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Re: Recovery of Solar Heat from Attic



George Weinert <gweinert@llnl.gov> wrote:

>Thanks for the response.

You are welcome.

>>>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...

>>Perhaps this was Ed Palmer of Solar Attic, Inc. at 15548 95th Circle, Elk
>>River, MN 55330-7728, (612) 441-3440/7174 fax/email SolarAttic@aol.com. Their
>>system may be covered by US Patent No. 5,014,770, issued May 14, 1991,
>>which may expire in 2008, or perhaps sooner.
>
>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: nick@vu-vlsi.ee.vill.edu (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. <jgrooms@mindspring.com> 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.

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


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