Posted by Allison Bailes on Fri, Sep 03, 2010
In 2003, I finished building a high performance home and moved into it. Shortly thereafter, I enrolled in a HERS rater class and got myself certified as a home energy rater. So, with all that experience plus my background in physics plus the fact that I spent summers in my teen years helping my grandfather work on air conditioners, you might think I'd've had a good handle on HVAC.
If so, you'd be wrong. Oh, I knew the basics - that a refrigerant moved heat in air conditioners & heat pumps, that furnaces burned a fuel and then moved the heat to the living space, that duct systems in most homes have a lot of problems. But what I really found when I became a home energy rater was that I had waaaaayyy more to learn. Over the past seven years, I've mostly taught myself what I needed to know and have gotten to the point where I know HVAC issues pretty well.
Let me tell you a story about how incomplete knowledge could get a new home energy rater into trouble. About 6 years ago, I did a Manual J heating & cooling load calculation for a client, and they sized the systems on my recommendation (actually a bit larger).
A year later, I got the call. The house wasn't cooling below 80 degrees F, and the air conditioners were running continuously. I went out and tested the house for infiltration. No problem there - it was as tight as I had modeled. I tested for duct leakage, and that wasn't it either. Then I went out to the house with a flow hood (balometer) and measured the air flow. Ah ha! The 7 tons of air conditioning capacity was moving only 5 tons of air (2000 cfm instead of 2800 cfm).
The point of my story is that putting in a correctly sized air conditioner is only part of the story. The air distribution system has to be properly designed as well.
Another place where ignorance can get a new energy auditor in trouble is duct sealing. Most heating and cooling equipment is 
greatly oversized and is attached to a duct system that's too leaky and too small. Energy auditors know how to measure duct leakage, so it's easy to go out and start telling everyone they need their ducts sealed.
The problem is that if the static pressure in the system goes up too high as a result of the duct sealing, the evaporator coil can freeze up. In fact, David Richardson, an EVER rater and HVAC contractor (and author of yesterday's guest post on combustion safety), said that his local utility duct sealing rebate program inadvertently gave him a lot of business in the '90s for this very reason.
I've been wanting to do it for a couple of years now, but last Friday, we held our first Advanced HVAC for Raters class here in Atlanta. Thirteen home energy raters & building analysts came to the class, and we covered a lot of the basics with them:
- Identifying different system types
- Understanding the refrigeration cycle (They acted it out!)
- HVAC design fundamentals
- Air flow and static pressure
We've got another Advanced HVAC for Raters class coming up on 24 September in Asheville, NC, so if you're in the energy rating or auditing business and you want to improve your understanding of HVAC, sign up for it. (There's a $30 rebate if you sign up by the end of next week!)
If you want to go even deeper, sign up for the 3 day class on HVAC Air Diagnostics and Balancing that we're teaching 8-10 November. It's a National Comfort Institute (NCI) class that we're sponsoring and will be geared towards energy raters and auditors. David Richardson (mentioned above) will be teaching the class for us, so you'll benefit from his HVAC knowledge and experience as well as his HERS and NCI expertise.
This is an area where anyone with expertise can find their services in demand. There are certainly some good HVAC contractors out there, but clearly many of them don't understand air flow, and that's why there are so many crappy duct systems. Whether you take our classes, someone else's, or learn it on your own, as an energy rater or auditor, you NEED to understand HVAC on a much deeper level than you got in your initial training.
Posted by Allison Bailes on Thu, Sep 02, 2010
[Guest post by David Richardson]
There are certain events that you can mark as life changing. For me, one such event would be the three day training class that I took back in May of 2001. It’s often said when you’re ready for a certain truth to present itself to you, the time will happen when it’s right, and this was the right time for me to learn about combustion safety.
For years I had noticed contradictions in many HVAC code references and installation practices that simply didn’t add up. Unfortunately, I didn’t have the knowledge or the background to make sense of these concerns. When I asked others whom I considered more knowledgeable on these topics, I was told that that’s the way it’s always been done or that’s the way code says it has to be done.
This just didn’t seem like a very good reason to me. When we responded to a carbon monoxide (CO) alarm, we went straight to tearing the furnace apart and searching for cracks in heat exchangers. You see, most HVAC guys are taught that CO comes directly from cracks in heat exchangers so checking the heat exchangers was our Pavlovian response whenever CO was mentioned.
