solar heat gain factor table

IMHO the typical USA under-insulated home with oversized fossil fuel heating and AC is the failed design in need of our greatest attention. [4] Factors such as color, tint, and reflective coatings affect these properties, which is what prompted the development of the shading coefficient as a correction factor to account for this. Remember when choosing the coefficient for each window: If you live in a warm climate, choose windows with an SHGC closer to 0, In colder climates choose a window with an SHGC closer to 1, When reading an Energy Star or NFRC tag, they report the SHGC on the WHOLE window, including the frame, not just the center point of the glass. /TT4 19 0 R I have not been able to find glass at local Vermont suppliers with both low U values and high SHGC. You might have to order windows, rather than just the sealed double or triple-pane IGUs. hb```g`` ,@Q ?>K kwlsEGyGG#h`@ %X Watch out: other very important factors need to be considered in arriving at an accurate picture of solar heat gain through windows. /ArtBox [0.0 0.0 612.0 792.0] 0000049380 00000 n E a9` zY ZOy 7!K?e. Passive solar heating is a design strategy that attempts to maximize the amount of solar gain in a building when additional heating is desired. The whole window; meaning the window frame and glazing (glass) or: Center of the glass; meaning it only includes the SHGC for the the glass, Coatings bounce heat and light out or inside the home to increase or decrease light and heat that enters the house, Glazing comes in single or multiple layers to keep mother nature outdoors. The most important factors are budget and energy efficiency. 0000040162 00000 n I saw that a lot: first, the designer included too much south-facing glazing; then the homeowners installed interior shades to cut down on the glare. Note that the photo at the top of the page shows a passive solar house from 1982. (13) Design roof overhangs, patio or deck coverings, and landscaping to preserve unobstructed sunshine in winter, and shade west- and east-facing windows during summer months. This Solar Value Index uses south window glazing net BTUs of heat per day per square foot of glazing, and multiplies by the Heating Degree Days and by the price of electricity. Glazing in conditioned spaces has a solar heat gain coefficient of less than or equal to 0.40, or has an overhang with a projection factor equal to or greater than 0.30. [For those unfamiliar with the terminology U-factor (inverse of R-value), which measures the rate of heat losses through that window to the cold outdoors. 0000027861 00000 n Kansas City and cities along the northeast coast also look promising for wintertime daylighting, space heating, and PV. 0000037935 00000 n But this angle represents a brief moment and most of the arch of the sun's path, while still influencing the solar gain, is much lower during the periods of time on both sides of noon. 0000021224 00000 n West-facing windows are a bigger concern, needing shading of some sort during hot late afternoons. endstream endobj startxref Our energy use for the area is almost off the chart lower than other homes mainly due to passive solar design at not much/or no higher cost than conventional. Adjustable awnings, curtains, window shades, exterior shutters, or even deciduous trees, or other shading methods, can provide more flexible and more complete shading than a fixed roof overhang. MIT Press, 1992. 0000008169 00000 n So if you have your heart set on high-solar-gain glazing, you should keep looking. When integrated over the wavelengths of solar short-wave radiation, it yields the total fraction of transmitted solar energy across all solar wavelengths. 0000052240 00000 n 0000009623 00000 n For example, in triple glazed windows, SHGC tends to be in the range of 0.33 - 0.47. 0000020026 00000 n Some important factors for the amount of solar heat gain are the: Table 2 shows the amount of solar heat gain per square foot of window glass for the cities listed previously. What Is Solar Heat Gain Coefficient? E Its likely that if the floors were a dark color, the house would have performed slightly better, but glare likely would been a much greater problem. He led a course in Sustainable Architecture for Lifelong Learning Collaborative, an adult ed organization in Providence, R.I. Bob has degrees in applied mathematics and in philosophy from Brown University, and psychology from UCLA. The solar gain is not stored near the windows to be lost at night but is captured through an open door into the main building. In passive solar and solar-tempered homes, typically there are more or larger windows facing south, and fewer or smaller windows facing other directions. (2) To exploit solar heat gains from windows in mid-winter (and minimize heat gain in summer), we can, as much as practical, locate more and larger windows facing within 15 degrees of south, and try to reduce the glazing on walls facing north and west (and perhaps east). be adjusted for thermal lag and time delay. You must be a magazine subscriber to access this feature. 