Rising energy costs and increasing environmental straining, combined with more demands for comfort at home, require efficient control and heat metering for the benefit of the individual consumer, which avoids waste of energy. Halldor Kristjansson reports.
Maximum individualisation of the heat supply is becoming more feasible than ever. As for blocks of flats, this will cause the installation of thermostatic radiator valves and a heat station for each flat - known as the Flat Station.
The heat supplied to a block of flats should match the real heat demand of the individual consumers, and any difference makes up an energy-saving potential. The energy-savings can be obtained by means of local control equipment (temperature and balancing controls). Otherwise, overconsumption will take place for the following reasons: the flows in block pipes can not be balanced; the heat generation or the supply temperature may not be stable; the insulation effect differ from preconditions; the wind one day is from the south and the next day from the north; the heat balance is influenced by electrical installations and humans; the residents differ in their preferences about hot tap water (HTW) temperature and indoor temperature, etc.
For instance, elderly people and parents to babies may choose higher indoor temperatures, whereas lower temperatures are preferred in bedrooms.
The optimal design involves thermostatic valves on all radiators and a substation with a heat meter for every flat, the so-called Flat Stations. The flat station is indeed 'flat'; it has thin box geometry, so it can be fitted nicely into an internal wall. The Flat Station allows each family to optimise the indoor comfort and hot tap water preparation with the heat cost from time to time, providing maximum energy-savings.
According to measurements of a few groups of houses in Denmark between 1991 and 2005, individual billing resulted in savings of 15-30 per cent. Savings of 15 per cent, out of an energy cost of EUR1000 per year, would generate EUR1500 for the consumer over the next 10 years, provided that energy prices are fixed.
The Flat Station System is compared with a version of a riser pipe system. The block distribution system is heated in the basement using oil boiler, gas boiler, or district heating which has the best potential of long-term sustainability and will probably be the future scenario for most block buildings.
As for the riser pipe system, the basement is filled with hot tap water and room heating pipes connected to several riser pipe pairs drilled up through the floor and ceilings of flats. The HTW system heat losses are bigger than the net heat for preparing the HTW, as the HTW and circulation pipes are kept hot all the time. Also risk of hygienic problems is increased. Only one third of the HTW and circulation pipe heat losses is utilised for room heating, the rest are final losses.
As for the flat station system, the basement only includes the primary heat distribution pipe pair, connecting the staircases and the boiler or the district heating substation. All HTW and room heating pipes are placed inside the flats, usually behind nice-looking skirting boards. The HTW pipes are mostly idle, and most families would not utilise a circulation pipe. Even if the total length of pipes may be slightly larger than the riser pipe system, the heat losses are lower due to shorter operation times of the different parts of the system. And as for investment, it is more convenient to lay horizontal pipes inside flats than to drill riser pipes through concrete floors.
The flat station piping makes it possible to make individual adjustments of the room heating season. A resident on the top floor would typically prefer the longest heating season, which he can decide by himself in case of flat station system. But with riser pipe systems, this would keep the risers hot for an extra 500 hours, or alternatively, the top floor resident would feel cold. This is an example of how energy-savings are related to both individualisation of controls and comfort level.
And comfort level is indeed an important factor involved with energy consumption. Economic growth results in increased demands of comfort, which especially in case of non-controlled systems leads to a rapidly increasing heat consumption. The future saving potential of local automatic controls is therefore often underestimated. Together with increasing energy prices, this makes investment in local automatic controls far more feasible than at first sight. Examples of increasing comfort demands are higher indoor temperatures, elongated heating seasons, more air ventilation, and a stable suitable hot tap water temperature.
So, evaluation of the energy-saving potential of local automatic controls only becomes credible when also considering the comfort level. Energy-saving data have to be cleaned for differences in comfort level. If the comfort level were not considered, the most efficient energy-savings would be obtained by simply turning off the heat! No controls needed! But as far as the future brings increasing demands for comfort as well as energy-savings, a maximum individualisation of controls is the most relevant issue.
Flat Stations are well maintained, as their condition influence the individual consumer's bill directly. On the contrary, experience shows that jointly owned substations hidden in cellars are poorly maintained, causing unnecessary losses. In energy crises, the flat station design makes it possible for the authorities to obtain the necessary energy-savings by raising the energy price. This will especially be relevant for many European countries in the near future, as they increasingly rely on imported primary energy.
In the future, both energy prices and comfort demand will rise. The Flat Station System is an important opportunity for energy saving activities.
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Halldor Kristjansson, Application Consultant, Danfoss A/S - District Heating, Nordborg, Denmark,
www.heating.danfoss.com.