Deployable Doubt Dispellers

Page 1 of 2
• posted on February 23, 2006, 4:00 pm
The most popular forms of solar heating seem uneconomical these days, with high costs and low solar fractions (20% for some FSEC-certified water heaters), so they seem to require customers who are concerned about climate change, among other things. If solar house heating were to simply cost less than other forms of house heating, more people might use it...
After hearing lots of doubt that low-cost solar house heating can work with a high solar fraction outside of the Southwest from local architects and reporters and others who read SBIC guidelines that say houses in Phila can only be 60% solar-heated at best and seeing lots of "solar houses" that are only 30-50% solar-heated vs those "with no other form of heat," I think we should dispatch Deployable Doubt Dispellers ("D-cubes") to regional Infestations of Doubt, eg unboltable 8' cubes that stay 70 F for a few cold cloudy days, with little windows so people can peer in to see big dial thermometers inside.
Lots of people (eg AIA and SBIC and SBSE) seem to have forgotten that things like this can be engineered, notwithstanding high-school physics and houses by PE Norman Saunders, who calculates needs for "purchased heat" with Gaussian weather stats in the same way that other engineers calculate 100-year floods:
The ASHRAE 1954 Handbook gives the 1% and 2 1/2% temperatures for Boston as 0 and 8 F (-17.8 and -13.4C.) For -15C, the holding time for our houses is three days, giving a standard deviation of 7.8 Kelvin degrees. In December, the 1% temperature is 2.1 standard deviations down... and so can be expected to occur about once every 4.5 years. This suggests the need to purchase heat [or wear a sweater :-] in December once in 35 years.
NREL says 1000 Btu/ft^2 of sun falls on a south wall on an average 30 F day with a 38 F max in Philadelphia. A direct-gain "mass and glass" D-cube (like most solar houses) with an 8'x8' R4 south window with 50% solar transmission could be 80 F on an average day if 0.5x8'x8'x1000 = 24h(80-30)G Btu, with a thermal conductance G = 26.7 Btu/h-F max. Subtracting 16 Btu/h-F for the window leaves 26.7-16 = 10.7 Btu/h-F for other surfaces, eg 4x64ft^2/R28.5 = 9 for the ceiling and non-south walls, with 2 2" polyiso foilboard "R13" layers, counting R2.5 for the indoor foils, which makes G = 25. If the cube temp falls to 70 F after 5 30 F cloudy days, 70 = 30+(80-30)e^(-120/RC) makes time constant RC = -120/ln((70-30)/(80-30)) = 538 hours, so it needs thermal mass C = RCxG = 538x25 = 13,450 Btu/F, eg 13450/4/8 = 420 nestable 9" square x 13" tall 4-gallon ROPAK plastic water tubs stacked 7-high x 10-wide x 6-deep in a 91" x 90" x 54" wall, over half the cube's volume.
An indirect-gain D-cube might have an 8'x8' isolated sunspace or air heater with R1 glazing with 90% solar transmission (eg \$1/ft^2 20-year corrugated Dynaglas polycarbonate greenhouse roofing) with one-way plastic film dampers and half the insulation, eg one 2" layer of foil-faced board for walls and ceiling with G = 5x64/R15.5 = 21 Btu/h-F. If the air heate gains 0.9x8x8x1000 = 57600 Btu = 6h(T-30)64ft^2/R1 [the daytime sunspace loss] +18h(T-30)64/R16.5 [the night loss from the air heater] +24h(T-30)4x64/R15.5 [the 24-hour loss for the rest of the cube], T = 98 F, If we keep it 80 F max with ventilation, C = RCxG = 11,107 Btu/F, eg 347 water tubs stacked 7-high x 10-wide x 5-deep in a 91" x 90" x 45" wall, about half the cube's volume.
An isolated-store D-cube might have less mass with a higher temp swing: 8'x8' of Dynaglas solar siding might be T (F) inside for 6 hours on a Jan day if 57600 = 6h(T-30)8x8/R1+18h(T-30)8x8/R16.5+24h(70-30)4x64/R15.5, so T = 122 F. If the cube needs (70-30)21 = 840 Btu/h and each stacked tub has 3.25 ft^2 of surface and 5 Btu/h-F of slow-moving-air to water conductance, N tubs with Tmin = 70+840/(5N) water can keep the cube 70 F. With an average water temp Ta = (122+Tmin)/2, the tubs lose Et = 120h(Ta-30)64ft^2/R16.5 Btu over 5 days. If the rest loses Ec = 120h(70-30)4x64/15.5 = 79,277 and 32N(122-Tmin) = Et+Ec, N = 69 and Tmin = 72, so we might have a 7-high x 10-wide x 1-deep 91" x 90" x 9" tub wall, about 10% of the cube volume, with a 1" foilboard wall between the tubs and the living space, hinged at the top, with a passive Thermofor vent arm to open it when the room cools to 70 F.
An active D-cube might have 32' of fin-tube pipe below a 2" foamboard ceiling and walls and a 6'x6'x2'-deep unpressurized EPDM-lined heat storage tank on the ground with a PV-powered 10 watt pump for heat collection. If 57,600 Btu = 6h(Ts-30)64ft^2/R1 [daytime glazing loss] + 6h(70-30)4x64/15.5 [daytime loss from the rest of the cube = 14,865 Btu] + 6h(Ts-Tw)160 [stored heat], then the sunspace temp Ts = 48.5 + 0.714Tw, so Tw = 115 and Ts = 131. We might distribute heat from the tank with more fin-tube under the floor or a damper and Thermofor arm or a Honeywell 6161B1000 damper actuator (which only uses 2 watts when moving) to allow warm air to rise out of the floor... 84 ft^2 of tank surface with 5x84 = 420 Btu/h-F of slow-moving airfilm conductance could supply 840 Btu/h at 70+ 840/420 = 72 F. Keeping the cube 70 F for 8 hours and 50 F for 16 hours on a cloudy day takes (8h(70-30)+16(50-30))21 = 13440 Btu, so the tank might store heat for 2x6x6x62.33(115-72)/13440 = 14 30 F cloudy days in a row. With a \$60 1"x300' PE pipe coil in the tank, hot water for outdoor showers could be an option for certain climates and seasons.
We might deploy D-cubes to Rifton and Port Jervis and Harlem, NY, Kempton and Phila and Pottstown and Bryn Mawr, PA, a wintertime MREF or ASES conference or DOE Solar Decathlon, the Chicago Museum of Science and Industry, and lots of YMCAs and high schools.
Nick
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 23, 2006, 5:31 pm
| The most popular forms of solar heating seem uneconomical these | days, with high costs and low solar fractions (20% for some | FSEC-certified water heaters), so they seem to require customers | who are concerned about climate change, among other things. If | solar house heating were to simply cost less than | other forms of house heating, more people might use it... | | After hearing lots of doubt that low-cost solar house heating can | work with | a high solar fraction outside of the Southwest from local | architects and reporters and others who read SBIC guidelines that | say houses in Phila can only be 60% solar-heated at best and seeing | lots of "solar houses" that are only 30-50% solar-heated vs those | "with no other form of heat," I think we should dispatch Deployable | Doubt Dispellers ("D-cubes") to regional Infestations of Doubt, eg | unboltable 8' cubes that stay 70 F for a few cold cloudy days, with | little windows so people can peer in to see big dial thermometers | inside.
Nick...
AIA is headquartered close by you in downtown Philly - why don't you drop in and discuss such a project with them? If you can get the AIA to buy in on the project, I think your "D-Cubes" would be fairly easy to fabricate...
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 23, 2006, 5:39 pm
Talk is all you do nick, so just do it, and let us know the results.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 24, 2006, 12:58 pm
A small cube won`t simulate a building specificaly in air infiltration, since you will caulk it shut for zero air infiltration, unless you do a blower door test to make it within accepted living standards. It would not be hard or expensive to experiment, just do it, numbers only go so far.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 25, 2006, 7:54 pm

