Trane 5/12 ton ycd, low ambient , 55 space temp

[kraftykid]

Hi new to this site, but have some questions about low ambient mechanical cooling, with a space temp of 55 degrees year round, and told to disable economizers.

2 Trane ycd's .....sorry I do not have the full m#/S#
1 is 1h/1c 5 ton
1 is 2h/2c 7.5/10/12 ton?
ALL CAP TUBES
#1 stupid idea to disable economizers (Wisconsin)
#2 if humidity is questionable, use enthalpy controls

Mods:
Fan cycling switches
Lo press switches
Clixon freez stats
CCH
Timers on lps (I recomended delay on break, trane already has delay on make and break, not really necessary) (questionable 30 sec to 2 min depending on what year unit is from)

Method used to disable economizer: jump out OA sensor
Problem: resistance above 75 degrees? brings on cond fan #2

Possible problems:
Evap icing
damage to condensate pan/trap/line
compressor short cycling
liquid compressor slugging
oil foaming/blowout
not air balanced
condenser coil freezup? Wisconsin?

Recomendations for low temp applications like this (some not worth it, if mechanical cooling needed, use a Liebert)

#1 use economizer using adjustable temp controller like the A119 with ucp seeing steady temp, then switched resistance temp to either allow economizer to work or not (this should work, please comment on this!!!!!!!,,,also, does mechanical cooling lock out at 20 degrees? Trane cooling rated at 0 to 115 degrees)
#2 hot gas & controls
3 electric evap defrost
4 electric heaters in return
5 heat tape for condensate
6 insulate liquid line
7 speed up blower fan for lower td
8 suction accumulators
9 heated liq line receivers with ORI/ORD valves
10 txvs

Trane has a 3 min auto reset lockout after 4 lps trips 1 hr to restart I think.
Manual reset after 4 hps trips, with 15 min between restart man reset after.
Changeover from econ to mech after economizer has full open signal, and does not see 0.2 degree/min change...3 min changeover occurs

Anyone have some helpful input to this?
Has anyone ever tried this?
Are the compressors even rated for use at these temps?
Base of RTU's close to roof line. Any other problems? (Economizer screen freezing/ no oa if econo used, or condenser damage due to ice dam?)

Thanks guys

[Healey Nut]

Your first mistake is to use a unit that is designed to cool/heat a space for comfort cooling ie space temp range 67/85 ish degrees F .
You need a specialty system designed specifically for your intended use . No amount of modification and fooling around with a rooftop unit is going to provide you with the conditions and reliability you need for the application .
You need a specialized system period ....

[kraftykid]

A lee temp liebert is what would be needed. They can control head pressure well below freezing oa temps, and still be able to maintain 55 degree space temps, and can be ordered, and designed for oa temp/humidity controls for indoor fan, although not too many I have seen bring in oa.

Has anyone modified a trane rtu for theese types of conditions, without use of economizer?

[dlove]

A lee temp liebert is what would be needed. They can control head pressure well below freezing oa temps, and still be able to maintain 55 degree space temps, and can be ordered, and designed for oa temp/humidity controls for indoor fan, although not too many I have seen bring in oa.

Has anyone modified a trane rtu for theese types of conditions, without use of economizer?

what is this going to be used for and what load does it have.

[kraftykid]

Huge sealed insulated chemical drums. Probally highly flamable, and wrecked with moisture I'm guessing.

[kraftykid]

possible plastic aditives? or paint aditives?