[bldg-sim] suggestions other than eQuest
JRR
energy.wwind at cox.net
Sun Apr 24 15:50:15 PDT 2005
The "air fired" surge gravel ( 2" to 6" ) rock bed storage is easily
beaten by an
"over square Water fired" active / passive combo. Ours has been running
since
January '87. After accounting for an 85% reduction in DHW load from active
solar AND 50% reduction in wall plug load via lighting and other
measures AND
savings from a 2.5 / 4 ton 2 speed heat pump ; we still beat Energy 10
V1.6 estimates of our energy use by 700+ kwhr /month. Our E-10 model has
been refined over 28 iterations against weather data. This design won
an ASME region V design contest in 1980. General Tips >>>
1) WALLS 2x6 stud 24" OC 1" blue styrofoam sheathing on outside,
steel diagonal bracing. R-19 fiberglass. Tan brick veneer all walls above
grade. 57s gravel 4 ft deep below basement slab; 1" styro Tbreak inside
basement
walls to footings, 2" Styro outside basement walls to footings. S side
basement is 100%
height walk out.
2) WINDOWS -- You have to use casement or awning windows because they
seal air leakage better than anything else. Patio door only 1 allowed,
South side only.
N/E/W sides LoE2 glazing, S side LoE2 or double clear. All windows & patio
door have night insulation. Prefer fewer larger windows over more numerous
smaller windows for E/W/S. ie Andersen CW-24s a 4640 Double casement.
N side gets CW-14s a 2440? Single casement.
Patio Door gets lightshelf daylight hours in heating season..
3) SKYLIGHT -- ONE only above freezer openable . Freezer precharges
skylight
shaft with warm air !! Now you are ready for a quick blow off to shed
heat at sundown
or to keep kitchen smoke contained ........... we have 10 ft ceilings
in the Kitchen.
4) OVERHANG 2ft on E W N sides, 4 ft on S --two story height. We are
at 38-45-00 N.
5) Roof is 6/12 pitch 20 deg W of South, recommend 8/12 or 12/12 for
new install.
Basement slab w/ 900 ft + HDPE pipe, would use REHAU PEX for new
install.
6) You will find a fan does not provide the flow pressure required to
spread out the heat
in a really large rock bed ( ~ 2" water gauge ). You need a centrifugal
blower ( ~ 10" WG)
it will be louder than a fan.
John R Ross P.E.
Renee J. Azerbegi wrote:
>I live in a passive (and active) solar home with rock bed storage in my
>sunroom in Golden, Colorado. We did not design this house ourselves....
>There is about 4 feet of rocks underneath wooden boards with about 1/2" of
>space between the boards and the rocks start about 1 foot below the boards.
>There is also brick on both walls. It gets really hot in this room in the
>winter (and in the summer since it was not designed with proper overhangs so
>we need to add some exterior overhangs as well). There used to be a duct and
>fan to blow heat to the floor above, but it was removed by the previous
>owners probably due to aesthetics since it was right in the middle of the
>sunroom. Due to the airspace, there are a lot of bugs and dust that collect
>on the rock bed. Frankly, I think the sunspace itself is quite sufficient
>with the brick and glazing alone, and due to indoor air quality concerns, we
>will likely take out the rock bed or seal it up. So if you do this rock bed,
>make sure it is well sealed so bugs and dust cannot collect on it,
>especially if you are going to blow air through it. And if it is already
>going to be located in a sun room, it may not be necessary if you have brick
>or another high mass feature in the space. It sounds like yours is going
>over tile. You'd have to design it to make sure the rocks below the tile
>heat up.
>
>Renee Azerbegi
>
>-----Original Message-----
>From: postman at gard.com [mailto:postman at gard.com] On Behalf Of Graham & Megan
>Sent: Tuesday, April 05, 2005 3:19 PM
>To: bldg-sim at gard.com
>Subject: [bldg-sim] suggestions other than eQuest
>
>Lee,
>I tend to agree with many of Steve's observations. When I was at Berkeley
>we visited the Village Homes site in Davis, California. While this is a
>more temperate climate, the feedback we got at the time was that the houses
>performed quite well but the fan coupled rock stores in most cases were
>providing very marginal benefit in winter as the houses already had a number
>of other passive features. If my memory servese me correctly, the controls
>were two complicated for the simple home owner to manage to get the most out
>of the system. The summer benefits were likely greater. I believe there is
>some case study material on the Vital Signs website. Cris Benton at
>Berekeley I believe still runs the Vital Signs program if you can't find the
>website. A web search on Village Homes will turn up additional background
>information.