Many times the heat exchangers were just fine, and there was no CO in the building. “Must be the batteries in the CO alarm again,” was my response to the homeowner, feeling unjustifiably confident that I had solved their problem.
For years, I had read the work of Jim Davis, the father of modern day CO testing, but I could never grasp the complete concepts. 
A lot of what Jim talked about directly addressed the contradictions I found, but I just couldn’t wrap my mind around it.
Then I had the opportunity to attend a three day class put on by the National Comfort Institute (NCI) on CO/Combustion testing, and I was going to hear all I needed to know directly from Jim himself, as he was teaching the class. Those things that had been so confusing to me were about to be cleared up for good.
What I didn’t know was that my world was about to be turned upside down. For close to a week after the class, I couldn’t sleep. I kept thinking about all the situations that I had walked past that had the potential of being unsafe. All those CO alarms going off could have been a problem much more serious than bad batteries...and I didn’t have a clue on how to test.
I couldn’t believe that things were nearly as bad as Jim had said they were. That I would uncover those same problems once I started to test for CO seemed unlikely, yet I had to find out. I went out and purchased a combustion analyzer and draft gauge and started to test using NCI procedures. I didn’t have a lot of confidence in my skills at this point but was determined to find out what was really going on with CO.
My findings were pretty disturbing. The real world was not only as bad as Jim had said - it was worse, a lot worse.
Not long afterwards, I began to spread the word in the HVAC industry about what was going on with CO and how we needed to make combustion safety testing a regular part of our protocol. When NCI learned of my efforts, Jim Davis himself asked me if I would be willing to teach the NCI material to an industry that desperately needs to understand this issue. Without hesitation, I agreed and began immediately to teach my HVAC cohorts how to properly test for CO.
I knew I was doing the right thing when I started to get calls from my students telling me that what I had taught them helped them to save someone’s life. It’s a great feeling to be told something like that, and it brings a kind of inner satisfaction that I just can’t explain. Those who consistently test for CO get the same calls from their customers, who are extremely thankful that a professional trained in combustion safety may have saved their lives.
If you’re a homeowner with combustion appliances in your home, have you had them tested?
If you’re a professional in this field, how often are you testing your clients’ homes for CO?
David Richardson is an HVAC contractor in the Lexington, Kentucky area, as well as an NCI instructor and certified home energy rater. He'll be teaching a special edition of NCI's HVAC Air Diagnostics & Balancing Training in November.
Photos from NCI
Posted by Allison Bailes on Wed, Sep 01, 2010
I just read "How I (Almost) Saved the Earth" by Scott Adams, the cartoonist who created Dilbert, and, although it was funny, it was also a sad and telling account of the home energy rating industry. Adams recounted the frustration he experienced as he planned for and built a green home.
As I read, one sentence really jumped off the page for me:
"The next problem you discover when trying to build green is that there is no way to model the entire home's energy efficiency before it is built."
What?! Evidently Adams never found a home energy rater in all the research he did as he prepared for and then built his green home because modeling a home's energy efficiency is exactly what home energy raters do.
With a home energy rating, he would have known how much energy his home would use for heating, cooling, water heating, lights, and appliances. He could have had the rater run different scenarios to compare the effects of different insulation materials & locations, windows, overhangs, or HVAC equipment. The rater could have shown him reports like the one below, which compares two different scenarios for the same home.
How could this happen? Adams lives in California, perhaps the greenest of all states. He consulted with architects, engineers, builders, and solar contractors, but somehow he never found a home energy rater. If he wanted to build a green home, why did no one tell him to get it qualified as an ENERGY STAR home? That would have required a home energy rater.
I know first hand the difficulties of building a green home when you have to learn almost everything on the fly. From 2001 to 2003, I built a house that was way greener than most - structural insulated panels, passive solar, composting toilet, greywater system... I constantly had questions about methods and materials, and fortunately, I was able to get many of them answered by Southface Energy Institute.
Home energy raters were few and far between back then, though, and I'm not sure I even knew about them until after I finished the house. But why didn't Scott Adams find one? I really don't get it. He somehow missed out on a home energy rating, but he got his solar modules on the roof. That just goes to show that people don't understand the correct order to do things, which I outlined in this 5 step program for solar energy.
