Energy Efficient Technologies for Heating and Cooling

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There are many opportunities for reducing the environmental footprint of St. Lawrence University and meeting the goals outlined in the University’s Climate Action Plan. This report first presents types of geothermal heating and cooling and considers the feasibility of installing new geothermal systems on campus. Geothermal systems would reduce the demand on the existing heating system (for most buildings, natural gas-generated steam) and provide air conditioning to structures by utilizing the stable temperature of the earth. Expensive upfront costs make geothermal installations a serious financial undertaking, but the technology promises to pay for itself in the long term. Next, the report considers improvements to building envelope efficiency by repairing, replacing, or installing new windows. More efficient window glass and frames would also reduce energy needs for heating. Lastly, the report explores the environmental impact of different roofing materials and styles, keeping in mind monetary costs as well. Following these research findings are suggestions for university policies regarding geothermal, windows, and roofing.

Energy Efficient Technologies for Heating and Cooling

By: Mr. Hogan Dwyer

Executive Summary

I. Background

St. Lawrence University (“SLU”) has hired Wendel, a consulting company, to do an energy audit of the campus and create an Energy Master Plan. This plan will establish the current state of energy use on campus and outline a roadmap for improving energy use so that the University can meet its goals.

II. Introduction

The topics covered in this report are geothermal heating and cooling, windows, and roofing. Each is relevant to making the energy system at SLU more efficient in terms of carbon footprint and monetary cost.

III. Findings

Of the many types of heat pump systems, a closed-loop ground source best fits the heating and cooling needs of St. Lawrence University buildings. There are rebates and commercial partnerships available to institutions of higher education that make a new geothermal installation feasible.

Windows are important sources of passive heating via solar energy, but also contribute to energy inefficiency by leaking conditioned air to the outside. There are many aspects of windows to consider, including the number of panes, the type of frame, the type of glass coating, and the inclusion of warm edge technology. The measurements U-factor and Solar Heat Gain Coefficient are best for comparing performance between different windows.

Roofs have a significant energy cost over their lifespan, from the manufacture and transportation of materials to the envelope of a building to the recyclability of materials. There are many materials to consider for new roofs, none of which is perfect for every situation.

IV. Conclusion

I recommend that the University seriously consider installing new geothermal systems. Additionally, St. Lawrence should immediately address the windows in worst condition on campus. Finally, the administration and facilities should update policies regarding the installation of new windows and roofs to ensure that environmentally-friendly options are considered, if not required. The theme houses are obvious easy targets for these improvements, but I acknowledge the potential problems with making significant investments in these structures.

Background

An Energy Master Plan (“EMP”) is a roadmap for creating a more efficient, cost-effective, and robust energy system, including infrastructure (Fox). The EMP identifies goals and critical problems, and outlines the current status of the energy system (Fox). The EMP includes recommendations for how to achieve these goals and fix the existing problems (Fox).

St. Lawrence University has hired the consulting company Wendel to create an EMP because such a plan can help with two school priorities – meeting the Climate Action Plan, which includes the goal of net-zero greenhouse gas emissions by 2040, and decreasing costs of operations. The University received $112,500 from the New York State Energy Research and Development Authority (“NYSERDA”) to create the plan, plus $4,000 to hire interns to assist on the project (Kenmore).

Introduction

Due to the cold climate of the North County, heating is the greatest single source of energy consumption for St. Lawrence University. Along with being the largest area of consumption of fossil fuels, heating is also the most expensive aspect of SLU’s energy use (though not by as wide a margin). Thus, improvements to the heating system at SLU can significantly contribute to the goals outlined in the Climate Action Plan while also saving the University money in operations costs.

Geothermal is an up-and-coming renewable energy source in the U.S. Geothermal energy could not totally replace current energy sources of heat (natural gas) for the entire St. Lawrence University campus; there is simply too little heat available close to the surface in Canton, NY. However, installing geothermal systems would decrease reliance on nonrenewable fuels to keep buildings warm, while also providing energy-efficient cooling in the summer months. The cooling benefits of geothermal will become increasingly beneficial as the climate of northern New York State warms 3-10℉ in the next 70 years (DEC). Some may find the upfront costs of geothermal intimidating, but properly planned and installed systems pay for themselves in the not-too-distant future because they have such low operating costs (“Ground-Source Heat Pumps”).

