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David Allan's Solar Home


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Edna and David Allan, July 2014

(1) Trombe Wall (2) Solarium (3) Photovoltaic (4) Hot Water Panels (5) Eutectic Salt Chamber (6) Berm Insulation (7) Passive Solar Air Conditioner (8) Geodesic Dome

See also | Dave's New Rental Home | Related Sites

David and Edna Allan's Solar Home
Dave with pet lab, Winnie, around 1994

 

Solar Home Tour Video

A Tour of David W. Allan's Solar Home that Uses 10 Solar Principles - Located in the cooler central Utah climate at 6,000 foot elevation, the Allan's solar home integrates at least ten different forms of solar, including: trombe wall, solarium convection, photovoltaic cells, propylene-glycol heat exchange, eutectic salt chamber, berm insulation, black chimneys and under-ground intake for passive solar air conditioning, and dehydration of food. (PESN; June 24, 2012)

Solar Home Design and Explanation

The home is basically designed to be warm in the winter and cool in the summer. There is plenty of solar energy.  The problem is how to store it and optimally use it for self sufficiency. 

Nature gives us three methods of heating: convective, conductive and radiant; radiant is by far the most pleasant and desirable. Using these three methods, the home is designed so that each room is almost a zone to itself. The numbers before each point correspond to the illustration above.

Plot: Energy of the sun as a function of frequency of the electromagnetic waves1. Trombe Wall
    The plot to the right characterizes the energy from the sun as a function of the frequency of the electromagnetic waves. The direct sun provides about 1 1/2 kilowatts of power per square meter. The southern high living-room windows are positioned to let in the winter sun. The glass lets in the optical band of frequencies, which are readily absorbed by the dark brick on the south facing side of the trombe wall. The wall -- being at room temperature -- radiates in the infrared region of the frequency spectrum -- keeping the home warm at night, since it radiates from the center of the home. This infrared heat is like the warm glow from a bed of coals in a camp fire. Since the infrared frequencies are reflected by the glass, they are trapped in the house -- being absorbed readily by the human body. figure: tilt of the sun serves as a switch The roof extends out to the south above these special windows providing complete shading in the summer, and so that the sun rays start heating the trombe wall about the first of October and turn off about the end of March.

[click here for more information on Trombe Walls]

2. Solarium
    Partially cantilevered out to the south of the living room is a solarium. In the winter this room will often exceed 90o F. Since hot air rises, this room creates an upward pressure. Since cold air drops, the air on the north side of the house creates a downward pressure. The five convection tubes connecting the solarium with the north side of the house allow the hot air to flow providing warm air on the north side of the trombe wall (kitchen, dinning area, etc.) There are return air ducts in the floor joist as well as through the door ways when they are opened. In principle, one could grow vegetables in the winter months in the solarium -- letting it act as a greenhouse.

3. Photo-Voltaic
    The two arrays of photo-voltaic cells can supply 24 volts at 50 amperes (more than 1 kilowatt of power). This energy is stored in batteries. The refrigerator and fans run off of DC power. Inverters supply other emergency parts of the house: the water pumps, deep freeze, kitchen power, and the office and shop.

4. Hot Water Panels
    The hot-water supply system consists of six 4'X 8' collecting panels set at an optimum angle (60o) for this latitude (about 40o N). This system is powered by the photo-voltaics. It has temperature sensors and three pumps. The first pump carries propylene-glycol through the panels when they get sufficiently hot to carry the solar energy to a heat exchanger. A second pump circulates culinary water through the heat exchanger back into three storage tanks -- two large ones (250 gallons) and one 50 gallon standard water heater. The latter has propane backup capability, but almost never turns on. This system supplies all of our culinary hot water needs and provides, via the third pump, convective-radiant heat for the three bathrooms and the NW (Sterling's room) downstairs bedroom.

