IMI Marstair Cellar Cooler

[Abe]

The Liquid line, leaving the condenser coil, after the shut off valve is iced up all the way through to the expansion valve

How does this system work?

I dont see a receiver, does the system work with an expansion valve, ie AEV ??

Condensing unit is located on the roof about 20 metres up on the roof, evaporator is in the cellar!!!

Somebody who knows this equip, please help

[Andy]

Hi, on some of the IMI heat pumps a small device like a check-valve is fitted to the liquid line as it leaves the condensing unit. This device is an oriface plate, full flow in one direction(on cooling) as in the flow side of a check-valve, restricted flow on reverse cycle as the refrigerant is checked by the valve and metered through a small hole. Has one of these valves been invertently fitted?
Regards. Andy.

[frank]

got to agree Andy. most if not all of the IMI kit has the restrictor straight after the liquid line valve at the condenser. As these are a fixed metering device designed for a/c applications we tend to discard them and fit a normal tev. The IMI condensing units are really nice pieces of kit if you get the ones with head pressure control (the + range) as they use Copeland scrolls. We always use them on AHU cooling coils. Cheap and reliable.

[frank]

I'm not sure of the technical name for it but I will check the IMI catalogue and post the details.

[Brian_UK]

Yes, as the others have said IMI use an orifice in the liquid line off the condensing unit but normally only in A/C mode.

You can normally tell if one has been fitted because they are incorporated into a flared fitting about 80-100mm long with a union type centre joint.

The centre joint houses the orifice. The evaporator uit should have a capillary line inside, normally a shortish large bore tube. If you look up through the air inlet grille at the bottom you should see it.

Your first need is to check the charge and superheat etc. as they will start frosting up after the orifice if the charge is down. Also check the condenser fan speed controller if fitted. If with low ambients and full fan speed these units will drop the suction pressure quite hard.

I know I said the orifice is normally an A/C fitting but don't take that as gospel. With the orifice the whole of the discharge line from the orifice to the end of the cap line is in a mixed phase state so do any subcooling readings at the condenser itself.

[Abe]

Brian,

An " orifice" is fitted to this unit. It is located just after the shut off valve leaving the condenser.

As someone mentioned, these are prone to clogging up

I am going to remove this orifice

Am I doing the right thing?

Thanks to everyone for your help

Tot Siens

[Abe]

Marc,

On the first call I noticed something, the condenser fan was turning very slowly, the spares wholesaler did not have a replacement so I changed the run capacitor ( 3mfd) and the fan worked. Its running but appears slow, the silent type jogging along instead of running.

I looked at the shaft, I think it has had a fair amount of oiling up over the years by previous engineers. I know the fan is the original OEM fitted one, must be at least 10 years old.

Im not sure if these fans run at a high speed or just jog along . I looked at the plate , and I think the RPM is either 850 or isit 1850. I cant remember.

I accept that removing the orifice is not enough if I dont change the expansion device too. Im wondering now if I should get a replacement fan motor as well, just in case it is not operating 100%

[Brian_UK]

Fan motor speed...........

IMI tend to use two speed fan motors. The black wire from the motor gives the higher speed and is normally used with fan speed controllers. The red wire give a slightly lower speed.

Try changing the wires over to see if you get an improvement in motor control. It could be that one set of windings is breaking down.

---
A common problem with IMIs is that some clever joker fits a liquid line filter/drier AFTER the orifice as well as a sightglass. The next idiot then comes along and thinks, Ooo! lots of bubbles I better throw some more gas in this one......
---

[frank]

You can tell if a fan speed controller is fitted on these units as a small liquid line sensor with 2 small black wires attached will be visible just prior to the liquid line leaving the unit.
On start up the fan runs at full speed for 20 seconds or so and then slows right done until it senses a rise in liquid line temperature, from then on the condenser fan speed will vary according to line temp, as does the head pressure!.
When charging these units you move the white wire on the PCB from no.2 to no.1 (or vice-versa) which allows the fan to bypass the speed control and remain on full power.
This can also be used to test the operation of the speed control PCB.

