Volume 9, Issue 7 - July-August 2008

Climate Control

The Fenestration Industry Debates the Question: Is One Low-E Right for Every Region?

As you read this article there’s a very good chance that the price of oil has reached—or possibly exceeded—$150 a barrel. There’s a good chance you’re sitting in a room where the AC is blasting. 

You’re in the fenestration industry so there’s also a good chance you know solar control windows can help reduce those cooling costs. That’s great for cooling-dominant climates, but what’s about those areas affected most in the winter when heating costs are soaring?

To help offset those high heating costs some companies are promoting passive solar glazing products. Some window and glass companies that strongly favor this approach say passive solar glazing (with a higher solar hear gain coefficient [SHGC] than solar control products) can help consumers reduce their total heating costs. What more could you want—solar control for cooling regions and passive solar for heating regions. It’s not quite so simple, as most national window companies sell solar control windows primarily, meaning a low U-factor and a low SHGC, creating what some have called a “one-size-fits-all” market. Not everyone, however, agrees the one-size plan is the best path to take, and they are putting forth an effort to change that mindset.

Research and Data
Research and testing has shown that in Northern climates windows with a higher SHGC (approximately, one that’s greater than .4) can offer better energy cost savings compared to the more traditional windows. Why? Because the products can collect, store and distribute efficiently the free heat from the sun, in turn reducing the demand for space heating.

Consider a study conducted by the National Research Council Canada-Institute for Research in Construction (NRC-IRC) in partnership with Pilkington. The study compared glazing in twin side-by-side houses in Ottawa, Ontario. One house was fully glazed with low solar gain (LSG) glass (typically a soft coat/sputtered product) and the other with high solar gain (HSG) glass (typically a hard coat/pyrolytic product). The experiment took place during both summer and winter months and ultimately showed that differences in the way the glazings managed solar gains impacted energy performance more so than the differences in their U-factors. Results showed that “while both the LSG and HSG windows provided greater energy cost savings than the conventional windows, the HSG window produced the best overall energy cost savings for Ottawa and all Canadian locations that were modeled.”

If research shows that homeowners in heating-dominant climates, including the northern United States, can indeed benefit from the use of low-E, high-SHGC glazing, why isn’t it being used more? 

Does One Size Fit All?
Many window companies offer a standard glazing option rather than different glazing packages tailored to different regions of the country. Chris Barry, director of technical services with Pilkington North America, a member of the NSG Group, says this is done out of convenience. 

“It’s simplicity of manufacturing. It’s easier for the manufacturer to sell a universal, one-size-fits-all window to customers in both Miami and Montreal,” Barry says. “It’s easier for the manufacturer, but it’s wrong,” he adds, saying it needs to be about getting the right window to the right place.

Joe Hayden, senior certification engineer with Pella Corp. in Pella, Iowa, agrees. “Inventory control is one reason some manufacturers choose to go with a standard product line,” he says. “If you have one type of product line to offer versus two then it’s less inventory to manage.” He says Pella doesn’t offer a standard glazing, as the glazing selected for a given product depends on many factors such as energy-efficiency needs, structural (wind-load resistance) needs, the size of the product, whether or not safety (e.g. tempered) glass is needed, the personal desires of the customer, etc. 

“In general, I would say our most common offering is insulating glass with a low-E coated outer pane, a clear inner pane and argon-gas fill in between.” The company also offers a high SHGC option: a triple-glazed unit with a pyrolytic low-E.

While Andersen Corp. in Bayport, Minn., uses low-E or high-performance Low-E4® glass, which is a low U-Factor/medium solar gain product, as its standard glazing, Mark Mikkelson, manager, code regulatory and technical marketing, says the company does produce windows with a high SHGC via special order, along with other options such as a low solar gain product called High-Performance Low-E4 Sun. Mikkelson says the reasons for offering a standard glazing are often dependent upon the manufacturer’s business model and how their products are sold and/or distributed.

“As a window manufacturer, when you look at the products you’re going to stock on-the-shelf you want to go with a glazing option that’s good for that particular climate zone,” says Mikkelson. “So if you’re going to do that with a standard glazing you want one that will fit most of those applications. That’s why, for the most part across the country, we [Andersen] have gone with one standard option.”

Cardinal Corp., headquartered in Minneapolis, produces a variety of glass products and services a large portion of the residential window industry. The company manufactures a range of sputter-coated low-E glass—including one with a SHGC as high as .70. In fact, Jim Larsen, director, technology marketing, says the very first sputter-coated glass his company produced in 1982 was a high SHGC low-E.