Windows are relevant to heating as areas for air leakage and as opportunities to capture solar heat. However, window upgrades are not guaranteed to save money over the lifetime of the window, especially if current windows already have storm window panes (Garskof). Still, replacing windows in many situations will reduce a building’s annual carbon footprint.

Roofing is not an obvious topic for improving energy consumption on a college campus. However, installing, repairing, and disposing of roofs necessarily leaves an impact on the environment, as does the capability of a roof to retain heat in a building or reflect light from the sun. Any renovation of existing roofs or construction of new roofs should include explicit consideration of the energy footprint.

General Information

There are two basic types of heat pumps: ground source and air source. Ground source heat pumps utilize the heat of the earth (aka geothermal), while air source heat pumps simply adjust the temperature of nearby outside air. Ground source pumps are more efficient and have much better cold climate performance than air source ones (“Heat Pumps Potential”).

Open-loop ground source heat pumps use water from a nearby waterbody to transfer energy from the earth to the building air, while closed-loop systems pump fluid with a low freezing temperature through the ground and back into the building (“Ground Source Heat Pump”). The former is cheaper, but limited to areas with a waterbody that does not freeze in the winter, which St. Lawrence University does not have.

Because geothermal closed-loop heat pumps utilize wells that are dug vertically or horizontally in the ground, the geology of a site significantly impacts costs and energy-savings (“Ground Source Heat Pump”). As a result, digging a test hole at a potential site is absolutely necessary before deciding whether to install geothermal.

Dandelion

The Upstate New York startup Dandelion has drawn the attention of some members of the St. Lawrence community who would like to see the University install more geothermal capacity. Dandelion has brought down the cost of installing geothermal (for the company and its customers) by using state-of-the-art drills and software to install at multiple sites in a neighborhood at once (Hannun). The company’s other major innovation is offering zero-money-down financing, making their geothermal systems even more financially feasible (Hannun). While Dandelion specializes in residential homes, they may be open to retrofitting several buildings on the SLU campus, treating it like a residential neighborhood. Further, the University could partner with Dandelion to create a program that allows local residents to also have geothermal systems installed in their homes.

Rebates

Tax rebates are a common method for making renewable energy installations more financially-feasible. While the federal government is offering a major tax credit for geothermal systems until 2022, St. Lawrence is ineligible because the institution is tax-exempt. However, St. Lawrence can qualify for state rebates. The state energy development agency NYSERDA is offering up to $500,000 per building (no more than $1,000,000 to a single campus) for colleges to install geothermal systems. This rebate is available until Jan 1, 2019 or until funds run out (“NYSERDA Launches”).

According to NYSERDA, “[n]on-fuel switching installation of heat pumps for space heating and cooling has much smaller potential than for fuel switching” in terms of energy and monetary savings. Thus, they recommend looking into fuel switching alongside installing geothermal. Even so, the current low price of natural gas means that any new geothermal system that replaces or supplements a natural gas heating system would take a long time to pay for itself in energy-cost savings (“Heat Pumps Potential for Energy Savings in New York State (updated 2015)”).

Current Status

Kirk Douglas Hall is the only building on campus fitted with a geothermal heat pump system. The Kirk Douglas geothermal system was constructed alongside the building, so no retrofitting was involved. It is closed-loop and consists of 26 wells, ~450 ft. deep, buried underneath the main quad of campus. This site was tested for its geothermal potential in January of 2013. The below drill log might be useful when scouting for future locations of geothermal wells on campus.

In 2009, SLU hired Holabird & Root to perform a study of possible geothermal systems for the science complex (Bewkes, Flint, Johnson) on campus. The intramural fields adjacent to the complex were identified as ideal space for this type of system. Unfortunately, the current financial situation has rendered the recommendations unfeasible in near term (“St. Lawrence University Geo-Thermal Study”).

Windows

Some standard measurements of window glass help to compare options. The capacity of a window to lose heat is the U-Factor. A lower U-Factor is preferred in any climate where heating is a larger expenditure than cooling (“Selecting Energy Efficient New Windows in New York”). In a cold climate, like that of the North County, a good U-Factor is between 0.17 and 0.39” (Roberts).

Another measure is the Solar Heat Gain Coeffecient (“SHGC”), or the fraction of incident solar radiation admitted through the window (Holladay). Solar radiation is a renewable, passive source of heat that can significantly contribute to the heating of a building. In a cold climate, a higher SHGC is better, ideally somewhere in the range of 0.39 to 0.65 (Holladay).

