High Performance Enclosure Strategies, Part II: Low-E Storm Windows and Window Attachments
October 27, 2015
- Katherine Cort, Research Economist, Pacific Northwest National Laboratory
- Joseph Peterson, Research Engineer, Pacific Northwest National Laboratory
- Thomas Culp, Owner, Birch Point Consulting LLC
Hello everyone! I am Nicole Harrison with the National Renewable Energy Laboratory, and I’d like to welcome you to today’s webinar hosted by the Building America program. We are excited to have Katharine Cort, Joseph Peterson and Thomas Culp here today to discuss low-e storm windows and window attachments.
Before we begin, I’ll quickly go over some of the webinar features. For audio, you have two options. You may either listen through your computer or your telephone. If you choose to listen through your computer, please select the “mic and speakers” option in the audio pane. By doing so, we will eliminate the possibility of feedback and echo. If you select the telephone option, a box on the right side will display the telephone number and audio PIN you should use to dial in. Panelists, we ask that you please mute your audio device while you are not presenting. If you have technical difficulties with the webinar, you may contact the GoToWebinar Help Desk for assistance.
If you would like to ask a question, please use the “Questions” pane to type in your question. Please indicate which speaker you are addressing your question to.
If you are having difficulty viewing the materials through the webinar portal, you may find PDF copies of the presentation at the website listed here and you may follow along as our speakers present. The associated case study is also posted there. Today’s webinar is being recorded and the recording will be available on the DOE YouTube channel within a few weeks.
We have an exciting program prepared for you today that will discuss how window attachments and coverings, such as storm windows and cellular shades, can be a cost-effective means of reducing energy use in residential buildings. This webinar will review some of the latest research in this area, including results from Pacific Northwest National Laboratory’s controlled Lab Homes 2015 experiments examining interior low-e storm window inserts and cellular shades. The webinar will also cover recent related activities by utilities, energy-efficiency programs and the recently launched Attachment Energy Rating Council (AERC).
Before our speaker begins, I will provide a short overview of the Building America program. Following the presentations, we will have a Question and Answer session, closing remarks, and a brief survey.
The U.S. Department of Energy’s Building America program has been a source of innovations in residential building energy performance, durability, quality, affordability, and comfort for 20 years. This world-class research program partners with industry to bring cutting-edge innovations and resources to market. Visit our website at buildingamerica.gov to find more information about the program and the Building America Solution Center, which provides expert information on hundreds of high-performance construction topics, including air sealing and insulation, HVAC components, windows, indoor air quality, and much more.
Building America is supported by 10 industry research teams and four national labs. Each of these teams and labs partner with dozens of industry professionals, including builders, remodelers, manufacturers, and utilities. The best and the brightest in the residential buildings industry can be found here.
And now, on to today’s presentation!
Our webinar today is High Performance Enclosure Strategies, Part II: Low-E Storm Windows and Window Attachments
If you would like more detailed information about this effort, please feel free to contact our speakers.
Our first speaker today is Katherine Cort, a Research Economist with Pacific Northwest National Laboratory. Katie is an economist with PNNL and team lead of Building America’s Window Retrofit Solutions program. Ms. Cort has over 15 years of experience analyzing energy-efficiency programs, technologies, and research and provides technical support for the Department of Energy's (DOE) Building Technologies Program.
Our next speaker is Joe Peterson. Joe joined PNNL in the summer of 2012. He serves as the primary technical lead and point of contact for work done within the PNNL Lab Homes. He has a master’s degree in electrical engineering and completed his thesis on Lab Home research techniques to simulate human occupancy in a controlled experimental setting.
Our final speaker today is Thomas Culp. Thomas is the owner of Birch Point Consulting, LLC which provides engineering and strategic consulting services in the areas of energy efficient window performance, building code development, glass performance, and glass coatings.
With that, I’d like to welcome Katie to start the presentation.
Katherine Cort: Thank you Nicole and thank you very much for joining us on our presentation on energy savings from window attachments.
Okay, there we go. Hopefully everyone can see the screen. I'm Katie Cort, Katherine Cort. I'm commonly known as Katie. I am speaking to you today from Richland, Washington where Pacific Northwest National Laboratory campus is located.
I'd like to recognize some members of the team who have been working with window attachments including Joe Petersen, who Nicole mentioned will be talking to you later. Joe is our onsite engineer and principle investigator for the Lab Homes experiments, which we have conducted this year focusing on inflating cellular shades and interior low-E storm panels.
Also on the team is Tom Culp from Birch Point Consulting who is our resident expert on all things window, window attachments, and coding related. And Tom is going to be talking to you a little bit more about technologies, how they work, and some of the field studies and modeling studies that have been conducted in this area.
I would also like to recognize some of our partners - Quanta Technology, who provided the interior insulated panels for the Lab Homes experiment, and also Hunter Douglas who provided their Architella Trielle insulating cellular shades for the Lab Homes experiment. Pictured to the right there is part of the Hunter Douglas team including Stacy Lambright and Drake McGowan.
We are very happy to have joint funding for our experiments this year, including both Department of Energy's Building America program and the Northwest Energy Efficiency Alliance or NEEA. NEEA being an alliance of energy efficiency organizations and utilities here in the Northwest dedicated to accelerating energy efficiency for residential, commercial, industrial and for both gas and electric here in the Northwest. They are taking a look at window attachments for window application in both potential applications in both commercial and residential buildings.
Just so we are clear what we are talking about, when we use the term window attachments I have taken this table here from the efficientwindowcoverings.org website. This is a website that was developed by DOE and Lawrence Berkley National Laboratory and Building Green to provide information and overview material on an assortment of different window attachments and allows someone to compare these products in terms of characteristics including energy performance, privacy features, installation costs, and that kind of that. If you see on the left I have highlighted with the red arrow the attachments that we will be talking about today including exterior low-E window attachments. We have a lot of past research we are talking about and field studies and then two interior attachments, these being the insulated window panels and the insulated cellular shades, which were the subject of our Lab Homes experiments this year.
The data from this pie chart here was taken from the Residential Energy Consumption Survey that DOE conducts periodically. I think it is interesting to know we have been looking at this data through the years and what we've seen is that the presence of single paned windows in homes has persisted over the past two decades despite the fact that there about approximately 3 million windows that are replaced each year with higher performing insulated windows. In addition, the homes that have the double paned windows, a good percentage of these, have windows that are not necessarily the high performing low-E windows but rather the clear glass windows. We see a tremendous opportunity for technologies that improve existing window performance of energy efficient window attachments to provide energy savings to a large segment of residential homes.
