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Old 07-26-15, 03:35 PM   #31
JRMichler
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I built a new house about 3 years ago. The insulation sweet spot resulted in a heat loss of 13,000 BTUH for a 1300 SF house at -20 F outside and 70 F inside. The next level of insulation would have cut the gas bill by $50 per year at a cost of $12,000. There was no real in-between amount of insulation, and the job was already over budget. No savings in the heating system, either.

I really wanted the U-0.20 or better windows, but the extra cost was prohibitive. I did get a house that cools down at 1 deg F per hour when it's 0 deg F outside. That, along with the woodstove, means that a furnace failure is merely an inconvenience.

And, yes, I'm a mechanical engineer. If money was no object, I would have put in the better windows and extra insulation.

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Old 07-27-15, 09:09 AM   #32
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Yep JRM. You called it.

Most engineers (I'm mechanical too) aproach things from a ROI point of view.

If an extra $1000 will save me $100 a year, I will do it. If it will only save me $10, I won't. I'm not sure how to make decisions any other way.

Austin
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Old 07-27-15, 11:12 AM   #33
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Quote:
Originally Posted by dablack View Post
Yep JRM. You called it.

Most engineers (I'm mechanical too) aproach things from a ROI point of view.

If an extra $1000 will save me $100 a year, I will do it. If it will only save me $10, I won't. I'm not sure how to make decisions any other way.

Austin
ROI decisions are easy to get a mathematical answer to.

I'm seeing more factors being included into the decision mix, especially from advanced thinking in Germany. I'm seeing the 'embodied energy' of a solution being entered into the decision mix.

This seems to be the reason that they favor using cellulose as an insulation material (even though it may have a lower R-value), over fiberglass or foam or mineral wool, all of which require substantially greater energy in manufacturing. They will go with cellulose and thicker walls.

-AC
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Old 07-27-15, 04:17 PM   #34
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Quote:
Originally Posted by dablack View Post
Yep JRM. You called it.

Most engineers (I'm mechanical too) aproach things from a ROI point of view.

If an extra $1000 will save me $100 a year, I will do it. If it will only save me $10, I won't. I'm not sure how to make decisions any other way.

Austin
Dablack,

I'm not sure. For me there are a lot of, let's say, hidden variables. Tomorrow the grid goes down, which is entirely possible in this country, and we don't know when it will be back up. Now the ROI goes out the window. Then there's funding people who want to kill us, I'm not especially keen on that. I think there's also the satisfaction factor of seeing meters spin backwards.

Also here's something I never expected, before I got my free intertie I had a strictly off grid backup system in. Well, a couple of years ago Outback modified (for free) my off grid inverters to offgrid/intertie. Now I have the best of both worlds and I'm selling 50 to 60 KWHs back to the grid during the summer. In fact I'm so far ahead I'm using electric heat in some of the winter months. And if the grid goes down I have backup, in fact, so much that a year or so ago we had severe flooding and lost power for a week. I loaned my genset out because I didn't need it!

Sure, when I design a circuit I use ohms law and Fast Fourier Transforms but sometime intuition and gut feelings work really well too!

Rob
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Old 07-28-15, 09:31 AM   #35
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Originally Posted by AC_Hacker View Post
ROI decisions are easy to get a mathematical answer to.

I'm seeing more factors being included into the decision mix, especially from advanced thinking in Germany. I'm seeing the 'embodied energy' of a solution being entered into the decision mix.

This seems to be the reason that they favor using cellulose as an insulation material (even though it may have a lower R-value), over fiberglass or foam or mineral wool, all of which require substantially greater energy in manufacturing. They will go with cellulose and thicker walls.

-AC
AC,

I get what you are saying and that is great that they are doing that. For a DIY guy like me, the embodied energy SHOULD show up in the price. When governments get involved and subsidize one technology and not another, that is when you get some weird numbers.

All things being equal, you would think cellulose and thicker walls be the best way to go. It wouldn't take me long at all to build another wall inside my exterior sheathed wall. Then fill that volume with cellulose. You lose some sqft on your foundation but that is pretty cheap to lose. I think I had my slab poured for less than $7/ sqft. Going all the way around my slab (26x52), if you wanted a 4" wide gap between walls and used an inside 2x4 wall, you would be looking at an additional $700 for the slab area. Add up the 2x4 framing and the volume of cellulose and you would have a pretty good number of what it would cost you. Also, you wouldn't need to worry about thermal bridges. It would also save you HUGE amounts of time running your wires and plumbing. hmmmm Looks pretty good.

For me, it always comes down to $$$ and time.
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Old 07-28-15, 09:44 AM   #36
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Quote:
Originally Posted by Robaroni View Post
Dablack,

I'm not sure. For me there are a lot of, let's say, hidden variables. Tomorrow the grid goes down, which is entirely possible in this country, and we don't know when it will be back up. Now the ROI goes out the window. Then there's funding people who want to kill us, I'm not especially keen on that. I think there's also the satisfaction factor of seeing meters spin backwards.

Also here's something I never expected, before I got my free intertie I had a strictly off grid backup system in. Well, a couple of years ago Outback modified (for free) my off grid inverters to offgrid/intertie. Now I have the best of both worlds and I'm selling 50 to 60 KWHs back to the grid during the summer. In fact I'm so far ahead I'm using electric heat in some of the winter months. And if the grid goes down I have backup, in fact, so much that a year or so ago we had severe flooding and lost power for a week. I loaned my genset out because I didn't need it!

Sure, when I design a circuit I use ohms law and Fast Fourier Transforms but sometime intuition and gut feelings work really well too!

Rob
Rob,

You are 100% right. But those are personal decisions. It is tough for me to tell someone posting online about that their build or insulation choices that they made the wrong choice because their meter won't turn backwards or that the grid is going to go down and then they will be sorry. Those are the things where we follow our heart (gut feelings). Going on gut is fine but that is what it is. No REAL numbers to back it up. Someone on this thread got slammed because he questioned the need for insulation that would not ever pay for itself. If someone wants to go past ROI on insulation, that is fine but we have to remember that it was a gut feeling that causes some of us to do that. For some of us, this is a hobby. We enjoy chasing that last kw, that last air leak, that last bit of waste. Will all that chasing pay back? Maybe......
Someone coming in and saying, that too much insulation won't pay back shouldn't be slammed. Without the governments using tax payers money, solar would be a tough sell. Even with the governments tax money it is questionable if it will ever really pay for itself compaired to other investments. With all that said, I'm very interested in solar for gut reasons.

Sorry for the long post. Lets keep it civil around here. Speaking of civil, mechanical engineers build weapons, civil engineers build targets. HA!

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