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Old 08-07-2008, 08:40 AM   #81
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Update: thoughts on radiant barrier effectiveness. This is highly unscientific since the RB was not the only change I made to the house in July, but here are the stats. June had an average high temp of 96.7 with 5 days above 100. July's average high was 99.8 with 16 days above 100. However, energy usage was 58 kwh/day in June versus 54 in July. Conclusion: reduced energy consumption in spite of higher temperatures indicates that the radiant barrier was at least somewhat effective at reducing the heat load on the house.

We will see if the extra insulation installed during the first week of August has any effect during the coming month.
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Old 09-13-2008, 10:56 AM   #82
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Update: I installed the radiant barrier in mid-July, and added several inches (40 bags) of cellulose insulation at the beginning of August. I estimate this took the ceiling R-value from the mid 30's to the mid 40's. Here are the average temperatures by month and our kwh usage (adjusted to reflect a 31-day period):

May: 77, 1360 kwh
June: 87, 1800 kwh
July: 89, 1680 kwh
Aug: 87, 1170 kwh

There are more environmental variables at work here (wind, cloud cover, humidity, etc.) but this is the best data I have. The 35% reduction in usage from June (before any improvements were made) versus August (after all improvements were complete) given similar temperatures is pretty impressive. It appears that the biggest impact came from the added insulation, although there could also be a compound benefit from having both the radiant barrier and the added insulation. In addition, I made some other changes over the July-Aug period, all of which may have contributed to this improvement:

1) Added soffit vents to improve attic ventiliation
2) Reprogrammed A/C thermostat (this may have cut usage 15% by itself)
3) Replaced recessed lights with airtight cans
4) Added UV film to some westward facing windows

Electric rates have come down some but I am still paying $0.145/kwh. Assuming this cuts my electric usage by 20% and I used 13,000 kwh last year, the $650 I spent on improvements will return $377/year, and payback comes in less than 2 years. If we keep the house for 5 years, the IRR of this project is 50%. Alternately, at a 10% discount rate, the NPV of this project is almost $800. The fact that I did all these things myself certainly made them more cost effective. The house in question is a single story 2000 sq ft ranch style home with a pitched roof in Dallas/Ft. Worth.
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Old 09-13-2008, 11:16 AM   #83
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Excellent, thanks for the analysis. Real-world numbers aren't that easy to find.
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Old 09-13-2008, 03:12 PM   #84
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I read this with mainly academic interest. Doing much handy-man work is not my bag. On the other hand, I'm glad that I opted for "extra" roof insulation when my FL home was built, exactly five years ago. I read then (and guess it's true), that doing so is one of the most cost effective energy-savers one can do (er, that's "have done", jeez, where is that silver bell...? Oh, servant.....!) Since the ex-girlfriend moved out a year ago, a/c stays around 82 deg. F, my electric use (last 12 mo's) is only 43% of when both of us lived here. I try some other frugal stuff, like turn off the water heater when I'm on a trip (2 or 3 months a year). Still, perhaps kick the woman out of the house is a major energy saver! I am researching the options for solar water heating, or the heat pump recovery units. Whether they pass muster with the HOA remains to be seen.
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Old 09-13-2008, 03:27 PM   #85
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the $650 I spent on improvements will return $377/year, and payback comes in less than 2 years. If we keep the house for 5 years, the IRR of this project is 50%.
Yes, thanks for putting the data together. Man, if I could identify some 2 (or 3 or even 5 ) year payback items, I'd jump on 'em. I've already added some attic insulation, and in a 2 story house I'm not sure how much more benefit I'd get from more. But I am going up there this fall and add some to some areas where I get condensation on the ceiling in the coldest weather (edges near the roof line - I know it's thin there in spots).

I'd suggest you put those records together, it may add some value to your house if you can prove that your utility bills are lower. I'd turn it around to an equiv delta on a 30 year fixed, and tell any prospective owners that this $XX average reduction in bills is like taking $XX thousands off the price of the house - compare net monthly mort plus utils.

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Old 09-13-2008, 07:33 PM   #86
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Originally Posted by pedorrero View Post
Still, perhaps kick the woman out of the house is a major energy saver!

Maybe; but some of the energy you are saving you would probably prefer to be expending.