Just to drive this point home a little more. It's probably not a mystery to anyone that windows are a major source of heating losses and gains in a building. Just how much? Take a look at the component load studies that LBNL conducted a few years back. It was estimated that 25-30% of the heat losses, this would be for both commercial and residential buildings, those heat losses are lost through infiltration and conduction through the window. Even a larger percentage of heat gains come in during the cooling season, so the windows are a large source of heat gains and losses through all seasons. It is interesting to note that when you take a look at newer buildings, which they did as part of the component load studies, you tighten the shell quite a bit and bring the insulation levels and roof to walls and floors up to a code level and even improve to a low-E double pane window you still have on a component load basis those windows accounting for about 60% of your heat losses in a building. Their point here being that if you are wanting to reduce the heating and cooling load of a building you really need to mind the gap. You need to look to the opening in the shell and that's really what window attachments are focusing on. Not only can they reduce the energy consumption in a building but they can do it, what we're finding, in an affordable manor. Often window attachments will meet the savings and investment ratios and payback thresholds for a lot of the different weatherization and utility programs that are out there. They can be applied to existing homes and they can be easy to install, so it's sort of lower installation costs. I don't have it listed here, but it's equally important, that they can add to their comfort level of a home and the aesthetics. For a lot of energy efficiency types of measures - sometime you will have the homeowner begrudgingly installing for the energy savings. For window attachments there's an actual aesthetic appeal in that they improve the look of the home inside and out and so this is a very important future that comes along with window attachments.
In this slide I'm featuring the comprehensive modeling study that was conducted by LBNL with assistance from DRI that looked at 11 different window attachments in 12 different climate zones and I looked at the energy savings potential in all these different climate zones. The bottom line conclusion is that, yes, there is a great deal of energy savings potential from window attachments, of course how much depends on the type of attachment, the season, the climate, and the operation of these attachments. Two kind of stand out, window attachments, that were consistently saving energy particularly in heating dominated climates where the low-E insulating storm panels and the insulating cellular shades. And that's part of the reason why we've focused part of our initial efforts and validation studies on these two technologies.
As part of our efforts related to window attachments, we've also done some market assessments and identified some of the market barriers to window attachments. This has driven a lot of the activities that have taken place in this program. I'm just going to go through a few of these. The first one being the identity...what we refer to as the identity crisis. This has to do with the fact that window attachments often slip through the cracks between insulating measures and windows. They are often not recognized by a lot of utility weatherization programs or even by consumers when it comes time to upgrading the energy efficiency of their homes. The second one has to do primarily with storm windows and that's a stigma barrier in that most people know what a storm window is and they have a picture of where the storm window is but the picture they have is probably of their grandmother's storm window - the older generation of storm window, which were maybe not so attractive - aluminum frame, maybe had to be removed each year, and had a tendency to get dirty and need to be cleaned and that type of thing. One of the challenges with this window attachment is overcoming the picture that people have in their head of what a storm window is and introducing them to the modern storm window that has some newer features. The third barrier is the fact that window attachments are not recognized by any sort of rating system. Unlike windows that have an NRC rating, or insulation that is rated for its energy performance, there is no equivalent rating for window attachments. Energy efficiency organizations and consumers have increasingly relied on these types of ratings to make some of their decisions so not having this, again, we see as a market barrier.
The fourth one is the do-it-yourself barrier. This one in one sense implies that this is low cost and easy to install, which is a good thing. It means that most of these are installed by the homeowner as do-it-yourself projects but that also means that it might be relegated to that list of do-it-yourself projects that just never gets done. It also implies that there is not a really well developed third party installation network for some of these products. This is not so much the case for window shades and blinds that has a pretty well established third party installation network but can be a problem for some of the other window attachments.
The final barrier has to do with permanence and persistence. This is a very big deal for utility programs. When they incentivize any sort of measure they want to ensure that that measure saves energy persistently over time and that it is installed and operated in a manner that will save energy over time. The perception by most utilities is that window attachments are not necessarily installed permanently and not necessarily operated in a manner that saves energy over time. That's another issue that we want to address with some of our programs and studies.
How we're going about addressing some of these barriers is the first bullet here has to do with the rating council and DOE, to address the fact that there is no rating for window attachments, has launched the Attachments Energy Rating Council. This is a council that has been set up as an independent public interest non-profit organization whose mission is to rate and certify the performance of window attachments. The purpose is to provide accurate and credible information about the energy performance of window attachments, which will help consumers make informed decisions about window attachments. We're really excited about the launching of this council and the expectation is that they'll have a couple of products rated by the end of next year, 2016, so we're looking forward to those results.
They also have a new website, which I've listed there, that you can check out if you want more information. There is also work being done by the Consortium of Energy Efficiency to develop tools and resources related to window attachments, including some product overview guides. These are available on the CEE site as well.
We've made some efforts to integrate some window attachments into some of the building energy simulation software and audit tools that are out there that now largely don't even or aren't even set up with a framework to examine window attachments. This ends up being a barrier when it comes time to audit. One of the things that we've done is have successfully integrated into the facility energy decisions is a system model, which is the Fed's model. It uses a lot of federal energy audits. Now when audits are performed, storm windows now come out as a possible measure for retrofit measure in some of this modeling work.
Finally, we've had some successes working directly with utility and weatherization programs, most notably here this past year, working with the regional technical forum, which is a policy advisory forum in the Pacific Northwest. It's staffed with a technical crew and they help identify regional priorities and make recommendations for energy efficiency measures, in particular for Bonneville Power Administration.
Working with them we went through their process and were able to get low-E storm windows adopted as a proven measure in the Pacific Northwest, which means that some of these different utility programs can now integrate low-E storm windows into some of their energy efficiency programs.
Finally, I just want to bring up the fact that we're amassing quite a bit of a library of resources in this area. Tom and Joe are going to talk a little bit more in depth about some of these recent studies. This is just to call attention to the fact that if you are looking for information in this area or you need to pull out some numbers or look for something specific to your region even, chances are there might be some information in some of these resources, which I have listed in more detail at the end of the presentation. With that I am going to turn things over to Tom Culp.
