Friday, 26 September 2008

Solar Air Heating in the season of mists and mellow fruitfulness

We’ve considered installing a solar-thermal hot water heating system at home - the rear roof of our house faces south-west which would be ideal. But we’ve been put-off by the capital cost and disruption, and also by the realisation that hot-water-heating is only a relatively small part of our total energy bill – which is dominated, in winter at least, by space-heating.

Because we have small children, our house is usually occupied even during the daytime, so in the Winter we have to set our “programmer” (timer) so that our central-heating is “on” for most of the day. In Summer we can of course turn our central-heating off completely. But Spring and Autumn are interesting seasons, because the outside air temperature varies unpredictably from balmy to freezing (so sometimes the heating is needed and sometimes not), and yet it is often sunny.

On the rear of our house we have a conservatory, which gets very warm when the sun shines. My wife realised that throwing-open the doors between the house and the conservatory on warm days provides a very effective way to air-heat the house – with no capital outlay. 

AlertMe makes this effect very visible, and shows us how to optimise it. The chart below shows a week earlier this month. All the inside rooms are averaged-together, and on 4 of the 7 days there is a significant proportion of the day when the conservatory is considerably hotter than the house. 


If we zoom-in and display the "typical day" from this data, we see that for about 6 hours of the day our conservatory can on average provide useful heating of our home, and we should open the doors at 11am and close them at 5pm.