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Heating-system designers think in terms of heat transfer from warmer to cooler. The typical home furnace warms air to 140 degrees, and the warm air is delivered to the various rooms in the home via ducts. When the thermostat reads 72 degrees or another desired setting, the furnace shuts off. Heat has been transferred from the warmer body (the furnace at 140 degrees) to the cooler body (the house at 72 degrees).The design of a conventional heating system represents a straight forward problem that has a direct solution: determine the heat loss of the building, then size the furnace and ductwork in order to provide a continual or “on-demand” supply of replacement heat. Active systems are easy to visualize—boilers, ductwork, pipes, and radiators—whereas the elements of a passive heat collection and storage system may be almost “invisible.” When faced with the problem of designing a solar home, early solar designers tried to assimilate the elements of an active, furnace—based system. Exterior solar collectors were utilized to build up high temperatures using water or air. This heat was then stored in a high temperature “heat sink” using beds of rocks or tanks of water (“heat sink” is a physics term for a medium that absorbs and stores heat—for example, water, concrete, or masonry, in particular arrays). Ducts or pipes transported the heat back and forth from the sun-exposed exterior collector components to the interior storage components of the system. Such active systems are complicated; they tend to require added-on costs to the home, and are some times difficult to justify financially. Further, some of them simply didn’t work very well or were plagued with mechanical problems, especially over time, necessitating continuous oversight and maintenance. IT’S HARD TO GET A DRINK IN A DRIZZLE “Solar gain” is the free heat derived from the sun. Sunlight is ubiquitous, but diffuse. Systems that involve rock beds and solar hot-water storage tanks attempt to concentrate a diffuse form of energy. It is both difficult and expensive to concentrate, build, and hold high temperatures in solar heating systems. Solar energy can be compared to a drizzle: there are tons of water in the air but it’s very difficult to get a cupful to drink. Almost all attempts to build active solar homes are based on trying to build up heat in some sort of storage reservoir that will have a temperature substantially higher than room temperature. Since the Trombe wall, for instance, needs to build up a temperature greater than normal room temperature in order to transfer heat to the adjacent living space, the home can become overheated during the day. If, as described in section 2, the Trombe wall reverses its air flow at night, the home may be subjected to uncomfortable cold flows of air. If we remember that our naturally heated home needs to stay comfortable all day and all night, twelve months a year, these wide variations in temperature should be avoided. In this section we are going to examine a solar heating system that stores heat in the floor at a temperature no greater than comfortable room temperature, and a system that uses windows and patio doors as solar collectors. The solar system technique described in this book is a departure from conventional heating design. As mentioned in section 1, most heating systems are designed by specialists working independently from those producing the general house design. This practice usually results in a worst—case design, with oversized furnaces and ductwork. Over sized equipment will necessitate higher construction costs and will also cause higher operating costs, as oversized equipment inefficiently cycles on and off. Passive or natural systems represent transient engineering problems; many elements of the calculations necessary to design these systems occur simultaneously, making the processes they involve difficult to analyze. Most heating designers don’t like this kind of “fuzzy” problem, and often they are not given all the site information necessary to design on anything more subtle than a worst—case or generic basis. It is a straightforward calculation to size a furnace on a worst—case basis and to provide a system of ducts to carry heat from a 140-degree furnace to areas of 72 degrees. However, to calculate exactly what is going on when heat is entering the home from the sun is much more complicated: some heat is being used directly to heat the home; some is being stored; and some is being lost back to the outside. Moreover, each one of these events influences each of the others. From the perspective of the