0000018332 00000 n It comes down to three ways windows are improved with the use of glass technology, coatings and gases: Review in-depth information on energy efficient glass for your window replacements. 0000059651 00000 n Column 8 shows (with red negative numbers) the average January daily heat loss per square foot of glass (assuming glazing is rated R-5 or U=0.2, with window coverings adding some insulation during nighttime hours to attain U=0.15). The higher the number, the more light transmitted without adding excessive amounts of heat. A product with a low air leakage rating is tighter than one with a high air leakage rating. Unlike the upstairs, the first floor has a tiled, concrete floor (with large amounts of thermal mass) to absorb heat to radiate later, stabilizing interior temperature fluctuations. 0000045710 00000 n Light-to-solar gain (LSG)is the ratio between the VT and SHGC. UA Table = (U-factor from Table C402.1.4 or C402.4) x Area B = Sum of the (FL Dif) values for each distinct slab on grade perimeter condition of the building thermal . Daylighting and heat gain are desirable especially in cold winter-heating-dominated climates of the northern U.S. Incredibly, south-facing windows gain about fifteen times as much light and solar heat gain as north-facing windows in December and in January. So overhangs tend to keep the house cooler in the Spring as well as late summer. Basically, any window frame material is going to insulate well whether it is wood, vinyl, aluminum clad wood, or fiberglass. Therefore, the sun is shining on your south-facing walls and windows during wintertime. Modeling thermal mass performance seems difficult or approximate. It can range in value 0000060982 00000 n SHGCs range from approximately 0.70 for single clear glass to 0.31 for low emissivity glass (toned or coated glass). Daylighting is good, and solar heat gain is good in winter and not good in the hot summer. Worth remembering that those early-'80's houses are one of the main reasons we are having such fruitful discussions today! Intro to roof overhangs and shading Designing roof overhangs to avoid shading windows at noon on Dec 21st results in some shading at the top of the window at noon in January, February and November, when you still want that sunlight (though at 10AM or 2PM you won't be shading the top of the window since the sun is lower on the horizon at that time of day). 0000034703 00000 n [3] Since the quantities compared are functions of both wavelength and angle of incidence, the shading coefficient for a window assembly is typically reported for a single wavelength typical of solar radiation entering normal to the plane of glass. David, comes through a product. 8 , fgMPW'J[2JM2~&e@l3-9wDWj2bXec&X.!X095 xref 0000060877 00000 n %PDF-1.3 % Engineering-wise, this makes sense, but not for human perception. The other two factors related toSolar Heat Gain Coefficient when choosing replacement windows are: Window Joe went to look at a home recently that required different solar heat gain coefficients based on the two factors above. 0000008611 00000 n That's good for south-facing windows, because in the cold winter, you want the sun beating in your windows, warming your home's interior (and providing daylighting too). Glass Color . 0000010399 00000 n The U-factor, Solar Heat Gain Coefficient (SHGC), Visible Light Transmit-tance (VT), and air leakage rate for all manufactured fenestra-tion products shall be determined by a laboratory accredited by a nationally recognized accreditation organization, such as the National Fenestration Rating Council. 0000035419 00000 n Passivhaus is known for having lots of foam insulation below slab floors (8" to 10" thickness might be common) to keep within their limited heat loss budget. 0000008360 00000 n 0000040918 00000 n 0000040295 00000 n The lower the U-Factor, the better the window insulates. 