View Full Version : High Roofspace Temperatures and DX Evaps!

15-06-2016, 06:11 PM
Hi Guys.
I was looking at the classic Remote Supermarket Pack / Condensing Unit feeding 4 evaps in a line.
With common liquid and Suction lines which run across an insulated Floor (The roof of the chill chamber below).
The rest of the roof space is your typical unvented single skin warehouse shell.
Given the high temps that exist in the roof space at this time of year.
Has anyone ever looked at or drawn a conclusion, regarding the effect these high Heat loads would have on the Liquid and Suction Lines.
Which I would assume would affect the efficiency of the evaps ect?
I hope you get what I am asking!

15-06-2016, 08:35 PM
Are the lines insulated?
What do you call high temp? 35C? more?

15-06-2016, 10:38 PM
Hi Chemi.
Thanks for replying.
The suction line is insulated but the liquid line is not.
The system is on 404a.
Not sure of the actual temps up there as I can only access the roof space using a scissor lift.
But I know it gets very hot as I have been up there previously. the heat accumulates over time.
Much the same as a lot of older cold store roofs.
Historically I have used large woods fans to move air around in the roofs.

16-06-2016, 12:38 AM
I think the venerable Dossat bible mentioned this, you may have to drive up condensing pressure so liquid line can't absorb heat, have seen it in lidl warehouse where roof space hits 35/40, liquid lines flashing (fitted sight glass at TEV), but given most packs are oversized it probably only results in longer compressor run times

16-06-2016, 06:49 AM
Wise words Al.
I thought there might be something happening given the sustained heat load.
I will have to dig out my Dossat bible. (Pre Windows)
Thanks Grizzly

16-06-2016, 10:17 AM
Liquid line can possibly get flash gas once subcooling diminishes & more heat gained above saturated condensing pressure.
Would have to have enough transient time for this to happen, also any liquid risers up to roof if fed from anywhere below causing any pressure drops.
Have seen those liquid amplification pumps advertised, but never seen them in my neck of the woods.
Also most compressors suggest maximum superheat at compressor 20k.
Some of our older roof spaces can reach 60deg C, known as "super hot" & not much time to sort out superheat, don't know if that is possible in UK , if not it's a matter of time the way things are going with the climate change.

16-06-2016, 07:15 PM
Thanks Ranger.
If I find out more I will keep you guys posted!