Cheap differential thermostat?

[ericmark]

I have a problem with mothers room getting too hot, opening a window can cool a room at night, however during the day it can actually be hotter outside than inside, so there are times when opening a window actually makes a room hotter, so thought is fit a fan to blow air into the room from outside and use thermostats to control it.

10 am and camera is showing 29°C at the moment, but eTRV is showing 21°C so it is direct sun on the camera, outside 20.2°C so no real point opening window now, left it too late. So something automatic is called for.

So easy enough to use something like the STC-1000 pick them up at around £10 set it so if inside exceeds 22°C turn on fan, however could be blowing in air hotter than already in the room, so looking for something with two sensors which will work a relay according to which sensor is hotter.

Sure I could make something, but if there is a cheap one already made then I would go for that.

I can find them for USA This is 110 volt so not any good for me and also 12 volt versions, but looking for something like this

but 230 volt version. Think used for solar water heating, but for 230 volt only found them at silly prices, could buy an Air-con for less.

 

[JohnW2]

I can find them for USA This is 110 volt so not any good for me .... but looking for something like this .... but 230 volt version.

The link you have provided "for USA" includes the statement ...

"We will ship the temperature controller with 110 V or 220 V versions based on the voltage of your countries."

Kind Regards, John

 

[Edddd]

A standard thermocouple type thermostat measures the temperature internally then applies the differential sensed by the thermocouple. So all you would need to do, in theory, is disable or spoof the internal measurement and the thermostat will just measure the differential.

Could even place the thermostat in a temperature-controlled enclosure (a fridge?, not necessarily in the room to be measured) and extend the thermocouple terminals with two copper wires to the indoor measurement point. The thermocouple wire ends are then connected to the copper wires at this point and the thermocouple junction is placed at the outdoor measurement point.

 

[ericmark]

I have found 12 volt versions which you can by with British pounds, it seems they are used for solar water heaters, I think it may be worth looking at 12 volt fans, they also may be easier to get to run to pump air in rather than suck air out. However cost is a major consideration no point is spending as much as a air con, or even near that price.