Lo E3-366 and LoE2-172/272: good improvement in SHG rating

[av]

Some manufacturers have already switched to LoE3 as their standard Low E coating. I think we can all agree that Solar Heat Gain (SHG) is the most important factor for cooling efficiency in a place like Southern California. This is what the Cardinal website shows [cardinalcorp.com]:

SHG:
- LoE2-272: 0.41
- LoE3-366: 0.27

Now that is a nontrivial improvement, with only a moderate penalty in transmitted light that drops from 72% to 66%. Cardinal doesn't list numbers for LoE2-172 that Polybau uses. Is LoE2-172 an older version? How does it compare to LoE2-272? I assume they are in the same ballpark. I think Polybau also offers something they call Low Extreme as an option that is probably just LoE3, but being so new, it doesn't show up in their literature yet . I will call the dealer to find out and get a quote for how much more it will cost.

LoE3 seems like something worth getting in warmer climates. Is anyone else considering it?

[Cheryl]

Loe 172 and 272 are one and the same. Cardinal has changed their name in the last year with the introduction of Loe 366. I did some research on the topic of Loe-366 performance. It does just what it says it will, reduce solar heat gain. Using the RESFEN 5 program from Lawrence Berkeley National Laboratory, I ran simulations for all the major areas in California. The RESFEN 5 program is a program that calculates heating and cooling energy useage in residential buildings. I ran simulations on existing homes with new replacement windows. To be fair, I also ran simulations on other manufacturers Loe products as well. Suprisingly, for all of California, except inland and desert areas, the use of Loe 366 (or other high solar control Loe products such as HP Sun) actually results in higher energy bills. This is because of the loss of positive solar heat gain the the winter months. While you save on cooling costs in the summer, you spend more in the winter on heating bills. Even in Los Angeles, where they divided it into 3 areas, only the 1 inland area showed reduced overall energy bills. There is no magic glass package that is best in all situations. Not yet, anyway.

[av]

Thanks for sharing that information with us. I took a quick look at the LBNL page and I will play with RESFEN when I get a chance. Your simulation results are enlightening, but one has to realize that there are so many assumptions made for an "average" house. To really benefit from RESFEN, I would need to run it myself and use all the proper inputs.

The comments that follow are not directed at you. They are just meant to be a general discussion.

I quickly glanced at RESFEN and I realized that one would even need to customize energy rates, as RESFEN uses one rate for each state, which is unrealistic for California. Furthermore, many areas in California have progressive rates, meaning that as your usage for the month goes up, you move into higher rate brackets. This can create a situation where someone who uses 150 units of electricity one month and 50 units the next can end up paying a lot more than someone who uses 100 units for both months, even though the total amount of electricity used is the same for both persons. This makes energy costs not proportional to actual energy usage over the span of a year. So just a week long terrible heat wave can make your electricity bill skyrocket for that month.

Other things to consider: having a brand new very efficient A/C unit versus having a much less efficient 20 year old unit will have a big impact on simulation results. The difference between new and old heating gas furnaces isn't as dramatic as for A/Cs. Other factors include personal habits. Do you leave the windows covered when you go to work or is there always someone at home and the drapes are always pulled to expose the windows? What is your tolerance for hot weather versus cool weather? In the winter, some people want to wear a T-shirt indoors while others feel more comfortable breathing cool air and wearing a sweater. That means a very different winter indoor temperature has to be used as input to RESFEN.

I think there is so much variation between an average scenario and individual cases that it may not be too wise to make decisions based on the averages. It is probably worth going through the trouble of running RESFEN.

In our case, even though we don't live in the hot areas of L.A. county such as the San Fernando Valley (around 15 degrees hotter), our cooling bill tends to be more than our heating bill.

At the end of the day though, we are not changing our windows just to save energy. Any of the good newer windows will be a dramatic improvement over our existing single pane cheap aluminum windows. We are also doing it for increased comfort, which includes reduced noise levels, and more importantly, more uniform temperature distributions indoors. For instance, there are two large windows on my side of the bed, and on the coldest winter nights, the side of my body facing those windows gets very cold while the other side is nice and toasty

[Cheryl]

You are absolutely correct when you conclude that there are many variations in the RESFEN program. For example, you can even choose window and glazing packages for the specific elevations of the house to achieve maximum energy savings. The research I posted was intended only to analyze general trends in the replacement market. As such, existing frame buildings were used with slab on grade foundation as the basic assumption. Newer building and buildings with basements or crawlspaces will yield different results.

[FenEx]

Cheryl is right... but there are many other variations to consider as well... which is why the RESFEN program is only moderately accurate at best. Although partially funded by the government.. it is not accepted for government programs.

AV

As noticed in several other posts you have made, I can see that you are trying to research all avenues. Unfortunately, you are putting together a few scrambled pieces of info that are not accurate. RESFEN will not provide the comfort you seek, nor will NFRC ratings. I do know qualified energy consultant organizations in your area that can help you find a definitive solution. Glass in any form is NEVER the total solution by itself. Nor is a HP AC unit that is sized without including air leakage testing. As you seem to be very bright, you should find it easy to realize that not every answer is available online.

Don't believe everything you read... unless you live in the lab that a product was tested in. The real world results prove otherwise.

[av]

FenEx, I develop algorithms and write code for large scale physics simulation. I know their limitations, so I can certainly appreciate how approximate answers from simple-model codes like RESFEN can be.

In an ideal world, one could develop a full blown model of the house, with material properties and leak rates fine-tuned by actual measurements, with measurement-based models of wind velocity distributions, humidity rates, light reflectance from neighboring buildings and slabs/asphalt, tree locations, etc. But an engineering approach, or even simple common sense, suggests that you very quickly reach a point where it simply makes no economic sense to do that for a single house, especially in a mild climate. I know any slight performance differences between the two windows I am considering will be dwarfed be the significant improvement over my current very low quality windows with weep holes you can see through! That's good enough for me. Of course, my obsessive side wants to know more, but basically I am trying to get bits and pieces to pick one window over the other, but knowing that either should be fine.

Maybe I should start a new thread listing the slight pros and cons of the two windows to solicite comments and suggestions, something other readers may also find useful.