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Old 20-10-2017, 15:19   #1
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Danfoss BD35/50 sizing?

I have a couple extra compressors on board BD35 and BD50..

In the box we have a ISOTHERM cooling plate.

What would be the best compressor we should use?
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Old 20-10-2017, 17:54   #2
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Re: Danfoss BD35/50 sizing?

Assuming box is well-insulated

and the plate is small enough to be charged by the smaller size compressor

Then either will do, if you are allowing a thermostat to do the cycling. Probably very similar total AH/day energy consumption.

However if you are explicitly turning the compressor on and off for a limited run per day, e.g. to coincide with a genny run, the larger one will likely get the job done more quickly.

If you are turning it on after the House bank has reached X% SoC, amps acceptance has started to decline, then (assuming a bank chemistry that should be charged to 100% Full for longevity) you also need to verify that the "extra free" amperage available is sufficient to run the load as well as finishing charging the bank by the end of the solar day.

Too small solar, then the smaller compressor may be a better fit.
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Old 20-10-2017, 19:04   #3
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Re: Danfoss BD35/50 sizing?

Considering that (roughly) half the time the compressor will be running at night, and therefore off batteries), one could argue that the size of the solar really doesn't matter. To a first approximation, total energy usage (power x time) doesn't much depend on the size of the compressor. As John points out, the larger compressor will just cool more quickly, so will run for a shorter time than a smaller compressor. So, total amp-hours should be comparable for either compressor.

In my case, I chose the BD50 for 2 reasons: 1. If I need more capacity for any reason, 2: shorter run times are quieter! (I do hear the fan running)
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Old 20-10-2017, 19:28   #4
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Re: Danfoss BD35/50 sizing?

The fact this will be a eutectic plate system implies to me the compressor may well not run at all except when "free excess" power is available.

Otherwise why spend the extra money, carry the extra weight and (most importantly) sacrifice all that fridge space?

If you're letting a thermostat cycle the compressor, may as well put in an evaporator system instead.

IMO
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Old 20-10-2017, 20:05   #5
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Re: Danfoss BD35/50 sizing?

John:
Good point, missed the point that it is a cold plate system.
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Old 20-10-2017, 20:25   #6
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Re: Danfoss BD35/50 sizing?

I would recommend going with a BD50 for a holding plate system where the point is to pull out more heat from the box than is coming in and storing energy inside the holding plate. There is a different operational mindset if a holding plate system vs an evaporation system, something many people overlook.
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Old 21-10-2017, 07:16   #7
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Re: Danfoss BD35/50 sizing?

Quote:
Originally Posted by deepthought View Post
I have a couple extra compressors on board BD35 and BD50..

In the box we have a ISOTHERM cooling plate.

What would be the best compressor we should use?
OP states he has a cooling plate , this could be a thin plate evaporator or a holding plate , maybe he will clarify .

As for which compressor I like to go with a BD35 just because it's COP , coefficient of performance is better. So if the box is well insulated and you have the proper sized plate for the box you will see lower amp hr usage from the more efficient compressor . If you have a holding plate and want to only run it when you have plenty of power then the BD50 would be the better option . It all really depends on how your system is set up . IE battery bank size , solar array size ........

Regards John
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