[bldg-sim] suggestions other than eQuest

[Steven Gates]

Is there a more fundamental issue that is being missed here?  Lee Elson's
description includes the phrase "insulated rock floor with active air
recirculation".  It also includes "ICF", which I am not familiar with.

The description of the system appears to be a floor/rock-bed that uses a fan
to recirculate air between the rockbed and the space.  So solar falls
directly on the floor surface, but the floor also captures/releases heat
convectively using a fan.  

If that is the case, it is critical that the convective leg be simulated.
Assuming the space will not be allowed to be uncomfortably warm, and that
the rockbed temperature must be at least 70F to have any heating
effectiveness at all, this implies a very low delta-T between the rockbed
and the space when convectively charging or discharging the rockbed -
corresponding to a large, potentially drafty, airflow.  It also suggests
that the convective thermal capacity of the rockbed may be quite limited,
corresponding to a temperature swing on the order of 5F or less.  

It is essential that the fan energy of this system be modeled; with such a
small delta T between the rockbed and the space, the cost to run the fan may
exceed the cost of the heating energy saved by the convective component of
this system.

It would be helpful if Lee described the system in more detail.
eQUEST/DOE-2 does not simulate either convective rockbeds or the combined
radiant/convective rockbed floor that this building appears to use.  Do any
programs have this capability?  


-----Original Message-----
From: postman at gard.com [mailto:postman at gard.com] On Behalf Of Blake, Jeff
Sent: Sunday, April 03, 2005 8:03 AM
To: bldg-sim at gard.com
Subject: [bldg-sim] suggestions other than eQuest

Lee,

Doe2 (2.1 or 2.2) is not the right program for looking at heavy thermal mass
buildings.  The limitation is a function of the thermal response factors
used to represent time-delayed heat transfer through opaque surfaces.  This
method is a legacy of the original DOE2 design requirements which were
somewhat hindered by slow computers.

You should use a simulation program that uses a more fundamental heat
balance approach.  There are several but I believe that ESP-r (ESRU,
University of Strathclyde) is one of the best.

Jeff Blake

-----Original Message-----
From: postman at gard.com [mailto:postman at gard.com]On Behalf Of Lee Elson
Sent: Friday, April 01, 2005 3:55 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] suggestions other than eQuest


I'm designing a 3500 sq foot residence at a 5000' desert-like elevation
(Nevada).
The site has good sun exposure and the climate is generally dry. Typical
temperatures in Feb are 20-40 F. The building is mostly oriented east-west
and has
a 2' deep insulated rock floor (for thermal mass) with active air
recirculation.
ICF's will be used as well as tile over concrete (above rock floor) in south
facing rooms.

I'm trying to get a realistic estimate of temperature swings and auxiliary
heating
requirements. I've used eQuest, which seems pretty impressive and easy to
use.
I've entered the floor plan layout, specified the glazing (clear glass on
the
south side) and the building materials. The calculations are a bit
disappointing:
with 12% of the total floor space in south facing glass, the aux heating
required
is not too different (~20%) from a house with standard insulation and no
added
south facing glass. Another oddity: when I change the south facing glass
area from
5% of the available south wall to 90% of the south wall, I get an *increase*
in
aux heating requirements. The eQuest developer thinks this is due to
inadequate
thermal mass/heat recirculation modeling.

I suspect that eQuest is not doing accurate modeling since other houses with
a
similar design in this area get much better thermal performance. Can anyone
suggest either software or a service provider that might be able to do a
more
accurate calculation?

TIA

Lee Elson




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