Basic passive solar design concepts are the framework: compact massing w/ slight elongation of the south face orienting most glazing south overhangs sized for full winter solstice solar gain & summer solstice shading super-insulated envelope elimination of thermal short circuits and infiltration through the envelope thermal mass floors & walls placed to receive direct sunlight night-time insulation of glazing natural thermosiphon stack effect for ventilating during the summer nights. Energy Systems Design Strategies The technical aspects of energy systems design were divided among the four Lawrence Tech. teams as follows: Heating Systems Design, Materials Selection & Envelope Construction Systems, Plumbing Systems Design, and Electrical Design; each team was responsible for doing systems research and design and documentation in their own areas of specialization, while sharing the resulting work with other teams and integrating system interfaces. The basic passive design concepts (listed above) formed the framework for incorporating energy systems into coherent designs. The competition directives gave restraints that eliminated other sustainable design concepts that could increase energy performance; notably the requirement to provide power for an electric clothes dryer eliminates much of the incentive for including the solar chimney which provided passive drying and night time ventilation for the 2002 LTU entries. This solar chimney is still a desirable alternate that could work with all of the 2004 LTU entries, to help cool the homes in the summer. Other concepts not used in this competition which offer dramatic energy savings will be explained at the end of this letter under the heading of "Next Steps in the Zero Energy Home Concept". Michigan building products were used wherever available and suited for the purpose, even if they were not the most energy-efficient and durable products available; viewers of these entries should not assume that the use of any product in these entries constitutes a recommendation by the designers for it's use in other projects. Every design project has different conditions that may make some of these products less desirable; project designers and builders should do their own research to determine what products are best for a particular construction project. All Michigan products listed in this letter will be followed with a (MI) label. Michigan building products Manufacturer Structural Insulated Panels (SIP): W.H.Porter or Insulspan Strawbales, Earth plasters (Jessica's only) Local farms & building site Concrete floors & gravel fill: local mines/ ready-mix plants Triple Low-E glazed, argon-filled windows: Sunrise Windows Fiberglas entry doors w/ thermal breaks Taylor Doors Amorphous photovoltaic panels: Unisolar Wastewater heat exchangers: Solar/ Refrigeration Research Oriented strand board (OSB): Louisiana Pacific plant in MI Kitchen cabinets: Merrillat Air-pressurized assist system for toilets: Sloan Flushmate Leaf & Debris guard for gutters: GutterMate Rigid (blueboard) Insulation: Dow Refrigerator, Stove, Microwave: Whirlpool Solar Windows & Siting: To enable better understanding of site based design considerations in passive solar design, a different actual site in Detroit was assigned to each student. Students were allowed to proceed with designing upon the assumption of a perfect solar window, just as all their competitors were. However, the students were required to map out that "perfect solar window" on their site plans, so that a future owner siting their design will be able to optimize the necessary solar access. Mike actually chose to allow minimizing the shadows on his narrow site to shape his home design, just as a solar urban insertion must. Should the defined solar window be obstructed in any way, the solar energy output will drop accordingly. Also, students were not allowed to site their own new landscaping and buildings in such a way that any of the new work would shade the solar home or collectors. The four different sites make a clear statement about inserting Zero Energy Homes into the existing urban fabric, as well as about designing new developments to provide the perfect solar window for each home. The home with the best solar window potential in the existing urban fabric is the one with the street to the south of the building, where the street right-of-way places other buildings at sufficient distance south of the home that they are generally not obstructions (however, privacy is less). Street trees can be a problem; any shading (even from bare tree branches) should be avoided for most PV panels. The next best situation is having the street on the east or west sides, provided you can get enough street frontage that you can place your house far enough to the north on the site that a standard sized building or mature trees on the lot south of you wouldn't end up shading you. Most cities make no effort to protect solar window rights; check the zoning for building height restrictions to find out what the worst case scenario is for your site. Street on the north is potentially the worst site (as Mike's project demonstrates), although if your site is deep enough, it could still be workable; again check zoning for the building height restrictions, as well as for front setback requirements that are often substantial - these can keep you from placing your home as far north as might want to where the best solar access often is. North entries get the worst winter weather. Always build your solar home at least as tall as the adjacent home to the south - then you will get at least some solar gain to your top stories. In new solar residential development, designers knowledgeable as to the seasonal sun angles on their site can design and arrange solar homes so each has a perfect solar window, relatively high densities are still achieved, and there is a place for taller vegetation in the designs as well. One good example is Village Homes in Davis, CA (designed in the 60's it was full when it opened and has had a waiting list ever since); here detached homes and duplexes were lined up along slightly curving streets that ran east and west predominantly, although there were a few north-to south linkages provided. Each home had solar rights that were protected by a neighborhood design review board with jurisdiction over all new construction and major building and landscape alterations; shadows through the year were known even before the buildings were built. Common greenspaces and recreation areas also running east and west protected the solar access of homes with the "street to the north" configuration. Sun Path Charts: (Example is at bottom left) Knowledge of the implications of the path of the sun through the cycles of the day and the year at the buildings actual site (latitude) impacts every aspect of passive solar design. A design for a building is specific to its latitude, and a passively conditioned building should never be built far from the latitude (or climate) it was designed for; it may be so unsuited to its new location that it will require energy intensive active conditioning systems to compensate. By reproducing the angle of the sun's rays at different hours in different seasons in drawings or models, the designer can determine the appropriate size and positioning of windows, optimal projection of overhangs, optimal angles and positions for different types of solar collectors, and type and placement of other shading devices or reflectors (example at left). The building can even have openings and markings designed to celebrate an anniversary of a moment in time (a birth, etc.) with a solar event, much