Screw Chiller Operation Ambient Temperature

Your second paragraph is correct; the specification is nonsense. I hope someone fries the idiot who wrote it (at the specified unlimited temperature, too). Not often does Hellfire make it into an engineering goal.

But not to give up totally.... Whoever wants this probably just means some kind of chiller that can be run in a desert, say dry bulb not to exceed 120°F more than 2% of the time. This makes the refrigerant condensing temperature about 140°F max. Oh well, military intelligence is to intelligence--as military justice is to justice--as military music is to music.

Now comes the research part: finding a suitable refrigerant. I don't have enough data to make a selection. What are they chilling, and what temperature do they want? Worst case, a two-stage system with an exotic refrigerant choice.

It is for air conditioning application, thanks for your comment.

This is why they manufacture 'Desert Chillers'.

First, you need to get some additional information from the customer, and we need some additional info from you:

Please confirm they mean the condensing has to be done using air at the (potentially Hellfire) temperature or do only they mean that the screw compressor can't have a water jacket (which they typically don't)?

What is the altitude and geographical location? If you're needing to design for condensing, they MUST specify the condensing upper temperature limit or you should NO-BID! If you know the location, maybe you can go through the ASHRAE Fundamentals book (or elsewhere) and find the 1% 3% or 5% DB temperature to get an idea of your condensing surface area required.

Start with the heat the condenser must reject (process heat plus compressor input HP) then using the standard air side equation: Heat Load = 1.08 x CFM x Delta-T (which is accurate at sea level only, hence the 1.08... here in Tucson at 2600 feet ASL we must use 1.0 because the air is less dense here due to altitude.)

Or is it that they are talking about the compressor cooling alone, (Compressor case cooling is typically handled by the low temperature of the refrigerant taking the heat of compression away with it, but you haven't specified any operating conditions so I'm guessing.) and it is going to be installed in a compressor room without cooling?