“We produced it in volume for almost ten years, but eventually all of our customers moved away from that toward the solar control characteristics of our low-E2 product for two reasons,” explains Larsen. “One was the rapid expansion of SHG requirements in the south and the need to have a product that could comply with the market there. The second reason goes back to customer concerns that there were always complaints against the high solar gain products for lack of comfort.” 

As far as other reasons why high SHGC products have not been used more in the United States, Herb Johnson, product manager, primary and coatings, with AGC Flat Glass North America, says much has to do with the fact that Energy Star® has not required a minimum SHGC for northern climates.

“I think because of the way the Energy Star program has evolved there’s been somewhat of a loophole for the heating-dominant climates when it comes to solar heat gain,” says Johnson. “When [Energy Star] says “any” SHGC for the north the result is that U-factor alone has become the sole criteria. As companies have developed lower and lower U-factor products they’ve been able to ignore solar heat gain since it did not matter for Energy Star certification. The problem with that comes along with the SHGC? that’s dropping. So you get this one-size-fits-all approach where manufacturers have been able to fit the bill with a U-factor number.”

Rob Struble, manager of business communications growth initiatives and performance glazings with PPG Industries, agrees.

“The products that have a high SHGC also often have a U-factor that doesn’t fall in line with the direction [in which] Energy Star appears to be moving,” says Struble. 

Tom Culp with Birch Point Consulting in LaCrosse, Wis., says companies that sell more on a regional basis versus a national basis do tend to sell the glass most appropriate for that specific region.

“With the consolidation of the window industry, though, there are just more big companies and not as many working on a regional basis,” says Culp.

All Weather Windows in Edmonton, Alberta, is a window manufacturer that operates within one specific area: Canada. Aaron Latimer, national marketing manager, says his company is working to communicate to consumers the importance of having the right glass for their windows, given that the country is in a predominantly cooling climate.

“We’re focused on the fact that consumers will become more aware of data [such as the NRC’s research] and we need to promote and sell windows that actually produce lower overall energy efficiencies for their homes,” says Latimer. “Our message is to sell the high-SHGC product in the Canadian marketplace. Even under those circumstances we’re only recommending the low-E SHGC product when it faces the direction of the sun and the higher SHGC product for the balance of the home.”

Dividing Lines
Those who favor a high SHGC for cold climates do say such a product can reduce heating costs greatly in the coldest months. 

“The primary advantage of a high SHGC is the ability to take advantage of the free heat from the sun,” says Johnson. “In northern climates, because of the fact that you have a higher number of heating days [than cooling days] your year-round annual energy savings are greater by taking advantage of high solar gain.”

Culp agrees.

“With a hard coat low-E [pyrolytic] the U-factor might be somewhat higher, but looking at overall performance, you may be trading on U-factor a bit, but you’re gaining the use of the sun,” says Culp, who adds that pyrolytic low-E glass still has a lower SHGC than clear glass. “In addition to hard coat low-E glass, there are also some very good soft coat low-E products designed for northern climates with higher SHGC,” Culp adds.

Likewise, Latimer says the message his company is working to bring to consumers is twofold.

“The first is energy savings and the advantages of improved energy efficiency in the home,” Latimer says. “Second is the reduction of greenhouse gas emissions. So while the consumer is saving energy by purchasing the right glass he’s also reducing his overall environmental footprint.”

Passive solar design is a key element when it comes to harnessing the heat from the sun. This design method allows a home’s windows, walls and floors to collect, store and distribute solar energy in the form of heat in the winter and reject it in the summer. Passive solar heating is most effective when the entire house is designed specifically for that purpose. According to the Whole Building Design Guide, “it’s best to incorporate passive solar heating into a building during the initial design … taking into consideration local climate conditions, such as temperature, solar radiation and wind, to create climate-responsive, energy-conserving structures that can be powered with renewable energy sources.” The Guide also points out that depending upon the climate, passive solar design might include orienting the windows to the south and shading the windows [with an overhang or deciduous trees] to avoid summer sun.

Because of the additional considerations that go into passive solar design, some people say it can be a deterrent to homeowners.

