Controlling Shop Temperature - Differential Temperature Switch?

dalmatiangirl61 · Jul 11, 2021

As my shop is warming up today, I'm wondering how to better control the temperature. Between the concrete and cast iron the temperature does not change rapidly, in the winter time if its warmer outside than inside I just leave the door open during the day, but in summer I cannot leave the door open at night when its cool outside. I see thermostat switches, but not seeing differential temp switches.

Is there a switch available to control a window fan that could be set so that anytime there is a 10 degree difference in outside vs inside temperature it turns on a fan? Ideally something that could be switched for summer vs winter? (in fall/spring it can be 70 outside and 40 inside)

Its 101 outside today, shop is about 85, from about midnite to 5-6am it will be about 60 outside.

Bill D · Jul 11, 2021

I am planning to use a time clock on a vent fan so it comes on to cool the shop around 2 in the morning. Should be easy enough to set up relay logic with a NC and NO switch controlling a relay.

kustomizer · Jul 11, 2021

I bought one of these and the optional 67 controller, I have it come on at 2am and run till 8, so far I am happy with it. It is made in China but I have to say the quality is second to none, their help line is in California and are quite helpfull

AIRLIFT T14, Shutter Exhaust Ventilation Fan 14", Temperature and Humidity Controller - AC Infinity

specfab · Jul 11, 2021

If you use a 3-phase fan, you can also consider reversing the flow in vs. out, as long as you have controllable restrictions (such as vaned shutter in front of fan)

Rob F. · Jul 11, 2021

dalmatiangirl61 said:
As my shop is warming up today, I'm wondering how to better control the temperature. Between the concrete and cast iron the temperature does not change rapidly, in the winter time if its warmer outside than inside I just leave the door open during the day, but in summer I cannot leave the door open at night when its cool outside. I see thermostat switches, but not seeing differential temp switches.

Is there a switch available to control a window fan that could be set so that anytime there is a 10 degree difference in outside vs inside temperature it turns on a fan? Ideally something that could be switched for summer vs winter? (in fall/spring it can be 70 outside and 40 inside)

Its 101 outside today, shop is about 85, from about midnite to 5-6am it will be about 60 outside.

Dont you have a 3 story building? Can you just open windows on the ground floor and also on the top floor? The heat will rise, drawing in colder outside air with no electric bill. Open the windows as soon as the inside and outside temp are the same or slightly cooler outside.

Tony Quiring · Jul 11, 2021

Easy...

A couple thermo-switches like Allen Bradley or used thermostats.

Set inside one for temperature to start running as "cool" mode so it closes on temperature RISE.

Set outside one to "heat" mode so it opens on temperature rise.

Connect in series to a contactor is thermostats or fan if Allen Bradley.

If using contactor it can slave off light switch so it follows lights, no lights, no fan.

Since not in series then BOTH must be closed to run fan.

Inside one closes when temp gets above set point so "fan enable" is when inside is above your lower set point.

Given you do not want to blow in "hot" air the outside control opens when it gets above that set point so the fan will come on when inside reaches that set point and then until outside gets to to the outside set point.

Cheap and easy.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Gordon Heaton · Jul 11, 2021

I have my A/C condenser, air compressor and RPC idler in a small room built onto the back of the shop. The room is not air conditioned, but it has a 1200cfm blower to pull outside air through. The blower is controlled by an Arduino connected to two temperature sensors: one for outside air temp and one for the equipment room. When I'm in the heating mode the blower comes on any time the OAT is 2deg warmer than room temp. In cooling mode the blower comes on if the OAT is 2deg cooler than the room. The mode switch is made manually by me. The blower runs for at least three minutes after each start, after which the sensors are polled again to update the status.

You could use a similar setup for your shop. The temp spread and blower cycle are easily changeable, and the OAT, room temp and 'fan on' indicator are all displayed inside the shop.

Edit: As for reliability, I've had this setup running 24/7 for four years without issue. I use a solid-state relay controlled by the Arduino to switch the blower. Its also cheap. Not counting the blower I believe I'm into it less than $40.

dalmatiangirl61 · Jul 11, 2021

I'm going to look into the fan unit mentioned by Kustomizer, 1 unit, plug and play, assuming it can do what I want. A timer would work well enough in summer, so long as we don't get a cold front.

Rob F
I thought stack effect would work better, but it just doesn't, and at this point I have caulked all the windows shut because they were so drafty, not only did it allow me to heat the shop, it also keeps that space cooler in the summer.

I definitely need a way to push outdoor air into that area, this past spring it took a month of nice warm days with doors wide open for shop to warm up.

rimcanyon · Jul 11, 2021

Gordon, who programmed the Arduino? You, or was it something you purchased?

Gordon Heaton said:
I have my A/C condenser, air compressor and RPC idler in a small room built onto the back of the shop. The room is not air conditioned, but it has a 1200cfm blower to pull outside air through. The blower is controlled by an Arduino connected to two temperature sensors: one for outside air temp and one for the equipment room. When I'm in the heating mode the blower comes on any time the OAT is 2deg warmer than room temp. In cooling mode the blower comes on if the OAT is 2deg cooler than the room. The mode switch is made manually by me. The blower runs for at least three minutes after each start, after which the sensors are polled again to update the status.

You could use a similar setup for your shop. The temp spread and blower cycle are easily changeable, and the OAT, room temp and 'fan on' indicator are all displayed inside the shop.

Edit: As for reliability, I've had this setup running 24/7 for four years without issue. I use a solid-state relay controlled by the Arduino to switch the blower. Its also cheap. Not counting the blower I believe I'm into it less than $40.

thermite · Jul 12, 2021

dalmatiangirl61 said:
I'm going to look into the fan unit mentioned by Kustomizer, 1 unit, plug and play, assuming it can do what I want. A timer would work well enough in summer, so long as we don't get a cold front.