Now I'm clicking...
Thomas Culp: Thanks Katie. As she's giving me control, as we hand that over, I'll be talking a little bit about some of the technologies, how they work, and kind of the development from initial concept to lab testing, to field studies, to now we're at the stage of wide-scale deployment and to give a little bit of history on how these technologies have advanced. Let me make sure I've got control now.
I'll be primarily talking about low-E storm windows. I'll mention a little bit about the insulated cellular shades and Joe, who will be following me, will talk a little bit about the specific studies both for low-E storm panels and the interior panels, as well as cellular shades.
Let's see if this advances. Before I dive into the details I did want to spend a moment talking about what low-E storm windows are and what they are not. Katie mentioned this briefly. There seems to be a lot of misperception. People remember their grandmother’s old storm windows that had to be put up in the fall and taken down in the spring. We really want to emphasize that modern storm windows and panels have significantly evolved and are not your grandmother's old storm windows. Modern storm windows and interior panels are designed to blend in with existing architecture, be permanently mounted, and are available in both fixed and operable windows. For instance, the photo on the left shows interior windows low-E panels with fixed inoperable. The photo on the right shows operable exterior low-E storm windows, including insect screens. As you can see they are aesthetically pleasing. These are white but can come in any color. They are slim and in many ways hard to distinguish from the primary windows. As we'll talk about, low-E storm windows are a great new tool for updating the energy performance of existing windows without the full cost of window replacement. It talks about up there that the cost can be 1/3 or even 1/4 of full window replacement, yet get to a similar level of performance. We did want to emphasize that, of course, if your existing windows deteriorate, if your frame is rotted out, if you have other problems, then replace it and use as high of a performance window as possible. Where it's impractical or undesirable to replace a window, because of cost or historical considerations, then low-E storm windows are a good option.
Now to go through a little bit of the history and how these technologies work - first, the initial concept came up in the late 1990s when Lawrence Berkley National Labs suggested that low-E storm windows could be a cost effective insulating and air sealing measure for the existing windows. Basically the premise is that it acts as an air sealing measure for your primary window. We always worry about, in energy and weatherization programs about, sealing the rest of the home - rim joists and so forth, and then very little is done about the window, except maybe around the perimeter. The window itself is left there as a very leaky source of air leakage but applying a panel can significantly reduce the air leakage through that primary window. We'll talk about some of the results we saw in the case studies.
You also create a dead air space - a space between the panel and then the primary window. This reduces conduction and convective heat losses across the whole window. Finally, with the addition of low-E glass you reflect radiant heat back into the home. You reduce the radiative heat loss out that window. Using low-E glass versus regular clear glass, you could have a 35% improvement in performance.
These images here are from heat transfer modeling, using the therm software from LBNL, and showing the temperature profiles. On the left there we have the single glazed fixed wood window, which on the very cold glass temperature, which is not only indication of heat loss but it also can form condensation or even ice on that single pane.
In the middle, as you add a clear glass storm window you now create that air space and you are insulating it more and you significantly raise the temperatures, helping to reduce that condensation but also reduce the heat loss. Then finally, the step on the right, when you add the low-E glass you are reducing radiant heat loss as well and you can warm that glass even more and cut that heat loss even more.
You see this in real life as well. This is a field image, an IR field image, taken from the outside of a home. Light colors show heat loss. There are three windows here. In the center is the original single pane window, a picture window. On the left and right are two windows that have had low-E storm windows added over them. As you can see, it's very clear that the low-E storm windows on the left and right have significantly reduced the heat loss outside that window.
Now the other technology that we’ll be talking about today is insulated cellular shades. These are another new measure for significantly improving the energy efficiency of existing windows. They operate in many ways by some of the same premises. This is a product from Hunter Douglas Architella Trielle honeycomb fabric. If you look on the left image there you can see that it's multiple cells within the cellular shade. There are actually 5 spaces in there so that will reduce your conductive heat loss across that space. In addition, there is an air space between the blind and the window itself. Finally, it's a Mylar, this image does not show it, but this product also comes with an option to have a Mylar metalized film on this interior cell, which acts as a low-E layer, again, reducing radiative heat loss across this space and lowering the U-factor or increasing the R-value over the whole assembly.
When you look at IR images you see a similar story where, in this case, on the left window it shows the primary window with no window covering and significant heat loss. This same window with the insulated cellular shade dramatically reduced heat transfer and heat loss of that window. This particular image and the insulating benefit, of course, is the primary benefit in the winter where we can see significant heating savings. Katie talked a little bit about the overall of how windows contribute a large percentage of the overall heat loss out of the home. This can significantly reduce that. On the cooling side, cellular shades also play a significant role in that during the summertime that solar gain is unwanted and cellular shades have been shown to reduce unwanted cellular gain through the windows by up to 80%, so significantly reducing your heat gain and cooling load that must be supplied to the home. Joe will talk a little bit more about the cellular shade testing that has been done in the last part of this presentation.
Speaking about low-E storm windows again, don't worry. This is a cluttered big table. This is more here for your later reference. We often get asked, "What is the performance of a low-E storm window over different types of primary windows." People are used to where they are learning about U-factors for new windows. What is it when you put a low-E panel over an old existing window? This is a paper that was just recently published through PNNL. The reference number is at the bottom and it's at the end of the presentation as well. It's also based on some prior work we did with ATI test lab that did simulations using window and therm software to calculate the performance of low-E panels over different types of primary windows. For instance, in that first top chunk you see for a single glazed wood window the U-factor can be reduced from .88 down to .34 or .36 for a low-E storm window either on the outside or the inside. In general we see that over single pane windows the U-factor decreases about 60% by the addition of a low-E panel, so very significant. Over double pane clear glass windows, these double panes that are older, don't already have low-E glass, the U-factor decreases between 43-57% with the addition of a low-E panel.
The normal low-E glass that's used in these also reduces the solar heat gain by about 17-28% depending on the specific window type. That's with the regular low-E. In addition to that there's also solar control low-E option that's available. It's similar low-E glass but it has a slightly tinted look to it. It provides a little bit more solar control so if you are in the southern part of the country you can look at that as an option. That will lower the solar heat gain even more.
There goes...this is just a similar table, even busier, for over metal frame products. Again, this is for your later reference. It has similar performance improvements.