[Abe]

Unit does not have a head pressure control fitted to it. Anyway, today ( Sunday) I have been working all day on unit. I have relocated condensing unit from roof ( three stories up) to outside wall just a couple metres away from evaporator.

I removed "orifice" and fitted capillary tube metering device. System is working like a charm. Stella Artois in barrels will taste perfect Im assuming.

Thanks to all for a whole lot of valid information on this one, wish I could buy you all a beer!

[herefishy]

Originally posted by Aiyub
wish I could buy you all a beer!

I resemble that comment!!!!

(inside joke)

[BritCit_Juve]

A little bit of pertinant info for you all out there

I have heard that IMI have been having problems with their cellerators when they have been matched with basic R407c condensing units (no head pressure control). In this situation the units can in low ambients suffer excessive refrigerant glide. They have since started to only offer the cellerators with the (+) model.

Why would anyone, in the UK especially, want to install condensing units without head pressure control on equipment that is going to operate all year through?

[frank]

to what extent is the glide causing problems? - a lack of temperature control, icing, hunting, etc? It would be interesting knowing a little more.

[BritCit_Juve]

Sorry for the delay Frank

From what I can figure in low ambients, with the fan running full belt, the lower the evaporating temperatures are dropping with the result that the evaporator is freezing up.

I dont have any other info at the moment but when I do I will let you know.

[frank]

This is always the problem when the system has a fixed metering device without head pressure control.

When the ambient falls low ( as during the night ) and the condenser fan continues at full speed the liquid sub-cooling also increases. The sub-cooled liquid is then passed through the capillary and the "set " pressure drop - and hey presto! the low internal load is insufficient to evaporate the liquid refrigerant and we end up with icing.

This will happen with all refrigerants working just above zero deg C in an A/C situation and is no differant with R407c.

Frank

[Abe]

Frank

This unit "does" suffer from periodic icing up of evaporator, no doubt as per your explanation, ie: no head pressure condenser fan control, lower ambients exarcebating problem.

Evap has a dinky thermostat which " somewhat" helps when I turn the knob to warmer position and cut the compressor off

But then, the cellar temp suffers

Either IMI Marstair " should" fit either fan controls, or else defrost heaters with time switch !

Which is nonsensical considering this is only a Cellar Cooler

My prognosis: Evaporator is too small, design does not accomodate for evaporator icing

[BritCit_Juve]

Hi Aiyub

Marstair sell the condensing units with headpressure control fitted for low ambient operation, or without head pressure control for high ambient use.

Unfortunately accountants are in charge of the buyers purse and cheapest option rules so units are purchased without fsc for uk use.

Marstair offer a Fan Speed Control kit for retrofitting to the unit, as well as a de-ice thermostat kit for the cellerator.

[brookbank]

Before you purchase a de-ice stat or fan speed control, make sure you check the evaporater coil is clean.
These units foul in the core of the evaporator due to mould growth and you can only realy spot it by droping the pan and shining a torch on the front of the coil.

Running time is shorter in low ambients if the cellar is near the outside of the building so iceing is less of a problem than say a computor room a/c

Also if it has a tev. make sure it has a CSR start kit for the compressor.(also an extra)

I've have not seen a liquid line restrictor on an IMI cellar cooler , easy check was the liquid line insulated?

[Mark]

hi all
The cellar cooler split system explained can be piped using two different methods.
method A with the expansion device connected to the outdoor condensing unit (as supplied)allowing pipe runs up to a maximum of 80 meters (suction and expansion lines).

method B with the expansion device removed from the outdoor /ducted unit and connected to the indoor unit to give a suction and liquid line.(this restricts the maximum pipe run to 22.5 meters).

Method A allows the pipe run to be much longer but requires the need for expansion line to be insulated.
Method B eliminates the need for insulating both lines as it makes the (expansion) line know a liquid line but limits the maximum pipe run.

