Update: I’ve been vigorously reading up on solar heating in the last couple of weeks and realised that what I’ve done here is technically called a Sunspace. I changed the title of this post to reflect that but left the text as is. Anyway, the temperature measurements are worthy of note. In the Sunspace itself, given full sun the temperature seems to peak at about 33C. In the adjoining lounge room when both french doors are wide open, the temperature peaks at about 25C. Not a lot of heat makes it to the rest of the house, however. Obviously the convection currents won’t move enough air for this to happen. In my readings, this is exactly what is to be expected. To get around this you have to introduce fans and ducts but I always wanted a passive system. Now that I’ve proved the concept and have some experience I’m working out a plan of attack to at least heat the kitchen/dining room area with passive solar. That should be fairly easy and I quite like the fact that the bedrooms at the back of the house stay cool. There is also the issue of a lack of thermal mass which I may or may not address in the future. In any case, for the price and amount of work, I’m very happy with the results so far and reposing in a toasty lounge room on a cold but sunny day is a nice way to spend an afternoon.
A couple of years ago I bought a copy of The Food and Heat Producing Solar Greenhouse. It was written back in the 70s inspired by the Appropriate Technology movement which had grown partly out of the 60s counter culture and also with an eye on the oil crisis at that time. It’s a great book full of practical and technical information on how to build an attached solar greenhouse for the home. Being attached, the greenhouse is able to provide some heating for the house whilst also functioning as a greenhouse for growing food and potentially also providing a nice space to hang out in.
I had originally planned to build the attached greenhouse as part of my house renovation. However, a variety of factors led me to hold off at that time. The main problem was the orientation and shape of the house meaning there was no easy way to simply add the greenhouse without undergoing fairly significant building that would require a permit from the council. I decided to finish off the renovation and then use the front porch area to experiment with the attached greenhouse idea. Last weekend I put this experiment in to action.
This is the before shot of the porch. I insulated the walls and roof as part of the reno with an eye on conducting this test.
And then simply attach the glazing to this frame. I had already used this glazing on my stand alone greenhouse in the backyard and had very good results with that. It’s double layered, 6mm polycarbonate which I picked up from a place called Growfresh in North Geelong. Works out to about $50 for a sheet that is 1200 x 2400. Those dimensions happened to be almost a perfect fit for 3 sheets. Here’s the final result.
Inside the greenhouse are two 44 gallon drums filled with water. These act as heat storage, heating up during the day and then releasing heat overnight to even out the temperature swings in the house. After a couple of sunny days and cold nights I have noticed a definite effect inside, with temperatures inside a couple of degrees warmer than they otherwise would have been.
This configuration is not exactly optimal. The house faces N-NW which is good. However, with the lounge area extending outwards, the greenhouse space only starts to get direct sunlight from about 11am. Even so, it does warm up very quickly and with full sun it was in the mid 30s inside the room itself at about 2pm (given an outside temp of about 19 degrees).
Anyway, this is just the start of the trial. I’ll be playing around with it for a while and see what sort of heat gain I can get. If it proves to be valuable enough, I’ll consider doing the work to add a proper small greenhouse to the front of the house which would get full sun all day long.