Subject: Some sunspace heatflow basics
From: nick@ufo.ee.vill.edu (Nick Pine)
Date: 19 Nov 1996 06:35:56 -0500
Meanwhile, in Connecticut...
>>>What is a lean-to sunspace? .
>> . .
>>A simple glazed wall over the . .
>> south side of an existing g . house .
>> house, like this: g . .
>> g ss . .
>> ------------------------------------
>To contain heat, the lean-to sunspace would need side walls...
Yes, but if it's only warm during the day, the sidewalls don't have to
have much insulation. They could be a single layer of polyethylene film,
like the south wall.
>Would this look a bit like 1/2 an A-frame...
Sure.
>in other words, like a pup tent...
The added-on part would look like half a pup tent, sliced lengthwise through
the top, perhaps between lengthwise cub scouts, by a man with only 3 teeth and
a hideous laugh and a large chainsaw, by the light of a silvery full moon.
>>>I was thinking about glassing in my porch and using it like
>>>a big solar heater.
>>Sounds good, with no little thermal mass inside it, so it can get cold at
>>night. And plastic is cheaper and much easier to install than glass...
>why not put a thermal mass in it?
You can get more solar heat out of it for the house if you don't.
>wouldn't that mass absorb heat during the day, and release it slowly
>over the night?
Yes, but most of that stored heat would go back outside through the low
thermal resistance of the solar glazing at night. Better to keep it inside
the house at night, behind an insulated wall.
>Are you telling me that it is better to transfer the heat into the house
>while the sun is out and seal off the sunroom during the evening?
Yes. Let it get cold at night. Keep the thermal mass in the house.
>If that is the case, I would be well served to put a pair of fans, one
>pushing and one drawing when I get home from work to 'harvest' the hot air?
You would be better served to do this during the day while the sun is shining,
since this sunspace does not store heat, so it gets cold quickly at night.
I'd use 2 thermostats in series with the fans, a heating thermostat in the
house and a cooling thermostat in the sunspace, to turn on the fans when the
following things are both true: the sunspace is warmer than, say 90 F, and
the house is cooler than say, 75 F. A couple of Grainger's DPST $16.55 5E266
thermostats might do this.
And one fan is probably enough, a $12 20" window fan in an opening at the top,
with a dry cleaner bag over the inside, hinged at the top, to keep house air
from flowing out into the sunspace at night. You could have an open window near
the bottom of the other side of the sunspace with a similar one-way damper
that only allowed house air to flow into the sunspace.
Larger or more fans raise the sunspace solar collection efficiency: moving
1 cfm of air with a temperature difference of 1 F transfers about 1 Btu/hr
of heat. Full sun is about 300 Btu/hr-ft^2 (or about 400 Btu/hr-ft^2 with
some sort of ground reflector to the south.) A sunspace with 100 ft^2 of R1
glazing in full sun receives about 300x100 = 30,000 (30K) Btu/hr of peak heat.
Or the net heat equivalent of about 1-2 gallons of oil per square foot of
vertical south glazing per winter.
Looking at fan size extremes...
If the sunspace were completely sealed off, with no fan, it would heat up
until the thermal loss through the glazing equals the solar input. Suppose
it's 37.5 F outdoors (the average daily max temp in Hartford, CT in December,
where an average 820 Btu/ft^2/day fall on a south wall) and house wall behind
the sunspace and the endwalls of the sunspace are perfectly insulating. Then
the sunspace temp T adjusts itself until 30,000 Btu/hr = (T-37.5)100ft^2/R1,
or T = 37.5 + 30000/100 = 337.5 F, theoretically. Radiation losses limit T to
something like 130 F, but linear arithmetic works well at low temperatures.
The solar collection efficiency of the sunspace, defined as the heat provided
to the house divided by the solar input, is zero, because the sunspace is hot,
but it doesn't heat the attached house at all.
If the fan were huge, and it moved 68 F house air at a very large rate into
the sunspace, the sunspace would be very close to 68 F, and air would return
to the house at a temperature very close to 68 F. The thermal loss through the
glazing would be (68-37.5)100ft^2/R1 = 3050 Btu/hr, and the house would gather
30,000 - 3050 = 26950 Btu/hr of heat (about 8 kW) and the sunspace collection
would be 26950/30,000 = 90%, but the huge fan would make the house drafty
and consume a lot of electrical power.
If a typical window fan moved 1000 cfm of 68 F house air into the sunspace
with 100 ft^2 of R1 solar glazing, in full sun, and all the sun went into
heating the air, the air would return to the house at 68 + 30000/1000 = 98 F.
But some of that solar heat is lost through the glazing: if the sunspace has
temperature T, the glazing loss is (T-37.5)100ft^2/R1, and the fan carries
away (T-68)Q of heat for the house, so if the solar energy that flows into
the sunspace equals the solar energy that flows out of the sunspace with no
heat storage in the sunspace), 30,000 Btu = (T-37.5)100ft^2/R1 + (T-68)Q.
