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Asking for design suggestions

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Posted by Jeff on February 19, 2009, 2:29 am
 
I'm looking for advice on alternate plans to add solar heat.  I'm in
Albuquerque with very good sun but freezing winter nights.  I would like to
heat the two bedrooms on the north side of my house that get little or no
benefit from the solar gain the back (south) of the house gets.

PLAN 1:  Use a roof-mounted collector to heat a water/glycol mix (because I
would plumb the heating circuit through the attic) and retrofit those two
rooms with radiant floor heat.  The house is on a slab and it looks as if
it's possible to lay radiant tubing on top of the slab, install flooring
(wood, laminate) over it, and not have to pour new concrete.  Initially I'd
use a solar-powered pump so the fluid would circulate only when there was
sun.

Cons:
- Since I think floor heat is uses water that's around 80 degrees, there may
be too much heat and no way to control it.
- No provision for nighttime heat, although perhaps the slab will radiate
for some time after sunset.
- No provision for turning the system off for the summer.  I thought I'd
drain it.
- Floor heat retrofit is somewhat expensive and complex.

Pros:
- Lower temperature requirement of the floor radiant system means it would
provide heat sooner and longer.
- Water/glycol solar fluid wouldn't freeze in the attic.
- Shorter, relatively simple plumbing to the two rooms.
- If the fluid is too hot coming directly from the roof it could be used to
preheat domestic hot water and/or to heat a storage tank, then be routed to
the floors.

PLAN 2:  Essentially the same as #1 but instead of the floor heat I would
install baseboard heaters or radiator panels.  I think both require a hotter
fluid, around 120-140 degrees.  I would still use a water/glycol mix and
bring the heated fluid to those two rooms through the attic.

Cons:
- Not enough heat for a long enough part of the day to be effective.
- No excess heat for DHW or storage in addition to the radiator heat used by
the two rooms.
- Radiators are fairly expensive, I'm not sure about radiant baseboard
units.

Pros:
- Simplest plumbing.
- No requirement for a new flooring system.

PLAN 3: Use an air collector and a solar powered blower system, if a blower
is necessary.  If I did that perhaps I could route the air into the house
heating duct system and heat the whole house.  That would require a damper
system to close off the collector(s) from the main ducts at night and in
cloudy weather.

Cons:
- Little or no nighttime heat.
- No heat storage for cloudy weather.

Pros:
- Most likely the easiest installation.

Eventually I would expand any system by adding storage to get through nights
and cloudy days, as well as to preheat domestic hot water.  It may be more
economically justified to deal with the DHW first, although I'm looking more
for comfort than return on investment.

I hope you can provide some guidance.  Thanks.  - Jeff



Posted by Morris Dovey on February 19, 2009, 10:49 am
 
Jeff wrote:


I don't have enough first-hand experience to address PLAN1 or PLAN2, but
can offer you a look at a PLAN3 approach applied to a 30'x40' steel
building with 10' ceiling height at

    <http://www.iedu.com/DeSoto/solar.html>  (commercial site!)

If you click on the photo, you can see other photos of construction
detail. I built the panels, but did not do the installation and do not
own the building.

I've visited several times in winter, and every time I've visited the
temperature has been above 70F - and the owner told me that when he goes
to get his pick-up truck out in the morning, the temperature has
generally been warmer than 65F - but note that he only opens the
overhead door twice a day.

Of course, this is in sunny tropical Iowa where nighttime temperatures
don't normally fall much below 10F.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/

Posted by Jeff on February 19, 2009, 9:41 pm
 Morris:

I looked at your site and found it interesting.  Of course the vertical
installation makes sense.

My first thought was that since my house isn't essentially one big room as I
think the metal building is, my south rooms would be warm but not
necessarily the north rooms.  Or the south side would be much warmer and
they're not the problem.

What do you think about ducting the collector output 25 or 30 feet?  I ask
because mounting vertically would put my collector(s) on the south wall and
of course that's across the house from the rooms I want to heat.  I'd guess
the input air could still come from the southside rooms and that may set up
a thermally created air flow that may reduce or eliminate the need for a
blower.

How thick are your type 3 panels?  Have you ever mounted them externally
rather than as a part of the wall structure?  What are the baffles made of?

-Jeff

Only twice a day, huh?

Morris Dovey wrote:
:
: I don't have enough first-hand experience to address PLAN1 or PLAN2, but
: can offer you a look at a PLAN3 approach applied to a 30'x40' steel
: building with 10' ceiling height at
:
:    <http://www.iedu.com/DeSoto/solar.html>  (commercial site!)
:
: If you click on the photo, you can see other photos of construction
: detail. I built the panels, but did not do the installation and do not
: own the building.
:
: I've visited several times in winter, and every time I've visited the
: temperature has been above 70F - and the owner told me that when he goes
: to get his pick-up truck out in the morning, the temperature has
: generally been warmer than 65F - but note that he only opens the
: overhead door twice a day.
:
: Of course, this is in sunny tropical Iowa where nighttime temperatures
: don't normally fall much below 10F.
:
: --
: Morris Dovey
: DeSoto Solar
: DeSoto, Iowa USA
: http://www.iedu.com/DeSoto/



Posted by Morris Dovey on February 19, 2009, 10:10 pm
 Jeff wrote:

You're perfectly correct - OTOH, north-facing panels don't work very
well. :)


You might be able to do that if you have a clear run for the ducting.
I'd be inclined to draw warm air from the ceiling of the south room(s)
and blow that (down) into the north room(s).


They're about 7-3/4" thick. I have mounted them externally (but not on a
house!), but that creates more problems than it solves. Notice the width
of the discharge openings - even with external mounting you'd need a
header, jack studs, etc to support the wall and roof above the panel.

I'm not sure what you're referring to as baffles - the dividers parallel
to the glazing are plywood, the slats in the absorber are aluminum.


The customer is a farmer with a fairly set daily routine. He begins and
ends his day with a drive out to check a small beef herd. He /likes/
being able to climb into a warm truck in the morning. :)

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/

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