April 23, 2018
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Passive solar heat systems can work well

By Tom Gocze, BDN Staff

Sunny days are certainly welcome this time of year. They make me think about how to keep warm using the sun. Many homes do well on sunny days during winter without any additional heat while the sun shines.

The trouble starts when the sun sets or it is cloudy outside. Houses get cold.

Wouldn’t it be nice to be able to store solar heat for these times? We have done this for years with solar collectors and water storage tanks. These are called active systems, since they actively collect heat and store it.

I like to think about passive systems. Passive systems use no moving parts to get things done. They are simple and can work well if a little consideration is given to design.

Back in the 1970s and ’80s there was a big push for passive solar heating. Many people put a lot of windows on the south side of the house to gather as much solar energy as possible. What happens is that if you overglaze the south side, the house gets really hot on sunny days. And everything inside the house will fade from the sunlight.

And if it is cloudy, you freeze. And you freeze at night.

In addition, many people touted their passive solar home as the best thing ever and claimed not to use any fuel. Unfortunately, they did not consider four or five cords of wood as fuel.

That is not really 100 percent solar-heated. Well, it is, sort of, but there are more elegant ways to get there.

One concept that I would like to try sometime is to build a really massive house, inside a highly insulated shell. There would be some south-facing glass, but not too much since we need to balance the nighttime losses against the solar gain. The usual acceptable amount of south-facing glass is 6 percent of the floor space. More than that and overheating and nighttime chilling become an issue. A massive solar house might get away with a little more glazing.

A cement block or concrete house (I really meant massive!) with R-60 foam outside would be an interesting way to accomplish this.

There are other schemes to accomplish a massive structure. We could build a log home with those nicely machined logs that interlock. Then, commit an aesthetic crime and cover the exterior with the heavy insulation. Logs offer us a very nice thermal mass to help carry all that solar gain. Unfortunately, as they are usually used, there is not a very high insulation factor here. I believe there are some companies that are offering this as a packaged system.

Another way to get a massive house is a concept that was first offered by a Maine architect, J.B. “Tommy” Thomas of Somesville. He suggested using a double layer of drywall throughout the house. This spreads a lot of mass throughout the house and stores that passive gain quite nicely.

One great thing about a massive building is that it is slow to heat up and slow to cool down. A simple wood or gas stove is a great backup for a passive home. The mass could store up the heat and slowly discharge it after the fire goes out. One might also consider using off-peak electricity, which is usually available at a discounted rate during nighttime hours as the backup system.

Designing such systems is a fun project that does require some preparation and homework. The good news is that this is simple math which anyone can do. It is a fun wintertime project, depending on your view of entertainment.

The idea of solar heating is not rocket science and not ridiculously expensive to implement. It does require a little work and is easy to integrate into a new home. The problem is that improvements usually might require another house to be built to prove any changes!

But that is half the fun!

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 bangornews.com/thehomepage.html.

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