like Stonehenge does. Building Envelope Components Structural Insulated Panels (SIPs detail below): We have focused on creating a low-cost super-insulated, continuous building envelope (with plenty of thermal mass inside) to conserve every bit of warmth possible within the building. Although the irony of building a zero fossil fuel energy home with insulation manufactured from non-renewable fossil fuels has not eluded us, the quantity of petroleum saved over the building life far exceeds that embodied in the walls. Accordingly we are using the thickest panels standardly available from W.H.Porter (MI) or from Insulspan (MI) as the primary enclosing element, in combination with 3" thick Dow blue board insulation (MI) continuing the enclosure completely around the concrete radiant floor slab (bottom and sides). Dow's highest density foam can support up to 100psi without crushing, allowing it to even be used under some footings such as those under lightweight SIPs or Techbuild (below) panels. Where this foundation insulation is exposed above grade (or as a taller aesthetic base), students have the choice of finish materials to cover the blue board insulation: either a super-thin brick veneer clipped and mortared into a mounting system (such as "Z-brick"), or a stucco or Exterior Insulating Finish System (EIFS) coating over a mesh anchored to the insulation. Most have chosen the Z-brick, which has the substantial thermal advantage over standard sized brick veneer of not requiring a supporting brick ledge (a sizeable unavoidable thermal short circuit). TECHBuilt Systems (OH): Our foundation walls and the insulation on underground heat storage tanks are made of these steel framed panel assemblies that function similar to, and are competitors of SIPs. They use the same kind and thicknesses of EPS foam insulation used in SIPs panels, but the structural integrity comes from steel framing members set into the inside and outside edges of the foam insulation panels, instead of a wood stressed skin. This system is approved for use in below grade construction in well-drained conditions as there is no wood or organic materials to rot or attract insects. The metal & foam components can theoretically be made in a closed loop recycling system, though that is not yet done at present. The panels have slightly higher embodied energy than SIPs, but there are no VOC glues to off-gas, so they can be used for the whole shell of homes of persons suffering from environmental illnesses. Sunrise (MI) best triple-glazed, vinyl framed windows & Taylor Doors (MI) entry doors complete the super insulated wall surfaces with tight insulated fiberglass construction and a thermal break that dramatically cuts infiltration and conductive heat losses. Shallow Frost-Protected Foundations (detail at left): To make a continuous subsurface insulation envelope easier to do, and to conserve concrete (which contributes dramatically to global warming), we are utilizing shallow frost-protected foundations for all slabs on grade. This system eliminates the need for foundation walls to extend down below the frost line, by the means of providing an equivalent level of frost protection by extending insulation out horizontally (the same distance that frost-free depth is below the surface) from the reinforced thickened concrete slab foundation. The horizontal insulation just below the topsoil slows down the flow of heat from under the foundation of the building to the point that the there is no danger of the soil that supports the building dropping to a freezing temperature where there would be a danger of frost heaving. This system successfully performs even in much colder climates in Canada. Minimizing Infiltration: Another critical aspect to super-insulated design is minimizing infiltration. Not only do building leaks allow heat to escape with the air, but warm, relatively moist interior air which moves into the building envelope contributes to severe moisture damage, mold and mildewing of the building materials as the moist air comes into contact with cooler surfaces of building materials within the walls and roof, and condenses. In conventional construction this problem is dealt with by trying to ensure that a continuous water vapor membrane encloses the entire interior of the house, located within the wall on the warm side of the insulation. In practice this is extremely difficult to achieve, as it requires an obsessive level of attention to detail that is beyond the level of care that most construction firms are prepared to go to. Also, if the membrane is close to the interior wall surface, future modifications by the residents are likely to puncture the membrane and defeat its protection. One additional benefit of SIPs and of TECHBuilt construction is that the plastic foamed insulation that is the core of the structural panel serves as a very effective and thick moisture barrier. As long as a hole is not drilled completely through a panel from outside to inside, the moisture barrier effect holds. This means that the utilities (plumbing and wiring) can be installed into factory prepared chases just under the interior stressed skin or wall surface without requiring that additional time be put into preserving a delicate membrane. The SIPs manufacturers state that infiltration as low as .05 air changes per hour have been measured (TECHbuilt may be higher); as a safety factor our calculations use .2 air changes per hour. With infiltration rates that low, we must by law add additional ventilation with a heat recovery ventilator. Strawbales, earth, & other natural building materials: Though no guidelines were given regarding conserving the embodied energy within building materials, Jessica opted to get her building materials atuned with the goal of minimizing fossil fuel useage. By building with natural building materials, homeowners avoid using petroleum based foam insulation in above ground applications (still needed below grade), and at the same time reduce the amount of embodied energy in the building structure because materials are harvested from the suface, not mined, and use little process energy, much of it manual labor. Straw is a sterile agricultural "waste" product that is often burned if there is no market for it (hay is never used for building as the seeds can sprout in the walls). Jessica also utilizes thinner straw/ clay slip wall construction between conditioned and unconditioned spaces or for exterior walls bearing on 2nd floor beams. In this type of construction, loose straw is tossed with a runny clay slip until lightly coated (like mixing dressing into salad) and then is packed into forms tightly to dry. The forms are heavy plywood skins over 2x6 wood studs at 24" on center, with horizontal 2x2 wood strapping at 24"OC to create a thermal break (all wood can be salvaged lumber). The plywood skins are removed when the clay is dry, leaving a flush surface with interesting texture that can be left unfinished. Jessica is also using cob (earth from the homesite wet-mixed with straw fibers for tensile strength) to create thermal mass in ground floors, fireplace (outer shell, not firebox), interior walls and a built-in bench (see the benefits of thermal mass explained below). Earth floors have a warm, rich color and polished texture like burnished leather. Most building sites contain at least some natural resources (earth, stones) suitable to home construction, while others (straw, un-milled wood, reeds) are generally regionally available. Natural building materials also have the added benefit of producing high indoor air quality, and (properly assembled using time-tested techniques) are durable