Im thinking of putting some simple cooling in to help with British summers. It will consist of:
a 9" 1400rpm extractor fan in the loft to run 24hrs during the summer. In the day it will dump a bit of heat, at night it will draw in colder air. The attic is currently unvented but far from airtight.
a 4" tangential fan blowing into a south facing wall cavity near the bottom, with exit flap at top of wall. Again it should be advantageous to run it 24hrs when cooling is wanted. However I expect flow rate to be crap. But it only costs 10 to buy and eats 15w, so if I get the time I shall.
Fan plus window ventilation in each room to be run at night. Bringing colder air in at night will cool the place and reduce th temp of the houses's thermal mass for the next day. Its a brick house.
I'm hoping this simple system will provide a worthwhile comfort increase in summer. If there are any points I should look out for I'm all ears.
As an alternative, you might consider a single "whole house fan". This fan installs in the ceiling of the living space such that it draws air from the house, and exhausts air to the attic. It will pull air into any open windows in the house. It can be used during the day to provide cooling (from the increased air velocity), and you can run it at night to cool the thermal mass of the house. You need to provide an exit vent in the attic. A set of air actuated louvers closes off the fan opening when it is not running. As sold here, these fans tend to be fairly high capacity -- around
3000 CFM to 6000 CFM -- the sizing rule of thumb that some use is 3CFM per square foot of floor space, or about one air change every three minutes. I have have installed one of these in the my last two houses, and would not be without one -- they work quite well, especially if the ambient temperature drops to a comfortable level at night.
I like the sound of that. It may be a problem from a noise point of view though, having a powerful fan mounted to a PB ceiling outside bedroom doors. Will look into this more, thanks.
Jim Baber wrote: I have a different problem than N Thornton has with his British summers. I have chronic respiratory health problems that require me to use air conditioning, and I live in Fresno California, where the temperatures in summer are high and the area has the 1st or 2nd worst pollution in the United States.
The average hourly temperature for each hour for the past 74 days has been 80.5 F, with an average of 96.8 F at 17:00 and an average of 71 F at 08:00 for the same 74 days. My air conditioning load is severe considering that one of these
74 typical days will have over 6 hours with the outside temperature above 90 F.
I concur with Gary about the beneficial effects of a wholehouse fan, but I cannot run mine 24 hours a day as you could in England. By running mine only when the outside air is cooler than the inside air, AND only when the inside air is less than 82 F, I have been able to typically reduce the time I run my air conditioning by 75%. The wholehouse fan uses 450 Watts / hour as opposed to
6000 Watts / hour for my air conditioning. Our wholehouse fan is typically run
6 hours a night (01:30 - 07:30), and it 'chills' the house enough to replace about 6 hours of the air conditioner operation during the hottest time of day (12:00 - 18:00).
One major benefit of banking the cooler thermal mass of the house and its contents until needed in the afternoon is the obvious savings in electrical energy in kWh.
But, the second major reason is because I am on an Time of Use electrical rate structure the cost of electricity is much higher (@$0.32524/kWh) in the peak demand period (12:00 - 18:00) vs all the rest of the time (@$0.09015/kWh). This means that all of that electricity I saved with the fan is very expensive electricity. To even make this more attractive I am generating power myself in my PV solar arrays and exporting whatever I don't use to the utility grid for which I get credit against my bill for whatever they would have charged me if I was buying it. This means not only am I not paying $0.32... for cooling the house between noon and 6 PM the utility is paying me $0.32... for the same saving since that is the best PV solar production.
I also use it to warm the house on warm afternoons in the winter instead of burning gas to heat the house. Not as spectacular a savings, but it all counts.
Yes indeed the wholehouse fan is a great thing for me.
