Can one ref-compressor unit be used to have 2 independent temperatures

[821326]

Hi,

I am involved in fishing boat refrigeration units and I have a doubt. If some of you could help me in this it will be great!

The design requirement is to cool two compartments at two different temperatures to be controlled independently.
The two compartments and the temperatures are:

Fish hall : -16 oC
Chill bath : -1 oC

I am in need of using a single compressor-condenser unit for this application.

I am thinking of using two evaporators with expansion valves and individual temperature controllers for each cabin which will ON-OFF the ref-supply to each evaporator using solenoid controlled ON-OFF valves.
Compressor will run continuously and only OFF if both evaporator coolent supply valves are closed as a result of required temperature achievement.

Is this possible and practiced?
What issues will rise?
or Do I have to revert back to 2 individual compressor systems for each cabin?

Thanks.

 

[Compositepro]

It might be easier to use a glycol loop between the fish hall and the chill bath. When the chill bath needs cooling turn on a pump to circulate glycol to the fish hall for cooling.

 

[EnergyProfessional]

you can do all that. Keep in mind, the lower the temperature the less efficient the cycle will be.
If you only have one system, all "cold" is generated based on the lower efficiency for the lower temperature.

Two independent systems may be more economical since the -1°C system will be much more efficient.

 

[BM4BRANES]

valve mgf's all make evap pressure regulators(EPR).An epr on the warmer coil will do the job but you'll need an unloading compressor to manage part load conditions.

The key concept missed is redundancy. Putting all the eggs in one basket will be a huge blunder! saving a few dollars up front will cost many more lost later on an application that screams DIFFERED MAINTENANCE.

 

[HEC]

Have designed built and successfully operated a similar system. Ammonia chilled water system, return water chiller at -1C and an ice tank at -10C. The compressor suction pressure was run at the lower temperature/pressure and a back pressure modulating valve was used to ensure the return water chiller did not get cold enough to freeze. There was a bank of compressors to service the load. this was a combination of Screw and Reciprocating.

The issues raised in other replies of efficiency and reliability must also be addressed. I presume from your fishing boat remark that this system will be giong to sea. In which case, two compressors woud be best from reliability/availability stand point. An enhancement of this is to use both compressors to service both spaces. Use advanced control system (PLC) to detect which space is on and run variable suction pressure set points to maintain most efficient operation.

Mark Hutton

 

[CH5OH]

your refrigeration cycle would be something like:
1 compressor, 1 condensor
compressor on/off cycle defined by lowest temperature
(vapour pressure @ -16 degC)
1 evaporater and expansion valve with its temp. bulb on outlet evaporator (4 degC superheated = -12 degC)
1 evaporater and expansion valve with its temp. bulb on outlet evaporator (4 degC superheated = 3 degC)
between this evaporator and the common return line to compressor (suction) there will be a pressure regulating valve, keeping the evaporator pressure equal to the vapour pressure @ -1 degC