Anyone with temperature controller experience?

[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

[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