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?main_page=product_info&cPath=1&products_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?main_page=product_info&cPath=1&products_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?main_page=product_info&cPath=1&products_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?main_page=product_info&cPath=1&products_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/searchdatacenter/definition/economizer#:~:text=An%20economizer%20uses%20outsid e%20air,or%20computer%20room%20air%20conditioners.

[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.

[Doug Garson]

I think I found the solution (basically what George and Malcom suggested) described in this web site, leave it to the farmers to come up with a solution.
https://farmhack.org/tools/outside-air-exchange-control

https://farmhack.org/sites/default/files/tools/image-gallery/Outside%20Air%20Exchange%20Schematic%20and%20Wirin g%20Diagram_0.jpg

[Malcolm McLeod]

... Not sure I understand why I would not want to exchange the air. ...

I've always considered an Engineer's primary function to be determining how things can go wrong. Then address each of those things in a given design or process.

So how can an 'exchange' air system and food go wrong, and what - or perhaps who - gets hurt? Are you sure a filter will suffice? Even when it's not there?

If you have good answers for these questions (and all the others as well), speed on brother.

[Doug Garson]

I've always considered an Engineer's primary function to be determining how things can go wrong. Then address each of those things in a given design or process.

So how can an 'exchange' air system and food go wrong, and what - or perhaps who - gets hurt? Are you sure a filter will suffice? Even when it's not there?

If you have good answers for these questions (and all the others as well), speed on brother.
I appreciate your concern although I do not understand what the danger is. The food gets exposed to outside air several times onsite, when we unload it from the delivery truck, when we move it from the cold storage to the church basement where it is sorted and bagged, again when some of it is staged outside to be loaded into cars for delivery to our two pop up distribution sites and when it is staged for distribution at our drive thru. We are in a residential area, the air quality is generally good, especially in the winter when the rain keeps the dust down, there are no wildfires or pollen. I don't see any issue with using filtered outside air in the winter to reduce the demand on the air conditioners in the cold room or to replace stale air in the summer. If we had an air exchanger with no outside air entering the room and we had some spoilage there would be no way to vent the bad air. We have this situation now and often wish we could air the room out to get rid of odours from spoilage.

[Bill George]

Its an simple Economizer setup, setpoint controlled by outside air temp. Below the setpoint the outside air kicks in and above the air intake turned off and the AC is allowed to run. OSA thermostat controls the changeover, and one relay NO and NC contacts. The control on the AC controls its temperature. Another control in series with the OSA fan and damper controls it. I have seen just a window AC doing the job, no messing with OSA fans and dampers. Cheap and it works and was in a food warehouse for years keeping the candy cool.

[Doug Garson]

Its an simple Economizer setup, setpoint controlled by outside air temp. Below the setpoint the outside air kicks in and above the air intake turned off and the AC is allowed to run. OSA thermostat controls the changeover, and one relay NO and NC contacts. The control on the AC controls its temperature. Another control in series with the OSA fan and damper controls it. I have seen just a window AC doing the job, no messing with OSA fans and dampers. Cheap and it works and was in a food warehouse for years keeping the candy cool.
Yes we could do it without the outside air fan, adding the fan is intended to save energy by taking advantage of cold outside air in the winter and also give the ability to bring in fresh air when needed year round.

My thinking is, outside air set point 5 C, inside set point (for vent fan) 5 C and Coolbot (AC) set point 6 C. So AC only runs when outside air can't keep room below 6 C.

[Bill George]

Having worked in the commercial HVAC/R field for many years Economizers were common on building A/C units But they always took OSA humidity into the switching factor. Very few Walk in coolers used outside air primarily because of the contamination factor, even filtered air was not clean enough for some storage. I perhaps worked on one in those 30 years, not worth the expense installing and cleaning, filter changes and other maintenance.

[Keegan Shields]

Doug, you have industry professionals on this thread telling you not to use outside air for a whole host of reasons. The fact that what you are proposing isn’t standard practice is another important data point. Don’t try to reinvent the wheel.

If it’s cold outside, then your walk-in refrigerator isn’t consuming much power to keep the room cold. The easiest way to save your organization money is to increase the rooms R-value.

[Doug Garson]

Doug, you have industry professionals on this thread telling you not to use outside air for a whole host of reasons. The fact that what you are proposing isn’t standard practice is another important data point. Don’t try to reinvent the wheel.

If it’s cold outside, then your walk-in refrigerator isn’t consuming much power to keep the room cold. The easiest way to save your organization money is to increase the rooms R-value.

I hear the recommendations not to use outside air but I've yet to hear a specific reason. I don't understand how bringing in outside air in a residential area is a risk. Using air exchanges to offset the load on the A/C unit may not be common in commercial operations but from what I see online it is common practice on many farms. The whole cold room idea using air conditioners and Coolbots comes from the same farm DIY community. We are increasing the rooms R value to R20 using rigid foam insulation.
This project is months away as we wait for our grant application to be approved. If in that time I learn of a tangible danger in the ventilation idea I'll delete it from the project. I'd really be interested in knowing what the specific danger is. At the moment it represents about 5% of the overall project budget so it can be easily deleted although some method of bringing fresh air to reduce odours seems like a good idea even if not an automated system to reduce A/C load.

[Maurice Mcmurry]

I helped build two coolers inside a ship and another in a restaurant. We were directed to make them air tight. I was told air infiltration would allow humid air that could contain pollen, soot, fumes, etc. to enter the cooler. Humidity= latent heat. When humid air gets in the load goes up. Another obstacle is that when the outdoor temperature becomes a disadvantage you need thick insulation and a vapor barrier between the two environments.

