Don't know what the heck I am doing!!!

[sjl2725]

First off, I am a Turf Equipment Mechanic at a top ranked golf course... We don't have a building maintenance staff, so I double as facilities maintenance... I know just enought about HVAC to get myself in trouble.

Here is the problem. We have a chilled water system that seems to be operating correctly. Coolant Leaving Temp is set to 44F. Our Pro Shop is always warm. I changed thermostats with another slightly unused room to make sure it wasn't a control issue. If I turn the Tstat to 80, I can watch the chilled water valve close. When I turn it to 60, I can see it open. To my knowledge, we have no control issues. With the chilled water at 100% constantly, we still cant get the room to cool off. Belts on blower are new and tight, the coils in the AHU aren't frozen, coils in the chiller unit are a little dirty, but the unit is still cycling on and off when setpoints are met.

The air return is a hole in the side of the wall that just leads to the room next door where the AHU's are. Doesn't appear to be any dampers or anything.

What should the temp at the vents be? What should the temp in the cold air duct leaving the AHU be? Like I said, I know very little about this. Anyone know why I can't get this room out of the high 70's?

If anyone is close to Branson Missouri, you get free golf at a #1 ranked public course (statewide) for showing up and fixing our problem!!!

 

[walkes]

Too bad, I was in the neighborhood at Holiday Hills last summer.

Usually, the ahu's are selected to provide a 55°F discharge air temperature to provide a 75°F 50% RH condition in the space.

Has the space changed over the years?
Are they leaving the door open?
Is the coil in the AHU dirty?

You should also check the return water temperature to the chiller.(AHU coils won't freeze with a chilled water system supply of 44°F). If you are getting a 47°F return or generally less than 54 or 55°F then your chilled water isn't being used. Your coil could have a blockage in the piping or it could be air-locked.

You could have a water flow issue too, you can check the pressure across the pump to determine the actual flow rate based on the pump curve.

Air at the vents should be around 55°F and may be up to 58°F if ductwork isn't properly insulated from the AHU. Higher than that and you may have water flow issues.

 

[rogzog]

If there are any strainers on the chilled water lines to the unit make sure they are clean.

If the AHU has a bypass damper, make sure it is functioning properly.

Check for dirty air filters.

 

[willard3]

Hire an Engineer, this is what they do for a living, solve problems.

 

[Drazen]

before spending time on other things, you should measure air leaving temperature in fan coil at room of concern.

 

[sjl2725]

I did hire an mechanical company to check things out. We have a flow issue, which could be caused by a strainer/filter that is full (which we cannot find and have no drawings), there is also a VFD for the aux pump that isn't functioning properly. Line pressure was over 100lbs. Tech said it should be in the 30's, so indicative of a blockage. He also said something about a pressure sensor being bad and a bypass valve/actuator that isn't communicating... tracing that back may lead to the malfunctioning VFD.

In the process of trying to find drawings before the tech comes next week. Thank all of you for your advice.