Help solve a passive solar dispute with my husband...

8 years ago

So, it's a gorgeous sunny winter's day here in Melbourne, but only about 2 degrees outside. We have a small north-facing toilet/laundry/back door area that catches all that sun. We can close that section off with a sliding door, and usually do if we're heating or cooling, because that section does not have insulation in the roof. But when it is sunny outside, I much prefer to have the door open to enjoy the sun. Hubby says we're losing heat. What do you think? (Please excuse the unstyled photos!)

Featured Answer

Scott Johnstone

8 years ago

Why not change the door to a glass, or double glazed door and both win? You could put a blind on it or in it to screen the area off when you want too.

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Comments (16)

d. steel
8 years ago
I'm afraid to say Hubby is probably correct. It depends on what the actual air temperature in the sunny area is doing.

If you stand in that sunlight it feels nice and warm, that's radiant heat, that's the heat energy, lightwaves, hitting your body and warming it up. But the cold overnight air in the room is dense, there're lots of air molecules in there and they need plenty of those lightwaves, that heat energy, to warm them up. As they warm up, absorbing the heat energy, the bonds between them weaken and the air becomes less dense, lighter and it rises. This movement of the heat energy contained in the air is called convection. But different densities of air will move sideways too, they will diffuse. These movements will create currents in the air, convection currents.

So....in the morning when the sun is shining how much is it warming the air in that area? How warm is the air at the top of the room and how cool is the air at the bottom? How does this compare with the air in the heated main room? If there is a difference then it will create convection currents. This means that all that nice hot air at the top of your insulated main room will start to move and when it moves into the side room with the uninsulated ceiling it will lose its heat, become more dense, sink and add to the movement of the air.

If you really want to know if this is actually happening or not you could go all Dr Karl on it. Get a candle, thermometer and a ladder.....
User
8 years ago
Hang a thermometer. Let the North sun in during the day, insulate the rest of the house by closing it off at night.
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Najeebah
8 years ago
slightly off topic, if you'd like to sit in the sun, is it possible to move or reduce the size of the bathroom/laundry and use a portion as a sunroom?
User
8 years ago
Brilliant, Scott!
tangerine9
Original Author
8 years ago
d.steel Thanks, I guess, although I did not want to hear this!
Scott, this idea has been considered, however the bigger plan is along the lines of Najeebah’s suggestion. We want to relocate the toilet and laundry, remove the dividing wall, and create a small living space there. Large, double-glazed glass doors to the backyard, a new deck and slatted pergola, deciduous vines growing up, lots of passive solar features… *sigh*.
In the meantime, I think I’ll hang a thermometer, thanks chookchook.
User
8 years ago
I do my best, I'm not a permanent staff, I'm just a TEMP.
PRO
Envirotecture
8 years ago
You are both right!

I would suggest that when the sun is shining you are gaining more heat than you are losing but once the sun goes down the reverse happens. For now (renovations, adding insulation aside) I'd suggest opening your internal door during the daytime and then closing it as soon as the sun goes down.

It sounds like you're on the right track for the eventual reno
tangerine9
Original Author
8 years ago
Oh god chookchook, I just got your joke!
tangerine9
Original Author
8 years ago
Envirotecture, this would mean I am right, as this is the process I was following!
rkelaart
8 years ago
Arent the building materials that will be exposed once you open up the space of importance here? I thought that opening up the thermal mass of a property (ie concrete slab floors) to periods of radiant heat then the overall temperature of the house would increase across longer periods of a winters day. On the other hand if no significant thermal mass exists within the property (ie the house may be clad in timber and be built on stumps) then any increase in temperature through radiant heat will be shortlived.
d. steel
8 years ago
rkelaart, if you look really closely at the picture you might just glimpse the timber floor of the room in question (which we have been told has an uninsulated ceiling/roof also)

Scott Johnstone, that's simply great! (thumbs up emoji)
PRO
Envirotecture
8 years ago
Yes you are probably correct but only when the sun is shining (depends on the actual temperature outside, surface area of the building fabric, and the insulation values of the walls and roof); chances are the heat gain is greater than heat loss at that moment.

rkelaart. Yes. the thermal mass makes a big difference in retaining heat although this initial question was really about the balance of heat loss and gain when the sun is shining.
Loretta O'Sullivan-Pippia
8 years ago
I would have to agree with envirotechure...and I would look it like this - if it is sunny, warm and no wind and you open the door/window you will be warm and so will be the room. If it was sunny and windy, the wind will cause a decrease in temperature and you will be cold and so will the room, so sit behind the closed glass window and you and the room will be toastie. If it is overcast and cold, you won't get any heat from the sun, so close up the room and put the heating on or go back to bed and snuggle up. When the sun moves and it is no longer heating you and the room, close the window and door and go catch the sun in another part of the house. I think we all do that naturally anyway, it's just common sense. And in a really hot summer, you will be wanting to shade that room to cool it and yourself - the exact opposite.

Obviously, if you have good insulation, thermal mass etc etc the effect of heating that room will last much longer than that moment, but you will still want to catch the sun in winter and you will want shade in summer.
Loretta O'Sullivan-Pippia
8 years ago
Also, in Australia, the northern aspect is the best aspect in terms of light, sun and wind and if you read environmental info on house building, all available freely online in your local council building planning websites, you will see it is recommended to put windows along the northern aspect and to close off the southern and western aspects. So your plan to put big glass doors along the northern aspect will make for a beautifully functioning home. Your local council will have info specific to your latitude.
PRO
anewhouse.com.au
8 years ago
last modified: 8 years ago
Sun shining and you are gaining around 520 watts of heat/m2 of window. (Gain around 650 but loss 130 watts)

No sun and you are just losing around 130 watts of heat.

This link explains the calculation http://www.anewhouse.com.au/2015/02/energy-through-the-windows

Help solve a passive solar dispute with my husband...

Scott Johnstone

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