Re: [EnergyPlus_Support] LOW TEMP RADIANT SYSTEM shut-off

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

Posting this message on behalf of Rick Strand (not clear if his original 
post was distributed to the list):

Florian:

The low temperature radiant system is designed to shut-off when it 
predicts that condensation is a possibility at the surface that is part 
of the system.  Inside the program, the procedure works as follows.  The 
radiant system turns on based on availability and controls.  This leads 
to a calculation of a new surface temperature for the surface that is 
associated with the radiant system.  If the dew-point temperature of the 
zone is within 1C of the predicted surface temperature, the radiant 
system shuts down due to the potential for condensation.  The error 
messages should be letting you know both the predicted surface 
temperature and the zone dewpoint temperature.

Unfortunately, with the current configuration of the low temperature 
radiant model, the shut-off cannot be "turned off".  In other words, 
there is no way around this as the condensation of moisture is not 
desirable from either a modeling or a realistic standpoint.  The best 
approach is to do exactly what you attempted to do: add an air stream to 
attempt to dry out the space.  I would also recommend looking at the 
humidity levels within the space.  I have seen in several files that 
contain radiant systems that the moisture levels rise significantly 
because the user did not add any infiltration.  When people are in a 
space, there is no infiltration, and a radiant system is being used, 
people add moisture to the space, but there is no mechanism for moisture 
to leave the space.  What happens is that moisture levels rise to 
saturation and the radiant system is not able to turn on at all.  So, 
you might want to check this in your file.

I hope this helps.  Please let us know if you have further questions or 
comments about the radiant model or EnergyPlus.

Thanks,

Rick Strand
EnergyPlus Development Team

Florian Stift wrote:
> Dear E+Users,
> 
> I am simulating a single zone which is cooled by a "LOW TEMP RADIANT
> SYSTEM"!
> I wanted the system to be continuously "ON", so I defined a very low
> zone cooling setpoint, like 2degC. 
> 
> When I was realising that the system shuts off when condensation
> occurs on the inside of the ceiling surface, I added a Purchased Air
> System to serve the zone with a limited amount of conditioned air,
> e.g. 0,5ACH with 22deg.C.
> 
> There is no condensation any more but the LOW TEMP RADIANT SYSTEM
> shuts off when the zone air temperature falls below that 22degC from
> the Purchased Air Schedule, but I still have defined that schedule for
> a Setpoint of 2degC.
> 
> How can I manage to tell the LOW TEMP RADIANT SYSTEM to be ON all the
> time??
> 
> Thanks in advance for any help!
> 
> Best Wishes,
> Florian
> 
> 
> ------------------------------------
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------------------------------------

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