Ha
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Old 07-01-2009, 08:02 PM   #87
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I've installed thermometers in the attic. One of these days, I'll go up there and disconnect the solar gable fan and see what the temperature does, if anything.

I'm also looking forward to watching what effect the soon-to-be-added ridge vent has.
I have some numbers. We've had a long string of hot, sunny, days so the results aren't too affected by cloud cover and rain. It's as controlled as I can get it.

Before:
Standard comp roof with fairly light-colored shingles, soffit vents, gable vents, and 2 turtle vents. The solar powered gable fan was disconnected because of roof work.

All temps were measured ~5:30PM.

Date Outside Attic Difference
6/4 87 115 +28
6/5 91 117 +26
6/8 94 120 +26
6/14 97 125 +28


After:
Metal roof with light-colored underlayment, soffit vents, ridge vent, gable vents. The turtle vents were removed. The solar fan is still disconnected.

Date Outside Attic Difference
6/18 96 109 +13
6/22 98 115 +17
6/23 99 111 +12 (this measurement is at 6:44PM)
6/25 103 117 +14
6/28 101 115 +14


I'll re-connect the solar gable fan this weekend and see what that does. I'm also going to finish installing radiant barrier sometime in the next few weeks. Currently, it's only on the southern-facing gable wall.
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Old 07-01-2009, 08:36 PM   #88
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Old 07-04-2009, 05:55 PM   #89
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Well, I just Maxed out the Insulation to Double, Installed a Attic fan runs on solar and A Water Sprinker systems that goes on every 1/2 hour for 5 Min. on super Hot days..
Adding Trees was another Big issue.. placed in the right Area and getting the right one's...

The walls are already packed to the Max and Added another Pane to the Windows ( Plexiglass ) and a Seperate Sliding Vynial Storm Window . I also added Auto tint that goes dark in the Sun..to the south and west Side Windows, along with of course good Blinds.

Last month cost me ave of 10 cents a Sq ft to Cool the House. Kept at 77 during the day and 72 at nite. and use low wattage 6" fan in the Rooms , not the High Wattage Cieling fans..to keep the air circulating..
and we Keep the Downstairs Vents 50% closed, since keeping the upstairs cool , sinks downstairs on it's own anyway..Thus keep the Upstairs Cooler will Keep the Downstairs cool on it's own.

And got the Kids a Generator and Exercise Bike for them to play their TV's and Radio's... Keeps them in shape too...LOL
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Old 07-05-2009, 09:11 AM   #90
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I added radiant barrier (the roll kind) in late 2007.

For comparison:

PERIODkWh
June071477
June081432
June091329

This year's June was particularly hot...

I also changed to CFLs somewhere around the same time.

Next up, a new roof with improved ridge venting, and lighter colored shingles.
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Old 07-08-2009, 08:08 PM   #91
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Update: I think everything I did last summer (radiant barrier, window film, insulation, attic vents) was a big waste of time and money. Looking at my electric usage since then, I can't see any benefit. Here's a table of my daily KWH, average temperature, and cooling degree days (standardized to a 30 day month). For a given level of outside heat, the house still takes the same amount of energy to cool. Now, our thermostat program has changed over time, but it's not drastically colder in the house than it was last summer.

Grrr...so irritating! Nothing seems to have an effect on my electric consumption!
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Old 07-08-2009, 08:49 PM   #92
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soupxcan,
Where did the CDD data for your location come from, and do you happen to know what the cooling baseline temp was (CDDsub76? CDDsub78?).

Observations:
1) Your insulation wasn't finished until Jul of last year.
2) Your non-cooling electrical use appears to be approx 15 kwh/day (just a wag based on your winter electrical bills. You do run a furnace fan during this time, but let's ignore that)
3) Compare your Jun 08 electrical use to your Aug 08 electrical use. The outside environment was nearly identical (avg temp/CDD). Subtract your non-cooling electrical use for both months ((15KWH/Day avg) from your total use= amount of electricity used to cool home.
Jun 08: 58 kwh/d - 15kwh/d = 43 kwh/day to cool the house
Aug 08: 38 kwh/d - 15 kwh/d = 23 kwh/d to cool your home.

So, based on this very small sample, it looks like you cut your cooling costs by 46% That's not bad at all--you still live in Texas, ya know! Did you go on vacation in Aug of last year or were there other factors at work?

