Refrigeration - Evaporator vs. Holding Plate

[SV THIRD DAY]

Originally Posted by Richard Kollmann

No. The point is when there are mutable eutectic plates they perform much better when not in series and each plate has its own TXV refrigerant control.

Not according to the testing we have done.
When the plates are plumbed in series with the TXV on Plate 1 and the sensing bulb on plate No 2, then as far as the system knows and cares the plates are one large plate. Now of course plate No 1 freezes down first followed by plate No 2. But once the system is in equilibrium running two plates in series off of a single compressor is more efficient than running a separate compressor for each plate.

[missourisailor]

Okay, it is apparent that I'm doing a piss poor job of asking the question that I want the answer to.

So lets try this another way.

Given that a BD 35 compressor can only remove so many BTU's in a given time span. If I wanted to shorten the recovery time after reloading the freezer, is there enough extra capacity built into a Cool Blue unit that a second hold over plate is all that is needed?

Or am I looking at upgrading to a 50 series compressor?

[kmacdonald]

Originally Posted by missourisailor

Okay, it is apparent that I'm doing a piss poor job of asking the question that I want the answer to.

So lets try this another way.

Given that a BD 35 compressor can only remove so many BTU's in a given time span. If I wanted to shorten the recovery time after reloading the freezer, is there enough extra capacity built into a Cool Blue unit that a second hold over plate is all that is needed?

Or am I looking at upgrading to a 50 series compressor?

I bet it depends on a multitude of variables.

[Richard Kollmann]

Originally Posted by SV THIRD DAY

Not according to the testing we have done.
When the plates are plumbed in series with the TXV on Plate 1 and the sensing bulb on plate No 2, then as far as the system knows and cares the plates are one large plate. Now of course plate No 1 freezes down first followed by plate No 2. But once the system is in equilibrium running two plates in series off of a single compressor is more efficient than running a separate compressor for each plate.

You are probably right using separate compressors for each plate would would not be wise. I said having mutable plates each having its own expansion valve connected to one compressor is more efficient than plates in series.

[SV THIRD DAY]

Originally Posted by missourisailor

Okay, it is apparent that I'm doing a piss poor job of asking the question that I want the answer to.

So lets try this another way.

Given that a BD 35 compressor can only remove so many BTU's in a given time span. If I wanted to shorten the recovery time after reloading the freezer, is there enough extra capacity built into a Cool Blue unit that a second hold over plate is all that is needed?

Or am I looking at upgrading to a 50 series compressor?

YES and NO....that's the truthful answer but that's not what anyone wants to hear now it is.

First Technautics doesn't currently use BD35 compressors. The BD50 or equivalent has been the standard for years now.

Now adding the second plate WILL result in faster temp pull down times due to the increase in surface area available for heat transfer and from the additional BTUs stored in the eutectic solution inside the plates. That's the advantage of the Holding Plate Energy Storage vs a Cyclic no carry-over capacity flat evaporator plate. You are not just relying on the Compressor running and it's BTU Removal rate for pull down when adding food to the Box, you also have the Energy Removal Capacity stored in the Holding Plate.

Now....Heat-in is Heat-out....so can you add more heat to your Box than the BD35 compressor can handle? YEs...but what do you mean by "handle"?
If the compressor runs continually without cycling off then yep....you have more heat coming into the box than the compressor can pull out. But if your compressor is cycling bingo...your compressor has extra capacity by definition. So what compressor "Run" time are you willing to accept? Now no one wants a compressor to run 24hrs/day and on our typically installs we see 4-8 "On" Cycles per 24hr. With the on cycle being 0.75-1.5hrs each. The off cycle tells you how good the insulation is OR tells you how much Eutectic BTU capacity you have.

An Important Note:
Adding a second holding plate won't dramatically change your daily power usage. Remember Heat-in is Heat-out. But what you will change is the Speed of pull downs after adding food to the Box (faster), the length of compressor run times (longer) and the length of compressor off times (longer). You will see a slightly HIGHER total power usage per day...why...because you will have a lower average temp in your Box so you will be maintaining a larger Delta T from Ambient to inside your Box.

I tried to answer but this isn't a one word deal, which is why it's hard for people to really wrap their heads around and understand.

[a64pilot]

Another thought, Rich’s Cool Blue system can likely get away with just adding a second plate, cause I assume it has excess condenser capacity.
Excess condenser capacity may also give it the ability to operate in higher ambient temps. Not all systems I assume you can just add a second plate, then you may not have enough condenser.
It is all moving heat, there is no such thing as cold, it’s just less heat.
If you remove more heat from the box, you have to have enough condenser to get rid of it.

Biggest “trick” to making an air cooled fridge system just as efficient as a water cooled one is by having a large enough condenser and fan.

Remember back in the 60’s house AC’s had one condenser the size of a small car radiator.
Now they are huge, wrap around the whole unit and if you look carefully, then have gone to great lengths to make the fins huge and varied to cool the condenser, spiral wrapped etc.