Moving on, LBNL came up with this concept and did some initial calculation and we've done some more recent calculations that show, yes, this should work. The next step is, let's test it. Let's see, does this work under real life conditions? So the first step was in 2000 -2002 LBNL used their mobile testing facility or MoWITT facility. It could be moved but it was stationed up near Lake Tahoe, Nevada up in the mountains for cold whether climate. It has two bays where you can do side-by-side instrumented testing with window options. In this case we have one bay that had a single pane window and then a low-E storm window added over that. Then that was directly compared in side-by-side testing with a new double pane low-E replacement window. This data on the right, the details don't matter, but basically this instantaneous heat loss through each of those windows, the bottom line shows the single pane. Then the gray and black dots up above it are the side-by-side comparison of the low-E storm window and then the brand new double pane low-E replacement window. As you can see, the improvement is basically the same. This was very promising that, hey, yes, this concept has worked.
A little bit later LBNL together with Building Green did some calibrated IR imaging, this time from the interior. This is showing an interior from the left - an interior low-E panel over a vented single pane wood frame window. On the right is those single pane sashes were replaced with double pane low-E argon sash inserts. These are taken from the interior. In this case dark colors show heat loss. As you can see the two options behaved fairly similarly. We're seeing similar improvement from either replacement sashes or from a low-E panel. In fact, when you look around the perimeter, the low-E panel is actually doing arguably a little bit better around the perimeter, just from sealing versus the sash inserts. The main point is that you can get similar performance with a low-E storm window or interior panel.
Really the next step was, let's scale this up. Let's look at what happens when you put in a whole home. In 2003-2006 DOE, HUD, NAHB Research Center, and LBNL conducted a field study on 6 weatherization homes in the Chicago area bungalow type homes where all had single glazing with the addition of low-E storm windows. The details are in the paper referenced at the end but the heating load of the home, on average, was reduced by about 21%, which gave a simple payback period of about 4.5 years. So, that's very cost effective.
Additionally, we did blower air testing. In this case we saw overall home air leakage reduced by 6-8% just by adding the exterior storm windows. Nothing else was done to the home. No other air sealing. This shows how, in these builder homes, the primary windows can be very leaky so just adding in a storm window or panel to that can significantly reduce the air leakage of the entire home, which contributes to the energy savings.
We followed this up in 2011-2013 with a similar study in Atlanta this time, still with NAHB Research Center. This was DOE funded. We had industrial partners with Larson Manufacturing and QUANTAPANEL where we did similar studies in 10 older homes with single glazing around Atlanta. We wanted to test a warmer climate with a mixture of both heating and cooling seasons. By adding low-E storm windows, these are all low-E storm windows over the single pane windows, we saw approximately 15% heating savings. On the cooling side we saw a range from 2-30%, which is very large variability. We believed this large variability happened because these are old homes in established neighborhoods where you have a lot of variation not just in orientation, which way the home is facing - the windows are facing, but also the degree of trees around there - tree coverage and shading. We saw energy savings in all cases but it did depend on the specific situation of the home. Heating savings were more consistent. Again we saw significant air leakage reduction just by adding panels. In this case these homes were older and leakier and we saw 17% reduction, which were 3.7 air changes per hour. For those of you getting involved in new construction, that should surprise you a little bit because the modern building codes require new construction homes to have their total home air leakage less than 3 to 5 ACH. Just by adding the storm windows we were able to reduce these homes air leakage by about that much. That showed the original homes and the original windows are that leaky and that the opportunity of adding the storm window can make a significant improvement in air leakage and energy savings.
Addition energy savings, we were careful to do some occupant surveys to look at other attributes as well. It kind of came out surprising that everyone appreciated the energy savings but that's not tangible. All these items ranked higher to the occupants than the energy savings they saw. Number one was improved appearance. These were older homes with beat up windows and by adding the exterior storm window it actually improved the aesthetics. They also commented on reduced drafts, improved comfort, presumably thermal comfort, and finally reduced noise. Adding that second panel improved the acoustics, especially for single pane windows.
Then part of this same research funded by DOE, NAHB Research Center, QUANTAPANEL, and Larson we did address two large multifamily buildings in the Philadelphia area. This is just one of the two buildings. They are identical, side-by-side. They are three story large buildings with 101 total apartment units. They already had old, very old, beat up clear storm windows over single glazing and metal frame windows, so not very efficient. We wanted to test, okay, what if you take these old style storm windows and replace them with new design low-E storm windows outside? These are exterior windows. In this case we saw a 20% reduction in the heating energy use over two heating seasons. Then we saw a 9% reduction in the cooling energy use. Similar to the single family homes, we did blower guard testing to individual apartment units. We saw an average leakage reduction of around 10% so this was interesting because, as I said, the baseline was not single pane windows. The baseline was single pane windows with these old style, clear glass storm windows. It shows that as we've gone to more newer design windows there are more benefits in energy consumption, not just from the low-E glass but also from air tightness and the design of the windows. It's a very positive study.
Another point we wanted to make was that low-E storm windows, even though a lot of these studies have been kind of on these older buildings and that is the focus, low-E storm windows and panels are not just for low income weatherization homes. They are a good retrofit option for windows to upgrade your existing windows in almost any building type where it's impractical, too expensive, or undesirable to replace the old windows. These are all real life examples courtesy of QUANTA where this includes homes of all types - historic buildings. This is a historic library in the upper century. Historic homes that are under historic covenants are not allowed to replace the windows. Even large buildings - this building on the right I think is a 26 stories - it's an old bank building in Hartford with single pane windows. It would have been cost prohibitive, by far, to replace the facade on that so instead they added low-E interior panels on the inside and it's been converted to residential apartments. It's a good option in many cases.
