air con investigation

[pumpmann]

I need too investigate an exist ducted air con system that is not conforming (cooling capacity insufecient)
the duct system is served by means of a chilled water AHU.
Any tips on where to start my investigation?

 

[DrRTU]

Run the loads and verify the equipment / system. How do you know the equipment is deficient? Have you re-commissioned the system?

 

[GMcD]

I would also strongly suggest checking the building envelope characteristics to see if they conform to the plans and specs. All too often, what seems like a poorly performing HVAC system and temperature control issue goes right back to a bad envelope - somebody put less insulation in the wall to save $$, the windows were substituted with lower performing windows to save $$, and some really badly thermally bridged construction details were used that compromised the overall thermal resistance of the walls and roof.

Re-commission the building envelope first, including blower door testing, THEN re-commission the HVAC and controls.

I can remember back 30 years ago when I got my first "too cold in the front office" complaint, and of course it was the heating engineer that was assumed to be at fault. I popped some ceiling tiles along the front outside wall and saw snow blowing in through cracks at unsealed building envelope construction at the soffit to wall interface. Pictures taken, report written, back up to the General Contractor and Architect to deal with. This has happened more often than not over the years when I get the too hot/too cold calls.

 

[IRstuff]

Was it EVER conforming? That's where you start. Why would you start an investigation without any facts or design specifications?

A VERY typical situation is that the system was designed for a lower load than currently exists, more people, or more equipment, etc.

TTFN

FAQ731-376

 

[chicopee]

You can start measuring the air velocity and temperature at the duct outlet and calculate the flow rate. You can then compare the ducted air velocity to that recommended by ASHRA, compare the calculated cooling rate of the air flow and the heat gain in the room.

 

[SAK9]

You need to start by asking when the problem started( like the Doctor!).If it is a recent problem,it means it "worked" in the past and therefore could be an issue that needs to resolved at the equipment level.If there is a maintenance manual,get the AHU parameters such as airflow,chilled water temperatures and rise,coil leaving and air entering temperaures,pressure drops(air/water) from it and verify them on site.Any departures from the design values will give you some pointers.

A design check is meaningful only after this investigation.

 

[pumpmann]

what is the recomended / typical supply air temperature (range) if the required room temperature is 23C?

 

[pumpmann]

see attached scada image. please note that it was taken not on a hot day therfor the temperatures don't seem to high.
my concerns is:
-high delta T (10C) over coil
-low fan delivery of supply air fans (rated for 150pa, actual is expected to be much higher, RA fan is expected to be stronger)

what is your comments?

 

[pumpmann]

Is there ways of verifying the actual load within a room by measurements?
Speculation is that there could be a geothermal well running below the room
How do I determine the heatload thereof?