My Green Home Is A Passive Solar House And Here's The Proof
In our Solar Energy For Homes page, guest author and solar energy expert Michael Martinez writes about why this green home is a passive solar house:
The house described in these pages uses passive solar heating – you can see how the many windows in the sunroom-office have been performing their job recently. In fact, one of the factors in favor of purchasing that house was its southern orientation.
Well, the time has come to test, record and share the value of those features.
The object of the experiments documented here is to show how you can save on heating on a sunny day just by having windows on the south side and opening the curtains to let the sunshine in.
Therefore, yesterday morning, November 14, being a fairly typically sunny late fall day, I took the following pictures: (pardon the poor quality!)
1.- 10.47 AM: the temperature outside is 2 degrees Celsius (= 35.6 Fahrenheit).
2.- 10.47 AM: the sunroom-office curtains are closed but the sun is filtering through somewhat. The door between the sunroom-office and the rest of the house is open, and so is a large window between the sunroom and another room (it has no glass yet).
3.- 10:47 AM: this is the actual thermostat setting in the sunroom-office: 21 degrees Celsius (= 69.8 Fahrenheit).
4.- 10:47 AM: this is the actual temperature in the sunroom-office: 22.5 degrees Celsius (= 72.5 Fahrenheit). This means that at that early time of day and in spite of the curtains being closed, the sun was already providing an extra 1.5 degrees Celsius (= 2.7 Fahrenheit) of heat for free.
5.- 10.48 AM: I opened 4 of the 6 south-side curtains partially (those are temporary curtains and that's how I've been opening them during the day. Later, there will be roman blinds which can be open all the way. For the next experiment, I will remove them completely to simulate a normal situation.).
6.- 11 AM: I closed the door between the sunroom-office and the rest of the house (but not the window).
7.- 12:55 PM: this is the actual temperature in the sunroom-office: 24.5 degrees Celsius (= 76.1 Fahrenheit). The temperature has gone up two degrees in less than an hour, due to the door being shut, in spite of the sun itself having weakened in intensity.
8.- 3:50 PM: the sun has cooled considerably, yet the temperature, at 22.5 Celsius, is still 1.5 degrees over the thermostat setting.
9.- 4:40 PM: the day is waning rapidly and the sun has shifted over to the west entirely, yet the thermostat, though it's back down to the room's heat setting, still has not kicked in. You can tell because there are no wiggly bars in the temperature window; when present, those bars indicate that the baseboard heaters are working.
Conclusion Of The First Experiment
The results of this first passive solar house experiment are encouraging: between around 10 o'clock in the morning and approximately 5 o'clock in the afternoon, on a fairly cold November day, the sun was the only source of heat for the sunroom-office.
Moreover, during the time that the door to the rest of the house was open, some of the heat collected in the sunroom-office certainly contributed to heating the rest of the house, at least partially, but that was not measured this time.
1.- 9. 52 AM: the sunroom thermostat is set at 21° C (69.8° F). You can tell that's the setting by the small arrow, upper left, in the small window.
You can see that the sun is entering the room and hitting that wall (the lower portion of the thermostat is brighter).
2.- 9.52 AM: But the actual temperature is 22 degrees, even though the drapes are still closed. (This could be due to the sun hitting the thermostat, but see next reading of that thermostat.)
3.- 9.53 AM: we remove the curtains entirely, to allow the sun to enter fully (as it will with the future window treatment referred to in the first experiment).
4.- 9.54 AM: the outside temperature (in the sun) is 4 degrees C (-13° F) in the sun.
It's certainly colder than that in the shade but I didn't check.
5.- 10.11 AM: the sun is higher in the sky, but still entering the sunroom (see how white bar at bottom of picture has shifted downwards).
In less than 15 minutes after removing the drapes, the temperature has already climbed to 24 degrees C (75.2 degrees F)!
6.- 10.13 AM: some of the heat has escaped to the main room of the house, where the thermostat has climbed by half a degree already.
7.- 3.34 PM: the sun has already shifted away from the sunroom, yet the thermostat is still half a degree higher than the setting of 21° C (69.8° F).
