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 Mobile ViewACOUSTICAL SEALANT CHOICES AIR CONDITIONING & HEAT PUMP SYSTEMS AIR LEAK DETECTION TOOLS AIR POLLUTANTS, COMMON INDOOR BASEMENT CEILING VAPOR BARRIER BASEMENT HEAT LOSS ENERGY SAVINGS in buildings AFUE DEFINITION, RATINGS AIR BYPASS LEAKS AIR CHANGE RATE ACH HEAT SAVINGS AIR CONDITIONING HEAT PUMP SAVINGS AIR LEAK SEALING PROCEDURE APPLIANCE EFFICIENCY RATINGS ATTIC LEAKS, CONDENSATION & ATTIC MOLD COOLING LOAD REDUCTION by ROOF VENTS ENERGY AUDIT - How to Use a Free One ENERGY SAVINGS MAXIMIZE RETURNS ON ENERGY SAVINGS PRIORITIES ENERGY SAVINGS RETROFIT CASE STUDY ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE ENERGY SAVINGS RETROFIT OPTIONS ENERGY STAR PROGRAM ENERGY USE MONITORING GLASS vs HEAT MIRROR SOLAR GAIN/Loss HEAT LOSS in buildings HEATING COST SAVINGS METHODS HIGH MASS TRADEOFFS, HEATING vs COOLING HOUSE DOCTOR, how-to be INSULATION INSPECTION & IMPROVEMENT INSULATION LOCATION - WHERE TO PUT IT RADIANT BARRIERS REFLECTIVE INSULATION ROOF COLOR RECOMMENDATIONS Skylight Energy Efficiency SOLAR ENERGY SYSTEMS THERMAL MASS in buildings TIMERS for ELECTRIC WATER HEATERS VENTILATION, BALANCED HEAT COST SAVINGS WIND ENERGY SYSTEMS WINDOW EFFICIENCY Features & Ratings WOOD, COAL STOVES & FIREPLACES EVAPORATIVE COOLING SYSTEMS EXTERIORS of buildings FOOTING & FOUNDATION DRAINS FOUNDATION CRACKS & DAMAGE GUIDE BUCKLED FOUNDATIONS due to INSULATION? HEATING SMALL LOADS FRAMING DETAILS for BETTER INSULATION FRAMING DETAILS for DOUBLE WALL HOUSES FRAMING METAL STUD PERFORMANCE FREEZE-PROOF A BUILDING FROST HEAVES, FOUNDATION, SLAB GREEN BUILDING CONSTRUCTION CODES GUIDES GREENHOUSE DESIGN for SOLAR HEATING GREENHOUSE / SUNSPACE GLARE HEAT LOSS in BUILDINGS HEAT LOSS RATE CALCULATIONS HEAT LOSS DETECTION TOOLS HEAT LOSS INDICATORS HEAT LOSS PREVENTION PRIORITIES HEAT LOSS R U & K VALUE CALCULATION HEATING SYSTEMS COMBUSTION AIR for TIGHT buildings HEATING SMALL LOADS RADIANT HEAT RADIANT HEAT Floor Mistakes to Avoid RADIANT HEAT TEMPERATURES RADIANT SLAB FLOORING CHOICES RADIANT SLAB TUBING & FLUID CHOICES HOUSEWRAP INSTALLATION DETAILS HUMIDITY LEVEL TARGET ICE DAM PREVENTION INDOOR AIR QUALITY & HOUSE TIGHTNESS Air Pollutants, Common Indoor INSULATION IDENTIFICATION GUIDE INSULATION INSPECTION & IMPROVEMENT INSULATION LOCATION - WHERE TO PUT IT INTERIORS of buildings LEED GREEN BUILDING CERTIFICATION LEED Building Designation & IAQ MOISTURE CONTROL in buildings Nanomaterials Hazards NOISE / SOUND DIAGNOSIS & CURE NOISE CONTROL for HEATING SYSTEMS NOISE CONTROL for FLOORS NOISE CONTROL for PLUMBING NOISE CONTROL for ROOFS ODORS & SMELLS DIAGNOSIS & CURE PLUMBING SYSTEM INSPECT DIAGNOSE REPAIR STRUCTURAL INSPECTIONS & DEFECTS ROOFING INSPECTION & REPAIR ROOF VENTILATION SPECIFICATIONS SOLAR ENERGY SYSTEMS BLOCKBED RADIANT FLOORS - SOLAR DESIGN FLOOR, CONCRETE SLAB CHOICES FLOOR, CONCRETE SLAB POURED FINISH GLASS vs HEAT MIRROR SOLAR GAIN/Loss GREENHOUSE DESIGN for SOLAR HEATING GREENHOUSE / SUNSPACE GLARE PASSIVE SOLAR DESIGN KEY ELEMENTS PASSIVE SOLAR DESIGN METHOD PASSIVE SOLAR ENERGY MONITORING PASSIVE SOLAR FLOOR TILES, PHASE CHANGE PASSIVE SOLAR HEAT PERFORMANCE PASSIVE SOLAR HOME, LOW COST PASSIVE SOLAR PERFORMANCE PROBE PASSIVE SOLAR Roof & Window Overhangs PHOTOVOLTAIC POWER SYSTEMS POLYCARBONATE GLAZING REMOTE ELECTRIC POWER, PHOTOVOLTAIC ROCK-BED SOLAR HEAT STORAGE DESIGN SLAB INSULATION, PASSIVE SOLAR SLATE THERMAL MASS for SOLAR HEAT STORAGE SOLAR COLLECTOR AIR or GAS COLLECTION SOLAR COLLECTOR EFFICIENCY COMPARISONS SOLAR COLLECTOR FILMS SOLAR COLLECTOR OUTGASSING SOLAR COLLECTOR WOOD HOUSINGS SOLAR GAIN CALCULATION SOLAR HEATING SYSTEM DESIGNS SOLAR HOT WATER HEATERS SOLAR HOUSE EVALUATION SOLAR MODULE MANUFACTURERS SOLAR SHADES & SUNSCREENS SOLAR SHADES, LOW-E EFFECTIVENESS SOLAR WATER DISINFECTION SOLAR HOT WATER HEATERS SUNSPACE DESIGN for SOLAR HEATING SUNSPACE GLAZING for SUNTANNING STORM WINDOW INTERIOR STORM WINDOW PLASTIC CHOICES STORM WINDOW WEEP HOLES SUNGAIN, FILMS, LOW-E GLASS SUNSPACE GLAZING for SUNTANNING SWIMMING POOL SOLAR HEAT, INDOOR SWIMMING POOL SOLAR HEAT, OUTDOOR DIAGNOSIS THERMAL MASS in buildings STRUCTURAL INSPECTIONS & DEFECTS SUMP PUMPS GUIDE SWEATING (CONDENSATION) on PIPES, TANKS THERMAL EXPANSION of MATERIALS THERMAL MASS in buildings THERMAL MASS FLOOR SLABS THERMAL MASS in UPSTAIRS THERMAL MASS WALL DESIGN THERMAL MASS in HOMES - STUDY THERMAL MASS TRADEOFFS, HEATING vs COOLING THERMAL TRACKING & HEAT LOSS VAPOR BARRIERS & CONDENSATION in buildings ATTIC CONDENSATION CAUSE & CURE BASEMENT CEILING VAPOR BARRIER CONDENSATION or SWEATING PIPES, TANKS CRAWL SPACE VAPOR BARRIER DEW POINT CALCULATION for WALLS DEW POINT TABLE - CONDENSATION POINT GUIDE FELT 15# ROOFING, as HOUSEWRAP/VAPOR BARRIER HOUSEWRAP AIR & VAPOR BARRIERS HOUSEWRAP INSTALLATION DETAILS HOUSEWRAP PRODUCT CHOICES HOUSEWRAP at SILLS, SOLES, TOP PLATES HUMIDITY LEVEL TARGET MOISTURE CONTROL in buildings RAIN SPLASH-UP SIDING DAMAGE VAPOR BARRIERS & AIR SEALING at BAND JOISTS VAPOR BARRIERS & CONDENSATION in buildings VAPOR BARRIERS & HOUSEWRAP VAPOR CONDENSATION & BUILDING SHEATHING WATER BARRIERS, EXTERIOR WOOD SIDING FLASHING DETAILS VENTILATION in buildings MOISTURE CALCULATIONS MOISTURE METER STUDY MOISTURE PROBLEMS: CAUSE & CURE ROOF VENTING ENERGY SAVING DETAILS ROOF VENTING NEEDED? 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This article discusses solar houses: this solar energy payback analysis explains how to evaluate the extent to which your house makes use of solar energy & renewable energy, discussing solar fraction, heat loss coefficient, and auxiliary heat use in buildings. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Our photograph of solar collectors and water tank (below) show a typical home solar hot water system in Guanajuato, Mexico. For better accuracy in calculating solar energy gains also see PASSIVE SOLAR HEAT PERFORMANCE. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. How Solar is My House?