If you're building a home and reading this, please don't make Adams's mistake.
- Find yourself a good home energy rater first.
- You don't need an engineer to do the HVAC design. (A physicist and architect team can do just fine!)
- Insist on getting your new home qualified for the ENERGY STAR homes label.
If you're a home energy rater, make sure that every architect, builder, engineer, and solar contractor who works in your area knows about your services. They can't recommend what they don't know.
Posted by Allison Bailes on Tue, Aug 31, 2010
I visited a new house earlier this year that had a basement wall that looked fine* at first glance. At left you see this wall, with its 2"x4" framing and fiberglass batt insulation. That wall you're looking at, though, has a major problem, and it didn't take much digging to find it.
One of the first lessons in building science that new HERS raters get is the definition of the building envelope, sometimes called the thermal envelope to distinguish it from the weather shell. Understanding the building envelope is huge to home energy raters or other energy auditors because that's where they should look first for opportunities to improve a home. Here's the definition:
- The building envelope is the boundary between
conditioned space and the various types of unconditioned spaces that surround a house (ground, outdoors, garage, attic...).
- The building envelope comprises two key components: insulation and air barrier.
- The building envelope's insulation and air barrier completely surround the conditioned space and are in contact with each other.
In the diagram at right, the blue area is conditioned space, and the dark blue line shows the building envelope. That's where all the insulation is, and that's where the air barrier is. Wherever you find insulation, you have to have an air barrier right next to it.
So, take a look at what I found when looked a little deeper. There's clearly no air barrier on the side shown in the first photo, and, as you can see at left, there's no air barrier on the back side either. (No, in case you're wondering, the paper facing on fiberglass batts does not qualify as an air barrier. It can't be sealed well enough to stop air movement.)
So, what's the problem with this misalignment of air barrier and insulation, you ask? The side I took the photos from is the mechanical room in the basement. It's outside the envelope and connected to the garage and the outdoors. The other side of that wall is supposed to be inside the envelope and is connected with the conditioned part of the basement. The lack of an air barrier on that wall adds an enormous amount of infiltration to the house, and the Blower Door test will find it.
This house is a perfect example of why third party verification is so important in qualifying homes for programs like ENERGY STAR. Someone who's trained in building science and understands the building envelope will find this misalignment problem. Even if it eludes them on their visual inspection, they'll catch it in the Blower Door test.
*Some of you may look at that wall and say it doesn't look fine at all, even if it had an air barrier behind it, because fiberglass batts require 6-sided encapsulation, and these are exposed on one side. To that I say, I agree completely with you. ENERGY STAR, however, requires 6-sided encapsulation only for IECC climate zones 4 and higher, somehow thinking that everyone in climate zone 3 and lower is in cooling-dominated climates. More about this later.
Posted by Allison Bailes on Mon, Aug 30, 2010
When I wrote about my trip to the Southeast Building Conference in July, I mentioned how some products on display there really annoyed me because they're either bad to the bone or overhyped. The main one in the latter category is foil-faced bubble wrap sold as insulation.
Green Building Advisor recently wrote an article about foil-faced bubble wrap and did a balanced job of it. They presented the pros and cons and gave anecdotal evidence of this product having solved condensation problems.
I'll grant that foil-faced bubble wrap has its applications, as the GBA article proclaimed. I've just never seen it installed in a way that would allow the product to do what it does best - reduce radiant heat gain.
First of all, let's be clear. Foil-faced bubble wrap is a radiant barrier. It's not insulation. A radiant barrier reduces heat transfer by radiation and has two excellent applications in homes. Insulation reduces heat transfer by conduction through solid materials.
So, when I walked up to the bubble wrap booth and asked the guy what the R-value of it was, he immediately said 15.4. I told 
him, no, it's R-1, and then he started talking about the thousands of dollars they've spent on testing. Pretty soon, he was telling me he didn't have time to talk with me any more.
Here's my problem with his claim. R-value is for conduction. The reduced heat flow by conduction through this product is due solely to the air trapped in the bubble wrap. That yields about an R-1. What they're trying to claim is that the reduction in heat transfer by radiation can be included in the R-value.
