Head cooling

Had a discussion today with a technician: when and why is head cooling (with the upper fan mounted above the compressor head) necessary on freezer compressors?

Those we installed always had this, also on the racks which came from Profroid, Sodifri and the German supplier( which name I can't remember right now),

Is it because they mainly work on higher superheat temperatures, resulting in higher discharge temperatures?

Could it damage the compressor or discharge reeds if you rmove the fan, whatever the manufacturer recommends? Perhaps by lowering the superheat?
It is an additional cost: first to install it and afterwards you have operational costs) and it don't contribute to the cooling process itself.

Do you guys adjust superheat to the recommended +/- 20 K , evaporating at -30°C or lower, resulting in a partially frozen body, rusty after some time and always leaking water?

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Is it because they mainly work on higher superheat temperatures, resulting in higher discharge temperatures?

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Actually, it is due to the higher operating pressure ratios across the compressor with low temp refrigeration which result in higher discharge temperatures. High superheat conditions at the compressor inlet only aggravate this situation.

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Originally posted by Prof Sporlan
Actually, it is due to the higher operating pressure ratios across the compressor with low temp refrigeration which result in higher discharge temperatures. High superheat conditions at the compressor inlet only aggravate this situation.

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Yes I'm aware of this but will head cooling cool down so dramatically the temperature around the HP valves (reeds?)?

That's what I'm was thinking : the high temperatures are in the gas itself due to high superheat and high compression ratios and will be pumped immediately away to the condensor.

It will at least cool the iron of the body which will be heated by this hot compressed gasses.
But the iron of the body is thick.

I'm asking this because we have a lot of single freezer compresor where we didn't installed this fans. We never had problems with it, at least no more as those with a fan mounted.
So is it worth to install them (cost to install them and opertional cost for the client afterwards)

We instaled 20 years ago Copelands with a standard copper coil with water in it wrapped around the body.

Peter

hi peter,


the fans hardly do anything, because its in open space and rorating in circular movement, most of the air goes sideways.

by us its a lot hotter and I never use them.

I belive its competely useles.

chemi :)

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Originally posted by chemi-cool
hi peter,


the fans hardly do anything, because its in open space and rorating in circular movement, most of the air goes sideways.

by us its a lot hotter and I never use them.

I belive its competely useles.

chemi :)

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That was also my opinion Chemi.
We had a burned one at a client and I said to our technician that he could remove the fan and say to the customer that he didn't need any anymore. He (client) was of course happy but surprised why we had installed them in the past. I said him that this was done regulary in the past but that practical experience has learned over the years that they're as good as useless.

And indeed, hadn't tought on that yu mentioned: they blow horizontal and there isn't any guidance to the body for the air.

The ones that I saw in my commercial days had a heat exchanger coil underneath them, between the fan & the head. These were oil cooling coils, and the fan was just there to force the air over the coil. There was no directional control of the air on those either, but there isn't on a desk fan, and that pushes air in the right direction! ;)
I forget now why my seniors said that they were fitted, but I think it was something to do with the greater pressure ratio in a L.T. compressor causing excessive heat in the oil?
No doubt Marc will now demonstrate my foolishness! lol :D :D

the problem of over heating compressor heads was eliminated when liquid injection to cool the heads intodused for the first time.

using the fan to cool a coil is a different story and the reason that they are over the compressor head is to save space.

chemi

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Originally posted by chemi-cool
the problem of over heating compressor heads was eliminated when liquid injection to cool the heads intodused for the first time.

using the fan to cool a coil is a different story and the reason that they are over the compressor head is to save space.

chemi

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The compressor that was broken initially was a demand cooling (or liquid injection) with an oil cooler on top of the cilinders. (R22 freezer application gives to high doscharge temperatures)

Hello peter

Cylinder head cooling fans are recommended on all applications when the SST is below -18 due to the reasons marc explains.
One other reason would be on a pack etc aiding the cooling of cylinder head gas temperatures may help prevent nuisance tripping of head /body sensors etc .
Basically in some cases head cooling fans are recommended but not required;).

Regards Mark:)

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Originally posted by MarkFiddy
Hello peter

Cylinder head cooling fans are recommended on all applications when the SST is below -18(R404A) due to the reasons marc explains.
One other reason would be on a pack etc aiding the cooling of cylinder head gas temperatures may help prevent nuisance tripping of head sensors etc .
Basically in some cases head cooling fans are recommended but not required;).

