# Monthly Archives: January 2012

## Nick Pine: A solar yard furnace — a “box on the lawn” approach

Taken from the SolarHeat yahoo group at:

http://tech.groups.yahoo.com/group/SolarHeat/message/27383

=======================

Dynamic U-value Ud = VRhoaCa/(e^(VRhoaCaRs)-1) W/m^2-K, where

V is the air velocity in meters per second,
Rhoa is air density, 1.2 kg/m^3,
Ca is air’s specific heat, 1000 J/(kg-K), and
Rs is the wall’s static thermal resistance in m^2-K/W.

Using V = 1/3600 (1 meter per HOUR :-), and Rs = 5.7 m^2K/W (US R32),
Ud = 0.058 W/m^2, like a US R98 wall. V = 10 meters per hour makes
Ud = 1.7×10^-8 W/m^2K, ie a US R-value of 334 million :-)

This is exciting, no? We often try to make lots of air flow through
an air heater in order to keep temperatures and outdoor heat losses
low, but that uses lots of fan power and requires large air ducts
to move heat to a house. With “dynamic insulation” we might make
very hot air or water without much fan power or outdoor heat loss
and move it to a nearby house through smaller ducts.

My friend T just got her 100 year old house in New Jersey airsealed
and insulated with dense-packed cellulose in the formerly empty 2×4
wall cavities. It has no solar heat now, but it might have about
40′x8′ of solar siding on the southeast and southwest walls.

With 100 F air inside for 6 hours per day, each square foot of R2
twinwall polycarbonate siding with 80% solar transmission would gain
0.8×980-6h(100-35)1ft^2/R2 = 589 Btu on an average 31.5 F December
day with a 35 F daytime temperature.

If the December gas bill says it used 65 therms at an average 40 F
outdoor temp and an 85% furnace efficiency and it used 600 kWh/mo
(68.2K Btu/day) of electricity indoors and 65×10^5/0.85 Btu
= 30d(24h(65-40)G-68.2K), the house conductance G = 539 Btu/h-F,
so it would need 24h(65-31.5)539-68.2K = 365K Btu of heat on
an average December day, which could come from 365K/589 = 620 ft^2
of solar siding on the southeast and southwest walls.

The house needs 1826K Btu for 5 cloudy days in a row, which could
come from 1826K/(140-80)/62 = 488 ft^3 of water cooling from 140
to 80 F in a 9′x18′x3′ tall plywood box on the lawn with a \$195
15′x24′ folded EPDM liner from

one_EPDM_Pond_Liners_15

At 140 F, with R30 insulation, it would lose 24h(140-31.5)486ft^2/R30
= 42K Btu on an average day. A 12′x20′ twinwall roof with a 34 degree
slope would gain 12′x20′(0.8(980sin34+610cos34)-6h(140-35)/R2))
= 126K Btu/day. If the tank is 4′ tall, the box would be 11′ tall.

The box could provide about 126K-42K = 84K Btu of house heat
on an average December day at a rate of about 84K/6h = 14K Btu/h
in 14K/(140-70) = 200 cfm of 140 F air. A 20′ duct (40′ round trip)
with a 0.2 “H20 pressure drop with 0.2 = 0.1×40′/100′x200^2/D^5
would have a D = 6″ diameter. It might be an underground foamboard
box with 2 6″x6″ cavities.

(A more remote box might have hot and cool (80 F house return) tanks
and 2 car radiators, with one cooling 140 F air that exits the other
in order to provide cooler air near the twinwall and a near-infinite
mesh collector thermal resistance. This sounds complex for a heating
system, but it’s child’s play compared to what Google is up to, eg
video hangouts with tracking reindeer noses and antlers.)

With only 320 ft^2 of solar siding on the southwest wall, the box
would need to collect 42K+365K-320ft^2×589 = 219K Btu/day. It might
do that with a 16′x20′ twinwall roof and a 17′ box height.

Nick

Filed under erik-green, solar

## Every schoolday can be like a fieldtrip day to Valve

What if every day was like this?

“It was the most amazing field-trip. I pity whoever has to take them on the next field-trip because it’s not even going to compare to what they experienced today at Valve.”

Well, it could be, if kids were allowed to do/learn what they want with their time (their time!) like they are at Sudbury Valley School. (So… it is for our 7-year-old son. Lucky kid! Lucky parents! Lucky family!)

## In the news…

“As for keeping up with the news I wonder what passes for “news.” Who played Mozart that day or composed a new symphony? Who wrote a beautiful poem? Who fell in love with their child that day? Who suffered of loss and pain? Who was born? Who died? Which bird finished its tour of the sky? Which penguin made it alive through the ice? How many people died of hunger? Who is suffering? Who is enslaved or abused? What games of joy and connection people played that day? Who had a new wise thought or a peaceful scientific discovery?… Most of what is happening in the world is not broadcasted.” — Naomi Aldort

- Raising Our Children, Raising Ourselves, Naomi Aldort

## An energy use analogy — car vs lights

If you have 20 65W can lights/downlights in your house on 8 hours a day, then per year that is: 20*65*8*365/1000 = 3796 KWh

Recall that 1 gallon of gas is 36.6 KWh

And if we recall that it takes approximately 3 times more fossil fuel to deliver 1 unit of energy at your house (power plants are inefficient), then the cans actually use 11388 KWh of “primary”/”source” energy.

That’s the same as using 311.15 gallons of gas. Visual 300 gallons of a gas for a second. Yikes!!!

