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Old 05-03-2020, 07:51   #166
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Re: The Worst pleasure boat refrigeration.

Quote:
Originally Posted by ayates View Post
The OEM thermostat is on the fridge evaporator, and the freezer is along for the ride.

The top wave form is the current drawn by the compressor, against the secondary Y axis. The other two wave forms are the fridge and freezer temperatures, against the primary Y axis. All three wave forms are synced to the time azis.

Basically the thermostat continuously cycles the compressor, even when the temperature of the fridge is way too high. As soon as the evaporator gets cold, the compressor is turned off until the evaporator absorbs heat from the fridge. As it has little thermal mass, it doesn't take long to warm up. The duty cycle decreases as the fridge cools.


Alan.
Interesting results. It looks like you're seeing about a 3* C difference between fridge and freezer with the fan. Last year, I was seeing an 18 - 19* C difference with the stock condenser fan, no evap fan and just some added insulation. I've since added a little more insulation to the outside of the box in a few areas.

What size fan are you using and is it always on or only running when the compressor does? I'm using a Noctua NF-A4x20 FLX (moves 5.5 cfm) blowing across the middle of the fridge evaporator, wired to run constantly. Depending on results, I can slow the fan down to reduce airflow.

I'm thinking that if the freezer stays too warm with the fridge at the correct temp, I'll try reducing the evap fan speed to allow a slightly colder thermostat setting, or possibly adding a fan in the freezer as well (although due to the much larger evaporator I'd expect a smaller effect). I can also try adding some extra insulation to just the lower part of the box if I can find a little extra space around it. I'm definitely going to slide a piece of insulation in between the condenser coil and the bottom of the box to reduce heat infiltration into the bottom of the freezer in hopes of keeping it colder. Realistically, if I can keep the freezer around 10* F / -12* C I'll be plenty happy with it.

As far as the cycling when the fridge isn't cold enough, I haven't found mine to do that excessively, but I also haven't instrumented it like you have. I'm hoping the evap fan will reduce that by keeping the evap temp and box temp closer together. If it does cycle like that and isn't having trouble keeping up on hot days, I'll try dropping the compressor speed (currently at 3500 rpm). Running the evap warmer with the fan should increase heat transfer capacity at a given compressor speed, so it's possible that the compressor ends up effectively over-sized as a result and would need a speed reduction. Or more airflow across the evap to increase heat transfer and prevent the cycling.
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Old 05-03-2020, 09:06   #167
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Re: The Worst pleasure boat refrigeration.

Quote:
Originally Posted by ayates View Post
I ran numerous tests with a NovaKool RFU9000 fridge/freezer; 9.1 cu ft of which 2.5 cu ft was freezer. Normal thin evaporator plates.

This was the "best" scenario where the fridge did not freeze, but got a low as possible. Ambient temperature was 20C. The fridge was loaded with 4 litres of water at room temperature (20C). Power consumption was ~ 50 AH/24 hour period.

I could get a much faster cool down with a fan on the evaporator, the compressor would run continuously during that time, but the fridge would settle below freezing.


Allan.
Your graphic display is interesting and not typical of normal applications because of 4 liters of warm water with water never reached an equilibrium with box temperature. During this temperature transition the graph shows unusual inefficient cycling. It is impossible to interrupt graph at its present size maybe your logger software will allow modifying to see only one of the single compressor cycles much larger.

Once compressor is stabilized cycling, I counted cycled of on and off 4 times per hour. It is not unusual to over power the evaporator’s trying to lower an excessive heat load but what concerns me is the refrigerant pump down time on each compressor start up. Looking close at graph peaks they seam to each be a typical 10 minute first start up of the day. I would expect this pump down to last no longer than one minute unless compressor was running at low speed. I do not know if the start up pump down time can be reduced but adding air flow across too small of a evaporator will increase efficiency by lengthening compressor run times.

If better evaporator cooling is reach Yes compressor can run with thermostat set as long as necessary to achieve your product or box temperature desired using less energy than cycling compressor would.

