This multifamily residence has 28 dwellings where 67 persons are living. It is heated by two brine-to-water heat pumps fed by a field of 10 borehole heat exchangers. The heated area is of 1.771 m². The two heat pumps, each with a heating capacity of 32.6 kW, are fulfilling the needs for heating and cooling. The hot tap water is provided through solar collectors in addition with electric water heaters.

Project description

This residence was built in 2003. It has 28 dwellings distributed over 4 buildings, two with two storeys and two with three storeys. The heated area is of 1. 771 m². It is located in Besançon in the east centre of France, in a relatively cold climate.

The insulation is good and the buildings have been awarded with a high energy performance labelling. The heating need is of 74,0 kWh/m²/year.

The heating and cooling system uses two identical non reversible heat pumps with a heating capacity of 32,6 kW each. Each heat pump is connected to 5 borehole heat exchangers with a depth of 100 m and a diameter of 32 mm.

The cooling needs are fulfilled in free cooling mode.

The hot tap water is provided by a collective system using thermal solar panels in addition with electric water heaters.

The distribution for heating and cooling is made through thermal floor for each storey. The supply water temperature in the thermal floors is 30°C for heating and 18°C for cooling.

Heat pump system

The heat pumps are brine-to-water machines with compressor driven by electricity. Each one is using five 100m-deep borehole heat exchangers as heat source.

An additional heating resistor of 15,0 kW is also available in case of very cold outdoor temperature. Since 2003, it has been used only during 8 hours in 2005.

The heating capacity of each heat pump is 32.6 kW. The nominal electric power is 7,2 kW, fed in three-phases.

The nominal operating mode is 35°C (condenser output) and 0°C (evaporator input). The maximum temperature output at the condenser is 55°C.

Each heat pump is loaded with 6,8 kg of R407C refrigerant.

The cooling is made in free cooling mode, without the heat pumps. The cold water from the borehole heat exchangers is used in the heating/cooling floors through an intermediate heat exchanger.

The hot tap water is produced through 52 m² of solar collectors in addition with 24,0 kW of electric water heaters.
Operation experiences 

The measurement campaign was made during the complete year 2006. It was funded both by eDF and ADEME during a campaign intended to monitor the performance of ground coupled heat pumps in real conditions.

The heating system was stopped from June 8th, 2006 to October 4th, 2006. During this period, the cooling system was turned on but operated really only between July 20th and July 31st, 2006, during the hottest days of the summer.

One heat pump operated during 1.577 hours (compressor and circulator running time) and the other during 2.286 hours.

No operational problems were experienced.

Costs, economic efficiency, incentives

The operating cost can be estimated at 3,3 €/heated m² during year 2006 (based on an average electricity cost of 13 c€/kWh, excluding yearly subscription costs).

Regulations, guidelines, benchmarking

No information available

References
No information available

¹ Measured during January 2006 to December 2006
² 2 x 32,6 kWth
³ Appliance alone
⁴ Heat pump only, including all pumps and auxiliary systems SPF=2,72
⁵ Only indirect emissions (thus excluding possible refrigerant leaks) due to electricity consumption both for the heat pumps and the auxiliary systems. Measured during year 2006.

Valencia University

Type of building:
Existing university building comprising seminar rooms, laboratories, offices and workshops

Purpose:
Heating and cooling

Heat pump system:
An existing ground source heat pump (heating capacity 17 kW, cooling capacity 15 kW) with six vertical borehole heat exchangers, will probably replaced by a Hiref heat pump (heating capacity 20 kW, cooling capacity 18 kW), system to be optimized 

Distribution system:
Fan coil units

More information:

An electrically driven ground source heat pump system is used for heating and cooling an efficient office building with flexible room concept built in the year 2002 in Aachen. The heat source consists of 28 borehole heat exchangers with a depth of 42 meters each. In summertime the building is conditioned by free cooling via the borehole heat exchangers. The control concept was optimized continuously over a five years monitoring period. In the year 2007 a Seasonal Performance Factor (SPF) of 4,3 was reached.