I tried to convince someone you could solar heat a house and they asked "where has this been done?" I explained that in the US most solar heating is for hot water and pools, but I read that up to 40% of the solar heating was used to heat homes in Europe. If I had just one example to show that person of an average house that was solar heated, I think that they would have been convinced.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 26, 2006, 12:21 pm

You might understand that if you learned "Ohm's law for heatflow."

You and your internal electrical usage.

E = IR, in electrical terms. Enough to increase the product of the internal gain and the house thermal resistance to 30 F or so.

That's 1800ft^2/R100 = 1.8 Btu/h-F for the ceiling plus about 144ft^2/R4 = 36 for windows plus 2736ft^2/R30 = 91.2 for walls plus about 30 for 30 cfm of air leakage (if you caulk the house tight), ie a total of 159, so you can keep it 70 F on a 30 F day if 70 = 30+Q/159, where Q = 6360 Btu/h, eg 1.86 kW, ie 45 kWh/day or 1342 kWh/mo. Kinda high. Upping the walls to R60 would reduce G to 113 and the electrical usage to 957 kWh/mo. A new house with more zoning or less heated space (eg closets on exterior walls) might have G = 90, with 760 kWh/mo. Replacing the windows with R60 walls would make G = 56, with 473 kWh/mo. An air-air heat exchanger could help.
Nick
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 26, 2006, 12:59 pm
You say 957 kwh a month , what a joke, 957 Kwh @ .125 kwh is 119.62\$ a month. So now you show a heating source, a heating source that is 50% more than Ng in my area. I use apx 150-180 kwh a month that is true conservation. Remove your overpriced over estimate of usage of electric heat and you cant do it. Post real life usage numbers.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 3:53 pm

The US national average is 833.

