Temperature Differential Thermostat ?

[Furkin]

Hi,
I'm toying with the idea of transferring hot/warm air from the attic down to the floor below, but only if it's higher temp at the ridge than the floor level - which of course, would be different at any given point.

I was wondering if anyone knows of a switch/stat (cheap or home made) that differentiates between two temps [poss ground floor level and ridge level] ?

There is a hell of a lot of wasted heat in the attic, whilst the living rooms are cold.

 

[mikely]

If you connect an upstairs and downstairs thermostat in series you should achieve what you want. Assume Live is connected to the ‘common’ of the downstairs thermostat, connect the ‘call for heat’ output of the downstairs thermostat to the common of the upstairs thermostat and the ‘call for cooling’ output of the upstairs thermostat to your fan (presumably what you want to move the warm air). Now if you set both thermostats to say 20C, if downstairs is below 20C and upstairs above 20C then the fan will shift air from up to down.

 

[Furkin]

Thanks Mikely:
I had been half thinking that there may be a way of using two stats (similar to 2-way switching was my logic ?!?!).

Sorry to be dim - but: To follow your reply, would they work at say 20degs 'difference between the two' or an actual heat temp of 20degs ?

I don't want a 'static' setting of say 20degs (or any other),,,,
if the bottom floor is 10degs and the attic is 18degs, then I want the transfer.
If the attic is 20degs and the bottom is 18degs (or higher) I don't want the transfer.

As long as the attic is warmer than the bottom (at whatever temp/s) then I want that heat transfer.

Apologies if I'm not grasping your reasoning here.

 

[mikely]

No, it would not work at 20C difference between the two. But if both thermostats are set to the same temperature it would transfer heat if the attic is warmer than the bottom floor, but only if the attic temperature is above the set temp and the bottom floor is below. So in your example, if you set them both to 17C it will do what you want. It would probably be best to set the upstairs higher than the downstairs so that it only operates when the upstairs is several degrees above the downstairs temp.

 

[Furkin]

Thanks again.

Ideally, it needs to work at 'any' temp,,,, as there is a vast difference here in Cornwall throughout the year.

What sort of stats have you in mind ? If they're cheap enough, I can always give it a bash. If it works - great, & others might benefit from my trials also.

 

[mikely]

It will work at any temperature either side of the set temperatures. So if downstairs is set to 18C and upstairs to 22C, so long as the downstairs temperature is below 18 and the upstairs above 22C, the system will switch on your heat transfer system. If you want the system to work whenever the upstairs is warmer than downstairs, then that is more complex.

You could use any basic mechanical thermostats so long as they have single pole double throw (SPDT) contacts on the output. Assuming it has one, I would connect the anticipator heater on the downstairs thermostat but not on the upstairs.

Out of interest, how do you intend to transfer the warm air?

 

[londonboy]

I have not fully read the replies.

Is your loft insulated to the recommended 270mm?

 

[Furkin]

Mikely: Cheers again mate.
I'll look out for some cheap stats to try. It's only an 'experiment' at the moment, but I hate to see all that heat just thrown away.
Transfer: I intend to use a fan & ducting.

LBoy: No, I only have 100mm at the moment.

 

[londonboy]

Insulate to recommended depth first, then see if the lofts still getting hot

B&Q often have deals on insulation.

 

[Furkin]

LBoy: I don't have any heating in the property,,,,, the only heat in the attic is from the sun. None is lost from the living quarters.
I put a heater on in the evening when I need it,,,, even then, there isn't enough heat to escape into the attic.

 

[electronicsuk]

I found 'AKO 14723 230 Volt Differential Thermostat' in the first few results of a Google search. You would also need to purchase some suitable remote probes to go with it.

 

[Furkin]

Thanks Matthew,

Yep - I just came across that item (& another) which looks ideal.
The AKO one is a bit on the dear side for an experiment,,,, but it shows there are specific things out there.

I've also e-mailed a couple of 'project' sites, to see if I can build one, or if there are modular ones available also.

Thanks for looking.

 

[mikely]

It seems that differential thermostats are commonly used in solar applications to detect when the solar collector is warmer than the thermal store, which is really exactly what you are doing. Such as http://www.novusautomation.co.uk/acatalog/copy_of_N231-S.html . I suppose the only consideration is that such a unit would always transfer heat from warmer to cooler even perhaps when you don’t want it, but you could always add a room thermostat as well. Good luck with the project.

 

[Furkin]

Cheers for your help.
Your link shows an item very similar to the AKO one (above).
There is a Titan one as well which dosn't have the luxury of a digital readout.
Am in touch with their technical people to confirm it does what I want.

If I get it sorted, i'll report back here in case anyone else is after a similar project.

all the best