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Re: [EnergyPlus_Support] Re: Mixing objects assumptions
Ana,
In EnergyPlus an air balance is done at the system level. So zone
exhaust air is added up for the
system and the outside air (ventilation air ) is forced to be >= to the
sum of the zone exhaust air.
At the zone level, the program checks to make sure that the supply air
flow to the zone is >=
than the zone exhaust. If it isn't, the exhaust flow is limited and a
warning message is issued.
The exhaust fan's energy elec consumption is for the full, unlimited
exhaust flow.
There is no attempt by the program to balance exhaust flow at the zone
level by inducing
infiltration air or air from other zones.
anarui.oliveira wrote:
> I find the documentation isn't completely clear to me on this point.
>
> So, if I have a zone which, in reality, has only forced exhaust, and
> which receives air by pressure difference from an adjacent zone, what
> would be the best way to model it, for the purpose of heat balance
> and thermal loads calculation?
>
It depends on the situation; if you have a forced air system with
adequate supply air flow to balance
the total zone exhaust in zones served by the system, the best thing is
to do nothing - assuming your
zones are all adequately conditioned and at pretty much the same
temperature. If this is not your situation
(your building is not pressurized, maybe heated and cooled radiantly)
you should balance zone exhaust
with mixing or infiltration. If a zone is supplying mixing air to
another zone, balance that with infiltration.
Just make sure that each zone has an air balance. Again if you have a
standard forced air system none
of this is necessary.
Fred Buhl
> If I use just the mixing and infiltration objects, is it actually as
> if I was continuously increasing the zone air volume? Should I add a
> mixing object to extract the correspondent airflow to some dummy zone?
>
> If I implement an exhaust fan, since the mixing object does not use
> inlet nodes, I suppose I'll get unbalanced flow errors?...
>
> Thanks again,
> Ana.
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Edwin Lee"
> <leeed2001@...> wrote:
>
>> There is also a cross-mixing object, which is described in the
>> documentation, that simulates air exchange between two zones, and
>>
> therefore
>
>> affects both zones energy balance.
>>
>> On Mon, Apr 28, 2008 at 9:36 AM, Richard Raustad <RRaustad@...>
>> wrote:
>>
>>
>>> When mixing objects are used, the user is responsible for
>>>
> accurately
>
>>> predicting the air flow into and out of a zone. Only air entering
>>>
> a zone
>
>>> is used in the heat balance. Infiltration and mixing (into a
>>>
> zone) are
>
>>> included in the heat balance predict step (mi and minf in Eng.
>>>
> Ref. Eq 2
>
>>> and 5) Supply air entering a zone is included in the heat balance
>>> correct step (msys in Eng. Ref. Eq 5). The return air leaving the
>>>
> zone
>
>>> is assumed to be balanced based on the supply and exhaust node
>>>
> mass flow
>
>>> rates (mixing and infiltration are not included here). You can
>>>
> read more
>
>>> about the assumptions for balanced flow in the text near these
>>>
> equations
>
>>> in the Engineering Reference.
>>>
>>>
>>> anarui.oliveira wrote:
>>>
>>>> Hi, everyone.
>>>>
>>>> I think I've read this somewhere, but I can't find it now:
>>>>
>>>> - When doing the heat Balance for a Zone Air volume that is
>>>>
> receiving
>
>>>> air with a mixing object, does E+ assume that an equal amount
>>>>
> of air is
>
>>>> withdrawn from that zone, for heat balance purposes?
>>>>
>>>> Thank you in advance,
>>>> Ana Rui.
>>>>
>>>>
>>>>
>>> --
>>> Richard A. Raustad
>>> Senior Research Engineer
>>> Florida Solar Energy Center
>>> University of Central Florida
>>> 1679 Clearlake Road
>>> Cocoa, FL 32922-5703
>>> Phone: (321) 638-1454
>>> Fax: (321) 638-1439 or 1010
>>> Visit our web site at: http://www.fsec.ucf.edu
>>>
>>> UCF - From Promise to Prominence: Celebrating 40 Years
>>>
>>>
>>>
>>>
>> [Non-text portions of this message have been removed]
>>
>>
>
>
>
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>
[Non-text portions of this message have been removed]
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