>Regards,
>Graham
>----- Original Message -----
>From: "Steven Gates" <steve.gates at doe2.com>
>To: <bldg-sim at gard.com>
>Sent: Tuesday, April 05, 2005 12:41 PM
>Subject: [bldg-sim] suggestions other than eQuest
>
>
>
>
>>Lee,
>>
>>OK, the rockbed is being charged with warm air from inside the house; not
>>from a solar air heater which could produce air at a considerably warmer
>>temperature. If the maximum space temperature you are comfortable with is
>>80F, and the rock bed must be heated to at least 75F to later produce 70F
>>
>>
>in
>
>
>>the space, then we are talking about a 5F MAXIMUM temperature differential
>>between the rock bed and the space.
>>
>>While I make my living by writing energy simulation software (DOE-2), I
>>believe there are many times when a full-blown computer simulation is not
>>justified. So, before getting bogged down in trying to model a rockbed
>>system in a detailed energy simulation program, it might be useful to
>>
>>
>first
>
>
>>look at some rough numbers, and make a decision as to whether the rough
>>numbers justify a more detailed analysis.
>>
>>So, for what it is worth, here is my 15 minutes of thinking:
>>
>>To move 1000 cfm at 1" static will require about 0.25 kW of fan energy.
>>
>>
>But
>
>
>>the air has to first be used to charge the rockbed, and then again to
>>discharge it. So double the fan energy to 0.5 kW/1000cfm of heated air
>>delivered to the space. At $0.10/kWh, this amounts to $0.05/1000cfm per
>>hour.
>>
>>The amount of heat that can be delivered per 1000 cfm is: 1.08 * 1000cfm
>>
>>
>*
>
>
>>5dT = 5400 Btuh. Adding in the fan heat, the net heating effect is 5770
>>Btuh. At an equivalent 80% furnace efficiency and $1.00 per therm of
>>natural gas, the gross savings in natural gas are $0.072/1000cfm of heated
>>air delivered to the space. Assuming the system can provide 100% of the
>>annual heating loads, the savings on the heating bill are 1 - 0.05/0.072 =
>>~30%
>>
>>The location described gets a lot of winter sun, which even in a
>>conventional design will act to significantly reduce heating loads. What
>>would the house cost to heat if intelligently designed (well insulated,
>>reasonable south glass, some thermal mass), but without the rockbed? $1500
>>per year? What does the rockbed cost, $20,000? Does a potential ~$500
>>
>>
>per
>
>
>>year savings justify the cost of the rockbed?
>>
>>Of course, these numbers are very approximate, and the actual savings may
>>vary due to a variety of factors:
>>1) If natural gas is not available, then the system may be more
>>
>>
>attractive.
>
>
>>2) The 5F delta T may be too large. 80F space temperature in a cold,
>>
>>
>dry,
>
>
>>5000 ft desert climate may result in extremely low humidity in the space.
>>This may tend to desiccate the occupant's skin and sinuses, and they may
>>
>>
>not
>
>
>>find it comfortable.
>>3) Many hours, the fan will be charging the rockbed with the house being
>>cooler than 80F. So effectiveness during those hours is reduced.
>>4) Rockbeds tend to be dusty, and may become moldy. You may need to use
>>
>>
>a
>
>
>>high efficiency filter, which may raise the required fan static to do the
>>job.
>>5) This quickie analysis assumes that the solar system can provide 100%
>>
>>
>of
>
>
>>the annual heating; some auxiliary heat will almost certainly be required.
>>6) All losses from the rockbed to the ground are neglected.
>>7) The bright sun will act to fade the furniture more rapidly than in a
>>conventional house. What is impact on the furniture replacement budget?
>>The sun may also degrade the finish on cabinetry more rapidly, especially
>>
>>
>if
>
>
>>varnished. Deduct maintenance costs from the energy savings.
>>
>>For many experienced people using this listing, the above may come across
>>
>>
>as
>
>
>>too preachy. To those people, I apologize. But I understand that a lot
>>
>>
>of
>
>
>>graduate students also subscribe to this listing, and I want to emphasize
>>that considering too many details when first approaching a problem can get
>>in the way of the answer. It is often useful to first look at the forest
>>before focusing on the trees........
>>
>>Lee, I would be interested in knowing what your ultimate conclusions are.
>>
>>Steve
>>
>>-----Original Message-----
>>From: postman at gard.com [mailto:postman at gard.com] On Behalf Of Lee Elson
>>Sent: Monday, April 04, 2005 4:18 PM
>>To: bldg-sim at gard.com
>>Cc: bldg-sim at gard.com
>>Subject: [bldg-sim] suggestions other than eQuest
>>
>>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 transferred 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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