Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
2

Cooling consumption difference between VAV system and PAU+FCU system for air side loop

asked 2017-10-08 04:40:42 -0600

katsuya.obara gravatar image

I have two models implementing two different air side loop as below (plant loop and internal loads are same):
1.VAV system
2.PAU+FCU system

Looking at result, system 2 consume 20% more for cooling which is caused by air side cooling load removal difference as below (26%difference).
1.13,341MWh
2.18,067MWh

When I look at heat gain (People,light,small power,solar heat gain, conduction), I cannot find such difference. 1.12,068MWh
2.11,946MWh

Can anyone tell me what could be the reason causing this difference?

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted
4

answered 2017-10-09 07:48:57 -0600

Check for differences in outdoor air quantity and control. The VAV system will bring in outdoor air while the system ooperates. The zone equipment also brings on outdoor air but does not use Controller:OutdoorAir. The outdoor air is fixed with the runtime of the zone equipment.

edit flag offensive delete link more

Comments

I would like to confirm my understanding. Do you mean that
Since HVACTemplate:System VAV is variable air volume against HVACTemplate:DedicatedOutdoorAir which is constant air volume, OA introduction in VAV may be much smaller than PAU. That may lead to the result I am having?

katsuya.obara gravatar imagekatsuya.obara ( 2017-10-09 21:26:24 -0600 )edit

Yes, that is a possibility. I am suggesting you investigate the amount of outdoor air introduced by each system. Plot the node standard density flow rate for each system using:

Output:Variable,OANodeName,System Node Standard Density Volume Flow Rate,timestep;
rraustad gravatar imagerraustad ( 2017-10-10 07:50:57 -0600 )edit

Your comment was right. VAV system was not introducing OA which leads to zero ventilation load.

katsuya.obara gravatar imagekatsuya.obara ( 2017-10-29 20:50:26 -0600 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

 

Question Tools

2 followers

Stats

Asked: 2017-10-08 04:40:42 -0600

Seen: 73 times

Last updated: Oct 09