Nice try, guys, but no cigar. The problem here is that for a radiant barrier to work, it must have an air gap on one side or the other. If they staple this stuff to the underside of the rafters in an attic, it will greatly reduce heat gain in the attic, and the temperature will be about 20 degrees lower. That's because there's an air gap.
The only place I've seen this stuff used is to wrap duct work. I've heard of it being used in above grade walls in Florida and on foundation walls of encapsulated crawl spaces, but the former 
wouldn't be allowed in Georgia, and I just haven't seen the latter here.
For bubble wrap to be effective on ducts, the installers would have to put in spacers to keep the bubble wrap from being in contact with the ducts. Not once have I seen spacers on bubble-wrap insulated ducts. Since ducts require either R-6 or R-8 insulation, depending on location, building inspectors should start failing this application every time they see it.
I mentioned above that radiant barriers have two excellent applications in homes, and those are in the attic and in windows, the two places where the most radiant heat gain occurs in a building. In an attic, follow these guidelines:
- Use it only in hot or mixed climates where you have significant cooling loads. It's a waste of money in a cold climate.
- Install it along the roofline rather than on top of the flat ceiling. In new construction, use a sheathing material with a foil facing, such as LP TechShield or Georgia Pacific's Thermostat plywood. In existing homes, there are numerous radiant barriers for retrofit, such as PolarPly or foil-faced bubble wrap.
- Make sure to leave an air gap. If you install a radiant barrier roof deck and then spray foam on it, you've wasted your money on the radiant barrier because there's no air gap, and all the heat just conducts right through it.
In windows, radiant barriers are called low-e coatings, but they work on exactly the same principle - by installing a material with a low emissivity between where the heat is coming from and where you don't want it to go. Foil-faced bubble wrap does NOT work for this application. Well, I guess it could be used here - if you didn't care about getting light or views through your windows.
If you want to go a little deeper, you can read Martin Holladay's article called Understanding R-Value or this Radiant Barrier Fact Sheet from Oak Ridge National Laboratory, which does a lot of good research on buildings.
Posted by Allison Bailes on Wed, Aug 25, 2010
My grandfather (yes, the first of this line of 3 Allisons!) was an electrician, plumber, and HVAC contractor, and I had the great fortune of being able to spend a month or two every summer from the time I was about 12 working with him and my uncle Dickie. I'd go out on calls with them all day long, where we'd run wire in a new car dealership, snake out a drain, or replace the freon in an air conditioner. (Don't ask what we did with the old freon; this was the '70s, you know.)
My real education about heating, ventilating, and air conditioning (HVAC) systems has come over the past decade, however, as I've spent a lot of time inspecting and testing duct systems, determining equipment efficiency, and learning the intricacies of Manual J heating & cooling load calculations. One of the biggest lessons I've learned is that HVAC design is a lot more than Manual J.
Most HVAC contractors, home energy raters, and others in this field know about Manual J. Many people even know about Manual D, which describes how to design the duct system. Not so many, however, know about the missing links - Manual S and Manual T. If you want a properly designed HVAC system, you have to go through the whole process in all four protocols: J, S, T, and D. (It's easy to remember the order. As a friend of mine says, first J, then STD.)
Here then is a brief description of each manual.
Manual J
This one is for determining how much heat the house loses in winter and gains in summer. You do this room-by-room for the whole house, which allows you to determine how much conditioned air each room needs for both heating and cooling. It factors in all the surfaces of the building envelope, with their areas and insulation levels. Each wall is given its proper orientation, because windows and doors are attached to them. Other important data include the location and tightness of the duct system, the infiltration rate of the house, the internal loads (appliances and people), and where the house is located.
The results specify the BTUs of heat lost by each room in the winter and gained in the summer. The heat gain is split into two parts: Sensible (related to temperature) and latent (related to humidity). The heat gained or lost in a room then determines how much conditioned air that room needs, in cubic feet per minute (cfm).
Manual S
Once you know the amount of conditioned air necessary in each room, you have to select the equipment. What air conditioner, heat pump, furnace, or boiler are you going to install? With forced air systems, this part is critical because every piece of equipment has different characteristics - sensible and latent capacities, the amount of air moved, and the static pressures being the key ones for the next stages.