conventional heating and cooling technician, this is a “fuzzy” or transient problem. We will simplify this transient problem by looking at temperature averages for the day, month, and year. In fairness to the conventional system designer, it’s important to ac knowledge that their job is to guarantee adequate heat and coolness with a wide margin to cover seasonal variation. Experimentation can some times lead to “call backs” or other expensive liabilities if a system doesn’t work to the homeowner’s satisfaction. A system designed on a worst-case basis may cost more to buy and operate, but it also doesn’t represent a potential liability to the designer as it will always be more than capable of doing the job. The same principle is invoked by highway builders who construct a four—lane expressway because once a year, on the Fourth of July, all four lanes will be utilized by the traffic. ROOM TEMPERATURE STORAGE Engineers and designers schooled in heating and ventilating have found the idea of creating heat storage at or below room temperature to be strange. Early on in the development of the system described by this book, some of the typical responses were: “Can’t be done”; “Remember Newton’s Laws of Heat Transfer—heat only goes from hot to cold”; ”Low temperature room storage will take heat from the living space. You’ll create the equivalent of an ice cube in the drink.” (That is, the drink remains at 32 degrees Fahrenheit until the last ice cube melts; in this case the “drink” is the living space and the “ice cube” is the heat storage in the floor. The skeptics are concerned that the floor won’t let the house come up to temperature.) Or, “The heat sink will act detrimentally to the comfort of the living space.” KEEP THE FURNACE OFF We will use daily averages to help analyze this transient heat problem. Let’s start by thinking in terms of how we can keep the furnace off. If the furnace doesn’t have to run at all, and instead heat is being supplied naturally and free to the house from the sun, isn’t that the name of the game? The Trombe wall described in section 2 is elegant in its simplicity but aesthetically crude. Pictures of a blackened concrete wall along the south side of a home certainly would not survive among glossy photo spreads in Better Homes and Gardens. In addition it blocks out a good portion of the cheery southerly sun. From a technical standpoint, the movement of warm air over the surface of a smooth vertical wall will cause laminar flow; that is, a thin boundary layer of air will build up and the warm air passing over this boundary layer will not readily give up its heat to the concrete. An airplane wing is an example of a surface that produces laminar flow. There is very little heat being transferred to the wing as it slips smoothly through the air. On the other hand, a rough surface interrupts the flow of air causing turbulence, which in turn causes greater heat transfer. Picture the fins in a baseboard radiator versus a smooth pipe along the baseboard. The fins provide much more surface area per running foot than smooth pipe would provide. This increase in surface area allows the heated water inside the pipe to give up or transfer its heat to the air. This concept will be crucial when we discuss the construction of the Solar Slab. Remember the goal described in section 2 of utilizing materials you are already committed to purchase for your new home, and rear ranging them in a different configuration in order to collect and store heat. Consider what we would need to buy for a full basement. The cellar floor will require a 4-inch concrete slab and we will need a poured or concrete block cellar wall. That gives us tons of material with which to work. Let’s see how we can rearrange these materials. Start by moving the 4-inch concrete slab from the cellar floor to the first floor, eliminating the basement. This is the equivalent of placing the concrete Trombe wall horizontally flat. Next, let’s take some of the concrete blocks that we would have used to build the cellar wall, and place them under the concrete slab. Instead of arranging them with their holes vertical, let’s lay them on their sides with the holes lining up horizontally to form air passages running north to south. When the concrete is poured over these blocks, it will bond to the blocks and make a huge concrete “radiator”—the radiator’s “fins” are the ribs in the concrete blocks (see the illustrations). 28 Thermal mass is comprised of building materials that absorb heat effectively, charging up like a thermal battery and then yielding this heat back into the home living space through periods of time when the building is not actively gaining heat from the sun or from some other source. 