What you need to know is how many amps the single-phase supply in your building supports, as this number varies by area. A heat pump requires high current values (that is, amps) to operate, which means that an inspection by an experienced electrician is necessary before deciding which heat pump is suitable for your space.

II. Three-phase heat pump

On the other hand, a three-phase heat pump requires connection to a three-phase power supply, as high loads are needed for the pump’s operation. The connection is made directly and the current (amps) is sufficient for their operation.

Skroutz Tip: In the case where a change from single-phase to three-phase supply is required to install the pump, there is a financial charge from the respective provider for the change, followed by a small increase in the four-month fixed fee.

In terms of energy, apart from connection to the electrical grid in the case of hybrid systems, there is also the possibility of connection to natural gas. This offers even lower operating costs (since the price of natural gas is lower than that of electricity), and also allows for use in combination with a gas boiler as a backup.

Skroutz Tip: In existing buildings, as long as the boiler (oil or gas) is in good condition, it can remain installed for supportive operation, so that in extreme weather conditions it can, if necessary, operate together with the pump.

Skroutz Tip: In some cases, it is possible to connect a heat pump to a solar water heater, with solar panels, for even greater cost savings.

6. Performance

What are the COP and EER efficiency ratings?

COP (Coefficient Of Performance) refers to the efficiency rating during heating operation, while during cooling it is called EER (Energy Efficiency Ratio). This is a measurement that indicates the efficiency of a heat pump under standard operating conditions and is defined as the ratio of delivered energy to the consumed electrical energy (COP = Produced Energy / Consumed Energy).

The percentage of consumed electrical energy depends largely on the COP. It usually ranges from 3 - 5, depending on the pump and the conditions in which it operates. This means, for example, that when a heat pump operates with COP = 4, the thermal energy it provides is equal to 4kWh, consuming 1kWh of electrical energy.

The maximum value of the COP of an air/water heat pump corresponds to outdoor air temperature conditions (DB/WB) 7/6°C and water inlet/outlet temperature of 30/35°C.

The efficiency rating COP is not constant, but is affected by the ambient temperature. The lower the outdoor temperature, the more the COP decreases, resulting in higher electricity consumption.

Skroutz Tip: The higher the COP, the more environmentally friendly the pump is, as it leaves a smaller energy footprint.

Skroutz Tip: When a heat pump operates with a night-time electricity tariff, its operating cost is significantly reduced. The same applies when it is combined with underfloor heating instead of AKAN-type radiator units.

What to Consider Before Purchase

When choosing the right heat pump, we usually take into account the existing heating units and the thermal losses of each space. Indicative questions that can be asked are the following:

• Are there already installed units (e.g. radiators, fan coils, underfloor system)?

If there are already installed units, we can easily connect the appropriate pump to our system. Alternatively, if it is a new building or we want to make a complete change including the heating units, there is greater flexibility regarding the final choice.

• What are the outputs of each radiator in relation to the supply temperatures?

Here things are simpler, as what we need to know is the temperature of the water required in order to cover the space where the radiators are installed (or will be installed).

• What are the heat losses in each area?

The study for heat losses should ideally be carried out for the constant temperature we wish to be supplied and maintained in the space (e.g. 21°C), and it is also advisable to check the performance of the heat pump at the lowest ambient temperature where it will be installed.

• What insulation does the building have?

Finally, the insulation of the building also plays an important role. In the case of a newly built property, the choice of the heat pump's power can be lower, which results in reduced electricity consumption costs. The opposite applies to older buildings with lower quality thermal insulation.

For the most part, the main choice of heat pump for use in a residence is the air-to-water type. The initial cost of purchase and installation is lower compared to geothermal heat pumps, and it can be installed as the main heating system in the majority of areas in our country, whether the building already has central heating installed (e.g. oil or natural gas boiler) or not.

Skroutz Tip: In any case, the recommendation for which heat pump is most suitable for our needs should be made by an experienced engineer. After conducting a study, they will suggest the appropriate pump that will offer maximum efficiency with the lowest annual operating cost. If we choose a heat pump with greater power than what the building requires, apart from the higher initial purchase cost, we force it into continuous restarts, resulting in strain on the pump and increased operating costs.

Program "I Change Heating System & Water Heater"

Heat pumps are included in the program "I Change Heating System & Water Heater" and according to the program guide, they concern the following actions:

1. Purchase of a new solar water heater with a subsidy of 50%-60%, depending on income.
2. Purchase of a heat pump with a 50% subsidy for replacing old systems.
3. Supplementary installation works (transport, placement, consumables) covered by 50%-60%.

Discover all heat pumps, here!

Fun Facts

1. In 1852, Kelvin was the first to practically discover that a refrigeration machine could be used for heating.
2. The first heat pump system was built and presented between 1855-1857 by Peter von Rittinger. A few years later, in 1948, Robert C. Webber accidentally discovered the geothermal heat pump while experimenting with his freezer.
3. In 1938, the first commercial heat pump was installed at Zurich City Hall in Switzerland, which still operates today, heating the building for almost a century.
4. "Heat always transfers from a high-temperature system to a low-temperature system." The above statement is a fundamental conclusion of the 2nd Law of Thermodynamics. A heat pump does exactly the opposite, as it reverses the operation of the system!