Re: [EnergyPlus_Support] Heater element exponent

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

The baseboard heater in EnergyPlus, BASEBOARD HEATER:WATER:CONVECTIVE, is 100% 
convective.  The equation in the Input Output reference which defines the heat 
output as a function of UA is incorrect.  And, unfortunately, there is no 
section in the Engineering Reference for this model.  The revised description 
for the UA field follows:

Field: UA
The overall heat transfer coefficient for the baseboard heater in watts per 
degree Celsius at design conditions. The UA is used in an NTU - effectiveness 
calculation. An estimate of the UA can be obtained from:

q = UA x (Twater,avg - Tair,avg)
 
where q is the heat transferred from water to the air in watts; Twater,avg is 
the average water temperature in degrees C; and Tair,avg is the average air 
temperature in degrees C. Or the LMTD temperature difference can be used.

So, for convective heat transfer, the non-linear output of the heater as a 
function of water and air temperature should be accounted for by the model.  
But there is no radiant component, so that effect is lost.  For the Fall 2007 
release, there will be a new radiator model which is a combined convection-
radiation model.

In the current version, a true radiator can be approximated by using LOW TEMP 
RADIANT SYSTEM:HYDRONIC on a small surface.

Mike



On 5 Apr 2007 at 9:29, Sebastian Dietz wrote:

> Hello,
> 
> currently I'm modelling a simple heating system, including boiler, pump 
> and radiator (baseboard). Whatever, I didn't find an option to enter the 
> heater element exponent (emission index) in the Baseboard 
> Heater:Water:Convective objekt. Does anybody know, how to represent non 
> linear properties of a radiator in EPlus?
> 
> thanks in advance
> sebastian
> 
> -- 
> Sebastian Dietz
> Fraunhofer-Institut for Solare Energiesysteme ISE
> Heidenhofstrasse 2, 79110 Freiburg, Germany
> Phone: +49 (0) 7 61/ 45 88-51 36
> Sebastian.Dietz@xxxxxxxxxxxxxxxxx
> http://www.ise.fraunhofer.de
> -------------------------------------------
> 
> 
> 
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> 
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> 
> Attachments are not allowed -- please post any files to the appropriate folder
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> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
> 
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> 
> 
> 
> 
> 


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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