Image Credit: Image #1: Martin Holladay
More Musings of an Energy Nerd
UPDATED on August 22, 2017 with a new author’s postscript.
Longtime readers of GBA know that I get frustrated by exaggerated energy savings claims. A glaring example is the statement that “a Passive House building uses 90% less energy than a conventional building.” A variation on this claim: “A Passive House building uses 90% less energy than a code-minimum building.”
It doesn’t, of course. The oft-repeated falsehood is based on a boast made by Wolfgang Feist in the 1990s. Back then, Feist claimed that a new Passivhaus residence needed 90% less energy for space heating than a “conventional” residence in Germany. (It’s important to remember that space heating energy is just one small part of the energy-use pie.) The “conventional” residence that Feist was talking about was an average German home, not a new house meeting modern code standards. (Many German homes are decades, or even centuries, old.)
These days, Dr. Feist and the Passivhaus Institut are usually more careful in their statements than many of their enthusiastic followers. That said, it’s easy to find a Passivhaus Institut document online that includes the boast, without any qualifications about space heating or the age of the housing stock that is used for comparison. Here are two sentences from a Passivhaus Institut press release published in December 2015: “Feist built the world’s first Passive House almost 25 years ago. Still today, this terraced house in Darmstadt (Germany) consumes about 90 percent less energy than conventional buildings.”
As I said, it doesn’t. Let’s peel the onion and figure out why.
What two homes should we compare?
Let’s say that a young couple has money in the bank and wants to build a new energy-efficient home. The couple is weighing the added cost of meeting the Passive House standard (either the European standard or the…
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25 Comments
For additional data, my pretty good house in Maine
In our first full year, we used about 9500 kwh. House is all electric. Conditioned area is about 1650 square feet of interior space. House hit Passivhaus air tightness, R-70 ceiling, R-42 walls, R-16 under slab, triple pane Intus windows. Resistance water heater. Hot tub in unconditioned, but insulated room, probably adds quite a bit to load. We keep heat from minisplits at around 70-72° and use A/C rarely.
PV produced about 8000 kwh, so out of pocket energy cost was only $335 for the year.
If enough people provide real life data, we'll have some useful info to support (or not) Martin's point.
Why be annoyed?
I've asked posters here who are contemplating going the Passive House route why they want to pursue accreditation and got a few different answers, from wanting to show they were part of a community, to getting predicable results from their build.
I don't see why these motives, or a myriad of others are a problem - any more than deciding to build a Pretty Good or code minimum house - as long as they are based on a clear-eyed understanding of that the results will be. So what's to get annoyed about in Martin's analysis?
Is there a morality component to the discussion that is being avoided under all the talk of data? For some reason whenever Passive House comes up there seems to be a subtext of "you are either for us or against us" that enters into the discussion. It reminds me of the many splinter groups of marxists who would fight among themselves in the entrance of my Montreal college back in the '70s while the world passed them by.
Martin is an Energy Nerd. He gets upset by bad data wherever he sees it. If Passive House purged itself of these claims I bet he wouldn't spend as much time picking holes in it.
Response to Stephen Sheehy
Stephen,
Thanks for your data -- it's appreciated.
With the caveat that Passive House adherents are likely to ignore your house (since it's not a certified Passive House), here's how your numbers look: The cost of your annual energy use of 9,500 kWh is $1,330 (at a statewide average electricity cost of $0.14/kWh). That translates into 80.6 cents per square foot.
A code minimum house in Maine uses $1.02 per square foot, so your house uses 21% less energy than a code minimum house.
The three relevant tables are shown below.
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Response to Malcolm Taylor
Malcolm,
Thanks for your comments. Like you, I think that the Passive House approach is admirable. The problem isn't the Passive House approach; it's simply the exaggerated claims.
-- Martin Holladay
Response to Martin
In Maine, communities with more than 4000 residents are required to adhere to the state building code, which incorporates the 2009 IBC and 2009 IEEC. Smaller communities may, but aren't required to, adopt either or both codes. My little town hasn't adopted either.
I'm not surprised that my house only used 21% less energy than the code minimum house. I suspect most of the advantage is in heating cost, since most other electricity use employs typical energy star rated appliances which are widely used. As I mentioned in my earlier comment, the hot tub probably uses a good deal of power.