Frames

The frame of a window impacts its capacity to hold heat in or conduct heat out of a building. Aluminum frames are poor insulators, especially when they lack a solid core. Vinyl frames with a solid core are more efficient, but vinyl is unfortunately not recyclable (“Vinyl vs Aluminum Windows”). Fiberglass windows are better than vinyl in appearance, paintability, strength (resistant to developing air gaps), and (possibly) insulating ability, but are also significantly more expensive (“Vinyl vs Fiberglass Windows”).

Glass Coating

One way in which new windows are more efficient than traditional windows is that many are manufactured with chemical coatings that impact the emittance of the glass. Emittance is the ability of a material to radiate energy (“What is Low-E Glass?”). Standard clear glass has an emittance of 0.84. Glass with a low-emittance (“Low-E”) glass coatings can have an emittance as low as 0.04 (“Window Technologies: Low-E Coatings”). A “passive” low-E coating maximizes solar heat gain in a building, while a “solar control” low-E coating limits the ability of solar heat to get into the building (“What is Low-E Glass?”). Windows with a high SHGC and a low-E glass coating are best for “heating-dominated climates” like that of Canton, NY (“Window Technologies”).

Double vs. Triple Pane

The most significant factor of window U-factor is the number of panes. Some older windows are single-pane, but most building construction today uses double pane windows. Double pane windows have a layer of gas between the panes, often argon that greatly adds to their insulating properties. Triple pane windows (three layers of glass) are sold by many manufacturers today, but they are not commonly used. Homesteaders from the Canton, NY area informed the author that triple pane windows are generally low quality and consequently do not actually provide efficiency benefits over double pane. Window manufacturer Fibertec, on the other hand, claims that “[w]hen comparing factors such as the SHGC, or U-values, there is an approximate improvement of 20-30% in a triple pane window’s energy ratings” (“Triple versus Double Pane Fiberglass Window”). Similar conclusions can be drawn from the published findings of the Efficient Windows Collaborate. Triple pane windows are also more resistant to condensation, which is especially relevant for cooler climates (Erdmann). For many, the price difference between double and triple pane is the deciding factor. Since prices for triple pane vary significantly, this evaluation must be done on a case-by-case basis (Erdmann).

Warm Edge Spacer Technology

“Warm edge windows” have an edge that conducts less heat than conventional aluminum-framed windows, improving energy efficiency and reducing condensation (“Warm Edge Technology”). Window spacer manufacturers claim that up to 80% of heat loss occurs at the edge of a window, and that spacers reduce heat loss at the external edge by up to 94% (“Warm Edge Technology”). These are likely optimistic figures; the window glass manufacturer FENZI Group claims that warm edge spacers reduce thermal transmission of windows by 10% (FENZI Group), and the U.S.-government sponsored Berkeley Lab says U-factors improve 6% in standard windows and 12% in high performance windows (Van Den Bergh).

Three types of spacers are available - flexible plastic or silicon, plastic/metal hybrid, and stainless steel (FENZI Group). In terms of performance, there is little difference between the three types, so other factors are usually taken into account when choosing which type to use (FENZI Group). There are many factors to consider (see www.fenzigroup.com/portals/0/pdf/News3_11_WarmEdge_ENG.pdf). One major factor is linear thermal expansion, which impacts the potential of a spacer to crack due to changes in temperature. Cracking compromises the benefits of the spacer. Homogeneous steel is best at resisting this thermal expansion (FENZI Group).

Current status

Windows on campus are predominantly double pane with vinyl framing. According to Assistant Director for Sustainability and Energy Management at SLU, warm edge spacers and low-E coatings are uncommon. No thorough record of windows on campus is available. A survey of some buildings near the campus center by the author of this report produced the following window counts:

  • Academic buildings: Piskor - 140, Carnegie - 92
  • Theme houses: 78 Park St. (Commons) - 51, 72 Park St. (Habitat) - 24
  • Dormitories: Dean - 263, Whitman - 216

To get a sense of potential savings by installing new windows in campus buildings, one can consider savings estimates for residential homes. ProVia windows states that for a “typical home” (Calculated by combining “an even mix of 1,700 sq. ft one-story and 2,600 sq. ft two-story homes with natural gas heat and electric air conditioning”) in Burlington, VT (which has a very similar climate to Canton, NY), expect savings of “$553 a year when replacing single pane windows [and] $197 a year over non ENERGY STAR qualified double-paned, clear glass replacement windows” (ProVia).

