Subject: Re: Recovery of Solar Heat from Attic

From: [email-masked] (Nick Pine)
Date: 5 Jan 1996 18:07:58 -0500

George Weinert <[email-masked]> wrote:
 
>A few years ago, I read about a company that was going to build heat 
>exchangers to go into your attic space to recover heat during daylight 
>hours, and bring some portion of that heat into the living space of 
>your home...

Perhaps this was Ed Palmer of Solar Attic, Inc. at 15548 95th Circle, Elk
River, MN 55330-7728, (612) 441-3440/7174 fax/email [email-masked]. Their
system may be covered by US Patent No. 5,014,770, issued May 14, 1991,
which may expire in 2008, or perhaps sooner.

>I also seem to recall having read about a study done on a home in 
>Minnesota(?) which blew hot (warm?) attic air into the house any time 
>the attic rose above 68F(?).  I seem to recall that the home had 
>significantly reduced utility bills, and that the payback time on the 
>equipment was rather short.

I seem to recall a documented 25% savings, with a conventional roof. 

>I am interested in perhaps building and installing such a system in my home,
>if it's actually cheap enough, reliable enough, and effective.

It seems to me that a system like this can be cheap, reliable and effective,
especially if your next steep-sloping south roof is made of clear thin single-
layer Dynaglas or Replex corrugated polycarbonate plastic (not fiberglas),
like mine. This material costs about $1/ft^2 and it is commonly used in
commercial greenhouse roofs, and it has a 10 year guarantee against yellowing,
and an expected mechanical lifetime of at least 25 years. Its lifetime can be
extended and the attic made cooler in summer by covering it on the outside
with a large sheet of 15 cent/ft^2, 80% greenhouse shadecloth.

>Any construction details or pointers would also be greatly appreciated.

Well, the plastic comes in standard lengths of 12' and a width slightly more
than 4', so it can be overlapped 1 corrugation for support on 4' centers. And
you want to keep warm house air out of the attic at night, to avoid heat loss
and condensation. Which to me means a passive plastic film backdraft damper
near the bottom of the supply duct, near the attic floor. The duct itself might
be a polyethylene film tube, say 24" in diameter, bought from a commercial
greenhouse supplier for about 30 cents per linear foot, with a large slow fan
at the top pushing warm air down from near the roof peak into the house. The
return duct might be a 2' x 2' piece of 1-2" foil-faced foam in the floor at
the other end of the attic, with a hinge on one edge and a $50 Grainger 4Z451
reversible 115VAC gearmotor and some sort of spool attached to the shaft to
wind up a 1/16" nylon string attached to a screw eye in a rafter, with a couple
of limit switches. You might control this with one or two cooling thermostats
in the attic and a heating thermostat in the house, in series with the fan,
eg 2 or 3 Grainger 2E158 thermostats ($14.05 each.) 

>BTW, I live in the mild climate of the SF Bay Area, so I beleive my attic
>actually does warm up significantly even on 'cold' days (mid 40's, brrr ;-)

Seems like this should work pretty well there, especially in the spring and 
fall, even with a conventional roof. Some of my Phila area neighbors tell me
their attic fans with thermostats turn on in the middle of the winter...
 
A transparent roof should be able to collect at least the heat equivalent
of about 1 gallon fo oil per year per square foot of vertical south-facing
projection of the roof glazing. 

Or maybe you'd like a small nuclear engine in your attic :-)

Good luck. 

Nick

---

From: [email-masked] (Nick Pine)
Date: 11 Jan 1996 12:42:08 -0500

Peter Swartman <[email-masked]> wrote:

>I used to install solar water heaters and have been in hundreds of attics.

OK.

>In the winter they are colder than the house and in the summer they are
>hotter.

How about in the spring and the fall?

>Unless you have some sort of heat pump, you will NOT get any heat
>out of an attic.

None? Perhaps not as much as if it were transparent, as you say later on...
You should talk with my neighbor, who tells me that he often hears his attic
fan with a cooling thermostat turn on in the winter.

>If you remove the south half of the roof and glaze it,
>that is a different story.

How about just glazing over an existing dark roof, say with some thin
polycarbonate or polyethylene plastic, with an airspace?

>As far as heat produced, the best conditions are when the temperature
>difference (outside and inside the house) is lowest.

Ah, the spring and the fall...

Nick

---

From: [email-masked] (Nick Pine)
Date: 11 Jan 1996 13:14:17 -0500

George Weinert <[email-masked]> wrote:

>Thanks for the response.

You are welcome.

>>>hours...

>After reading the patent abstract, yes--this was the company I had vaguely 
>remembered.  Unfortunately, the invention described is an air-to-liquid heat 
>exchanger, I was hoping to use an air-to-air heat exchanger.

