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properdouble
19-05-2015, 08:39 PM
Hi Guys
I have a walk in freezer room on which compressor has failed.
Once sourcing for new one with supplier we have found that condensing unit is half the capacity of evaporator.
Condensing unit is at 1.8kW and evaporator maximum capacity at -32C evaporating is 3.7kW.
i have recommended too customer to replace condensing unit but due to cost he decided to go with compressor.
Upon replacement i have recovered 2.7kg of R404a,replaced drier ,danfoss expansion valve ,new orifice NO.2 ,pressure tested,evacuated and begin charging.
I have charged to air on condenser plus 15K to achieve condensing temp.
At this point charge was 1.3kg of R404a.
Suction pressure was 20PSI evaporating at -26.5 with room temp around 8C.
Superheat 20K.
Subcooling 5K.
I was only getting beggining of evaporator frosted and sight glass nearly empty which got me concerned.
I have attempted to adjust superheat on the valve but my suction pressure shoot up to 40 PSI and discharged pressure raised condensing at 40C with external temp on condenser of 17C
Then i decided to readjust TEV back to where it was and adjust charge. I have left room at -4C and will go back tommorow morning first thing to check up on it.
My question is what would be best solution in order to get room to temp, adjust superheat by opening valve and flooding more liquid to coil,reducing charge thus leaving evaporator starved or installing size up orifice.
To be honest that system never runned effieciently being down to temp only in the morning when doors where shut all night it did struggled during the day.
Place does bake cakes all day loads of it and load ambient cakes often so there is pulldown required hence bigger condensing unit would have worked magic here.
Any thought on this would be greatly appreciated.
Thanks.

install monkey
19-05-2015, 09:39 PM
keep gassing:o

monkey spanners
19-05-2015, 09:52 PM
You need a full sight glass and the room down to temperature before you can check and adjust the superheat. How clean is the condenser?

The evaporator may have been oversized originally to lower the TD so as not to dry out the cakes too much.

Magoo
20-05-2015, 04:46 AM
The initial design would have been around a close system TD to reduce product weight loss, as per normal the load in rates would have gone out the window, and doors are open continuously.
Be very careful with selection of new compressor set, and re select a new TXV for evaporator, double check distributor selection if one is installed.

properdouble
20-05-2015, 08:22 PM
Hi Guys
Thanks for responds.
I have gone to site and put extra 0.5kg which cleared sight glass .At about -16 superheat was 20k and 5k subcooling.
I adjusted TEV by opening valve 2.5 turn and got 10k superheat and 10k subcooling but i was evaporating at -22 with room at -16 still.
Room was not goming down below at all so i readjusted setting to original and got about -28 evaporating with high superheat again.
I left site and guy called me 4 hours later to tell me that temp was -17 i will check with him what temp in the morning.
question is do you select orifice size to match evaporator capacity or condensing unit capacity?
Also mind you for frozen food storage ,normal usage that condensing unit is still to small for that room so it will always struggle as it has in the past.
Thanks in advance.

monkey spanners
20-05-2015, 11:01 PM
I'd give the evap, unit and room details to the tech department at the wholesalers and get them to size the orifice. If the room has a lot of food in it that is warm it will take a while to bring down the temperature. It can take a day or two! Many rooms are sized to be a holding room, designed to be re stocked with food near the correct temperature.

2.5 turns is a lot to have to adjust a TEV, it would make me wonder if the orifice was the correct size, or if the valve was functioning correctly.
As a rule of thumb (and thats all it is) i would expect the evaporating temperature to be 12c below the room temperature, sometimes its less and sometimes its more depending on the system.

Magoo
21-05-2015, 12:50 AM
System capacity is governed by compressor capacity and TXV should match compressor.

properdouble
21-05-2015, 07:50 PM
Hi
Thanks for reply. I have installed brand new TEV. Site rang this morning saying is not working. Went in to find timer 20 amp C rated breaker feeding compressor contactor tripped and main 3 phase 32A breaker tripped. unit is single phase but incoming supply is 3 phase as it used to be 3 phase condensing unit back in the days so it looks. Now i reset everything works again i checked all components down condensing side nothing down to earth all heaters fans etc fine. Defrost feed has 16A separated breaker so that is to be excluded. I am really lost here.
By the way should i be getting continuity between neutral and earth, earth live on all terminals . Soon as i disconnect main neutral incoming from switchboard i don't get any continuity between them.
And way it does tripped straight after defrost obviously i run it trough cycle and seen cutting in after defrost it was drawing 11A on start up and 9 thereafter with amps dropping with temp.
I am lost and sure it will trip tonight again and timer will stop soon at defrost cycle end.
Any thoughts on that would be appreciated.
Thanks

PaulZ
21-05-2015, 11:20 PM
Hi pd
If it's tripping after a defrost then there may be too much load for the compressor.
Was the new TX sized to the compressor or the evap, see Magoo's post, some more info on the compressor and evap would be good.
You say it draws 11 amp on start but trips a 32 amp breaker, could be more than an overloaded compressor or your amp meter is not accurate.
If it is only an overloaded compressor you can install a crankcase pressure regulator this will hold the suction back after defrost and stop the compressor overloading.
Regards
Paul

Martin Davies
23-05-2015, 10:51 AM
Hi have you fixed this now? Sounds like you have lost a neutral somewhere if you have live coming back through earth? Or when it's been converted from 3ph to 1ph something has not been done correctly? Get a sparky in first to test the supply probably.

With the temp problems, does the condenser have fan speed controller?

properdouble
23-05-2015, 11:51 AM
Hi Guys
I rang guy yesterday morning and he was happy saying room is at -20 and working. I suggested that because electrical issue was intermittent to leave it empty still over weekend and if it is good on monday then use it.
Whatever i have desconnected and recconected when i was testing circuit must have sort it out. The only thing i have replaced was 20A breaker feeding condensing unit contactor.
More or less i did reccomended that they get an electrician to test supply should it do it again as i cannot see anything wrong with any components. Alternatively there was cranckase heater that was disconnected which dosent surprise me as this compressor was never getting cold so i left it as it was originally upon fitting new one. We have had chilli nights around 5 degrees tough lately so just came to my mind that perhaps oil got little cold and hence high starting amps at night?
Anyhow it is working and touch wood it stays that way before i go bold lol.
Thankd again for your input on the subject much appreciated.