Anyone with temperature controller experience?

[Doug Garson]

I'm volunteering for a food bank and trying to set up a cold room to store produce and other perishables. The main cooling will be done by a pair of air conditioners controlled by a Coolbot which enables the air conditioners to cool the room down below the usual lower limit for air conditioners (around 16 C). Neat device and they have a website with lots of useful information for this application. https://www.storeitcold.com/build-it/
In the winter, when the outside temperature is below the desired cold room temperature (around 5C), we'd like to blow the cold outside air into the room and exhaust the warmer room air out to reduce the load on the air conditioners. I need a controller with 2 temperature probes, one inside and one outside that will turn the fans on when the outside temperature is below 5 C and the inside temperature is above 5 C. Any suggestions?

[stephen thomas]

I'm not very good at it, and have to re-learn a lot every time i do it, but have built a couple heat treat furnaces, and currently a very large convection oven for blowing plexiglass canopies (& sometimes cooking wood to kill creepy-crawlies )

The controller on the oven has 2 probes so i can monitor and control both the hot side, and the chamber.

These guys have a forum, and they are (or were a couple years ago) very personable and helpful on the phone. Geared to do-it-yourselfers. They want you to be successful. And the products are top-notch and economical for the quality and features.

https://www.auberins.com/index.php?m...roducts_id=464

I am not in the shop right now, but this one "looks" like the controller on my oven:
https://www.auberins.com/index.php?m...roducts_id=464

Read a bit, browse the forum, and call them up for advice for your low - temp app.

smt

[Edward Weber]

Sounds like what you really need is an air-to-air heat exchanger

[Doug Garson]

Sounds like what you really need is an air-to-air heat exchanger

Not sure an air to air heat exchanger would be applicable in my case. Air to air heat exchangers recover heat from exhaust air to heat incoming air and reduce heat loss. I'm trying to increase heat loss. I got the idea from a Youtube video which just used two fans with backdraft dampers and a single controller to turn the fans on when the room was above the setpoint. I'm trying to take it to the next level and automate it to only turn the fans on when it is cold enough outside since in our climate, in the winter, it could be below 5 C part of the time (overnight) and above 5 C by mid day or cold enough one day and too warm the next.

[Doug Garson]

I'm not very good at it, and have to re-learn a lot every time i do it, but have built a couple heat treat furnaces, and currently a very large convection oven for blowing plexiglass canopies (& sometimes cooking wood to kill creepy-crawlies )

The controller on the oven has 2 probes so i can monitor and control both the hot side, and the chamber.

These guys have a forum, and they are (or were a couple years ago) very personable and helpful on the phone. Geared to do-it-yourselfers. They want you to be successful. And the products are top-notch and economical for the quality and features.

https://www.auberins.com/index.php?m...roducts_id=464

I am not in the shop right now, but this one "looks" like the controller on my oven:
https://www.auberins.com/index.php?m...roducts_id=464

Read a bit, browse the forum, and call them up for advice for your low - temp app.

smt

Thanks, I'll have a look and see if they have a solution.

[Edward Weber]

Not sure an air to air heat exchanger would be applicable in my case. Air to air heat exchangers recover heat from exhaust air to heat incoming air and reduce heat loss.

They work both ways

[Doug Garson]

They work both ways

OK but I'm looking for a controller to turn the fans off and on. A heat exchanger is just a piece of hardware, not a controller. A pair of fans with or without an air to air heat exchanger a can do what I want but in either case I need a controller to turn the fans off and on.

[John Stankus]

There are automatic fan systems for greenhouses that are temperature triggered.
Depending on how sophisticated you want to get a simple thermistat controlling a solid state relay for your fans. Omega Engineering (Omega.com) is one source for thermostatic switches. You may want to set up an outside Thermostatic switch and an inside (if the outside temp is too high, you don't dump extra heat into the area).