0000031934 00000 n It was an experiment, and I can now, after 5 years, say it exceeded my expectations. (7) East-facing windows provide sunlight early in the morning when a house interior is the coolest, so they are more useful than west-facing windows. I think that the key design criteria for passive solar involves locating and sizing windows, thermal mass, and doing sufficient insulating and air-sealing so that only solar heat gain can provide most of the home's wintertime space heating, yet avoid summertime overheating. Only 22 cities are examined, and only in the northern U.S. Solar Heat Gain Coefficient, or SHGC, is the amount of solar radiation, or heat, that passes through windows into the home In other words, SHGC tells you how well the windows block the sun's heat from coming inside An SHGC closer to 0 means that little solar heat is let in An SHGC closer to 1 means more solar heat is let in Figure 1 depicts the grouping of northern U.S. cities by solar heating potential, as listed in Table 1. (16) Reduce the amount spent on larger and more complex supplementary space heating systems to allocate funds for more insulation, air-sealing measures, and more energy-efficient windows and doors. 0000022755 00000 n But overall, if values are changed to reflect other information sources, a similar overall pattern will emerge, unlikely changing any of the main conclusions of this modeling effort. typically fall in a range between 0.1 and 0.3. 0000020266 00000 n For double glazed windows SHGC is more often in the range of 0.42 - 0.55. I'm old enough to remember the passive solar homes of the 1970s and 1980s. 0000025050 00000 n That's good for south-facing windows, because during the hot summer, you don't want the sun beating in your windows, causing solar heat gain in your home's interior. 0 Locations needing a lot of heating, that have high electricity prices, and that have good net solar gains, get higher scores. The specific microclimate of any building location should be used in building design, rather than the rough approximation of solar potential shown in this map or Table 1. One shading method is to have roof overhangs stick out above the south-facing walls enough that they cast shade on south-facing windows in late August. >> 0000008689 00000 n Vertical fenestration that is located on the street side of the street-level story only, provided that. *dPeU|A#rJ]dwiuEZDu-KIVc"*f}*%,?bAL& GH D. Thank you for sharing your thoughts, Bob. I enjoyed the bright sunlight and warm interior temps mid-winter too. Is this correct? Well-insulated and airtight energy-efficient homes are likely to use electric minisplit heat pumps, resistance electric heat, or radiant electric heat as backup or alternatives for passive solar or solar tempered space heating. Yet, the living room and the sun room, get a little bit more but welcome heat, while the bedrooms on the top floor facing west get a wallop in the afternoon. For the months of December and January, the sun is low on the horizon during midday. 0000013076 00000 n Lack of sufficient thermal mass was likely a common problem too (resulting in large interior temperature fluctuations in winter, i.e., overheating). Extending them would have an effect on the top of the window but not extend very far down the window. (Plus the low utility bills and resilience in case of power outages.). Get building science and energy efficiency advice, plus special offers, in your inbox. Meanwhile, the solar heat gain through east- and west-facing windows is more intense due to the greater amount of solar radiation around June (for the northern hemisphere). Subscribe to receive updates from Energy Saver, including new blogs, updated content, and seasonal energy saving tips for consumers and homeowners. 0000014163 00000 n 0000041109 00000 n http://www.cardinalcorp.com/products/coated-glass/loe-180-glass/, PPG Industries manufactures two low-e/high SHGC products: Sungate 500 and Sungate 100 window glass with SHGC of about 0.7. Shading Coefficient (SC) SHADING COEFFICIENT (SC) is the ratio of the solar heat gain through a fenestration product to the solar heat gain through an unshaded 1/8-inch-thick clear double strength glass under the same set of conditions. For south-facing windows, designing overhangs to maximize mid-winter solar gains yet reduce summertime solar gains is useful, but more of a detail than a major contribution to passive solar heat gain management. 0000050463 00000 n I used Google Sketchup, the free version, to roughly model shadows on my soon to be built house. 