enough to equal or exceed the performance levels required by residential construction codes in the areas of fire, earthquake, windstorm, weather, and pest resistance. In areas where building codes enable using local natural materials without much red tape, home ownership becomes accessible to low income families who can put some sweat equity time into building their home; most natural building systems utilize readily available hand tools and are easily learned (no special skills or strength required). All materials listed above are available throughout Michigan and should be recognized as Michigan-made building materials (though not manufactured). These materials & others such as fieldstone stem walls, and a thatched roof of local reeds a foot thick (with a cob ceiling plastered on the bottom side for fire-safing), are used in the Oxford, MI studio left, and in other beautiful pioneering buildings in Michigan. Thermal Mass: Thermal mass serves as a battery (or flywheel) for heat energy, both from the sun and from other sources. By storing heat energy when abundant and releasing it when it is scarce, it also helps to even out the temperatures in a space, much like the way adding a battery or capacitor to an electrical system can even out variable power inputs. The concrete floor slab is the main mass in each home, but some students have added mass walls in the middle of the building as well. Ideally they are situated to catch as much sun as possible; floors should be dark colored to soak up the maximum amount of heat and hold it down low, but walls are best light-colored to reflect the energy (& light) around the building. For solid masses(masonry, etc.) maximizing surface area of a relatively thin mass (4' thick or less) provides the most even temperatures in a space. Containers of water (or other fluids) used as mass should be dark-colored, and can be much larger in cross section; as water is warmed from one side or the bottom of its container it begins to rise, creating a convection current that causes the heat to transfer more rapidly throughout the whole container. Water has a higher capacity (specific heat) to store heat; it can easily store 2 to 3 times what concrete or masonry can per unit mass (weight). Windows: We have selected Sunrise (MI) windows and patio doors for their high-efficiency, whole unit design that utilizes multiple low-E (emissivity) coatings on three layers of glass, with argon-filled sealed spaces between, and warm-edge technologies such as low transmissivity spacers. Though windows this good can produce during the day a small net heat gain in any direction they are facing (so say the manufacturers), at night they still lose far more than they gained during the day. Though the vinyl frames are not as good as the fiberglass frames that expand and contract at the same rate as the glass, preserving the seals, we were unable to find any fiberglass frames made in Michigan. Another concern with vinyl (PVC) is the environmental pollution and health hazards to factory workers. Night-time window insulation system: Our calculations showed that there were few strategies that reduced heat loss as greatly as the addition of night-time window insulation over all glazing. An additional benefit is increased privacy - interior lighting can't shine forth to reveal all your activities to your neighbors. But one must take care in insulating windows; when windows are insulated from the inside, it is very difficult to ensure that the insulation seals tight to the window frame. If not sealed, any air reaching the colder glass will subsequently have its moisture condensed out on the glass surface, which can lead to considerable water damage. The proper place for insulation is on the cold side of the vapor barrier/ glass pane; outside the house. It is essential for the exterior insulation to be easily operated from within the building (even automated) or it won't get utilized. We were unable to find products available off-the-shelf which fulfill this function well. Potential insulation types include hinged insulating shutters, exterior venetian blinds or louvers, exterior rolling shutters, or a coiling insulating shade. The hinged insulating shutters would occupy precious southern wall space and have operating hardware challenges, exterior venetian blinds or louvers would suffer from infiltration losses & might make some shade even when it is not wanted. There are workable off-the-shelf exterior rolling shutters made of either vinyl or aluminum slats but these are developed for security; their thermal performance is not worth the cost. They do, however have a well-designed operating system that is easy to use and/or automate. Therefore in the 2002 LTU competition entries we proposed insulated shades fabricated to fit the openings out of lightweight, UV durable material such as Reflectix, with a facing of awning fabric to the exterior for aesthetics. Reflectix is both a radiant barrier (given an adjacent min. 1/2" airspace) and a hinderance to conductive losses. The shades would have a horizontal wood slat stiffening rib adhered between the Reflectix and awning fabric at 12" centers to guard against minor impacts or wind suction pulling them out of their tracks, and the bottom rail would be weighted with solid metal to allow gravity to produce smooth downward motion. The shades would move in an oversized rabbeted track in the edge of the window trim (min. 1/2" from the glass), both edges of which would have a soft brush-type weather-stripping adhered to minimize infiltration while also adding as little resistance to movement as possible. Rolling shutter type operators would provide either low-cost manual operation (interior pulleys or cranks), or full automation (Somfy rolling shutter motors and control systems triggering the lowering of the shades at sundown each day and raising them at sunrise). At least all high clerestory window shades should be motorized; the energy draw for motorizing all window shades was included in our electrical calculations. In the summer, the photocell control (& thus shades) could be switched off; that power would then be available to be used by motorized operation of clerestory windows and chimney vents. Another helpful summer strategy which we did not take time to fully develop is the once-per-season manual conversion of vertical shades to horizontal spring-loaded awnings. The same Somfy motors (which are also used for coiling awnings) could be used to provide interior control of awnings to shade windows while admitting light and view. While most of the 2004 LTU entries do not bother with specifying these exterior window insulation devices, due to the fact that they are not off the shelf equipment and their effect is not modeled by any of the building energy analysis software we used, they are still an alternate which could be useful for conservation. Solar chimney/ passive dryer: As designed for the 2002 LTU entries (though only an alternate not shown in most of the 2004 entries), this is a tall interior volume that penetrates the ceiling and roofline, which provides passive ventilation due to stack effect, and passive drying of clothes or food. This enables eliminating the high cost of running a conventional clothes dryer off of photovoltaic panels ($4300 in additional PV equipment for the Whirlpool dryer). Super-insulated like the rest of the house, the solar chimney has a solar hot air flat-plate collector filling the entire southern exposure, a 12 VDC fan with insulated exterior shutter at its eastern peak, and a insulated shutter covering the larger passive western vent (both vents have insect screening). Additional