We've done some of the modeling. We did some field studies so the next step as we scaled from the lab to field studies is how do we get going to broad application, expand the use of these more broadly. That's where programs come in, not only education such as today with Building America, but also working with weatherization utility programs. Katie spoke about how recently we were working the regional technical forum out in the Pacific Northwest and with the utilities. Another aspect is that back in 2009 the ability to include low-E storm windows was added to NEAT and weatherization assistance software. On the side please let me know if you would like instructions on how to do that within NEAT. I have kind of a little handout on how to do it. This is software that is used by many state weatherization programs. In 2010, Pennsylvania added low-E storm windows weatherization priority list for single family homes. This followed a NEAT analysis for 37 home types. It covered a range of housing across Pennsylvania. We saw the SIR or Savings Investment Ratio range from 1.3 up to 2.2 over different window types. This savings investment ratio, if you're not familiar with that, must be greater than 1 to qualify as a cost effective measure. Basically you are getting more time value of money back compared to the initial cost of the measure. As you can see, these are very well cost effective and these were done with loan (inaudible 42:32) pricing. A number of these areas use propane fuel and in parts of the country you see electrical resistance heating. When you have high price fuels like that the SIR is even higher and it's even more cost effective. Then with support, funding from Building America, PNNL, and I was involved. We did calculations using expanding the NEAT analysis and also using RESFEN, which is another software package from Lawrence Berkley National Lab to expand this analysis to 22 cities to all 8 climate zones - all the way from zone 1 in the southern tip of Florida up to zone 8 in Alaska. The paper numbers are down below. Two studies, one in 2014 and then we recently updated fuel prices and dove into the data a little more. This was just released this month. You can look up the paper numbers and at the end as well. The details are in the papers but in general this is kind of a summary slide for overall single pane windows and double pane metal frame windows. It was shown to be cost effective in climate zones 3 through 8, which is the blue line up, with an SIR or savings investment ratio ranging from 1.2 to 3.2. Again, this was with natural gas. With propane or electrical resistance heating it will be even higher. In about the upper 2/3 of the country just regular low-E storm windows are recommended. In this south central area, kind of between the blue and green lines, solar control low-E storm windows are recommended. There you have a balance between both heating season and cooling season.
South of that in the very far south, mostly Florida and the Gulf Coast, we have solar control low-E storm windows still offer significant energy savings and benefits but you need to look at it on a case-by-case basis.
This is a similar chart but now over double-pane wood or vinyl-framed windows. Now, in this case, your primary window is already a better performer. It's still not up to par with modern low-E windows but it's a better performer so your cost or energy savings are a little different. Your cost effectiveness is a little different. It's cost effective in climate zones 6-8 as well as the Eastern part of zone 5 and, of course, it will be recommended over an even larger range where you have propane or electrical resistance heating.
This study we also want to emphasize that it is very common when you talk about window technologies and people talk about cost effectiveness, they talk about the cost upgrade of choosing a better window over a baseline window, and they don't talk about installation cost. This is the fully loaded cost effectiveness including the full product and the installation cost. This is actually being quite conservative. If you have already chosen to do a storm window then the cost effectiveness of choosing a low-E storm window is even better.
To make that point, here are some charts from this recent paper. On the top this is the fully loaded cost effectiveness, including installation cost, where [inaudible 45:53] are the highest in the colder zones. This is split into the base energy savings, plus the air leakage savings. Then as you go to southern zones we still have significant energy cost savings when it goes down. The payback period is shortest in those northern zones but it's cost effective in basically zones 3-8 but that's the fully loaded cost. If we, like similar to other measures, adjust the incremental cost of using low-E glass versus clear glass as a short payback period in all climate zone types in all window types. If you've chosen to do a storm window, it always makes sense to do a low-E storm window. With that I'm going to hand it over to Joe. Joe Petersen is with Pacific Northwest National Lab. He's an engineer who is the technical lead on the PNNL Lab Homes and he'll talk a little bit about control testing done on some of the low-E storm panels as well as give more detail on the [inaudible 46:59] studies.
Joe Petersen: Thank you Tom. As Tom said, we've done a lot of research related to interior and exterior storm windows. Now what we need to do is a little bit more focused study on the evaluation of these windows in these laboratory homes. The unique thing about the PNNL Lab Homes is its two double wide homes that allow for technologies to be integrated into one and then have the two homes be compared side-by-side. It allows for a very controlled simulation of each of these technologies. These homes were specifically developed to be representative of the Pacific Northwest and the climate that we've seen in this area. Some of the initial partners that are part of the PNNL Lab Homes are Building America and the City of Richland and Bonneville Power. Those are some of the most notable ones.
Here's an aerial view of the PNNL campus. The blue box is where the Lab Homes is located. As you can see in the bottom left you can see the climate zone. The star is where Richland, Washington is at, right near the Washington/Oregon border in climate zone 5, like I said. The basic characteristics of the Lab Homes, so it's a 3 bedroom/2 bath, 1500 square foot factory built manufactured home through the HUD code. Within both the heating and cooling experiment we had the ability to introduce heat in a couple different ways. During the cooling season we have a heat pump that cools the Lab Homes and during heating season we generally used a forced air furnace because, you know, it's 100% efficient. We also have Cadet wall heaters that can supply supplemental heat to the space.
We have R-22 and R-11 walls and roof and ceiling. The window area we have is 195 feet squared or 13% of the floor area. This note right below it, and I'll talk a little bit more about this later, only 74% of the windows or 144.8 feet squared were covered by interior low-E storm windows. I'll talk more about that later but basically why that is is QUANTA does not make an interior storm window large enough for the sliding glass doors. We have incandescent lighting and other things you would normally find in a manufactured home. We have a bath, a kitchen, a full house, refrigerators, range, and dryers but most of these are not powered on or running when we do some experiment.
Within the homes we have expensive metering and monitoring technologies not only for the power but for the dynamic heat flow through the space. I'll talk about that a little bit more in a minute too.
Here is the flow plan of the Lab Homes. As you can see there are three bedrooms and then the living space. If you look to the top left you see the technologies that were integrated and kind of where they were throughout the homes. I'll star first with the orange bars. Those are the interior low-E storm windows. Those were placed on 74% of the window area within the Lab Homes. You can see those in the master bedroom, bath, and so on. The blue square is the Hunter Douglas cellular shades. Those were on all of the window areas within the homes so you can see Hunter Douglas has the ability to manufacturer these cellular shades large enough to cover these really large sliding glass doors. That was nice. The blue or the green bar was, is, the sliding glass door retrofit. Due to the fact that Quanta does not make interior storm windows large enough to cover the sliding glass door, we needed a way to kind of eliminate some of that window area. What we did was take a bad insulation and reflective coating insulation and kind of effectively blocked off the window. This was to reduce infiltration, reduce solar heating, and all the light effectively coming through that window. If you look at the other sliding glass door here, this one did [inaudible 51:54] interior storm windows retrofit on it. That comes into play when we look at some of the savings because this is spacing west and, you know, when the sun sets you'll get a lot of solar heat gain assisted with this. We'll talk about that later.