--
Jim Baber
(see my 10kW grid tied solar system at "
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1350 W Mesa Ave. Fresno CA, 93711 (559) 435-9068 (559) 905-2204 cell
NREL says Fresno in August is 81.9 F, with an average daily min of 63.8 and an average humidity ratio w = 0.0092, which makes Pa = 29.921/(1+0.62198/w) = 0.3461 "Hg, which makes the dew point about 9621/(17.863-ln(Pa)) = 514.7 R or 54.7 F. Evaporative cooling might help.
I doubt that's a good idea in England either. IMO, an attic should be well- vented, and a WHF should only run when the outdoor temp is cooler, or maybe a little bit warmer than indoors, with internal electrical usage.
You might run it when outdoor air is cooler and indoor air is > 56% RH, and turn on an indoor mister when the indoor air is warmer than 82 F.
The wholehouse fan uses 450 Watts / hour...
Just watts. "Watts / hour" is meaningless. I like Grainger's $73 4TM66
3-speed 16" reversible window fan with thermostat, which moves 5850 cfm with 90 watts on the highest speed.
Doing that well may require 2 fans, one to move outdoor air through the house and another ceiling fan to mix it around in the house. The outdoor air won't cool much mass if it just passes through the house in a compact stream. It's also nice to have moving vs stillish air near the mass in order to raise the surface airfilm conductance. Gary might run a WHF in Billings in July, when the daily min temp is 58 F and the daily max is 87 and w = 0.0080. With a F cfm fan and constant day and night temps, he might have something like this:
1/F
58/87-----/ ---www----- T RC = 6K/400 = 15 hours, with the fan off. | | | 1/400 | 70 = 87+(T-87)e^-(12/15) = 47.91+0.449T -----www----| makes T = 49.2 F, so it looks like | he needs a longer time constant --- 6,000 Btu/F to keep the house 70 F max when --- it's 87 F outdoors for 12 hours. | -
If 2" of concrete floor over hollow blocks adds 32'x32'(5+2/12x25) = 9387 Btu/F and raises RC to 38 hours with the fan off, 70 = 87+(T-87)e^-(12/38) = 23.3+0.732T, and T = 63.8 F at dawn. If 63.8 = 58+(70-58)e^-(12/RCn), RCn = -12/ln((63.8-58)/(70-58)) = 16.5 hours = 15387/(400+F), F = 532 cfm. Not much.
But why waste coolth by keeping the house close to 63.8 F just after dawn? If the slab is T (F) at dawn and we keep the house air 70 F all day with a cooling thermostat and a slow ceiling fan (without which cool air will stay near the floor) and an occupancy sensor, the house will only need
12h(87-70)400 = 81,600 Btu of coolth, max, and 81600 = (70-T)x15387 makes T = 64.7, so RCn = 20.6 hours and F = 347 cfm, or less, with indoor mist.
Nice, if the outdoor dew point is above the indoor house wall temp, to avoid condensation...
thats way cheap. I've been looking at 9"/12"ers at £100, about 150usd, and 550cfm.
But more importantly most fans dont seem to have dB ratings, and that is a real issue considering the fans would be above bedrooms and run at night, and mounted on a springy PB ceiling.
Thats my #1 concern here. A WHF will move air through the already coolest parts of the house, but not through the rooms where cooling is needed most. Not sure how to address that. Would still be a benefit though, and much less cost than multiple fans.
Our current whole house fan is in the hall ceiling just outside the bedroom, and we often run it on low speed at night on a timer, set to turn off around 2am or so. The noise is kind of a low frequency rumble that is not very loud, and does not keep anyone awake. But, I suppose this could vary from brand to brand.
The fan is a 30 inches in diameter, and is belt driven through a step down pulley -- not sure what the final rpm is, but you can see the individual blades turning on low speed. If you are concerned about the noise, I would be sure to get one with two (or more) speeds. I think the price was about $150ish.
Some of the WHFs are fairly awesome on the highest speed -- the one we had in our last house would pull the drapes in at a 30 deg angle on several windows :-) -- good for a quick cool down.
