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lawrence_craig 11-05-2021 23:49

Digital Thermostat in Fridge
 
I have installed one of the digital thermostats in my fridge running off a Danfoss BD35 with a air cooling unit (Bav46 2007 standard unit) as the metal thermostat failed.

I have read on Richard Kollmanns site that the thermostat should be measuring the temperature of the evaporator plate and not the box temperature. Therefore should I place the temperature probe inside the air cooling unit inside the fridge? Where abouts on air cool unit should I place it? Top (inlet), Bottom (outlet) or middle?

Also any hints on upgrading this system would be appreciated. I have heard adding a plate evaporator in the fridge improves performance Vs the air cooled unit but unsure of the logic behind this.

Thanks a lot

OzeLouie 12-05-2021 01:26

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by lawrence_craig (Post 3405608)
I have installed one of the digital thermostats in my fridge running off a Danfoss BD35 with a air cooling unit (Bav46 2007 standard unit) as the metal thermostat failed.

I have read on Richard Kollmanns site that the thermostat should be measuring the temperature of the evaporator plate and not the box temperature. Therefore should I place the temperature probe inside the air cooling unit inside the fridge? Where abouts on air cool unit should I place it? Top (inlet), Bottom (outlet) or middle?

Also any hints on upgrading this system would be appreciated. I have heard adding a plate evaporator in the fridge improves performance Vs the air cooled unit but unsure of the logic behind this.

Thanks a lot

This depends on the type of evaporator used. Can you picture the evaporator and post here?
First thing to understand about the digital controller is that SET is the actual cut out temperature while HYS is a number of degree of differential, the number of degree rise above SET before cut-in occurs...

If the evaporator is the fan forced type then it is important to place the probe on the cooling coil preferably where the last cooling occurs. With SET value as a negative temp value, the HYS (number of degree differential) must be so that re-start occurs after coil has warmed sufficiently to defrost after each run cycle. (Usually about +3C) So if SET (cut off)is say minus 10C then HYS needs to be 13C. (Off at minus 10C restart at +3C)

If the evaporator is a static cold plate then place the bulb midway in the cabinet away from the evaporator but recommend putting it into a small sealed container of liquid. That will better represent product temperature and considerably reduce the number of inefficient start ups per day . (Runs longer, off longer)

lawrence_craig 12-05-2021 02:06

Re: Digital Thermostat in Fridge
 
It is the cooler with an air fan that forces the box air through a plate heat exchanger

https://imgur.com/PSVPUjP

OzeLouie 12-05-2021 02:36

Re: Digital Thermostat in Fridge
 
OK you need to find a spot on the cooling coil that is the last area to lose frost when compressor is off and put the probe to read the temperature there. Set controller as described above for a 'fan forced evaporator. Best to allow the fan to run constantly.

lawrence_craig 12-05-2021 03:56

Re: Digital Thermostat in Fridge
 
Interesting how you mention the fan should run constantly. The standard unit has the fan turning on/off in line with the compressor, however, thinking about it, there is not much harm in it running constantly is there? Low power usage and keeps the air circulating over the plates to exchange residual temperature. Is this your conclusion as well?

OzeLouie 12-05-2021 04:07

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by lawrence_craig (Post 3405665)
Interesting how you mention the fan should run constantly. The standard unit has the fan turning on/off in line with the compressor, however, thinking about it, there is not much harm in it running constantly is there? Low power usage and keeps the air circulating over the plates to exchange residual temperature. Is this your conclusion as well?

Yes and once the thermostat settings are set then it will self defrost each off cycle

Richard Kollmann 12-05-2021 05:28

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by lawrence_craig (Post 3405608)
I have installed one of the digital thermostats in my fridge running off a Danfoss BD35 with a air cooling unit (Bav46 2007 standard unit) as the metal thermostat failed.

I have read on Richard Kollmanns site that the thermostat should be measuring the temperature of the evaporator plate and not the box temperature. Therefore should I place the temperature probe inside the air cooling unit inside the fridge? Where abouts on air cool unit should I place it? Top (inlet), Bottom (outlet) or middle?

Also any hints on upgrading this system would be appreciated. I have heard adding a plate evaporator in the fridge improves performance Vs the air cooled unit but unsure of the logic behind this.

Thanks a lot

You are confusing a heat induction evaporator thermostat that is not self defrosting used to keep box temperature zone at below freezing all the time. While a fan air convection evaporator relies on a thermostat settings to defrost evaporator on each cycle of compressor. Icebox convection conversion Fan units on boats are really for drink cooler boxes and not refrigerator temperatures. When convection evaporators are used on true separate zone temperature refrigerators there will be a heat cycle daily to defrost evaporator. Yes you can run fan air across convection evaporator 24/7 but box temperature will still be no more than a good cooler.

skipgundlach 12-05-2021 09:04

Re: Digital Thermostat in Fridge
 
My first freezer/fridge was a Frigoboat (details in excruciating detail elsewhere in CF).

It had 2F hysteresis in both freezer and refrigerator, measuring content, not plate, temperatures.

It worked a very nice treat, until it didn't.


Both boxes have NO/NC magnetic contacts which control the circulation fans (one each box) and lights, which come on when the door is open, turning off the fan/s - the compressor is not interrupted if it's running when the freezer is opened; that's been a very nice feature at minimal cost.

I now have a Sea Frost evaporator (3, in series) plate system with, as seems the industry norm, the probe for the on/off at the bottom of the last plate, with a 6.5F hysteresis (per mfr instruction) - but also has a box thermometer showing what is happening in the box.

