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Net-Zero-Energy versus Passivhaus

Each approach to building a superinsulated house has its strengths

Posted on Jan 7 2011 by Martin Holladay, GBA Advisor

In Europe, builders interested in energy efficiency are gravitating to the Passivhaus standard. Meanwhile, American researchers — and a few American builders — have developed a fascination with the idea of the net-zero-energy house. The U.S. Department of Energy has established as a goal that new buildings in the U.S. will be built to a net-zero-energy standard by 2030.

Passivhaus buildings and net-zero-energy buildings have a lot in common. Both types of buildings aim to reduce the amount of energy used for space heating or cooling by designing envelopes with a low rate of air leakage, thick insulation, and high-performance windows.

While Passivhaus designers are content with achieving a very low energy budget, net-zero-energy home designers add frosting on the cake by including a rooftop photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) array sized to produce enough site-generated electricity to balance the home’s annual energy use.

While both approaches have merit, both approaches are also open to criticism.

Advantages of the net-zero-energy approach

The best aspect of the net-zero-energy approach is the fact that, in order to balance energy loads with energy production, designers are forced to evaluate the cost-effectiveness of each energy-efficiency measure and compare it to the cost of a PV array. The aim is to find the least-cost path to building optimization.

Here’s the way such analysis works. Say you are building in Syracuse, N.Y. Designers know that a 1-kW PV array — that is, an array that now costs about $7,000 to install — will generate 1,123 kWh per year in Syracuse. In other words, each $1,000 you invest in PV will reduce your energy expenditures by 160 kWh per year. [Update: in September 2012, the cost of a 1-kW PV system has dropped to $3,500. That means that a $1,000 investment in PV will generate twice as many kWh per year — about 320 kWh — as the calculations shown in this article.]

Using that investment in PV as a benchmark, it’s possible to evaluate other $1,000 investments. For example, what will be the effect of adding $1,000 worth of extra cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. to your attic floor? With a good energy modeling program, it’s easy to do the math; if the cellulose saves more than 160 kWh per year, it’s a good investment compared to PV.

Once you’ve designed a good shell, each incremental improvement adds to the cost of construction, but saves less and less energy. As thicker insulation or additional layers of glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. begin to cost more than PV, it’s time to question the logic of the investment. If you’re building a zero-energy house — that is, a home with a PV array on the roof — it doesn’t make much sense to invest in insulation upgrades unless the investment yields more kWh savings than a PV array.

In 2004, engineers at the National Renewable Energy Laboratory in Golden, Colorado developed a software program, Building Energy Optimization (BEopt), that performs the calculations necessary to determine the least-cost path to building a zero-energy home. For more information on BEopt, see BEopt Software Has Been Released to the Public.

Apples to oranges

Most Passivhaus builders defend investments in envelope improvements that cost considerably more than PV. Their main argument: comparing insulation to PV modules is an apples-to-oranges comparison. While PV modules may wear out in 30 or 40 years — and may require maintenance or repairs along the way — insulation is likely to last far longer and is virtually maintenance-free.

The argument has merit. Nevertheless, when large amounts of insulation are used to save only a handful of kWh per year — the classic example being a very deep layer of rigid foam insulation, in some cases up to 14 inches deep, under a slab foundation — it’s worth stepping back and considering the situation from a neighborhood perspective.

Far more energy will be saved when two houses are each equipped with 7 inches of sub-slab foam than when one house has 14 inches of foam and the other has none. This example raises the question of whether installing very thick layers of insulation in a handful of houses is a good use of the world’s limited resources.

Advantages of the Passivhaus approach

The best aspect of the Passivhaus approach is that it doesn’t fall into the trap of assuming that electricity production is best performed on a residential roof.

It’s hard to understand why so many researchers in the U.S. have concluded that homeowners need rooftop PV. In fact, generating electricity on residential roofs rarely makes sense, for the following reasons:

  • Residential roofs are often shaded by trees or neighboring buildings.
  • Many residential roofs don’t have the optimal slope or orientation for a PV array.
  • A rooftop PV array greatly complicates re-roofing.
  • Most homeowners don’t want to be responsible for maintaining and repairing energy-generation equipment.
  • It’s far cheaper to generate electricity from utility-scale wind turbines — or even from a solar thermal plant in the desert — than from small PV arrays.
  • The cost of tax credits and subsidies doled out to homeowners who install PV arrays increases the tax burden and the cost of electricity for the general population.
  • Programs that encourage the installation of residential PV arrays draw investment dollars away from more logical investments (like improved air-sealing measures) which yield more energy savings per dollar invested.
  • There are far cheaper ways to reduce carbon emissions — for example, upgrading old coal-fired power plants with cleaner technology — than the installation of PV arrays.