I think Edward's comment on Air to Air heat exchanger is not efficiency, but rather isolating the the air masses. (The following is conjecture with no experience) Is there an issue dumping outside air, in a food storage area from a health and contamination standpoint? I'm thinking mold, pollen, bacteria etc. (again no real knowledge or understanding, other than whatever the plan it may be useful to have the County Health Dept make sure it meets whatever critieria they may have)

John

[Bill Dufour]

Any makeup air should go through some filters to keep out mice, snakes, bugs and flying insects. Exhaust air ducts should also be screened to keep out bad stuff when the fan is off.The heat exchanger does that and keeps the humidity inside more stable.
Bill D

[Doug Garson]

I'll look at automated greenhouse systems, our contractor recommends looking at Honeywell controllers. I suspect any instrument tech could put together the necessary hardware with one hand tied behind their back, it's outside my area of expertise so I'm struggling.
Good points on screening and filtering the air to keep out critters and dust and mould etc., our contractor brought that up also. We will be including screens for both vents and a filter for the incoming air. I'm thinking we could run the incoming air into a plywood box with a replaceable furnace filter.

[Rob Luter]

I'm volunteering for a food bank and trying to set up a cold room to store produce and other perishables. The main cooling will be done by a pair of air conditioners controlled by a Coolbot which enables the air conditioners to cool the room down below the usual lower limit for air conditioners (around 16 C). Neat device and they have a website with lots of useful information for this application. https://www.storeitcold.com/build-it/
In the winter, when the outside temperature is below the desired cold room temperature (around 5C), we'd like to blow the cold outside air into the room and exhaust the warmer room air out to reduce the load on the air conditioners. I need a controller with 2 temperature probes, one inside and one outside that will turn the fans on when the outside temperature is below 5 C and the inside temperature is above 5 C. Any suggestions?

I'd suggest you consult an HVAC company locally. There are similar applications in service now. No need to re-invent the wheel.

[Maurice Mcmurry]

I have read several discussions about this. The answer I see most often is that "Air to air is is not used in refrigeration" for the reasons listed above. The temperature differential in winter is often taken advantage of in a gas or liquid cycle. Heat recovery is a common approach to utilizing winter temperature differentials to maximize efficiency. For example the walk in cooler is allowed to run all winter and the refrigeration loop is used as a heater.

Most applications for "Economizer" are geared towards HVAC but the principles are used in refrigeration too.
https://www.techtarget.com/searchdat...0conditioners.

[George Yetka]

You have the fan system in place already? Fan with a gravity damper, and a seperate overpressure damper to exhaust? if this is the case you need something to turn on the fan with outside temp below 5. A stat can do that assuming the fan has a relay for start stop. You will need outside air temp sensor wired to the stat as remote temp sensor , a stat set to heat at 5C reading the remote sensor that way it keeps trying to run until it makes its 5C.

[Malcolm McLeod]

I don't know of a packaged/integrated 'controller' to perform this, but then I've never needed to shop for any such device this simple.

And this is a dirt-simple boolean logic problem: wire 2 t'stats in series (1 outside, closes <5C; 1 inside, closes >5C) with the series-ed output energizing a relay/contactor/starter (sized to your fan(s) load). When both t'stats 'see' the appropriate temperatures, the fan turns on. Match the t'stats' contact amp rating to the coil rating of the relay.

I have done a considerable amount of automation work in the food/beverage industry and I would strongly recommend following the suggestion to use an air-to-air heat exchanger* for the reasons stated. I would also recommend that the relay incorporate both NO contacts (for the fan) and NC contacts (to disable the 'regular' cooler). Then add a switch to enable/disable the entire fan circuit.

If you want to build a HMI for visualization, look at a Red Lion Graphite controller. You can build graphics and write your own logic, add analog IO for T/Cs, or RTDs, or temp transmitters, and/or discrete IO for t'stats. All in a relatively affordable package.

*- Just realized this may not be obvious - you don't want to 'exchange the air', rather you want to keep the inside air in and the outside air out. Plumb the exchanger ducts accordingly.

[Doug Garson]

Thanks for the input, I'm following up on some of the suggestions and still waiting for a response from Inkbird. Project won't be going ahead until June or July unfortunately as we are waiting for a grant to be approved.

Not sure I understand why I would not want to exchange the air. Seems to me if we filter the incoming air to eliminate mold, pollen etc. we will have a cheaper and more flexible system. For example we could use the system manually in the summer to control humidity or just refresh the stale air especially if we get some spoilage.