[Equest-users] Mixed-mode natural ventilation

Nathan Miller nathanm at rushingco.com
Mon Dec 14 08:56:44 PST 2009

My firm has received credit for MMV in a LEED project by utilizing a
custom calculation.  This was entered in as an Exceptional Calculation
Method (ECM) in the LEED template . 


We first created an additional VAV system serving all of the spaces that
would be included in the MMV scheme. We then had eQUEST spit out an hourly
report of the fan, heating, and cooling energy for this system, as well as
the ambient exterior air temperature. 


For this particular project, the building automation system will signal
the occupants when the outside temperature is "appropriate" for natural
ventilation and shut down the HVAC system in the perimeter spaces. It is
then up to space occupants to open windows to allow for ventilation and
conditioning.  Thus, we took the hourly output spreadsheet and zeroed out
the fan, heating, and cooling energy for occupied hours in the natural
ventilation temperature range. The interior spaces were left on a separate
VAV system that remained on during all occupied hours. We took the energy
savings calculated from this spreadsheet and applied it to the total
energy usage from the proposed run when all the spaces were served by a
single VAV system. 


The major inaccuracies of this approach are that we have modeled separate
VAV systems for MMV and traditionally conditioned spaces, when in reality
there is one system and the individual fanboxes are shut down (there is
also static pressure reset on the VAV system, so there should be at least
some savings on the central fan in reality). Additionally, the spaces are
modeled as though they are conditioned rather than allowing their
temperature to float during natural ventilation mode. 


The LEED reviewer accepted this methodology without any comments. (They
did make me change my roof from U = 0.064 to U = 0.063 for the baseline
case, which tells you the areas the reviewers tend to fixate on. Anyway,
that is a different discussion.)


Nathan Miller

Senior Energy Engineer/Mechanical Engineer

direct: 206.788.4577

fax: 206.285.7111 


From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Kevin
Sent: Sunday, December 13, 2009 8:14 PM
To: Equest-users at lists.onebuilding.org
Subject: [Equest-users] Mixed-mode natural ventilation



I was wondering if anyone has had success incorporating mixed mode natural
ventilation into their ASHRAE 90.1 baseline model and submitting it to the
USGBC.  I am currently using it in my building mechanical system and would
like to take advantage of the energy savings.

Thanks for the help.


Kevin Luoma


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