AC load calculation

[usama81]

please help

i have small project one floor only offices type and with total construction area 800 m2 and the AC system will be VRV system and we have wall mounted exhaust fan in each toilet and the fresh air will be through the infiltration from doors and windows, so firstly i did rough calculation for it as i consider every 25 m2 = 1 tr so we should get almost 32 tr, then i did the detailed calculation by HAP program and i checked all the required information with the Architect engineer in regard to the U-values, number of people, ...etc i got only 20 tr. is it possible that the load for 800 m2 is only 20 tr? please suggest what should i check.

 

[DRWeig]

What are your design temperatures? Is the building well-insulated? Are there lots of west-facing windows?

In my area (Georgia, US), 40 m2 per ton is quite reasonable for an office space. A well-insulated building with minimal ventilation might be 50 m2 per ton.

Best to you,

Goober Dave

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[sprinkler1000]

A couple of comments.

Take into account net área, not gross área when making those estimates.

If they are offices, and they are conditioned, you are not supposed to open windows. You will have to bring fresh air in the right quantities.

The value of 20 TR for 800 m2 is low. You may be underestimating fresh air loads and people loads.

 

[317069]

You should check for the forum policy first then for an HVAC course.

 

[EnergyProfessional]

it deend son if you used HAP correctly. I'm not familiar with HAP, but in Trane Trace you can differentiate plenum, duct return, where OA is places etc. and that all will have impact.

most load in offices are plug load, ligthing and people. Depending on people density and how good your office equipment is it can vary a lot. Old lighting was 2-3W/ft², new lighting is 0.8 W/ft² etc. Your glazing will be important too, as is location. Are you in alaska or florida? You now see how your first approach of using a ft²/ton approach was not good.

I would caution from ventilating with infiltrated air. first, thsi isn't code compliant. Second you get humidity and other comfort issues. If exhasut is excessive you may have problems opening or closing doors and meet ADA.

and most importantly, you'll need to hire an HVAC engineer.