Fig. 5 Profile: Single-family home

Fig. 6 System diagram.

Fig. 7 Geothermally heated bridge in Berkenthin.
© H.S.W. Ingenieurbüro Rostock

Fig. 8 Road surface heating prevents black ice.
© H.S.W. Ingenieurbüro Rostock

Fig. 16 The new gas absorption heat pump for the school building in Plaidt.
© E.ON Energie AG, München

Fig. 17 System diagram for the pump system of the school building.
© E.ON Energie AG, Munich

Fig. 18 Comparison of the costs and CO2 emissions per year between electric heat pumps (EHP) and gas heat pumps (GHP).
© E.ON Energie AG, Munich

Fig. 19 School in Plaidt
© E.ON Energie AG, Munich
11 / 12

In practice: Single-family home with electric HP

In a new single-family home with 127 m² of heated building area and a low heating energy requirement, a heat pump is used for heating the building and for providing domestic hot water heating. The device, which is placed outside, has a heating capacity of 7.5 kW (with A2/W35 as per EN 14511) and uses the external air as the heat source. Supplementary electric heating elements, which are installed in both the DHW and space heating storage tanks, operate in accordance with individually set parameters. The rooms are heated using underfloor and wall heating. The towel rail in the bathroom is also operated with the low heating circuit temperature. This building is being investigated as part of the “WP Monitor” (HP monitor) project.

From May 2011 to April 2012, the system achieved an annual performance factor of 3.3, which is a relatively high value when compared with the other results in the “WP Effizienz” monitoring project. The heating circuit was operated at average temperatures of 35 °C/28 °C. The DHW storage tank was charged at average temperatures of 47 °C/42 °C. 84 % of the heat provided was used for space heating and 16 % to supply DHW. The heat pump was operated for 2,100 hours during the year. The two electric back-up heaters were rarely in operation so that less than 1 % of the heating requirement for space heating and DHW was provided using these electric back-up heaters.

En passant: Bridge technology

The road surfaces of bridges, particularly in geographically unfavourable locations such as above water, in gorges, shady areas and low-lying areas, ice up considerably more quickly in winter than road sections with direct contact with the ground. This considerably increases the risk of accidents and forces the winter gritting services to begin operations at a much earlier point in time, even if the general road conditions do not require this. Automatic de-icing spray systems can provide help, but they are controversial for ecological and economic reasons.

One solution is to use shallow geothermal energy, which has been tested for the very first time in Germany as part of a pilot project when resurfacing the Berkenthin road bridge across the Elbe-Lübeck Canal. A heating coil has been embedded in the asphalt surface of the bridge. Besides heating the road surface in winter it is also possible to cool the asphalt in summer, which thus reduces the risk of rutting and lengthens the service life of the surface material. The road surface is heated and cooled via a heat pump that is connected to a single well system.

In practice II: School building with thermal heat pump

The heating system in the school building, which was built in 1907 in Plaidt, underwent refurbishment in 2010, whereby two electric heat pumps with the ground as the heat source were replaced with a newly developed gas-absorption heat pump. This also uses the ground as the heat source. The 1,500-litre buffer storage tank was not replaced. To cover peak loads, a gas-fired condensing boiler has been installed instead of the electric heating element. The heat is transferred to the building via radiator-based heating. Hydraulic balancing was carried out to ensure that the heat, which is generated highly efficiently, can continue to be distributed effectively and to keep the level of the heating circuit supply temperature as low as possible.

During the 2011 / 2012 heating season, the gas heat pump achieved an annual utilisation rate of 137.5 %. The annual utilisation rate for gas heat pumps is the ratio of the heat volume released by the gas heat pump to the heat volume added from the natural gas and is therefore not directly comparable with the annual utilisation rates generally specified for condensing boilers. The system was operated for 2.335 hours during the year.

According to measurements made across a heating season, replacing the old electric heat pumps with a new, natural gas-based absorption heat pump/gas-fired condensing boiler system has enabled energy costs savings of 39 % and a CO2 reduction of 44 % for the overall system (GHP, central heating). This is shown by the billing figures from the local energy supplier.


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