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Air cooled condenser (R407C) operating at -30C/-20F
- Thread starter Lubos
- Start date
Lubos:
The capacity of the TEV is a variable, dependent on the pressure differential across the valve. Greater pressure drop across the TEV equals greater TEV capacity. So it's important to keep the head pressure high enough to maintain the required pressure drop across the TEV. If the inlet pressure to the valve is due to low condensing pressure because the outside air temperature is too cold then you need to install the appropriate head pressure controls. Otherwise this can cause multi-circuit evaporators and parallel evaporators connected to a single refrigerant distributor to receive an unequal percentage of the total refrigerant so when each circuit is not subjected to the same heat load, the lightly loaded circuits will allow liquid refrigerant or low temperature vapor to enter the suction line and throttle the TEV. This will cause normally loaded circuits to be deprived of their share of the refrigerant. The net result is a loss of refrigerated evaporator surface and a potentially oversized TEV. You can check the temperature of the suction outlets of each distributor circuit before the suction header. Unequal temperatures at these locations are the result of unequal loading.
The capacity of the TEV is a variable, dependent on the pressure differential across the valve. Greater pressure drop across the TEV equals greater TEV capacity. So it's important to keep the head pressure high enough to maintain the required pressure drop across the TEV. If the inlet pressure to the valve is due to low condensing pressure because the outside air temperature is too cold then you need to install the appropriate head pressure controls. Otherwise this can cause multi-circuit evaporators and parallel evaporators connected to a single refrigerant distributor to receive an unequal percentage of the total refrigerant so when each circuit is not subjected to the same heat load, the lightly loaded circuits will allow liquid refrigerant or low temperature vapor to enter the suction line and throttle the TEV. This will cause normally loaded circuits to be deprived of their share of the refrigerant. The net result is a loss of refrigerated evaporator surface and a potentially oversized TEV. You can check the temperature of the suction outlets of each distributor circuit before the suction header. Unequal temperatures at these locations are the result of unequal loading.
Lubos
I support what imok2 has posted. I will add that during off periods the condenser enclosure may need to be heated to maintain minimum operating temeratures for the oil fail switch if equipped.(I had data on this, but now can I find it, NO!)
Using a pump down control will ensure refrigerant is not logging in the crankcase, a crankcase heater alone is not enough in this instance (MHO).
Also a suction accumulator maybe.
For head pressure control, I would use a pressure switch to turn on/off the condenser fan(s). Its simple and easy and low cost.
Good Luck
pennpoint
I support what imok2 has posted. I will add that during off periods the condenser enclosure may need to be heated to maintain minimum operating temeratures for the oil fail switch if equipped.(I had data on this, but now can I find it, NO!)
Using a pump down control will ensure refrigerant is not logging in the crankcase, a crankcase heater alone is not enough in this instance (MHO).
Also a suction accumulator maybe.
For head pressure control, I would use a pressure switch to turn on/off the condenser fan(s). Its simple and easy and low cost.
Good Luck
pennpoint
For this low of temperature you need the following:
1. Condenser flooding head pressure control. It is the only thing that will work. Sometimes called a "Headmaster" after the brand name of the valve by Alco controls.
2.Heated, insulated receiver. You will HAVE to have a receiver with the system mention in #1.
3.Crankcase heat. Probably slap two of them on.
If this is an existing system, and the spec is -20F, but it never really gets this cold, you can tape cardboard in front of the condenser to get by. Sounds mickey-mouse (it is) but it works.
Or b...
Move to CA or FL!
Clyde
1. Condenser flooding head pressure control. It is the only thing that will work. Sometimes called a "Headmaster" after the brand name of the valve by Alco controls.
2.Heated, insulated receiver. You will HAVE to have a receiver with the system mention in #1.
3.Crankcase heat. Probably slap two of them on.
If this is an existing system, and the spec is -20F, but it never really gets this cold, you can tape cardboard in front of the condenser to get by. Sounds mickey-mouse (it is) but it works.
Or b...
Move to CA or FL!
Clyde
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