In a well-insulated home, it is possible to use an energy-efficient heat pump for heating as well as for the production of sanitary hot water. In some cases, the same device can also be used to cool your home in the summer. There are a number of options available that are worth considering, the most important of which involve the type of source and whether to go with an air heating or water heating system. We’ll help you decide.
Basic illustration of an air/water heat pump. (Illustration source: photolia)
In the most basic sense, the functioning of a heat pump can be compared to that of a refrigerator or freezer. In a refrigerator, heat is extracted from the inside of the unit, thereby reducing the interior temperature. However, the extracted heat still has to go somewhere: on the back of the refrigerator there is a metal grid-like structure with small conduits that releases heat into the ambient air. Besides keeping your vegetables, fruits and other foods cool, your refrigerator also partially heats the space around it. A heat pump does exactly the same thing. It extracts heat from a source (air, water or the ground), and this extracted warmth is then used to heat the home.
Different types of heat pumps can be distinguished based on the source and the system used to distribute the heat.
1. Outside air as source
- Air/air heat pump: Heat is extracted from the outside air and converted to warmer air by a heat exchanger. This heated air is then distributed throughout the home by means of a forced air system (a fan and a network of ducts).
- Air/water heat pump: Outside air is used as a source here as well, but the extracted heat is transferred to a water circuit that can be used for underfloor heating, radiators and sanitary hot water.
The cost to install air source heat pumps is lower than for other systems, but they do have one drawback: if the outside air gets too cold, the efficiency of the system decreases. Air systems are predominantly used in temperate climate zones and are not recommended for regions with long, cold winters.
2. Ground as source
In this case, heat is extracted from the ground and converted into hot water. This is called a ground/water heat pump. The temperature of the ground remains much more constant throughout the entire year, so the efficiency of this system is higher, even during cold winters. We can distinguish between two types of systems: a horizontal and a vertical ground heat exchanger.
- Horizontal ground heat exchanger: Flexible PE piping is installed at a specified depth (e.g. 1.5 m) beneath the ground level in the garden. This closed loop then transfers its heat to the heat pump. The surface area required for this is much larger than that of the space to be heated, so this system is not suitable for a smaller garden in the city.
- Vertical ground heat exchanger:
One or more vertical holes are drilled into the ground. In each opening, one descending and one ascending PE pipe is installed, which together form a closed loop. The liquid mixture in the PE pipes draws the heat from the ground and transfers it to the heat pump. Such a system can be deployed in ground having a limited surface area, but boreholes obviously still need to be made. Since the colder return water can lower the temperature of the ground, the efficiency of this system may start to decline toward the end of the heating season. If the temperature of the ground drops too much, the ground is said to be depleted. A proper balance must be struck between the extraction of heat from the ground in winter and the natural rewarming of the ground in summer. The latter can also be achieved by reversing the function of the heat pump in summer: the home is cooled and the excess heat transferred to the ground.
3. Water as source
A watercourse or, better yet, groundwater can also be tapped as a heat source. Two wells are drilled into the ground at a reasonable distance from each other. In contrast to a vertical ground/water system, this is an open system. Groundwater is pumped from the first well to the heat pump. The heat is transferred to a heat exchanger, and colder return water is then pumped to the second well. If desired, this system can be reversed in summer, with the colder groundwater from the second well being used to cool the home. Excess heat is then stored in the first well.
When choosing a heat pump, seek the advice of your installer.