All the components of a Nutherm geothermal heating system have been specifically designed to maximize the efficiency. Some of these components are described in more detail below.
The conventional method of heating and storing water has certain drawbacks with regard to hygiene and taste. Domestic hot water systems are a potential multiplying ground for Legionella bacteria, which have an ideal growth temperature range of 35-45 ºC. As a result of this, regulations state that stored hot water must be heated to a temperature of at least 60ºC for 10 minutes once a day, to kill the bacteria. In conventional boiler heating systems, these temperatures are easily achieved, but the efficiency of a heat pump is affected by high flow temperatures.
To overcome these hygiene problems without having to run the heat pump at high flow temperatures, our DS series hot water systems contain a hygienic hot water module, either fitted inside or outside the cylinder.
A thermal store is heated to a temperature of 55 ºC by the heat pump, and is not used directly. As water is drawn from the hot tap, water from the mains supply is diverted past water from the thermal store via a specially designed, high-performance plate heat exchanger. By keeping domestic water separate from the thermal store, germs from the cylinder are prevented from being introduced into the system, avoiding the hygiene problems of conventional hot water storage systems entirely. The high efficiency of these heat exchangers ensures that water can be heated from, for example 10 to 50 °C, in fractions of a second. A Waterkotte 54 kW hot water module provides 20l (on demand at taps) of fresh water at 50ºC per minute. This system complies with all regulations regarding water hygiene.
Our domestic hot water kit is designed to take pressure so, if the mains pressure and flow rate input to the system are sufficient, the whole system will be pressurised, hot and cold. This eliminates the need for electric pump showers.
With the DS series, thermal stores with a capacity of 300-400 litres are preferable. Where greater quantities are needed, single-tank storage volumes of up to 2000 litres are easily available. However, this is usually only necessary in large commercial installations.
Domestic hot water production is always given priority within the heating system. As soon as the temperature in the hot water thermal store is reduced by 5°C, for example, the flow from the heat pump is diverted from the under-floor heating and the total output is dedicated to restoring the temperature of the thermal store to the set point of 55°C. This gives very fast recovery times. The temperature of a 400l thermal store can be raised from 50 to 55°C in around 10 minutes with the full output of a 14.2kW heat pump (a typical domestic set-up). The high thermal mass of an under-floor system means that the floor stores energy for a long period of time, so the space heating is not compromised while the heat pump is dedicated to hot water production.
The convenient cooling function is included in Waterkotte Ai1 Compact Device models and available as an accessory in the DS series.
With the use of an additional heat exchanger, built into the Cooling Module, Waterkotte heat pumps are very simply modified to allow Natural Cooling. Since the ground is at a temperature of around 10ºC all year round, it can be used as a low temperature reservoir in the summer to achieve passive cooling. Brine in the collector bypasses the heat pump, absorbing heat from the heating circuit through the cooling heat exchanger, and discharging it into the ground. Cool water runs continuously through the heating circuit, bringing the temperature of the room down to a comfortable level on hot summer days. As with heating, the distribution is uniform over the floor surface, which ensures gentle cooling. Unlike with air-conditioning systems, which produce dry air and cold draughts, this system provides cooling that is entirely free from air vortexes and currents.
In the Natural Cooling mode, with the exception of the regulator and circulating pump, the heat pump is switched off. Natural Cooling requires no additional devices or ventilators, making it an energy-saving and inexpensive building cooling method. The cost of operation is comparable to that of a common light bulb.
The electric heat generator is a component of every machine in the Ai1 and DS 5023 series.
The heat pump is sized to produce 70% of the peak heat load of the building, which represents approximately 95% of the total annual heat requirement. The electrical back-up is called in by the control system on the few coldest days of the year, when the heat pump and back-up simultaneously meet the total heating demand.
The back-up also supports the heat pump in the initial heating-up process, which, since the building fabric must be heated to room temperature, has higher power requirements. Often the structure has to be dehumidified. Not only does the presence of moisture reduce the effectiveness of the insulation, but the evaporation of water from the structure has very high heat requirements. The back-up aids the heat pump in meeting these extreme heating demands so that, the first time the installation is put in operation, greater safety is achieved and the heat source is protected from being put under excessive strain.
Waterkotte heat pumps contain recognised refrigerants that comply with international standards. These refrigerants are approved and recommended by manufacturers of the relevant compressors. The refrigerants used are exclusively new, non-inflammable safety refrigerants, which will be required by law in the future. According to the latest industry research, used together with synthetic oil, they ensure low friction, the very lowest wear and tear, and thus the greatest longevity for the compressor.
The refrigerants used are: