aircooledfool
New Member
Posts:8
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| 17 Aug 2011 09:55 PM |
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I'm hoping to find other ICF home owners to share information regading electric usage. My home is located in central Texas. 3465 heated/cooled. Roughly 2800' is on ground floor. Roof system is truss with foam on underside and gable ends. ICF is 6".
Let me know if you are interested in sharing KHw usage. |
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dmaceld
Veteran Member
Posts:1465
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| 17 Aug 2011 10:51 PM |
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Do you have an average daily use graph for the past year on your electric bill? If so, what is the minimum kwh usage during the shoulder months, i.e., when neither heat nor a/c would have run but very little, if at all? For my 2000 sf house in SW Idaho it's about 50 kwh/day. My max average consumption above that for heat or cooling is about 55 kwh/day.
My power consumption is higher than I expected. I haven't been able to nail down for certain why.
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| Even a retired engineer can build a house successfully w/ GBT help! |
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aircooledfool
New Member
Posts:8
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| 17 Aug 2011 11:13 PM |
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Here is my usage for 2011. This summer has been the hottest on record in Texas. I'm not at all happy with these numbers and we suspect issues with the HVAC design/performance:
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January |
February |
March |
April |
May |
June |
July |
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KWh |
2463 |
2243 |
1708 |
1931 |
2098 |
2810 |
2821 |
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Day in Period |
35 |
29 |
30 |
29 |
32 |
29 |
30 |
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KWh Avg per Day |
70.37 |
77.34 |
56.93 |
66.59 |
65.56 |
96.90 |
94.03 |
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arkie6
Veteran Member
Posts:1453
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| 17 Aug 2011 11:28 PM |
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How much foam in attic? Type? Total R value? What about your windows? How many square feet of glass on the east/west sides of home?
Your electric usage is high in March & April when heating/cooling load should be very low. How many people in home? What type of water heater do you have? How many computers do you have running at any given time? How many big screen TVs? Do you have a pool with a pump?
What size/type/efficiency is your heating/cooling system? Do you leave the fan running continuously? |
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aircooledfool
New Member
Posts:8
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| 17 Aug 2011 11:41 PM |
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The underside of the deck is open cell and thickness would be around 8". Gabel ends which are framed 2x4 are filled with close cell. Window are high effinceny vinyl and we do have a significant exposure on both east/west side. I don't know the square feet of surface but will take measurements. There are two adults and one child. Hot water heater is State high efficency electric with circulating pump. We didn't install times on the hot water heater or circulating pump so I know that is an issue we need to address. Two flat panels, no pool. HVAC is Goodman 16-Seer heat pump. During the heating months, thermostat was set at 68. During cooling months we set the temp at 75 during day and 70 at night. The main living areas of the house stay comfortable with thermostat at 75 but two bedrooms on the opposite ends of the house suffer from low air volume thus the need to run the temp cooler overnight.
I have a wood burning fireplace and suspect I loose sigfiicant heat/cool up the chimney even with the damper closed. I'm looking at some inflatable products that can be used to seal air loss in the chimney while not in use.
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dmaceld
Veteran Member
Posts:1465
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| 18 Aug 2011 12:40 AM |
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What is your Kwh use per cooling degree day? Can you get that info from the power company website? Here's the pc graph for my home for the past year. It looks like in July/Aug last year my total consumption was about 6 kwh/CDD. How much was non-A/C I don't know.  |
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| Even a retired engineer can build a house successfully w/ GBT help! |
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arkie6
Veteran Member
Posts:1453
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| 18 Aug 2011 07:29 AM |
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Posted By aircooledfool on 17 Aug 2011 11:41 PM
The underside of the deck is open cell and thickness would be around 8". Gabel ends which are framed 2x4 are filled with close cell. Window are high effinceny vinyl and we do have a significant exposure on both east/west side. I don't know the square feet of surface but will take measurements. There are two adults and one child. Hot water heater is State high efficency electric with circulating pump. We didn't install times on the hot water heater or circulating pump so I know that is an issue we need to address. Two flat panels, no pool. HVAC is Goodman 16-Seer heat pump. During the heating months, thermostat was set at 68. During cooling months we set the temp at 75 during day and 70 at night. The main living areas of the house stay comfortable with thermostat at 75 but two bedrooms on the opposite ends of the house suffer from low air volume thus the need to run the temp cooler overnight.
I have a wood burning fireplace and suspect I loose sigfiicant heat/cool up the chimney even with the damper closed. I'm looking at some inflatable products that can be used to seal air loss in the chimney while not in use.
Your roof R values are below what I would consider acceptable for an energy efficient house. Most energy codes require R38 minimum. Your ceiling R value is only ~R28 (8" x R3.5) and your gable ends are only ~R21 (3.5" x R6) unless you have rigid foam over the outside of the framework. Actually, your whole wall/ceiling R values are significantly less than those numbers when you figure in the ~R1/inch thermal short circuit of the wood framing. As you suspect, that constant running of the hot water heater circulating pump is an energy hog. |
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jonr
Senior Member
Posts:5341
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| 18 Aug 2011 08:44 AM |
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I agree, heating/cooling KWh per DD and COP is what you want to measure for comparison purposes. |
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aircooledfool
New Member
Posts:8
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| 19 Aug 2011 08:51 PM |
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My electric provider (Green Mountain Energy) doesn't offer the KWh per DD and COP metric. Is there another place to obtain the DD or COP? Also, I am confused about the foam insulation on the underside of my roof deck. Informaton on www.sprayfoam.com says, "Sprayed polyurethane foam has an aged R-value of approximately 6.0 per 1 inch thickness". If that is accurate, my insulation R value would be well over R30. One reply to this post said the R value was only R28 (8" X R3.5). What is the correct R value? |
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arkie6
Veteran Member
Posts:1453
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| 19 Aug 2011 10:15 PM |
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Posted By aircooledfool on 19 Aug 2011 08:51 PM
...I am confused about the foam insulation on the underside of my roof deck. Informaton on www.sprayfoam.com says, "Sprayed polyurethane foam has an aged R-value of approximately 6.0 per 1 inch thickness". If that is accurate, my insulation R value would be well over R30. One reply to this post said the R value was only R28 (8" X R3.5). What is the correct R value?
You said you had open cell foam under the roof deck. Open cell spray polyurethane foam (SPF) is ~R3.5/inch. Closed cell foam is ~R6.0/inch (aged value). See the following link: http://www.sprayfoam.com/spps/ahpg....pNav=1
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Dana1
Senior Member
Posts:6991
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| 26 Aug 2011 06:26 PM |
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In places where code calls out R38 min on standard assemblies it's usually relaxed to R30 for insulated unvented roof decks (aka "cathedral ceiling", or "compact roof"). On the roof deck 8" of open cell is pretty good (or at least meets code) if you have 8" covering the rafters too, for a true whole-assembly R28, but pretty skimpy if you have exposed rafters thermally bridging to the roof deck. R30 between rafters yields ~ R26 for whole-assembly R. R28 comes in a bit less than code.
On the gable ends the center-cavity R20 is totally undercut by the ~ R3 studs & plates, yielding a whopping R14. (Wet spray cellulose would have given you R12 for a heluva lot less money.) This is why high R per inch foam-budget is better spent on the exterior, where it thermally breaks the studs rather than letting the framing waste it's high potential R. Half-inch foil-faced iso under the siding on the gables with R13 batts in the cavites would deliver a higher performance wall for dramatically less money.
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