"How Solar is My House? Gauging passive solar performance can be confusing unless you understand the measures used" - - links to the original article in PDF form immediately below are followed by an expanded/updated online version of this article.
This article is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Gauging passive solar performance can be confusing unless you understand the measures used. A lot of numbers get tossed around in evaluating, comparing, and marketing solar homes. Just as a bucket of water can be described as either 40 percent empty or 60 percent full, different numbers can rate the same house while giving very different impressions. What is Solar Fraction? What does Percent Solar Mean?In passive solar homes, an often misleading, though widely used index of solar performance is the solar fraction in any of its various forms. In a retrofit project, a percent solar calculation is relatively straightforward, since a reduction in fuel use, all other things being equal, can be attributed to solar energy. Of course, if conservation measures are taken first, as they should be, the savings from conservation must be accounted for. When calculated from the new, lower heating load after tightening up the house, the percent solar savings will be higher than if it were derived from the original heating load. For most purposes, it is wiser to quantify the savings in BTUs, or their dollar equivalents, and forget about percentages altogether. in new construction of solar homes the numbers get more slippery still. A solar firm is often asked to design a home that is, say, 50 percent solar "like our neighbor's house." The designer must ask, "fifty percent of what?" One method of computing a solar fraction, now in disfavor, compares the house to itself if the sun never shone or to itself it if were flipped around to face the north. It counts as solar gain all the heat that actually escapes out the south glazing from whence it came. In large aperture designs, this loss thro8ugh the south glazing is substantial, often accounting for one quarter to one third of the building's gross heat loss. The resulting solar percentage might appear high but offers no clue about the thermal performance or the wisdom of the design. Calculated this way, a leaky house with oversized south glazing is likely to attain a high solar fraction and high fuel bills as well. Definition of Solar Savings FractionThe Los Alamos National Laboratory developed another solar percentage figure for use in estimating solar and auxiliary contributions in passive solar design. The Solar Savings Fraction (SSF) represents the ratio of the useful solar contribution to the net heating load of the building, that is, the load assuming the south aperture is thermally neutral with no losses and no gains. While the SSF constitutes a more conservative and realistic index of solar performance, it should be used only to compare one system to another in the same house or two different houses with the same net heating load. For marketing purposes, one might want to compare the thermal performance of a solar versus a non-solar home of comparable size and insulating value. Still, it would be more accurate to say that the solar home will produce a 30 percent savings in fuel costs compared with the conventional home rather than to say that the house is 30 percent solar. Definition of Heat Loss CoefficientThe number frequently used to compare the thermal effectiveness of the building shell is the annual BTU heat loss normalized for the square footage of the building and the heating degree days. The heat loss coefficient of a standard, contemporary home typically ranges from 8 to 10 BTUs/(degreeF-day ft2). This number is useful for design purposes, but tends to show large aperture passive buildings as poor performers because of the high losses through the glazing. To make sense of this number you must know what assumptions were made. Was nighttime insulation used? What were the air change rates and thermostat set points in the building? Were the data measured, or calculated, or obtained by some combination? Auxiliary Heat Use in Solar Home EvaluationFor most purposes the bottom line in quantifying thermal performance of a solar or other energy-efficient home design is the auxiliary heat use. How much is it going to cost to keep warm? To make comparisons easy, the annual fuel use in BTUs is often normalized