One-family house in Dresden

The described heat pump system consists of a two-circuit brine-to-water heat pump for heating and domestic hot water supply using two vertical boreholes as the heat source. It is the heating installation of a detached house in Dresden, Saxonia. While in the laboratory test rig the natural refrigerant propane was used the heat pump of the pilot plant installed in the one-family house is charged with R 134a. In the year 2004 the measured Sesonal Performance Factor (SPF) was 3.64.

Project description

Building, overall energy concept

Photo 1: Detached house in a suburb of Dresden, Saxonia

The new building with a heated floor area of 150 m² has a design heat load of 5.2 kW, according to the standard DIN 4701. Considering domestic hot water needs and the turn-off times required from the energy supply company (3 times 1 hour per day) the total heat load was estimated to about 8 kW.

The heat delivered is distributed to a floor heating system (supply temperature 35°C) and a domestic hot water storage tank of 400 liters. Within the storage tank there are two heat exchangers one on the upper part and the other one below.

The heat source of the described ground source heat pump system consists of two vertical boreholes, each with a depth of 60 meters. The heat pump control is related to the heating load of the building (dependent on the outdoor temperature).

Heat pump system

Photo 2: Pilot heat pump without casing at the customers home

The development of the described two-circuit heat pump for heating and domestic hot water supply took place in the course of a research project at the Technical University of Dresden. While in the laboratory test rig propane was used as a natural refrigerant, the heat pump of the pilot plant installed in the one-family house is charged with R 134a. The deciding factor for this choice was the product liability.

Photo 3: Heat pump plus control unit and buffer storage

A weak spot of customary heat pumps is the generation of domestic hot water since the SPF decreases as a result of higher supply temperatures. To receive a better SPF the domestic hot water is very often generated by insufficient low temperatures of about 40°C to 45°C. Aimed at saving energy the auxiliary electric heaters for storage tank disinfection are usually not used. For this reason the proposed heat pump system utilizes two circuits to produce useful heat within one device. One loop is connected to the condenser and the other one for higher water temperature is coupled with the desuperheater. In parallel operation the heat of lower temperature is fed for instance into the floor heating system while the hot water tank is charged by the circuit of higher temperature from the desuperheater.

For a detailed description of the two-circuit heat pump system read the paper presented at the IEA Heat Pump Conference 2005 in Las Vegas.

Monitoring: Data recording is carried out via computer with ISDN/Watchdog. The software pcAnywhere is used for data transfer to the host computer at the university.

Figure 1: Schematic of the heat pump system

Figure 2: Logarithmic pressure, enthalpy-diagram

 Enlarge image 

Operation experiences

The average Seasonal Performance Factor (SPF) of the system for the monitoring period March 2004 to January 2005 was 3.64.

Diagr. 1: Seasonal Performance Factor of the installation (2004/2005)

Diagr. 2: Balance of heat supply in the year 2004

Diagr. 3: Domestic hot water generation in the year 2004

At the beginning of September 2004 some improvements were made at the expansion valve and at the control adjustment. An evaluation of data measured indicate there are still some possibilities to improve the performance of the installation. It is planned that the measurements will take some heating periods to get more information about the behaviour of the plant and to work out still more improvements in design and control technology.

Costs, economic efficiency, incentives

No information available.

Regulations, guidelines, benchmarking

No information available.

References

Müller B. 2005. Development of a Two-Circuit Heat Pump for Heating and Domestic Hot Water Supply. IEA Heat Pump Conference, Las Vegas, Nevada, 2005

¹ SPF data covering the period March 2004 to January 2005
² at B0/W35, tested by KKW Kulmbach
³ at B0/W35, tested by KKW Kulmbach
⁴ monitoring by TU Dresden