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Re: Preheating water by running pipes through attic? - Page 4

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Posted by Steve O'Hara-Smith on August 19, 2008, 7:54 am
 
On Mon, 18 Aug 2008 13:04:54 -0400


    Hmm good point - I'm too used to slate.


    Not seen that happen in unventilated lofts but it makes sense.


    Also too used to mild winters where below freezing is rare.

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Posted by Robert Scott on August 19, 2008, 3:15 pm
 
wrote:


OK, for people in your type of climate, the reason against using the attic to
pre-heat domestic water is to limit air-conditioning costs.  The money you save
on hot water by using the attic to pre-heat it is more than cancelled out by the
extra money  you spend on AC, as compared to what you could have saved by
passively venting your attic.


Robert Scott
Ypsilanti, Michigan


Posted by Steve O'Hara-Smith on August 19, 2008, 8:16 pm
 On Tue, 19 Aug 2008 15:15:13 GMT
---@---.--- (Robert Scott) wrote:


    It might be if air conditioning were common here - which it isn't.
Round here the temperature gets below 0 C or above 25 C maybe two or three
times a year - almost a perfect climate, apart from the rain.


    What we do in these parts usually is put insulation in the loft so
as to thermally isolate it from the house. In summer it gets hot up there
and in winter it gets cold (range perhaps 5-40 C).

    It does strike me that it may well be reasonable to use the loft as
a solar collector here.

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Posted by Robert Scott on August 20, 2008, 11:46 am
 wrote:


Where is "here" exactly?

OK, so if ice dams and air conditioning costs are not an issue with you, then
look at the cost/benefit ratio.  You can't run potable water directly through an
automotive radiator, so you are probably stuck with a large number of home
heating-type fin tubes.  Without active air circulation, they are going to be
very inefficient, so you will need lots and lots of them just to erase maybe 1/4
of your domestic water heating bill.  What do you pay now for water heating?
$5 a month?  So you might save $ a month with your inside attic collector.  If
the fin tubes plus installation cost you $000, then you will just break even
after 20 years.

On the other hand, if you installed a real solar collector outside the roof, a
much smaller unit could deliver more heat, and it could deliver that heat
year-round, instead of just in the summer, as with your in-attic collector.
Most of the heat the falls on your roof gets conducted away by the wind.  What
remains has to travel through the insulating properties of the wood sheathing.
Then it has to transfer to air without the benefit of active circulation, then
it has to transfer again into your "collector".  A collector on the roof
prevents much of the wind-conducted losses and avoids two air-to-solid heat
transfers.  About the only benefit to the inside collector, as was pointed out
by earlier posters in this thread, would be to disguise the collector for
appearance sake.


Robert Scott
Ypsilanti, Michigan


Posted by Steve O'Hara-Smith on August 20, 2008, 9:45 pm
 On Wed, 20 Aug 2008 11:46:46 GMT
---@---.--- (Robert Scott) wrote:


    Western Ireland.


    Or a heat exchanger between water running through a car radiator
and potable water, perhaps a second coil in the tank.


    I was wondering about cheaply glazing the roof.


    What wood sheathing ? Roofs round here are tiles on felt on wood
frame.


    It may well not work out as feasible - but it's an interesting
possibility to explore a bit.

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C:>WIN                                      |   Directable Mirror Arrays
The computer obeys and wins.                | A better way to focus the sun
You lose and Bill collects.                 |    licences available see
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