The metering and monitoring within the laboratory homes - we have 42 individually controllable breakers and what that means is they are all motorized and can switch off and on via a predefined schedule. That's how we integrate some of our occupancy, being light bulbs introduced heat to the space with our Cadet wall heaters. We also have a bunch of temperature and relative humidity sensors throughout the homes, so, 15 interior temperature thermocouples. Those are all the ambient temperatures thermocouples that kind of give us a dynamic flow of heat through the space. Twenty-two interior and exterior glass surface temperature thermocouples - this is actually going to be increased based on some of the studies we've done here just we can make sure we understand the temperature on different surfaces of the primary window and low-E window. We had 2 relative humidity sensors and 2 mean radiant temperature sensors, some water things that aren't really applicable here, but we have that capability. The data logging technology that we use is Campbell Scientific CR1000. This gives us minute data, 15 minute averages, or hourly averages. We'll talk more about that later when we talk about the savings. Here are the basic window characteristics. As I said, the baseline home is made to be representative of the Pacific Northwest. We have a double pane clear glass window with an aluminum frame. Those are the baseline windows. You can see in the table below the U-factor, solar heat gain coefficient, and the visible transmittance of each of these. We are looking at the low-E storm windows, interior low-E storm windows, behind the baseline windows. We can see a reduction in the U-factor, solar heat gain, and visible transmission. We also see that for the patio doors too, even though we weren't able to actually test that. Basically what this equates to is with the interior low-E storm windows we see about a 53% reduction in U-factor, 19% reduction in solar heat gain coefficient, and about a 17% visible transmittance. Just as a comparison we have the R-5 triple pane argon windows that were studied by Sarah Widder, who's also at PNNL. As you can see there, it significantly reduced the solar heat gain and U-factor but it's just, you know, a good middle ground that the low-E storm windows give us. Installation of the interior storm windows, if we look at the top left here, generally what you take is the measurement of the bottom sill and the vertical and the horizontal and that's the measurement that is sent to the manufacturer. What they do is they generate this track that the low-E storm windows can slide in and out of. This track has a seal around it, a rubber gasket, that fits into the seal. It's fairly easy to install. Use a blind stopper, as shown here, to get them about an inch from the primary window and then screw the track into the sill. Then it's fairly simple to put this or place the panes in there. Generally the low-E coating is facing out or away from the conditioned space. In general these can go over trim. Unlike the exterior storm windows, they don't have any weeping holes or weep holes or anything like that. Then general, if you have a really leaky home, these will help increase the air tightness for that home. Here are some simple infrared images that we have of the master bedroom. These were taken during the heating season, so in the winter, as you can tell. The first column is the baseline home and then this one is the experimental home. The experimental home has the low-E storm windows installed in them so you can see these are the exterior infrared images. You can see on the outside we have about a 43º Fahrenheit for the baseline home, which is the standard baseline windows and then a 39.4º Fahrenheit with the low-E storm windows installed. That's a temperature delta of about 3.6º Fahrenheit and as Tom said, that's due to the low-E coating reflecting some of that conditioned heat back into the space and trapping it. Similarly, if we are looking at the interior of the space, this is the same window just from the inside; we can see the baseline home at about 60º Fahrenheit for the surface and the experimental home at about 66.6º, so almost a 6.7º difference between the two. The baseline home, the heat transfer between the primary windows is a lot. It's losing a lot of energy and a lot of heat through the window. That's kind of mitigated through the low-E storm. Can we validate or can we kind of validate some of those infrared images with kind of some of advanced metering techniques?
What we tried to do was we wanted to get kind of the complete picture of the dynamic flow of heat from the internal conditioned space to the outside ambient air temperature. We have here at the top the interstitial space temperature, which is the temperature between the primary window and the low-E window and existing window and existing surface temperature. That's the outside temperature of the panel of the primary window. Existing window interior surface - this is the temperature of the low-E window. Interior space. Interior storm interior surface temperature - this is the temperature seen at the conditioned space. This is the data logger that we had.
Basically, what we can see is exterior glass temperature comparison during the heating season. We have the average outdoor air temperature during this day was 40º. What we can see is Lab B. That is the experimental home with the low-E storm windows. Lab A is the baseline home. What we're looking at is the outside surface of the primary window. We see is that Lab Home A is significantly warmer than Lab Home B on the outside surface of the primary window. That's exactly what we saw with the infrared images.
Similarly, if we look at the interior space and the interstitial space, we can see the same kind of thing that we saw with the IR images. The experimental home, Lab Home B, is 4-6º warmer than the baseline home, Lab Home A. That's because the low-E coating is reflecting a lot of that internal heat back into the space. As you can see, we have an interstitial space here, which is an elevated temperature and things like that. This gives us a nice dynamic presentation or a good story as to how the low-E storms can save energy and, you know, increase the comfort in the space.
Over the course of the heating and cooling season we did a couple different experiments and here are some of our findings. The average savings for low-E storm windows was 8.1% annually when we are specifically looking at coverage of 74% of the window area. This could be more if we had both the sliding glass doors covered with an interior storm window or an exterior storm window possibly, but this is compared to 12% for a triple pane primary window.
The experimental period, as you can see, during the summer cooling we have the storm windows in Lab Home B as the operational scenario. We saw an average energy savings of about 4.2% in the winter heating season. We saw about 8.1% in general. We use Energy Plus models to kind of extrapolate this into an annual savings number. We found that to be 7.8%, plus or minus, from 1.5%. For comparison, here are the R-5 results that were brought by Sarah Widder and these were about 12.2, plus or minus, 1.3%. Not quite as good but comparable given we only had about 74% of the window area covered.
These are the HVAC load profiles over a representative day for both the heating and cooling season. Though these graphs show continuous lines, these are actually the average hourly values for the HVAC load. On the y-axis we have watt hours. On the x-axis we have time in hours. Then on the secondary axis we have temperature and degrees Fahrenheit. The dotted line is the outdoor air temperature and then these two dotted lines are the internal temperature. Our internal set point for both heating and cooling season was 71º. During the winter, during the heating season, you can expect most of the heating to be done in the morning due to the fact that that's when no sun is out and no solar gains are expected. We can see a peak reduction in HVAC load between the baseline home, which is in blue, which has no window attachments, and then the experimental home which has the low-E windows on it. We can see a basic reduction in HVAC load that continues throughout the day. As the temperature increases throughout the afternoon, you know, the solar gains associated with the envelope heating up, reduces the need for heating. In the evening you can see that Lab Home or experimental home stays warm longer than the baseline home. That's due to the fact that the low-E coating and extra pane of glass is trapping additional heat within the space.
