Searle Cooler Freezing Up

[piston broke]

I am currently working on a low temperature cold store. Indoor unit: Searle KS40-4, Condensing unit: Copeland Mod MC-HB-2F13KE-TFD, Expansion valve: Danfoss TES 2. (Orifice 2 I think), Refrigerant R404A.

This equipment was selected by a supplier when we gave them the details. The old equipment we correctly identified as being far too big. It was twice the size.

Now after 6 months operation the evaporator keeps freezing solid the bottom 50% of the coil. We have taking out gas, changed expansion valve, pressure tested, evacuated and recharged.

I've added refrigerant, taken it out, adjusted valve but no matter what I cant get 'even' freezing across evaporator. Defrost cycle ok, heaters ok.

There is a spreader from the valve to evaporator but they all appear to freeze evenly but the top third of the coil just won't free even when we get the suction line to freeze right back to the compressor.

Any ideas?

PB

[stuartwking]

Hi piston broke,
Whats your super heat and suction pressure?. How is the air flow to your coil?, Dont suppose the part of the distributor the feeds the top of the coil is choked?,. I would more worry about the SH and performance of the system?,

[Peter_1]

Drain heater or pan heater broken?

[Billy Ray]

Hi piston broke

firstly i would go back to your supplier & ask them why they have recommened/supplied to you a medium temperatute cooler for your application!!!

this will freeze up quite quickly. although would expect it to be uniformed freezing unless as stuartwking noted you have a restriction in the distributor!!

Fundamently you have the wrong cooler installed!!

Billy Ray

[Peter_1]

Billy Ray, even a 4 mm spacing must freeze equally.
I understood that solid ice is forming at the bottom of the evaporator, is this correct.

[stuartwking]

Have you tried running your system without the evap fans?
If you still dont get a frost on the top part of the coil with no fans then there must be a choke,.

[Electrocoolman]

It sounds as possibly the defrost is set up / operating incorrectly.

What type of defrost is it...electrical?

As Peter1 says possibly an element gone u/s.

The other possibility is that the defrost parameters are set incorrectly. I would look at termination temperature, drain down time and possibly the location of the evaporator probe.

Is your orifice sized correctly for the evaporator duty?
You say that the evaporator was originally far too big. Has the condensing unit also been changed (downsized). Is it now too large (capacity) for the evaporator?

[chillin out]

Check to make sure none of the heaters are on when in cooling mode as this would certainly cause this.

You may have to check the spider for any restrictions.
Best way to do this without have to open it up is to put it onto cooling and heat each leg with a blow torch. Now check how long it takes for each leg to cool down again.

It could also be an oil blockage in one of the legs, again just blast it with the torch to get rid of it.

Chillin

[chillin out]

Also check to make sure nobody has fitted a heater too high up in the coil as this would make it terminate it's defrost too early.

Chillin

[Grizzly]

I am currently working on a low temperature cold store. Indoor unit: Searle KS40-4, Condensing unit: Copeland Mod MC-HB-2F13KE-TFD, Expansion valve: Danfoss TES 2. (Orifice 2 I think), Refrigerant R404A.

This equipment was selected by a supplier when we gave them the details. The old equipment we correctly identified as being far too big. It was twice the size.

Now after 6 months operation the evaporator keeps freezing solid the bottom 50% of the coil. We have taking out gas, changed expansion valve, pressure tested, evacuated and recharged.

I've added refrigerant, taken it out, adjusted valve but no matter what I cant get 'even' freezing across evaporator. Defrost cycle ok, heaters ok.

There is a spreader from the valve to evaporator but they all appear to freeze evenly but the top third of the coil just won't free even when we get the suction line to freeze right back to the compressor.

Any ideas?

PB

PB.
Have you considered that there may be nothing wrong with the plant?
Quite often in the past I have been called to attend equipment that is no longer performing.
And after a few delicately asked questions have discovered things like " Ah we had a load of Blackberries in the other day". etc etc.

Meaning some Cold Stores have seasonal products
which affect the balance within a Cold Store hugely.

Basically what I am trying to say is your freezing up evaporator COULD be as a consequence of the seasonal rise in warm and humid products.

Also as the guys are all suggesting "DEFROST ISSUES"
A evap freezing up would suggest a high moisture content in the store.
Which will cause the evap to freeze from the btm up!
Have you tried increasing the number of defrosts or lengthening the defrost duration.

