[bldg-sim] suggestions other than eQuest

[Lee Elson]

First, let me say that I've been a bit overwhelmed with the quality (and 
quantity) of responses. I appreciate all the discourse and am struggling 
to check out all the suggestions.

It is a good idea for me to address some of the issues I described 
originally. "ICF" stands for insulated concrete forms which consist of a 
foam form (about 2" thick) into which concrete (9-12" thick) is poured. 
These will be used for exterior walls for the single story structure. 
Although the insulating (sound and heat) properties are great, and the 
costs are reasonable, there is little heat storage by the concrete 
because of the interior foam.

Some details on the rock floor. It will be a layer of 2" rocks, about 4 
feet deep. There will be insulation underneath and a concrete and tile 
floor above. Part (about 1/3) of the tile floor will be in direct sun 
when conditions allow. There will be a couple of plenums (consisting of 
stacked concrete blocks with spacers near the bottom) running the length 
of the rock floor and there will be an air barrier of some sort that 
will channel warm air from the plenum to the outer portion of the rock 
floor. Other plenums near the ceiling will allow warm air to be forced 
(with fans) down to the rock floor where it will circulate back into the 
house through floor registers (after having given up heat to the rocks). 
This rock floor will be used over the entire structure (about 3500 sq 
ft). The builder/designer says that he's used this approach and it works 
pretty well. There is sufficient heat transfered to the rocks to make 
them a reasonable thermal mass. This system also redistributes air from 
the warm (south/high) side of the structure to the cold (north/low) side.

I realize that this type of thermal mass may be difficult to model in 
detail and that it is important to look at the energy cost of the fan(s) 
in all of this.

I hope this description helps.

Regards,
Lee Elson

Steven Gates wrote:

>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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