Regards Mark:)

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Hi Mark,

That was one of my questions 'Do you work on freezer packs with suction as low as -10°C? The body is then completely in ice, body tends to rust and the floor is always soaking wet.' We don't do it but then work with higher discharge temperatures.

The compressors we mostly uses are Copelands and don't have the gas sensors.

I read that it is recommended but is it realy needed? It can also be some sort of selling trick from the manufacturer.

Perhaps a good idea like Marc describes to monitor it,difference with and without.
But you have to agree with Chemi that those fans blow not directally on the compressors heads but more horizontally.
So the net effect of these fans is seriously reduced.

We have a client with a Mycom 2 stage R22 compressor with watercooling in the cilinder heads. This helps a lot and is very effective.

Peter:
“Yes I'm aware of this but will head cooling cool down so dramatically the temperature around the HP valves (reeds?)’?
Ans: yes, the greatest effect in desuperheat is at the discharge of the valves.

“But the iron of the body is thick” (heat sink) and it has fin type configuration on top of head for greater heat dissipation.

I would not recommend the removal of these fans because cylinder and head temperatures could become so hot that the oil loses the required viscosity for proper lubrication. Resulting in ring wear which could cause discharge gases to blow past the rings and pressurize the crankcase preventing oil return from the system. Metal debris dropping to the crankcase will eventually cause stator spot burn when arriving between the rotor and stator. Some conditions to look for are
Discolored valve plate which can’t be rubbed clean, burned discharge valve reeds. Burned and worn pistons, rings and cylinders; stator spot burn from metal debris. The greatest reason for re-expansion and heating of the suction vapor is the effects of cylinder heating and the greater the compression ratio the greater the amount of valve leakage.
Roger


:D

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But you have to agree with Chemi that those fans blow not directally on the compressors heads but more horizontally.

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Hi peter :)

My point is that as the cylinder heads are hot ,there is a natural convection of heat to air movement and this heat would be naturally dispersed by the forced airflow from the fan.:) aiding overall cylinder head temperature heat rejection and losses.

Regards Mark:)

Yes Peter, they do help! and marc your such a Putz! You just love to pick out little bits and pieces and nibble away.
:D ME

Hi:)
with proper control of the suction superheat there is no good reason to fit head cooling to any 404a compressor. A head cooling fan is simply a means to ensure that compressor manufacturers are not made liable for failed compressors that have run with high suction superheats.
Had it a head cooling fan no, well we said it should have had at that application:(
Yesterday I was looking a mono screw compressor that was to be run on R404a, what I found was that if I didn't fit a suction liquid heat exchanger the discharge superheat would be too low and the oil separation would be affected.
R404a is generally a cooler running gas than R502 was, but as I remember the Prestcold units I worked on in the past with R22 no head cooling, but the the R502 units at the same conditions head cooling was employed:) , mainly due to the motors absorbing higher currents.
Regards. Andy:)

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Originally posted by shogun7
[B]Peter:
“Yes I'm aware of this but will head cooling cool down so dramatically the temperature around the HP valves (reeds?)’?
Ans: yes, the greatest effect in desuperheat is at the discharge of the valves.

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Ever measured if removing or reducing head cooling reduces superheat? Biggest advance should be reducing superheat at he outlet of the evaporator.

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“But the iron of the body is thick” (heat sink) and it has fin type configuration on top of head for greater heat dissipation.

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Never saw fins on the cilinder heads, besides on the body itself.

Saw andy gave alomst th same answer and that was my discussion with a technician. He even was sure when you see frost on the body that you have liquid on the suction. Never have frost on the body itself he says:eek: :confused: :confused: :eek:

from the -very- little i know..demand cooling seems to work far better than head fans

i agree with chemi the wire grille does not direct the air towards the compressor and greatly reduces it effectiveness meaning ie works so fantastically well it doesn't need directing or it's more of a token gesture...

pic is of copeland comp on R22 low temp

cheers

richard

hi richard,

I see you have a new position.

good luck!

chemi

it's all your fault chemi -you wouldn't pay the money ;-)

cheers

richard..

hi marc, peter,

if you realy want to employ head cooling, I would suggest the use of centrifugal fan.

in this way you can be sure that the air DO hit the compressor head and upper parts.