There's agreement in the May 08 (before insulation) and the Sep 08 (after insulation) data set: September was slightly warmer, and yet you used less than 1/2 of the energy for cooling that you'd used in May. That's pretty darn good, isn't it?

You're still short of enough data to draw big conclusions. It looks like Jun 09 was not in keepng with the rest of your data set. I'd let the data pile in for the rest of the summer before getting too sad or elated.
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Old 07-08-2009, 09:18 PM   #93
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Temp and CDD data from:

National Weather Service Climate

They calculate CDD as average temp minus 65.
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Old 07-09-2009, 12:05 PM   #94
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FWIW, I track average daily kwh's every month. The last month I have data for is May -- 2009 average usage was 26/day vs 42/day in 2008. We didn't do anything different that we can think of. When I do year over year comparisons of the same month, the usage swings wildly and for no apparent reason. Have 17 years of this data. Have not really tried to correlate it to weather patterns using objective data from places like the NWS. Just observation. I wish I had more answers than questions.
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Old 07-11-2009, 05:26 PM   #95
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I don't know if this has anything to do with my lack of improved energy efficiency, but apparently you are supposed to change your HVAC air filter every couple of months. Duh. Waiting 2 years to change it is not advised. Having made this change, we'll see if the AC runs any less this month.

Ah, the joys of being first time homeowners...
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Old 07-11-2009, 05:27 PM   #96
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Originally Posted by soupcxan View Post
I don't know if this has anything to do with my lack of improved energy efficiency, but apparently you are supposed to change your HVAC air filter every couple of months. Waiting 2 years to change it is not advised. Having made this change, we'll see if the AC runs any less this month.
Might help...
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Old 08-18-2009, 08:08 PM   #97
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July's usage was 1643 kwh with an average temp of 87 and CDD of 652. This compares to 1628 kwh last July when the avg temp was 89 and CDD was 729. Therefore, I used MORE energy despite the fact that it was COOLER - so overall I am less efficient this summer with the radiant barrier than I was without it last year.

I'm considering tearing the RB down. It just doesn't seem to be working, and I am wondering if it is keeping heat in the attic. It's still +110 in there after the sun goes down. Could the RB be preventing air circulation and effectively "insulating" the residual heat left over from the sunshine? I just can't believe that all the things I did have not reduced my electric consumption by at least a small (but noticable) amount. Maybe the RB is actually working against the other changes I made?
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Old 08-18-2009, 08:42 PM   #98
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When in California had a flat roof no attic house -- every few years would go up and swab the roof with a silver aluminum fiber sunstance substance.

Here in Minnesota - had a new roof put on - new regulations require twice as many roof vents on top and under the eaves. Haven't used the ac this year. Notice the house is cooler. Also helps to open all the windows at night and close them up in the morn...and oh yes..helps not living in tejas in the summer...also installed new energy efficient windows and will get $1500 tax credit from Obama.

August Bill - 345 kwh $42.93

Last August 461 kwh $54.92
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Old 08-18-2009, 08:50 PM   #99
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Yeah, but look at the June 2008 numbers. Exactly the same CDD as you had in Jul 2009 and yet you used 10% less electricity overall. Using the same methodology as I posted before (subtracting out your non-cooling baseline electric use, since your insulation/RB wasn't expected to make things like your refrigerator and TV more efficient), you had a cooling energy use of 38 kwh/day in Jul 2009. You used 43 kwh/day to cool your house in Jun 08. That's a saving of about 12%.

You still need more data.

Regarding the RB--the idea tends to be overhyped, but it does work. Unless you've got something unusual going on with the installation, I doubt it could make your cooling costs higher than without.
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Old 08-18-2009, 10:57 PM   #100
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If any vents were covered when the RB was installed it would work against you. You may want to check. Also, have you considered installing an attic fan? I installed a solar attic fan and the temp is noticeably different. I think I paid about $50 for the fan and about $90 for the 10w solar panel to go with it. I then added another solar panel in parallel a little later because the south facing panel was not getting enough sun to keep the fan working later in the day. I faced the second panel towards the west. This combination runs the fan fast in the hottest part of the day and then keeps it running into the evening until the sun gets pretty low in the sky, albeit at a slower speed. Was it worth the $220? I think so. I don't know if it saved much energy for cooling because our solar electric takes care of all of our electricity needs and then some, but the room affected by the cooler attic seems cooler.

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