Future Sunroom

I have already posted this article once before. I am reposting it because it will be one of the key house heating systems in future and want this information to also be within the context of my description of the home's complete space heating system.

I plan to build a sunroom that will cover the entire south wall surface of the house. This sunroom will have a number of important functions. The primary ones being solar heat capture and added insulaiton. The sunroom will act as a greenhouse that traps solar radiation thereby heating the interior air of the sunroom during sunny days to relatively high temperatures. On such days the doors and windows can be opened to allow this hot air into the home. The hot air flowing into the room will cause negative pressure in the sunroom that will suck in cooler floor-level air from inside the house. This creates a circular thermosiphon effect where hot air goes into the home through the top half of the open doors and cold air from the house goes into the sunroom through the bottom half. Considering the size of the glass space and the relatively limited enclosed volume of the sunroom (which will only be two meters wide), on a sunny day this sunroom can provide the house with a substantial amount of extra solar heat. To ensure maximum solar radiation penetration, the sunroom will be single-paned and will use normal glass. The wood structure will be as thin as possible to block as little solar radiation as possible. And the inclined glass roof will be as steep as practical to ensure the least radiation reflection in winter. The floors will be made of white concrete; this will help absorb excess air temperatures to ensure against overheating while the white color keeps most of the solar radiation heating the air rather than the concrete. This stored heat will then be released during the night, helping to moderate nighttime sunroom temperatures.

The sunroom will act as insulation in several ways. The relatively dead air space created by the air-tight sunroom's enclosed volume provides increased conductive heat resistance to the south wall and windows of the house. I am considering lining the interior of the sunroom's glass with low-e film to reduce radiative heat losses (any comments as to the practicality and wisdom of doing this would be highly appreciated). The thermal mass within the sunroom helps moderate the sunroom's nighttime temperature, thereby helping further reduce conductive heat losses. And the sunroom will act as air-lock entry for my two entrances. This ensures less heat and cool is lost whenever I enter or exit these entrances.

This sunroom will also help cool the interior of the house. The very top of the sunroom will not be made of glass but rather of wood and PV panels. This will create a 'roof overhang' that will block summer solar radiation from entering through the south house windows. Also I plan to incorporate special exterior roll-down shadecloth curtains to help further block solar radiation heating any of the south wall's surface. I am also planning on adding cool tubes to the house for summer cooling. I plan to combine this with a solar chimney, and the sunroom would act as the solar chimney. Placing vent windows at the very top corners of the sunroom and leaving them open in summer would cause hot air to rise up and out of the sunroom. This air would be replaced by air from within the house through open doors and windows on the south wall. The negative pressure created within the house would help to suck air through the cool tubes into the home, thereby providing cool fresh replacement air during the hottest times of the day. Whether I implement this cool tubes-solar chimney combination will depend on the hottest summer interior temperatures reached once the house is completely finished.

The sunroon will also act as an outdoor living room. It will provide a convenient place for solar cooking. It will be an ideal location for storing a large quantity of split firewood (all the way at the east side). It will also be ideal for our house dog (better he shed fur in the sunroom than in the house). We will also use it for some solar drying activitites and possibly for some small gardening tasks like sprouting seeds and growing some herbs. And no doubt as time passes I will find many more uses for it and think of possible modifications to help reduce resource use of one form or other.

The structure of the sunroom will be made of wood and glass with concrete tile and brick floors. As mentioned the concrete tiles and bricks will be white for the reasons already mentioned but also to reflect more radiation onto the south walls (which in future will have mounted solar thermal water heating panels for an active solar space heating system) and into the south wall windows for extra solar radiation and daylighting. The glass will be single-paned with possibly a low-e film. The supporting structure will be made of wood treated with white protective paint. I do not like the use of wood for reasons mentioned in previous posts. It requires a lot of maintenance to last a reasonable amount of time. But I feel it is the only practical choice I have. Since I plan to build the sunroom myself, and I know how to work and design with wood, it is what I am left with. I don't want to make a massive masonry structure that would block a lot of light and have unnecessarily high embodied energy. And I don't want to use metal since it is such a powerful heat conductor; plus the fact that I do not know how to weld at this scale and would require a lot of energy to do so. As for PVC, it would be ideal, but, as mentioned earlier, I am trying to now avoid this product where possible on the recommendations of Greenpeace - not to mention that I would need to learn how to build with it (but this is a minor consideration). So for now I plan to use wood unless some better alternative suggests itself before its construction.