GeoThermal Design

Heat sources

Natural energy sources Heat pumps work on the basis of drawing renewable thermal energy from the environment - from air, ground water and soil - and releasing it into the heating circuit.

The heat source from which thermal energy is drawn determines the type of heat pump

used. OCHSNER experts can advise on the most appropriate heat pump system for local conditions. Factors such as availability of a heat source, useable ground area, construction type, size and insulation of the building, type and temperature of heat distribution in the house, etc. all influence the decision.

Tip: The heat source with the highest temperature will produce the highest energy efficiency ratio and therefore the lowest heating costs.

Water as heat source If ground water is available at a reasonable depth and an appropriate temperature, it offers the highest seasonal performance factors (consent may be required). A constant temperature of +8°C to +12°C will provide the best heating performance. The ground water is fed from the extraction well to the heat pump and from there to the deep well some 15 metres away.

Geothermal heat as heat source 98% of the geothermal heat close to the surface of the ground is stored solar energy. Even on freezing winter days, the ground temperature is warm enough for a heat pump to operate economically. Earth collectors buried in the ground absorb the heat. A heat transfer medium circulates through these ground collectors, absorbing the heat and transferring it to the heat pump. Earth collectors operate in two different ways, depending on the heat transfer medium used: direct heating and brine.

Direct geothermal energy With direct expansion the working fluid used by the heat pump (R

407C) circulates as the heat transfer medium in the ground collector. This avoids the need for an intermediate heat exchanger and brine circulation pump. Direct geothermal energy systems currently offer the lowest running cost of all geothermal heat systems, because with direct geothermal energy you benefit from up to four-fifths (80%) of free environmental energy.

OCHSNER also supplies this system for active cooling in summer. Horizontal collectors are used.

Geothermal heat with brine In brine-type systems a mixture of water and anti-freeze (brine) is circulated as the heat transfer medium. This absorbs the heat and transfers it to the heat pump. The ground collectors can be laid in various different ways:

• If there is sufficient land available, horizontal collectors are the most cost-effective solution. In new builds, depending on the soil type and heating requirement for the house, the area over which the collectors are laid will be roughly 1 to 1.5 times the area to be heated. In existing building stock the area will be larger, depending on the thermal insulation.

• If there is little space available, spiral trench collectors or ground probes (  Boreholes) can be used.

Note: Some of these systems have to be registered or require consent.

Air as heat source If neither the ground nor ground water is suitable as a heat source, it is perfectly possible to use the outside air. This heat source is also ideal for conversions or for bivalent systems. The defrosting device built into the heat pump means that it can continue to operate at temperatures down to -18°C or below. In such casesR.H.Hydronics recommends the use of split units, with the heat pump installed indoors where it is protected and the evaporator installed outside to minimise losses.

Advantages: no air ducts, very quiet, long service life and more economical than compact units.