29a The Solar Slab utilizes completely conventional materials, including concrete blocks and poured concrete. Construction of this foundation is neither difficult nor costly, yet the result will be a house with exceptionally effective thermal mass as its base. 29b The Solar Slab concrete heat exchanger: a section drawing. If this combination of poured concrete slab over horizontally laid blocks is ventilated by air holes along the north and south walls, air will naturally circulate through this concrete radiator when the sun is out. Remember, we oriented our new home with the long axis of the building running east to west. When the sun is out in winter, the south wall will be warmer than the north wall. As heat is transferred into the home by the south glass or by heat transfer through the wall, air that is next to or alongside the south wall will rise. Warmed air will then be pulled out of the ventilated slab, and the cooler air along the north wall will drop into the holes along the north wall. This thermosiphoning effect will naturally continue to pull air through the Solar Slab. 30 The Solar Slab: a sill detail. For the Solar Slab to effectively heat the home, it must be thermally accessible to the living space. It is therefore not cost—effective or thermally practical to utilize the lower level for a basement-storage area instead of as a living space. STORAGE OF TRAPPED SOLAR HEAT As heat from the sun “drives” the thermosiphoning, heat in the home, which has been trapped as in a greenhouse, will be taken up via the ribs as warm air passes through the concrete blocks, which in turn are thermally bonded to the concrete slab. Heat from the sun comes to us as light or short wave energy. Since glass is transparent to light, sun light passes through glass and strikes objects within the interior of the home. As soon as it strikes an object, for instance the floor covering above the slab, light changes form—to long-wave energy or heat. In a highly insulated solar home, this heat will now be trapped. The temperature of the ventilated slab will rise as the trapped heat is absorbed by the concrete. Since concrete has almost no R—value it has little resistance or ability to stop the transfer of heat. Any heat transferred to the ventilated slab anywhere in the building will migrate evenly throughout the array of concrete blocks and poured slab. We will explore this benefit further when we discuss the use of a wood-burning stove as backup heat. The heat storage benefit is free, provided you are willing to trade a full basement for a Solar Slab. The solar home, properly designed, can achieve thermal balance every day. The energy produced by the east-, south-, and west-facing glass will be either consumed directly by the heat demand of the home, or absorbed by the first floor heat sink as the heat comes into the home. If the heat comes in too fast to be absorbed by the mass, the home overheats. Overheating can be a major problem in passive solar design, and in any respects, passive solar design presents a significant cooling challenge. THE OLD NEW ENGLANDERS’ SALTBOX One of the designs my company offered, the Green Mountain Homes’ 28-foot by 38-foot Saltbox, will be used to explain the way the Solar Slab relates to the functionality of a solar home. For illustrative purposes, we will situate this solar home in Hartford, Connecticut, north latitude 41 degrees 5 minutes (41°5’).The floor-plans and a cross section for the Saltbox 38 are shown in section 5. Many of the plans and calculations in this book use a basic house design known as a saltbox. While designers and builders of solar homes can adopt a wide variety of house styles and construction techniques, the saltbox is useful as a model, since its design has a classic simplicity. The solar home shown here was built in 1978 in Virginia. Note use of deciduous trees for summer shading. We will present detailed solar calculations in section 6, but in order to help explain how the system works we need briefly to examine the Solar Slab, which as you recall is comprised of a 4-inch concrete slab bonded to 12-inch concrete blocks. We can calculate that a standard concrete block is about 50 percent concrete, or the equivalent of 6 inches of solid concrete. Therefore, the 4—inch slab and 12-inch concrete block are the equivalent of 6 inches + 4 inches = 10 inches of solid concrete. Discounting air passages along the north and south walls and the amount of concrete blocks displaced by ductwork, for a 28 by 38 foundation the volume of concrete equals 754 cubic feet. Assume that