Combining the best of both approaches

Although I’m well aware that the expected service life of insulation is longer than that of a PV array, I think that it’s sensible to use the cost of PV as an upper limit or “reality check” when considering the cost of any envelope improvement. It’s a useful way of reining in an out-of-control designer who’s about to go over the cliff.

That doesn’t mean, however, that a superinsulated house will necessarily benefit from a rooftop PV array. If you do the math, you’ll discover that homeowners who invest in PV pay more for their electricity than homeowners who buy their power from the grid. If we go back to the example of the house in Syracuse, NY, we discover that a $1,000 PV array saves only $19 per year, assuming that grid electricity costs 12¢ per kWh.

In other words, these homeowners are deliberately choosing an expensive source of electricity. (There is an exception to this rule: in areas of the country with generous PV subsidies, tax credits, or feed-in tariffs, the installation of a PV array can sometimes save a homeowner money. That’s only possible, however, when the homeowners pass along some of the cost of their PV array to utility ratepayers or taxpayers — in other words, their neighbors.)

The fact that PV-generated electricity is very expensive is a further reason to be wary of any investment in insulation or windows that yields fewer annual kWh savings per dollar invested than PV.

A designer who advocates installing insulation that costs more than PV is anticipating a future with fuel costs that exceed the current cost of PV-generated electricity. That's an unlikely scenario, considering the fact that the cost of electricity generated by utility-scale wind turbines is now much lower than PV-generated power, and considering the fact that PV prices are still dropping.

If a homeowner borrows money to pay for insulation that costs more than PV, the mortgage amounts to an investment that only pays off if future fuel prices exceed the price of today's PV-generated power. To me, that's a risky stock to invest in.

So here's my recommendation: design your house using the net-zero-energy approach to cost optimization — but don't buy or install the PV array.

Are some elements of the Passivhaus standard arbitrary?

Passivhaus proponents have been known to bristle when energy experts suggest that a few elements of the Passivhaus standard — for example, the airtightness limit of 0.6 ach50 or the annual space heat limit of 15 kWh/m²/year — are arbitrary.

Passivhaus proponents have proposed the following explanations for the 0.6 ach50 limit and the 15 kWh/m²/year limit:

  • The purpose of the 0.6 ach50 limit is to avoid structural damage to the building.
  • The purpose of the 15 kWh/m²/year limit is to make it possible to deliver space heat through a home’s ventilation ductwork.

For example, on the first point, here is what Dr. Wolfgang Feist had to say: “The airtightness is one of the things that we really have to stick on in almost all climates. There are only a few climates where this might not be a [requirement], but very few — like in San Francisco. In San Francisco you might not need to have it airtight, but in almost all other climates you need that. A major part of the airtightness requirement is to avoid structural damage. You have bad indoor air with humidity, and if there is an exfiltrationAirflow outward through a wall or building envelope; the opposite of infiltration. through the construction you get really big problems of condensation in the structure. This is the major reason to make it completely airtight, and even in subtropical climates and of course in tropical climates, it has to be airtight because you get structural damage without airtightness.”

Feist’s statement doesn’t bear up well to close scrutiny, however. Plenty of wall systems are robust enough to be fairly immune to structural damage related to air leakage — for example, ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. walls. Moreover, there have been examples of extreme structural damage without air leakage — the most famous being SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. homes in Juneau, Alaska, that suffered catastrophic roof damage due to convective loops through the SIP seams. These convective loops led to condensation and rot, even when no exfiltration occurred.

Finally, almost all wood-framed homes with air leakage rates of 2 or 3 ach50 are doing fine, with no evidence whatsoever of structural damage.

Why does heating energy use need to be so low?

When it comes to the 15 kWh/m²/year limit, there is a good deal of evidence that the limit was chosen to allow space heat to be delivered through ventilation ductwork — at least in central Europe.