heat can come from the flue of the (masonry) woodstove which could be routed through one north corner. Winter ventilation is via a return duct (to the heat recovery ventilator) near the top of this space, such that the heat in the air of the chimney is not lost to the house even as the humid air is removed to promote clothes drying. The damper in this exhaust duct would be shut at the beginning of the summer cooling season to prevent hot air in the chimney from being circulated into the house; summer ventilation of the chimney is via passive stack effect and the 12VDC fan. Summer clothes drying is best done outside on clotheslines to avoid adding humidity to the house. A clothes rack is suspended from a single pulley at the top of the solar chimney, so it can be raised or lowered from below (even easier with the addition of a counter-weight). Corner wheels on the rack keep it aligned in the chimney without marring the walls. Most clothes will dry within one day, with heavy fabrics such as thick sweaters taking no more than two, even in the depths of winter. Summertime drying is as few as three to four hours outside. Contrary to popular opinion, passive drying is not primitive, labor & time intensive; it actually shortens the required handling time of the laundry and produces more aesthetic results. Also passive drying (if exposure to direct sunlight is avoided) extends the life of the clothing by reducing needless wear (tumbling fills a lint trap with rubbed off bits of clothing). Clothes are removed directly from the washer, shaken/ snapped to remove wrinkles and hung directly on their hangers on the solar chimney rack, where the weight of the water in the clothes (& clip-on weights for that just-pressed look) pulls the clothes into the proper drape desired in wearing, mostly wrinkle-free. Ever missed the electric dryer buzzer and come back to find chaotic creases baked in the hot clothes jumbled in the bottom of the dryer? No more. A food dryer is easily made from a mesh fabric hanging sweater shelving unit; food is laid on squares of window screening on the mesh shelves inside and the entire unit is wrapped in insect screening, then all is hung from the clothes rack in the top of the solar chimney. Most fruits and vegetables will dry in two to four days. When drying food, the user should install a remote thermometer sensor in the top of the chimney, with readout below, as temperatures higher than 120 degrees cook the food & lose food value, while if the temperature drops too low and humidity is high, foods can start spoiling or molds can start growing. Visual inspection of the finished food product as it is packed into sealed storage containers is another must. Creating a favorable microclimate: One of the most important strategies for passively conditioning a building is to use landscaping elements to create a favorable microclimate, that is, a sheltered zone around the building where temperature (and humidity levels) are even a few degrees closer to the desired conditions inside the house. This reduces the amount of winter heat loss and summer heat gain because the building now has much less thermal work to do to maintain its temperatures in an already moderated environment, much the same way an animal seeks out an environment closest to the conditions its body functions require. Our designs incorporate strategies such as winter windbreaks of coniferous trees to the north and west, earth berms on the north, west, or east sides, deciduous vines on vertical trellises on the west side to shade west windows, shade trees on the (south)east and (south)west facades (just outside our solar window), and use of light-colored, lower albedo (heat absorption & re-radiation) paving and maximizing growing ground cover. Another strategy that many of our designs utilize, similar to creating a favorable microclimate, is placing unconditioned spaces adjacent to the home, to moderate heat losses and gains through the common wall to the passively tempered space. The effects of a favorable microclimate or attached unconditioned spaces are much harder to quantify because there are so many variables, so we have not made any attempt to include their effect in our heating calculations. Because we have chosen to overlook such advantageous contributions to the buildings energy performance in our calculations, it is quite likely that our designs would use less energy than we have predicted, minimizing the requirement for backup woodfired heating. Attached unconditioned spaces: These spaces (porches greenhouses, garages, etc.) contribute to the thermal performance of the home by reducing winter heat losses and summer heat gains through the common wall with the home, and in many cases can contribute an additional daytime solar heating fraction which can be directed into the home through vents at the top of the attached space. They may also serve as air-lock entries, minimizing infiltration losses, as shading devices in the summer, or as additional living or storage space. Constructing them is much less expensive as they don't need to be super-insulated. Thermally they are separated from the home, with the home's super-insulated envelope unbreached by any of their construction. Their floor slab and foundations are separate from the home, and though they don't require any insulation of the floor or foundation, they do require foundations that extend down to frost line. Full-size typical masonry construction can be used if desired, or regular stick-framed construction for the walls and roof. Many of the porches are designed to be three-season porches, with some of the fenestration openings designed to have removeable glazed storm and bug-screen panels which can be interchanged once each season to suit the heating or ventilation requirements of the space. Such glazing need only be single (or at most, double) paned construction. Brine Pools: Anne's design utilizes brine reflecting pools on the south side of the dwelling to increase winter gain through the windows, as well as providing auxiliary heat storage. There is a salt gradient in the pool from almost fresh at the top (least dense) to almost saturated at the bottom (most dense). The sun heats the dark pool bottom, and because of the density gradient, the heavy brine at the bottom can't rise to the surface in a convection current as normally happens with fluids that are heated from the bottom. Thus the heat remains trapped in the lowest layers, loosing heat only through slow molecule to molecule conduction, not rapid convection; effectively insulated by the upper layers. The technology can produce warm water even through winters in temperate climates, and in hot arid weather can be relied on the heat fresh water pumped through tubes on the bottom to steam that can drive a generator. Most examples have been utility scale near the oceans, but it can work in the microcosm as well. We have no way to calculate what the contributions of the brine pools would be, since it involves fluid dynamics calculus. Active Systems Design Heat Recovery Ventilator: Stirling Technologies' (OH) heat recovery ventilator can recover up to 95% of the heat energy (sensible and latent) that would otherwise be lost with the exhaust air. These units transfer heat energy from the exhaust air to the fresh makeup (supply) air coming in by means of passing the two separated air streams on either side of a special membrane that wicks some of the air moisture through and most of the heat, without passing air molecules. Thus the HRV can help keep interior air from becoming too dry in the wintertime, while helping to keep extra moisture out of the house in the