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This article discusses how to make accurate measurement of the performance of passive solar heating systems, and the effect of air infiltration and the effect of incidental solar gains on passive solar systems. References to texts and guidelines for sizing thermal mass and using thermal mass are included.

Readers should also see PASSIVE SOLAR PERFORMANCE PROBE and SOLAR HOUSE EVALUATION and readers concerned with accurate calculation of the passive solar designs and similar energy savings assessments should see PASSIVE SOLAR DESIGN METHOD. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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Passive Solar Heat Performance Evaluation: the Impact of Air Infiltration & Incidental Solar Gains

• Passive Solar Heating Performance: Q&A on the Impact of Infiltration Losses & Incidental Solar Gains - PDF version, use your browser's back button to return to this page
• Q&A on Passive Solar Heat Loss & Gain Calculations - PDF version, use your browser's back button to return to this page

This article discusses how to accurately evaluate the performance of passive solar heating systems and the impact of air infiltration or incidental solar gains on passive heating performance. This material is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. The text below paraphrases, quotes-from, updates, and comments an original article, "Remember Thermal Mass?" (see links just above) from Solar Age Magazine and written by Steven Bliss.

How to make a more accurate estimate of the performance of passive solar heating systems

Question: The article entitled "The Best Passive Heating Data Yet" (Solar Age 7/83) seems to be an accurate overview of the Class B monitoring program. However the article does not clearly explain the limitations of the method of deriving the passive solar contribution to building energy demands.

Air infiltration rate skews passive solar gain estimates: While the auxiliary and internal gains of the passive solar heating system are directly measured, the solar contribution is arrived at indirectly by a subtractive technique. There is one potentially big source of error in this technique for estimating passive solar performance, namely the building's air infiltration rate. [See BLOWER DOORS & AIR INFILTRATION for added details about measuring a building's air infiltration rate.] Any error in estimating the air infiltration rate shows up as an error in the estimate of passive solar heat contribution.

Incidental solar gains can skew passive solar gain estimates: Incidental solar gains are another source of uncertainty in estimating the contribution of passive solar heating systems (or cooling systems) to a building's energy use. These include gains through non-south apertures (windows and doors) and the solar heating effect on conduction loads of the building's walls and roof.

For this reason, it would have been interesting to have included a few non-solar homes in the Class B program as controls. -- A.L., Madison WI.

Answer:

According to Joel Swisher at SERI, the one-time air infiltration measurements made concurrently with the coheating procedure were used to separate out conductive losses from air infiltration losses to obtain the building heat loss coefficient. The overall losses due to air infiltration over the heating season are extrapolated from the blower door and tracer gas results and corrected for average monthly wind speeds.

As for the incidental solar gains, Swisher agrees that this presents a problem but that achieving true scientific controls is not a realistic goal, particularly in inhabited homes. In the 1982-83 season Class B study, SERI monitored non-solar homes for comparison purposes. When the subtractive methodology was applied to these homes, solar gains in the 5 to 20 percent range were found.

This would indicate that some of the poorer performing solar homes monitored are not doing much better than a non-solar home, which is likely to be the case.

Question: Commodor 64 Solar Software

Were there any heat loss and heat gain calculation programs for superinsulation design that ran on a Commodore 64 computer back in the 1980's? - Ed Bond, Washington MA

Answer

Most software for passive solar design calculations in the 1980's would work just fine for superinsulated houses. Of the 50 programs for solar calculations listed in the 1985 Spec Guide, five were heat loss/heat gain programs that would run on the Commodore 64. They were available from Compusolar (Jasper AR), and Solarcon (Ann Arbor MI).

Another possibility in that era was Canada's HOTCAN program, devised specifically for highly insulated, tightly-sealed houses. It was available from Hotcan Energy Software, Ottawa, ON, Canada.