Manual T
From the room-by-room loads and cfm requirements, you can determine how to distribute the air in the room so that you get enough to meet the needs (the higher of the heating and cooling cfm requirements from Manual J). The questions you answer here are: Where will the supply registers, diffusers, or grills be located? Where will the return grills be located? What type of register, diffuser, or grill will you use? How big does it need to be?
Good choices here will eliminate problems of feeling drafts from the moving air or having inadequate mixing of the air. It's possible to get enough conditioned air into a room but still have it uncomfortable because all the air just sits at the register.
Manual D
Finally, once you know how many cubic feet per minute of conditioned air you need for each room, what equipment you're using, and how you're distributing the air in the room, you can design the duct system. Here you look at the location of the air handler, the distance to the ducts, how many turns the ducts have to make, and how much air needs to be delivered. The type of duct has a big impact on the results, as sheet metal ducts have a lower friction rate than flex duct or rigid fiberglass duct board.
Basically, with Manual D, you're trying to balance the delivery of the correct amount of air against the friction rate of the ducts and the static pressures in the system.
Pulling It All Together
When you get all four manuals done and have a well designed HVAC system, the result can be a high performance system that's more efficient and comfortable than what's typically installed. Of course, you can have the best HVAC design in the world, but if it's not installed as designed, your performance goes out the window. That's why it's a good idea to have every new system fully commissioned - and that's the topic for a future article!
Energy Vanguard can help you with a complete HVAC design. Chris Laumer-Giddens, an architect and a master of Right Suite Universal, can do the whole process outlined above for you. Request a quote here.
Posted by Allison Bailes on Mon, Aug 23, 2010
If you're in the market for a new heating & cooling system and you're looking at heat pumps, make sure you understand how they're rated for efficiency - and which rating is more important for you.
Most people - and this includes those in the HVAC business - when asked what the efficiency of a given heat pump is, will tell you the SEER rating. That's only part of the answer, though.
Heat pumps, you see, work both ways. It's basically an air conditioner with a reversing valve that lets it run backwards in winter. They cool in summer and heat in winter, and each function has its own rating.
- SEER stands for Seasonal Energy Efficiency Ratio and applies only to cooling. (It's not a great measure of efficiency, but that's the topic of another article.)
- HSPF stands for Heating Season Performance Factor and is basically the SEER rating for winter.
Heat pumps don't work so well when it's really cold outside because they pump heat from the outside air into the house. (Ground source heat pumps, sometimes misleadingly called geothermal heat pumps, don't have this limitation because the ground doesn't get so cold, but I'm just talking about air source heat pumps here.) The colder the outside air is, the less heat they can pump inside. For this reason, you don't see many heat pumps in cold climates.
You don't have to go to cold climates, however, before heating becomes more important than cooling. Here in Atlanta, for example, homes often have annual heating loads that are two or three times more than the cooling loads. If that's the case for you, too, then you need to look more at the HSPF than the SEER when you're shopping for an efficient new heat pump.
Currently, the minimum SEER and HSPF that you can buy are:
If you buy an air source heat pump with a higher SEER rating, it will usually have a higher HSPF rating, too, but make sure you focus on the latter number if your heating load is higher than your cooling load. If you're in the market for a new heat pump, here's a guide to help you choose:
- Consider improving your building envelope with air sealing and insulation to minimize the amount of heating & cooling your home needs.
- Look at your energy bills for the past 12 months (or 24 or 36 if you can get them). Determine whether you're spending more on heating or cooling.
- Even better, get a home energy rating, which will show you the annual heating and cooling loads for your home.
- To size the system properly, get a Manual J heating & cooling load calculation to determine the peak (rather than annual) loads.
- If heating dominates, consider getting a heat pump with an HSPF of 8 or higher, rather than the minimum of 7.7.
- Also, make sure you get a thermostat with adaptive recovery to minimize your use of supplemental heat in the winter.
Posted by Allison Bailes on Thu, Aug 19, 2010
Yesterday, our first HERS rater class students had their first shot at the national HERS rater test. I'm happy to report that 100% passed the test, and the high score was 98%.
If you read my earlier article about the difficulty of the HERS rater test, you know that many students don't pass it on their first attempt. It's a hard test, which it needs to be, and many HERS training providers try to squeeze too much material into too short a time.
Here's what I attribute our success to:
- The test is not the culminating event of the class.
- The students have three chances to pass before they leave the class.
