[EnergyPlus_Support] Cooling and Heating Priority

["tianzhen9" <tianzhen9@xxxxxxxxx>]

Dear Energyplus User Members:

I have a encounted a problem in my research.

I am doing a research about radaint cooling slab system and 
simulating a building with radiant slab cooling and VAV system.

Now my problem is about the heating and cooling priority for the air 
system and radiant system.

The example file only has radiant cooling system. So the cooling 
priority is set as 1 for the radiant system. But when combined air 
system and radiant system. The problem is which one has higher 
priority.

For the office building I am simulating, the radiant system 
untertakes most sensible cooling load from lighting, occupancy and 
equipment. So I want to set cooling priority as 1 for the radiant 
system.

During the long process of my modelling, I notices that there is 
interesitng result. If the air system could cool the space, the 
radiant system does not work, or the result is not correct,even I 
set the radiant system as cooling priority 1. Mike guess is 
that "minimum air flow overcool the space". So it means that the 
radiant system only works when the minimum air flow rate can not 
satify the cooling demand. 
If it means that the air system has higher prioity from the 
beginning of design this progrm?

If it is true, there will be other problems. For a simple building, 
this will not cause other problems. But for a big building, this 
will cause other problems.

If I use autosizing for the air sytems, the air flow rates will all 
based on the air system. And these air flow rates will bigger than 
flow rates of combined air system and radiant system. Because of 
this, the radiant system will not work or the result will be 
incorrect. 

If I specify the air flow rate,there will be warnings "SimHVAC: 
Maximum iterations exceeded for all HVAC loops...". And actually it 
is hard to specify the air flow rates because the some design data 
are unknown.

So could someboby tell me how can I handle this problem.I focused on 
this for few months and have not got any result.

I sincerely appreciate your help.

Best regards,

Zhen Tian





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