Monthly Archives: August 2009

PHPP — comparing Excel files for Passive House / PassivHaus

OK, so you’re a Passive House / PassivHaus consultant and you are ripping your hair out because something small has changed between 2 model files in Excel / PHPP and you can’t figure out what it is? What programmers usually use is a program called “diff” on unix. And there’s WinMerge in Windows. Etc. But what do you do with a gigantic complicated Excel file with 69 separate worksheets? Well, I’ll tell you what:

1) So here’s what I finally found which seems to work rather GREAT
for finding differences between 2 excel files!

“Florencesoft™ DiffEngineX™ for Microsoft® Excel compares workbooks.”

I used it “out of the box” without changing any options, and it did basically
what I wanted it to. Perfect. And fast! Worth every penny!

2) The one additional step is you will need to unprotect all
worksheets in both files you are comparing. Luckily I found a guide
to that which worked perfectly as well!

3) The only additional thing missing which would be helpful (since
it’s not an option in DiffEngineX) would be a little VBA script to
hide or delete the worksheets in the DiffEngineX results (an excel
file, nice) where 0 differences were found. I will probably write
this (and share of course).

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Filed under erik-green, house, passive house

Passive House. A good idea?

I still think Passive House (PH) is a good idea because it doesn’t need replacing in 30 years
(like the PVs), but I kinda dislike the following…

1. It is hyper-concerned with hitting the heating/cooling loads 4.75 kBTU/(ft²yr)
which is impossible without quite a lot of solar in our climate. (more on solar in a sec)
But then has what I consider relatively easy to hit targets for appliance usage,
and solar hot water. And maybe one should have saved some of their money
on insulation to buy an electric car or a personal vegan chef or something?

An aside:
You could say that being very strict on heating/cooling makes a lot of sense, because
“what if energy prices double or triple?” Well… the answer is… my energy will not
double or triple in cost. It’s on my roof!!! (PVs) The same essentially goes for anyone.
People will start converting to solar heating rather than pay thru the roof for oil or natural
gas for heating and electricity produced from the same sources.

And at the same time, the prices of solar PV panels keeps coming down.

OK, more on PH…

2. It’s a shame it can only model “passive” solar (more windows on S. Fewer on other orientations).
So it really impacts the design. I personally don’t want to live “inside the heat battery”.

3. It penalizes smaller homes because a small house has more shell per space inside.
So a house that is smaller than another could use less energy overall, but not qualify
for PH.

4. There is no factoring of number of occupants in the house.

5. The excel files are pretty crazy. Well.. it’s very nice actually that they are transparent, but annoying
5.1. the Imperial Unit pages refer to the SI pages rather than do calculations in Imperial Units.
5.2. there are areas that are in all german with no references to the literature. Maybe
if I were certified I would have access to someone who could give more info.
5.3. I find “bugs” but no official way to report them

6. Diminishing returns. In that… one can maybe get pretty close to PH without much extra money
spent, but to get ALL THE WAY there starts getting ridiculous. So where is the point that you should
stop and use PVs and air-source heat pumps (or active solar heating/cooling) instead. Assume all
the mechanical stuff needs replacing in 30 years. Maybe use BEOpt (ask NREL if you can try it?)

7. You can say that the insulation doesn’t need to be replaced in 30 years, but the PVs do, but
7.1 PVs will be cheaper and better in 30 years when you buy new ones
7.2 The fancier windows WILL need to be replaced!

And from my calculations, the marginal difference in 30 year spending on PV electricity to power extra
heat pumps (superinsulated vs full-on PH) is about the price of the fancier windows vs the very good windows.

So you are maybe just choosing whether to spend money on human ingenuity in the form of
air-source heat pumps and PVs, or fancier windows. Perhaps the more insulation can be justified, but
from what I can tell… one needs to really get into R-113 levels in walls/roof to meet PH without increasing windows
on the S and reducing elsewhere.

Please let me know where there is fuzzy thinking.

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Filed under car, erik-green, house, solar

Solar Panels and Payback

It’s instant! First month!