summer (making air conditioning unnecessary). In our designs fresh air is supplied to the bedrooms, through the living spaces, and is exhausted from the kitchens & baths (and from the solar chimney in the wintertime). Costs are lowered by providing only a single 6" dia. duct (either supply or return) to each room, with the rooms themselves serving as plenums connecting the supply to the return by means of louvered doors on the bedrooms and baths. Mechanical timer switches in the bathrooms and kitchen allow residents to run the HRV fans top speed anytime they are showering or cooking or otherwise introducing pollutants, yet the timers turn the HRV fans off after the period (up to an hour). Anything that introduces air pollution into the Zero Energy Home should be avoided, as it increases the need for HRV use, thus running up the electrical bill (the HRV uses far more electricity than the simple 12 VDC solar chimney exhaust fan). Indoor air pollution is minimized by using low or no VOC (volatile organic chemical) building products (no carpet is used), and by ensuring that the woodstove (or fireplace insert) is an air-tight model with an outside source of combustion air ducted in to it. Additionally, a re-circulating range hood is to be provided over the electric stove to filter out grease and particulates from cooking before that air can be drawn into the exhaust duct and foul the HRV filters, hindering its functioning. The HRV exhaust duct must be located at least 10 feet from any cookstove. Lifestyle choices have an impact here as well; smoking & personal care products (such as powders and aerosols) which introduce a lot of air-born particulates that can foul the HRV filters & reduce its efficiency should be avoided if possible. If they cannot be avoided, such activities should not be done in the bathrooms as the air is drawn directly into the filters from that point - the bedrooms or living spaces are more appropriate locations that let particulates settle out of the air before it goes to the HRV. Compliance with these recommendations will save the residents considerable money due to lower electricity demands and lower requirement for maintenance of the HRV and its filters. In our calculations, we used ventilation figures for non-smoking, low-polluting residents, allowing only a small margin of extra ventilation above the required minimum by state codes (15 cfm per occupant). While the HRV has the capacity to move sufficient air to remove any level of pollution short of a house fire or a manufacturing process, increasing its useage to high levels will increase the heat loss and electricity consumption to the point that the home may have difficulty hitting the Zero Energy mark. Hydronic Heating System: Both space heating and domestic water heating are capable of being supplied by any of three energy sources (solar, wood stove, and electric) working in combination in this system, though the electric heat is designed to kick in as a last resort, as that requires repayment from expensive PV (photovoltaic) panels. Heat is distributed through the building via radiant floors. Domestic hot water is supplied from a well-insulated Marathon plastic tank. The heat storage reservoir for the solar collectors and the (masonry) woodstove is a 200 gallon domestic "flywheel" tank, and for the radiant floor via heat exchangers. Excess heat from the domestic "flywheel" tank is routed to a larger "seasonal flywheel" tank. Domestic hot water and space heating are provided by the solar collectors or from the "seasonal flywheel" tank for almost the entire year, with a backup source like a wood-fired stove available to meet any shortfall. Only DC pumps are used, because they use only slightly more than half of the power of the AC pump equivalents, and power supply for them can be maintained even through utility grid outages. Closed loops are preferred because they can be circulated with a much smaller pump as there is no "head" of atmospheric pressure to overcome, only tiny frictional losses from the tubing walls. The drawings at mid left shows the 2002 LTU hydronic system which lacked a "seasonal flywheel". Seasonal thermal flywheel: This concept involves using an appropriate size mass of water (which has greater heat capacity than the sand shown in the working built example at bottom left) in an underground super-insulated concrete tank to store surplus heat energy from the summer for use in the winter. A loop of PEX tubing coiling on the floor of the tank provides a readily effective way of transmitting the summer's heat into the thermal mass; convection currents within the tank will diffuse the heat rapidly through the tank, with some temperature stratification. Another PEX loop at the top can be used to send heat to an uninsulated ground loop as a dump load if the seasonal flywheel tank gets near to boiling. The thermal flywheel is ideally sized to receive all the surplus heat produced in the summer from a solar hot water collector array which has been sized and configured to provide almost all of the yearly domestic hot water & space heating requirement, which is much lower than most homes due to implementing the best (hot) water conservation strategies including lowest-flow fixtures and appliances, waste-water heat recovery units, and insulating all pipes. Solar hot water system: Two to four evacuated tube solar thermal collectors are adequate to meet all but a tiny fraction of all the space & domestic water heating loads, when paired with flywheels for storing the heat (at least six are needed without a seasonal flywheel). Evacuated tube collectors were selected over the flat plate collectors manufactured in Michigan because tube collectors perform much better on the cloudy days that Michigan has so many of, and these cloudy days are the worst case condition that should be designed for in a Zero Energy home. Evacuated tubes perform better because the vacuum is far more effective at preventing heat loss, and there is only about a tablespoon of heat transfer fluid in each tube that could cool down to the ambient outdoor air temperature overnight, whereas flate plate units have a lot of water/heat trapped in the collectors overnight, radiating heat to space. Evacuated tubes heat up to design temperature in a few minutes after being exposed to sun on a winter morning, as opposed to a couple of hours for flat plate units (shown from the 2002 LTU entries on the next page; but not used in 2004 LTU entries). The potable water in the drainback loop system is circulated by a 12 VDC pump directly driven with a single Unisolar 32 watt panel, with a (thermal) differential controller and an adjustable resistor (controls pump speed) to ensure the pumps only run when there is sufficient heat in the water off the panels to heat the tank or the floor. The direct drive system protects the collectors by ensuring that there is always power for the pumps when there is sun, even if the grid goes down. Radiant Floor Heating: Water is supplied at about 90 degF into the floor slab, resulting in a floor (and furnishings) surface temperature just slightly warmer than human skin. With almost no cold surfaces around, people radiate almost no body heat and cooler air (65-70 degF) feels comfortable. Unlike buildings heated with forced hot air, the air at the floor is actually a few degrees warmer than the air at the ceiling, so heat losses through the roof are minimized and convection currents & cold down-drafts are basically eliminated. The whole house is one temperature zone because (unlike forced air systems) substantial change in room air temperatures results from a couple of degrees difference