0000011938 00000 n Thank you Bob for sharing this very thorough article! HUrF}WoND{_2#J$v:>-%uE">Tw[~Aq}$,N.7n@0v]Av8`o Note (in the last two columns, #9 and #10) that Denver has better net solar heat gains than anywhere else in the list. While you may like having free heat in the winter, it might be too much of a good thing in the summer months if you live in a climate zone with extreme seasons. Same for east or west-facing windows, early or late in the day, respectively. 0000026181 00000 n /C2_2 13 0 R A new, affordable but well-insulated window (with cellular blinds used at night) would attain values similar to those listed in the table. 0000045996 00000 n Metal is an excellent conductor not only of electricity but also of hot and cold air. First, thanks for sharing your many helpful comments and ideas on GBA articles on Q&A. 0000019351 00000 n And if you design for best wintertime performance, you will get undesirable solar heat gain in the late summer. 0000022887 00000 n 0000024359 00000 n Is this really necessary? This is covered in the U-Factor article, but it is worth mentioning because it also impacted the solar heat gain coefficient for the Northern Zone. The amount of solar gain a space experiences is a function of the total incident solar irradianceand of the ability of any intervening material to transmitor resist the radiation. I used double-pane windows, and four large double-pane IGUs (for site built fixed windows). Cost of electricity varies over time as well. 643 0 obj <> endobj 0000019003 00000 n Long stretches of overcast days produce large heat losses through large windows, with minimal solar heat gains to compensate. Will New Windows Save Money On Energy Bills? In buildings, excessive solar gain can lead to overheating within a space, but it can also be used as a passive heating strategy when heat is desired.[1]. Most insulating glass units in windows sold in USA are closer to SGHC=0.3 for avoiding excess solar gains in summer. , 0000010168 00000 n Fortunately, retailers will tailor their stock to homes in your area. /ExtGState Solar, wind or other renewable energy source supplies not less than 80 percent of the energy for service water heating. Note from the cells highlighted in yellow: During the winter, from November through February, one south-facing window would produce more light and solar heat gain than the total gain of three windows facing north, east, and west, respectively. 0000044969 00000 n The window area is 400 sq ft and the secret is low mass. At the bottom of the table, the yearly gains are totaled for south-, north-, east-, and west-facing windows. (9) Design for the local climate, considering winter temperatures (heating degree days and winter design temperatures), cloudiness (or average percent of available sunlight in January), and costs of electricity (or fuel for heating). hbbd```b``A$cXDDr@3N,IF@L@s&00Lg`` ) 0000052866 00000 n 0000023459 00000 n Remember, always rely upon the NFRC and Energy STAR ratings to tell you exactly how effective the replacement windows you might buy will work in your home and climate. Glare would not be the reason shades were drawn at that hour for south-facing windows in any home, unless someone needs a dark interior, like trying to sleep late. transmitted portion of the solar heat gain coefficient is given by:[4], T Window specifications and climate data for your specific construction project are more important than the generalizations made here. {\displaystyle T(\lambda )} Even for east- and west-facing windows, losses exceeded solar heat gains except for Denver. A passive solar building's south-facing windows need good solar access from 9 or 10AM through 2 or 3PM midwinter, when the sun is low on the horizon. = Other internet data sources may include somewhat different data, but the patterns of data would lead to similar conclusions. , 0000040580 00000 n 3M's Sungain Film brochure mentions "Solar Input," which represents the shading coefficient times 0.87. Consequently, south-facing windows capture far more light, and thereby produce far more solar heat gain, than windows facing other directions. 0000037411 00000 n / %PDF-1.6 % << Is it, say, the angle of the sun at 11:00am and 1:00 pm? Terms | These tables give the solar data needed for designing an air conditioning system by either the traditional hand- calculating procedures or digital computer techniques. Next seven cities are all located in the northeast, along the Atlantic coast (Providence; Hartford; Boston; Portland, Maine; New York City; Philadelphia; and Concord, N.H.). The lower the SHGC, the less solar heat it transmits and the greater its shading ability. 0000042979 00000 n To optimize the heat gain through windows heavily insulated shutters will change all the numbers. 