What heating to install?

[Doctor Drivel]

Backboiler? Forget it.

[Mark]

Why? I had a central heating system operating off a backboiler once. It's not ideal, but it did work.

Mark

[Doctor Drivel]

So you should know better then.

[hightower]

I see there's a lively group of regulars then :)) I'm definitely going to go for broke on the insulation end of things, as ultimately this reduces our need for heating and therefore reduces our burn of whatever fuel we choose for the CH and DHW. Is the general consensus that the green sources we COULD feasibly use in our small plot - solar (for water heating) and GSHP (with bore hole :( ) may not be worth it?

The idea of solar hot water is appealing, especially given that Cornwall gets a lot of sunlight, but our need for hot water isn't massive. Even if we could integrate this with some form of thermal store which feeds radiators (is this possible?), so that it gives at least a bit of a kick start to the process of getting water up to temperature for CH, is it really that practical? I'm prepared to spend whatever I need to, and if this means a big installation bill and tiny annual costs or a small installation cost and regular annual outlay then so be it. As far as I can see, none of the alternative sources make a very good primary source of heat for both DHW AND CH so maybe a variety of different approaches would be best?

It does seem almost a crime not to use the 'free' solar input.....

Cheers again for the entertaining and educational responses.

Rich

[The Natural Philosopher]

I think so if you DIY it.

As I said, feeding the DHW and CH water through a bunch of black painted copper pipes under glass on the roof will give you at fair amount of heat input - even on cold (but clear) winter days..

In summer it probably is enough to heat a tankful to 60C..

Solar is great at providing medium amounts of low grade heat - not bad for things like underfloor heating etc, except that is needed at night, and the sun shines in the day..so you have to store that heat, which is not that easy.

Heat pumps are also very efficient if you don't mind freezing the garden. In cornwall that may be a good bet, as the winter temps are not low.

Another thing if you can bear the hassle is solid fuel or woodburning stoves..if you have an acre or two of scrub and woodland to carve up with a chainsaw...you can be almost self sufficient with that. But carrying wood, cutting it, and ash disposal makes it fairly labour intensive. You CAN run a back boiler off it too. Needs a separate pump and primary circuit to integrate with a conventional boiler though. Gravity feed is sort of OK ish, but its not very efficient. And you need big pipes.

I don't think solar electric is cost effective, but windpower might be - in cornwall anyway. If you don;t mind windmills and the like.

If starting from scratch I would probably put in a decent underfloor heating circuit (that might cope well with low grade solar heat)and a combi to start with after insulating to the hilt, and then look at ways of reducing the oil used in the combi by other means as later add-ons.

Big windows on south facing walls do that anyway.. IF you can combine with LOTS of masonry or concrete, you get a good solar input in winter, and a house that stays cool through the heat of the summer day and warm throughout the winter night.

There is nothing more depressing than a cardboard box of a house that needs heat in the evening, and windows open all day to cool it..

If, like us, you actually live in the house 24 hours a day, go for a well insulated house with a LOT of thermal mass in it.

Our NW facing kitchen is cool in the summer due to the massive chimney and concrete floors, and toasty in winter when we light the Aga.. ..the living room is South East facing and gets loads of sunlight, and the massive open fires keep the brickwork in the chimneys warm long after the fire has gone out. and the double insulated curtains keep the heat IN once the sun goes down..

[Dave Liquorice]

A properly sized system (collector area v heat output) shouldn't freeze the ground. I believe that most of the heat isn't coming from above but from below. In this country soil temperature varies very little summer to winter at 1m to 2m depth where a GSHP coil is buried. Though I guess once you start to pump the heat out you create a temperature gradient and it will be steeper on the surface side.

Agreed, and the energy costs in producing the PV cells aren't small.

Wind is very intermittent, the generally accepted level of output from a wind turbine ove a year is 1/4 to 1/3 of it's rated output. There are quite a few small turbines around here and 50% of the time I pass them they are stationary...

If you have a handy stream and a bit of fall hydro may be worth a look. I believe there are small systems (ie of the few kW range) available "off the shelf" in Canada. 24/7 availabilty assuming the stream doesn't dry up. We only have the fall, no stream, at least not without creating a reserv... er "garden pond" and storing the available water of which there is rarely a shortage.

Agreed, thermal mass is wonderful, provided you never let it cool down. The three days it takes this place to warm back up again are uncomfortable.

[The Natural Philosopher]

Oh, mine is about 3 hours.,..

[David Hansen]

On 29 Jun 2006 11:16:41 -0700 someone who may be "hightower" wrote this:-

Worth it in what terms?

In financial terms, assuming current fuel prices, these things are long term investments. The same is true of double glazing.

However, as with double glazing, that is not the only criteria to assess things.

Yes.

While thermal stores are best matched to underfloor heating, some can produce outputs suitable for feeding radiators.

Consider mains electricity. Would you want all of this to come from one source?

[Dave Liquorice]

Can't have all that much thermal mass then. B-)

The air gets warm in a couple of hours but several tonnes(*) of cold stone right through the middle of the house sucking the heat out is very noticeable.

(*) How much would a rubble built but solid stone wall 18" thick, 18' high and 25' long weigh? 675 cu feet, 25 cu yards. Is that as near as damn it 25 tonne?

[The Natural Philosopher]

About 50 tonnes.

It may be instructive to work it out actually..

I came up with a specific heat of 0.84 Kilojoules per degree C per kg..

So 50 tonnes is 50 Megajoules input for every degree C rise.. so using wonderful online converters about 13KWh for every degree C rise..

So to raise it ten degrees with a 10KW boiler takes about 13 hours..

That why you need the insulation outside of it..in winter the house here is extremely stable temperature wise around the masonry..and its the floor that GETS heated, and the chimneys too..by fires..so the air doesn't get warm till the masonry is.

The first time I switched the UFH on before the controls had been hooked up, I left it on overnight..from a dank 3 degrees winter day, the next morning it was too hot to be comfortable..with a 12KW boiler..I've got about 30 tonnes of concrete flooring to heat, roughly. 100 sq meters

150mm thick..15 cu meters...35 tonnes appx..yep. Its about right.

I think that really shows that if you have a poured/screeded insulated concrete floor, there is a huge mass to be heated up, and that in general use that mass is going to have a very moderating influence on temperature..and you also have very little to gain by switching heating off during the day..its simply not going to lose that much heat anyway.

I would say that in summer the average deviation from the diurnal mean is only about +-2degrees C from late afternoon to sunrise..with the sorts of temperature around now being 10C by night and 30C by day, thats

20C +- 2 degrees with no heating, but of course there is a fair amount of heat in the form of people and electrical equipment, so in practice its a bit higher than that..probably 4-5 degrees.