Here is some simple math. Our PV array is going to cost $36,000 I believe to install I have heard. It will generate 7200 KWh of electricity every year until the thing dies. Oh, and first some assumptions:

1. Let’s say it lasts 30 years, which I think is reasonable.
2. Let’s ignore the loan that is helping finance it, because if one assumes inflation of 4% a year, then over the 30 years lifetime of a 5.25% loan (1.25% after factoring in inflation), one has really only paid slightly more than $36k in 2009 dollars.
3. Let’s also ignore subsidies and tax credits, etc. Some of which we will get, but some not because Stow, MA’s municipal electric company has not yet decided to take part in the state program that would give their customers access to some funds for PVs.
4. And let’s also ignore the fact that there is NO NET METERING yet in Stow (that’s OK, we’ll only use electricity when the sun is shining).

OK, so here’s the math:

$36000 / (30 years * 7200 KWh/year) = $0.16/KWh

WOW!!!! That’s less than I pay now for very dirty electricity (we buy offsets via MTC Wind Fund) but there is no direct way to select a Green supplier in Stow, MA.

Anyway, point being… this is a great deal even if you don’t care about global warming or energy security, etc.

From a practical standpoint what it means is that if one adds up the increase in our mortgage and our electricity bill each month, it will be less than our electricity bill had we installed no photovoltaic array.

That you are using no fossil fuels is icing on the cake!

Go sun!

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Filed under erik-green, house, money, solar

How big a PV array do I need to run my all-electric car?

One hears reports that soon-to-be-coming (or already in existence Tesla Motors) electric cars get effectively 200 – 250 MPG using some method of fairly(?) converting the electricity use into “gallons of unleaded” (is that with or without the 10% ethanol like we have in MA! 🙂

Anyway, let’s use some math to see what that means in KWh per year and see how many solar PV panels we would need to charge
such a car.

250 miles/gallon * 1 gallon unleaded / 114,000 BTUs * 3413 BTUs / 1 KWh * 2000 KWh / PV array => 14,969 miles!

OK, so that is enough miles for one year of driving for me. And the array we are installed (30 panels * 200W/panel=>6KW) will hopefully output approximately 7200 KWh per year, so the 2000 KWh I plugged in above is just a fraction. So assuming we can charge the car solely when the sun shining, that means we will still have 5200 KWh (433/month on average) left for “household operations”. That should be fine since in Shutesbury we averaged close to 4200 KWh/year (350 KWh/month), but we will probably(?) have an electric stove and oven this time(?) so that will use a bit. Plus some air-source heat pump usage for heat and AC. Still thinking about a pellet stove for heat on occasion. And aiming for nearly 100% solar for hot-water, instead of the MA typical 60%. More on that in another post.

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better than compact fluorescents?

those long fluorescents!

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Filed under contrarian, erik-green, house

Driving to Green Buildings: The Transportation Energy Intensity of Buildings

I am feeling too cheap and lazy to register to read this article, but it brings up a point I think about a lot — that you really have to consider a green house in context with all the other lifestyle decisions one is making. Including driving/commuting. And food choices. Our car use is definitely a bar in the excel bar chart detailing our energy use. And so should the food we eat and the junk we buy of course. And there are other things besides energy use of course. Like air and water pollution, and habitat segmentation.

And I am hoping we can at least use our PV panels to charge an EV electric vehicle someday. And use the direct sun (solar thermal) to heat the house as much as possible.


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The non-techie passive house

I like this! It makes a lot of sense. Worrying about every last detail is kinda interesting for the building-science geeks and engineers amongst us, but the ultimate goal of all this fussing, I think, should be exactly what this builder says… to establish rules-of-thumb so that most people don’t have to do this complicated and expensive modeling to know how much insulation to add to their home and where and how, etc.


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passive house retrofit

I like this passive-house retrofit i saw at because of it’s pragmatic approach. $200-$250 heating bills.

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Keeping the forest at bay

I have to agree with this author… in the northeast where the forest is almost impenetrably dense in summer, at least some lawn is nice to have. It keeps some distance from your house from the jungle. Our new place with have quite a bit of lawn and vegetable garden in front (to the south) since we need to clear at least a bit for our 30 solar panels to function.

In Defense of the Lawn mowing the wilderness…

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Filed under contrarian, erik-green, house