the Solar Slab temperature is 60 degrees at 7:00 AM and the daytime rise in Solar Slab temperature is 8 degrees. The Solar Slab temperature at 5:00 PM is then 68 degrees Fahrenheit. Picture what this means: The entire first floor of the living space is now up to 68 degrees; that’s 754 cubic feet of concrete at 140 pounds per cubic foot, which is 105,560 pounds or 52 tons inside the house, covered with the floor covering of your choice, sitting there at almost 68 degrees. Surely you have experienced sitting on a sun-warmed rock after sundown. It’s nice and warm, and takes a long time to cool off. Re member, the design goal is keeping the furnace off, or requiring it to do very little work. The heat stored in the first floor of the living space, and dispersed evenly throughout the first floor, has to be beneficial to the heating and comfort of the home. In section 6, the thermal balance calculation will show how extra heat provided by the sun is trapped by the greenhouse effect (the con version of light energy to heat energy), stored, then released as needed from the Solar Slab. Because the Solar Slab is an effective heat exchanger, with its fins of concrete, the sun’s heat is stored in the Solar Slab at the time it enters the house and strikes the floor covering over the slab. The surface area inside the blocks calculates to be 366 square inches while the top surface is 119 square inches (7 inches x 15 inches). The ratio of square feet of surface area within the blocks below the floor surface to square feet of floor is 366 ÷ 119 = 3.This means that air passing through the blocks is exposed to three times more surface area than if the air had simply passed over a flat surface, This ratio plus the roughness ‘of the surface inside the blocks make the Solar Slab an effective heat exchanger. KEEP THE HOME COMFORTABLE ALL DAY In a building in which the solar design components have been properly sized and located, while the windows and patio doors are collecting solar energy, the temperature of the home will hold steady at between 68 and 70 degrees, and will not overheat. If the glass area is too large for the heat storage capacity of the mass, the house temperature will rise to uncomfortable levels, and the occupants will be forced to open windows to ventilate, thereby losing the benefits of both immediate comfort and storage of the sun’s free heat for use later in the evening. Greenhouses are examples of spaces that overheat during the day and get very cold at night. On the other hand, too much thermal mass and not enough glass to collect heat will result in a chilly, cave— like space that will never come up to the comfortable temperature. The home must have a proper balance between the square footage of its glass solar collectors and the dimensions of its effective thermal storage mass. A prevalent mistake in solar design is using too much glass. The thought pattern seems to be that if some south glazing is good, a lot more is better. As we discussed above, over-glazing will cause overheating and detrimental negative temperature swings at night. In fact, in some cases, the cost to heat the over-glazed home at night will exceed the benefit derived on sunny days. This consideration is especially important in the northeast, where we have about 50 percent sunshine in the winter and long cold winter nights. The good news in the northeast is that our heat season is so long and severe that almost any measure we take to utilize the sun’s free heat can result in significant cost and energy savings. SUNNY DAY IN WINTER MULTILAYERED THERMAL BREAK’ WALL CONSTRUCTION FOR TIGHTNESS and HIGH R-VALUE. EXTERIOR OF WALL THERMALLY ISOLATED FROM INTERIOR. 1. EXTERIOR SIDING 2. STYROFOAM OR FORM R RIGID INSULATION 3. 1/2” PLYWOOD 4. FIBERGLASS BATT INSULATION and STUDS 5. VAPOR BARRIER 6. INTERIOR FINISH 34 How does the Solar Slab work? Here is a sequence of illustrations showing its operation in three modes. First, a sunny day in winter. Heat from the sun and when necessary a small backup woodstove is stored in the thermal mass of the radiant floor as sun-warmed air is drawn by vents through channels made by aligned concrete blocks beneath the poured slab and the home’s finish flooring. HEAT IS REMOVED FROM SECOND FLOOR CEILING and DELIVERED TO FIRST FLOOR BY SMALL FAN THROUGH A DUCT CONTAINED WITHIN AN INTERIOR PARTITION COMMON TO BOTH FLOORS. LOW ANGLE OF WINTER SUN PENETRATES BUILDING UP TOR-32 OR R-40 CEILING CENTRAL WOOD OR COAL STOVE PROVIDES ALL NECESSARYDAY. HEAT IS STORED IN RADIANT FIRST FLOOR BY AIR, WHICH HAS BEEN WARMED BY THE SUN and PASSES THROUGH THE SOLAR SLAB CONCRETE HEAT EXCHANGER and THERMAL MASS. EAST, SOUTH, and WEST WINDOWS and PATIO DOORS ACT AS SOLAR COLLECTORS. STORED SOLAR HEAT RADIATES UPWARD INTO THE HOUSE. THE HEAT LOSS THROUGH ROOF and WALLS IS LOW IF HIGH R-VALUE MATERIALS ARE USED and CONSTRUCTION IS TIGHT. THERMO-SHUTTERS ON MAJOR GLASS AREAS ARE CLOSED AT NIGHT TO KEEP HEAT IN (R-VALUE OF INSULATED GLASS IS INCREASED SEVENFOLD). 