The whole idea of a defrost is to remove the extracted moisture from the collection point (evaporator).
So if this is Iceing up defrost more.
You mention a suction line freezing back to the compressor is this during setup or as a consequence of the blocked evap?
Lastly there is also the possibility that you could have a poor airflow through the evap that or a partially blocked coil would cause your problem.
In the Past I have had huge problems with cardboard dust.
Microscopic particles that clog everything.
I apologise if all this sounds condescending, it's not meant to be.
I don't know how to ask some of the questions without sounding so!
You may well of tried most of the above but maybe there is something mentioned that is of help?
Cheers Grizzly

[piston broke]

Thanks to all especially Billy Ray. I'm back on site later today but before that I'll be talking to the supplier. Everything was changed, evaporator, CU and pipework. Defrost cycle, heaters, drain heaters all work ok. The coil does freeze all over before the F25 brings on the fans. I did get it to work before but it was a delicate balance.

The store is used in a lab and the door is rarely opened.

[Peter_1]

Indoor unit: Searle KS40-4, Condensing unit: Copeland Mod MC-HB-2F13KE-TFD, Expansion valve: Danfoss TES 2. (Orifice 2 I think), Refrigerant R404A.

A 40-4 is also made for freezer applications according to the Searle catalog I have here in front of me.
What I see is that a Orifice 2 is too small, you should have a 3.
A ZF13 gives +/-3.5 kW at te -30°C, so again a 3.
If you have a 3 and the coil is not frosting equally, then there's another problem (moisture building up in the orifice, blockage, oil in the distributor, debris in distributor or capillary lines ?)
Best way is like CillinOut said,measure every circuit as it cools at the same rate and same temperature, especially the place on the coil where superheat starts must all be on the same place for each circuit

[philfridge]

I am currently working on a low temperature cold store. Indoor unit: Searle KS40-4, Condensing unit: Copeland Mod MC-HB-2F13KE-TFD, Expansion valve: Danfoss TES 2. (Orifice 2 I think), Refrigerant R404A.

This equipment was selected by a supplier when we gave them the details. The old equipment we correctly identified as being far too big. It was twice the size.



I've added refrigerant, taken it out, adjusted valve but no matter what I cant get 'even' freezing across evaporator. Defrost cycle ok, heaters ok.

There is a spreader from the valve to evaporator but they all appear to freeze evenly but the top third of the coil just won't free even when we get the suction line to freeze right back to the compressor.

Any ideas?

PB

Hi the problem is as stuartwking says that the evaporator coil is blocked at top feederline. Ive had this before with searle coolers and have had to change them after trying everything to resolve the issue. Otherwise you will never solve the problem .
regards phil

[piston broke]

Right, I'm just on my way there, I'll check the orifice size. I'm sure it's a 2.

Then I'll change if necessary, buy a new touch probe and check spreader temps.

Cheers, I'll let you know how it works out.

[Chunk]

As said above a KS 40-4 is a high temp evap and a KS 40-4L is for a freezer.

I have had similar faults to yours but with electrical controls being the issue(incorrectly positioned suction probe being the main cause).

Good luck.

[Billy Ray]

piston broke / Peter_1

The KS40-4 has a 4mm fin spacing (6 fins per inch) which is not a correct selection for evaporarting temperatures below -10degC.

Searle advise at -10degC evaporating, the KS40-6 (6mm spacing / 4 fins per inch) would be a better selection!

4mm fin spacing (6 fins per inch) evaporating at -25 deg C is a wrong selection.

Unless the room has a desicant dehumidifier & the dew point is below -30degC, the supplier has miss advised.


Back to issue of uneven frosting. As Grizzly pointed out there may not be a problem at all.

Checking all the items as previously noted by others will confirm this or not. A simple check would be to measure the superheat on each circuit prior to the pipes joining the coil suction header.

Another line of investigation would be liquid sub-cooling at TEV inlet. Flash gas can give the apperance of poor liquid distribution across the coil, i dont know why, it just does.

Your cooler in question should be a KS40-4L as the L denotes the electric defrost.

Peter_1, I can see no referenece in my Searle book either way to suitablity or not. The supplier who selected the cooler has advised wronlgy.

Billy Ray

[bernard]

Hi

You say after 6 months this problem started so it has run ok until then,there should be three defrost elements one in the middle of the coil and two fitted to the bottom of the coil.Check the amp draw on each heater they should all be the same.I,ve had a problem in the past where the bottom elements are only drawing an amp or less as only a small part of the element is working.The Defrost probe should be in the top right hand corner looking from the rear.

Regards Bernard

[piston broke]

I have removed expansion valve and blasted nitrogen back through the suction. Replaced with orifice No.3 (the old one was a 4 by the way). Re-fitted valve, vacced and charged, and hey presto it works. I also repositioned F25 sensor to stop premature defrost termination and have gave it more defrosts than normal.

It is the wrong coil, I checked another freezer on site and the coil is a KS40-6.