On the second graph here, this was in the summer, so in the cooling season, similar we have watt hours on the y-axis. Hours are on the x-axis and then temperature. The dotted line is the outdoor temperature, outdoor air temperature, and then the other two dotted lines are the internal temperature hovering around R-71 degrees set point. In the morning you would expect no cooling to be going on and then you can see as the envelope heats a peak load reduction due to the interior storm windows between the baseline home in blue and then the experimental home in red. Then you can see a similar operation throughout the evening as the afternoon/evening and one theory for that is the interior storm windows can only offer so much benefit and as the envelope heats up to 85-90º the gains associated with the envelope cause the two homes to perform similarly for part of the day. You can see in the evening a similar trend.
The next thing that we evaluated was the Hunter Douglas honeycomb cellular shades. Due to the functionality of these cellular shades, they can automatically be moved up and down with predefined schedules. This is done through motors within the actual blind themselves. It's actually quite handy. You can preprogram a schedule into, via an app, into some Hunter Douglas technology and then these blinds will follow that schedule. There are a couple of things that we wanted to test given the advanced functionality of these shades. The first one would be optimum operation. The optimum operation is the implementation of the Hunter Douglas HD green mode. What this is is roughly based on the solar calendar and then the geographical location of where the blinds are going to be installed, so the latitude - the geographical latitude. This not only...this not only has to do with, you know, the optimization of the heating and cooling loads but is also for the customer to introduce light into the space. That is also taken into account. The insulating values of these shades, it would be the most optimal operation of these shades is for them to be down and operating all the time but obviously that isn't a real world application. During the optimum operation we had the Hunter Douglas shades being operated to the HD green mode and then the baseline home had no window attachments at all. What is the added benefit or what is the reduction in HVAC load that we can see for that? The second one was cellular shades compared to standard vinyl horizontal blinds. In this experiment we had the Hunter Douglas blinds operating to the HD green mode, just as in the other operational scenario. Then we had the baseline home with the standard vinyl horizontal blinds operated to the same HD green mode. We can...this will give us another metric of comparison between the Hunter Douglas blinds and the standard horizontal blinds.
The third measurement scenario that we have is the static operation mode. In general what this is is both window attachment technologies - the Hunter Douglas blinds and then the vinyl horizontal blinds remained closed for the full duration of the day. This was an attempt to get at the insulating values associated with each of the technologies. It's important when we go forward looking at these different scenarios to keep in mind what the baseline technology is for comparison.
HVAC energy savings is generally based on the operational schedule and baseline technology. This is a general overview of the experimental period, the operational scenarios, the number of experimental days that were in the experimental period, the baseline technology, and then the average energy - HVAC energy savings seen from this. As you can see from the first one, the static operation, this was done in the cooling season, so during the summer - 14 experimental days. And this, the baseline, is compared to the standard horizontal vinyl blinds. We see the Hunter Douglas blinds having a 13.3% reduction in HVAC loads when compared to the standard vinyl blinds.
The second one we had, the summer cooling season, this was optimum operation comparison, so both the Hunter Douglas blinds and the standard vinyl blinds were following the HD green mode operational schedule, which was based on the solar calendar. We can see the Hunter Douglas blinds outperformed the standard blinds by about 10%.
Then we have the winter heating season. This is in the winter. The optimal operation. The baseline is no window attachments in the baseline home and then Hunter Douglas honeycomb cellular blinds operating in HD green mode in the experimental home. We can see 17.6% reduction in HVAC energy load just based on a baseline home with no window attachments.
Look at each one of these experiments we have representative data that gives us a little information or background on kind of what's happening. As with the other ones, we have time on the x-axis in hours. We have watt hours, HVAC energy usage, on the y and then on the secondary axis we have temperature. Now remember again, even though it showed this as continuous these are hourly averages. These are actual watt hours. We have the baseline home, which has the standard vinyl...excuse me. No. We have the baseline home, which has no window attachments on it. Then we have in blue. Then we have the experimental home in red that has the Hunter Douglas blinds operating to the HD green mode. As you can see, as you can see, most of the operation is done in the morning and this you can see a peak load reduction associated with the...you can see a peak load reduction with the Hunter Douglas blinds as compared with a standard baseline home with no window attachments, so an experimental period of 9 days and then a 17.6% savings of HVAC load.
The second one that we're looking at is the static operation in the cooling season. During this experiment we have the baseline home, which is in blue, has the standard horizontal vinyl blinds closed for the duration of the day. The experimental home has the Hunter Douglas honeycomb cellular blinds closed for the reminder of the day. We have outdoor air temperature. As you can see this is a relatively warm day in tri-cities. Then we have the purple and turquoise lines are the internal temperature of each one of the Lab Homes. As you can see, in the morning we would not expect any cooling to be happening but during the day or as the envelope begins to warm up we see peak load reduction associated with the insulating properties of the Hunter Douglas cellular shades. That remains throughout most of the day, even when we get really high outdoor peak temperature. As you can see, during the latter part of the day the experimental home, which is in turquoise here, had the Hunter Douglas cellular shades on there. This stays warmer longer than the other baseline home with just the standard vinyl horizontal blinds. This is attributed to the insulating values and the shades being able to trap a lot of that heat or conditioned air within the space.
Finally, we are looking at the cooling season optimum operation comparison. What this is is the baseline home, which is in blue, has the standard vinyl blinds horizontal vinyl blinds operated to the Hunter Douglas HD green mode. The experimental home, as before, has the Hunter Douglas cellular shades operated to the HD green mode. As you can see, no...during the morning no cooling is required. During the mid-morning and early afternoon we see peak load reduction associated with the operation of the Hunter Douglas cellular shades. That remains throughout the rest of the day. Seven experimental days and the benefit of the Hunter Douglas cellular shades was about 10.4% in savings compared to standard vinyl horizontal blinds operated in the same way.
