solar powered extractor fan

[victorg]

my mum has a conservatory, on really sunny days (like weve been having) it gets dangerously hot in there with no windows open, there is access to the house so cant always leave windows open, there is a ventillation fan that my mother doesnt use as it eats up leccy. can anyone advise on connecting a small solar panel to kick in on really sunny days to switch the fan on automatically?

 

[JohnD]

A typical "bathroom" extractor fan uses 25watts of electricity, meaning at (say) 9p per kWh, it will run for 40 hours for 9pence.

This bigger 150mm (6") fan uses 26watts http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=100593&ts=49806&id=11640

How much power does the fan you mention use?

 

[breezer]

decent solar panel will cost more than you will save

 

[victorg]

its 30w, is an issue as to keep the plants alive it needs to be on all day whilst shes out.

 

[JohnD]

its 30w, is an issue as to keep the plants alive it needs to be on all day whilst shes out.

let me see now... 30 watts... so it runs for 33 hours 20 minutes to use 1 kwh at a cost of about 9p... If you give her fifty pence that will probably cover its use during an average summer month... you could perhaps get a central-heating room thermostat to control it... I think the problem is that your mother is not aware of the actual cost of running a low-power appliance like a fan.

A kettle, or an immersion heater, would use 9p worth of electricity after about 21 minutes use, but the cost of running the fan is about a quarter the cost of running a light bulb, and a hundredth the cost of running a kettle or a heater.

 

[breezer]

would a central heating stat not turn it off when it gets hot?

surley you need a frost stat?

 

[JohnD]

would a central heating stat not turn it off when it gets hot?

surley you need a frost stat?

Good point.

But I don't think a frost stat would do it either. A stat with both NO and NC contacts would do it, there must be one somewhere; or one designed for air-con.

 

[breezer]

a timer would work for sure

 

[Steve]

aren't stats adjustable so they can cover either heat or cold? one would think there would be a switch under the cover or something? Or 2 "output" terminals, one for cold one for heat etc.

 

[victorg]

i understand the maths and have worked it out, however, when she uses this thing a lot her leccy bill ends up loads higher than normal for the summer.

 

[breezer]

aren't stats adjustable so they can cover either heat or cold? one would think there would be a switch under the cover or something? Or 2 "output" terminals, one for cold one for heat etc.

most dont have change over contacts

 

[Steve]

i understand the maths and have worked it out, however, when she uses this thing a lot her leccy bill ends up loads higher than normal for the summer.

you're sure its not an air conditioner? (which actually cools the air) Or is it actually a small hole in a window, with a fan inside, which you can see daylight through when operating?

 

[victorg]

yes im sure its not an air conditioner.

 

[victorg]

timers a good idea though, could just pop it in and on for 15 mins every hour and see how it affects the leccy meter, cheers

 

[Steve]

"her leccy bills end up a lot higher for the summer"

yes, her fridge works harder, her freezer works harder, and i'll bet theres other things she has that use a lot of electric during summer.

And to keep the conservatory cool, a small extraction fan isn't going to do much good. this would be better, in fact, 2, one at each side, one blowing in, one blowing out. this might just work.

But you are likely to need that small fan on constantly to keep the conservatory "cool". As soon as it switches off, the room will heat up very quickly (we're talking 1 minute to undo half an hour's work by that fan). Strong stuff, that sunshine. There may be something wrong with it if it uses as much electric as you claim.