[Equest-users] [Bldg-sim] Roof Conduction Load

[Joe Huang]

Just to repeat what David and Rodrigo have already sad, DOE-2 calculates conduction loads 
in a two step process. In LOADS, a constant reference temperature is specified, which 
DOE-2 uses to calculate the amount of heat flow through the surfaces. This is the LOADS 
loads summarized in the LS-E and LS-F reports.  In SYSTEMS, DOE-2 calculates the true 
temperature of the zone based on the loads passed from LOADS, as well as the actions of 
the HVAC system.  In the course of this calculation, the heat flows ("loads") from LOADS 
are adjusted, but this is not done surface by surface, but in total using the so-called 
"Zone Conductance" times the difference between the actual zone temperature and the 
reference temperature used in LOADS.  At this point, heat flows through internal walls are 
also considered, using the  difference between this hour's zone temperature and the 
previous hour's zone temperature of the adjacent space, e.g., the Attic or Plenum.  If you 
are interested in this number, I believe it can be extracted in an hourly report.

In reference to Rodrigo's question, I don't see any benefit in forcing a heat flow between 
the room and the attic by using different reference temperatures.   You will simply get a 
constant heat flow at that temperature difference throughout the simulation. In reality, 
attics are generally colder than the room in the winter and warmer than the room in the 
summer, so the derived heat flow with this temperature difference doesn't get you any 
closer to reality, in my opinion.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 8/19/2013 12:05 PM, David Wood wrote:
> Hi All,
>
> The LS-C report comes from the LOADS simulation portion of DOE 2.2. The plenum reference 
> temperature used in LOADS is adjusted in the SYSTEMS portion of the program and the 
> loads in the spaces adjacent to the plenum are corrected
> correspondingly.
>
> Dave Wood
>
>
> On Thu, Aug 8, 2013 at 8:58 AM, Rodrigo Cerqueira <rodrigo.cerqueira at mra.qc.ca 
> <mailto:rodrigo.cerqueira at mra.qc.ca>> wrote:
>
>     Hi,
>
>     This happens because the load calculation is made with a fixed temperature (see
>     picture). All the spaces, include plenum zones, have the same temperature by default
>     (70°F). So, all roof load appears in the plenum spaces. To considerate the roof
>     load, you have to change this temperature in plenum spaces and a part of roof load
>     will appear like "internal surface conduction". But I'm not sure if this is a good
>     practice. Maybe someone else has an opinion about that.
>
>     *Rodrigo Cerqueira, *ing. jr, M.Ing.**
>
>     *Simulation énergétique *
>
>     signatureCouriel
>
>     *De :*equest-users-bounces at lists.onebuilding.org
>     <mailto:equest-users-bounces at lists.onebuilding.org>
>     [mailto:equest-users-bounces at lists.onebuilding.org
>     <mailto:equest-users-bounces at lists.onebuilding.org>] *De la part de* Bhartendu Awasthi
>     *Envoyé :* 8 août 2013 06:35
>     *À :* equest-users at lists.onebuilding.org
>     <mailto:equest-users at lists.onebuilding.org>; bldg-sim at lists.onebuilding.org
>     <mailto:bldg-sim at lists.onebuilding.org>
>     *Objet :* [Equest-users] Roof Conduction Load
>
>     Hi All,
>
>     I am doing an energy simulation model in eQuest. I noticed that the load through roof conduction in LS-C is zero where as in LS-B (for plenum space) it is showing some load.     
>
>            
>
>     As per my understanding this load should appear in LS-C also.     
>
>     Also, if I reduce the U value of the roof, the load through roof reduces and can be accounted in LS-B only (plenum space).     
>
>            
>
>     Refer attached LS-C and LS-B reports.     
>
>     Any help will be appreciated.     
>
>            
>
>            
>
>     Thanks&  Regards     
>
>            
>
>     Bhartendu Awasthi     
>
>
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>
>
>
> -- 
> Regards,
>
> David S. Wood
> Principal
> Wood, Byk & Associates
> office:    610.347.0710
> mobile:  610.247.1208
>
>
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