When using these small 12 volt compressors the application engineer who may be the person buying and installing unit should select evaporator size that is compatible with boxes normal expected heat load. If a compressor cycle time of two per hour is achieved system efficiency will be as good as it gets.
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Old 05-03-2020, 09:25   #168
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by rslifkin View Post
On my Novakool RFU9000, the thermostat cycles on fridge evap temp. The freezer is along for the ride (with a significantly bigger evap than the fridge). That's why I'm concerned I may see higher freezer temps with an evap fan in the fridge (fridge evap will be warmer for a given fridge box temp, so t-stat set warmer to maintain, meaning freezer may be warmer).

From AYATES graphs and your observations the controller may have some kind of AEO. Danfoss has a number of these tweaked for the size of compressors in use. The three I have looked at have been included. It seems as long as the compressor speed and time of operation can be changed to accommodate either the change in thermal load or the matching/mismatch of the hardware they are installed in, they are the cats meow. The concern about one plate getting too cold or warm (and if true) may be the AEO's inability to correct using time of compressor operation or compressor speed the imbalance and/or thermal load introduced by the addition of fans. From what I gather from reading the little bit of info given to us by Danfoss is that the algorithm seems to be matched to the system and tweaking is done by speed and time only. I wonder if the system were severely mismatched (meaning longer run times than the max allowed) what the AEO would do. If it defaults to max time then it has to establish a DC (unless of course it runs continously) and if the DC is incapable satisfying the thermostat???? Maybe A64 has some answers, I think he uses one.
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Old 05-03-2020, 09:31   #169
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Re: The Worst pleasure boat refrigeration.

My fridge definitely doesn't have the AEO module, as I've got the 12v / 120v AC/DC control module, which doesn't come in an AEO version. Based on the resistor value installed, it's running at a constant 3500 RPM.
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Old 05-03-2020, 11:02   #170
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Re: The Worst pleasure boat refrigeration.

If you understand operation of AEO control modules they are of no value if evaporator is too small for systems condensing units output. AEO modules are also not recommended for eutectic holdover plates because on beginning warm start it takes 40 minutes for compressor to reach maximum output.
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Old 05-03-2020, 12:46   #171
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Re: The Worst pleasure boat refrigeration.

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It is impossible to interrupt graph at its present size maybe your logger software will allow modifying to see only one of the single compressor cycles much larger.
Here is the data zoomed in for both the cool down phase, and the equilibrium phase. The is for the OEM thermostat set at #4 with no evaporator fan. i.e. the standard OEM configuration (except for additional insulation surrounding the unit (other than the door)).


Allan.
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Old 05-03-2020, 12:53   #172
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Re: The Worst pleasure boat refrigeration.

It's interesting that you're showing amp draw that high. I typically showed similar numbers very briefly at the start of a cycle, but mine was typically down to about 3.8 - 4 amps by the time it cycled off the couple of times I checked it (and to me, that indicates low evap temperature and that it's not loading the compressor well, which hopefully the fan will help).
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Old 05-03-2020, 14:02   #173
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by rslifkin View Post
It's interesting that you're showing amp draw that high. I typically showed similar numbers very briefly at the start of a cycle, but mine was typically down to about 3.8 - 4 amps by the time it cycled off the couple of times I checked it (and to me, that indicates low evap temperature and that it's not loading the compressor well, which hopefully the fan will help).
Amps indicate work being done only at that time.

As temperature in box gets colder volume of heat removed will be less so amps of work accomplished will also be less.


A Danfoss BD compressor delivering 500 Btu in a 70 degree F box will produce only 200 plus Btu at zero degree F. Compressor manufacturers all provide Btu versus evaporator temperature as well as amperage charts. Changing of evaporator temperature or compressor speed affects amperage.
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Old 05-03-2020, 15:19   #174
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Re: The Worst pleasure boat refrigeration.

Quote:
Originally Posted by ayates View Post
Here is the data zoomed in for both the cool down phase, and the equilibrium phase. The is for the OEM thermostat set at #4 with no evaporator fan. i.e. the standard OEM configuration (except for additional insulation surrounding the unit (other than the door)).