Stephen
Remembering the measures you took to make you make your house efficient, it's obvious that you are a profligate and irresponsible inhabitant and that occupant behaviour is to blame for the lack of a 90% energy savings. I hope you, your wife and the cat are suitably chastened.
My other favorite PH claim
My other favorite Passive House claim is that "it doesn't cost anymore to build a Passive House or "we are building PH for only 5% more than a standard code built house." I heard this claim over and over during my PHIUS training. I naturally took this with a grain of salt, and whenever I asked for more exact numbers as to build costs I was always given some sort of whitewash answer.
If you want to build a PH certified home that's fine, but to say it isn't going to cost more than a code built home is ridiculous.
BEOpt
I have found BEOpt, which is available for free (for now :/) from the Dept of Energy to be very useful in comparing PH measures to code construction, and to try to find sweet spots (perhaps leading to Pretty Good House levels of insulation and glazing). I have not accurately input material costs yet, but that can even better help make intelligent decisions on terms of where to put one's hard earned money. What I don't know is how accurate the BEOpt calculations are, and I don't really have the expertise to guage that. Any insight into whether I can trust BEOpt output would be very helpful.
If only
It seems most new residential in the Midwest and South hasn't caught up with current efficiency minimums. Comparing to code-minimum makes sense for readers of this site but some questionable 90% claims could be true when compared to the majority of homes being built, which do not seem to fit the current energy models. Help bring the bottom up while keeping the top from floating away.
Reply to Malcolm
While my wife and I try our best, the cat adamantly refuses to be reasonable and when no one is looking, turns up the thermostat, runs the dishwasher empty except for his dish and insists on clean beds every hour. The dog is too intimidated by the cat to be of any help. The cat thinks Passivhaus means he can lay around all day and do nothing.
Response to Brian Knight (Comment #9)
Brian,
Your point -- that "the majority of homes being built ... do not seem to fit the current energy models" or minimum code requirements -- is an important one.
The Passivhaus approach (and the PHIUS approach) include quality assurance methods -- for example, mandatory blower-door testing -- which add value to the resulting house. That's worth something, especially considering the low level of code compliance observed in most of the U.S.
Anyone building a custom home probably cares about quality assurance. That said, I imagine that there are less expensive approaches (for example, the Energy Star approach) that also include quality assurance inspections and blower door testing.
-- Martin Holladay
Quality assurance and costs
I agree with Martin's comment #11 that that biggest advantage of a certification program is quality assurance. When I embarked on my pretty good retrofit, I was pretty confident that between the GC's expertise and mine, we knew how to do things right. Of course we didn't, but even if we had known, making sure it actually gets done as specified is exhausting. Having an external standard helps make sure you have a complete checklist of things to consider, and it helps to prevent disputes about doing things right from seeming as personal.
I agree with Kye that most Passive House projects are probably a lot more than 5% over the cost of conventional construction. Some of that has to do with the rigid nature of the energy targets--once you'd done all the reasonable things to get close, the standard sometimes forces you do take extreme measures that don't really make sense. That's unfortunate, because just before that point, you really do have opportunities for real savings through installing smaller HVAC systems that help offset the cost of a better envelope.
But it's important to also keep in mind that there are lots of custom houses that cost double what standard construction costs without any energy savings at all. It's easy for costs to escalate quickly when there are mistakes in design or project management, and when any aspects, whether they have anything to do with energy or not, stray outside of what the contractors are experienced in.
Marc Rosenbaum had a blog post here a few years ago talking about "handprint" vs. "footprint":
https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/reflections-buildingenergy-2015
The concept, roughly speaking, is to consider the handprint, meaning what you or your project can do to move the world towards lower energy consumption, not just what minimizes your own consumption (footprint). The handprint of a Passive House project might include educating contractors and getting visitors to your house interested in low-energy building. For a prospective homeowner, the best opportunity might be to hire a team who has successfully built a passive house, and ask them to instead build a pretty good house.
The handprint of a passive house project might justify the expense, even when the energy savings doesn't. Perhaps the exaggeration of benefits is done in an attempt to enlarge the handprint, but I think it's better to be honest and realistic about the challenges as well as the benefits.
