More temp control...

[Cellar_Rat]

We have discussed building and ventilating wine shed / cellars before. I have a slightly different requirement:

My wine room heats up during the day in this hot weather and because it is insulated, it remains that heat.

I would like to install a automatic fan that cuts in when the temp inside is greater than outside. I've at night I could cool the it down again with free cool air (not aircon). Could I do it with two room stats (one inside one outside) wired in parallel?

Any ideas?

[ms67]

as well as the "free" cool air you mention, you can also get "free" air-flow. so then no need for the fan. Have your warm air outflow vent through the roof (or highest point possible). Put your cooler air inflow(s) low down. Convection will take care of moving the air. Now all you need to do is open and close vents automatically. there's plenty of off the shelf products that'll do that for you, cheaply.

With the air-flow you have got through doing this you should have a perfect set-up for evaporative cooling that i mentioned elsewhere some days ago. All in all a pretty green and cheap set-up.

[fatbloke]

How about just a fan that's connected to a heat sensitive window opener - like you see on greenhouses, but linked to start a fan so that any heat does it's thing and rises out of the opened window/vent......

might work, might not, either way it's a thought.....

regards

jtfb

[chris_b]

The quick answer to your question is "no". A thermostat closes (or opens) a switch when the temperature passes a temperature you set with the dial on the front. A pair of them can't be arranged to do the sort of sum you want; regrettably you need some sort of brain to do that (it's called a computer or a person )

Chris_B (electronic engineer)

[Cellar_Rat]

Thanks Chris - you could see me thinking how could I use 2 stats as logic gates to oppose each other. Does nobody do 2 way stats?

[goldseal]

I think you could do it via X10-enabled thermostats and some configurable X10 software, but the words 'sledgehammer' and 'nut' might be appropriate here

[chris_b]

Thanks Chris - you could see me thinking how could I use 2 stats as logic gates to oppose each other. Does nobody do 2 way stats?

I've seen stats that have two-way contacts inside. However the basic logic isn't on your side because a stat does something at a particular temperature, hence you can't use them to cover your stated requirement which was a general "if it's hotter indoors than outdoors, switch on the fan".

if you're prepared to downgrade your specification then you can do something. Eg you set the indoor one at 30C and the outdoor one at 20C. Then you could wire a pair of two-way stats so the fan would come on if indoors was hotter than 30 AND outdoors was lower than 20. Anything else is computer-land as you need two sensors which read the actual temperature and a brain to subtract the values and make a decision. It's not that hard (or expensive) to do with the sort of microcontroller that's used for schools, the grief is in building it and making it safe to switch mains etc etc.

Chris

[Cellar_Rat]

Eg you set the indoor one at 30C and the outdoor one at 20C. Chris

Yup that would do it.

outdoor 'makes' until 15 reached.

Indoor 'makes' when 20 or above reached.

Is the outdoor one a cooling stat, or are they both just 2 way stats? Any hardware suggestions?

Another thought - is it better to suck in cold or blow out hot?

[chris_b]

Yup that would do it.

outdoor 'makes' until 15 reached.

Indoor 'makes' when 20 or above reached.

Is the outdoor one a cooling stat, or are they both just 2 way stats? Any hardware suggestions?

Another thought - is it better to suck in cold or blow out hot?

Two-way would be easiest, I tried to draw it in text but the forum machine strips spaces out of lines. If anyone can tell me how to stop it I'll post the "circuit"

Basically you wire a pair of stats up with the Normally Closed contact of the outdoor 20C one joined the the NO of the indoor 30C one.

Chris

[Cellar_Rat]

Is it ...............
'Outside' normally closed (opens at 15) wired to 'Inside' stat's normally open (closed at 20).

OF to ebay to find some stats now

[chris_b]

@CR - I've PM'd you so we can communicate in pictures..

[benarnold]

If anyone can tell me how to stop it I'll post the "circuit"

If you use the HTML button on the toolbar above the post box - it is the one with the two angle brackets, the penultimate one on the right - then anything between those tags will appear in a fixed-width font with all the spaces you type...

            |HH|
            )  (
            (  )
           _)  (_
          |      |
          ||||||||
  _______ ||||||||
  |~~~~~| ||||||||
  `--,--' ||||||||
     |    |      |
   __|__  |______|

[chris_b]

Thanks Ben

Still can't get the drawing to look as good as yours :-). Just rememberd I can attach a jpeg (doh) so I'll do a circuit and post a a jpeg...

Chris

[chris_b]

Here's a wiring diagram for a pair of two-way (or changeover) stats
wired up to do what you want. My previous post was incorrect and I'll edit that. I've PM'ed you more details - if anyone else is interested I can supply the writeup or you can get it from CR

Chris

[chris_b]

As far as a fan blowing or sucking, it depends on the type of fan. If you're planning on using a kitchen-extractor type then I suggest you arrange it to suck as those don't work against any sort of back pressure (though I suspect that's not really going to be a problem unless your cellar is airtight).

At least as important is to decide where to let the cold air come in and how it will flow through the room. You want it to go past the all wine containers and air will take a path of least resistance. You may have to make some ducting out of cardboard or something. Probably best to put the fan towards the top of the room and the inlet near the bottom. Otherwise it will depend on how the room and wine is arranged.

Chris