“The fact that more is involved in passive heating is part of the reason why it hasn’t taken off as much. Thermal mass (see sidebar on page 24 for a definition of thermal mass as well as the DOE‘s other four elements of passive solar design) is a big issue as to why it doesn’t work for typical houses,” says Larsen, who explains that thermal mass can be an extremely expensive building component. “If I had an old building with a lot of thermal mass or I was willing to pay to put thermal mass in a new building design, then that’s a great opportunity to utilize passive solar gains. But without that you end up with hours and hours and hours of overheat.”

“What we’ve found with the high-SHGC products typically used is that not everyone designs right for passive solar and when you don’t, we’ve found that customers won’t be as comfortable as they would be with our standard low-E glass products,” says Mikkelson. “Also, with replacement windows you don’t really have the opportunity to change the addition of overhangs, and proper orientation of the house in ways that are important for passive solar design.”

Hayden agrees.

“Typical homeowners probably aren’t going to understand how to best design a passive solar home. It really involves someone with a little more knowledge of thermodynamics and the nuances of optimal home heating and air conditioning,” he says. 

A complete design may be the best way to ensure a house fully harnesses passive heating, but any house can have passive heating gains. 

“As long as you operate the house correctly you will get passive heating gains,” says Marc LaFrance, technology development manager, Building Technology Program, within the Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy. “Everything we do in the energy sector, and every type of equipment or appliance or heating system has variability based on the building characteristics and the occupants; it’s a variable type of consumption.”

Likewise, Culp points out that while some people in the industry say a great amount of work is necessary to ensure comfort from passive heating, it’s just not the case.

“It’s true that you will see a lot more in savings if you do [a total passive design], but all the modeling done in test homes show that even without those features a high-SHGC low-E window still saves more energy,” says Culp. “Comfort is important, but it’s secondary if we’re really trying to promote energy savings.”

And Larsen says he’s certainly not against solar gain in the north and agrees that it can be beneficial. The issue, he says, is knowing the trade-off. 

“The trade-off is that you really need an active homeowner to get the true benefit of the passive solar gain without the discomfort penalty,” he says. “You have to practice opening and closing the windows during the swing season, opening and closing your blinds and certainly looking at having some building attributes that are more advantageous toward using passive solar gain.”

He continues, “You must always go for comfort first. One of the premises and the reason why high SHGC didn’t stay a fixture in the northern marketplace is because a typical house ended up sacrificing on comfort.”

Latimer has a slightly different take on comfort.

“I live in a climate where there is snow on the ground five months out of the year, so comfort in our mind is avoiding a draft from the cold; not intense heat from the sun,” he says, adding that his company, too, sells the comfort factor to customers, but it does so by way of the frame and not the glass. “It will reduce air infiltration to help make the room more comfortable.”

For Struble, the true benefits of passive solar design may still be a bit murky.

“There’s no doubt that people use a [high SHGC] product to try and capture some passive solar heating, though how much of that they are really able to harness is something for which I think there’s a lack of any real measurement. For example, if the house is not designed to capture the solar gain … a lot of that passive solar benefit is negated simply by the design of the house.”

Potential Changes 
While a SHGC value is not required currently for windows to meet Energy Star criteria, the DOE is working to revise the requirements, including the addition of a minimum SHGC for certain zones. Should the Energy Star criteria be revised, all of the glass and window companies interviewed for this article say they offer the products and the capabilities to meet those requirements; not everyone, though, sees the changes as necessary.

“As we [Pella] see it, the Energy Star right now seems to be at a pretty optimal position. We’d be better off to focus our efforts and energies on putting programs or incentives in place to get people to replace their single-pane windows,” says Hayden. “There’s a great deal of single-pane windows still in the housing stock today—our estimates are billions of square feet. And if we put efforts and energy into getting those products replaced with current Energy Star-qualifying products the savings could be significant and I think we could achieve much better savings going that route than by trying to tweak the criteria to drive new technology.”

Mikkelson adds, that he, too, is uncertain the change is necessary. “Those of us who believe in the lower SHGC products as the best standard glazing are trying to advise the DOE that customers are not asking for that type of glass in widespread demand,” he says. 

In response to concerns that DOE is proposing to require SHGC in the North, Rich Karney, Energy Star program manager, says the DOE is simply proposing to establish criteria that will give appropriate credit for higher solar gains.

“The belief that DOE plans to require high solar gain is a misconception created by the preliminary table we put out in the spring that listed a SHGC minimum in the North,” says Karney. “Many stakeholders failed to notice the footnote that stated DOE would also consider trade-offs if the energy savings analysis supported them.” He explains that the energy savings analysis does support trade-offs in the northern two zones (see map on page 23). 