Roofing

General Information

Wallender; Bullard; “Roofing Shingles Vs. Cedar Shakes Costs”)

Low cost – asphalt (shingles and rolled), composition (fiberglass, asphalt, minerals)

Medium cost – standing seam metal, metal (steel, zinc alloy, aluminum), tile, faux slate (rubber), plastic polymer, wood shingles and shakes

High cost – slate, copper, “green” roof

Environmental Footprint

The expected lifetime of a roofing material is a significant determinant of its overall environmental impact. Asphalt shingles widely vary in quality and thus life expectancy, but generally last 15-30 years (Bullard). Metal and wood shakes and shingles last around 30-50 years (Bullard). Plastic polymer generally lasts at least 50 years, while slate can last 150 years (Bullard).

The durability of a roofing material impacts the life of a roof in places with inclement weather. Some manufacturers provide hail ratings for their roof products, providing a simple quantitative measure for comparing durability (Bullard). The durability of asphalt shingles is best determined by the manufacturer’s hail rating (Bullard). Plastic polymer, metal, and slate are known for their durability (Bullard). Wood is one of the least durable options, as it is not naturally fire-resistant and can be easily damaged by weather (Bullard).

Roofing materials also differ in insulating capacity. Wood shingles are about two times more insulating than asphalt (Bullard). Asphalt absorbs solar heat, while metal and plastic roofs reflect it, which is beneficial in warm climates (Bullard). Slate is extremely dense, which helps maintain a heating differential between the inside and outside of a building (Bullard). Green roofs also provide good insulation (“Other Types of Roofing that Can Save Energy”). Energy Star certified roof products reflect solar heat, so this certification is less relevant in colder climates (“Roof Products”).

Many roofing materials are heavy and transporting heavy materials requires more fossil fuel combustion than lighter materials. Using local materials reduces this environmental impact. Slate and wood are both local to the Northeast U.S. and thus can be locally sourced for buildings in Canton, NY (Bernard).

Another way to reduce the footprint of a roof is to choose recycled materials and/or materials that are easily recyclable. Recycled shingles, made from plastic, metal, or rubber, are a nice option (Chiras). Asphalt shingles are from nonrenewable petroleum, but they are usually recyclable (Bullard). Wood is not recyclable, but, since it biodegrades, wood roofing will not take up space in landfills after being replaced (Bernard).

A study looking specifically at the full life-cycle of concrete, asphalt, and stainless steel shingles in Ontario, Canada found that extruded concrete had the smallest greenhouse gas footprint, lowest cost, and highest energy efficiency of the three options (Loureiro et al.). Extruded concrete roofing appears uncommon in the U.S. (as garnered from internet searches).

Current status

The majority of buildings on St. Lawrence’s campus are asphalt shingles. Exceptions include Kirk Douglas (standing-seam metal), Sullivan Student Center (standing-seam metal), Johnson Science Center (EPDM), and large residence halls and academic buildings (EPDM). Some roofs are likely in need of repairs or replacement. Brown Hall has had leaking problems for years and Madill and Gunnison Memorial Chapel both have aging slate roofs.

Conclusion

Geothermal

In light of the success of the Kirk Douglas geothermal installation, I recommend that the University seriously consider additional closed-loop geothermal systems. The theme houses are promising candidates due to the small size of installation. Unfortunately, the University is likely unwilling to make that investment because of the possibility of demolishing and replacing the buildings in the near future. If the current trend in fire codes in New York State continues, sprinkler systems will soon be required in the theme houses. The SLU administration and Board of Trustees are more likely to advocate for rebuilding the aging buildings entirely than to put in expensive sprinkler systems. If demolition is a real possibility, then geothermal systems for the theme houses is a risky investment and thus not recommended. Nonetheless, the University should seek to implement geothermal for new building projects, particularly buildings that may be used in the summer and would benefit from capacity for cooling. The University should revisit the possibility of geothermal heating and cooling for the science complex, due to its proximity to the intramural fields, as well as buildings near the main quad.

Windows

My first recommendation is to perform a survey of the condition of windows for all buildings on campus, in order to have up-to-date information for making informed decisions. The survey should include both the types of windows in use and the current state of these windows. Second, I strongly recommend replacing deteriorated window/window frames before replacing windows in good condition. Two known locations of deteriorated windows are 17 College and 58 Park, but the survey may reveal other locations. Similarly, another immediate issue are the single-pane windows at 78 Park (Commons College). These should be replaced with double or triple pane as soon as possible. Upgrading to triple pane comes at more significant financial cost, so switching to triple pane from single or double is recommended only on a generous budget. To see the differences between specific window options, I recommend using data from the Efficient Windows Collaborative. Another useful resource for weighing options is the Berkeley Lab’s Windows and Daylighting Software, available at https://windows.lbl.gov/software.