Good :-)
Nick
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 26, 2006, 3:04 pm
<snip>

In some areas (NY for example), there were a lot of folks 'burned' by the solar-heated home craze in the late '70's. So the building code now requires a high burden of proof that a home is solar heated exclusively. Otherwise, it must have a more conventional heating plant that is large enough to fully heat the home. What a seller might consider 'solar heated' may mean to the buyer, 'solar heated if you like to wear sweaters a lot and enjoy 50-60 degree home'.
So, building a home in one of these areas means you pay the 'up-front' costs for two heating plants, the conventional one required if you ever want to get a building permit, and the solar one to save energy/planet.
Solar 'boosting' or 'supplementing' is a lot more appealing to many since the solar plant doesn't have to be as large, and you still get some of the benefits.
But a major factor to a lot of folks is, "How will this affect my resale value?" If the average buyer and the bank don't agree on what you think is the increase in home value, you may have a 'white elephant' on your hands. Until the public at large (including mortgage companies) start to see the true value of such systems, you may be better off just tearing it down when it comes time to sell.
daestrom
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 26, 2006, 5:34 pm

Maybe 1 in 5 home buyers would want a pool and you can not take out an in ground pool. But people do it anyway, rationalizing that it will improve resale value when they really just want a pool for recreation and/or status. Pools are very expensive and cost a lot to keep up. They do not pay themselves back like solar thermal, but rather keep costing more and more. I would install a solar thermal system such that I could take it out if the new owner wanted. But with natural gas quadrupling in price over the last 5 years and talk of bringing in LNG tankers, the price will probably continue to go up. The new buyers might like to look at the low heating bills before they put the removal clause in the contract.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 3:47 pm

The good news is, if you don't plan to ever use it, then there's no reason not to make the second plant pure resistance-electric, which is really cheap to install, just expensive to operate.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 3:57 pm

Not if the house is well-engineered, like those of PE Norman Saunders.
Nick
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 10:48 pm

To get the building permit, you must either show proof of a conventional heating plant that will provide enough heating to meet code, or have a PE stamp the design stating that it will be adequately heated (maintained at least 68F) for 7 days of sub-zero temperatures (the so-called 100 year blizzard).
Considering the cost of such an extreme solar system, it is almost always cheaper to go with dual heating systems.
Of course, Philidelphia may be different building code, and/or have a different '100-year blizzard' standard.
daestrom
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 28, 2006, 11:10 am

Interesting. That might involve a \$5 immersion heater in a large unpressurized solar heat storage tank. Norman suggests one 5 kW space heater, but some of his clients never bought those.

Steve Baer says the greatest discovery of solar investigators has been that if we use lots and lots of insulation, a house will need very little heat, from the sun or any other source. IMO, a house with lots of insulation and airtightness and an integrated solar heating system (eg polycarbonate "solar siding" vs rooftop panels) can be inexpensive, with a solar heating fraction that is close to 100%.
Nick
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 28, 2006, 3:30 pm

Nick...
Do you have URLs, references, books? Anything else?
Thanks,
Paul
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 28, 2006, 10:49 pm
...and needs an expensive heat exchange system so it's occupants don't die in their sleep, like many have, from CO poisoning.

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 3:45 pm

There's one On Hayes Park Road in Barrington, RI. Currently on sale for about \$600,000 on account of the owners decided to give up their jobs and become starving artists.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 3:52 pm
On 25 Feb 2006 18:27:33 -0500, snipped-for-privacy@ece.villanova.edu wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 4:05 pm
On Sat, 25 Feb 2006 17:56:42 -0600, snipped-for-privacy@webtv.net (m Ransley) wrote:

The question you should be asking isn't where would the BTUs come from, but where are those 150 KBTU (per hour? or per day?) going? If it's taking you 150,000 BTU/Hour to get 45 DF temperature diff between the inside and the outside of a 1800 sqft house, then there's something seriously wrong.
1800 sqft is what, a 24*36 2-story house? That gives a surface area of about 3650 sqft. times a dT of 45F gives about 164,000 BTU. SO you appear to be averaging around R=1. Maybe you should consider CLOSING one of those Argon-filled windows.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on February 27, 2006, 4:45 pm
Goedjn wrote:

If it was a day, the wording points to that, that's ~R24 (using your numbers). Since Ransley mentioned R30 walls, R24 is a believable net number.
R