Low Ambient Design

[jwasir]

Hi,

I would like to know about the additional points/equipments that should be taken care of when designing a system for low ambient conditions for eg -60F (-51°C).

Normally for systems operating till -40F (-40°C), we generally use fan cycling with low ambient package (flooded condenser).

Regards,

[TXiceman]

You may need to add receiver heat as well. Hopefully you can get the compressor and receiver into an indoor area. Getting one started at these temps can be a real bear.

How large is the system.

Ken

[wambat]

Specific Requirements for Extreme Low Ambient Conditions or The Low Ambient Kit and Heated, Insulated Receivers.

Operating a refrigeration system under extreme low ambient conditions requires a more aggressive approach in order to maintain the minimum design condensing temperature and receiver pressure for an effective compressor start.
A condenser and receiver exposed to these low ambient conditions will suffer the effects of ambient sub cooling resulting in condenser and receiver pressures corresponding to the equivalent pressure corresponding to the ambient temperature.
For a complete read please go here: http://www.heatcraftrpd.com/resources/techtopics/Tech%20Topics%20Condenser.pdf :D

[smpsmp45]

We had done a cold store for Antarctica - Surprised. It was meant for some experimentation. Ofcourse it was an air cooled condenser & we had used heaters to increase the Condesning pr in the system It worked very well.

[Samarjit Sen]

Hi jwasir,

For very low ambient conditions, you have to use refrigeration compressor which can and are designed for such temperatures. At low temperatures the mettulurgy changes.

It also depends on the variation of the ambient temperatures and what is the inside temperatures to be maintained.

[jwasir]

Thanks ALL,

The system is designed for -40F application.

Its chiller with 20 TR capacity.

System is equipped with sufficient glycol concentration, heated receivers, low ambient kit, comp are heated and are suitable for particular application.

For some reason, when wind chill drops to -60F, system shuts.

Any ideas!!

[Gary]

Seems like this situation would be ideal for LPA:

http://www.refrigeration-engineer.com/forums/showthread.php?t=1814

[Samarjit Sen]

Hi jwasir,

I went through the reference which gary has provided and I guess it answers your question.

At present I am also working on some what a similar project and your questions have helped me to find the right solutions. If I come accross some other information, I shall share with the RE.

[TXiceman]

For some reason, when wind chill drops to -60F, system shuts.

Any ideas!!

Wind chill will not have any effect on dry mechanical equipment. Wind chill comes from the apparent temperature due to surface evaporation of a living surface such as a plant, animal or human.

In an application like you are describing, the best thing to do is to get the compression equipment, evaporator and receiver into an indoor area that is not subject o such extremes. If this is not possible, it needs a house or enclosure around the unit and you may even consider ducting the condenser air with a recycle or bypass arrangement to get some heat into the system. Of course you will still most likely need a heated and insulated receiver.

If the compressor housing will see the -60 dF or C ambient, you need to look at alternate compressor to get one that is suitable for such extremes. You also have to look at the valves and pipe used in the system.

One company that can help with a special application like this and use a ducted condenser is RAE Corp in Pryor, Oklahoma, www.rae-corp.com. I would bypass the sales group and speak to the manager of application engineering, Jay Kindle.

Ken

[The MG Pony]

Why not use thermo syphone system? christ at those extreams you seem to have free cooling?

[jwasir]

The MG Pony,

Do you have any data on Thermo Syphone System.

[The MG Pony]

Not sure if there is any thing large scale but look up heat pipes, or depending on the conditioned temp simple take in out side air and run it through the boxes after being filtered and the humidity adjusted.

Seems like the mechanicle system can be moth balled during the cold periods and take advantage of the low temps that naturaly occure would be a far better options in the long run rather then consuming electricity to get the room cool