Also on some of the IMI Marstair heat pump systems there are two expansion devices ,one on ahu on suction line other on the expansion line situated on outdoor unit.
personally i think the need of a fan speed controller is imperative (especially in the uk)on these units to help prevent indoor coil frosting.(both applications)
hope this explains how the cellar cooler works using two piping methods regards mark

[rbartlett]

i agree with brookbank

most cellar coolers are badly maintained and in dire need of a chemical clean....

get the indoor unit chemical cleaned/pressure washed and then
'most' icing problems disappear.. ..either that or they are short of gas -or both ;-)


personally i feel fan speed control on cellars isn't that imperitive as most are located on the ends of buildings and exposed to the weather and hence their running times are greatly reduced in cooler climes.

cheers

richard

[Mark]

hi all
Was the issue of cleaning the evaparator not covered in past posts?.
I was merely expanding on the installation techniques ,so people can get a better understanding of how the cellerator system can be piped and how it works. .
The issue of a FSC covers different field/seasonal conditions ,it may be -1 oc outside.(uk) but In the cellar which has obviously different running conditions,the need to limit the frost formed on the evaparator helps the unit run more effeciently.
This particular angle i was trying to cover in my post so that people can read everyones threads and form there own opinion.
And covers the original questions raised.
regards mark

[Peter_1]

QUOTE [To understand what the fan speed does to LMTD and TD in maintaining head pressure during lower than design ambient conditions you should go to my http://optichiller.co.uk site and in the "Optichiller Explained" click on the LMTD explained link located a little down the page. [/B][/QUOTE]

Marc,
Link seems not working.
Was it replaced or removed?

Peter

[Peter_1]

Originally posted by Aiyub
Brian,

An " orifice" is fitted to this unit. It is located just after the shut off valve leaving the condenser.

As someone mentioned, these are prone to clogging up

I am going to remove this orifice

Am I doing the right thing?

Thanks to everyone for your help

Tot Siens

Hi Aiyub,
Why did you said "Tot siens"? Because this is a Dutch expression?
But it has to be "Tot ziens"

[Peter_1]

Oh...that's the reason. Never thought in that direction. Then it was correct spelled I think. Sorry.
Always amusing for us to read because South African sounds like a dialect of us but spoken by a child who don't knwo all the right words (like I in English)
But anyway, South African is almost 100% understandable for us and the language is mutch more ritcher then Dutch is.
We in Dutch use for new items (computers, fax, email...) almost always the English expressions. They not. They invent new words for it. We say computer like the English, they say 'Rekenaar'., a Zebra is a Streepjespaard (or translated Stripehorse)
More difficult for us to speak is the double negation.
I think you both can almost read Dutch text, is it?

[BritCit_Juve]

Check the head pressure control board. If it has a cappiliary to it then it is a pressure sensing device and will allow the fan the full operating range. If the pressure drops below 240PSI then it will allow the fan to stop.
If it has a black sensor head fitted to the liquid line then this will be limited to just above the stall speed of the fan.
In both cases they are set to maintain around 280PSI on R407C or 240PSI on R22. The sensor version is limited by its high min speed setting to ambients above 10°C below which over condensing can occure.
The pressure version will get lower but not much.
The expansion device on the liquid line means that the line from there onwards is in expansion and should be insulated.
You may get freezing of the expansion line especially if the mesh on the inlet to the restrictor is blocked, the ambient is below 10°C, you have a low refrigerant charge, there is minimal, load and/or the line isnt insulated.
Since 2000 the marstair condensing units have had head pressure control fitted and this has tended to be the pressure activated type.
I wouldn't recommend removing the expansion device as this is what allows the condensing unit to operate on a 20m lift without having to worry too much about liquid recievers or oil return.
One point however is that this system shouldf be fitted with oil traps every three meters up the vertical riser and if these aren't in then the compressor oil will be blocking up the evaporator coil not where it should be ;-)

[bernard]

Marstair cellar cooling.

You have a choice of fitting the expansion device on the outdoor unit or indoor unit. If you fit it on the out door unit the dishcharge line becomes part of the evaporator and this line should be insulated as well as the suction line. Therefore the dicharge line after the expansion devise will frost up espesially if it has not been insulated.