P_ 18
PULSE HEAT - DISTRICT HEATING FOR LOW ENERGY BUILDINGS
Text originally published in “Fjernvarmen” by Gunnar Boye Olsen, Energiselskabet ved Andelssamfundet I Hjortshøj. Translated and adapted by Kathrine Windahl, DBDH
- Better insulated pipes.
A project supported by the Danish District Heating R & D Account shows that heat loss in low-energy buildings can be reduced by using pulse heat in combination with solar. The technique is not yet fully developed, but the preliminary results from tests in 18 houses close to the Danish city Aarhus are positive. With the shrinking heat loss in new Danish buildings the proportion of heat lost in district heating pipes gets bigger compared with the consumption. The low heat consumption will also mean that a larger proportion of the water flow in the district heating supply is circulated in order to ensure an adequate supply temperature. Nonetheless, there is still good reason to establish district heating supply to new residences in dense urban areas and dense low-rise buildings. There will still be a considerable heat consumption compared to the building area - a consumption which in many ways is better supplied with district heating than with for example heat pumps which cause heavy loads on the power grid in the cold periods and which have global environmental problems. The heat loss in the district heating supply for low-energy houses can be reduced by better district heating technique. There is a number of options:
- Thinner pipes, which due to small diameter have lower heat loss and which have enough capacity for houses with low consumption. Thin tubes, however, may cause capacity problems, if heat exchangers are used for hot water. The solution will therefore require a hot water tank or a very large driving thrust. One variant is that only forward flow is thinner. - Local summer supply, e.g. local solar in individual buildings, as well as a halt for district heating 3-5 months of the year, when solar takes care of the supply. This saves typically 25- 30% of heat loss. - "Pulsating district heating", where the district heating is delivered in 1-2 day pulses, which means that much of the pipe loss in the intervals between pulses is saved. In the ecological building the housing cooperative "Andelssamfundet i Hjortshøj "in the northern part of the Danish city Aarhus, the combination solar and district heating has been tested since 1998, and since 2008 two new housing groups (group 7 and 8) have tested a combination of pulsating district heating (pulse heat) and solar. The testing of the heat pulse combination with solar is supported by the Danish District Heating R & D Account.
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