35 On a cold winter night, solar heat stored in the home’s slab during the day radiates upwards into the living space. The temperature of the entire floor will not vary more than 1 degree. A small wood or coal stove will normally provide adequate supplemental heat, and a small conventional furnace will double as an air mover for the solar heat exchanger, as well as providing backup heat (see section 7). Nighttime window insulation prevents the loss of heat through the largest of the windows and patio doors. TEMPERATURE OF ENTIRE FLOOR WILL NOT VARY MORE THAN 10. SUMMER COOLING HIGH R-VALUES IN THE WALLS and SECOND FLOOR CEILING HELP KEEP HEAT OUT. NIGHTTIME COOL AIR DROPS INTO VENTS ON FIRST FLOOR, and THE SOLAR SLAB STORES NIGHT’S COOLNESS. IF A HEAT PUMP OR AIR CONDITIONER IS USED IN HOTTER CLIMATES, RETURN AIR IS PRE-COOLED AS IT PASSES THROUGH THE SOLAR SLAB. THE SIZE and DISTRIBUTION OF WINDOWS HAS BEEN STRATEGICALLY DESIGNED TO MAINTAIN BALANCE BETWEEN SOLAR INSOLATION and THE STORAGE CAPACITY OF THE HOME’S THERMAL MASS. 36 During a sunny summer day, because of proper siting, glazing, and sizing of thermal mass, the Solar Slab will aid in cooling the house, as excess solar heat is absorbed during the warm hours of the day. Before the home can overheat, the day has ended (this is called “thermal lag”). The same attic fan used in winter to redirect heat from the second floor ceiling can be used in summer to vent warm air out through the attic vents. In air conditioning areas, air-to-air heat pumps can also be used in tandem with the Solar Slab. WARM AIR DRAWN OUT OF SECOND FLOOR BY A SMALL FAN IS EXPELLED FROM ATTIC THROUGH APPROPRIATELY SIZED VENT. A VENTED ATTIC SPACE BUFFERS THE HOME FROM OVERHEAD SUN and HELPS KEEP THE HOME COOL. THERMO-SHUTTERS CAN BE CLOSED PARTIALLY OR COMPLETELY ON MAJOR GLASS AREAS TO LOCK SUN. Let’s return to the objective of keeping the furnace off. The furnace was off all day as the solar home collected and stored heat. During the evening, the occupants will need very little supplemental heat to maintain 68 to 72 degrees until 10:00 PM (bedtime),because the entire first floor of the house was 68 degrees at 5:00 PM. Basically, the backup heat is only heating the difference between the Solar Slab temperature and the desired room temperature. feels comfortable, then no backup heat is needed at all. As the Solar Slab gives up its heat to the first floor living space, the Solar Slab temperature will start to decline. The first floor room temperature at 7:00 AM will be the same as the Solar Slab temperature. Stored heat has been given up to the house through the night, and the Solar Slab is now ready to absorb the next day’s free solar heat. This solar home will stay ready to instantaneously accept any solar heat available. If the sun comes out for just a few minutes between clouds, that heat will be collected, as there are no sensors that have to react to turn pumps on. In addition, this solar home will absorb excess heat from cooking, lights, and yes, even the heat given off by human bodies. A particularly nice way to heat a solar home is to throw a party and invite lots of people over on a cold winter day! Remember, heat travels from warm bodies to cold bodies. We are each a small furnace, running at 98.6 degrees. THE THERMAL FLYWHEEL Do you remember the old John Deere tractors that had an external heavy-metal flywheel? The tractor’s small engine slowly got the huge flywheel spinning. Once up to speed, very little energy was needed to keep the tractor moving. That is called mechanical inertia. A body in motion doesn’t want to stop. Likewise, the Solar Slab provides thermal inertia to the home so that the home “wants” or tends to stay at a steady temperature, using very little purchased fuel in the process. With this kind of thermal inertia built into the solar home, we can downsize the backup heater, and instead size equipment for less than worst—case conditions. Why haven’t other people used this building technique? The answer most likely lies in the difficulty of trying to calculate the effect of a “room temperature heat sink.” Some would say that this approach seems to violate conventional heating theories. My approach to the problem of heating a home with the sun was to make my best engineering