in the heat transfer medium supplied; there is little difference in the heat energy supplied to zones, thus not much point in having more than one. More is gained with a single zone because the radiant floor tubing can transfer solar heat rapidly away from the south-facing windows; thus improving the floor's capacity to absorb more energy by storing some in the northern half of the slab, and preventing overheating of south spaces. This is achieved using a simple reverse return layout for floor slabs (shown at bottom left of previous page). Radiant floors are cheapest in concrete slabs, where less expensive PXC tubing (7/8" dia at 16"o.c., max 400 l.f.) is acceptable. Floors directly above a radiant floor can be adequately heated in a super-insulated building with a single underfloor perimeter loop (5/8" PEX) that doubles back in front of the windows. Such floors are receiving radiant energy from below that keeps them warm to the touch, except close to the exterior walls (the Kaufman house at left bottom demonstrates this - no heat upstairs). A closed loop was chosen because it extends the life of an expensive plumbing system that is literally set in concrete and not easily replaced (though spot repairs are not difficult); distilled water in the coils prevents sedimentation and slows deterioration in the hydronic system. Additional heat from the storage tank heat exchanger is supplied as needed via a mixing valve (regulated by a differential controller to prevent over-or under-heating) to meet the design temperature for the radiant floor supply. Woodfired waterfront heater: This loop holds domestic water is flowing directly through the "waterfront" chamber or stainless steel loop in the heat source instead of having heat transferred to it by means of a heat exchanger. Because it is critical that the water in the woodstove always be in constant motion at any time that there is even residual heat coming from the stove (in order to prevent the build-up of heat and pressure in the lines to potentially explosive pressures), we chose not to have a heat exchanger (which could potentially clog over years of exposure to domestic water) in the line between stove and storage tank. Also the industry recommendations for redundant temperature/ pressure relief valves have been followed. As an additional precaution an off-grid DC power system supplies the 12 VDC woodstove pump, ensuring a week's worth of back-up power when the grid goes down. The Leprachaun (at left) is a tiny cast iron woodstove that is beautifully enameled in brillant colors, with a window in the door kept clean by air-wash design, and a single cookplate (capable of heating a pot of water to boiling). Outside combustion air ducted into the bottom of the woodstove prevents inadverdant cooling & de-oxygenating of the building (caused when room air is drawn up the flue). To install the waterfront; firebricks are removed from the bottom & back of the (door latch side) wall in the exact shape of the waterfront, then holes for the supply and return pipes are drilled through the back wall. After it is inserted, all seams are filled with fiberglass rope filler & a woodstove sealant. A very hot short burn is recommended to clean out cresote from the stove, & boost domestic hot water temperatures without overheating the house (up to 33,000 BTU per hour in this stove). The calculations multiply this by 80% to account for less than ideal wood & burn conditions. In most of the 2004 LTU entries, the supplemental heat beyond what the seasonal flywheel could supply is so small that it is limited to 1-2 months at a rate of at most an hour's burn per week, or in some cases, as little as a single Yule fire, or even no supplement at all. Such miniscule fuel requirements can be met by the trees and shrubs growing on the site. Masonry (wood) stove: Given a super-insulated structure like these homes, most of the 2004 LTU entries have opted to substitute a masonry stove for the cast-iron Leprechaun used in the 2002 LTU entries, in order to prevent overheating the building when supplementing the heat stored in the seasonal flywheel of the hydronic system. These stoves even out the release of heat to the space, spreading the heat of an hour's intense fire out over a day. The firebox temperatures during a burn can peak at an average of 1000 degrees F, such that the wood & combustion gases are almost entirely consumed for the cleanest, most efficient use of fuel possible. Unlike the cast-iron stoves, creosote is not an issue, even when burning paper or brush, as long as the fuel is dry. Domestic water conservation (bottom previous page): Domestic hot water conservation translates directly into fewer burns needed. Low-flow (1 gpm) aerators & showerheads were used along with a conserving clothes washer. Plus wastewater heat exchangers from Solar Research (MI) transfer up to 50% of the heat going down the drain to the cold water supply line feeding the hot water heater (the GFX vertical exchanger performs better, but isn't MI made). Electricity conservation: Lighting: During the day, adequate light is provided by windows, high clerestories with internal "borrowed light" windows into adjacent spaces, and solar tube skylights into windowless interior habitable spaces. Sunrise (MI) windows' frames are extruded vinyl with welded and reinforced corners (a pultruded fiberglass frame like the top performing Dorwin windows is not made in Michigan). Center of glass R values (Sunrise = R10) are misleading performance indicators; they do not account for heat loss through and around the frames (the biggest heat loss). Instead, ask for the equivalent whole unit R (or U) value (Sunrise = R4.2), which is how the window performs in its entirety in the wall (varies somewhat with window size and shape). Electric lights at night, or for concentrated tasks are to be compact fluorescent lamps (by TCP), as this type is the lowest consumption residential fixtures readily available and relatively cheap (1/3 power consumption & 10 times lifespan of incandescents). For fixtures frequently turned on and off, and for many utilitarian uses such as all-night lights in passageways, closets, exterior path lights, and storage or utility rooms, we would prefer to use LED lamps (1/10 consumption & 50 times lifespan of incandescents), but high initial price is a drawback. There are M-16 lamps to replace halogens, and self-contained outdoor path lights available with LEDs now, and many of the automotive LED fixtures are affordable and suitable for utilitarian uses such as nightlights under handrails on steps, or for storage rooms. Appliances: Whirlpool's (MI) appliances chosen were the most efficient made in Michigan, and the prices are reasonable. Appliances with electric resistance heating (range/oven, clothes dryer, toasters, hairdryers, coffee makers, etc.) are the least efficient way to use electricity. Those using compressors for moving heat "upstream" (refrigerators, freezers, air conditioners, de-humidifiers, and heat-pumps) are a close second. For that reason, passive clothes drying and space cooling saves much energy and money. Mike found a single compartment clothes washer/dryer by LG that used less energy annually than the Whirlpool clothes washer LTU used in 2002, thus saving us from having to provide an additional $4000 for a 4th inverter & PVs. The chosen upright refrigerator is deliberately small for a family; due to its flawed design (cold air pours out the opened door), a true family-sized chest-style model (Sundanzer) could easily run on the energy used by the small upright. A chest-style also has stable stratification of temperatures inside, allowing