Needs calibration, or new sensors??

[alexb]

I've got two Liebert Challenger 3000's and a MiniMate 1-ton.

All three units exibit the following behaviour when the outdoor ambient goes up close to about 60-65... The humidity level goes up past the setpoint, making the unit go into dehumidification mode. It stays in this mode until the temp drops the below temp. setpoint & the room is too cold. Apparently the re-heat is not working or not turned on.

These units don't have any fresh-air intake; how is the level of humidity so greatly correlated to the OD ambient? Our building is not full of holes; its well-insulated.

Then, to maintain the temperature setpoint, I end up raising the humidity setpoint to match ambient humidity - at least it allows the compressor to shut off. A third Challenger 3000 does <b>not</b> exibit this behaviour; it maintains temp & humidity just fine no matter what the OD ambient.

Are these units in bad need of sensor calibration, or should the senors be replaced?

[The Doctor]

if your unit is not set up to reheat during dehum, then you will likely overcool. Is your temp in the low 60s in the room? when your temp gets into that range and lower, your humidity will rise. but this is a longer shot than a basic maintenance issue like airflow, filters, refr. charge would have at being the culprit, but only after:

1. check reheat dipswitch, and then call for service to check reheat operation if that is not it.

sensors are a very unlikely culprit at this stage, especially more than one, given what you've described. I've worked on hundreds and hundreds , if not more, Lieberts and only replaced a couple sensors, on the older units mainly--the canister type.

[alexb]

A good example of what I was seeing...

With 45 OD Ambient______________(Normal)_________
Temp ambient: 73
Temp setpoint: 72 (2degree variance)
Humidity ambient: 45
Humidity setpoint: 50 (5degree variance)
Compressor normally cycles on/off as usual...

With 75 OD Ambient________________(Abnormal)_____
Temp ambient: 69
Temp setpoint: 72
Humidity ambient: 60
Humidity setpoint: 50
Compressor's been running for hours...


With the higher OD ambient, the higher humidity causes compressor to come on, to dehumidify, pushing the indor ambient way below setpoint. Apparently reheat is a problem, but what causes humidity to shoot up so far when OD ambient changes?

[gbfromsd]

what's yer hot gas solenoid doing while all this is going on?

[The Doctor]

A good example of what I was seeing...

With 45 OD Ambient______________(Normal)_________
Temp ambient: 73
Temp setpoint: 72 (2degree variance)
Humidity ambient: 45
Humidity setpoint: 50 (5degree variance)
Compressor normally cycles on/off as usual...

With 75 OD Ambient________________(Abnormal)_____
Temp ambient: 69
Temp setpoint: 72
Humidity ambient: 60
Humidity setpoint: 50
Compressor's been running for hours...


With the higher OD ambient, the higher humidity causes compressor to come on, to dehumidify, pushing the indor ambient way below setpoint. Apparently reheat is a problem, but what causes humidity to shoot up so far when OD ambient changes?

The answer to your question is: you're on the Eastern Seaboard. That area is locked in with moisture. That is to say, that is not unusual for that region.
I worked there for a place called Site Support Services, which is primarily a Liebert rep, in good business for 17 years as such, and they work on any critical environment, and subsequent equipment you can come up with. Check them out on their website if you have problems--they can deal with it effectively.
You're around Ellicott City? Man, I grew up not far from there, do I miss that place!

[alexb]

You're around Ellicott City? Man, I grew up not far from there, do I miss that place!

Thanks for the info on the HVAC establishment. --I'm near Frederick Rd & St. Johns Ln. in Ellicott City. --Small world...

[Airmechanical]

since you are not the technician you should call leibert for a certified leibert guru to make some adjustments and recommend some settings!

and remember the leibert will try its hardest to bring conditions to there set points, temps should not get too far out of range if reheat is operational

also it would not be a bad idea to have a seperate digital hygrometer to double check the environment temps and humidities!



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[alexb]

I found out what is causing the wild humidity swings in our area. It <b>is</b> related to OD humidity. This past week, there was high pressure over the northeast, dropping dewpoints down to ~10F with 60F dry-bulb (dry for this area).

A digital hygrometer has been measuring the humidity all week (the one with the round piece of paper that spins...) when that high pressure moved in, I watched the indoor humidity drop from 50 down to 10. Apparently the huge Trane RTUs do a better job at outdoor recirc. than what I thought.

Odd -- those Trane RTUs aren't ducted into this area I'm talking about - they're serviced only by the Lieberts.

BTW, the humidfier obviously doesn't work on the Liebert; the setpoint is 45%, and the unit indicates 15% ambient humidity.

[Randy S.]

Most computer rooms are actually very poorly isolated from the outdoor conditions, especially humidity.

I'd have a good look at reheats to start with.

[Airmechanical]

BTW, the humidfier obviously doesn't work on the Liebert; the setpoint is 45%, and the unit indicates 15% ambient humidity.

computers hate low humidity as much as they hate high humidity!



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