As for window frames around campus - I recommend replacing deteriorated frames, like those at 17 College, with vinyl, which is already the standard on campus. Further, I recommend replacing all aluminum frames. Especially those with a hollow core, with vinyl. Known locations of aluminum frames are 25 Park St. (Beta), Commons Hulett and Jencks (Pub56), 13 University (ATO). If there are budget constraints, the University should re-do as many windows as possible with vinyl, rather than replacing a smaller portion of the aluminum frames with more efficient and costlier fiberglass. This is because there is little difference in insulating ability between fiberglass and vinyl.

Additionally, all new windows purchased for the campus should have high-solar-gain Low-e coating. “According to energy experts, the window manufacturers best able to handle requests for high-solar-gain glazing include ... Fibertec Windows of Concord, Ontario; and Thermotech Fiberglass of Ottawa, Ontario” (Hollaway). Luckily, these companies are not far from SLU, so transportation of windows should not be an outlandish expense. New windows should also have warm edge spacers. Based on the data provided by the FENZI Group, I recommend steel spacers due to their resistance to thermal expansion. However, I caution the University to check the quality of spacers before purchase, as the quality has a significant impact on the effectiveness of any type of spacer of lowering the U-factor (Van Den Bergh).

Roofs

Installing new roofing is a significant investment and will likely only occur as roofs deteriorate beyond repair. With that in mind, the University should set a policy for future roofing projects that considers sustainability. The first options that should be considered in any new project are a “green” roof, which can double as an educational space and attraction to prospective students, and slate roofing, which uses local materials, can be salvaged from previous uses, and is incredibly durable. If these are beyond the budget of the project or the strength of the building, the University should look into extruded concrete shingles, based on the LCA performed in Ottawa. Recycled metal is the next recommended option, as these are also durable and easily slide off snow, a common occurrence in the North Country. If all these materials prove infeasible, the University should look for recycled shingles (also applicable to roofing repairs of any existing roof). If possible, asphalt should be avoided and existing asphalt roofs should be recycled when being replaced. I recommend considering Brown Hall for a “green” roof, as this roof is both flat and in need of renovation. Further, I recommend repairing Madill and Gunnison Memorial Chapel, if needed, using slate.

References

Bernard, Murrye. “Sustainable Roofing Materials.” The spruce, 17 February 2017, https://www.thespruce.com/sustainable-roofing-materials-1821784.

Bullard, Laura. “6 Best Roofing Materials RanRanked by Durability and Cost.” House Method, https://housemethod.com/renovation/6-best-roofing-materials-ranked-by-durability-and-cost/.

Chiras, Dan. “Eco-Friendly Roofing Options.” Mother Earth News, June/July 2010, https://www.motherearthnews.com/green-homes/natural-building/eco-friendly-roofing-zmaz10jjzraw.

Department of Environmental Protection (DEC). “Impacts of Climate Change in New York.” 2014, https://www.dec.ny.gov/energy/94702.html.

Erdmann, Brandon. “Are Triple Pane Windows Worth the Investment?.” Angie’s List, 10 November 2015, https://www.angieslist.com/articles/are-triple-pane-windows-worth-investment.htm.

FENZI Group. “Summary Analysis Of The Different Families Of Warm Edge Spacers Available On The Market:  Guide to making an informed choice.” FENZI Group, www.fenzigroup.com/portals/0/pdf/News3_11_WarmEdge_ENG.pdf.

Fox, Kevin. “Energy Master Planning Perspectives and Best Practices.” Federal Utility Partnership Working Group Seminar, 18-19 May 2016, Cincinnati, OH. https://energy.gov/sites/prod/files/2016/05/f32/fupwg_spring2016_fox.pdf.

Gargaro, Kyle. “Geothermal Leadership Should Take a Curtain Call for Tax Credits.” ACHR News, 26 March 2018, https://www.achrnews.com/blogs/17-opinions/post/136795-geothermal-leadership-should-take-a-curtain-call-for-tax-credits.

Garskof, Josh. “5 Things to Know Before You Replace Windows.” Money, 3 May 2016, http://time.com/money/4282356/replace-windows-need-to-know/.

