HVAC performance verification 1

[Baldor]

Hello all,

Is there a method to verify the actual performance of a packaged unit? I have a 15 ton roof-mount on a metal building (insulated) that doesn't seem to be working as well as it should. Total heat losses for the building, including sun load are calculated to be 38KW.
The unit is new, but it is also a new design. I am looking for a test to find the unit's actual performance vs. what's labeled on the side.
I have at my disposal instruments to measure temp, air flow/volume, humidity, etc.

Thanks.

 

[willard3]

I would ask the contractor who installed it these questions to start.

 

[Drazen]

If you can measure outdoor dry and wet bulb temp, you can use psychrometrics to calculate actual thermal capacity.

By measuring supply dry and wer bulb, volume flow, it is actually sufficient to calculate enthalpy difference.

Next step is to check reference conditions in manufacturers specs, and eventually find correction factors that correlate to your actual conditions.

 

[trashcanman]

Yes there is. It is called Test and Balance. There are many companies that do this.

 

[KiwiMace]

The ARI or AHRI standard 360 is free online. Read what it says about the test conditions. The difference between the std ambient and your ambient will define the actual performance of the unit. You look about right for sensible/latent design capacity though, a trap many fall into.

 

[MintJulep]

Installation conditions can reduce performance. A common example is bad return or discharge duct configuration resulting in non-uniform flow through the coil.

Single point measurement of inlet or discharge won't detect that.

 

[Baldor]

Thanks a bunch!
Between the several replies, I found way to do this researching your suggestions, not to mention learning something in the process. I'm using psychrometrics initially, then having the supplier evaluate afterwards. The ARI 360 standard also pointed me to ASHRAE Standard 37, which I'm about to purchase.


Appreciate it!

 

[MintJulep]

ASHRAE Standard 37 should be educational, but it's written for laboratory testing. The method is really not suitable for field tests.

 

[Shophound]

Pardon my English:

BTUH = CFM * delta h * 4.5 * density/0.075

I agree with measuring entering and leaving dry and wet bulb temperatures. Convert them to enthalpy on a psych chart or online converter. Do the calcs once you know the CFM. It may not be dead on but it should give you a reasonable estimation what the system is delivering in terms of real time capacity.

Also keep in mind that outdoor ambient temperatures affect system capacity. ARI rates most air cooled condensers at 95 degrees dry bulb ambient. Above that the system capacity will derate.