calculations, and then build and monitor a prototype. This represented both a professional and financial risk on my part, but it was well worth it. I was sure that my approach would work, but what I didn’t know was how well. By measuring all energy entering the test building, and keeping careful records of the Solar Slab temperatures, we were able to verify the effectiveness of the design. A PATENTED DESIGN As I started to make heat loss and solar heat gain calculations in 1975, I became more and more convinced that I was on to something unusual, and decided to protect my invention by applying for a U.S. Patent. In order to receive a patent one must prove that the idea or design is original. One of the unique aspects of the Solar Slab design is that the maximum achievable temperature is room temperature. Conventional thinking says that room temperature storage will be at best neutral, or at worst, will result in a drain of heat from the room. Remember the key concept of temperature difference (in engineer’s jargon, “Delta T”), and the laws of heat transfer—heat will only flow from hot to cold. The Monitoring Effort As explained in section 1, Professor A.O. Converse, of the Thayer School of Engineering at Dartmouth College led a team that independently monitored our prototype, and he and I co-authored several papers which were presented at various solar conferences. His work culminated with the “Final Report Monitoring Studies of Green Mountain Home’s Hybrid Systems,” December 8, 1978. Page 7 of this report states in part, “We certainly conclude that the purchased energy requirements were quite low and the percent solar is well above 40 percent.” New Mexico’s Sandia Laboratories published their report on Green Mountain Homes in July, 1979 (its reference number is SAND 79 - 0824). The monitoring effort with the Thayer School was centered around a Green Mountain Homes Model N-38 in Royalton, Vermont (see the floor plan). Professor Converse and I had a unique opportunity to install instruments in the superstructure of the N-38 during construction. We also placed measuring devices in an “X” pattern within the Solar Slab and installed vertical probes in the gravel layer under the concrete blocks and inside and outside of the footings. 3-color The first principle of good solar design is siting a home with a southern exposure and utilizing the natural features of the site, including trees that provide shelter from harsher weather that tends to come from the north. 4-color A passive solar home will to a great extent heat and cool itself with minimal use of conventional HVAC equipment, and with no additional conventional expenses over the cost of a comparably sized non-solar, fossil-fuel dependent house. 41-color A solar home uses thermal mass — a material that readily absorbs heat to collect and store the warmth of the sun during the day. This thermal mass will then radiate heat back into a home’s living space during the cooler nighttime hours. This book describes a technique for constructing a Solar Slab, using ordinary concrete blocks and a poured slab, which transforms the conventional house foundation into a particularly effective thermal mass. 42-color Because of improvements in the standards for wall-framing, windows, and insulation, even conventional houses are now far more energy-efficient than our ancestors’ homes. As a result, it has never been easier to build a solar house. 43-color Top: Thermo-shutter designed to insulate windows during the cooler night (or shade the windows during times of intense sun) can be decorated to harmonize with the room decor. Lower right: Air grilles located in the first riser of the stairway discharge warm air collected at the second floor ceiling. 44-color Interior of the solar borne shown on the first page of the color section. The airtight wood/coal stove provides the only backup heat needed by this 3,500- square-foot home, and also provides domestic hot water. 