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re: seek passive solar design faq/guide
24 may 1996
gcp  wrote:

who is this uksian gcp, anyhow? :-) will he/she unlurk, with a real name?

>william r stewart wrote, and nick pine wrote [blah blah blah...]

>just to tidy up some bits.

ok...

>> (sounds like a solar panel to me :-)
>(i wrote that!)
>>>>yep.
>>>but they are also very expensive, and normally live on the roof, which makes
>>>them fundamentally different from these inexpensive sunspaces. 
>there's inexpensive and there's cheap  :-)

and 'frugal.'

>maybe a false economy?

maybe. to me, rooftop panels make no sense at all, economically.
putting bare water heating panels in a sunspace makes more sense.
what we use for glazing is a tradeoff between aesthetics, cost, and
replacement maintenance. a matter of personal taste, when all is said.

physics is not a matter of taste: panels in a sunspace gather more heat
than rooftop panels. low-thermal-mass sunspaces (in many forms) are more
efficient than htms at heating attached houses. isolated sunspaces work
better than direct gain houses, trombe walls are the pits, performance-wise,
and heat stored in a high temp store can keep a house warm longer than
heat stored in the same thermal mass in the house itself, etc.
(repeating obvious truths to people who won't listen.)

>>> brick sunspaces have lots of thermal mass behind glass with no night
>>> insulation, as do many trombe walls and direct gain houses. this is a
>>> very inefficient way to heat a house in a partly cloudy climate, because
>>> the thermal mass stores lots of solar heat during the day, and most of that
>>> solar heat disappears through the glazing at night. 

>didn't i mention something about tim somewhere?

i don't recall that. what's a tim? or is this your friend tim?

>me again:
>>> >> if you design your house to be superinsulated, it has been shown that,

love that phrase... like "thus we can easily see..." skipping over
pages and pages of hard mathematics, or enshrouding shaky assumptions...

>>> >> even for houses orientated to minimise passive solar gain, addittional
>>> >> energy costs for space heating can be made insignificant.
>>> 
>>> absolutely true. but at what price?

>this is from a case study book published by the riba (royal institute
>of british architects) - so it's kosher!

i suspect architects, even kosher ones. altho they were the guys who
inspired us solar architects in the 1800s... have they evolved with
the same fervor as the british admiralty over the years?

>two types of house were built on a site (in milton keynes) one to
>building regulation standard the other superinsulated.  that was the
>only difference i.e. window style was normal;  indeed, orientation of
>the house was to minimise solar gain!

ok. (architects at work.) where is milton keynes?
are these cornwall houses, surrounded by palm trees and pirates? 

>the 'super' houses cost 2000 pounds more to build than standard, and i
>think there would be less difference now.  (at a guess the market
>value of the houses would be >100,000 so you see this is not a
>significant sum - and the 'super' houses sold first.)

i could see that a house like this might not cost more than its "normal"
neighbor, if all one does is stuff another layer of 1l/m^2 r3 (uk) fiberglass
in the wall, but not if it means tightening up the house to 0.1 natural
air changes per hour, vs 1 or 2. perhaps the "normal" house had 0.1 ach
already...? what sells first may be largely a matter of hype.

>space heating costs were then 10 to 20 pounds a year.

unbelievable. i'd like to know more of this story,
eg their climate and electrical consumption. 
and the window type and area... 
how big are these houses? 

are they bathing machines full of incandescent bulbs?
do people live in them in the winter?
is there a winter?

>as i said:
>>> >> with windows available now (r-10+) and orientation to make best use of
>>> >> winter sun i think it is possible to reduce space heating costs to
>>> >> zero in an otherwise normal house.
>>> i agree, if you are willing to live with very few windows.
>no.  i believe (but i have been known to be wrong  :-)

let's check this with a few numbers if possible, gcp... 
can we do a little thermal arithmetic here, or do you rely on unseen forces?

>that in the rmi (rocky mountain institute) these sort of windows
>contribute more heat than they lose -  north facing in the winter.

that sounds possible, esp in a cloudy climate with lots of diffuse
solar radiation, which comes from all over the sky, not just the south.
but what's the whole picture here?

>>> >> these houses cost little more than a normal house
>>> whoa!!!
>see above. 
i repeat. whoa!!! in rhetoric, an assertion demands no more than a
counterassertion. i've supplied some numbers, and well-known physicks
accepted by all but a few self-styled ae gurus, who shall remain nameless,
like you, and you've supplied an incomplete anecdote thus far, i ween. 

>>> >> on the latter a recent design here in the uk (scotland in particular)
>>> >> has aimed at reducing cost rather than increasing efficiency of a
>>> >> solar panel.
>>> what a strange and excellent idea :-)
>that's what i thought and as someone has already asked me, and to
>satisfy my own curiosity, i shall attempt to find out more.

good. but we still have that inescapable economics, that if all a "solar
collector" does is collect solar energy worth s pounds per square meter
per year, and the complete system cost is c pounds per square meter, with 
labour and all the bits and pieces, it will take at least c/s years (ie
forever) to pay for itself, not including maintenance, hail, hurricanes,
reroofing problems, roof penetration leaks, and the cost of electrical
power to run it. of course we do things now that never pay back, but
wouldn't it be nice if a solar heating investment paid off better than
putting money in a bank account? wouldn't that make it more interesting
for nigel average?

and solar collectors should go in warm sunspaces if possible, where they can
collect heat more efficiently or work without insulation, and their "waste
heat" can heat an attached house, vs being blown away in the wind, and where
if they never freeze, they won't need antifreeze, heat exchangers or pumps
(imho.) not that i'm trying to tell you what to do, mind you. go waste your
money on ugly expensive complex inefficient systems if you like.

>(though i am of the opinion, if it is not a retrofit, highly efficient
>nonimaging optics systems plus storage is the solution(!) for hot water.)

i like non-imaging opticks :-) i lent my laser pointer to the father thereof
at a lecture a couple of weeks ago. he brought along a cassegrainian version
(~1mx3m for the primary reflector) of what may become a standard for roofs
of large buildings, and set it up on the roof of the franklin institute in
philadelphia to let us all watch it work. but there was no sun :-( hence,
yes, storage... but you know, prof winston came very close to saying that
his optics are expensive overkill if all you want is hot water for showers,
vs. higher temperatures for process steam or tropical icemaking or libr
absorption air-conditioning. (many would say the same for thermomax.)

i like richard komp's version, a 4' x 8' panel with 2:1 cpcs that fail to
focus the sun on half the normal number of pvs, which are somehow attached
to "big fins" (i think) that are clipped to copper pipes. these things make
150 w of electricity and 1600 watts of hot water at the same time. now if
we could do similar solar co-generation with some sort of transparent
electrodeposited pvs which can produce lots of power at high temperatures
and cost $1/peak watt, and plate them on to a window or some polycarbonate
plastic, or glue them on to some big fins attached to some copper pipes
inside a sunspace, or collect their "waste heat" with an air-water heat
exchanger, as they are starting to do in appleby restaurant sunspaces,
that would be even more interesting, even without the ni optics... 

cheerio,

nick



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