Separating rooms with and without AC
It’s unseasonably hot here in Seattle, and I’ve got the little $98.00 air conditioner working hard to cool the big living room space. It’s 15′ x 25′ with a sloping ceiling from 8 to 11 feet. The AC is up high in a clear story window.
There is a floor to ceiling passage to the kitchen, 3 feet wide, which is the same ceiling height.
I was thinking of blocking off the door so the cold air wouldn’t migrate to the kitchen and hung a twin bedsheet over the opening (how tacky!) but the sheet isn’t long enough, it’s about 2 feet short.
So if I was just gonna leave it, would I put the 2 feet opening at the top, bottom, or is it even gonna matter?
I was thinking of putting the opening at the top, the theory being that the cold air from the AC will fill the room from bottom to top and if the opening is at the bottom, the cold will flow right out.
Comments? Suggestions?
Replies
Energy transfer goes from HOT to COLD. The hotter/hottest air of the other room is near the ceiling. I think that the heat would transfer faster if the opening was at the ceiling.
You've already hung a bed sheet. Get some clingy Saran wrap and stretch it across the opening at the top, both sides. That'll let in some light at the ceiling. Hang the bed sheet at the bottom edge of Saran wrap.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Good idea on Saran wrap. But there's a larger picture on heat transfer: you're right in pointing out that heat transfers from hot to cool, but part of the action is also the weight of the cooler, denser air which falls and displaces the warm air above, thereby setting up a cycle of convective air.
So, the continuous curtain combination (sheet and Saran) will reduce convective currents from one room to the other, but will not do much to reduce heat transfer across the thin curtain. (R-0.?)
I'm not counting on any actual barrier to thermal transfer with the sheet, just the convective mixing. I'll give the plastic wrap a go.
Believe it or not, the thin sheet blocks MOST of the heat transfer to contain the colder air conditioned air. But, yes there will be some heat gain due to the thin sheet.I wouldn't want a bed sheet for a front door in 25 degree Winter cold, though.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Yes, I do believe what you say about the greatest benefit resulting from stopping, or reducing air movement. This is a case where the temp. difference will not be very great--maybe 10 or 15 degrees. So the R-value of the barrier is not as important as its role in preventing convection currents.
Heat transfer across the curtain being R-0. Uh no. You have the sheet and you have the two air films. Relatively speaking, this isn't the same as 'nothing'. An inside air film (i.e. not affected by convection of wind), is relatively significant. Small point, but it is far from R-0 even though your point is well taken. The delta T across the curtain, we are only talking about maybe 5+Fdeg; pretty small.
It really has little to do with the principles of conductive heat transfer (i.e. hot to cold). But you are right, non the less about needing to close the top. But he has to close both top/bottom as you imply.
It really has little to do with the principles of conductive heat transfer (i.e. hot to cold).
I wasn't thinking "conductive". More or less the air flow, so that is more like convective. I just figured the hot air would want to come into the cooler room.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
But conductive is the principal of 'hot to cold'. Convective is the principles of air movement and 'hot air rises'. I was just trying to keep the lingo in line a bit. I'm a bit anal about that kind of thing.
I guess you could say that the heat from the warm air is being "conducted" to the cooler air..... a bit. But it is the actual air that is moving more so than just a heat transfer. So..... just how many angels have you calculated can sit on the head of a pin? :-)
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
my experience says 2 things. opening at the top will work better, the cold does pool, I have proven this in ac'ing large spacesget a bigger ac......
Am I the only one wondering why he would want to cool the living room and not the kitchen? Do they not cook and only eat takeout in the living room? I'd move the AC to the kitchen and forget the living room.
What kind of spray paint will best cover the duct tape patch on my trailer roof?
Rustoleum has that spray-anything paint now. I'd choose white for the color, Just as Obama's energy chief suggests.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Don't cover it with paint, put tape all over the roof in a sort of plaid pattern, make a design statement with it.
Ya know, that's exactly what a woman would say.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
I believe your analysis is correct. Blocking the bottom will be more effective than blocking the top.
When I went to block the top , I could feel warm air migrating from the kitchen (warm) to the living room (cooler), and I blocked that off too. I can see there is some pressure differential between the living room and kitchen, as the sheet is slightly bending into the opening from the living room side. Part of that is the pressure induced by the A/C itself, (although it dumps air OUT as well as IN ) but even if I turn the A/C off I can see the cold air (which is heavier) has filled up the living room and is pressing against the sheet.It is functioning as desired. The living room is a good 10 degrees cooler than the kitchen.
problem is that 11 foot ceiling
problem is that 11 foot ceiling
A REALLY big piece of saran wrap at about the 7 foot high mark from all 4 walls will help with that problem! ;-)
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
So you get to actually SEE what is happening. It is convective heat transfer. The kitchen warm air goes out the top. It's only a sheet, so the cool air goes in the bottom. You have to cover the entire opening since your cover is not rigid/sealed like a half wall in a room would be.
In theory you only have to close top OR bottom, since cutting off either one will prevent the airflow. In practice cutting off the bottom will be more effective. The AC creates a layer of cold air near the floor, and it will flow like water to fill the available space. Cutting off the bottom prevents it from flowing out of the room.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
tip I did in my hot mobile home, run a return vent from the hottest area to the a/c closet return, the hot air will get suck first thought the coils. and it will cool quicker. so if you had a 4 inch pvc pipe running from the peak of the 11 foot ceiling to the a/c closet. you can try it temporary see if it works.
Right, but since it is only a sheet, air movement isn't restricted like it would be with a wall or solid other solid material.
But air movement IS restricted. Could be restricted more, but it's restricted enough to make a difference.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
Right you are. It is slowed down considerably. But the fact that the sheet billows in toward the kitchen shows that it is significant (convection).
The fact that it billows in towards the kitchen shows that there "wants" to be significant convection. The billowing of the sheet could only occur if that convection was being prevented to a significant degree.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
Yes, of course, Dan. It shows the resistance ... actually it shows the relative negative air pressure in the kitchen. The sheet does work and the stress on the sheet shows how much it is working.
That 10 degrees gives you about a 2% air density difference, so, yes, you would see the sheet pucker even without any flow. Maybe you can plot sheet deflection vs. temperature difference and sheet tensioning and write it up for FH.
If your doorway isn't too wide, use a shower curtain and (twist to expand) rod.
Lower the rod so the curtain drapes across the floor to stop the heavier colder air from sneaking out along the floor.
It's not perfect, but it doesn't mar the trim/wall, is somewhat impermeable, can be easily swept aside when you need access or passage through, and maybe you can get a color that lessens the ugliness.