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[EnergyPlus_Support] Making the Radiant Floor more realistic



>From a realistic standpoint, I believe that the floor/ceiling radiative transfer is too large for a radiant floor.  With a completely empty retail space, it makes sense, yet with ~40% of the floor covered by merchandise etc, I'd like to figure out a way to decrease the radiative exchange therefore decreasing the capacity of the radiant floor.  

 

For example, comparing with a baseline all air/passive floor system, the floor temperature is just under the setpoint temperature ~75 F while the interior roof temperature reaches ~83 F during the Las Vegas design day (exterior roof temperature ~170 F) which seems realistic.  With just a radiant floor of ~70 F the interior roof temperature is ~75 F which does not seem reasonable.  

 

How can I decrease the radiative exchange.  I've decreased the thermal absorptivity of the interior ceiling from 0.9 to 0.01 which did have somewhat of a change but surprisingly not much.  I don't want decrease the floor absorptivity because the thermal connection between the skylights and the floor.

 

This is important for two reasons.  First, getting a greater understanding of the space air/surface temperatures for determining thermal comfort.  Second, understanding what the change in the radiant floor capacity and therefore impact on the plant system.

 

Thanks in advance

 

Ian Doebber

Arup

 

 

________________________________

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Michael J. Witte
Sent: Wednesday, October 25, 2006 7:45 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Further Insight : Skylight / Radiant Cooling Strange Behavior

 

We have confirmed that this is a reporting error just for the zone level window 
heat gain/loss report variables. When radiant cooling is active, the zone 
surface heat balance is called extra times to update the surface temperatures. 
The accumulation of Zone Window Heat Gain/Loss was not being reset to zero 
within this loop. This will be fixed for the next release. Until then the 
workaround is to use the surface-level Window Heat Gain/Loss report variables 
when using radiant heating/cooling systems.

Mike

On 23 Oct 2006 at 22:29, Michael J. Witte wrote:

> Digging into this further, the problem appears to be the values reported by 
> "Zone Window Heat Gain" and "Zone Window Heat Gain Energy". When the radiant
> cooling is active, these zone variables do not agree with the surface
> variables 
> "Window Heat Gain" and "Window Heat Gain Energy". So, use the surface 
> variables instead and I think you will find the results to be more
> reasonable.
> 
> Checking the change in cooling load with and without the skylights, at hour 
> 10:00:
> 
> Zone Window Heat Gain = 5.53E+04
> Window Heat Gain = 1.38E+04
> Change in cooling load w/o skylights = 5.89E+03
> 
> So, this appears to be a reporting problem with the zone level window heat
> gain 
> report variable and not a problem in the overall heat balance.
> 
> Mike
> 
> 
> Mike
> 
> 
> On 19 Oct 2006 at 13:37, Michael J. Witte wrote:
> 
> > Ian: 
> > 
> > If you delete the skylights, does the cooling load on the radiant system
> > change 
> > by the same order of magnitude as the reported heat gain from the skylights?
> > I 
> > suspect this may just be a problem with the reported window heat gain
> rather
> > than a real heat balance problem. The reported window heat gain is just a
> > side 
> > calculation for reporting purposes, that value is not actually used in the
> > heat 
> > balance.
> > 
> > Mike
> > 
> > 
> > On 15 Oct 2006 at 15:42, Linda Lawrie wrote:
> > 
> > > At 04:27 PM 10/13/2006, Griffith, Brent wrote:
> > > >I believe this is a known bug (CR6897). But unfortunately it isn't a
> > > >quick job and I don't think it was fixed in V1.4 (which is already
> out).
> > > 
> > > As Brent says, this is a known or suspected problem. If you submit 
> > > your file (either send direct to me or upload to the support web 
> > > site), it may help our developer in tracking it down.
> > > 
> > > 
> > > Linda
> > > 
> > > EnergyPlus WebSite: http://www.energyplus.gov <http://www.energyplus.gov> 
> > > Owner: EnergyPlus_Support list
> > > Member: EnergyPlus Development Team
> > > 
> > > 
> > > 
> > > [Non-text portions of this message have been removed]
> > > 
> > > 
> > > 
> > > The primary EnergyPlus web site is found at:
> > > http://www.energyplus.gov <http://www.energyplus.gov> 
> > > 
> > > The group web site is:
> > > http://groups.yahoo.com/group/EnergyPlus_Support/ <http://groups.yahoo.com/group/EnergyPlus_Support/> 
> > > 
> > > Attachments are not allowed -- please post any files to the appropriate
> > folder
> > > in the Files area of the Support Web Site.
> > > 
> > > EnergyPlus Documentation is searchable. Open EPlusMainMenu.idf and
> press
> > the
> > > "search" button.
> > > 
> > > Yahoo! Groups Links
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > 
> > 
> > ========================================================
> > Michael J. Witte, GARD Analytics, Inc.
> > EnergyPlus Testing and Support 
> > EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com> 
> > 
> > 
> > 
> > 
> > 
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov <http://www.energyplus.gov> 
> > 
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/ <http://groups.yahoo.com/group/EnergyPlus_Support/> 
> > 
> > Attachments are not allowed -- please post any files to the appropriate
> folder
> > in the Files area of the Support Web Site.
> > 
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.idf and press
> the
> > "search" button.
> > 
> > Yahoo! Groups Links
> > 
> > 
> > 
> > 
> > 
> > 
> 
> 
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support 
> EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com> 
> 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov <http://www.energyplus.gov> 
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/ <http://groups.yahoo.com/group/EnergyPlus_Support/> 
> 
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
> 
> EnergyPlus Documentation is searchable. Open EPlusMainMenu.idf and press the
> "search" button.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 

 

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