Brian Knight has a point
I think a most important point was made by Brian Knight in comment 9. Comparing to code minimum only scratches the surface. Where I grew up (rural Mississippi) there effectively was no code--(Sheathing, what sheathing? You mean siding? I have seen this with my own eyes.). And in many places, I bet "no code" is still the case. Another point to be made is that not all states have adopted IRC 2015. I'm pretty certain that my local Virginia county has not--code is county by county. So good start Martin, but for the next iteration, I'd like to see you pin the code adopted in localities to the houses being built "code minimum" in that place.
Data point
Martin, if you want pretty good data points too, our pretty good retrofit of a ~2200 sq. foot house in central NH has used 6800 kWh in the last year with electricity as the only energy input. That year includes 4-5 months during which we weren't quite finished. The lack of construction work and the better envelope should reduce the consumption for those months this year.
Occupied by two people. No cat, so that probably accounts for most of the difference relative to Steve's numbers. Or else it's the occasional visits from a pair of dogs. They are pretty good, but not at all passive, so there's definitely some additional BTU input when they are here.
Antonio
You are no doubt right, although I guess that begs the question as to whether it might be more important from an energy conservation perspective to enforce the new codes than try and increase the number of Passive Houses.
Martin was quite specific though (and this is borne out by the quotes in the sidebar) that he is responding to claims that Passive Houses use 90% less energy that those built to a "code minimum".
Response to Malcolm Taylor
Malcolm,
I agree with your point about code enforcement. It's easy to criticize the construction industry in North America -- I do it all the time -- but the solution to the problems in our industry isn't necessarily the Passive House approach.
If code mandates aren't being enforced, we need to come up with strategies (as home buyers or as communities) to address the enforcement problem.
If we need better quality assurance programs and blower-door targets, let's come up with ways to implement them. All of these issues can be addressed without necessarily adopting the Passive House approach.
-- Martin Holladay
4,500 kWh Plug Load?
Looking over our electricity use last year, it was 2.4K kWh for "plug use," and this includes electric stove/range and electric clothes dryer. 4.5K seems way too high, at least for the person who is efficiency minded and might have a Passive House, pretty good house, or improved older house.
Now if comparing all homes, it sounds right. Our utility tells us we use app. 60% less electricity than 100 comparably sized all electric homes in our area.
Aim High
Thanks for this comparative analysis. It seems that the best Passive Homes do set a very high bar, which is a good thing. Here is my data from last year:
2,160 sf, IN (4A), 9,903 kWh, 55 cents/sf. ($.12/kWh)
2015 IECC comparison for S. IN:
2,400 sf (two story), IN (4A), 14,142 kWh, 71 cents/sf
Details of our home- Split-level (split foyer/bi-level), circa 1982, tract home, R-70 in attic, 2x4 walls with fiberglass, brick siding with air gap, newish double pane vinyl windows, all electric, 13 SEER/8.5 HSPF split 2.5 ton heat pump, ducts inside between floors, 50 g. electric resistance water heater.
We compare very well with 2015 IECC, although our lower level 4 feet below grade is more efficient than two story by design.
Next on our list- HP water heater (split or relocate tank to garage), DC replacement ceiling fans, metal roof (with air gap?), new split heat pump when current one fails.
Finally, our usage jumped 10% last year when our older son moved back in. Now four living here.
@ Joe Dwyer
Joe, you are a great example of what can be achieved in existing construction by just getting back to basics and making incremental improvements. Talking about R60 walls and R90 ceilings is fun, but there are many lessons to be learned from a common sense approach.
Even with R-9 (R13 fiberglass in 16"o.c. framing) walls, after adding the HP water heater and higher efficiency HP mini split, your consumption will be close to 50% of the norm. That's awesome! Are you already using LED lighting, E.S. appliances, and eliminating phantom loads as well?
Plug load numbers
Joe,
You're right that plug load energy use ranges widely in the U.S. Plug loads are a growing piece of the residential energy use pie, for several reasons -- heating energy use is dropping, and Americans' love of electronic gadgets is growing.
That said, one family can easily have a plug load budget that is 3 or 4 times higher than the family next door.