Allan.
I'm thinking the OEM thermostat is the capillary style, can they actually have less than 3 deg of hysteresis? Your temps move less than 3 deg for a satisfied thermostat to a demand call. My cap style OEM had a 14 deg hysteresis. I have included my BD50F spec sheet and it falls in line with yours (assuming your plate is somewhere near zero degrees F) If I'm reading correctly, the DC is 66% which puts the consumption at 79 daily is that anywhere near published data? Before I reworked my box, I bled energy to the tune of 1.8 deg F/min. I have included a pic of mine


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File Type: pdf Danfoss BD50F _03-05-2020_.pdf (1.27 MB, 19 views)
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Old 05-03-2020, 15:20   #175
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by Q Xopa View Post

I have a portable Engel and an installed Cool Blue cold plate unit. So I guess I have an each way bet.

Your Cool Blue will be orders of magnitude more efficient, I mean blow it out of the water more efficient.
I too have similar systems, average amp draw on my Cool Blue is 4 ish amps once everything is cold, my Engel runs about 3 amps. Now the Engel is run colder as a deep freeze the Cool Blue is a spillover.
The Engle is 1.4 cu ft. The Cool Blue is 14 cu ft. Yes the Cool Blue ten times as big and only draws just a little more, but don’t forget it’s not as cold either, but still, ten times the capacity for only a little more power is huge.

Now this doesn’t mean the Engle is junk, it’s operating with many disadvantages, due to space etc I’m sure its condenser is smaller than optimum and the thing only has about 1” of insulation. Remember people want a big interior volume in a cooler size box, and that kills it.

Plus we run into a size issue, I believe it’s covered by the square cube ratio, you can double the interior volume, but not even come close to doubling the size of the box, it’s why a 16” Pizza contains a whole lot more Pizza than a 12”
So the larger the box size you have the more efficient it’s going to be based on size, because it has less exterior wall per cu ft to have to insulate.

Portables have lots of advantages, they can easily be replaced when necessary for a fraction of the price of a built in, and with no work, unplug and plug in the new one.
But efficient, they aren’t, they can’t be, not with the limitations that’s placed on them.
So if you go the portable route, be sure you can feed the things.
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Old 05-03-2020, 15:39   #176
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by ayates View Post
Here is the data zoomed in for both the cool down phase, and the equilibrium phase. The is for the OEM thermostat set at #4 with no evaporator fan. i.e. the standard OEM configuration (except for additional insulation surrounding the unit (other than the door)).


Allan.
Hope we here if a capillary style thermostat can be that tight. If not what is causing the high DC because it sure doesn't seem your bleeding energy!


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Old 05-03-2020, 16:48   #177
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Re: The Worst pleasure boat refrigeration.

OEM thermostats that control evaporator temperature always have wide range off and on differentials 15 to 20 degrees. The wide differential provides a very cold evaporator and the desired box temperature within 3 degrees. So your box temperature can be where you want it and because the thermo condition of every box is different these thermostat do not display temperature. If OEM thermostats did show temperature they would never be correct. Hopefully after installing this thermostat a mid range number on dial will provide closed to your desired box temperature.
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Old 05-03-2020, 17:11   #178
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by Richard Kollmann View Post
OEM thermostats that control evaporator temperature always have wide range off and on differentials 15 to 20 degrees. The wide differential provides a very cold evaporator and the desired box temperature within 3 degrees. So your box temperature can be where you want it and because the thermo condition of every box is different these thermostat do not display temperature. If OEM thermostats did show temperature they would never be correct. Hopefully after installing this thermostat a mid range number on dial will provide closed to your desired box temperature.

Richard, so are you saying that at the sense point the temperature is changing the prototypical 15 to 20 (to get the internal delta P) but it translates to only 3 degrees in free air. My data--14 deg of hysteresis with the same delta T on a free air temp probe. If the temp probe has to be attached to food or otherwise some form of mass to see only 3 deg of change then OK. If you look at the data maybe the probe is in the water because the temp slopes are delayed relative to the respective on/off compressor time points.



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Old 05-03-2020, 18:01   #179
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Re: The Worst pleasure boat refrigeration.

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If you look at the data maybe the probe is in the water because the temp slopes are delayed relative to the respective on/off compressor time points.
Note sure if you were referring to my measurements or not. But my temperature probes were free air. You can see small boxes in this photo, along with the evaporator fan, and a 4 litres of frozen water in the freezer to provide some mass to be more realistic.


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Old 05-03-2020, 18:10   #180
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Re: The Worst pleasure boat refrigeration.

Interesting placement for the evap fan. I mounted mine off to the side and the drip tray blowing across the evap.
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