45-color In a building that is tightly constructed and well insulated, you will need to be sure to provide for an adequate exchange of fresh air. You might want to consider including a solar cat in your household: not only will a cat infallibly follow the path of the sunlight over the course of the day, but with its frequent trips in and out through the door, the cat will help insure a comfortable exchange of air. 46-color Three solar homes, all warm and comfortable even in the depths of winter. Note in the bottom picture how the snow lays very evenly on the roof Proper insulation and venting of the roof allows the snow to melt away slowly without causing “tell-tale” icicles or creating ice-dam problems. In addition, we also installed a device to measure the incoming solar energy (insolation). All energy consumed by the building was documented. Meters measured the electricity consumed by the furnace and the second floor blower as well as the electricity used for all other purposes. A fuel meter was installed to measure the number of gallons of oil consumed by the furnace. Solar Principle # 3 39 Provide effective thermal mass to store free solar heat in the daytime for nighttime use When sunlight strikes surfaces, the solar energy is converted from light to heat. Design a home’s thermal mass to effectively absorb the warmth of sunlight as it enters the building in winter, thereby avoiding overheating. Achieve thermal balance by sizing the storage capacity of the thermal mass to provide for the heating needs of the building through the night. In summer, a properly sized thermal mass will serve to cool the building because of “thermal lag” — that is, excess heat will be absorbed during the daylight hours, and by the time the mass has heated up, the day is over and that stored heat can be discharged by opening windows to increase circulation during the night. As evidenced in the Thayer report, the home was very energy-efficient and compared favorably with several active solar homes which were also being monitored by Converse and his colleagues at that time. The efficiency of our design had exceeded my expectations, and the monitoring verified information that we had predicted in the U.S. Patent application. The ongoing independent monitoring of the prototype and the knowledge gained by working with solar homes located over a wide area with diverse design requirements allowed us to continually refine and improve our design methods. PARTIAL RESULTS OF THE INFORMATION MONITORING EFFORT 1. The temperature was consistent and evenly distributed throughout the concrete slab and concrete blocks, with any difference in temperature being within one degree. This observation helped in the design of back up heating systems. That thermal consistency is particularly beneficial to the wood burning home; since the heat from the woodstove “migrates” evenly throughout the first floor, the de sign of a home that uses a woodstove as backup heat is essentially the same as designing for solar. The engineering problem is the same in the sense that the woodstove is an uncontrolled centralized source of heat that needs to be distributed evenly throughout the building and stored, if necessary, for use after the stove finishes its burn. 2. More than 100 percent insolation was measured on sunny winter days. This was attributed to the reflection up and into the building from snow cover on the south patio. This factor saves some of the homeowner’s energy, because the south patio can be left unshoveled, allowing the snow cover to reflect the sun’s heat and light into the building. 3. The temperature outside the footings (4 feet in the ground) reached a maximum of 68 degrees Fahrenheit in September, and slowly decayed to a minimum of 45 degrees in February. The huge reservoir of heat at 45 degrees or better in the ground below the gravel layer is transferred into the home when it is unoccupied and unheated. This effect is described in section 7. 4. A 12-degree temperature drop was measured as the air passed through the Solar Slab in summer. This indicated that the Solar Slab was indeed absorbing energy. This heat transfer and absorption was later incorporated into the design of air-to-air heat pumps for summer air conditioning. 5. We learned that the solar heating system’s electrical energy usage, though small in magnitude, was a relatively significant part of the total usage because of the low overall heat demand of the solar home. Through trial and error, the second floor blower was reduced in size from the original 1/3 horsepower squirrel-cage type to an inline 1/40 horsepower duct fan, thereby almost eliminating it as a significant energy user. Everyone’s Legacy U.S. patent law is very different from most of our other laws in that it discriminates; that is, it grants exclusive use of the invention to the inventor for seventeen years. We don’t have many laws that obstruct free trade to the extent that our patent law does. In an effort to remedy this obvious conflict, the law gives the invention to the “People of the United States” after seventeen years. This book, hopefully, makes this gift more meaningful, as it is an attempt to explain to lay people as well as professional builders how best to utilize this invention to heat and cool homes yet to be built. Next: Insulation, Venting, and Fresh Air |