Insulation of Accumulators

Hi guys,

Is it necessary to insulate an accumulator on a low temp installation ?
I just worked on a blood plasma freezer that keeps the product at -30c. It has a top mounted condensing unit.

I replaced the compressor as well as the accumulator.
The original accumulator was not insulated from the factory.
It was however mounted on a drip tray to collect the condensation and defrosted ice with those being sent to a heated drain pan.

The freezer uses a capillary tube,hot gas defrost,and R404a refrigerant.

I have seen some low temp installations where the accumulators were insulated ,and some where they were not.

I am of the opinion that insulating would result in a more efficient setup due to less of a heat gain from outside the cabinet.

I changed comp from copeland air cooled semi-hermetic to equivalent Btu tecumseh refrigerant cooled hermetic.
The accumulator is in warm air stream of condenser.
In light of this would insulating accumulator be a good idea ?

Your thoughts are appreciated.

Quote:

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Originally Posted by fridgedoctor

Hi guys,

Is it necessary to insulate an accumulator on a low temp installation ?
I just worked on a blood plasma freezer that keeps the product at -30c. It has a top mounted condensing unit.

I replaced the compressor as well as the accumulator.
The original accumulator was not insulated from the factory.
It was however mounted on a drip tray to collect the condensation and defrosted ice with those being sent to a heated drain pan.

The freezer uses a capillary tube,hot gas defrost,and R404a refrigerant.

I have seen some low temp installations where the accumulators were insulated ,and some where they were not.

I am of the opinion that insulating would result in a more efficient setup due to less of a heat gain from outside the cabinet.

I changed comp from copeland air cooled semi-hermetic to equivalent Btu tecumseh refrigerant cooled hermetic.
The accumulator is in warm air stream of condenser.
In light of this would insulating accumulator be a good idea ?

Your thoughts are appreciated.

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Remember what the slop pot (accumulator) is used for.
It is to protect the compressor from liquid returning down the suction
line. If it was insulated it would be colder and therefor not as efficient.
The pan underneath catches the drips and the ambient temp warms up
the accumulator.

cheers taz

.

do not insulate accumlator to protect compressor from liquid

I am thinking that an accumulator should be insulated for a freezer, but uninsulated for a cooler, or ac application...but unfortunately do not have any support from tech manuals for this view. I am thinking that while you want to be sure that refrigerant doesnt condense in the accumulator, you do want to preserve efficiency

I would have thought insulate it if you have a heat source like liquid line coil inside slop pot.
If no heat source do not insulate so any liquid return can boil off from ambient heat etc

see next post.

I taught refrigeration at a local collage. We had the same question... to insulate or not insulate.
So we contacted Refrigeration Research and acquired the internal components for an accumulator, then we built one using high pressure industrial glass. Then we could see the internal workings of the accumulator. We also installed sight glasses in the suction line after the accumulator.
The system was a small freezer with hot gas defrost.
When we put it on defrost, the liquid came back in the suction line. and would fill the accumulator approx 1/2 full. The liquid was then metered out of the accumulator slowly through the oil return hole. You could see small amounts of liquid in the sight glass after the accumulator.
HOWEVER, the glass accumulator was not insulated, and there was very little BOILING of the liquid in the accumulator. Therefor the liquid left the accumulator through the oil return hole. It left surprisingly fast. The accumulator saved the compressor from SLUGGING, however the accumulator metered the refrigerant in smaller quantities which the compressor could handle.
Before we built this, I believed that you should NOT insulate the accumulator so it could get heat to boil the refrigerant out.
After we built this demonstrator, I changed my mind and now I believe that you should insulate the receiver.
It does not seem to matter to the refrigerant, but it will stop the accumulator from frosting and creating problems with rust and water dripping on the exterior.

Accumulators will rust if not insulated. An non insulated accumulator will also increase refrigeration load and drip water all over the place.

What a good question!
I was taught that the accumulator should be able to hold the full charge of the system, this being the case "research" case woulld be a fair and acceptable, but many modern systems (lets say bigger than just a cabinet) only have small "pots" and could only handle a small percentage of the total charge (we are all trying reduce total charge in systems), this being the case, you would need to add some energy or have some form of flood back preventer. I also remember that you could purchase accumulator heaters,

According to "Air Conditioning and Refrigeration" by Rex Miller:

Quote:

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The oil-refrigerant mixture in the suction line has been
studied over the range of -50 to +40°F (-46 to +4°C).
The value of -40°F (-40°C) was chosen as a minimum
evaporator temperature because it appears adequate for
commercial refrigeration. Yet, it is conservative enough
to provide a margin of safety. More important is the
requirement that the temperature of the suction gas at the
accumulator be 10°F (-12°C) or higher. Particularly
with refrigerants such as ***** 502, in the low-
temperature range up to 0°F (-17.8°C), the oil and
refrigerant separate into two layers, with the upper layer
being the oil-rich layer. At these low temperatures, the
oil-rich layer can become so viscous that it will not flow.
When the refrigerant below the heavy oil layer leaves the
accumulator, the very thick oil settles over the oil-return
port and stops all oil return. This condition will occur re-
gardless of accumulator design. If temperatures below
10°F (-12°C) at the accumulator are to be used, auxil-
iary heat must be added to keep the oil fluid.

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Do not insulate. The whole point of a suction accumulator is to boil off liquid refrigerant before it enters the compressor. So technically we want the ambient heat around the accumulator. There are suction accumulators with liquid line heat exchanger (eg: Scotsman Ice mod# CME2006remote) where the liquid line subcools even more by entering the accumulator and leaving headed towards the expansion valves. By insulating, you are making the accumulator less efficient. How much less, who knows, so why bother?