USING THE GROUND AS A RELIABLE AND EFFICIENT HEAT SOURCE

Basically, this energy source is available in every garden. Ground source heat pumps use heat absorbed by the ground to provide buildings with an environmentally sound and efficient heat supply. This has been an established solution for decades and for good reason. The ground can be considered an ideal heat source. Due to the fact that this energy source maintains a constant temperature throughout the year, ground source heat pumps achieve good results, continuously and reliably. Given professional engineering and expert installation, ground source heat pumps are a reliable means of supplying the required amount of source energy free to your door, all year round.

GROUND SOURCE HEAT PUMPS WITH GEOTHERMAL COLLECTORS

Ground source heat pumps are principally based on the use of geothermal collectors, frequently also referred to as horizontal collectors.

These are embedded in the ground, below the frost line, at a depth of around 1.5 metres and deeper. The plastic pipework is routed in loops. Brine circulates through this pipework and transfers the extracted heat via a heat exchanger to the actual heat pump refrigerant. In this way, the solar energy which heated the ground can be made available for heating purposes. One of the principle requirements for ground source heat pumps with geothermal collectors is therefore that the area above the collectors is open and undeveloped. In order to prevent damage to the pipework from the outset, it is also advisable not to plant deep rooting plants above. Important information for all those who are thinking of providing heat with a ground source heat pump – geothermal collector systems must only be registered; they do not require permits.

GROUND SOURCE HEAT PUMPS

SYSTEM COMPARISON

Ground source heat pumps are not all alike. Generally, they are classified according to type and operating mode, and have distinct differences regarding layout, costs and performance. Here you can find comparative information on the various types of ground source heat pump.

HORIZONTAL COLLECTORS

OBSERVE SURFACE AREA REQUIREMENTS

Any region with heavy rainfall is predestined for a geothermal collector heat pump, because the water in the ground can store the sun's heat efficiently and transfer it to the collectors. Surface area requirements associated with the collector solution must be observed. As a rule of thumb, the surface area required to embed the geothermal collectors must be approximately 1.5 to 2 times greater than the living space to be heated. Calculation example: for 120 square metres of living space, 180 to 240 square metres of geothermal collectors must be embedded in order to achieve the correct sizing for a sufficiently powerful heat pump. Soil conditions play a major role. Cohesive soils that absorb moisture are ideal. By comparison, loamy soils have a specific heat capacity (in joules per kilogramme and Kelvin) of approximately 1230, silt soils as much as around 1345. Sandy soils, however, only have a heat capacity of around 800. This means that, in sandy soils, a correspondingly larger collector area must be allowed. Your OCHSNER partner will be happy to answer any individual questions. Detailed engineering and individual consultation should take place prior to every heat pump installation. A point to note: although the surface area required for geothermal collectors is certainly significant, the time, effort and therefore cost of installing them in a new build where the garden has not yet been landscaped is comparatively low.

DIRECT EXPANSION

GROUND SOURCE HEAT PUMP WITH HIGH EFFICIENCY

The direct heating or direct expansion system is a speciality – the refrigerant in the heat pump circulates through the horizontal collector and evaporates. The heat transfer medium in the heat pump circuit is free of chlorine and is ozone-neutral. It picks up geothermal energy directly via the seamless duplex pipes of the horizontal collector. This results in excellent performance figures and high operational reliability due to the fact that no intermediate heat exchanger or brine circulating pump is required. The collector in these systems is frequently referred to as the "evaporator circuit". Installation is subject to applicable regulations in each case and is sometimes notifiable or subject to permits. The deciding factor – direct geothermal heating systems achieve the lowest operating costs and the best heat yield of all the common geothermal collector systems available today.

GEOTHERMAL PROBE

VERY EVEN TEMPERATURES ALL YEAR ROUND

Heat pumps with geothermal probes represent another system type. For this process, just a small borehole can already be sufficient to sink two U-shaped plastic pipes into the ground. The depth of the borehole is decisive for the sizing and efficiency of these ground source heat pumps. For a conventional detached house, experts recommend a depth of approximately 100 m to ensure a suitable heating output. Several parallel boreholes are also an option. Minimum distances must be observed, however. This kind of system offers a unique advantage – as temperatures at depths of 10 m and below remain more or less constant throughout the year, heat pumps with geothermal probes operate highly effectively. The all year round use of a heat pump with a geothermal probe comes at a relatively high outlay, due, in no small part, to deep boreholes and the associated technology. In addition, these systems generally require permits and may prove, subject to ground conditions, not always practicable. In areas where the groundwater is just below the surface, it may be possible to use groundwater heat pumps as an alternative.

COOLING WITH A GROUND SOURCE HEAT PUMP

RECHARGING THE GROUND, YOUR ENERGY STORAGE TANK, IN SUMMER

Generally, ground source heat pumps can also be used for cooling in summer if they are sized and designed to do so. A differentiation is drawn between passive and active cooling. In passive cooling, only the brine circuit in the geothermal collectors is used to transfer heat from area heating systems or radiators via the collectors to the ground which, at approximately 10 degrees Celsius, is significantly cooler in summer than the air inside the building. In this way, the temperature inside the building can be lowered by a few degrees. Passive cooling does have one disadvantage however – the ground warms up slowly so that, if the summer is long and hot, the cooling effect can decrease. With active cooling, the heat pump process is set in motion but in reverse direction – the heat pump now uses the building as a heat source and transfers the heat via the geothermal collectors to the ground. Heat extraction from the house is significantly greater than with passive cooling. However, the heat pump process does require more power. One benefit of cooling in summer is that waste heat is transferred to the ground so that the ground is used as a "storage heater". This way, the waste heat from the house can contribute towards a higher heat yield in winter.

CONCLUSION

SIZING THE GROUND SOURCE HEAT PUMP APPROPRIATELY

Irrespective of the type of ground source heat pump chosen – appropriate sizing is decisive for efficiency and sufficient system performance. In order to individually and appropriately size a ground source heat pump, three values and components are particularly critical:

  • the heat demand of the respective building
  • the sizing of the heat pump
  • the geothermal probe or geothermal collectors

For obvious reasons, undersizing – less than the actual heat demand of the home – is not expedient. Oversizing also has a negative effect on the overall performance and therefore on the efficiency of the heat pump. For geothermal probes, deep borehole calculations are the decisive factor with regard to intended performance characteristics. If geothermal collectors or horizontal collectors are used, the collector area must be correctly sized. It is always advisable for owners and building contractors to seek a detailed, expert consultation and take serious note of the professional advice received. Each requirement is different and must be considered and engineered individually. OCHSNER partners are happy to answer any questions concerning heat supply using renewables. The result – a heating system which delivers cosy and environmentally sound heat at all times.