Might be a good idea to switch to these LED versions (\$25 at home depot–1 year cost payoff) using 10.5W instead of 65W. They would gulp the energy 6 times slower! And no mercury and instant on. (Our CFL can lights take a moment to warm up…)

2 favorable reviews here:
- one
- two

- Visualize Energy

Filed under erik-green

## Stressed out in School — 1987/1988 style

STUDENTS BLAME STRESS PROBLEMS ON COMPETITION
Boston Globe, Nov 19, 1987

ACTON – Forty-nine students at Acton-Boxborough’s junior and senior high schools have been hospitalized in the last three years for the same ailment — stress and stress-related conditions.

Dr. John Kulig, director of adolescent medicine at New England Medical Center, said teen-agers under a great deal of stress tend to get depressed or develop headaches, chest pains and abdominal pains.

Studies indicate that 20 percent of high school seniors exhibit signs of mental illness attributable to stress. An equal number of college students show stress-related symptoms, according to Dr. Paris C. Faigel, director of health services at Brandeis University.

Author: Associated Press
Date: Nov 19, 1987
Start Page: 41
Section: METRO
Text Word Count: 345

==================================

STUDENTS AT SUBURBAN SCHOOL PLAGUED BY STRESS BLAME SEVERAL FACTORS
JOHN KING , Associated Press
Nov. 18, 1987 6:26 PM ET
ACTON, MASS. ACTON, Mass. (AP) _ Forty-nine students at Acton-Boxborough’s junior and senior high schools have been hospitalized in the last three years for the same ailment – stress and stress-related conditions.
Students blame intense academic competition at the schools in the affluent Boston suburb, while administrators point to a failure to teach adolescents how to cope. Experts on stress and adolescence say the problem is not unusual, but that it is not common to hospitalize such students.
A dozen high school students interviewed Tuesday said they felt pressure from parents to perform well in school. They also cited a highly competitive atmosphere that leads to peer stress and demanding teachers.
”I feel it,” said Ed Dischino, a junior. ”You can’t see it because nobody talks about it in terms of stress or pressure. But it’s here.”
High school Principal Lawrence McNulty did not want to talk about stress Wednesday, saying, ”We’re not interested in making mountains out of molehills.”
But Andy Palmer, the school’s counseling director, is keeping a list of students who have been hospitalized.
”We’re in an affluent community. There are higher expectations here,” Palmer said Wednesday. ”I don’t think the answer is to lessen the demands but to teach coping skills to help the kids deal with it.”
Most students admitted to hospitals were suffering from depression or had made suicidal gestures, about one-third had alcohol and drug problems linked to stress, said Palmer. A few were admitted because of stress syndromes attributed to family problems, he said. The students were hospitalized at the recommendation of family doctors or by an area agency that provides counseling or other services, Palmer said.
Palmer is visiting other schools to see how they deal with stress. He also is asking the school committee to adopt a crisis intervention policy. The school system is a few months into a six-month study during which students, parents, teachers and therapists are being interviewed.
Dr. John Kulig, director of adolescent medicine at New England Medical Center, said teen-agers under a great deal of stress tend to get depressed or develop headaches, chest pains and abdominal pains, as opposed to the ulcers and high blood pressure associated with adult stress.
He and Dr. Paris C. Faigel, director of health services at Brandeis University, said it was highly unusual for students to be hospitalized for stress and related ailments.
”I’m not sure in the past we would have identified these kids as suffering from a stress syndrome. Maybe it’s a good sign,” Faigel said. ”Mabye it means we’re finally paying attention to the young folks and the stresses of their lives.”
Studies indicate that 20 percent of high school seniors exhibit signs of mental illness attributable to stress, Faigel said. An equal number of college students show stress-related symptoms, he said.
”I just think we’ve forgotten to teach the coping skills,” Faigel said. ”Those skills begin at home and kids nowadays are reaching adolescence about the time mom and dad are caught up in their own mid-life crisis and are distracted by it and unable to help their kids.”
In the past, Acton-Boxborough, which has 1,400 students in the high school and 700 in junior high school, was overshadowed by its suburban neighbors. But in recent years it has won several academic and athletic honors.
”About 95 percent of the kids who graduate from here go to college,” said junior David Hickey. ”There’s a lot of the snob appeal, kids saying ‘I’m going to Harvard.’
”All the parents are really stressing the need to go to a good college. So the parents put a lot of pressure on their kids, or the kids put a lot of pressure on themselves because they don’t want to upset their parents.”
Freshman Cheri Mehigan is new to the school. But she’s learning fast.
”I can’t use the phone after 7:30,” she said. ”All of my brothers are wicked brains and are in college and I got one C-plus.”

## 24F and 900W

Today (1/3/2012) was an average of 24F from midnight to midnight (eyeball estimate at the historical data charts at wunderground.com and weatherspark.com)** And the eMonitor is saying we used ~22KWh to run the air-source mini-split heat pumps for heating (and also a little help with hot water heating). So that’s approximately 900W average continuous. 24F is pretty close to typical for a Dec day in MA… And if you pay 20 cents/KWh for your “GreenUp” electricity that one can get from National Grid or NStar in MA… Then that’s 0.900KWh * 30 * 24 * \$0.20/KWh = \$129.60 for heat for the month. That’s the pocketbook.

Now what about from the house’s perspective?
Assuming a COP of maybe 2.5 on the heat pumps during this time, and assuming the weather is not too bad (we had some decent sun today — 27KWh from the PVs — and not too windy) then that’s 2.5*900W = 2250W. That’s a load of a hair dryer and a third to keep the house at 68F on a winter’s day. Glad to be using a heat pump instead. A hair dryer would get a little expensive, though probably still less than many are paying to heat their New England home.

Gotta like lots of insulation and carefully taped external sheathing.

** Note on weather: I do still have my networked “weatherdirect” thermometers tracking temps, but I haven’t set up any logging yet. I really should do that so I can do some useful graphs instead of all this hand-waving with estimates.