7: Space and Water heating – part 1 of 2

This area represents the major ongoing energy cost for any domestic building. As we have seen from earlier analysis, in a normal building to 1980s standard this category of energy consumption accounts of at least 75% of the energy cost. And it is here that, after the insulation improvement, the greatest changes are to be made to the existing building.

From the information we have the following definitions of heat generation…

  • AECB Silver standard – Low power gas condensing boiler
  • AECB ‘PassivHaus’ standard – Highly efficient gas boiler with solar supplement
  • AECB Gold standard – Large solar heating supplemented by Low power gas condensing boiler

Currently the heating is a wet system with a very old boiler, probably Class G. The system has been tested and works, but does provide some clues about where improvements are needed. For example, in one very small room there is a double panelled radiator that almost fills one wall. Seems a case for a significant upgrade of the insulation in this area. There is a 100 litre hot water tank with an immersion heater and a cold water supply tank in the cold side of the loft space. There is some pipe lagging, but it is neither complete nor robust.

We have two great advantages. Firstly the building’s orientation is great as the rear faces almost due south. Secondly, there is a pitched roof facing that direction with a large area of flat roof beyond that, all ideal for solar energy collection. Hence, subject to suitable calculations, it seems that we should strive towards option c above. It may turn out that other limitations make this not a feasible option, but it is well worth investing time in the research.

There are many aspects to this type of heating scheme, especially when coupled with the other improvements.  Here’s the outline.

Firstly, heating provided by solar input is inherently a low temperature heating. When normal boiler powered radiators are used the water temperature is around 60oC. \but solar generates water at about 40oC most efficiently. So an alternative heat delivery mechanism is needed to use this free warmth. The two options are wet underfloor heating or warm air.

Underfloor heating

At its simplest, wet underfloor heating comprises a long pipe laid in a zigzag fashion on an existing floor and then covered with the final flooring. For it to be effective it should be laid on a well insulated substrate and then protected from damage through the heat conducting layer that covers it. All of this adds about a 50mm layer to the existing floor so reducing door and ceiling heights.

In our case the door heights are already close to an acceptable minimum and, in the main area where we could apply this heating solution, we have a poorly insulated solid concrete floor. So, on both these counts we have rejected this solution.

Warm Air

One area where we do hope to be successful is in making the building airtight. It is not easy, as the building shape is complex, and no doubt there are many potential leaks from earlier construction. But we think it is doable. Hence the inclusion of the MVHR system to provide ventilation. This delivers a fresh air feed to all major parts of the house.

There is a separate blog about this system where you will find more details. But this system can be used to supply warmed air so long as the temperature of the air does not exceed 50oC. If the temperature is exceeded then the many bits of fluff and so on that get into the air distribution pipes will generate a ‘burning’ smell, most unpleasant. So this is an ideal heat distribution system when sourced from solar.

On to part 2 (from 4 September 2010)

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