::On the modeling of natural ventilation, I've not heard of anyone who's
::coupled thermal with CFD for annual simulations, and if they did I'd
::guess they're still waiting for the results! There are, however,
::several programs (EnergyPlus, ESPr) that do link up with a multi-zone
::air-flow network program (EnergyPlus uses AirNET/CONTAM) to "ping
::pong" with the thermal
::program. My experience doing an earlier linking of COMIS into
::EnergyPlus showed increases in runtimes of 2-3 times (that's on top of
::the standard run times most people have seen).
A clarification on the reference to ESP-r several days ago...
ESP-r has included a very efficient mass flow solver within the simulation
engine for over a decade. For most users the inclusion of a flow network
in a model does not cause much of a slow-down of the assessment
process - perhaps 10-20%.
Of course, some flow networks or flow network control scenarios
work best with short timesteps. It does take longer to run simulations
at a one minute timestep than a 15 minute timestep.
The solver takes directives as to whether the
user wants to ping-pong or use an onion approach. Those that
take the onion approach notice an increase in the computing
resource, but there seem to be fewer models that require an
onion approach and the efficiency of the solver still applies.
Entities in the mass flow network can also act as boundary nodes for
the in-built transient 3D CFD engine so that changes in weather conditions
or pressures in adjacent rooms are accounted for within the
CFD domain. The CFD solver typically runs in adaptive mode
(new wall functions are determined at each timestep based on
detected changes in boundary conditions and flow fields). This allows the
truly passionate to look at changes in rooms over time. Currently, few
people seem to have carried out transient multi-domain assessments
beyond 1000 timsteps.
We know of groups that have also adapted ESP-r to communicate
with external CFD solvers in order to explore the benefits and
drawbacks of communicating with other tools.
In Europe, natural ventilation studies seem to have been normal
practice for quite a few design teams. There are multiple tools
that address issues related to natural ventilation and thus many
designers can test their ideas out.
-Jon Hand
