instant hot water...

[The Natural Philosopher]

Not true. It is standard pactice to run water pipes to bathrooms through the roofspace. Ok they have to have little foam sleeves over them, BUT on an icy january day I know from my experience the first flush of water is warm, then it goes ICY cold, then it gets hot, so those pipes are definitely *not within the insulatione enevleope* - or at least not within a very good one.

Which is why I spent a fair amount of money this week on getting may favorite chippes to build boxes full of fiberglass around them.

Mostly in winter, unless teh HW pipes are fully inside the house living space. Chances are they are not.

It always makes me laugh when peopel go n about energy saving bulbs and full kettles though, which ARE inside the house, all of which contribute to burning less oil. This (home) office, with its two computers, two monitors, two people, router, telephone PABX, radio etc etc. hardly EVER needs any extra heat...OK, I have to pay more ofor the lectricity...

Likewise the upper landing equipped with three 50W LV lamps, is always warm after dark..

[The Natural Philosopher]

Yes. Weird huh?

[The Natural Philosopher]

Not whebn taps are off it doesn't.,

[The Natural Philosopher]

I don't think its obvious from the original post that he lives permanently in a commercial kitchen though.

[Andy Hall]

In all of the notes that I have read regarding good practice, the recommendation for hot water or heating pipes run outside the envelope is to use pipe insulation with a thickness of at least the pipe diameter. One could easily work out from the temperature of the pipe, the surround and the U value, what the loss will be, but I suspect that it's negligible if the thickness of insulation is adequate.

That depends on the arrangement of the plumbing.

I agree with you there.

.andy

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[The Natural Philosopher]

Let me inform you, that the heatloss- at least to the water in question

- is NOT negligible, even with such isulation, because I have such, and the hot water runs bloody cold in winter. Until the pipe gets warm and the cold water is run out. You can put yoir hand on the insulation and feel the heat.

It will almost certainly stop them from freezing, but it won't keep them warm overnight.

[Andy Hall]

With the water stationary in the pipe, over a period of time of course it will cool. That wasn't really my point, though, it was more the energy loss.

Let's look at an example.

I'll take 19mm Armaflex insulation and 22mm tube which is a typical combination used domestically.

The heat transmission through a piece of material is given by

Q = (K x A x dT)/d

where K is the coefficient of thermal conductivity in W/m.K A is the area dT is the temperature difference.

If we take a 1m length of copper tube, its area is given by

pi x 0.022

Armaflex has a K value of 0.039

I'll assume that the water temperature is 60 degrees and the ambient temperature is 10 (a reasonable average over a year).

If you do the sums this works out to 7.1W per metre run of pipe.

In the context of the energy used to heat the water or the house, and your earlier comments about heat from IT equipment (I have that issue as well) this is not a significant amount.

.andy

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[IMM]

Tripe!

By burning more coal. Electricity is the dirtiest of fuels, and the least efficient from power station to point of burn.

[IMM]

He desires "natral constant flowing of hot water". A combi will give it.

[IMM]

Then a hot waterfall does that.

[The Natural Philosopher]

Well...If I take the runs around here...Ive got about 60m of central heating pipe, and probably about half that on hot water running through the loft space.. Say 90m in all to be conservative. So the average loss is 630W when all that is circulating. Heat loss to OUTSIDE the insulation envelope. About what the Aga kicks out to heat the whole kitchen, and, if averaged over a year, probably about 300 quid?

The point about electrical heat is that it is inside the insulation envelope, so, although expensive, it does heat the house.

The HW and CH stuff running in a cold roof is money thrown away.

If your figures are accurate, it is very instructive to see ho wthe practice of running CH pipes in a cold roof can lose a lot of heat, even when insulated to 'standards' and that additional boxing in and insulation is no bad thing.

Going back to the original point, it would seem that running HW continuosuly circulation could not only watse in a large house a couple of hundrd watts of heat AT LEAST , but also of course the pump is continously drawing what - 50W? to circulate it. Plus teh extra are of how water pipe and its capital cost...? So I have to say that as far as I am concerned the heat loss and installation costs outweigh the water savings. My major water usage is probably in loos and baths anyway, an baths always need cold water added.

[The Natural Philosopher]

No, its true. It is the area where distributoin of services is easiest.

That is true tho. Electricity is the stupidest way to make heat. Power stations run at 60% thermal efficiency at best, and the distribution network knocks that down to maybe 50% overall.

However there are very few COAL powered stations left in the UK. Most are natural gas or oil IIRC.

And it is a LOT easier to clean up a power station flue than e.g. a car exhaust, or a domestic burner.

[The Natural Philosopher]

Not without auxiliary circulation. No system will that has a length of pipe that can cool, between th e heat source and teh tap.

[Andy Hall]

On a cost/benefit basis, I'd agree with you.

.andy

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[Andrew Gabriel]

That's quite unrealistic -- 35% is more typical.

[IMM]

It depends on how good the insulation is. The heavier the better. Also having a boiler on a gable end wall with associated cylinder cam be boxed in with cheap ply or MDF to make a large insulated cupboard. Not a real problem, when you consider the space it saves in the house below and the noise reduction too.

[IMM]

It is not, and be told!!

Les than 40% in many cases, and some lower than that.

Domestic burner? It is cleaner to burn natural gas at point of use. far cleaner overall.

[The Natural Philosopher]

No, its not. Look it up.

Eevn fairly old stations are running well up towards 50%.

Car engines are able to get better than 30% these days, and some diesels up over 40%.

[The Natural Philosopher]

If its in insulation it isn't in a cold roof dummy!

[The Natural Philosopher]

No, its not. Power stations have scrubbers that remove sulphur from the flue gases. They alsio can be run under very well controlled regimes, maximising het output, and are properly maintained.

The only problem is that something like 40% of teh heat goes either up the coolling towers, or heating teh local sea.lake/river up in the case of those that use local water to run teh condensors. Great for fishfarming, but it would have been better to use it to run underfloor heating - JUST the right temp usually.

The overall best energuy efficieciency sets are combined cyle sets - often gas turbines - supplying local electriity, feeding teh grid, and supplying local hot water. sadly it needs something the size of a hospital to justify instaling one.