5. Eutectic Salt Chamber
    Potentially the most efficient heating system of the six is the eutectic salt chamber. The salt being used is sodium sulfate deca-hydrate (NaSO4 H2O -- Glauber's salt). Figure: Energy vs. Temperature relationship for Glauber's Salt At the right is a curve representing the energy stored as a function of temperature of a substance as it transitions from solid to liquid (phase-change). For example, it takes 80 calories to melt one gram of ice. In reverse, one gram (1 cc) of water gives off 80 calories as it turns to ice; this is called the heat of fusion. This heat of fusion principle is often used to save orchard blossoms from freezing if the temperature drops below freezing in the Spring by sprinkling them with water. As the water freezes, it gives off this heat of fusion and saves the blossoms. Thermal storage using water is not nearly so efficient, as water only stores one calory per gram per degree centigrade. Glauber's salt has the nice property that it melts at 90o F and has about 83 calories per gram. It does not take a lot of salt to heat several rooms. The salt in the chamber is stored in black tubes to pull in the day-time sun so that the salt melts. At night as the salt freezes at 90o F, the air is heated around the tubes like a radiator, which then rises, and like the solarium forces air through the floor joist -- dropping down in the cooler rooms needing heat with return air going through ducting under the floors.

More about Eutectic Salt Chamber

6. Berm Insulation
    The principle of a berm home (underground) is that if one goes about 2 meters deep (6 feet), the underground temperature is pretty much constant day and night and over the course of the year. In this area, it is about 54o F. One can imaging an insulated dome with the outside footings insulated down about 2 m. The temperature in this dome would remain 54o without doing anything else. Our home has three layers of insulation (R-factor of 37), and the concrete foundation is insulated on the outside down sufficiently deep in order to capture this ponderous heat source from the earth. All that is necessary is to add about 14 additional degrees of heating to make our home comfortable. The fireplace is more for ambience than for necessity.

7. Passive Solar Air Conditioner
    The passive solar air conditioner works on the following principle. Two black chimneys have been placed on either end of the solarium. On the East, South and West surface of these chimneys are glass panels with black tin sheets a couple of inches inside the glass surface. The black-tin gets hot in the summer sun, and with the door at the base of the chimney being opened during the summer the hot air created by the hot tin rises creating an upward flow -- venting out the louvers at the top of each chimney. The air is replace by cool air coming from the downstairs and in particular from a 50 foot underground tube which pulls air from an evaporatively cooled shaded area to the north-west of the house. The solarium vent tubes operate in reverse -- allowing the hot air from the house to flow through the black chimneys.

8. Geodesic Dome
    In ~2006, the Allans built a geodesic-dome green house www.growingspaces.com that has produced tomatoes and greens year around.  The design includes a large tank of water as a thermal mass to keep the temperatures above freezing through the night.  Dave uses a solar panel to power a small fan for circulation.  The venting panel on the top is also solar controlled.

Dave's Rental Home

This home is located just down the street from the above home, and was constructed in 2000.


Numbering code same as above

See also:

Trombe Wall - Essentials, Advantages, Related Sites
Eutectic Salt Chamber
David W. Allan Biography

Related Sites:

Solar Directory - Compilation of solar technologies and resources.
Showcase Energy Self-Sufficient Homes
Mr. Solar Home Page - Mr. Solar Home Page, information, products and services about every aspect of solar, wind & water power
Northwest Power CO -- Solar and Wind - photovoltaic and wind generation products and services.
Solardyne Corporation - direct source for renewable energy equipment and high-efficiency home appliances
Home Power Magazine - The hands-on journal of home-made power. We do it with solar, wind, and hydro.
Extensive solar links page
Home Power Magazine
Jade Mountain - "The world's largest selection of renewable energy products."
GO Solar Company
Provides information and consumer guides relating to solar energy and its various applications. Online solar catalog.
Maine Solar House
The step by step building of a solar house. Solar land, solar plan, solar heat, solar power, solar data.  Featured in TIME magazine.
Solar Ovens
Environment and energy conservation and emergency preparedness. Durable, reaches 400
Solar Oven
The American Solar Energy Society
ASES is a national organization dedicated to advancing the use of solar energy for the benefit of US citizens and the global environment.
JC-SolarHomes.com
Passive Solar Home Design
AccessSolar.biz - Recommended Solar Home Builder in Central Utah (Mt. Pleasant): Randy Tolbert: design consulting, contractor, critical component installation: (435) 462-3817. Tell him we sent you.

Page posted January 16, 2000 by Sterling D. Allan
Last updated August 23, 2014
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