• Solar Systems Design Software: design tool for architects familiar with passive solar energy - see www.iklimnet.com/save/solarsystemsdesignsoftware.html
• Energy-10 Passive Solar Design Software: Mother Earth News - see motherearthnews.com/.../Design-Homes-Software.aspx
• SolArch Solar Architecture Design Software (shareware) - see www.kahl.net/solarch

House Heat Loss Guesstimating by Turning Off the Heat ?

Several readers have asked why we can't just turn down the heat, wait an hour, and observe the new temperature in a building to form an estimate of the building's rate of heat loss. This is an experiment worth performing, if simply to form a quick subjective view of how quickly a building cools off on a cold day. But there are some serious inaccuracies in the "just turn off the heat and wait" approach to estimating building heat loss.

Here are some things that would be missing from this experiment, and some of these factors are major influences on the variability of a home's rate of heat gain or heat loss. Just turning down the heat and measuring temperature loss in a building fails to measure, estimate, or account for these varying conditions:

• Wind velocity and wind direction. Wind has a very a big impact on air infiltration or exfiltration losses in buildings, and its impact may vary depending on its direction and thus which side of the building is pressurized (not all building sides may be equally leaky).
• Sun , or the absence of sun affects the extent of solar gain offsetting heat loss in a building
• Absolute temperature differences between indoors and outside at the time of the experiment. The greater the indoor and outdoor temperatures from one another, the faster the heat movement through the building.
• Building occupancy - people's activities, the number of occupants (people generate heat), whether or not people turn fans on or off, room doors are open or shut, ovens are on or off, clothes dryers, showers, and other appliances, have an impact on heat generated or consumed in a building
• Building indoor temperatures are not even - the location at which you are measuring temperature, say at the heating thermostat, is not likely to reflect temperatures throughout the building; some areas will be warmer, and some cooler than the temperature registered by the building's thermostat.
• Snow cover - presence or absence of snow, and its effect on blocking some roof vents, or in acting as an insulating material as well as a sunlight reflecting material
• Relative humidity - moisture levels impact heat transfer rates, but probably not as a major influence
• Rain - wet conditions may impact heat transfer rates

Overall it makes sense to have a general idea how a house behaves, such as from the simple "turn down or off the heat" experiment, but you cannot accurately characterize a building's rate of heat loss, nor can you know just how leaky it is, nor will you know where the major sources of heat loss are, with just the simple test of turning heat off and measuring temperature change at an arbitrary time.

These difficulties lie behind other efforts to characterize homes and their energy efficiency. See ENERGY SAVINGS in buildings for our collection of energy-savings articles for buildings, and also see SOLAR ENERGY SYSTEMS and if you are using wind power, see WIND TURBINES & LIGHTNING.

When the object is to save energy in the form of heating or cooling costs, attacking the major points of un-wanted heat loss (or gain in a cooling climate) are likely to be most cost-effective.

Some thoughts on setting priorities of attention are at ENERGY SAVINGS PRIORITIES.

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

Questions & answers on how to evaluate the performance of passive solar heating systems in homes.

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• Additional technical contributors & reference sources for this article are listed below.

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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

• Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
  
• Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
  Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in buildings, and other topics.
• Thermal Mass Pattern Book, Total Environmental Action, Solar Age Magazine, April 1981 (out of print).
• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Thanks to reader Bill Marinelli for discussing the house heat loss method of turning off the heat and measuring the temperature change. 10/4/2009
• Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
• Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
• Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
• The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the InspectAPedia Bookstore
• "Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
• "Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
• "Heat Exchangers for Solar Water Heating Systems", U.S. DOE describes the types of solar water heater heat exchange methods between the sun and the building's hot water supply
• "Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
• "Solar Water Heating System Maintenance and Repair", U.S. DOE
• "Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
• "Scaling and Corrosion in Solar Water Heating Systems", U.S. DOE
• www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850 is the base U.S. DOE website for these articles
• "Active Solar Heating Systems", U.S. Department of Energy, including
• "Radiant Heating Systems" U.S. DOE
• "Absorption Heat Pumps & Coolers", U.S. DOE
• "Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
• "Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
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