meats to be just above freezing on the bottom of the refrigerator, with no risk of frost damage to delicate greens at the chamber top. Human powered entertainment equipment: A moderate kwh budget for entertainment appliances is in our base calculations, with the human-powered option described as an alternate in our specifications because it depends on user motivation. Pedal generators lower electricity consumption while producing physically fit people; When powering TV (previous page) they simultaneously give an incentive to exercise and a disincentive to becoming a media junkie. Note that power conditioning equipment is needed to protect electronic equipment (against variable current from inconsistent pedaling). But appliances without electronics and with variable speed motors (clothes washing machines, sewing machines, coffee and grain grinders, food processors and blenders, etc.) can be directly driven. Electrical system design: Though using the utility grid as a battery offers cost & maintenance savings, one is as much at the mercy of power grid outages as anyone else (utilities require that inverters which feed solar power to the home automatically shut down if the grid goes down, to protect their line workers). Consequently, though PV panels may be generating plenty of power none can be delivered to the appliances in the home until the grid comes back up (unless you have a battery bank stashing some of it away). A house-sized battery bank is very expensive, high maintenance, must be replaced every five years or so, and is a danger to the ignorant who mess around with it. Since the competition stipulates that power can be borrowed from the grid in winter and paid back in the summer, grid inter-tie is most cost-effective; a battery bank can't provide seasonal energy storage, so the PV array needed to reach Zero Energy with a stand-alone battery bank would probably be 1 1/2 times the size of an equivalent grid intertied system. Thus, back-up battery power is provided only for the life-safety critical load of the woodstove & flywheel pumps, but the charger for the battery system also provides a convenient DC power source for all the other DC loads. Back-up 12VDC battery system for critical loads: This tiny battery bank of six gel cell batteries wired in parallel to a battery charger handles all critical power loads needed to keep the house habitable during a power outage. In addition to the flywheels' and woodstove's water heater circulation pumps, the 12 VDC fan in the solar chimney and the DC pumps that circulate heat to the floor are also powered through this system, but only the aquastat on the woodstove is a DC powered automatic controller. Because of the AC controllers on the radiant floor system, the radiant floor pumps can't come on during a power-outage and drain down the batteries too rapidly. The radiant floor will take days to cool down to uncomfortable temperatures (and then days to heat back up again), but the family can compensate by wearing socks and shoes inside. There is still plenty of hot water and heat from the solar collectors & woodstove. In the summertime, the DC fan can still be run at night to keep the house cool, as it has a manually operated switch. Grid intertied array: This is a 3kw array roof mounted PV array at the best angle for maximum annual production of energy (about 27 deg altitude; nearly normal to the summer sun). 45 Uni-solar (MI) 64w framed panels are used because they are the cheapest Uni-solar product that is compatible with our roof construction of Insulspan (MI) structural insulated panels (or Techbuilt). Solar shingles require an attic space beneath for running the wiring panel to panel, as well as a roof penetration for each shingle. These 45 US-64s are wired in fifteen parallel strings of three each to match the power input requirements of the three GC1000L inverters that convert the power to AC for use in the house. The inverters were chosen for lowest initial cost and proven dependability as well as for the excellent data-logging equipment available from the same manufacturer to enable tracking the Zero Energy Home performance. All wiring and safety features are to industry standards. "Next Steps in the Zero Energy Home Concept" Beyond the state's guidelines for single-family houses powered only by sun and biomass & the limits of vision in the 2004 entries, a whole realm of dramatically more energy-efficient solutions opens up, including multi-dwelling buildings and untapped alternative energy sources (windpower, hydropower, and geothermal). Multiple Stories (below): All the 2004 LTU designs have some amount of 2nd floor space (some have basements, too) based on the dramatic savings potential shown in the 2002 competition calculations. Energy calculations show that a 1 1/2 story design allows shrinking the footprint of a dwelling by 33% (compared to a single story design), resulting in a 30% reduction in the overall volume and surface area of the building, and thus also a 28% reduction in energy consumption (and to construction and operating costs), and no increase in building height. Earth sheltered/ Underground homes (bottom left): Several 2004 LTU entries have included modest north and west earth berms or basements which help conserve heat via the microclimate effect (reducing the temperature differential between inside and outside which drives conductive heat losses), and by eliminating convective and radiant losses from those portions of the building skin in contact with the earth. These savings have yet to be maximized by either stepping the landscaped earth berms up to cover the majority of the building, or excavating the building down into the earth until almost covered (except the south walls). Such landscaping strategies could be a great amenity, turning a high density subdivision into private vistas of widely varied biodiversity, while providing light, air and private views for all rooms on the north, east and west sides of each dwelling. The TECHBuilt system offers the opportunity to do underground structures that are super-insulated while using a bare minimum of concrete for unsurpassed energy and environmental savings. Multiple Dwelling Buildings: Reducing the surface area available for heat loss is one of the best ways of substantially reducing heat losses, and dwellings which share a party wall or other connection with a neighbor (or an outbuilding) perform thermally far better (about 1/3 less losses) than single family dwellings. Unfortunately, most Americans have had their perceptions of multi-dwelling buildings tainted by living in light-weight, cheaply fabricated apartments during their youth; the experience of having effectively no acoustic and visual privacy from your neighbors can turn anyone off. But well done multiple dwelling buildings can actually increase one's privacy within the context of a high-density, cost-effective development by freeing up more land for lush edible landscaping screens that remove your neighbors from the views out the private side of your dwelling. Also, party walls of two wythe (layer) masonry construction with an airspace between (rather than light-weight wood framing) can cost-effectively provide complete sound and fire separation while also serving as thermal mass for a passive solar building and eliminating heat loss from that surface of the dwellings sharing the wall; the wall thus becomes a heat storage, rather than a heat loss element. High density development, especially mixed-use development which incorporates the stores, services, and businesses that we all need to get to within walking or biking distances, can reduce energy consumption