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
Hello Chris,
It is not a cultural nuance and I use virtual partitions almost everyday.
Why? I have to employ it when
1. I need to setup different internal loads for a space with multi-zone,
such as big open office (you mentioned it in your own definition);
2. I need to simulate displacement ventilation in a space (I will put the
virtual partitions horizontally though to separate occupied and stratified
spaces)
3. I need to define stack effect in some spaces
4. Some other reasons...
Regards,
Cheney
Chris,
Please see the responses below.
Gaurav Mehta, LEED? AP BD+C
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 Yates
Hi Chris and Curtis,
An interesting topic...
Curtis, please advice. The virtual partition, to my understanding, is
actually No partition. If there is no partition, why color or spectrum
characteristics will take effect? I am not so familiar with Energy Plus, but
does it have two types of "virtual partition", one is IR transparent and one
is not? I also did a quick test in IES VE which can calculate long wave
radiant exchange. The way to define virtual partition in IES VE is simply to
cut a 100% hole on a solid partition. I tested one room with a window first
and the same room divided into 3 equivalent spaces by virtual partitions. It
shows the results obtained from the two models are quite similar. It accords
with your test by Energy Plus.
Chris, I agree with you that virtual partition is not a 'must' to the
perimeter zone. However, in some projects, it is certainly a simplification:
without putting up daylight sensor and conducting extra lighting
calculation, you can input LPD obtained from lighting designer directly; Or
sometimes mechanical designer has specific design in perimeter area
and virtual partition method can easily accommodate it without modifying the
whole room...etc...etc...
Regards,
Cheney
Hi Cheney,
I'm interested in your results for these equivalent models. Have you
tried a sensitivity test with respect to time step? I'm wondering how
much more closely the air temperature will match between the 3 "virtual
zones" at shorter time steps.
If you can, log down the mean radiant temperatures as well. My hunch is
that mean radiant will show more divergence than air temperature.
Cheers
Chris Yates
Hi Chris,
I did not pay attention to the air temperatures in the three equivalent
zone. The original purpose was to test whether those "virtual partition" is
IR transparent. If they were, the overall sensible cooling/heating capacity
would be affected.
Then I looked into those temperatures after reading your email. Basically ,
the temperatures are represented in a 'beautiful' stratified manner. MRTs
are in the same manner, and divergence wise, no significant difference
compared as air temperatures.
I do not expect a simulation engine can trace the complication of the
physical state. The assumption behind the simulation engine is that, air
within the space is well stirred and represented by a single air
temperature. In order to see the stratified effect in some big space or
displacement ventilation effect, we refine the single space and come up with
more sub-space by "virtual partition". Air within each of the sub-zone is
well stirred but they are interacting with each other through the
boundaries, virtual partition.
even the most robust CFD simulation. I'd rather set up experiment and filed
measurement to explore specific physical state. Project wise, I believe the
assumption is fairly acceptable. Bear in mind, there are many other
assumptions which are rougher than this one but still survive.
Regards,
Cheney
Sorry, my typo error. "...The original purpose was to test whether
those "virtual partition" is IR transparent. If they were, the overall
sensible cooling/heating capacity would NOT be affected significantly. "
Regards,
Cheney