Trace Load 700 Question

[robinxie]

Could anyone answer my question please.
I want to calculate the heating and cooling load of a small locker room. The area is 500 sq.ft.. To reach the outside air requirement, vent airflow is 0.5cfm/sq.ft.. The system is VAV w/ Baseboard Heating. After the calculation, I got a funny result on Room Checksum Sheet as follows:
......
Vent 442cfm
Supply 246cfm
Return 246cfm
Exhaust 442cfm
......
Cl% OA 179.9%
......
Htg Btu/hr-sq.ft. -53.12
......

Does anyone tell me that's why.
Thanks a lot.

Robin

 

[robinxie]

I want to calculate the heating and cooling load, supply and return airflow, further to choose the baseboard, size the duct, choose the AC unit. But the results I got have no sense to be the design criteria. Is that the details you want to know? Or you want other details else?
Thank you very much, Mechatonics.

Robin

 

[Rob1972]

Robinxie:

There are a couple of questions that are typically asked when you call the Trane TRACE support center that might help you in this case.

1) What version are running? The most recent version is 4.1. If you are not running this version, I recommend that you update. Contact Trane to find out how.
2) Have you specified both your main supply airflow and vetilation airflow? If so, check the units on both and consider removing the supply air value. I suspect that the loads in space do not require 0.5 cfm/sq ft and so the program is just giving this to you for main supply and there is something in ventilation field that is forcing it to double.
3) Have you specified a supply air temperature? While this does not cause the problem that you are seeing, it may limit the flexibility that the program has to calculate required airflows.

If these suggestions do not resolve your concerns, I recommend that you contact the TRACE support center. Check the Help file for contact information.

 

[robinxie]

1. The version I am using is very old. It is 1.0.001. The old version will cause this kind of problem?
2. I did not specify main supply airflow. I just specified the vent airflow as 0.5 cfm/sq ft. This number comes from the ASHRAR outside air requirement. I feel this number is too large too. Whenever I input a larger vent airflow number, I suffered the same painful result. Do you know why it is?
3. I did not specify supply air temperature.
Thank you very much.

 

[Rob1972]

I would strongly recommend that you update your software. While this may not fix your specific problem, there have been many significant enhancements to the program since it was first released.

According to your input, 246 cfm seems like an appropriate airflow (i.e. 500 sq ft at 0.5 cfm/sq ft) so you really should be seeing 100% outside air (and not 180%). Have you set your ventilation flag to something other than Sum Room OA Reqs? If you have it set to one of the ASHRAE 62 flags then I recommend that you try running the calculation with Sum Room OA Reqs ventilation flag. If you are using ASHRAE 62 flag then the program is trying to solve for Equation 6-1 (as specified by ASHRAE Std. 62) and since this is clearly a critical zone for ventilation it is driving your over all ventilation requirements up.

 

[robinxie]

Got it. Thank you very much, Rob1972.