If Q = 1000 cfm, 30000 = 100T - 3750 + 1000T - 68000, so 101750 = 1100T,
or T = 92.5 F, and the glazing loss is (92.5-37.5)100 = 5500 Btu/hr,
and the house gets the rest of the 30K, ie 30K - 5500 = 24500 Btu/hr,
and the solar collection efficiency of the sunspace is 24500/30K = 82%.
Not bad, for a solar collector. One reason this is so good is that the
back of the collector is the house wall, not outdoor air. And it's nice
to be able to put a chair in your solar collector and read a book on a
sunny winter day.
Here's a more general formula:
T = (I+TaAg/Rg+68Q)/(Ag/Rg+Q) where
I is the total solar input in Btu/hr, eg 300 Ag, perhaps reduced
by a sunspace glazing transmission of less than 100%,
Ta is the ambient temperature, eg 37.5 F in Hartford
Ag is the sunspace glazing area, eg 100 ft^2
Rg is the sunspace glazing R-value, eg R1, and
Q is the fan cfm, eg 1000 cfm.
The sunspace solar collection efficiency is approximately (I-(T-Ta)Ag/Rg)/I.
This can be improved by adding a mesh absorber near the back wall of the
sunspace, eg some greenhouse shadecloth, which would allow the sunspace to
fill with 68 F house air, which would the moves sideways through the absorber,
horizontally from south to north, before being sucked back into the house
by a window fan behind the absorber near the top of the sunspace.
This can also work well by natural convection, eg with a 2 story sunspace
and a motorized damper in series with 2 thermostats... And you might put
some bare water heating panels or PVs inside the sunspace, too.
Nick
Nicholson L. Pine System design and consulting
Pine Associates, Ltd. (610) 489-0545
821 Collegeville Road Fax: (610) 489-7057
Collegeville, PA 19426 Email: nick@ece.vill.edu
Computer simulation and modeling. High performance, low cost, solar heating and
cogeneration system design. BSEE, MSEE. Senior Member, IEEE. Registered US
Patent Agent. Solar closet paper: http://leia.ursinus.edu/~physics/solar.html
Web site: http://www.ece.vill.edu/~nick
Subject: Re: [Q] Is burning wood environmentally sound ?
From: barrowsg@rapidnet.com (Gale Barrows)
Date: Tue, 19 Nov 1996 06:13:33 GMT
Alan \"Uncle Al\" Schwartz wrote:
>Brian K Petroski wrote:
>[snip]
>
>>Where in the burning of wood is there any negative
>>impact that is not involed in the buring of coal or oil? Lets get real
>>here! If nothing else the wood is a renewable resource. There is less
>>enviornmental damage with *responsbile* harvesting of wood (not clear
>>cutting) than with mining of coal or drilling and transporting oil (i.e.
>>oil spills).
>Wood is 10% by weight water, and the remaining solids are about 50 wt-%
>oxygen and 5-8% inorganic ash. Anyone who shipped 30% carbon coal would
>be laughed out of the industry (or slaughtered by the EPA). Oil shale
>can have a higher real burnable organic content than wood, and oil shale
>is rock.
>Wood is radioactive, hot with C-14, K-40, and tritium among other things
>(and add radioactive strontium, cesium... and most of the periodic table
>from areas kissed by the Chernoble plume). Coal has been in the ground
>for tens of million of years. All its beta emitters have long since
>decayed away to nothing.
>Coal isn't affected by fungi, bacteria, insect parasites, drought,
>wind... wood is. Have you ever heard of the gypsy moth, the tussock
>moth, the tent moth, the spruce budworm... aphids, grasshoppers...
>mistletoe, Spanish moss, and a whole host of epiphytes... and forest
>fires? Grow a woodshed and let the first "endangered species" show up
>(like maybe the Lesser Tight-Bunged Walking Fly) and you may not cut it
>down.
>Conifers emit copious tonnages of volatile terpenes causing massive local
>and downwind air pollution (the Blue Ridge Mountains make their own
>eye-searing smog). Deciduous trees shed their leaves annually, causing
>massive humic acid contamination of all waterways, watertables, and
>miscellaneous drainage. Have you ever SMELLED a female ginko?
>Environmentalism is that philosophy and dialectic opposed to progress in
>its every form.
>--
>Alan "Uncle Al" Schwartz
>UncleAl0@ix.netcom.com ("zero" before @)
>http://www.ultra.net.au/~wisby/uncleal.htm
> (Toxic URL! Unsafe for children, Democrats, and most mammals)
>"Quis custodiet ipsos custodes?" The Net!
Sounds good, but you still have not given any practical reasons not to
burn wood or to burn it.
Subject: Re: Economists on ecology (Re: GOODBY MIKE!)
From: umdudgeo@cc.umanitoba.ca (Roy C. Dudgeon)
Date: Tue, 19 Nov 1996 03:57:04 -0600
In article ,
antonyg@planet.mh.dpi.qld.gov.au (George Antony Ph 93818) wrote:
> While it is very difficult to predict the change
> in human societies, the only certainty is that they will not stay static.