8.- 3.34 PM: the heat from the sunroom is still heating the main room, where the thermostat also shows an actual temperature of 21.5° C (70.7° F)
The way I know for sure that the baseboard heaters are not contributing to this temperature is that both the above thermostat windows show no wavy bars in the lower left corner as in this shot of the bathroom thermostat. (The bathroom did not benefit from the passive solar heat because I kept that door shut.)
Of course, another way of verifying this is by touching the baseboard heaters, which I did; all four of them were cold.
Conclusion Of The Second Experiment
This second experiment clearly shows that even on a cold winter day, passive solar heat was the main source of heat for most of my house for nearly six hours (from some time before 9.52 AM to some time after 3.34 PM)!
Next Experiment: we test the sun's contribution on a day when the thermostats dips below 0° C (32° F)! Keep checking this page!
Third and last experiment
I was waiting for a really cold day to carry out one last experiment to share with you.
Sunday, January 23 was a perfect day, with a temperature of -19°C at 10 AM and the promise of a sunny day from the weather man.
I wanted to find out if I could repeat the previous results at extremely low temperatures.
1. - 10.01 AM: too cold to check the outside thermometer, so I took a photo of the TV weather report. It's minus 19° C°, which is minus 2.2 degrees Fahrenheit. And that's cold!
You can see from the weather chart that normal temperatures for this time of year are quite a bit higher.
2. - 10.02 AM: but the sun is shining, so this is a good day to see if the passive solar system is still working.
I tie back the sunroom-office curtains.
3. - 10.03 AM: the sunroom-office thermostat is set at 21°C (69.8°F), but as you can see from the two wavy bars in the lower left corner of the little window, the baseboard heaters are working at 2/5th capacity (this is guesswork on my part, based on the fact that the maximum number of bars is 5).
4. - 11.20 AM: the sunroom thermostat shows that the temperature is 22.5°C (72.5°F) and that the baseboard heaters are not on.
5. - 11.21 AM: the main room thermostat shows 21 degrees, but no wavy bars. This means that the extra heat from the sunroom is also heating that big room. (In fact, the only heater operating at that time was the convector located in the kitchen.)
6. - 1.30 PM: sunroom temperature has climbed up to 23.5°C (74.3°F). (Shortly after that it went to 24 degrees but I was unable to take a photo.)
7. - 1.32 PM: the bathroom is also benefitting from the sunroom's heat, as is obvious here by the lack of wavy bars.
8. - 1.33 PM: the main room temperature has climbed up to 21.5°C (70.7°F, all by itself.
9. - 2.44 PM: the sunroom temperature is back down to 21.5°C, due to the sun having shifted somewhat.
10. - 3.19 PM: as the sun continues to shift away from the windows, the sunroom temperature continues to go down – it's at 21 degrees now – the permanent thermostat setting. But the baseboards are still not required to produce heat.
11. - 3.20 PM: the situation is the same in the main room.
12. - 4.50 PM: the sunroom baseboards are back on – as shown by the single wavy line in the thermostat window.
Conclusions Of The Third Experiment
Having carried out this experiment at different temperatures, I'm satisfied that I was right to anticipate a substantial heat gain from those south-facing windows, and this gain would of course result in savings on my energy bill.
I have no way of evaluating these savings, since this is my first winter of living here with the new insulations systems, and before that I did not own this house. But merely knowing that most of the house is being heated by the sun during several hours on a sunny winter day is a very satisfying feeling.
In reporting these results here, I hope to encourage everyone to seriously consider looking for passive solar possibilities when purchasing an existing home, or designing for passive solar heating when building a new house – but also to take a good look at what is there already, in your present home, that could be taken advantage of.
What Happens In The Summer?
In case you're worried about the room overheating in summer, that's the beauty of a passive solar design: the reason that the sun is entering the house in November is because in late fall and winter the sun is low and if the windows face the south the sun doesn't strike them at all during the summer months! (Check out the sun's path diagram on our Solar Energy for Homes page.)
So, What Is A Passive Solar House?
This home-made experiment shows rather convincingly that a passive solar house is merely a house where very basic principles of passive solar heating are applied, and in that case a great number of houses could qualify as passive solar houses if only their occupants understood and applied those principles.
Is your house a passive solar house? Do your own testing and find out.
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