Dual evaporator system using a junction block and solenoid

[neslorelyks]

Hi all,

I recently joined and this is my first post. I am a mechanical engineering student and working on my senior design project which just so happens to be a solar powered bulk-liquid refrigerator. Before I ask my question I would like to give some background information:

- refrigerator is using a direct expansion heat exchanger to cool goats milk to 40 F
- before going into the refrigerator, the milk will be passed through an immersion chiller
- the water being pumped through the immersion chiller will be chilled (hopefully by the same compressor used to chill the milk)

My question: Can one compressor be used to circulate refrigerant through two different evaporator systems using a junction block and a switching solenoid? I planned to use the same condenser.

It seems trivial but I wanted to ask the experts and get a feel for how common this is implemented and any other ideas you all may have.

Thanks

[Brian_UK]

You can have as many evaporators as your condensing unit will handle, be it one large one or several smaller ones. Imagine it as a supermarket system.
http://sporlan.jandrewschoen.com/5-180.pdf

Investigate the use of EPR (evaporator pressure regulator) valves to control the temperature of each evaporator.

Information here --
http://sporlan.jandrewschoen.com/prvs.shtm

Sorry, forgot my manners - welcome to the forum, hope you enjoy it.

[neslorelyks]

Thanks for the quick reply.

I was probably unclear about my intent. I intend to use only one evaporator at a time (one evap. is for cooling milk and the other is for cooling water for immersion chiller). My question is kind of elementary and I guess I should be asking if there are specific valves designed to switch between two completely separate evaporator systems. The cheapest selection is best in this case and that was the reason I was thinking about a simple junction block with solenoid/ball valve.

If I understand the linked picture, these evaporators are running at the same time off of the compressors. Let me know if I am incorrect. Thanks again for the quick reply.

[Brian_UK]

You can, I believe, get three port valves but they tend to be for vapour and not liquid use.

Re the linked picture, yes the evaps work at the same time.

You could use simple solenoid valves, one in each evaporator liquid line prior to the expansion devices, valves or capillaries. (Please use valves)

This way you can also incorporate a pump down system by shutting both valves.

Be aware that you will need to ensure that the unused evaporator is not oil logged or full of refrigerant when not in use. There is a danger of liquid floodback.

[monkey spanners]

Hi,

Thats the way a lot of commercial milk cooling systems work. One condensing unit to make ice over night which switches over to cool the milk storage tank during milking. The ice water is pumped through a heat exchanger during milking to pre cool the milk before it is cooled in the tank.

They use liquid line solenoid valves to switch between the two evaporators, and i would recommend some check valves in the suction line at each evaporator exit. The condensing unit is run on pump down cut out. A relay makes sure the milk tank gets proirity over the icebuilder and that only one can try and run at the same time.

The pipework need carefull consideration to ensure oil returns ok, you would be surprised by the number of these where people have tee'd into a pipe from below allowing oil to run into the idle evaporator, and the compressor to snap a rod

[neslorelyks]

Thanks for all the replies. I will take everything said into consideration and will most likely have more questions later. Thanks again for the advice.