Industry technical experts recognized the limitations of SC and pushed towards SHGC in the United States (and the analogous g-value in Europe) before the early 1990s. 645 0 obj<>stream I would also like to hear more about your/GBA community's thoughts on thermal mass and its relationship with solar heat gain. >> A product with a low SHGC rating is more effective at reducing cooling loads during the summer by blocking heat gain from the sun. Long stretches of overcast days produce large heat losses through large windows, with minimal solar heat gains to compensate. A Very helpful You can maybe start to imagine how you might have different window needs if you are in Texas or Florida as compared with Rhode Island or Massachusetts. b +{roFw@Qv.Pb=Z"3>!06&rhS8EnVw\/bw +rt|bSL6),W=^O *cAL^u'MH} ^D;p.'*{6OQYbS2tAD2)T=z 0!"Tl,|Am5q/Up+XwNM7}!/;yy6Q@=vjI~}krN>+e_CC-ccB: p7B . https://www.greenbuildingadvisor.com/homes/passive-solar-home-1980s 0000055691 00000 n 0000051944 00000 n Intro to roof overhangs and shading 0000011785 00000 n Since I built that passive solar house back in the 1980's, there were no low-e windows available. 0000042979 00000 n %PDF-1.3 % << In practice though, most g-values will range between 0.2 and 0.7, with solar control glazing having a g-value of less than 0.5. /Thumb 2 0 R I used pleated or cellular shades at night, and sometimes insulating shutters to reduce heat loss during snowy days. /ColorSpace Different types of glass can be used to increase or to decrease solar heat gain through fenestration, but can also be more finely tuned by the proper orientation of windows and by the addition of shading devices such as overhangs, louvers, fins, porches, and other architectural shading elements. These tables give the solar data needed for designing an air conditioning system by either the traditional hand- calculating procedures or digital computer techniques. A product with a high SHGC rating is more effective at collecting solar heat during the winter. 0000038067 00000 n From this ordering of cities by average mid-winter solar heat gain potential, we may begin to conclude: Next, we need to explore solar heat gains and losses in more detail for each metro area. The NFRC (National Fenestration Council) describes Solar Heat Gain Coefficient (SHGC) as: Solar Heat Gain Coefficient(SHGC) measures how well a ( 0000023071 00000 n 0000033945 00000 n In January, one south-facing window produces more solar heat gain than the solar gains from three windows facing north, east, and west for all 22 cities. Yes the analysis assumed SHGC=0.5 for all windows, which wasn't stated earlier in the article. Subscribe to receive updates from Energy Saver, including new blogs, updated content, and seasonal energy saving tips for consumers and homeowners. Columns 1-3 lists the same city data, in the same order, as Table 1. << That's where your observation about winter sun angles before and after solar noon is most critical. Same for east or west-facing windows, early or late in the day, respectively. From what I've read, slab depth beyond 4" thick doesn't get you much additional heat storage or dampening of temperature fluctuations in direct gain passive solar designs. Additionally, the homeowner may choose to augment solar heat coming in the windows with exterior awnings or interior window blinds or curtains. Figure 1 depicts the grouping of northern U.S. cities by solar heating potential, as listed in Table 1. Is it possible to determine an appropriate period of shading for summertime sun that also allows peak wintertime solar gain? 0000023760 00000 n Cost of electricity varies over time as well. Windows orientation or direction (e.g., facing south, east, west or north); Solar Heat Gain Coefficient (SHGC), the solar gain potential, usually 0.35 to 0.7, or 35% to 70% for efficient new windows; and. 0000038387 00000 n So I'd recommend designing overhangs for minimal shading mid-winter, and not worry so much about summer (for winter-dominated northern climates). (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. It ranges from 0 to 1 and refers to the solar energy transmittance of a window or door as a whole, factoring in the glass, frame material, sash (if present), divided lite bars (if present) and screens (if present). (3) Overall, unobstructed south-facing windows gain more heat than they lose during mid-winter in almost all U.S. climates. In a room, its likely you have light coming from multiple windows on different sides of the home. I understand that some passivhaus builders pour 8 inch thick concrete slabs for heat distribution from solar gains. 3M's Sungain Film brochure mentions "Solar Input," which represents the shading coefficient times 0.87. 0000011246 00000 n 0000050787 00000 n Range: 0-1 Look for: Low numbers Air Leakage measures how much air will enter a room through a product. 0000057378 00000 n {\displaystyle E(\lambda )} HUrF}WoND{_2#J$v:>-%uE">Tw[~Aq}$,N.7n@0v]Av8`o 0000047504 00000 n East- and west- facing windows gain far more heat than south-facing windows during the summer months, until late August. So overhangs tend to keep the house cooler in the Spring as well as late summer. 