>
> Hence, restricting the definition of human carrying capacity to biological
> rules and to the socio-economic status quo is fundamentally flawed. In
> case you are not clear on that, this is what you and the unthinking types
> of 'ecologists' are guilty of. It is fortunate that there are ecologists
> who think in terms of the total physical-biological-SOCIAL system.
>
> You are, of course, perfectly right if you can think as far as calling
> social scientists anthropocentric: this is a basic tool of the trade.
>
>
> George Antony
Speaking as a Ph. D. candidate in anthropology, I would suggest that
this is not a basic tool of the trade. There is a long tradition of
ecological anthropology which examines the RELTIONSHIP between humans and
their ecological habitats, but which is anything but anthropocentric. In
fact, many of the writings by ecological anthropologists remind one of the
writings of deep ecologists, ecofeminists, or social ecologists.
Thus, while I agree that it is fortunate that there are social
scientists, and ecologists, who think holistically, in terms of the total
ecological, social, IDEOLOGICAL system--such as us anthros--it seems clear
that economics is not such an undertaking.
------------------------------Regards--------------------------------
Roy C. Dudgeon
---------------------------------------------------------------------
A THING IS RIGHT WHEN IT TENDS TO PRESERVE THE INTEGRITY, STABILITY
AND BEAUTY OF THE BIOTIC COMMUNITY. IT IS WRONG WHEN IT TENDS OTHER-
WISE.
--ALDO LEOPOLD, "THE LAND ETHIC". ---------------------------------------------------------------------
Subject: Venting a dryer indoors
From: nick@ufo.ee.vill.edu (Nick Pine)
Date: 19 Nov 1996 06:56:34 -0500
>>>>Maybe you can vent the dryer inside, or put a clothesline in your new
>>>>sunspace above the porch.
>>>
>>>Actually, I have done that. I have the dryer hose capped off with an old
>>>nylon that I clean out every 3 or 4 loads. The heat and moisture discharge
>>>right into the house.
>>If you make your house a lot tighter, you may want to try to condense
>>the moisture output of the dryer, instead of letting the vapor loose
>>in the house.
>The moisture is already a problem. If I made a plexiglass box with a
>slanted top, attached the hose to the lower side, and had the air discharge
>under the point of entry, would that take most of the moisture out?
> / |
> / |
> / |
> / shallow angle |
> / 15-20 deg. |
> / |
> / |
> / |
> 1 -| |
> --> | |
> -| |
> | |
> 2 -| |
> <-- | |
> -| |
> | 3 |
> |-----------------------------------|
> 1 is Dryer air going in (moisture)
> 2 is exhaust from unit, hopefully dryer than 1
> 3 pool of water dripping off of angled top
>Is this a good idea, or will it not work?
Not a bad idea in principle, but why the slanted top? It looks like a solar
still with no sun :-) Could you use a long and large diameter exhaust hose or
PVC drainpipe ($4 for a 4" diameter 10' length) running around the basement
ceiling instead, with a continuous downslope towards a bucket below the end,
inside the house? The heat transfer area needs to be large enough to reduce
the temperature of the airstream to less than 212 F, so the water vapor will
condense. Water will drip from the end of the pipe when it's working correctly.
A 4.5 kW electric dryer makes about 15K Btu/hr of heat, enough to evaporate
15 pounds (2 gallons) of water per hour or to completely heat a well-insulated
house. Disgusting. Why not use a clothesline, or vent the dryer inside a
sunspace, and let the moisture collect and run down the glazing and onto the
ground? Or try harder to recover that heat for the house in the winter. Is
bombing Iraq to keep the price of heating oil low a simpler solution?
As I recall, Swedish Asko dryers vent inside the house and condense water
vapor from damp clothing into a cup. The clothes start out dryer than most,
after a faster than normal spin cycle in Asko washing machines.
Cooling 4.5 kW dryer air to 212 F in a 68 F room requires a heat conductor with
area A and air film surface resistance R such that (212-68)A/R = 15000 Btu/hr,
ie 144A/R = 15K or A = 104R. If R = 2/3 (still air), A = 70 ft^2, eg 3 55
gallon drums in series. Or 70' of 4" diameter black plastic spiral drainhose.
Moving air past the pipe at 6 mph decreases the surface air film R-value to
about R0.2, so A might be 20' of 4" PVC drainpipe or 6" poly film duct inside
20' of 10" poly film duct (unpunched V4-10 convection tubing at $0.29/linear
foot from D & L Grower Supplies at (800) 732-3509) with a 500 cfm fan at one
end (eg Grainger's $60 560 cfm 36 watt 4C688 fan), perhaps in series with
Grainger's $6.46 2E250 160 F cooling thermostat near the tube output.
Nick
Nicholson L. Pine System design and consulting
Pine Associates, Ltd. (610) 489-0545
821 Collegeville Road Fax: (610) 489-7057
Collegeville, PA 19426 Email: nick@ece.vill.edu
Computer simulation and modeling. High performance, low cost, solar heating and
cogeneration system design. BSEE, MSEE. Senior Member, IEEE. Registered US
Patent Agent. Solar closet paper: http://leia.ursinus.edu/~physics/solar.html
Web site: http://www.ece.vill.edu/~nick
