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Contenu archivé le 2022-12-27

HEAT PUMP WITH FLAT PLATE COLLECTORS FOR HEATING A BUILDING IN PARALLEL WITH CONVENTIONAL OIL BOILERS

Objectif

The new CEGEDEL office block, designed to accommodate 170 people, is in Strassen on the outskirts of Luxembourg City. Most of the heating is provided by a set of heat pumps backed up during very cold periods by boilers which run on heating oil. The original aspect of this installation is a heat pump operating on water and water mixed with glycol with "energy stacks" installed on the roof. The aim is to achieve a fuel-oil substitution level of over 90%, which is possible even at very low temperatures because of the mode of operation of the heat pump. Instead of frost limiting the effectiveness of the energy stacks, this system of combining a heat pump with energy stacks even uses the frost to advantage and, what is more, is able to collect the latent heat contained in atmospheric humidity and rainwater.
Experience gained in 8 years of operation (from 15 March 1984 to 15 March 1992) has shown that the heat pump was overdimensioned. Between 340.000 and 440.000 thermal kWh are transitted per heating period to the heating system, compared with an estiomated 700,000 thermal kWh. The difference between the estimate and actual practice is due to the considerable internal supplies, i.e:
- heat generated by 130 people;
- heat generated by office machines, etc; and
- a total 60 kW generated by the lighting system.
In addition, a significant proportion of requirements (45% and 54% during the last 5 heating periods)) is covered by the system installed to recover waste heat from computer-room air-conditioning-equipment.
Because of this overdimensioning, the payback period originally estimated at 10 years will now be longer. Nevertheless, from the technological point of view the project is a success.
CONCLUSION AND PROSPECTS
The object, i.e. to achieve a maximum amount of fuel-oil substitution, has been achieved thanks to the heat pump "energy stacks" and the waste heat recovered from the computer room. Depending on how cold the winter is, energy recovery on its own can cover over 50% of the building's energy requirements. This considerable contribution was not taken into consideration when the dimensions of the heat pump were decided.
From the results of the project it would seem that:
- medium-sized administrative buildings,
- hotels,
- schools and,
- swimming pools,
are particularly suitable for heating by means of heat pumps powered by energy stacks.
It has been estimated that the heat pump will supply an amount of energy equivalent to 72 tonnes of oil per year. On the basis of economic assumptions valid at the time the system was designed, and those on profitability, it was calculated that the payback period on the capital invested would be a little over 10 years.
The 1985/86 and 1991/92 heating periods corroborated the above results. An adjustment to the controlinstructions even resulted a substantial increase in the contribution to the energy balance of the energy recovery unit of the computer room air conditioning system. This share increased from 11000 litres of oil equivalent during the 1984/85 heating period to 25000 litres of oil equivalent during the 1991/92 period.
Despite this technical success the energy savings achieved have diminished as a result of the price of fuel oil and currently stand at less than Lfrs 150000 per annum.
The heating installation includes the following parts:
ENERGY PRODUCERS:
- a four-stage (four-compressor) heat pump operating on water and a water and glycol mixture, with a rated power of 80 kW connected to 30 energy stacks;
- a heat exchanger to recover energy from the air conditioners in the computer room; the maximum heat output of this heat exchanger is some 35 kW;
- one air-water heat pump for recovering energy from the spent air in the ablutions block (thermal output some 8 kW);
- one air-water heat pump for recovering energy from the area where the inverters have been installed (rated heat output: some 10 kW);
- three boilers operating on heating oil, each with a nominal rating of 120 kW and fitted with two burners.
6 000 LITRE BUFFER TANK :
- regulating device;
- storage tank.
PROGRAMMABLE "VISOGYR" ELECTRONIC REGULATION :
- on/off trip switches for the various energy producers;
- temperature regulators for the various energy-consuming units;
- data-processing equipment for the data to be transmitted to a microcomputer.
DEC 350 PROFESSIONAL MICROCOMPUTER :
- for storing data transmitted by the regulating devices;
- for data processing: diagrams, energy balances, financial balances, etc.
HOW THE INSTALLATION WORKS :
The electronic regulation is so programmed as to ensure that the energy recovered from the computer room is always transferred to the 6 000 litre buffer store regardless of the outside temperature or the heating requirements in the building. This extra energy is therefore always available to meet any heating needs that may arise. When the energy recovered from the computer room is no longer sufficient to meet the building's heating requirements, the regulatory system switches on the other energy producers, namely:
- the small heat pumps which recover waste heat (from the area where the inverters are installed and from the ablutions block);
- the heat pump "energy stack"; and,
- the heating oil fired boilers (1, 2 or 3).
The three heat recovery systems, i.e:
- the system for recovering heat from the computer room;
- the heat pump in the ablutions block, and
- the heat pump in the area where the inverters are installed are sufficient to meet all heating requirements until the outside temperature falls to + 12 deg. C. Thereafter the four stages of the heat pump powered by the energy stacks cover heating requirements down to an outside temperature of around - 6 deg. C. Only when the temperature falls below - 6 deg. C do the regulatory systems trip the boilers. Between - 6 deg. C and around - 10 deg. C the various stages of the heat pump are successively switched on in order to adjust the heat pump rating to the heat available from the energy stacks backed up by the boilers. When the outside temperature falls below - 10 deg. C the last stage of the energy stack heat pump is switched on and from then on the building is heated exclusively by the boilers and the heat-recovery systems.

Appel à propositions

Data not available

Régime de financement

DEM - Demonstration contracts

Coordinateur

COMPAGNIE GRAND-DUCALE D'ELECTRICITE SA (CEGEDEL
Contribution de l’UE
Aucune donnée
Adresse
RUE THOMAS EDISON
2089 LUXEMBURG
Luxembourg

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Coût total
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