- Our class is three days longer than the typical class (8 days rather than 5).
In home energy rater training classes that last five or five and a half days, the national HERS rater test is usually the last thing the students do. All week long, they're hearing about the test, and the pressure builds. They know that as soon as they're finished, they'll pack up and go home, so the pressure is great to pass the first time.
In our class, the students still feel pressure because they want to be done with it after their first try, but they know that if they don't make it the first time, they've got two more shots - at no extra cost. That knowledge acts as a pressure relief valve, and that's pretty important because some people tense up during a test, and extra pressure only makes it worse.
The way we've structured our class, the students take the test at the end of the fifth day. During those five days, we mainly focus on the building science, pressure testing, and HERS protocols that they need to pass the test. We do some work with the software, starting on the first day, to get them familiar with it, but most of the training for REM/Rate happens in the last three days.
We also went out into the field twice in the first five days and visited three houses. On the first day of class, we did a walk-through of a house under construction and then a full field inspection with pressure testing of an existing home. On the fourth day, we went out and the students got practice with the Blower Door and Duct Blaster.
This is only our first class, although it's the 20th time over all that I've taught a HERS rater class. I don't know that we'll get 100% passing on their first attempt every time we teach the class, but I think my goal to have 100% pass rate by the end of each class is realistic.
Posted by Allison Bailes on Thu, Aug 12, 2010
The ENERGY STAR homes program has grown tremendously since it was introduced in the mid 1990s. In the initial program, version 1 of the guidelines, most homes were certified through a home energy rating and a single inspection that occurred when the house was finished. Version 2, introduced in 2006, required 2 inspections, one at the predrywall stage and one at final, as well as the completion of the Thermal Bypass Checklist.
ENERGY STAR version 3 is now out but doesn't become mandatory until 2012. It still requires 2 inspections, but the number of checklists has increased to 4. The version 3 guidelines are quite a bit more stringent than version 2. As I wrote in my earlier article (linked above), the stringency is ENERGY STAR's attempt to stay ahead of the ever increasing code requirements and to make the program really meaningful. Sam Rashkin, the head of the program, is a man on a mission.
If you've had anything to do with version 2 of the program - as a HERS rater, builder, or HERS provider - you understand the frustration in the process of qualifying homes for the ENERGY STAR label. Some of the requirements (e.g., Manual J and the limit to oversizing of cooling systems) have been difficult to enforce. Part of this is because of unwillingness of builders and trade contractors to change, but lack of understanding also plays a role. HVAC is usually the most difficult part, which is why Energy Vanguard is offering special classes in HVAC for raters now.
The ENERGY STAR program administrators
have decided to go after that lack of understanding by introducing a new training for its ENERGY STAR Partners. I first heard about this at the RESNET conference in February, when Zak Shadid announced their training intentions to the Training & Education Committee. The announcement of the train-the-trainer sessions showed up in my email yesterday, so the program moves forward.
The intention of the new training class, which will be available to HERS raters only through RESNET accredited HERS training providers, is to make sure that raters understand the new requirements in version 3. This new training class will be required for all ENERGY STAR rater partners as well as HERS providers and must be completed before 2012 to continue qualifying new homes for the ENERGY STAR label. Look for HERS training providers to start offering the class as early as November. The class will count towards RESNET's continuing education requirements for raters.
I know some HERS raters feel gouged by all the training and certification requirements of all the programs (ENERGY STAR, LEED for Homes, NAHB, EarthCraft House...) and will not take this well. In this economy, it's certainly a challenge to make everything work sometimes, and I face those same issues. The ENERGY STAR homes program, however, is the foundation for this whole industry.
The new training requirement is a good thing. As a whole, I think many home energy raters are undertrained, especially when they're newly certified. A 5 or 6 day HERS rater class is, in my opinion, woefully inadequate preparation. (More on that later!)
Posted by Allison Bailes on Wed, Aug 11, 2010
The Case of GWP, XPS, and SPF
This week I read and commented on Avoiding the Global Warming Impact of Insulation by Alex Wilson over at Green Building Advisor. I'd avoided the article for a while since climate change isn't what motivates me to do what I do, and I happen to think it may be trumped by a bigger problem anyway (i.e., peak oil).