But its working for now, as long as we keep it well defrosted I think it will be ok.

Changing the coil is not an option at present as it will cost us money and make us look rather foolish. We will do it if the problems come back but for now we will let sleeping dogs lie.

Thanks for all the input.

PB

[coolhibby1875]

hi piston i can assure you that a km40/4 is not the wrong cooler as i have worked on hundreds up and down the country and all fitted into deep freeze coldstores

[Peter_1]

Searle advise at -10degC evaporating, the KS40-6 (6mm spacing / 4 fins per inch) would be a better selection!
Peter_1, I can see no referenece in my Searle book either way to suitablity or not. The supplier who selected the cooler has advised wronlgy.

I have here the Searle catalog in front of me and you can use a KM.. 4 for a freezer application. I don't see any limitation.
You must use another catalog.

It all depends on the humidtiy level in the room and if fresh food is brought in at a regular base so that moisture is also brought in the room .

I agree that it is better to use 6 mm for a freezer but the symptoms the first poster described aren't related to a 4 mm fin spacing.

[Peter_1]

Another line of investigation would be liquid sub-cooling at TEV inlet. Flash gas can give the apperance of poor liquid distribution across the coil, i dont know why, it just does.

Let's take a distributor tube which can pass 1m³/s.
If 1 m³/s liquid passes, then you have a big enthalpy and a lot liquid ready to evaporate in the coil.
On the other hand, if 1 m³/s gaseous refrigerant passes through the same lines, this gas can't take heat any longer because it's already evaporated.

Don't forget that the volume change from liquid to gas is +/- 200 to 300.

So, the gaseous refrigerant blocks the small lines from feeding liquid to the coil.

I don't know if this explanation makes sense like I described the best I could.

If I remember well, they call this in English choked flow.
http://en.wikipedia.org/wiki/Choked_flow
This phenomena is something that happens also in turbine jets when the speed of the gas approaches 1 Mach (speed of sound)
This is one of the reasons why it is so difficult to fabricate airplanes which fly faster than 1 Mach.

[Billy Ray]

Peter_1,

your points are taken, i will stand corrected.

Billy Ray

[old gas bottle]

is there a tray heater in this thing? if its a med/high temp cooler it may not be fitted,, those later KS cooler ,s tend to have one heater in the centre of the coil block and no tray heater,that was for a butchers room,had to fit a seperate tray heater as that was doing what yours is doing. sounds like that to me,or if it has a tray heater the wattage is to low to creep up the coil block in tune with the other heater,and again that points to a heater missing .

[GXMPLX]

Only low temperature KS do have a pan heater. Probably KS40-4 does not.

I did not find Searle's catalog on these evaps in their site www.searle.co.uk so I set up an HTTP site that holds the catalogs.

It is (Sorry no longer available)

This site will be up for only 48 hours counting from now ... er well maybe now!

[old gas bottle]

there a old model now,i have two old stock ones to fit because they had nothing in stock of the new models,its just made to order now

[piston broke]

Thanks for all your input. It has been operating now for nearly a week. The coil is clear. It freezes evenly across entire coil coil when cooling. Holding -20.
It has 2 heaters, one in the middle and one below the evaporator on the drip pan.
I think the problem was the orifice. The new one I fitted was shaped for the flare nut whereas the old one was flat. I think it was the wrong type of orifice.
Once again, thanks to all IT WORKS HURRAH!

[Peter_1]

I think the problem was the orifice. The new one I fitted was shaped for the flare nut whereas the old one was flat. I think it was the wrong type of orifice.

The one with the flare is for standard nuts, the flat one is for the Euro coupling of Danfoss. I wonder how this connection could be ever gastight.

[monkey spanners]

I had a look at a freezer system put in by a friend of mine because of a similar problem. They had tried bigger orifices, adjusting the valve, all sorts. It would frost back to the compressor but still the top half of the coil did very little.
The distributor appeared to be just a couple of bits of 3/16" pipe poked into some 1/2" to the valve outlet. The 1/2" pipe was horizontal with the 3/16" coming out one above the other with the top one feeding the top circuit in the evap. Turned the distributor 90' so both 3/16" pipes were side by side and it worked fine then. All the flash gas was going to the top circuit.

Jon

[GXMPLX]

After reading monkey_spanners post one of my burnt memory neurons started kickin´.

I had a simmilar problem once and suction pressure went down once a week. Finally it was that the guys that cleaned and ordered placed product blocking the evaporators air intake, not at the evap but beneath it, so not enough air circulated and the top half got thermal load, the bottom half did not and blocked with ice.

The same thing happens if you install the evaporator too close to the wall not respecting manufacturer´s instructions.