0000021486 00000 n Shading analysis of the building site's landscaping and adjacent buildings is critically important. I would also like to hear more about your/GBA community's thoughts on thermal mass and its relationship with solar heat gain. 0000050694 00000 n << However I don't believe they sell sealed glass units retail, just to window manufacturers. 0000053840 00000 n 0000047056 00000 n 0000057926 00000 n Higher SGHC=0.7 could be used on south-facing glazing to increase solar gains, but still get decent heat loss performance (e.g., Cardinal LoE-180 glass with SHGC=.69, U=26). Beyond climate region, there are some other factors in place that impact how SHGC will affect your life. What about glare? 0000019574 00000 n The overall solar energy gain is expressed by the solar gain factor g and is given by [Fig. >> /C2_0 15 0 R 645 0 obj<>stream For January solar heat gain from south-facing windows, the highest numbers are triple the lowest. /Resources 0000040500 00000 n The Southern Climate Zone has hot summers and mild winters. The thermal mass also will radiate stored heat when the sun isn't shining to keep interior temperatures from getting too cool.) into a home or building through a product. 0000047743 00000 n HW=oFX72X?A(l5 $?ASN* southernwalls see about 6" of sun exposure at the bottom of each window. The first five columns list each month of the year, and the daily solar heat gain per square foot of window glazing for windows facing south, north, and east, or west , and the average heat gain over the four window directions. Designers and builders can use higher solar heat gain windows on south-facing windows and higher R-value (lower U-factor) windows on north, west, and east-facing windows to further increase solar gains and reduce heat losses overall. In June, the sun is closer to overhead at noon, so south windows have far less solar heat gain. 0000021316 00000 n The designer should distinguish between the maximum solar load on a surface which is important for load calculations against an average value that the surface experi-ences. 0000035512 00000 n product blocks heat from the sun. Go . The National Fenestration Rating Council (NFRC) operates a voluntary program that tests, certifies, and labels windows, doors, and skylights based on their energy performance ratings. 2225 0 obj <> endobj 0000039633 00000 n Which design principles from the 1970s are worth retaining, and which should be discarded? This article notes the importance of using south-facing windows to capture warmth (and natural lighting) in winter, yet not suffer as much heat gain in summer (vs. west and east-facing windows). This coefficient accounts for the time lag between the outdoor and indoor temperature peaks. Great article! AL rates 0000047504 00000 n %%EOF 3500 Thanks for your comments. . The window orientations were limited to true south, east, west, and north. 0000012727 00000 n It is defined as the ratio of solar radiation at a given wavelength and angle of incidence passing through a glass unit to the radiation that would pass through a reference window of frameless 3 millimetres (0.12in) Clear Float Glass. 0000025712 00000 n This information in an aid in choosing the best direction and size of windows facing different directions. 0000027723 00000 n 0000031018 00000 n Other factors like style, finish, hardware, and function can also play a big part in the curb appeal and aesthetics of your home. Since heat gain is desirable during January for homes in northern latitudes, locating windows on the south side is far more beneficial than other orientations, assuming that that south window is not blocked from getting sunlight from obstructions during midday. /CS0 8 0 R We don't have extensive open space, placing furniture near windows and glass doors. Very helpful. 0 If you started shopping prior to January 1, 2016, then you might notice some of the windows you were considering buying no longer carry the Energy STAR sticker. Since I built that passive solar house back in the 1980's, there were no low-e windows available. In Table 6, note that light from west or east facing windows in summer, is about the same as south-facing windows mid-winter. 0000007296 00000 n Here, is the wavelength of radiation and is the angle of incidence. %%EOF Remember, the solar heat gain coefficient ranges between 0 and 1, the lower the number the less heat (radiation) is let in, the higher the SHGC, the more heat is let in. Solar heat gain coefficients are expressed as decimals from 0.00 to 1.00.