I know it cost more than exial fan but it will do the job.

chemi

I don't want to use it because I feel/think/experienced that it doens't help that much.

No one came with real measured figures or statements that convinced me. But for that, we need a compressor manufacturer in our group.

Haven't searched but does every branch recommend them.

Hey, everybody start to spread out their titles, here are mine.

Peter I found this on a web site
Cylinder head cooling fans are recommended on all
applications where the saturated suction temperature
(SST) is below 0°F (-18°C). A cylinder head cooling fan
must be used for all R-22 single stage applications
below 0°F (-18°C) and all R404A/507 single stage
applications below -20°F (-29°C). A cylinder head
cooling fan is recommended (but not required) for any
two-stage (Compound Cooling) applications down to
-40°F (-40°C).

Roger

This is retrived from RSES Archives:
At many Kmart superstores, cascade secondary cooling systems are used, says Tony Papagna, manager of refrigeration systems design and installation. He says the store de-signed the system to achieve the highest energy efficiency ratio (EER) possible and to eliminate liquid injection of R-22, which saves approximately 3 percent in costs and to eliminate the operation of compressor head cooling fans. It also saves approximately $850 based on a 6 cents per kilowatt cost.

Papagna says the system features a low-temperature system with a constant year-round condensing temperature that provides a constant and stable subcooled liquid refrigerant independent of ambient conditions, eliminates the "hunting" of TXVs, as well as complies with uniform building and fire codes and ASHRAE standards. Papagna says complying with standards and codes was one of the main reasons for installing cascade secondary cooling systems.

The stores contain low- and medium-temperature systems. The low-temperature system is based on a -23° F suction temperature at a 70° F condensing temperature, which is based on a return gas temperature of 50° F with 36 required tons for the refrigeration load. There's no liquid injection and no head cooling fans. The design of the medium-temperature split-suction manifold is based on 13° (41 required tons)/40° F (53 required tons) suction temperature at 110° F condensing. He said the system uses 35 percent propylene glycol and a loop system for overhead piping.

For the installation of a cascade system, Papagna said they used 5 steel pipe instead of copper pipe. The system requires no traps, brazing, air evacuation procedures, TXVs or evaporator pressure regulators (EPR).

"A secondary cascade cooling system has many benefits," he explains. "You can reduce your refrigerant charge by 25 percent, the installation is simpler with less costly construction materials, it reduces the potential for leaks as propylene glycol's operating pressure is 50 psi, and it has quicker start-ups and pull-down times."

During a presentation on the low side of refrigeration systems and controls, Keith Oliver, associate manager of facility engineering, The Kroger Co., discusses the low-pressure side of parallel rack systems and air-cooled single condensing units, and how Kroger saved $500,000 in energy bills for 80 stores.
Roger


:D :D

I have never even seen any other compressor but a hermetic one, so please bear with me if my remark is just plain stupid.

Would adding the head cooling fan increase system COP? The air moved by the fan rejects extra heat after all...

Hi Dabit:) in a word yes head cooling should increase cop. If your compressor is pumping denser gas, effeciency will increase.
Mostly head cooling is to reduce discharge temperatures and thus allow the oil to lubricate better, at its design temperature. Oil will also breakdown and form carbon if overheated.
Ofcourse the simple answer would be reduce the suction superheat and then none of the above will be a problem.:D
Regards. Andy:)

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Originally posted by DaBit
I have never even seen any other compressor but a hermetic one, so please bear with me if my remark is just plain stupid.

Would adding the head cooling fan increase system COP? The air moved by the fan rejects extra heat after all...

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Perhaps the COP of the compressor but if you take in account the extra power for the fan and add this to the power of the compressor, is it (COP) then still increased? (SEER?)

Then, I would say that with refrigerants like R404a head cooling is seldom necessary to keep the discharge temperature into the safe area, unless the suction gas is superheated excessively. Which should not happen under normal circumstances anyway.

But what if we add head cooling to increase system COP? Discharge temps should lower, possibly resulting in a larger portion of the condenser used for condensing. Which is good for system COP.

We could even add a suction gas<-> liquid line HX to take even more advantage of this.

Would the increase in COP justify the extra component/installation/maintenance costs?

edit: Peter_1, we were thinking about the same..

You guys crack me up.... Just use ammonia, and that will settle it!