Rob F
I thought stack effect would work better, but it just doesn't, and at this point I have caulked all the windows shut because they were so drafty, not only did it allow me to heat the shop, it also keeps that space cooler in the summer.

I definitely need a way to push outdoor air into that area, this past spring it took a month of nice warm days with doors wide open for shop to warm up.

ALL the goods you need have been stock items for over 50 years. Johnson Controls and Barber-Coleman made their economic bones on managed building controls.

Grainger / Zoro have the basic control components for it long-since. Ignorant remote-sensor T-stats, etc.

Use of cooler night air here has cut my Air-con bill to trivial. Forced air IN also clears up the side effects of my heavy smoking habit. Running "make-up air" in ADJACENT to but not IN, the kitchen also helps the range hood exptractors keep steam, oils, and cooking odors out of the rest of the residence.

JF go for it. Adjust as you go. It can pay-off VERY nicely.

Bill D · Jul 12, 2021

If this is Nevada humidty is not an issue. Is it dry in your part of Texas? You do not want to pump in slightly cooler damp air at night and then use ac in the day to get the moisture out.
Bill D

Gordon Heaton · Jul 12, 2021

rimcanyon said:
Gordon, who programmed the Arduino? You, or was it something you purchased?

I used some public domain elements and did the rest with the help of a son-in-law who is a web programmer. I'm sure my code is kludgy but it works! I think I can find it if anyone's interested.

I put all the Arduino and display stuff in a standard 4x4x4 NEMA enclosure:

The OAT sensor is clipped to the inlet grille:

The blower is mounted on the opposite wall from the inlet:

This is a 4' X 16' X 8' High uninsulated room (just haven't got around to the insulation yet).

dalmatiangirl61 · Jul 12, 2021

Bill D said:
If this is Nevada humidty is not an issue. Is it dry in your part of Texas? You do not want to pump in slightly cooler damp air at night and then use ac in the day to get the moisture out.
Bill D

Nevada, night time air is cool and dry, there is no ac system.

drcoelho · Jul 12, 2021

I'd recommend not worrying about the differential, just use a simple air vent thermostat set to maybe 90 degrees for turn-on. Even if temp is the same inside/outside running the fan won't be worse than not running it, and most of the time you'll have hotter outside than inside.

thermite · Jul 12, 2021

Bill D said:
If this is Nevada humidty is not an issue. Is it dry in your part of Texas? You do not want to pump in slightly cooler damp air at night and then use ac in the day to get the moisture out.
Bill D

That's more likely in Atlantic coastal plain or Appalachian "jungle" and for-damned-sure the tropical GULF coast... than in the dry "out-West" arid lands.... but even so..

Actually one often CAN do.

Keep in mind that humidity figures are "relative" numbers. To the amount of vapour air of a(ny) given ambient temp can CARRY as vapour.

AS the night air warms up? RELATIVE humidity drops anyway. Even before de-hum or AC is involved. If-even.

The "number to watch" is also published by the weather folk:

"Dew point."

There's your possible "damager."

Condensing humidity onto hidden surfaces of cold(er) Old Iron and its electrical goods.

Or in much of Asia? Soggy bedding, clothing, and expensive suits growing MOLD colonies!

Some optimistic fools even try to have CARPET in upscale Hong Kong flats. Damned few, though!

Ours are all solid Teak fingerblock for the living spaces, porcelain/ceramic for kitchen and baths.

Humidity control is MORE important than temp. High-desert country fares very well.

Joe Gwinn · Jul 12, 2021

dalmatiangirl61 said:
As my shop is warming up today, I'm wondering how to better control the temperature. Between the concrete and cast iron the temperature does not change rapidly, in the winter time if its warmer outside than inside I just leave the door open during the day, but in summer I cannot leave the door open at night when its cool outside. I see thermostat switches, but not seeing differential temp switches.

Is there a switch available to control a window fan that could be set so that anytime there is a 10 degree difference in outside vs inside temperature it turns on a fan? Ideally something that could be switched for summer vs winter? (in fall/spring it can be 70 outside and 40 inside)

The classic HVAC outdoor air temperature sensor solution is to control the building using only measurements of outside air temperature, using a externally mounted temperature sensor that is always in the shade but allows free passage of ambient air, the whole thing being mounted high enough to ignore hot pavement et al. This should yield a clean enough signal to control the fans et al with perfect reliability.

Honeywell C7089U1006 Outdoor Temperature Sensor - Household Thermostat Accessories - Amazon.com

dalmatiangirl61 · Jul 12, 2021

Did a google search for "differential temperature controller", most of what I found seemed more applicable to process controls, and was quite expensive. I found the unit below and think it is more along the line of what I need. Your thoughts?
myDTC Differential Temperature Controllers - AE4 Solar Controller

The manual for it
https://www.mydtcstore.com/uploads/3/4/1/2/34122353/simpledtc_user_manual__2_.pdf

Gordon Heaton · Jul 12, 2021

That looks like a great 'ready to go' product.

Greenwud · Jul 13, 2021

Carel makes a temperature controller that has a differential mode. The last time I bought one it was the IR32 series, likely something newer available now.
Easy to program too...

Controlling Shop Temperature - Differential Temperature Switch?

Diamond

Diamond

Diamond

Titanium

Diamond

Titanium

Titanium

Diamond

Diamond

Diamond

Diamond

Titanium

Diamond

Stainless

Diamond

Stainless

Diamond

Titanium

Hot Rolled

Similar threads