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a Single family house (SFH-I) with low-energy design; b single family house (SFH-II) according to current heat insulation standards, c single family house (SFH-III) as an old building with an average heat insulation, d multi family house (MFH); for the definition of SFH-I, SFH-II, SFH-III and MFH see Table 1.1 and Chapter 1.3 respectively.

a Single family house (SFH-I) with low-energy design; b single family house (SFH-II) according to current heat insulation standards, c single family house (SFH-III) as an old building with an average heat insulation, d multi family house (MFH); for the definition of SFH-I, SFH-II, SFH-III and MFH see Table 1.1 and Chapter 1.3 respectively.

The SPFs assumed in the following are higher for those single family houses that are not so well insulated. The relative share of domestic hot water generation compared to heating decreases in that case. Domestic hot water generation requires a higher temperature level than heating, which leads to a lower COP of the heat pump.

- Ambient air with/without preheating (AW/AWO). For systems without preheating, the air is transported to and from the heat pump via insulated galvanised sheet steel ducts. Opposed to that, in the system AW, the ambient air is preheated with a so-called air well. This is a concrete duct of approximately 60 m length and a diameter of 25 cm. It is sunk into the ground at a depth of 1.5 m. The SPFs of the analysed reference systems are assumed to be 2.17 (SFH-I) and 2.37 (SFH-II) for systems without air preheating (AWO) and 2.40 (SFH-I) and 2.65 (SFH-II) for systems with preheating (AW).

- Ground-coupled heat pumps with brine circuit (GB). HDPE tubes are sunk 1.2 m deep as collectors. The heat carrier - like in all analysed media with a brine circuit (ground-coupled heat pump and vertical probe) - consists of 30 % propylene-glycol and 70 % water. Due to their relatively high surface requirement, ground collectors are only used for comparatively low heat capacity levels (in general smaller than 20 kW). Therefore only the systems SFH-I, SFH-II and SFH-III can be operated as heat source systems with ground collectors. For the compound system of domestic hot water generation and space heating SPFs of 3.43 (SFH-I), 3.65 (SFH-II) and 3.85 (SFH-III) can be achieved.

- Ground-coupled heat pumps with direct evaporation (GD). For the assumed systems with direct evaporation, copper tubes with a plastic coating are sunk at a depth of 1.2 m on a layer of sand. Due to the similarly large surfaces required, heat pump systems for the supply tasks SFH-I, SFH-II and SFH-III are analysed. The refrigerant R407a serves as the heat carrier from the collector to the heat pump. The annual work rates of these systems are at 3.76 (SFH-I), 4.00 (SFH-II) and 4.20 (SFH-III).

- Vertical ground probe with brine circuit (GP). At an assumed heat withdrawal capacity of 50 W per m ground probe, ground probe lengths of 2 x 60 m (SFH-II), 3 x 90 m (SFH-III) and 12 x 75 m (MFH) can be derived for the systems under review. The HDPE probes are designed as double-U-tubes and installed in boreholes that are afterwards filled with a suspension of bentonite, cement and water. The SPFs for domestic hot water generation and space heating are at 3.59 (SFH-II), 3.77 (SFH-III) and 3.73 (MFH).

- Ground water wells (GW). For the systems SFH-II, SFH-III and MFH, production and injection wells that are 20 m deep each are excavated. The lining and walling of the boreholes is done correspondingly. The extracted groundwater that serves as a heat carrier is discharged via injection well into the ground again after heat withdrawal by the heat pump. The SPFs are at 3.95 (SFH-II), 4.20 (SFH-III) and 4.15 (MFH).

In order to be able to give an estimate of the costs involved in supplying low-temperature heat with the heat pump systems defined above, investment and operation costs plus the specific heat generation costs for the reference systems defined in Table 9.7 will be presented below. Due to the location-specific geological conditions (e.g. condition of the ground, heat conductivity of the subsoil, distance of the groundwater conductor from the top edge of the terrain) significant differences in the design of the heat source system and thus in the cost structure of the compound system can occur. Additionally, the costs for electrical energy and the connection of the heat pump to the public electricity grid are widely dispersed depending on the respective conditions of the local utility. The costs discussed in the following can therefore only show a certain scale and average reference values. In individual cases and depending on the local framework conditions, lower but also higher heat generation costs can be possible.

Investments. The amount of specific investments into heat pump systems is largely determined by the applied technology and the size of the system. In general, the specific costs decrease with an increase in system size. This is mainly true for the heat pump aggregate including domestic hot water generation. In contrast to that, the heat source systems show a slight decrease of costs, with the exception of groundwater utilisation as a heat source. Thus specific investment costs of the analysed brine/water and water/water heat pumps are between 220 and 1,000 €/kW. The costs for heat pumps of direct evaporation systems are slightly lower. For heat source installations, costs for systems with vertical ground probes are between 540 and 600 €/kW, for systems with groundwater utilisation between 240 and 600 €/kW and with horizontal ground collectors using brine or direct evaporation between 240 and 300 €/kW. If rammed wells are used instead of the assumed boring wells, the costs can be reduced significantly, especially for smaller systems. For rammed wells, the investment costs for the entire heat source system of the analysed systems are at around 3,000 € for an 8 kW installation, at approximately 4,000 € for an 18 kW installation or at 13,000 € for a 60 kW installation (Table 9.8 and 9.9).

Table 9.8 Investment and operation costs plus heat generation costs of heat pump systems for the generation of domestic hot water and space heating for the reference configurations SFH-I and SFH-II (Table 9.7)

System

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