while improving quality of life in ways that single-family developments can not hope to approach; they can eliminate the necessity of each working adult owning and maintaining a car, by making it possible for some people to reasonably earn a good living and provide all the resources their family needs within biking distance of home. Currently transportation is responsible for roughly half of the average American family's fossil fuel consumption, thus transportation should be considered in the picture of any zero-energy development planned. Other alternative energy sources: The competition limited energy sources to solar and biomass because it was thought that wind power would be impractical in high density developments, and hydropower is not widely enough available for use in an intended prototype. However, windpower is a very cost-effective source of energy where the minimum wind resource exists, as it does in much of Michigan. Also, wind is the perfect complement to solar energy as it is greatest when weather makes solar power scarce, & vice versa. Windpower can also be compatible with high density development, as utility scale windmills can serve a whole neighborhood without cluttering the skyline or tying up lots of land; they can even be located miles from the developments they serve if those dwellings are all grid intertied. Hydropower is another excellent solarpower complement, producing the most power during the wintertime, though energy output is relatively constant for weeks at a time. However, hydropower resources are thinly scattered throughout Michigan, so a prototype design should not rely on the presence of running water with sufficient volume and head (drop). Geothermal heat in the USA tends to be the low temperature variety (except maybe Yellowstone, Hawaii, etc.), so that the heat must be concentrated with inefficient compressors/ heat pumps (compared to our hydronic circulating pumps). This heat is not cost-effective to recover when the electricity must be provided with expensive PV panels as in this competition.. But if you have access to a natural hot spring, you're golden - go for it! Solar (or hydrogen) Cooking: Cooking with an electric range/ oven uses undue amounts of electric power; cooking can be more efficiently accomplished by concentrating solar energy into an insulated, glazed container, or by means of an standard range/ oven converted to run on electrolyzed hydrogen or biogas (methane) from a methane digestor treating sewage. Solar ovens vary tremendously, from portable units that cook at low temperatures more like a solar crock pot, to durable concentrating collectors with insulated oven compartments that require tracking the sun's motion, yet can reach the high temperatures and quick cooking times of conventional ovens (at bottom left). Such solar ovens can be even be designed into the walls of a home so that the resulting wall oven can be utilized from inside the home much as a conventional wall oven would be. Solar ovens can cook entire meals, including casseroles and main entrees, meats, vegetables, and even baked breads, cookies, pies and cakes. Pasta is the greatest challenge, requiring a technique in which the dry pasta and water are heated separately but simultaneously in the oven to boiling temperatures, then combined to cook for the standard time. Low temperature "solar crockpot" type cookers can offer the convenience of requiring no attention at all while they cook; one can load the cooker in the morning of a sunny summer day before going to work and have a completed meal upon one's return at the end of the day, without hazard of a house fire or of burned food. However, low temp.cookers will not work well in cold weather. Hydrogen can be generated from water by using excess solar or wind generated electricity in an electrolysis process. Surplus summer energy can be stored for winter useage, and hydrogen can be efficiently utilized for co-generation of electric power and heat in a fuel cell, or can be burned in a modified (natural gas) range/ oven or in a modified (gasoline) internal combustion engine. Electrolyzed hydrogen is the cleanest burning fuel there is; the only emission is water vapor, and prototype hydrogen fueled internal combustion vehicles have actually cleaned the air as they run, by burning up some of the pollution in their intake air. Currently fuel cell cars are designed to be dependent on reformulating fossil fuels like gasoline & natural gas. By electrolyzing and storing hydrogen, zero energy homes could help to tackle the wasted energy and terrible pollution problems caused by our transportation systems. Trip reduction: Other essential transportation strategies include reducing trips by tele-commuting and by designing multi-use communities, where food production and residences are integrated with light manufacturing and shops, so that people can work and purchase most everything they need within walking & biking distance of home. Public transportation and car-sharing cooperatives can then supply the remaining transportation needs, sparing people the trouble and cost of having to personally maintain and insure vehicles. Such vehicles can run on alternative fuels such as H2, ethanol, or bio-diesel instead of fossil fuels. Ethanol and bio-diesel are biomass fuels refined from crops like corn and soy. Bio-diesel is made of esterified (salvaged waste cooking) oils, and can replace heavily polluting petroleum diesel fuel without requiring engine modifications. Bio-diesel is biodegradeable and non-toxic if spilled, and produces 68% less unburned hydrocarbons, 40% less particulates, 44% less carbon monoxide, and 100% less sulfates than petroleum diesel. Bio-diesel also lubricates engines, increasing their life. With engine modifications to preheat the fuel, cars can even run on straight vegetable oil! However, all of these biomass fuels are currently produced by agribusiness operations that intensively utilize petroleum for fertilizers and all cultivating, harvesting, processing, and transporting operations, so these fuels have such high embodied energy that according to some calculations they may be a net loss of energy, costing more fossil fuels than they replace when burned. While making use of used cooking oils for fuel may be more justified, it is clear that agribusiness farming methods are not sustainable as producers of alternative energy; in fact, even the food produced has farm more fossil fuel energy in it than the calories that can be recovered by eating it! Zero Energy Homes can help remedy these problems by using the home-site to cultivate organic foods, not grasses that require constant mowing with more fossil fuels. The following Lawrence Tech. University students participated in researching & developing these integrated energy systems for Zero Energy Homes: 2004 Competition Michael Oranchak Electrical Systems Paul Eland Plumbing Systems Steven Bugyi Building Materials Jessica Slomka Building Materials Anne Shishkovsky Heating Systems 2002 Competition Micheal Tyler Heating Systems Emanuele Arguelles & Christopher Hornbeck Building Materials Lisa Green Plumbing Systems Adam Dailide & Eric Schmidtt Electrical Systems For further information contact: Christina A. Snyder, Registered Architect (see contact info on the business card) proprietor of Sustainable Spaces (Appropriate architecture: solar heated, natural materials, co-housing, earth-sheltered, & whole systems designs) officer in Sustainable Systems, Inc. (Technologies & Resources for an Ecologically Sustainable Society: Design & Installation of Solar & Wind Energy Systems since 1989)

Copyright 2004 - Christina A. Snyder ES-13