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. This raises the question: Could a passive solar home be built successfully and cost-effectively in other cold, northern climates climates more challenging than the sunny but cold climate of the Rocky Mountain Front Range? Too much south-facing glazing can make a home very uncomfortable and unpleasant in February and March. 0000034811 00000 n 0000050182 00000 n 0000022435 00000 n He was a psychology professor for five years, and a software and web site usability and design engineer for 20 years. Passive solar design is a key element of creating resilient homes, Cold-climate glazing is surprisingly hard to find. In January, south-facing windows always account for more solar gain than east + west + north combined. 0000011938 00000 n 0000049162 00000 n How do visible light transmittance, and shading coefficient relate to one another? SHGC ratings are used to help in quantifying the energy efficiency of windows and skylights. For some locations, the heat is more pronounced and longer in duration than the short months of frigid temperatures with little snow. There is more total sunlight shining in summer (June to August in the northern hemisphere) than mid-winter (December to February). The other climate zones underwent more stringent Energy Star qualifications that took effect on January 1, 2015. To minimize this and reduce cooling loads, several technologies exist for solar gain reduction. startxref is thus the portion of absorbed and re-emitted energy across all assembly components beyond just the glass. You want to shade your south-facing windows from the sun to avoid solar heat gain. The NFRC label can be found on all ENERGY STAR qualified window, door, and skylight products, but ENERGY STAR bases its qualification only on U-factor and solar heat gain coefficient ratings, which are described below. 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. >> 0000052866 00000 n << To maximize wintertime interior daylighting and solar heat gains, south windows should be larger in size or in number than windows facing other directions. Overcast winter conditions are more likely for cities west of large bodies of water. For windows, skylights, and glass doors, a U-factor may refer to just the glass or glazing alone. hbbd```b``A$cXDDr@3N,IF@L@s&00Lg`` Choosing a window frame material that does a fine job of insulating against thermal (heat) transference is one way to reduce the solar heat gain coefficient. -- "Passive solar" requires sunlight to shine on thermal mass (e.g., concrete slab floors, masonry walls, large containers of water) so that most of the solar heat gain is stored in the thermal mass, to avoid overheating the interior air during the day. = The solar heat gain coefficient of the skylights. 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). 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. endstream endobj 701 0 obj<> endobj 702 0 obj<> endobj 703 0 obj<>stream 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.). It is easier to maximize wintertime solar heating in some climates than others. /MC0 0000019489 00000 n In the United States, The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE)[2] and The National Fenestration Rating Council (NFRC)[3] maintain standards for the calculation and measurement of these values. endstream endobj startxref Note (in the last two columns, #9 and #10) that Denver has better net solar heat gains than anywhere else in the list. These properties are the transmissivity "T" , absorptivity "A", emissivity (which is equal to the absorptivity for any given wavelength), and reflectivity all of which are dimensionless quantities that together sum to 1. South-facing windows gain about 3.5 times as much light and solar heat gain per square foot than either east- or west-facing windows in December and in January. 0000054516 00000 n (11) Make adjustments to window locations, sizes, and glazing options (SHGC and U-factor) to optimize natural lighting and solar heat gain in winter and summer seasons. 2252 0 obj <>/Filter/FlateDecode/ID[<83C04542AF040F4C833A7DC507AC7EE9><9975C82B1E27C340964B5370330FFFE6>]/Index[2225 55]/Info 2224 0 R/Length 124/Prev 708226/Root 2226 0 R/Size 2280/Type/XRef/W[1 3 1]>>stream 0000031213 00000 n 0000034904 00000 n The manufacturers may have improved the materials that made up the frames or the coatings to the glass to meet demands. [4] Though the shading coefficient is still mentioned in manufacturer product literature and some industry computer software,[6] it is no longer mentioned as an option in industry-specific texts[2] or model building codes. 0000037104 00000 n 0000010399 00000 n (17) Cities and towns can promote energy efficiency and public health by incorporating zoning laws and incentives that provide building lots with south-facing solar access, and protect solar access for existing buildings. 