You can control which rooms gets cooled by just opening windows in the rooms you want cooled. To get the flow balanced the way you want it between the different rooms, you may have to close the windows in some of the rooms part way (usually the rooms closest to the fan). Overall we find it to be a pretty flexible system. Although, if you have a good place to locate a high capacity window exhaust fan, I don't see why that shouldn't do the same thing. I think that a good window fan location would be one that can pull air through other open windows throughout the house, and in a location where you don't mind a fairly high velocity of exiting air.
Don't overlook the fact that if you use a WHF, you will have to provide an exit vent in the attic. Normal attic venting does not provide enough area.
Don't know why you'd do this, but you could probably mount a WHF in a piece of plywood and mount it in the window furthest from your room. Get the benefit of the fan and it would be quieter. Plus no extra attic venting.
this really confirms my brief thought to use a ceiling fan and make a thin flexible plywood cowl for it. Mount the fan on the roof rather than ceiling, with an extended drop rod. This would deal with the noise issue, provide sufficient air shift, come with 3 speed settings, and be cheap too.
I bet! I had a 1.4kW one once, wish I still had it. Sadly I dont. It could turn an oven into a cold wind tunnel in seconds. A bit too much really.
of course - so simple but I didnt think of it. Thank you. Much of the air flow will have to negotiate closed doors, but several in parallel should provide at least some airflow I hope. I'm not real convinced though.
I think that would probably be too noisy. Also be more expensive on wiring (with channelling), and look ugly. In terms of cooling function it would be almost ideal, but.
of course. There is no attic venting at present. My bigger concern though is the doors. There is only a very small area of gap under each, and ceilng fans are high volume low pressure. This strikes me as the one last problem. I _dont_ want horrible metal grills in the doors. Will think some more... perhaps slice a little off the doors. Thanks.
I'm surprised they are so expensive in the UK. Grainger's has a 120 V motor. You might look for window box fans in some large UK home building supply store or industrial hardware store, or convert your house to 120 V :-)
Put the fan in a window on one side of the house, and open a few house windows a bit on the other side. Use a cigarette or your velocity stick and open or close the windows a bit to ensure uniform air velocity or air temperature in every part of the house with the fan running, eg through the connecting doors of all rooms?
I think you'll find the blades on a ceiling fan aren't shaped to be very efficient. Most whole house fans, even the window versions, have a much more advanced shape. You might do better to buy two or three cheap box fans. Place a curved duct inside the box and they can pull a lot of air. They usually have three speeds and on "low" they're pretty quiet. Two or three set on low will be able to pull a lot of air through your building and you could turn them on/off individually to act as a kind of multi-speed control.
Cheap box fans are thoroughly noisy though. This will be operating above bedroom ceilings. They are also a fire risk, and will be operating out of sight or smell. Decent box fans I've been seeing at
90-150 GBP each in trade catalogs, x1.5 to get USD.
ya lost me there
This would work fine with the decent ones, but be about 15 times the cost of a ceilng fan, 300 rather than 20. If I need to do that, OK, but do I?
thats not so hard actually, the 120v. I've no idea what it would cost to import one, but more significantly our 50Hz tends to roast your
60Hz motors.
The fans in the sheds (stores) are not of acceptable quality, from either noise or fire risk point of view. Certainly I could buy them at
20 a piece, but theres no point installing something everyone complains about and wont use, and which is a fire risk. Unfortunately the decent ones are a lot more money.
Well... have already tried an unfanned version of this, and the cooperation just isnt there, so it doesnt work. Works great when people cooperate, but you know what its like...
Seems like every idea theres some kinda block with :( Oh and the whole house fan, the only location it could go theres something in the way that cant be moved! Life :/ The only option this leaves me with that I can see is one fan per room, with the attic having its own fan and not connected with the rest of the house. Unfortunately it means a lot of pricey fans, a lot of holes and a lot of chasing and wiring. I dont like that.
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