Heat Pump Systems
Heat pumps work on basically the same principle as a refrigerator, but are used the other way round. A refrigerator is meant to cool food and drinks, whereas the purpose of a heat pump is to heat a building or room.
While a refrigerator cools the food and drinks inside it, it heats the space (the room) outside the refrigerator. A heat pump, by contrast, cools the environment (outside air, the ground or groundwater) while heating the building in an environmentally friendly and economical way. This lets you draw on the energy store around your home: you use the free solar energy stored in the air, on the surface of the ground and in groundwater. The heat pump system draws on this stored energy and uses this free energy to heat your home or your hot water.
You take your free heating energy from the environment. To produce 10 kWh of heat, a heat pump consumes on average 2 to 4 kWh of electricity, depending on the application and the temperature level of the source and heating system.
This means that a heat pump can produce 2 to 6 units of heat from 1 unit of electrical energy. A standard electric heater produces only 1 unit of heat from 1 unit of electrical energy. This utilisation ratio is called COP (coefficient of performance) and expresses the efficiency of the machine.
Accordingly, a standard electric heater has a COP of 1, while the COP of a heat pump is between 3 and 6.
Compared with classic electric heating, a heat pump is 2 to 6 times more economical. The size of this saving depends on the type of heat pump, the environmental conditions (temperature of the air, ground or groundwater) and the type of heating system (underfloor heating, radiators, etc.).
A heat pump is also a cooling machine. In summer we can therefore run the heat pump in reverse to cool the building, and this time the environment (air, ground or groundwater) is heated.
With a heat pump, heating, cooling and hot water become available in a single unit.
Air-source heat pump
In an air-source heat pump, the outside air is cooled (heat is extracted), and this extracted heat energy is transferred into the building with the help of the heat pump. This heats the building or the hot water.
Of all heat pump types, the air-source heat pump is the most advantageous in terms of initial investment cost. Outside air is available everywhere in abundance, and this energy source is extremely easy to reach structurally. No special permit is required. In addition, air-source heat pumps have now become quite efficient.
The air-source heat pump is the most widely used type of heat pump in Turkey. Depending on the model, flow temperatures of up to 70 °C can be reached, so it can easily be chosen for radiator systems as well.
Ground-source heat pump
In a ground-source heat pump, the ground is cooled (heat is extracted), and this extracted heat energy is transferred into the building with the help of the heat pump. This heats the building or the hot water.
A ground-source heat pump is more efficient than an air-source heat pump. Because of the underground piping, the initial investment cost is higher.
The ground is also an important energy store in nature. There are two different ways of using the heat energy the ground has stored.
If the garden area is large enough, the heat energy of the ground is used by laying plastic polyethylene pipes about 1–2 metres deep. The cooling of the soil around the pipes does no harm to plants. Even so, it is recommended not to plant deep-rooted plants near the pipes. The ground from which heat has been taken regenerates in spring and summer thanks to increased solar radiation and rainfall.
The ground is thus ready for the heating season again. In new buildings, the excavation and earth-moving work needed to install the heat pump is not very expensive. For existing buildings, the cost of the same work is higher. The amount of heat energy that can be obtained from the ground depends on several factors. The type of soil is particularly important. For example, wet clay soil is very well suited as a heat source.
If the garden area is not large enough, wells must be drilled deep into the ground and specially durable polyethylene pipes placed in these wells.
In the drilling method, determining the well depths is very important. To determine how much heat energy can be extracted at which depths, a ground thermal response test is very useful. Empirical values exist for the amount of heat that can be extracted.
The ground-source heat pump is a less commonly used type of heat pump in Turkey and is available in a capacity range of 5 to 200 kW. Depending on the model, flow temperatures of up to 70 °C can be reached, so it can easily be chosen for radiator systems as well.
A ground-source heat pump is also a cooling machine. In summer we can therefore run the heat pump in reverse to cool the building; with the well application of a ground-source heat pump, natural cooling (without running the heat pump) is also possible by using the low temperature level in the well.
Water-source heat pump
In a water-source heat pump, the groundwater is cooled (heat is extracted), and this extracted heat energy is transferred into the building with the help of the heat pump. This heats the building or the hot water.
The water-source heat pump is more efficient than the air- and ground-source heat pumps; it is in fact the most efficient type of heat pump. Water, like the ground, is a source that stores heat energy very well. Even in the coldest winter conditions, the temperature of groundwater is between 7 and 12 °C. Groundwater is taken from a source with a pump and brought to the evaporator of the water-source heat pump. The heat energy of the water is then extracted in the heat pump, and the cooled water returns to the source. For this system to work reliably, however, the flow rate and quality of the groundwater must be checked beforehand without fail. Only in this way can it be established whether a sufficient amount of heat energy can be extracted.
The quality of the water must stay within the limits set by the heat pump manufacturer. If it goes outside these limits, the use of a suitable intermediate heat exchanger is recommended.
This is because the heat exchangers inside the heat pump are extremely sensitive to irregularities in water quality. Different materials may be used in the heat exchangers (for example stainless steel or copper). Both heat exchanger materials can be sensitive to certain elements in the water. In such cases, intermediate heat exchangers can be preferred.
With an intermediate heat exchanger made of a suitable material, heat can also be extracted from river water, sea water or flowing waters such as streams.
The water-source heat pump is a less commonly used type of heat pump in Turkey and is available in a capacity range of 5 to 200 kW. Depending on the model, flow temperatures of up to 70 °C can be reached, so it can easily be chosen for radiator systems as well.
With a professional simulation programme, the selection of the system and the solar collector can be made and the annual energy and CO₂ savings can be determined.
An example calculation is given below.
| Criterion | Ground-source heat pump (drilling) | Ground-source heat pump (horizontal) | Air-source heat pump | Water-source heat pump |
|---|---|---|---|---|
| Feasibility | Easily possible | Needs a large garden | Easily possible | Groundwater quality must be checked |
| Average COP | COP = 4–5 | COP = 4–5 | COP = 3–4 | COP = 5–6 |
| Efficiency | High | High | Medium | Highest |
| Cost of connecting to the heat source | Drilling and piping costs very high | Excavation and piping costs high | Air duct costs low | If the water quality is not suitable, an additional pump and intermediate heat exchanger are needed |
| Maintenance cost | Low | Low | Low | Medium |
| Natural cooling | Possible | Possible | Not possible | Possible |
| Active cooling | Possible | Possible | Possible | Possible |