Supply Air Temp to Room Question.

[murphymok]

Hi,

I am working on a fitness centre project where the interior space is very hot, around 29C. The design temp is 23C and the supply air off the AHU is 13C. However, the temp off the supply diffusers inside the premises is 16C and the temp further down the AHU duct is 17C. The building management insists that they have the design specs, displaying on their monitor. Any thoughts?

Thanks in advance.

 

[quark]

What temperatures you perceive in return ducting? 16[sup]0[/sup] grill outlet temperature with 13[sup]0[/sup]C coil outlet temperature is not very bad. I couldn't understand what you mean by 17[sup]0[/sup]C down the AHU duct. Is there sufficient air flow?

 

[murphymok]

The BMS temp sensor of the AHU said 13C, and when the contractor inserted a temp probe to the ductwork several meters from the AHU, the temp is 16-17C. The temp off the grill is again around 16-17C. Flow is adequate. 3-4C drop seems to be a large difference when considering the distance from the AHU to the FCU.

 

[quark]

Actually, the insulation should be designed for a max. temperature gain of 1[sup]0[/sup]C but I seldom see this low temperature gain. Just check the return air parameters and check actual heat load from the room. Also check the heat removed by the coil. This will give you an idea about your system design.

It will be helpful in analyzing the problem if you give WBT and DBT of room inlet, outlet and coil inlet and outlet conditions.

Regards,

 

[walkes]

Do you have a short circuiting effect on the air distribution? i.e. Is the supply air getting down to the occupied space and mixing or is the return drawing it in before being mixed?

 

[Drazen]

As I was "dressed" in maintenance for many years, I would propose you to apply one of the basic maintenance rules: "look at the simple things first".

Common sense already implies that it is too big temperature rise. If you don't have apparent heat source exactly on the position where there is a temperature rise, you should recheck BMS sensor (contractor's sensor can be checked even simpler: let him stick in duct different from the one he used first time). Maybe it didn't failed, it only needs recalibration (depending of the make of sensor). Maybe it did failed.

Don't let them say to you that they already checked it, if you are in charge for that, check once more. You can allways bet in drink or something like that to avoid them being offended by your recheck.

(After all maybe building management will only have to properly clean chiller condenser system heat exchange surfaces. Maybe.)

 

[ChasBean1]

Does the BMS temp sensor at the AHU read before the fan? Did you account for a couple degree rise across the fan? Could be more if the fan's oversized.