Solar space heating easy to achieve

Posted Aug. 21, 2008, at 6:33 p.m.
Last modified Jan. 29, 2011, at 12:47 p.m.

Before we start, let me correct an error I made in my column two weeks ago. I completely made up the Web address for Solar Rating and Certification Corp., or SRCC, from some nether part of my brain. The correct Web address is http://www.solar-rating.org/.

I am sorry for any confusion.

Now, let’s look at solar space heating.

There are two ways to use active solar space heating: hot air and hot water.

A hot-water space heating system uses the same collectors as a domestic hot-water heating system; you just use more collectors and a larger storage tank.

Solar hot-air systems are a simpler, but in some ways, a more confusing issue.

The technology is very simple. We have an insulated, thin box with a big window on the sun side to allow sunlight to enter. Inside the box, we have a thin metal absorber that we flow air over. The air cools the absorber and the heated air is shunted into the house. What could be simpler?

The solar air collector, if properly installed, acts like a one-way window that lets heat into the house but will not allow heat to be lost at night. That is a nice feature if you have space for it. And you like the looks of solar air collectors on the south side of your home.

So, where is the confusing part? It is in the marketing of the solar air collectors. If you think back to the construction I just described, you see how simple it is. If you get online (no e-mail addresses from me this time!) just Google solar air collectors.

When you go to purchase a pre-built air collector, they all are stupidly expensive. If anyone with some simple do-it-yourself skills wanted to build one, it would be hard to make it cost more than $10 a square foot.

Considering oil costs $5 a gallon and a solar collector generates 1 to 2 gallons of oil energy a year per square foot, this is a pretty incredible deal.

I hate to beat a dead horse (or high oil bill), but a highly insulated house can really become that highly solar-heated home we all yearn for. A superinsulated house that is at least R-40 can easily attain a solar heating fraction of 50 percent or more with a modestly sized system.

To achieve this, we need to store solar heat. A hot-water system can do this with a properly sized water storage tank. A hot-air heating system must achieve heat storage by adding thermal mass in the house. This can be achieved with wood beams, masonry or other similar material.

The more mass we can integrate into the living space, the more heat we can store in the building. This axiom holds true for passive solar-heated buildings, too. As we store heat in the building, a temperature drop in the building will discharge a fair bit of stored heat.

It must, however, be highly insulated or the mass is not very effective.

This heating thing, whether it is solar, wood or nuclear fission, is all a numbers game.

And it is simple arithmetic, not rocket science.

Questions for Tom Gocze should be mailed to The Home Page, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329. A library of reference material and a home-project blog are at bangordailynews.com/thehomepage.

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