“DOE expects to set criteria in these zones relative to an aggregate annual energy performance metric that depends on U-factor and SHGC. The criteria will not advantage either high or low solar gain products, but will enable both those windows with moderate U-factors combined with moderate to high SHGC as well as windows with lower U-factors and low-solar gain to qualify.”

Johnson says he thinks such a change is good.

“It’s great that Energy Star is evaluating the program and appears to be recognizing the benefits of solar heat gain in the northern areas. I think they’ve been very outspoken in that what they are trying to do is push the envelope to help homeowners conserve energy,” Johnson says. Assuming such changes occur, the impact on the residential window industry could be significant. For example, to achieve the necessary SHGC some manufacturers may choose to manufacture triple-glazed units, which not all companies offer at this time. Hayden says manufacturing a triple brings with it a lot of changes, such as accommodating another lite of glass in an existing product.

“The sash has to be a little larger and the hardware a little stouter to carry the extra weight,” says Hayden.

But triple glazing also brings with it thicker, heavier glass and, potentially, less visibility.

“With all the focus on lowering U-factors and the debate of high or low solar gain, it is important to keep visible light transmittance in mind because people like to see out of their windows,” says Mikkelson.

Companies may also choose to simply add to their glazing packages by making a high-SHGC glass readily available.

If that’s the case, one adjustment some window companies selling on a national level will have to take into account is a little more awareness of their shipping and distribution. This will help them ensure the right windows are sent to the right places. Hayden says since his company does not offer a standard glazing, adjusting to the possible revision would require very little if any changes. 

“Since we already offer a broad range of glazing options we’re fairly well poised to accommodate this aspect of the potential Energy Star changes,” Hayden says. “Other manufacturers with more limited offerings may have a greater issue with this. It may mean an end to the one size fits all business model they currently use, and may force them to expand their offerings.”

Mikkelson says his company will work with its sales representatives and customers on making sure the right mix of products—glass types, styles and options—are sent out as part of their yearly plan.

“That’s something sales representatives will work directly on with their dealers as to what they feel are the most appropriate products to stock,” Mikkelson says, adding that his company will provide whatever type of products are required. “I can’t say for certain that a particular glass type will be stocked as a standard, but we will certainly do what we can to make it available to our customers.”

Are We Ready?
So where does this leave the fenestration industry? Is it ready for such a potential change?

“Some are and some aren’t and there’s a lot of change to do yet,” says Barry. “Those who keep up with the changes will be successful. The tools are out there (RESFEN software, for instance); they just need to be used.”

Larsen says he sees most of the window companies as being prepared for such a change.

“Most [window companies] already have products … that probably will meet the requirements, whatever they end up being,” he says. “But, just because it’s a rated product doesn’t mean it’s a sold product and my fear, wherever we end up, is that everybody will rush out and add another option to their glazing matrix, advertise themselves as being Energy Star-compliant on certain products, but it doesn’t really bring about any determined changes. I don’t see where it will transform the market.”

According to Johnson, looking at the past and how window companies have evolved through numerous changes shows the companies are ready and able to take on whatever changes that may take place. 

“I think we’ve seen the industry’s ability to react—the fact that it’s evolved from clear glass to more and more units with coated products and the various changes they’ve had to make in their own manufacturing techniques to handle [so many new products] shows that,” says Johnson. 

What Happens Next?
Whatever happens with Energy Star, many companies on the window side as well as the glass side have expressed their concerns with the proposed changes. 

But, saving energy is what’s most important to many individuals, companies and organizations. Windows provide a great opportunity to do that.

“Our [DOE] goal is to achieve zero-energy homes by 2020 and to do that we need much higher performing windows,“ says LaFrance. “There are people paying [extremely] high bills in the winter because of the high gas prices, and a window is directly linked to the heat loss in the house. Having highly insulating windows is one way [they can] save on energy costs. These windows have been expensive in the past and our efforts are all about bringing low-cost, highly insulating windows to the market.”

Barry agrees, saying the type of windows in house isn’t the most important consideration, but rather the total energy savings that is most important.

“At the end of the year it comes down to what [a homeowner paid] and how much energy was wasted. The performance of the window is a part of that and somehow we have to get people interested in the total energy situation; somehow we have to get beyond individual components and look at the total picture. We’re getting there bit by bit.” 

Ellen Rogers is a contributing editor for DWM magazine.


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