for building area and heating degree days. Auxiliary heat requirements from 1 to 3 BTUs/(degreeF-day ft2) were reported in the mid 1980's from top-performing monitored houses. To interpret these figures, the assumptions, measurement techniques, and conditions (internal gains, thermostat set points) must be known. The building's shape and size also affect this measure, since these parameters affect the ratio of floor area to surface area of the building's shell. If height is held constant, larger buildings tend to perform better than smaller ones - at least on a square-foot basis. Incremental Costs for Adding Solar Features to a HomeSince costs ultimately decide the fate of most building projects, economic analysis must be done carefully. Few people buy a pair of shoes strictly on the basis of cost efficiency (dollars spent vs. steps taken). Appearance, comfort, and fit are just as important. In the housing market, people purchase homes, and living space, not just heating systems. The gross cost of adding glass and mass should not be counted as the incremental cost of solar if the homeowner enjoys the added views, light, and masonry surfaces. If a greenhouse is used as living space, the added space should be factored into any cost or performance per-square-foot calculations. In passive solar and superinsulated homes, the real cost of the "solar" or "conservation" package is the incremental cost added to the project to attain a certain energy savings. For a multi-use conservation or solar feature, the calculation of an incremental cost must take into account the costs of the building components replaced by energy-related components. For example, a masonry storage wall may replace a conventional wood-frame/drywall partition or it may replace a wall with elegant (expensive) hardwood detailing. Similarly, the real cost of adding an airlock entry might equal the simple cost of adding a trimmed doorway and a weatherstripped door - if the owners wanted a mudroom anyway. Choosing a reference cost for a wall that is never built is somewhat arbitrary. If the homeowner desired a brick accent wall anyway, the incremental cost of adding thermal storage might be zero, involving merely putting the wall in the right place. As a general rule, any passive solar feature will appear more cost-effective if it replaces an essential building component and adds an architectural amenity to the home. At the least, it should not represent an architectural cost, that is, an eyesore. Solar Home Payback AnalysisPartly as a response to energy-saving marketing, clients often focus on the payback of a solar project to the exclusion of more traditional concerns. The comfort, enjoyment, and added space that is provided may equal or surpass that of the den they added, or bathroom they remodeled last year at a similar cost. More importantly, the economic value added to the house is roughly equal to the dollars spent on the project - whether solar or not. In a very real sense, the payback is immediate and recoverable upon the sale of the house. Looked at this way, the energy savings that accrue, whether they are the result of reduced fuel bills or a freely-heated living space, could be considered frosting on the cake - and in this case, a gift that keeps on giving. Conclusions about Solar Home EvaluationWhether you are a designer, buyer, or seller of solar homes, it behooves you to understand the numbers you use. For marketing purposes, a projection of fuel costs addresses the energy issue squarely. It's a rare consumer who is not painfully aware of the cost of keeping warm. Some builders have gone so far as to guarantee an upper limit on fuel bills, agreeing to kick in any overage. Lending institutions (in the 1980's) began to mix a home-energy-use factor into their mortgage brews, thereby qualifying lower income borrowers for energy-efficient homes. For the designer, thermal and solar performance numbers are indispensible tools for achieving desirable and predictable results - to know what's achievable and what makes sense economically. And finally, for the consumer, when all is said and done - education is the best defense, or as we say in commerce, "caveat emptor." Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Questions & Answers regarding this article. Ask a Question or Search InspectAPediaHTML Comment Box is loading comments...
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