[Bldg-sim] Is there a point to "virtual partitions"?

[Chris Yates]

Dear Curtis, Gaurav and Cheney

I cannot profess to understand radiation exchange in the depth I really 
should. I do however have some experience of energyplus and one thing I 
wouldn't want to attempt in it is Virtual partitions. Under most 
circumstances its gradient based or node based displacement vent models 
are probably superior to the "stacked" volumes approach.

I'm still unconvinced regarding the need for virtual partitions to 
denote perimeter zones for the following reasons:

    * The 15ft perimeter in LEED appears to be relating to speculative
      office space that could be subject to fit-out. A fit-out would be
      undertaken with solid partitions. Therefore, why not model with
      solid partitions?
    * If, on the other hand, the perimeter zone requirement relates to
      varying access to daylight, modelling of daylight sensors may
      better serve this purpose.
    * The virtual partition seems to be a rather artificial boundary
      possibly subject to an expensive computational overhead and
      convergence issues.

Finally, I feel these points must also be weighed against the designers 
judgement as to whether Air temperature (or Space conditioning based on 
Air temperature) will vary significantly across the floor plate.

Best regards

Chris

On 26/01/2011 17:26, Curtis Pedersen wrote:
> Chris and other responders:
>
> Depending on what heat transfer modes your simulation includes, 
> results from a "virtual partition" can be incorrect.  If you have 
> intersurface long wave radiation exchange, a black partition will cut 
> the radiation exchange in half (check it out in a good heat transfer 
> text).  EnergyPlus, which does radiant exchange, has a feature called 
> "infrared transparent surfaces", which are black, massless, low 
> thermal resistance surfaces that compensate for the reduction in 
> radiation exchange.
>
> Curtis Pedersen
> Professor Emeritus, University of Illinois
>
>
>
>
> On Jan 26, 2011, at 10:28 AM, Chris Yates wrote:
>
>> Hello,
>>
>> /Virtual partition: a transparent partition with no mass and no 
>> thermal resistance.  If the simulation employs an air flow network it 
>> may also be considered as a hole allowing air to pass through the 
>> partition. Usually used to define a perimeter zone. (BTW this isn't 
>> quoting any source, just what I understand!)/
>>
>> I feel I may be describing a cultural nuance of energy modelling in 
>> the UK. So I'd like to ask the following:
>>
>>     * Do engineers in countries apart from the UK use "virtual
>>       partitions"?
>>     * What benefits do virtual partitions have over physical partitions?
>>
>> Any other comments will be gratefully received.
>>
>> Many thanks
>> -- 
>>
>> Chris Yates C Eng MCIBSE
>>
>> /Building Physics Consultant/
>>
>> Tel:+447960731576
>>
>> Email: chris.malcolm.yates at gmail.com
>>
>> Skype: christopher.m.yates
>>
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-- 

Chris Yates C Eng MCIBSE

/Building Physics Consultant/

Tel:+447960731576

Email: chris.malcolm.yates at gmail.com

Skype: christopher.m.yates

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