[SV THIRD DAY]

Originally Posted by Richard Kollmann

You are probably right using separate compressors for each plate would would not be wise. I said having mutable plates each having its own expansion valve connected to one compressor is more efficient than plates in series.

Yes I agree.
So the question is why not have multiple TXV for a dual plate system?
It boils down to cost and complexity. You make some efficiency sacrifices along the way to market. Most of our seriously outfitted cruising boats have a Dual Plate system in their freezer and then a separate single plate system in their refrigerator. It's nice from a budget standpoint to go with the classic Spill-over design, but then again, you make sacrifices for cost/budget all the time in life.

[Richard Kollmann]

Originally Posted by missourisailor

Okay, it is apparent that I'm doing a piss poor job of asking the question that I want the answer to.

So lets try this another way.

Given that a BD 35 compressor can only remove so many BTU's in a given time span. If I wanted to shorten the recovery time after reloading the freezer, is there enough extra capacity built into a Cool Blue unit that a second hold over plate is all that is needed?

Or am I looking at upgrading to a 50 series compressor?

A second same size holding plate when frozen will have twice the flywheel effect therefore warm food added in theory will raised box temperature only half as much as one plate did. It is also true it will take twice as long for compressor to refreeze all eutectic solution melted.

The BD50 change could produce 30% more energy (Btu) than the BD35 but remember at zero degree F eutectic freeze point both compressors only produce 1/2 their normal MBP capacity.

[missourisailor]

Originally Posted by SV THIRD DAY

....adding the second plate WILL result in faster temp pull down times .

Now we'll talking.

I'm okay with all other parameters of the system.
It's just the recovery that annoys me.

I just wanted to make sure that I'm not making a mistake by adding a second plate, when I should be looking at a upgraded compressor.

[missourisailor]

Originally Posted by Richard Kollmann

A second same size holding plate when frozen will have twice the flywheel effect therefore warm food added in theory will raised box temperature only half as much as one plate did. It is also true it will take twice as long for compressor to refreeze all eutectic solution melted.
.

Yeah Something is getting lost in the translation here.

I don't think that you are really meaning to say "... take twice as long for compressor to refreeze ".

I can see on initial start up, it taking twice as long to settle.
But on recovery, won't it take 1/2 as long with a second, similarly sized holdover plate?

[Richard Kollmann]

Rich.I think you are saying add second plate and change to BD50 compressor to get faster temp pull down time.

[Richard Kollmann]

Originally Posted by missourisailor

Yeah Something is getting lost in the translation here.

I don't think that you are really meaning to say "... take twice as long for compressor to refreeze ".

I can see on initial start up, it taking twice as long to settle.
But on recovery, won't it take 1/2 as long with a second, similarly sized holdover plate?

If the flywheel energy stored in both plates is partly consumed to keep box temperature from rising half as much as one plate. Why would it not take compressor twice as long to replace the melted eutectic ice.

[a64pilot]

Or said another way.
If you melt more fluid than a single plate will hold to pull the food down to set temp, then it will take longer to refreeze.
However if you melt two gallons total between the two plates, or two gallons on one plate, wouldn’t the refreeze time be very close?

If a single plate will store 1X amount of heat energy and a dual plate system will store 2X, but you only use 1X, then the time to replace the energy will be close to the same? The advantage of a dual plate is you can pull more than 1X and still keep box temp cold, where as a single will begin to heat up as soon as 1X of heat is absorbed?

[Richard Kollmann]

Originally Posted by a64pilot

Or said another way.
If you melt more fluid than a single plate will hold to pull the food down to set temp, then it will take longer to refreeze.
However if you melt two gallons total between the two plates, or two gallons on one plate, wouldn’t the refreeze time be very close?

If a single plate will store 1X amount of heat energy and a dual plate system will store 2X, but you only use 1X, then the time to replace the energy will be close to the same? The advantage of a dual plate is you can pull more than 1X and still keep box temp cold, where as a single will begin to heat up as soon as 1X of heat is absorbed?

It is the more rapid heat absorption of two plate's larger surface area that additional compressor running time is required.The idea that eutectic plates provide free heat absorbing energy is a mistake.

[a64pilot]

Originally Posted by Richard Kollmann

The idea that eutectic plates provide free heat absorbing energy is a mistake.

Agreed, any way that energy is stored whether by battery, a flywheel or even gravity, and later used there are losses both in storing and then in use.
Or you have a perpetual motion machine.

It’s what drove me nuts trying to figure out how the Prius we had, got such good mileage, logically it shouldn’t, most efficient way to use gasoline was to provide direct mechanical propulsion, not all the Rube Goldberg things a Prius has going on.
However there is a lot more going on that just merely storing energy from regenerative braking, a lot more, and I had to really delve into its operating principle to figure it out.