I'm interested to see Katrin Klingenberg's data on Passive House energy use, especially the plug load data. It's quite possible that the average family living in a Passive House has smaller-than-average plug loads. If I had to speculate, I might reckon that people who buy a Passive House aren't typical Americans -- they're interested in energy efficiency. So one possible explanation for lower energy loads is that this type of house appeals to a certain demographic.
If the Passive House standard ever became mandated by building codes -- unlikely, but this is a hypothetical exercise -- the energy savings associated with my "certain demographic" explanation would evaporate.
To be clear, I'm speculating here.
-- Martin Holladay
@ Brian Croston
Thanks. It's been an incremental approach over many years.
Yes, all phantom loads are gone and it's mostly LED lighting except for a few old CFLs still in use. Appliances are all HE, including a new ventless heat pump clothes dryer installed in late December. Whirlpool lowered the price by adding a non hybrid version and we jumped in. It works fine, except that it does take longer for heavy towels, etc. It's not a big deal and the heat stays inside with no outside make up air like with a standard vented dryer. Dryer is in the lower level of house.
Our "builders grade" home always amazes me with the corners they cut to save a buck. For example, the original 90 watt Broan ceiling ventilation fan in the bathroom recently started groaning so I replaced it with a new Broan that uses only 20 watts. Unfortunately, they used 3" vent pipe instead of the standard 4". Off to the store to find an adapter and tin snips were used in the opened up ceiling cavity to make the old 3" pipe fit to length with 4" industry standard fan air outlet.
Some pain and sweat always seem necessary to get incremental efficiency with an older home!
PH uses 90% less energy
I agree and have met a few energy academics that think every house in the US should meet PH standards. I think one in particular lives in a 10 ACH older home. Since I finished a PH custom home last year I can report to her that the construction costs were easily 15% higher than an equal code compliant home. My client asked me to build a PH home with a .35 ACH even though he knew he was going well beyond diminishing returns. Comfort was one of his reasons. I enjoyed the process.
If someone wanted to save the world from CO2 and could build a PH I would recommend building a PGH and sealing up grannies house next door and adding some attic insulation to it. Most folks do not understand how important diminishing returns are to the energy equation.
Metered comparison to 40,000+ homes
I hope this post is helps rather than muddies the waters. Attached are two annotated screen shots of how our 1938 bungalow compares to 40,000+ single family homes in the Madison, WI area. The screen shots compare our metered gas and electric consumption for the 12 previous months to metered data from the 40,000+ homes. (Data is updated daily).
To make the comparison fit Martin's example, I entered 2376 square feet as the heated area, rather than the actual 1164 square feet of our small home. (Martin wrote: "This modeled home is assumed to have 2,376 square feet of conditioned floor area).
I also chose to compare our 1938 home to homes constructed since 2000 to better match Martin's goal of comparing to new code compliant homes. No modeling here, just metered data. The square footage and date of construction for the 40,000+ comparison homes comes from the City Assessor's data.
Response to Jonathan Beers
Jonathan,
I'm not sure that the data you have provided add much to the discussion, but for what it's worth, here is my analysis:
A new code-minimum home measuring 2,376 s.f. in Wisconsin (assuming compliance with the 2015 IECC) would have an average annual energy bill of $2,086.
It appears that the average 2,376 s.f. house in Madison uses 520 therms of natural gas a year for space heating (costing $578) and 9,300 kWh of electricity a year (costing $1,302) for a total annual energy bill of $1,880 -- less than my modeled average for a code-minimum house. (Note: I assumed 6,250 heating degree days.)
Conclusion: either Madison residents are energy misers (good for them), or the plug load assumptions I used for the code-minimum house are too high. Either way, I don't think your data alter my fundamental conclusion about the "90% less energy" claim made by some Passivhaus enthusiasts.
For what it's worth, your data closely match the 2009 RECS data for Wisconsin, shown in the bar graph below. (It looks like residential energy expenditures in Wisconsin total an average of about $1,900 per year).
-- Martin Holladay
> he knew he was going well
> he knew he was going well beyond diminishing returns. Comfort was one of his reasons
There are comfort metrics, would be interesting to see this quantified. I'm pretty sure it's minor and easily offset with a little bit of thermostat adjustment.
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