PDA

View Full Version : Total suction superheat on remote systems



sokold
13-07-2011, 08:24 PM
Hi all, as the title suggests i'd like to ask about total SSH. Specifically refrigeration.

It's not always possible or practical to have the guages attached to the evap, so you end up having to deal with pressure drops, 50m pipe runs etc and end up checking the superheat at the condensing unit.

I've heard/read that about 15K shouldn't cause any problems. I tend to make sure that the compressor's not too hot and that it's not rattling away and sweating like the preverbial.

So i was wondering if there's a definitive answer, or because of the random length of pipe runs a ball park figure is the best way to go eg. 15k

Any thought's would be welcome

cheers

mad fridgie
14-07-2011, 12:34 AM
Really to broad a question, on many LT applications, then max compressor inlet SH is 10C

monkey spanners
14-07-2011, 12:37 AM
A trick i read in an old refrigeration manual was to turn the compressor off an watch the suction gauge, ( needs to be non damped) if there is a pressure drop over the suction line the gauge will jump 2 or 3 psi or whatever the pressure drop is, sit there for a very short time and then gradually rise as the system pressure equalises.
This will give you a rough evap pressure which when combined with a temp reading by the tev phial will give you what you need to work out the evaporator superheat.

The acceptable level of superheat at the compressor suction depends on the model of comp and the application but i seem to remember around 20/30K being ok but maybe others will correct me on this.

Jon :)

sokold
14-07-2011, 07:57 AM
thanks for the replies,


Certain comps. eg. maneurop rely on suction gas cooling and don't like high superheat, which is where the myth that they can pump liquid comes from i think.
So even if it had a 100m pipe run I'd still adjust the valve to keep the compressor shell temps sensible. The internal overload can take hours to reset if it trips out on high temp......that really spoils your day :)

So keeping it within say 15-30k should be a pretty safe set of ballpark numbers to go by ?

750 Valve
24-07-2011, 01:29 PM
I'd always aim to keep it under 20K, about 10K would be ideal.... unless you are talking co2 then 30K on LT and 20K on MT

Magoo
25-07-2011, 02:04 AM
hi Monkey Spanners.
that is good advise,stopping the compressor and checking momentary rise, filed and memorized.
magoo

D.D.KORANNE
28-07-2011, 11:40 AM
20K is what i use for compressor selection and haven`t had any difficulties ....... 10 k would be difficult considering about 7k tex valve superheat for evaporator ........ Ideally check with compressor manufacturer`s recommendation .

sokold
29-07-2011, 08:37 PM
I think i'm going to stick with 15K :)

bill1983
08-08-2011, 08:37 PM
don't forget it can be higher if additional cooling is supplied to the compressor. most manufacturers recommend 20k maximum before fitting a fan or injection cooling.