Solar Attic sells air systems too, albeit direct, vs. with heat exhangers. 
They bought this product and its (different) patent from another company,
and it now sells for $519 as I recall, vs $1700 in tax credit times :-)
If you are concerned about dust, how about combining it with one of these:

Article: 38 of sci.engr.heat-vent-ac
From: [email-masked] (Nick Pine)
Subject: Re: Advice Needed!!!  Replacement Central Air/Ventilation
Date: 1 Jun 1995 04:54:10 -0400
Organization: Villanova University

John W. Grooms Jr. <[email-masked]> wrote:

>3. We have allergies in our family. Any opinions concerning whole house
>air cleaners or humidifiers?

One nice new electronic air filter is made by Aqua-Air Technologies,
at (410) 489-5288. The ESSA electronic filter comes in 14 standard sizes,
and slips in place of a normal air filter in a hot air heating system.
It has a retail price of about $200. It's an inch thick, and it uses
three metal screens with two filter pads between the screens. The center
screen has a potential of 7,000 VDC, and the outer two are grounded. 
The filter pads cost about a dollar, and need replacing about every two
months. The device comes with a small 110-24V transformer which plugs into
a wall socket, and the power consumption is listed as 24VAC at 1.6 VA,
i. e. less than 2 watts. 

Here is the basic filter performance:

Typical Ambient Particle                
Size distribution (in microns) per m^3       Particle Removal Rates 
                                         
                       % by    % by          Electrostatic   ESSA
Size (um.)   Count     count   weight        ($800-1200)     ($200)

10+          1,000     .005%   28%  xxx x    99%             99+%
5-10        35,000     .175%   52%    x x    95%             99+%
1-5        264,000    1.32%    17%    x x    85%             99+%
.5-1     1,352,000    6.78%     2%    xxx    60%             90+%
.01-.5  18,280,000   91.72%     1%    xxx    40%             65%

                                    |||||_ bacteria/viruses/spores
                                    ||||_ cooking/tobacco smoke
                                    |||_ household dust
                                    ||_ pollen/mold/spores
                                    |_ dander/hair

Average synthetic dust weight arrestance: 79%

Single pass efficiency: 33% @0.3 um, 75% @0.5 um, 95% @1 um, 99% @3 um

Pressure drop: 0.05" @150 lfm, 0.1" @225 lfm, 0.15" @300 lfm, 0.22" @375 lfm

ASHRAE dust holding capacity: 20 gm/ft^2

Does not produce ozone

More than one person with severe asthma has told me that these really work,
that they have had their first night of good sleep in years, after spending
one night in a bedroom with one of these devices.

The air filter product is available now, and Aqua Air will soon have a
stand-alone console model with built-in fan, prefilter and charcoal filter.
One low-cost way of using the air filter now is to buy a $15 20" box fan and
mount a 20" ESSA filter on the suction side, with duct tape...

---

>I realize that this would probably have lower efficiency

The direct air product probably has higher efficiency that either heat
exchanger version. BTW, it seems to me that it would be very easy to make
an efficient air-air heat exchanger in the attic, with two long concentric
polyethylene film tube ducts running along the ridge of the attic... See
ASHRAE's 1993 Handbook of Fundamentals, page 3-4 for how to calculate the
efficiency of something like this.

>Any more information on this (or a pointer?).  I'm interested in how they 
>implemented this.

Talk to Ed Palmer...

>...re-roofing my southern exposure with ->transparent<- (translucent?) 
>glazing does not seem inexpensive to me (even though it would increase thermal 
>collection).  It would seem that this would cost several thousands of dollars 

It's cheaper than conventional roofing in labor and materials, so if you need
a new roof...  

How about just putting a layer of greenhouse polyethylene film (5 cents.ft^2,
guaranteed for 3 years, easy to change with cheap Al extrusion clamps,
recyclable) over your existing roof, over something like 2 x 4s glued on edge
to the roof on 4' centers, to make an airspace, perhaps with some greenhouse
shadecloth underneath, to try this out? You need some sort of summer venting,
or another layer of shadecloth on top in the summer, or both... Done right,
this would prolong the life of the existing roof underneath, like seat covers
in a car, or plastic slipcovers on couches :-)

>I am also concerned about putting what might be seen as a 'funky' roof on
>my house as this might have serious consequences on the re-sale value of
>my home (I'm in California--can you tell? :-) ).

Gee, I thought Californians were immune to this easterly aesthetic scourge,
in which everyone wants their house to look like it was built 100 years ago.
But perhaps you can do something to your house that will only take a day or
two to undo, if necessary, when the time comes to sell it? 

Nick