BENEFITS AND PRECONDITIONS FOR GROUNDWATER HEAT PUMPS Groundwater heat pumps hold a special position in the heat pump sector. These systems draw heating energy not from the ground or the ambient air, but directly from the groundwater. They score highly due to particularly high efficiency and durability. Groundwater heat pumps present building owners wanting to rely on renewables for generating heat with an interesting alternative and special benefits.
One benefit of using groundwater as an energy source is its constant temperature all year round.
Groundwater temperatures generally range from 8 to 12 degrees Celsius. This is already sufficient to ensure your supply of heating energy and domestic hot water using ingenious heat pump technology. To do this, you need a compressor. This works by compressing the groundwater and thereby raising its temperature to a usable level of around 40 to 60 °C.
AND SINKING WELLS, FIRST STEPS TOWARDS OPERATION
Extensive preparatory work and drilling is required before groundwater heating energy can be utilised. Two wide wells must be sunk during the installation of a groundwater heat pump. These are known as the delivery well and return well. The delivery well extracts the water; the return well brings it back again. They are therefore responsible for the constant circulation of the groundwater through the heat pump. It is essential that the wells are sunk deep enough for this system technology. The reason for this is that groundwater near the surface is subject to strong seasonal temperature fluctuations, which in the case of a deeper well would be less severe and no longer discernible with wells that are deeper still. If, however, the groundwater temperature drops too low, the heat pump could be damaged. Borehole depths from 5 to a maximum of 20 metres have proved to be ideal for the operation of groundwater heat pumps. Increased well depths would be detrimental to the economic viability of the entire system, due to the greater technical outlay and effort required. Another important factor is a sufficient distance between the delivery well and the return well so that the warmer feedwater and the cooled return water cannot mix. The return well must always lie downstream of the delivery well, in the flow direction of the groundwater.
FOR A GROUNDWATER HEAT PUMP
One important prerequisite for the operation of a groundwater heat pump is a permit from the local water authority. This also requires a pump test over several days. This preliminary work makes sense because it assures the building owner before the actual installation of the heat pump that groundwater of the required quality is available. It can be helpful to find out whether groundwater heat pumps are already in operation in the neighbourhood, or if any test drilling has been carried out. This enables a first assessment to be made as to whether your own site is fundamentally suitable for a groundwater heat pump. Another important piece of information – operating this system is generally not permitted in water protection areas.
BEFORE INSTALLING A GROUNDWATER HEAT PUMP
Only near-surface groundwater may be used for groundwater water pumps. Testing the productiveness of the delivery well requires a three day continuous pump test. During this time, the water temperature is checked to ensure that a temperature of at least 8 degrees Celsius is maintained at all times. This is required to guarantee reliable system operation. One further important aspect – to prevent corrosion damage, the amount of suspended matter in the water must not exceed or undershoot certain thresholds. A water analysis must therefore be carried out in advance.
FOR MAXIMUM OPERATING RELIABILITY
Groundwater heat pumps use a heat exchanger in which the energy stored in the groundwater is transferred to a refrigerant. The refrigerant is then fed into the heat pump. This closed circuit makes the groundwater heat pump a particularly durable and reliable system. Generally, two different types of heat exchanger can be used: plate heat exchangers and tubular exchangers. Plate heat exchangers (PHE) are particularly suitable if the water quality is very good. However, tubular heat exchangers (THE) can also cope with water of a lesser quality. This is due to various factors. The tubular HE pipework wall thickness is 0.6 mm whereas that of PHE is 0.3 mm. Stainless steel 304 is used externally and 1.4404 for the internal pipework. This ensures very good corrosion resistance and lowers the risk of mechanical damage. Tubular HE feature significantly larger internal diameters for conducting the groundwater. They are therefore less susceptible to blockages caused by suspended matter in the water, such as sand and other contaminants. This also reduces the risk of freezing. To ensure permanent operational reliability a filter should be installed upstream. In the case of higher iron and manganese content, OCHSNER recommends carrying out regular cleaning to prevent blockages.
FOR HIGH EFFICIENCY
If all preconditions for operating the system have been met, and the engineering and installation have been carried out professionally, nothing stands in the way of long term, eco-efficient operation. One of the decisive benefits of groundwater heat pumps is their high economic viability. Seasonal performance factors (SPF) of 6 are not uncommon – this means that the heat pump can generate up to 6 kW of heating energy from 1 kW of electricity. But even with an SPF of 4, groundwater heat pumps are still highly viable. Your OCHSNER system partner can answer any technical questions you may have, and advise you as to whether your home is suitable for this environmentally sound heat generator during an in-depth one-to-one consultation. Our experts will also advise you on the ideal type of heat pump for your home and the costs involved. In the case of groundwater heat pumps, development costs related to well drilling and the cost of accessories required by the installer must be taken into account when calculating the total outlay.