Remain research questions and things to think about as we move forward. So, operation and automation, so, as we've seen in the previous graphs the automation and operation of the window attachments can greatly influence the HVAC load specifically when it comes to the Hunter Douglas blinds and the HD green mode. What value does this have to not only the consumer but, you know, to utilities and other people? Other things to think about are coverage operation. Where is the best place to put these window attachments if not 100% of the window area can be covered at one time? One would think east and west facing windows would probably be better for low-E storm windows and shades to optimize or reduce solar heat gain as needed. Optimizing return on investment. Minimizing cost while maximizing benefit. What are the window attachments that performed similarly at a different price range and things like that that we can look at? Combination of window attachments. Now that we have the Hunter Douglas blinds and the low-E storm windows, what type of combination of attachments can we test in the Lab Homes and then what kind of savings can we see? How does that affect the envelope? Assessing the durability and unintended consequences and dot, dot, dot. This goes without saying. What is the durability of some of these low-E storm windows and what is the life span of them? These things all need to be tested.
Then with that I think that's it. So we have time for questions.
Nicole Harrison: Yes, thank you representers. We have time now for a few questions. We have a lot of great questions from the audience and I don't think we are going to get to all of them but we will answer as many as time allows.
The first question for Katie - In the testing that was being discussed today, did the test include infiltration performance among different types of interior storm windows?
Katherine Cort: The testing that we did for interior storm windows in the Lab Homes was just the low-E interior storm windows from QUANTA Technologies. There were no other types of interior inserts or panels that were tested.
Nicole Harrison: Okay, great, thank you. Tom, we had a couple of questions about condensation problems, both on exterior panels without eave vents and whether there was fogging and someone else had seen condensation problems on new exterior panel storm installs and they were wondering if you had any comments on that?
Thomas Culp: Yes, so condensation, basically the issue you are dealing with is you have warm moist air inside the home and you want to prevent it from hitting some cold surface and forming condensation. And so, the general rule is whatever is...whatever is to the inside of the home as tight as possible. So if you're adding an interior low-E panel, those are designed to be very air tight so they will improve your condensation resistance. They are making that inner surface warmer so you don't have condensation for on the side facing the room. By being air tight, it prevents warm air from getting into that space and forming in the cavity in between. For exterior storm windows, it's the same rule. You want what is inside to be tighter than outside so that warm moist air doesn't get to the cold surface and if there is any moist air in that space that it is able to be vented. What that means is you do want to, if there is any obvious leaks in your existing window, you want to caulking or whatever, you want to do whatever air sealing you can on the primary window but that's also the reason exterior storm windows have those weep holes, not only if there is any sort of mass liquid from rain or whatever but it helps to prevent that formation of condensation between the space. In either case you are improving the condensation resistance of the surface facing the homeowner. My home, when I added a panel, I used to get ice, I am in Wisconsin, in the corners. You add a panel and no longer have that ice formation. That's why you have to make sure to stop the...someone mentioned fogging. You want to make sure those weep holes are clear on the outside panel.
Nicole Harrison: Okay, great. Another question for Tom - Is there any consideration given for climate or latitude relative to low-E storm windows in the NEEA decision as proven? It seems that climate and aspect tuning should be part of that decision since passive heating may be desirable in northern climates.
Thomas Culp: Yeah, and that's a very good point. I showed the map and some of the calculations we did for the different climate zones across the country. For the work for the northwest and the RCF, we looked at and used some of the results from the different cities for that area. They have their own kind of definition of sub-zones and that was, they took our calculations but they also have their own tool where they do their own calculations for these different sub-zones. That was considered. To your point about the sun is your friend in the cold climates in the wintertime, they actually put in a provision that it must be a low-E storm window. It must emit less than a certain amount. We have a list of what products meet that, but also it has to have a minimum solar transmittance so you don't want the solar control low-E glass option. That is very good for down south but not what you want in the Pacific Northwest. It's in the details of the specification but they did account for that regional difference. Now it applied to any of the northern zones across the US as well.
Nicole Harrison: Okay, great, thank you. Joe, we had a couple of questions for you on the Lab Homes. One of them was - Do the interior storm windows open or did they have to be removed to open the primary window.
Joe Petersen: So these QUANTA interior storm windows were operable so they are designed to if you want to open your primary window you can actually slide the interior storm windows on a track and then open your primary window. That's one of the good things about this particular storm window.
Nicole Harrison: Okay, great. Then another question on the Lab Homes - Did the Lab Home testing measure only the center of the glass or did it include infiltration measurement?
Joe Petersen: Yes, we did do some infiltration measurements. If we're talking about the tightness right? We did do a blower door test prior to the installation of the interior storm windows and we did see a reduction of infiltration associated with the installation of the storm windows but it was still within the margin of error for our calculation. We just decided to leave it out. Oh, and the primary reason for this is the Lab Homes were already tightly built and the windows were, the primary windows were tight. In a home that was more leaky the improvement would be seen in infiltration a lot more.
Nicole Harrison: Okay, great, thank you. Another question for Joe - How did the storm windows affect emergency egress from the home? Are they always compliant with fire code?
Joe Petersen: Well, since they're operable I don't know I will defer to Katie on that.
Katherine Cort: I don't think they are designed to match the primary window so there is no change in any sort of egress issues.
Nicole Harrison: Okay, thank you. Alright, so I think we should probably move on since we're running out of time here.
Katie, did you have any closing remarks before we take our quick survey.
Katherine Cort: No, I don't think so, just thank you for the opportunity.
Nicole Harrison: Alright, thank you. So now we'd like to ask our audience to answer three short questions about today's webinar. Your feedback will help us to know what we are doing well and where we can improve.
The first question asks whether the webinar content was useful and informative. Please take a moment to choose your answer.
Alright, the second question asks about the effectiveness of the presenters.
Alright, and the third question asks whether the webinar met your expectations.
Alright, thank you very much for answering our survey. The next Building America webinar is on November 18 and it will focus on High Performance HVAC Systems, Low-load HVAC Systems for Single and Multifamily Applications. You can also subscribe to receive notices about upcoming webinars and news at the URL that is on the screen.
On behalf of the Building America program, I'd like to thank our expert speakers for their time today and our attendees for participating in today's webinar. We had a terrific audience and very much appreciate your time. Please visit the Building America website to download a copy of the slides and learn about the program. We also invite you to inform your colleagues about Building America resources and services. Have a great rest of your day and we hope to see you again at future Building America events. This concludes our webinar.