Help With Liebert 3000 Unit

[Chemee]

We have a room that is being converted to a calibration lab. The environmental conditions that have to be met are 68 F +/- 5 and less than 55% RH. A Liebert 3000 unit was installed. The installer left the setpoints at 68 F & 40% RH. The Liebert display reports the actual temperature & humidity are near these values. However, a chart recorder in the room says the temperature is 69 F & RH is 65%.

I know very little about HVAC and the project engineer will probably contact the installer. However, for future reference & to gain additional knowledge, how should we adjust the setpoints to achieve a RH less than 55%?

Thanks.

 

[AbbyNormal]

68F and 40% is pretty tough with DX cooling in an non-arid area. Pretty much need a desicant.Be an easy condition to maintain in the winter

65% sounds excessive, but you should be able to maintain 50%.

Usually labs are pressurized to prevent infiltration and therefore outside humidity from entering the space.

You would be better of having the tech adjust the setpoints, or better yet a factory rep.

 

[walkes]

Chemee,

Put your chart recorded and the sensor for the Liebert in close proximity to each other. If the chart reader is still reading a different measurement, have a tech come in to calibrate the instruments/sensors and verify the actual space conditions.

 

[cammax]

68 deg F is really to cold for a Liebert, I belive there spec's say they are ok down to 68 but they perform much better at 72 deg F and that should be there field Min setpoint for temp, as for humidity pushing this much below 50% on DX alone might be trouble some, I hope you have a tight vapour barrier and have all air tight openings (doors)

my info comes from Henry Fudge from Leiberts Training Center in Columbus,Ohio

 

[Chemee]

Thank you for your responses. We raised the unit setpoint to 71 degrees & placed a chart recorder by the unit. The recorder is reading a temperature of 70 F & humidity of 58%. We have been successful in dropping the humidity 7% by increasing the temperature. However, we still need to be below 55% & we can't go any higher on temperature due to environmental requirements. The Liebert is reading 69 F and 37% humidity (the setpoint was lowered from 40-35%). So the recorder & Liebert agree on temp but not on humidity. We will have someone check the Liebert's humidity operation.

Also, the room is not tight. There is no vapor barrier. So in-leakage is an issue. The room that is becoming this mini-lab is a room that served as storage for another lab. If this is an issue in 75 F weather, I know we are doomed during summer.

 

[AbbyNormal]

You won't Liebert publish performance data for anything less than 72F @ 50%.

I have a redundant pair of 40 ton industrial DX models doing a telco room data centre, and the client was pushing for 67F as a setpoint as the old systems had poor air distribution and therefore hotspots when the set point was any higher than that.

After a haggling period, I managed to get the client to agree with a 70 degree set point. The system maintains that temperature with no hot spots, however IT people are set in their ways and the room is maintained at 67F and 50%.

A humid climate, however a pressurized space with a big internal sensible load. So 68 at 50% is not impossible, but 68F @ 40% is not happening in the summer time.

 

[KiwiMace]

All your answers will be given in 2 minutes with a sling psychrometer. And a nice piece of kit to get the calibration lab started =)

Digital R. humidity is expensive to measure accurately; 3% is your typical RH sensor, with a big cost jump to 2%. Trust the instruments accordingly.

 

[AbbyNormal]

Slings not always that accurate. Impurities in the water, swing them too slow and they read high on the wet bulbs