[Equest-users] defining the windows for natural ventilation

[Joe Huang]

eQUEST, or more specifically the DOE-2 engine behind it, has had the ability to simulate 
natural ventilation through windows for RESIDENTIAL systems since the late 1980's.  I 
believe this capability was also added to all the other system types sometime in the late 
1990's, but I'm not certain and someone who knows DOE-2.2 well might want to describe the 
simulation there.

In DOE-2, natural ventilation is modeled with the same Sherman-Grimsrud model as used for 
infiltration, except that it is done during SYSTEMS so that it can be controlled based on 
the actual zone conditions of temperature and enthalpy.  The inputs are similar as for 
infiltration, except that the EFFECTIVE-LEAKAGE-FRACTION now refers to the area of window 
opening, rather than of cracks and leaks.  I once asked Max Sherman, co-author of the S-G 
Model, whether he thought his model was suited for modeling natural ventilation, and got 
the surprising response that he felt it was MORE suited than for infiltration, since the 
openings were so much larger and regular than are cracks and leaks.

The main limitation of DOE-2 natural ventilation is that it's a one-zone model, so it 
can't handle air flow from zone to zone.  That doesn't mean it fails completely in a 
multi-zone case, but just that you will get natural ventilation only in the perimeter 
zones with windows as if those zones were independent.  To model multi-zone air flow, one 
needs a network model like CONTAM or COMIS.  I was involved in linking EnergyPlus to COMIS 
15 years ago, but EnergyPlus is now linked to Airnet, the solver behind CONTAM.

I think it would be interesting to compare DOE-2 to EnergyPlus in their modeling of 
natural ventilation. Many of the inputs needed for multi-zone air flow modeling are 
difficult to determine, e.g., how much are the interior doors opened?  Also,  don't 
buildings designed for natural ventilation tend to be large open-plan, i.e., more like 
single-zone?   I'm not saying that multi-zone air flow modeling is unnecessary, but I'd 
like to know whether the simple single-zone model is conservative or overly optimistic.  
Then, I can decide how much effort to put into the multi-zone modeling.

Another observation about natural ventilation modeling in DOE-2 is that because it's so 
quick and implemented in SYSTEMS, the program actually checks to see if  natural 
ventilation can maintain indoor temperatures below the setpoint and if not, it closes the 
windows and goes on to mechanical cooling.

Joe

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


On 4/25/2013 8:39 AM, Daniel Knapp wrote:
> It looks like eQuest can simulate infiltration and can simulate the movement of air through open windows into an exterior space using the Sherman-Grimsrud method as pointed out by Paul Diglio.  Maybe this is all you need for your model in which case you are set.  I was more concerned about the fact that eQuest does not calculate the movement of air from zone to zone and is not a good simulation tool for calculating natural ventilation throughout a building.  It looks like it may well be a good tool for calculating natural ventilation in a given room with open windows though.
>
> Cheers,
> Dan
>
> —
> Daniel Knapp, PhD, P Phys, LEED® AP O+M
> danielk at arborus.ca
>
> Arborus Consulting
> Energy Strategies for the Built Environment
> www.arborus.ca
> 76 Chamberlain Avenue
> Ottawa, ON, K1S 1V9
> Phone: (613) 234-7178 ext. 113
> Fax: (613) 234-0740
>
>
>
>
> On 2013-04-25, at 11:18 AM, John Aulbach<jra_sac at yahoo.com>  wrote:
>
>> So what then is infiltration in eQuest? THAT is separate of the outside air introduced into the HVAC.
>>
>> There is the ability to perform rudimentary daylighting. It does ask for minimum footcandles in the data. So it must have SOME idea about natural illumination when the lighting controls step down.
>>
>> John Aulbach, PE
>>
>> From: "noa at gbwawa"<noa at gbwawa.com>
>> To: 'Daniel Knapp'<danielk at arborus.ca>
>> Cc: equest-users at lists.onebuilding.org
>> Sent: Thursday, April 25, 2013 8:07 AM
>> Subject: Re: [Equest-users] defining the windows for natural ventilation
>>
>> Are you sure about that?
>> How about natural lighting? Does it calculate it?
>>
>> -----Original Message-----
>> From: Daniel Knapp [mailto:danielk at arborus.ca]
>> Sent: Thursday, April 25, 2013 4:59 PM
>> To: noa at gbwawa
>> Cc: equest-users at lists.onebuilding.org
>> Subject: Re: [Equest-users] defining the windows for natural ventilation
>>
>> Hi Noa,
>>
>> My understanding is that eQuest does not calculate natural ventilation at
>> all.  The program is not designed to support calculations of the movement of
>> air between zones.  The outdoor air flow in the HVAC window is outdoor air
>> introduced by the mechanical system and not through windows.  I think you
>> would be better off looking to another tool (maybe EnergyPlus/OpenStudio?)
>> that explicitly supports these calculations.
>>
>> All the best,
>> Dan
>>
>>
>> -
>> Daniel Knapp, PhD, P Phys, LEEDR AP O+M
>> danielk at arborus.ca
>>
>> Arborus Consulting
>> Energy Strategies for the Built Environment http://www.arborus.ca/
>> 76 Chamberlain Avenue
>> Ottawa, ON, K1S 1V9
>> Phone: (613) 234-7178 ext. 113
>> Fax: (613) 234-0740
>>
>>
>>
>>
>> On 2013-04-24, at 11:12 AM, noa at gbwawa<noa at gbwawa.com>  wrote:
>>
>>> Hi all,
>>>
>>> I just understood that e-Quest dosn't calculate natural ventilation
>> without making some definitions.
>>> I found that in the detailed mode, in the HVAC window, I can define the
>> outdoor air flow, but how do I define what is the area of the window that
>> opens? It could be only half of the window area or all of it for example.
>>> So what are the parameters that I need to fill out in order to be exact in
>> the natural ventilation definition? And where could I find it?
>>>
>>> Thank you
>>>
>>> Noa Hakak,
>>>
>>> Green building project manager
>>> WAWA
>>> _______________________________________________
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