Auditorium high humidity

[tschnuckel]

I'm a facility manager for a 400 seat auditorium. I'm not the maintenance person and can't control the KCM software. For 5 years or more, the humidity during the summer with the A/C on runs between 75-80%. Room setpoint is 68*F. There is ZERO water dripping down the drain from the evaporator coil. When the space is full of people, the humidity doesn't go down. I've been using a data logger recently.

I originally thought it was a fresh air issue. Iowa summer. But the fresh air intake is closed at the mixing box.

There are two sets of pipes coming from the compressor. But I've NEVER seen the second "side" come on from the compressor. It's a Trane system with a Honeywell DA controller and that looks to be set up for 4 stage cooling. But it's like stage 3/4 never come on. (don't quote me on this, could be low room load when empty.) I've spent lots of time watching the thing and feeling pipes lol.

What the maintenance people have done is put in two 70 pint dehumidifiers ... that does nothing. I've been told this is the best they can do. The problem is, theater equipment is starting to rust. Curtains are damp and starting to smell like mold. Wallpaper is peeling. I was told, you run the events, I'll run the heat ... The building was new in 2009.

Other than installing a dehumidifier in the system, shouldn't this be able to keep it under 80% even when there are no people? I need to be able to pitch an idea, or have an intelligent conversation with another HVAC company because the maintenance manger has everyone believing this is just how it works. He's said the HVAC installer said it is fine so that's were it gets left ... I mean the inside of the fan box of the AHU is wet and black like soot. That can't be normal.

I can provide more equipment info and settings if need be.

[teddy bear]

Get out the building and find a new job. Your humidity may be high but the IQ of the mechanic is low. About as low as the IAQ in this facility is.
Try a mold test or monitor the CO2 levels when the facility is full of people.
ASHRAE says the %RH should be low 60% to avoid growing biologicals that make people sick. The CO2 levels are suggested to be 1,000 ppm.
This problem will real bad with the high outdoor dew points till sensitive people will get sick inside the home. The is problem is documented in the ASHRAE IAQ manuals. Becareful you do not lose your job as you create awareness.
400 occupants will add 100 lbs. of moisture per hour. The building it self needs 100 lbs of dehumidification per day per 3,000 sq.ft. of building when unoccupied to maintain <60%RH.
Is this a government building? Whole cares?
Keep us posted and be careful.
Regards Teddy Bear

[pecmsg]

Do you have the As Built Documentation?

For a theater you need a mechanical contractor.

[Juan Madera]

Curious, does it maintain setpoint when fully occupied?

As the FM, you should have the authority to access the controls software and also to call in a competent mechanical contractor to assess the system for you...

[Nuclrchiller]

Do you have the As Built Documentation?

For a theater you need a mechanical contractor.

This.

And locate the Sequence Of Operations, which should be on the Controls Prints. There should be a statement about dehumidification that will have the humidity setpoint that will put the system in Dehumidify Mode. That number will hopefully give you the advantage in conversations with the Maintenance Manager and, if needed, with your common supervisor. Good luck.

[tschnuckel]

So here is the sequence of operation. I left out the boiler stuff. It’s interesting to read the filter alarm because they haven’t been changed in 4 years (dates box) and the filter status is “OK”on the computer (WinControl software). There are no settings in the DDC for humidity or at least I can’t find them. The server room was open and the login instructions were on a sticky note oops.

There are sensors for CO2 on return air, RA humidity, as well as outdoor air humidity. But I don’t see when they are reported in the software. The outdoor air damper at the mixing box is still closed and the CFM meter confirms this at about 2 CFM. Looks like it should be cracked a little to provide some fresh air. Fan runs at 36% normally and will speed up some.


Air Handling Unit (AHU-1) and Condensing Unit (CU-1)

This is a single zone unit with a supply fan, DXZ cooling coil, hydronic coil, and a mixing box with outside air and return air dampers. Occupied or unoccupied operation will be determined by a time schedule in the DDC system. The system will be returned to an occupied operation of 2 hours upon activation of a push button on the space sensor or an operator software input.

A morning warm-up cycle will be initiated before the occupied cycle. During the warm-up cycle, the outside air setpoint will be zero CFM and the unit will be enabled to reach the occupied setpoint. The length of the warm-up cycle will be determined by the outside air temperature, space temperature, and the recorded time to bring the system to occupied temperature. After the warm-up cycle is finished, the unit will return to normal occupied operation.

Supply Fan: The DDC system will have the fan run continuously during occupied periods.

The DDC system will cycle the fan on after receiving a call for cooling or heating at the unoccupied setpoints of 60F (heating) or 80F (cooling).

The DDC system will modulate the variable frequency drive as required to maintain the space setpoint. The unit will operate at its minimum (40% of the maximum) CFM, unless it is unable to maintain its heating or cooling setpoint. If addition heating or cooling is needed, the fan speed will be increased as needed to maintain the space setpoint.

An alarm will signal, if the fan fails to start as commanded.

Mixed Air Control: During occupied periods, when the fan is running, the DDC system will modulate the outside air and return air dampers, to maintain the space setpoint with a minimum mixed air temperature of 53F.

During heating, the outside air dampers will be set to minimum CFM.

When the outside air Enthalpy exceeds 26 btu/lb., the outside air dampers will be set to minimum CFM.

During unoccupied periods, the outside air dampers will be closed.

When the fan is not running, the outside air dampers will be closed.

The minimum setting of the outside air damper will be determined by a C)2 sensor located in the return duct. The minimum setting will be according to the following reset schedule:
1) CO2 = < 700ppm Minimum Outside Air = 500 CFM
2) CO2 = 1000 ppm Minimum Outside Air = 2,500 CFM

Relief Air Control: The relief air dampers (CD-1) will modulate to maintain a positive pressure relative to the outdoor of 0.05” w.c.

The relief air dampers will be closed during unoccupied periods.

Filters: When the fan is running during occupied periods, the DDC will signal an alarm when air pressure drop through the filters exceeds 0.5” w.c.

DX Cooling Coil and Condensing Unit (CU-1): During occupied periods, when the fan is on, and the outside air dampers are unable to maintain the discharge air setpoint, the discharge air controller will maintain the discharge air temperature at its setpoint,

During unoccupied periods, when the fan is off, the condensing unit will be off.

During unoccupied periods, when the fan is on, and there is a call for cooling, the discharge air controller will maintain the discharge air temperature at its setpoint.

The DDC system will supply the discharge air temperature setting to the controller. Set point will be 54F (adjustable).