[Equest-users] CO2 sensors and outside air reduction. LEED for schools & ASHRAE 90.1-2004

Karen Walkerman kwalkerman at gmail.com
Wed Jan 14 10:29:45 PST 2009


First of all, changing the R-value of walls and roofs can have a significant
impact on overall energy use, especially in locations with extreme outdoor
conditions.  Granted, with more ventilation air required, the envelope is
responsible for a smaller piece of the overall energy use of the building.

So, to reduce ventilation air energy use:

A.  Use energy recovery ventilation!  In moderate climates, energy recovery
ventilation might not make a whole lot of sense, but climates where heat is
needed much of the year, ERV's make a lot of sense!

B.  Turn off the ventilation when it's not needed!  This includes time
clocks and CO2 sensors.  I've seen alot of schools with old unit ventilators
in each classroom.  These unit ventilators often stay on all night, bringing
cold air into the classroom and wasting tons of heat!

Regarding your CO2 questions:

1.  Decoupling the ventilation air distribution system from an airside air
conditioning system allows for the most options.  Installation of CO2
sensors in each space with corresponding ventilation air VAV supply results
in ventilation air being supplied only where it's needed.  But, this can be
cost-prohibitive, and where lots of spaces see similar occupancy, completely
unnecessary.

2.  It is permissible to vary the CFM between the base case and design case
for ASHRAE 90.1-2004 Appendix G (G.3.1.2.5 Exception), some programs,
including eQuest model DCV, so no change in ventilation rate is required,
just activation of DCV.

3.  In a building with 40 classrooms, you could create one branch of each
type of space (classrooms, offices), and control ventilation to each block
of spaces.  For high-use areas with varying schedules (caffeteria, gymnasium
and auditorium), have each space have it's own demand controlled
ventilation.

5.  If you model this in eQuest, you can still do blocks of classrooms,
especially if your occupancy schedule is the same for each classroom.

Hope this helps,

--
Karen



On Wed, Jan 14, 2009 at 12:01 PM, James Geers <jgeers at sfa-architects.com>wrote:

>  Previous posts have confirmed my suspicions that increasing the R-value
> of walls and roofs has little to no effect on energy performance, due to the
> outside air requirements.
>
>
>
> This raises a few questions:
>
>
>
> 1.   What is the most effective way to use CO2 sensors to dramatically
> reduce the outside air requirements?
>
>
>
>    1. Is it permissible to vary the CFM between the base case and design
>    case in the ASHRAE 90.1-2004 Appendix G model, and consequently in the LEED
>    template?
>
>
>
>    1. What is the most effective way to use CO2 monitoring in a building
>    with 40 classrooms and other large spaces.  If one sensor is triggered,
>    won't the entire zone get fresh air and defeat the energy savings?
>
>
>
>    1. If every classroom has a sensor, does any one have experience with
>    the replaceable / Mail in sensors to assure their accuracy.
>
>
>
>    1. If I model this in Equest, do I need a zone for every classroom.
>
>
>
> Thank you for any feed back.
>
>
>
> James F. Geers
>
> *Registered Architect***
>
> *LEED Accredited Professional*
>
> * *
>
> *SFA Architects***
>
> *300 West Fourth Street***
>
> *Cincinnati**, Ohio 45202***
>
> *513.721.0600**    ***
>
> *513.721.0611 (fax)***
>
>
>
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