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. [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. 0000033707 00000 n In colorado I found Milgard and Pella had high SHGC, low E options. Only their (1) net south-facing glazing heat gains; (2) winter heating degree days; and (3) cost of electricity, would be needed to create a more comprehensive list. So for a traditional Cape style home, the small overhang doesn't shade the windows much in any season. 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. SHGC is influenced by the color or tint of glass and its degree of reflectivity. 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. 0000059249 00000 n While the U-Factor can take any value, in general for windows it ranges from 0.20 to 1.20. Uncontrolled solar gain is undesirable in hot climates due to its potential for overheating a space. Thermal Radiation b. Earth-Sun geometry Thermal mass may be used to even out the fluctuations during the day, and to some extent between days. Finally, Anchorage, Alaska, along the far northern Pacific coast, with by far the lowest solar heat gain. trailer Seattle, Washington. The window orientations were limited to true south, east, west, and north. This simple computation provides a metric to rate locations for the value or cost-effectiveness of passive solar or solar tempered winter space heating. Even if it is not possible to build a classic passive solar home in other climates, solar gains can be used for substantial solar-tempered wintertime home heating. 0000018740 00000 n When designing a building, the solar heating potential can be computed. Table 2 lists solar gain data for the 22 northern U.S. cities. West-facing windows gain that heat in the afternoon, usually during the hottest time of the day, making west-facing windows particularly undesirable unless well shaded. (10) Calculate solar heat gains when designing, and compare to heat losses. The lowest numbers are about double the highest. When too much heat is let in by an inappropriate SHGC and too much heat is trapped in by an incorrect u factor, you have what is commonly known as the greenhouse effect. 0000011477 00000 n The larger the roof overhang, the more important it is to do shading analysis, as it makes a big difference in the size of the shadow. 0000040713 00000 n 0000022215 00000 n Its no accident that Cape style homes appeared in winter-dominated climate up north; and southern plantation style homes with big windows, big overhangs and wide porches in the cooling dominated climate of the southern US. Ive been under the impression that south facing super insulated walls are more efficient in the winter, than the solar gain potential if replaced by windows. In summary, there are many things to consider when choosing the best window replacement options. 0000022755 00000 n Glare can be an issue for south-facing window walls around noontime during the winter, for west-facing windows late in the day (especially during summer), and for east-facing windows in summer. Solar heat gain coefficients are expressed as decimals from 0.00 to 1.00. 0000041841 00000 n They also recommended ceilings be white, to reflect light back to the floor. (If interested, see interior photos in this GBA article: I see lots of examples where people try things without "doing the math" beforehand. Those panels closed during the 15 hour nights of winter make far more difference than thermal mass or solar gain. I think glare would be a bigger problem if you were sitting in direct sunlight, not at the other end of the room. Solar transmittance is used to compare different types of glass. 0000050604 00000 n >> 0000056162 00000 n Most manufacturers worked to retrofit products to meet the new and more stringent standards. Watch out: other very important factors need to be considered in arriving at an accurate picture of solar heat gain through windows. /GS0 3 0 R 0000043411 00000 n 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. 2023 The Taunton Press, Inc. All rights reserved. (For Denver, east- and west-facing windows do have a net solar heat gain of 25%, which is positive, but only one-third as much as south-facing windows 75% net gain.). 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]. Not that I watch it much (or at all) during daytime), but still :) The link to the original Q&A article in PDF form immediately below is preceded by an expanded/updated online version of this article. We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. 0000043952 00000 n For the months of December and January, the sun is low on the horizon during midday. 