Talylawdi
03-02-2016, 09:59 PM
Hi All
Was hoping some of you old wise engineers will help me with this one.
Carrying out a service in a large holding chiller today which has 3 off identical systems. Only two systems are running at present and it look's like it's been this way for some time as the motor is missing from the compressor and the condenser coil block is also missing from the redundant system. The required room temperature is 0c. Staff have told me the room used to be used as a low temp holding freezer, running at -18c.
The two running systems consist of
Evaporator - LU-VE CONTARDO - Model no. H1534 E4
Condensing unit - FRASCOLD - Model no. SA20-71
Compressor - FRASCOLD - Model no. V20-71
Running on R404a
T.E.V - DANFOSS TE12 with No.5 orifice
1'' 5/8 suction line
7/8 liquid line
Each system has it's own control panel
I Carried out a thorough inspection and clean of all equipment.
The equipment was struggling to achieve set point.
After defrosting both systems and carrying out a test run. To begin with, at the inlet of the distributor/spider there was frosting with a even frost traveling up each of the 18 1/4 lines which entered the face of the evaporator on the fan's side of the coil. Over a period of a couple of hours the Fan's side face of the coil frosted over, frost then worked it's way back through the coil eventually causing the suction line to frost back to the compressor. There was a accumulator in the suction line before the compressor inlet which was at one point frosted over also. The motor end of the compressor where the suction rotolock is situated on top of and the accumulator were the only rusty components on the condensing unit. The defrost interval was 4 hours, endurance of 60 minutes, stop temp of 50c, so i assume someone has been treating the symptoms and not the cause and the frosting issue has been happening for some time.
Evaporator coil and condensing coil were clean with all fans running correctly.
Both systems were behaving similarly
Tried to take all readings from system at the start of cycle when evap coil was clear of frost.
Suction pressure at evaporator - 3.4 Bar
Suction line temp at evaporator remained steady at 1c before any frosting started
Expansion valve outlet pressure - 5 Bar
Suction pressure at compressor - 2.5 Bar
Suction line temp at compressor remained stedy at 1c before any frosting started
Liquid receiver outlet pressure - 13 Bar
Condenser outlet temp - 23c
Discharge temp 60c
Liquid line sight glass clear
Evaporator Air On - 2.3c
Air Off - -1.5c
Condenser Air On - 10c
Air Off - 24c
As time went on as mentioned the evaporator frosted over, restricting air flow, preventing the liquid in the coil boiling off, the suction pressure dropped and liquid was returning to compressor.
Didn't make any adjustment to T.E.V as wanted to gather some more information on equipment first.
Both systems did eventually achieve set point. At that point before any defrost cycle the evaporator fans cleared the coil of frost and the condensate drain outlet was like a open water tap.
My question is when the evaporator was clear of frost at start, the super heat was around 10c which isn't low at evap outlet.
Why was there frosting through the distributor?
This seems to be the cause of the start of the problem. I pumped system over and disconnected pipe at inlet of distributor. Visual inspection showed no blockage, Blew through with nitrogen, also confirming no restriction. Re-connected everything and re-commissioned system.
I am now thinking there is some sort of balancing issue between cond unit and evap or possible t.e.v not sized correctly. Can't find any information on this condensing unit. As mentioned, staff have told me this was a holding freezer and it looks like this equipment was pulling temp down to -18c at the time.
Is it a low back pressure compressor?
Is it operating at a to high evaporating temp, possible outside it's envelope?
Is a 1.6 Bar pressure drop through the distributor and evap coil to high?
Sorry to be so long winded, but wanted to add as much detail as possible.
Have also attached a pic of T.E.V and side of evap at start of cycle.
Regards
Was hoping some of you old wise engineers will help me with this one.
Carrying out a service in a large holding chiller today which has 3 off identical systems. Only two systems are running at present and it look's like it's been this way for some time as the motor is missing from the compressor and the condenser coil block is also missing from the redundant system. The required room temperature is 0c. Staff have told me the room used to be used as a low temp holding freezer, running at -18c.
The two running systems consist of
Evaporator - LU-VE CONTARDO - Model no. H1534 E4
Condensing unit - FRASCOLD - Model no. SA20-71
Compressor - FRASCOLD - Model no. V20-71
Running on R404a
T.E.V - DANFOSS TE12 with No.5 orifice
1'' 5/8 suction line
7/8 liquid line
Each system has it's own control panel
I Carried out a thorough inspection and clean of all equipment.
The equipment was struggling to achieve set point.
After defrosting both systems and carrying out a test run. To begin with, at the inlet of the distributor/spider there was frosting with a even frost traveling up each of the 18 1/4 lines which entered the face of the evaporator on the fan's side of the coil. Over a period of a couple of hours the Fan's side face of the coil frosted over, frost then worked it's way back through the coil eventually causing the suction line to frost back to the compressor. There was a accumulator in the suction line before the compressor inlet which was at one point frosted over also. The motor end of the compressor where the suction rotolock is situated on top of and the accumulator were the only rusty components on the condensing unit. The defrost interval was 4 hours, endurance of 60 minutes, stop temp of 50c, so i assume someone has been treating the symptoms and not the cause and the frosting issue has been happening for some time.
Evaporator coil and condensing coil were clean with all fans running correctly.
Both systems were behaving similarly
Tried to take all readings from system at the start of cycle when evap coil was clear of frost.
Suction pressure at evaporator - 3.4 Bar
Suction line temp at evaporator remained steady at 1c before any frosting started
Expansion valve outlet pressure - 5 Bar
Suction pressure at compressor - 2.5 Bar
Suction line temp at compressor remained stedy at 1c before any frosting started
Liquid receiver outlet pressure - 13 Bar
Condenser outlet temp - 23c
Discharge temp 60c
Liquid line sight glass clear
Evaporator Air On - 2.3c
Air Off - -1.5c
Condenser Air On - 10c
Air Off - 24c
As time went on as mentioned the evaporator frosted over, restricting air flow, preventing the liquid in the coil boiling off, the suction pressure dropped and liquid was returning to compressor.
Didn't make any adjustment to T.E.V as wanted to gather some more information on equipment first.
Both systems did eventually achieve set point. At that point before any defrost cycle the evaporator fans cleared the coil of frost and the condensate drain outlet was like a open water tap.
My question is when the evaporator was clear of frost at start, the super heat was around 10c which isn't low at evap outlet.
Why was there frosting through the distributor?
This seems to be the cause of the start of the problem. I pumped system over and disconnected pipe at inlet of distributor. Visual inspection showed no blockage, Blew through with nitrogen, also confirming no restriction. Re-connected everything and re-commissioned system.
I am now thinking there is some sort of balancing issue between cond unit and evap or possible t.e.v not sized correctly. Can't find any information on this condensing unit. As mentioned, staff have told me this was a holding freezer and it looks like this equipment was pulling temp down to -18c at the time.
Is it a low back pressure compressor?
Is it operating at a to high evaporating temp, possible outside it's envelope?
Is a 1.6 Bar pressure drop through the distributor and evap coil to high?
Sorry to be so long winded, but wanted to add as much detail as possible.
Have also attached a pic of T.E.V and side of evap at start of cycle.
Regards