The article has gotten some building science types in a tizzy, though, mainly because of the recommendation to avoid extruded polystyrene foam (XPS) and closed cell spray polyurethane foam (SPF), two products that are used in a lot of high performance homes. Suddenly, builders feel that they've been misled about using these products.
But are XPS and SPF really the problem the article makes them out to be? I don't hold any pretenses that I was a great scientist during my short stint in academia, but I understand the process of doing scientific research, and reading the article raised some red flags for me.
In case you aren't familiar with the name,
the award-winning Alex Wilson is the editor of Environmental Building News (EBN), a great resource for green building information that's been around since 1992. He's well respected, has a reputation for providing in-depth, objective information on various products used in construction, and can recite arcane details about products on demand. I heard him speak at Greenprints this year, and I can tell you, he knows his stuff.
I'm not a regular reader of his blog, but the other articles of his that I've read have been informative and based on solid information. This one, however, seems shaky to me. Please understand that I'm not attacking Alex Wilson; I'm criticizing a particular report that gives the name of building science a black eye.
Briefly, the blog article is based on a longer report in EBN and is a look at the global warming potential (GWP) of different insulation materials. Wilson and his team calculated a 'payback,' the amount of time it would take for the material's GWP to be offset by the GWP of the energy savings they generate over their lifetime. They conclude that you should avoid XPS and closed cell SPF because they have high payback periods.
Here's my take on the problems with the article.
Ask the right questions.
When I read the article, the first question that came to my mind was, why are you looking at the payback over the lifetime of the product? It seems to me that it should be all about the net flow on a year-by-year basis. Does it really matter if the payback is 46 years when the GWP that's offset due to annual energy savings may be higher than the GWP of the offgassing?
They seem to have assumed that the blowing agent is released uniformly over the lifetime of the foam insulation, so if that's the case, all that would matter is that the payback be less than the lifetime. If, however, the entire amount that's released happened immediately, then payback would be relevant. That brings me to my next point.
Show me the data.
Wilson admits in the short article on Green Building Advisor that he's "not 100% sure that XPS is made with [high GWP blowing 
agents]." He decided on the basis of "various hints in technical literature" to use the high GWP materials in his calculations. In the full article, he says, "Note that the values are highly dependent on assumptions," and "Assumptions are key in this analysis."
To get their results, the EBN team had to assume that:
- The manufacturers used the high GWP blowing agents.
- The offgassing profile is uniform.
- The lifetime of the product is somewhere between 50 and 500 years, though the article doesn't say what numbers they used.
If it's not science, don't pretend that it is.
Science asks the right questions and is based on solid data. If you've done some calculations and created some nice looking graphs, it means absolutely nothing if there aren't any data behind them. It's a house of cards.
One of the commenters on the full article at EBN praised the article as a "rigorous inquiry." If you don't understand how science works, it may look like it is indeed rigorous because it's easy to overlook those statements about the assumptions and focus on the discussion about calculations and the professional looking graphs of payback.
In science, there's this nice little thing called peer review. The way it works is that you can't publish your research without it being looked over by other scientists. This prevents researchers from getting lost in a bubble and believing they've done something magnificent when in fact, they've just concocted a giant fantasy. If this EBN report had had to go through scientific peer review, it never would have seen the light of day.
The term 'building science' is in vogue with green builders and home energy auditors these days, and that's a good thing. But let's remember that science has certain requirements. I was never enough of a theorist to really understand string theory, but I knew enough to see that it was BS (and I'm not talking about building science) because too much of it was based on assumptions that couldn't be tested.
What they should have said
Based on the data available, the EBN team had no justification to recommend avoiding XPS and closed cell SPF. About as far as they could have gone would be something like this:
Some insulation materials MAY use blowing agents with a high global warming potential, and IF those chemicals escape, it COULD be bad news for climate change, depending on how rapidly they're released and what kind of construction they're used in and where the building is. Then again, maybe it's NOT a problem and using them actually helps mitigate climate change. Based on the Precautionary Principle, however, we advocate avoiding these materials until it's certain that the blowing agent has a low GWP.
If they'd said that, the state of building science would be better, and I wouldn't have had to write this article.
In case you're wondering, I have no connection with the XPS or closed cell SPF industries. I like polyisocyanurate and open cell spray foam and probably recommend them more than the other two anyway. I'm speaking out here solely in defense of science.