0000011092 00000 n Solar heat gain (SHG) describes the way radiation from the sun is turned into heat. SOLAR RADIATION Solar radiation has important effects on both the heat gain and heat loss of a building. North latitude location (degrees north of the Equator). /Rotate 0 And it would shade some of the top of the window during January, February and November, when you'd prefer full sun. Fortunately, retailers will tailor their stock to homes in your area. F N The last column (#10) shows the percent of net heat gain compared to the heat gain for window glass. Again, it would reflect off the floor and other surfaces to diffuse the light. South-facing windows also have increased solar heat gain in late August to consider. how glass is used in the house design. These cities are geographically dispersed, with more cities located in the northeast and Great Lakes regions. 0000026181 00000 n Is there anything else other than minding where you put your furniture? 0000010168 00000 n 5. 0000012014 00000 n Even though south-facing windows have much higher solar gain during December and January than other orientations, the situation in summer has changed significantly due to changes in the position of the sun at midday. All of the 22 northern U.S. locations examined previously exhibit the same pattern of superior winter energy performance for south-facing windows. We pull tight insulating shades over the windows in the evening to reduce heat loss. Will New Windows Save Money On Energy Bills? Single Pane SHGC Double Pane SHGC Glass Block SHGC Metal Operable Clear . 5.8.2.2 Labeling of Fenestration Products . 0000009935 00000 n 0000058978 00000 n 0000051599 00000 n For those trying to figure out directions and overhang sizes and angles, the best tool is the Solar Pathfinder and many new apps like that which show all angles and azimuths of the sun for any location throughout every day of the year. Your homes climate, orientation, and external shading will determine the optimal SHGC for a particular window, door, or skylight. 0000011169 00000 n North windows get almost no direct sunlight, so would be less of a problem. The advantages of south-facing windows become even greater when losses are incorporated. Note that the photo at the top of the page shows a passive solar house from 1982. n 0000053085 00000 n 0000048853 00000 n 0000039175 00000 n Davor, Only 22 cities are examined, and only in the northern U.S. 0000036366 00000 n 0000042410 00000 n 0000023459 00000 n 0000011323 00000 n Considering the dynamics of glass and solar energy, the simplest formula experts use to calculate the value for solar heat gain coefficient is: Solar heat gain coefficient = portion of solar energy transmitted + portion of absorbed solar energy that is emitted inside. The "solar input" in the 3M Sungain film brochure, also known as the solar heat gain coefficient, is the solar transmittance modified to account for re-radiated heat. The Northern Energy STAR Climate Zone recently underwent changes it its criteria of what constitutes a window that insulates well. My goal was to build an energy-efficient home using materials that cost no more in total than typical home construction. E. Which type of glazing is optimal for a given project depends My great aunt used to live with family in Oregon, but had to live elsewhere during the overcast winters there. 0000010245 00000 n Map. 0.80 0.70 0.70 . However, if shades are needed to reduce overheating mid-winter, likely there's a design error of over-glazing with west or south-facing windows. The National Fenestration Rating Council(NFRC) is an independent organization that tests windows and doors for the Energy STAR program. {\displaystyle F(\lambda ,\theta )=T(\lambda ,\theta )+N*A(\lambda ,\theta )}. /Metadata 9 0 R Window Joe says to always keep it simple and follow NFRC and Energy STAR ratings that are suggested for your specific county. 2279 0 obj <>stream 0000032190 00000 n Being in a solar home definitely cures the winter blues and Seasonal Affective Disorder (SAD). Even during winter afternoons, additional space heating may not be needed by the afternoon. 0000033574 00000 n David, Two cities along the Pacific northwest coast (Portland, Oregon; and Seattle). /TT3 20 0 R 0000049380 00000 n 0000054894 00000 n /Type /Page 0000010861 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). You might be able to find or make untreated triple pane glass units, or even try to use three layers of glass for your own site-built fixed window if you are looking for the ultimate cheap solution. The window area is 400 sq ft and the secret is low mass. Even if there's only one south-facing window in the room at mid-day in winter, light will bounce off the window sill and floor and diffuse the light, especially at the other end of the room. (12) Consider different glazing for windows facing different directions. NFRC U-factor ratings, however, represent the entire window performance, including frame and spacer material. 0000022599 00000 n Balcomb, J.Douglas, editor. Basically, any window frame material is going to insulate well whether it is wood, vinyl, aluminum clad wood, or fiberglass. 0000031802 00000 n 0000018276 00000 n We designed it to be in east west direction, and on the south side we have a large 2.5m wide doors. {\displaystyle N*A(\lambda ,\theta )} Unfortunately in the US, most windows sold are low SHGC.