Our temperature in the freezer varies VERY widely as a result. I'm not sure that's of issue (I mean, every other manufacturer than FBoat seems to get the on/off probe on a plate, so it must be appropriate).

Our reefer box, supplied by a spillover fan controlled by another digital thermostat, with the FBoat 2F hysteresis, maintains its temperature very closely other than when we warm load it, in which case it comes down until it cycles and then is fine again.

Why wouldn't I want my freezer controlled as it was before (box temp 2F hysteresis)? Seems to me that a more even (mine can vary by 20F!) box temperature would be desirable...

zstine 12-05-2021 09:40

Re: Digital Thermostat in Fridge
 
Youtube channel 'sailing too short' recently did a digital temp upgrade on their Seafrost refrigerator and freezer, show linked below. He moved the temp probe from the cold plate into the box area and seems happy. I have no personal experience, but you may gain something from watching....



https://www.youtube.com/watch?v=6261JqjJ6Io

Sailor647 12-05-2021 11:20

Re: Digital Thermostat in Fridge
 
We have two separate Frigoboat K-50 keel-cooled systems, one for the refrigerator (7 cubic feet) and one for the freezer (5 cubic feet). We upgraded to Carel electronic thermostats after the standard manual Frigoboat systems quit working - twice.

https://www.carel.com/product/ir33

The Carel temperature sensors (probes) dangle about 2 inches from the top of the boxes near the back. They aren't touching the evaporators or anything else except air.

I can tell you from experience that these thermostats made a huge difference in keeping the boxes at temperature AND reducing our energy usage. HUGE decrease in power consumption at anchor. The freezer makes 6 ice trays daily and keeps ice cream frozen. Plus, we can see the temperature of each box at a glance.

bcboomer 12-05-2021 12:50

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by Sailor647 (Post 3405898)
We have two separate Frigoboat K-50 keel-cooled systems, one for the refrigerator (7 cubic feet) and one for the freezer (5 cubic feet). We upgraded to Carel electronic thermostats after the standard manual Frigoboat systems quit working - twice.

https://www.carel.com/product/ir33

The Carel temperature sensors (probes) dangle about 2 inches from the top of the boxes near the back. They aren't touching the evaporators or anything else except air.

I can tell you from experience that these thermostats made a huge difference in keeping the boxes at temperature AND reducing our energy usage. HUGE decrease in power consumption at anchor. The freezer makes 6 ice trays daily and keeps ice cream frozen. Plus, we can see the temperature of each box at a glance.

Is this any different in function than the Inkbird control?
https://www.amazon.ca/Inkbird-Heatin...0848966&sr=8-5

lawrence_craig 12-05-2021 12:52

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by Richard Kollmann (Post 3405697)

You are confusing a heat induction evaporator thermostat that is not self defrosting used to keep box temperature zone at below freezing all the time. While a fan air convection evaporator relies on a thermostat settings to defrost evaporator on each cycle of compressor. Icebox convection conversion Fan units on boats are really for drink cooler boxes and not refrigerator temperatures. When convection evaporators are used on true separate zone temperature refrigerators there will be a heat cycle daily to defrost evaporator. Yes you can run fan air across convection evaporator 24/7 but box temperature will still be no more than a good cooler.

Ah makes sense, thanks.

If you are saying that it is an drink cooler and not refrigerator, what can I do to upgrade it to a refrigerator? Will a plate evaporator be more efficient?

To be clear, it is a Danfoss BD35 with air cooled condenser and the evaporator in the fridge is a fan air cooled as you suggest.

OzeLouie 12-05-2021 15:39

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by lawrence_craig (Post 3405958)
Ah makes sense, thanks.

If you are saying that it is an drink cooler and not refrigerator, what can I do to upgrade it to a refrigerator? Will a plate evaporator be more efficient?

To be clear, it is a Danfoss BD35 with air cooled condenser and the evaporator in the fridge is a fan air cooled as you suggest.

Lawrence, any suggestion that digital thermostats operate less than the old mechanical type or that 'forced air cross finned cooling coils are only suitable for 'drink coolers, is simply wrong! Just follow my earlier instructions.

Digital thermostats are far more versatile, accurate, more easily programmed to SET point and HYSteresis required and have the bonus of temperature read out. (The digital controller we use is also water proof!) They can do everything and more that the vague, antiquated mechanical ones ever did!

Now regards the misinformation that the forced air cooled evaporator is only suitable for a 'drinks cooler!!!
Nearly every one of the worlds millions of coolrooms or commercial refrigerated cabinets use this exact same forced air cooling method operating as refrigerators at 1C to 4c cabinet temp (Forced draft coil) and they seem to work OK!!!

bcboomer 12-05-2021 17:25

Re: Digital Thermostat in Fridge
 
We have an air cooled BD35 and evaporator with no fan to cool our fridge only converted ice box.

Will an digital controller make it any more efficient?

OzeLouie 12-05-2021 17:47

Re: Digital Thermostat in Fridge
 
Quote:

Originally Posted by bcboomer (Post 3406119)
We have an air cooled BD35 and evaporator with no fan to cool our fridge only converted ice box.

Will an digital controller make it any more efficient?

Yes it will if set up correctly.. Best to locate the sensor sealed in a small amount of liquid so that it best represents product temperature. This will also reduce daily start ups improving efficiency.

For a start put the SET value (cut off) at say +1C and the HYS at say 4C This will cause the unit to cut off at SET +1C and rise by HYS 4C to cut in again at +5C. Adjust warmer or colder later if needed.

Note: SET is an actual temperature setting cut-out while HYS (or differential) is the number of degree the temp rises above the SET value before starting up again.


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