 Project description

Photo: The new office building lies on the edge of a “solar housing estate” in the German town of Aachen and follows the energy specifications for the residential buildings of the estate.

The compact, four-storey office building without cellar has a north-south orientation. The large surfaced floor plan without load-bearing interior walls allows a flexible subdivision. Five parties currently use the building with approx. 100 workplaces in total. In theory, up to eight units would be possible per floor.

The reinforced concrete skeleton construction with load-bearing precast concrete facades was, for the most part, prefabricated. The building shell was therefore finished within 8 weeks and the whole building within 9 months. The high standard of insulation is in line with the construction method of a passive house but only reaches an average U-value of 0,48 W/m²K. This is, among other things, a result of the glazing in the slightly-heated staircase which, however, is located inside the insulated envelope, with a U-value of 1,6 W/m²K. The outer walls are insulated with 20 cm mineral wool and faced with square tiles ventilated at rear. The windows in the office zones consist of triple glazing in thermically separated aluminium frames (UW=0,80 W/m²K). The windows account for 41% of the facade surface area. Because of the glazing’s comparatively low g-value of approx. 50 % and cooling using thermally activated concrete surfaces, exterior shading was not installed. The annual heating requirement was calculated at 39 kWh/m² p.a. The air-tightness test of the building envelope produced an n50-value of 0,3 per hour.

Heat pump system

An electrically driven ground source heat pump is responsible for heat generation. Each of the 28 borehole heat exchangers is 42 meters deep. The heat pump supplies a buffer storage tank (900 liters) which feeds the concrete core temperature control (CCTC) with a maximum supply temperature of 28°C. The CCTC is divided into two control circuits (north and south) on each floor.

In summer, the heat is extracted from the rooms via CCTC and released into the earth by means of the borehole heat exchangers. The minimum supply temperature in summer is 18°C. In summertime the heat pump is not in operation (free cooling).

The energy requirements for cooling and heating balance each other out - the temperatures in the soil therefore do not build up during the course of the year. The borehole heat exchangers’ water circuit can also be used for cooling and heating the supply air by means of an additional heat exchanger.

Operation experiences

• The planners’ idea was a success. The operation of the building is both economically viable and energy efficient. The heat pump system can reach a high coefficient of performance because the temperature difference between the heat source and the supply is small, even with low outside temperatures. The energy equilibrium in the soil from the removal of heat in winter and the depositing of heat in summer also has a positive effect. However, evaluating several hundred measurement points over a five-year period was necessary to find the best control concept for operating the heat pump efficiently. For this, the accompanying EnOB monitoring was extremely important and will be continued.
• User satisfaction in the building is very high. It must be kept in mind, however, that today’s users were both the contractors and the planners. On the other hand, this has the advantage that they have first-hand experience of the problems occurring in the operation of the building and can optimise control parameters without great dispute about responsibility or financing and without having to schedule a lot of meetings. The idea of the building going into “series production” is today being put into practice. The same building is currently being constructed in France. A variation on the design is planned for further locations.

Costs, economic efficiency, incentives

• When constructing the building, high-quality, durable materials were used and importance was also attached to the comfort of cooling and mechanical ventilation - not necessarily the norm in offices. Nevertheless, with a net figure of 1,125 /m² NFA (cost groups 300 and 400), the investment costs are below the average costs according to the German building cost index (BKI). This was reached because additional costs, e.g. arising from the use of geothermal energy, were compensated for by savings in other areas such as exterior sun protection. Prefabricated elements also reduced construction costs.
• Monthly energy costs for heating, cooling, air conveyance, lighting, water heating and the lifts were amounted to 0,21 /m² for 2005. In comparable new office buildings these costs are between 0,80 €/m² and 1,50 /m².
• The monitoring campaign started in summer 2002. It was sponsored by the German Federal Ministry of Economics and Technology within the scope of the key research area, EnOB - “Energy-Optimised Construction”.

Regulations, guidelines, benchmarking

At 89 kWh/m² p.a., the primary energy characteristic value is below the target value of 100 kWh/m² p.a as defined in the incentive programme.