[Bill George]

If you think Residential air is clean take a good look at the air filter in your house. If a WI Cooler has smells, something has spoiled. The act of refrigeration condensing water on the evaporator coils removes a lot of odors and humidity besides cooling the space.

[Maurice Mcmurry]

I applaud efforts to maximize efficiency. The triple function heat pump that heats water + heats or cools the house with one unit that has economizers and heat recovery are a step in the right direction. We need a 4 function unit that takes care of refrigeration too.

[Bill George]

BTW what he wants to do is widely used in most northern climates. Economizer systems for air conditioning can be ordered as a option on most all RTUs and can be designed to be installed on AHUs used for heating and cooling. For food storage a closed system using water and glycol mix with one coil in the OSA and the other in the Space to be cooled using a pump to transfer the fluid, and fans at both ends. Pump has a check valve of course to prevent un-needed fluid movement when the pump is turned off by either the space or OSA Tstat.

[Keegan Shields]

I hear the recommendations not to use outside air but I've yet to hear a specific reason. I don't understand how bringing in outside air in a residential area is a risk. Using air exchanges to offset the load on the A/C unit may not be common in commercial operations but from what I see online it is common practice on many farms. The whole cold room idea using air conditioners and Coolbots comes from the same farm DIY community. We are increasing the rooms R value to R20 using rigid foam insulation.
This project is months away as we wait for our grant application to be approved. If in that time I learn of a tangible danger in the ventilation idea I'll delete it from the project. I'd really be interested in knowing what the specific danger is. At the moment it represents about 5% of the overall project budget so it can be easily deleted although some method of bringing fresh air to reduce odours seems like a good idea even if not an automated system to reduce A/C load.

The CoolBot units require an airtight room and an R value of 25.

I don't know of any commercially available refrigerator that vents in outside air. Maybe someone can post an example.

Modern HVAC systems (sans economizer) cool indoor air and do not pull air from outside to cool (or heat). I remember reading during the early days of COVID that this was a result of the Federal energy efficiency standards which have increased over time.

One way to increase the efficiency of HVAC systems is to seal all of the air leaks from the outside/attic and only cool/heat inside air.

Economizers made sense for something like a datacenter which is actively producing heat regardless of the outside air temperature.


How much efficiency will you really gain by using cold outside air? When its cold enough outside to pipe air into your cold room, your mini split will likely be off the majority of the time... so not much - unlike our datacenter example where the daily by product is heat.

[Bill Dufour]

In home refrigerators humidity controls exist so produce does not dry out too fast. No idea if they really make any difference or are just a selling point. Temperature differential might be a good search term. Also lag and lead.
BilL D

[Bill Dufour]

Anticipation is another term used in the industry regarding undershoot/overshoot and hunting. A home thermostat will probably undercool or over heat by 3 degrees F to reduce constant cycling as it hunts for the set temperature. A cooler often has to wait 3-5 minutes before it will restart. This is to allow head pressure to drop so it does not start under load. Not a furnace issue unless it is a heat pump.
Bill D

[Rob Luter]

I hear the recommendations not to use outside air but I've yet to hear a specific reason. I don't understand how bringing in outside air in a residential area is a risk. Using air exchanges to offset the load on the A/C unit may not be common in commercial operations but from what I see online it is common practice on many farms. The whole cold room idea using air conditioners and Coolbots comes from the same farm DIY community. We are increasing the rooms R value to R20 using rigid foam insulation.
This project is months away as we wait for our grant application to be approved. If in that time I learn of a tangible danger in the ventilation idea I'll delete it from the project. I'd really be interested in knowing what the specific danger is. At the moment it represents about 5% of the overall project budget so it can be easily deleted although some method of bringing fresh air to reduce odours seems like a good idea even if not an automated system to reduce A/C load.

I suspect your local Health Department (or whatever it's called in Vancouver) would be happy to educate you.

[Doug Garson]

Thanks for the advice on the ventilation question, I'm following up with my contractor.

[Edward Weber]

I've not followed this in days but many/most heat exchangers have a recirculate fiction, where no air is exhausted or brought in, simply "recirculated". +1 on proper insulation

[Bill George]

Thanks for the advice on the ventilation question, I'm following up with my contractor.

You need to talk to a commercial refrigeration company, not a HVAC person that just does A/C. I Did the commercial refrigeration for over 30 years and then taught the same for 12 more years.

[Malcolm McLeod]

... although I do not understand what the danger is. ...

So perhaps defer to a professional who does understand.

[Doug Garson]

So perhaps defer to a professional who does understand.
I gladly would if they would explain what the danger is. I am an Engineer so I think I'm capable of understanding a technical issue if someone tells me what the danger is as opposed to just saying don't do it. On more than one occasion in my career I've been told "you can't do that" by someone who claims to be knowledgeable in a field and debunked the reason. So if you know why it shouldn't be done, please share the technical reason. I doubt you are the type who would blindly take advice from someone just because they claim to know what they are talking about if they weren't able to explain why. I'm trying to do my due diligence so I can make an informed decision

[Malcolm McLeod]

... So if you know why it shouldn't be done, please share the technical reason. ...

I know only that I've never seen it done and that you've rationalized a number of 'technical reasons' in this thread. So perhaps seek the advice of a Horticultural Food Scientist or similar. At the risk of being Captain Obvious, a woodworking forum is perhaps not the place to seek such a professional.

Or, perhaps just speed on? Your inertia seems well defined.

Out.