Plenum Space temperature and effect of plenum load

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Hello all,

I am modeling a assembly factory of 40000 sq .ft. floor area with total
height of 19.6 ft and pitched roof (8 degrees). Conditioned height is 10 ft
only. When I used multi level space option in eQUEST (entered 10 ft is the
conditioned height), by default software creates three spaces (named as
conditioned space, Plenum space and under roof). After completion of
simulation, LS-C report (Building Peak Load Component)is not included roof
conduction load (My observation was plenum and conditioned space both are at
same temperature therefore no heat transfer between these two ). How much is
the plenum space temperature I have to consider ? and also Where this
plenum load accounted in simulation? . When I changed any modification in
the roof construction by using reflective surfaces there was no change in
supply flow (I think this was because of no reduction in load in the LS-C
report). How this roof conduction load reduction effected in the conditioned
space ?.

Do such loads (plenums) get directed straight back to the central air
handler, or do they also partially interact with the zones as well?

Can anybody please help me in this issue.

Thanks &regards

Uday Kumar

Uday Gorre's picture
Joined: 2012-05-10
Reputation: 0

A few of places to begin:

1. Does the factory actually have three spaces - conditioned, plenum
and space under roof? Or is the plenum directly under the roof? The
model should represent the building.
2. What are the constructions between the spaces? Is there a
ceiling in the factory? What is its R-value.
3. How did you define the light fixture sensible heat distribution?
4. How does the model HVAC system represent the return air path:
directly, by duct, or by plenum?

Read the LS-B reports for each of the space to see if internal
conduction is represented. The space beneath the roof should show
and change in heating/cooling loads when you change the reflectivity.

Re. Supply air - do you mean the self-sized supply air flow as
reported in SV-A? This air flow changes based on numerous
factors. Changing the reflectivity would have negligible effect on
the self-sized peak air flow, especially if you have defined a Min
Design Flow in the Air-Side HVAC Zone Parameters.

Or do you mean the hourly supply air flow throughout the year?

The manual is an excellent place to start for many of these questions.

>> Christopher Jones, P.Eng.

Chris Jones's picture
Joined: 2011-09-30
Reputation: 0