“Geothermal Clean Energy Challenge.” NYSERDA, https://www.nyserda.ny.gov/All-Programs/Programs/Geothermal-Challenge.

“Ground Source Heat Pumps.” NYSERDA, https://www.nyserda.ny.gov/Researchers-and-Policymakers/%20Geothermal-Heat-Pumps.

Hannun, Kathy. “Introducing Dandelion.” Google X Blog, 6 July 2017, https://blog.x.company/introducing-dandelion-2706eded169a.

Havardsson, Svavar. “Serious geothermal troubles for Reykjavik Energy.” Visir, 23 February 2017, http://www.visir.is/g/2017170229547/hverahlid-bjargadi-rekstri-a-hellisheidi.

“Heat Pumps Potential for Energy Savings in New York State.” NYSERDA, March 2015, https://www.nyserda.ny.gov/-/media/Files/EDPPP/Energy-Prices/Current-Outlook/Presentations/Heat-Pumps-Potential.pdf.

Holabird & Root. “St. Lawrence University Geo-Thermal Study.” 24 May 2009. PDF.

Holladay, Martin. “High Solar Gain Glazing.” Green Building Adviser, 31 July 2009, www.greenbuildingadvisor.com/blogs/dept/musings/high-solar-gain-glazing.

Kenmore, Abraham. “St. Lawrence recieves funding for energy master plan.” Watertown Daily Times, 16 September 2017, http://www.watertowndailytimes.com/news05/st-lawrence-receives-funding-for-energy-master-plan-20170916.

Loureiro, Daniel. “Design for the Environment/Residential Roofing Materials.” Wikiversity, 13 February 2018, https://en.wikiversity.org/wiki/Design_for_the_Environment/Residential_Roofing_Materials

“NYSERDA Launches $15 Million Initiative to Spur Ground Source Heat Pump Market to Help Combat Climate Change.” NYSERDA, 30 May 2017. https://www.nyserda.ny.gov/About/Newsroom/2017-Announcements/2017-05-30-NYSERDA-Launches-15-Million-Initiative-to-Spur-GSHP-Market.

“Other Types of Roofing that Can Save Energy.” Energy Star, https://www.energystar.gov/products/building_products/roof_products/other_types_roofing_that_can_save_energy.

ProVia. “Replacement Window Energy-Efficiency Calculator.” ProVia, https://www.provia.com/utilities-savings-calculator.

Roberts, Tristan. “How to Read (Those Darn) Window Performance Stickers.” Building Green, 30 May 2011, https://www.buildinggreen.com/news-article/how-read-those-darn-window-performance-stickers.

“Roof Products.” Energy Star, https://www.energystar.gov/products/building_products/roof_products

“Roofing Shingles Vs. Cedar Shakes Costs, Pros & Cons 2017-2018.” Roofing Calc, https://www.roofingcalc.com/roofing-shingles-vs-cedar-shakes/.

“Selecting Energy Efficient New Windows in New York.” Efficient Windows Collaborative, January 2016, www.efficientwindows.org/factsheets/New%20York.pdf.

“Triple vs. Double Pane Fiberglass Windows - The Pros and Cons of Double and Triple Glazing Fiberglass Windows.” Fibertec, 2014, www.fibertec.com/double-vs-triple-pane-windows/.

Van Den Bergh, S., et al. “Window Spacers and Edge Seals in Insulating Glass Units: A State-of-the-Art Review and Future Perspectives.” Energy and Buildings, vol. 58, 2013, pp. 263-280. http://wem.lbl.gov/sites/all/files/6122e.pdf.

“Vinyl vs. Aluminum Windows.” Fixr, 5 Janyary 2018, https://www.fixr.com/comparisons/vinyl-vs-aluminum-windows.

“Vinyl vs. Fiberglass Windows.” Fixr, 20 July 2017, https://www.fixr.com/comparisons/vinyl-vs-fiberglass-windows.

Wallender, Lee. “Basic Types and Cost of Roofing Materials.” The spruce, 17 February 2017. https://www.thespruce.com/basic-types-and-cost-of-roofing-materials-1822016.

“Warm Edge Technology.” Thermoseal Group, www.thermosealgroup.com/warmedge.

“What is Low-E Glass?” Vitro Architectural Glass, http://glassed.vitroglazings.com/glasstopics/how_lowe_works.aspx.

“Window Technology: Low-E Coating.” Efficient Windows Collaborative