Re: [EnergyPlus_Support] Re: Forcing system behavior

["Michael J. Witte" <mjwitte@xxxxxxxx>]

The point is well-taken that there are currently no diagnostics to warn when 
equipment is not meeting setpoints at either the zone or component level.  Some 
such reporting is planned for the coming year.

Autosizing of multiple systems serving the same zone is not supported, and 
probably will not be anytime soon.  

For this particular application, the zone is served by a combination of a VAV 
system and radiant panels.  This is one of the most difficult situations to 
model in EnergyPlus (but you already have learned that the hard way).  There 
are two types of hydronic radiant panels:  LOW TEMP RADIANT SYSTEM:HYDRONIC 
(which is autosizable) and LOW TEMP RADIANT SYSTEM:CONSTANT FLOW (which is not 
autosizable).  In this case, it is possible to autosize the entire VAV system, 
even though the radiant hydronic system is user-specified.  The calculation is 
from ZONE SIZING through SYSTEM SIZING, then the plant loops will add up all of 
the coil flows.  The problem is that the sizing algorithm for the VAV system 
does not know that another system is serving the same zone.  So, it will 
autosize the VAV system to meet the entire load.  Perhaps the following 
approach would help in tackling this problem:

1.  Fully autosize the VAV system.

2.  Run with the radiant hydronic system as priority 1.

3.  Review the results to determine the peak supply air volume flow from the 
VAV system.  The VAV boxes should max out at something less than full flow if 
the radiant hydronic system is contributing to meet the zone load.

4.  Specify that peak volume flow (or something a little larger) in the ZONE 
SIZING object and let the rest of the VAV system autosize off that.

5.  Let the plant loop autosize also.

Mike



On 10 Dec 2004, at 22:09, sm278424 wrote:

> 
> 
> As a user of E+, and especially in the early stage of design, you 
> want to autosize most things (everything, in fact, just see what 
> happens). 
> 
> The radiant panel definition requires a user-specified flow rate (you 
> aren't allowed to autosize). Because of this I now seem to have to 
> user-specify every parameter for the system and plant, otherwise I 
> get errors.  
> 
> I'm spending time making up input values for components I don't want 
> to design yet. In fact, this is why we're using E+ in the first 
> place, to see how the radiant system impacts on the air handling 
> system, the building envelop, and the thermal comfort of the 
> occupants. 
> 
> Part of the problem is that you don't get much in the way of useful 
> feedback, just wonky zone temperatures, or error messages that only 
> someone debugging the program code can make immediate sense of.  If a 
> coil is undersized (or oversized), it would be useful to get a 
> caution message, or something.
> 
> Seems to me these are pretty major issues.
> 
> Thanks once again
> Shaun Martin
> 





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