[BLDG-SIM] how much infiltration - an alternative approach

[Jon Hand (clcv10)]

Where design questions are about risk and variability,
and perhaps within the context of designs which
also pose questions about natural ventilation and IAQ,
solving both the building and the air flow domains makes
sense.

An alternative approach to investigating the patterns of
air flows in a building, including infiltration, is to describe
the air flow paths within a building and in the facades within
an air flow network and then let the computational engine
figure out what happens under different climate/operational
scenarios. Several tools offer these facilities and have considerable
libraries of flow components and some have very efficient
flow solvers.

In dozens of projects (including early design stage exercises) this has
worked well to identify:
* infiltration risk e.g. what happens if a school warden
   forgets to fully close some windows over the weekend
* for cost implications e.g. tightening up cracks on the windward
   side of the building
* what combinations of wind speed and direction are
   an issue for different parts of a building
* questions about facade details which have very non-linear
   flow/pressure performance curves
* how often predicted flow is close to Mfg claims
* how in transition seasons wind drive flows can be used to
   improve IAQ or transition into a scheme for natural ventilation

And yes, it is possible to not quite define reality within a flow
network.  Some practitioners will use wind tunnel tests or CFD
runs to improve the data on wind pressure coefficients. Some will
have blower door tests to confirm initial guesses about crack
areas.

And yes there is still some art to the definition of
flow networks. And while bulk flows are a lower resolution
than CFD they allow one to look at a thousand timesteps
and perhaps understand the temporal nature of a design.

An hour or so of preparation and a few minutes of
computational time  can provide design teams with quire
a bit of information.

-Jon Hand, Energy Systems Research Unit, Glasgow


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