According to the Passipedia Web page, “A Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. is a building for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling of the fresh air mass [ventilation air] which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air. ... All airtight buildings (any low-energy building needs to be airtight) require the use of an efficient ventilation system. In Passive Houses this system is also used for heating purposes, without the need for additional ducts, major technical interfaces, auxiliary fans etc. … The way to go therefore involves cutting back on one of the two systems: either on the ventilation system, e.g. by installing an exhaust system only; in this case the building will become a low-energy house with conventional heating; or on the heating system by using the ventilation system for heating as well – in this case the building will become a Passive House. This heating concept automatically implies extremely low energy consumption. After all, using the fresh ventilation air for heating without an additional heating system can only work in buildings with minimal net losses.”

In the colder regions of Scandanavia and North America, it’s extremely difficult to deliver enough space heat through ventilation ducts to keep a Passivhaus building warm in cold weather. This needn’t be a problem, however, since Dr. Feist says that it’s perfectly acceptable for a Passivhaus building to deliver space heat through other mechanisms. Feists’s concession is certainly useful. However, once it becomes permissible to use any type of heat delivery system, the justification for the 15 kWh/m²/year limit loses its original importance.

Thousands of dollars of insulation to save just a few BTUs

Ultimately, it really doesn't matter whether Passivhaus limits are arbitrary or firmly based in a consistent philosophy of conservation. What does matter is whether the extremely thick (and expensive) layers of insulation needed to meet the standard in a cold climate can be justified by anticipated energy savings.

In northern areas, meeting the 15 kWh/m²/year limit requires insulation levels that are hard to justify. For example, Phil Kaplan, an architect in Maine (and one of the Podcasters in GBA’s “Green Architects Lounge” series), is designing a superinsulation retrofit project for Claudia King, a homeowner in Falmouth. Working with energy consultant Marc Rosenbaum, Kaplan proposed a series of retrofit insulation measures (including 4 inches of polyisocyanurate foam on the exterior of the walls) to lower the home’s energy use. After running the numbers, the team found that they were still short of the Passivhaus goal.

By adding more insulation — including 2 additional inches of polyiso on the walls, for a total of 6 inches — the house could meet the Passivhaus standard. But these heroic measures would add at least $2,880 to the cost of construction, while only saving 950 BTU/sf/year. Assuming that heat is supplied by a ductless minisplit heater with a COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. of 2.0, the extra insulation would have a simple payback period of about 58 years.

“We wanted to know if we could meet the Passivhaus standard,” Claudia King told me. “We thought it would be really cool if we could get certified. We did all the figuring, and we found that we needed to do a little more upgrading — to add more insulation in the cellar and more foam to the outside walls. We calculated that the cost of doing wasn’t worth it for the gain we would get — the savings were not worth the extra investment. We could get the same gain for less investment by putting up some more PV panels, so the expense could not be justified.”

For more on this topic, see “Are Passivhaus Requirements Logical or Arbitrary?”

This article has been translated into Serbian: Dva Pristupa Energetski Efikasnim Zgradama


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  1. Ben Southworth

1.
Fri, 01/07/2011 - 09:12

Interesting comparison! One
by Kristen Simmons

Helpful? 0

Interesting comparison! One correction and a couple of comment.

To achieve Passive House Certification, specific heating demand needs to be ≤ 15kWh/(m2/yr) and for refurbishments seeking the Passive House EnerPHit Certificate ≤ 15kWh/(m2/yr).

Getting Passive House Certification does not preclude using site generated energy, be it pv, wind, etc. In the case of one project that I am working on, building to the passive house standard will allow the pv's (with net metering) to meet all the annual primary energy demand. If the client chooses, the project could even be net positive.


2.
Fri, 01/07/2011 - 09:20

Hit send too soon... My other
by Kristen Simmons

Helpful? 2

Hit send too soon...

My other comment is that cost benefit analysis depends very heavily on the assumptions that one is making about the cost of fuel and inflation over time, which really depends on the mindset of the person (the owner) who's doing the evaluation. Incentives can further skew this calculation.


3.
Fri, 01/07/2011 - 09:41

Get the facts straight please
by Marc Rosenbaum

Helpful? 2

The Passivehouse standard doesn't have a heating limit of 10W/m2. It does have an annual heating energy criterion of 15 kWh/m2/year maximum.
People invest their resources ultimately where it makes them feel good. It's hard for me to invest my resources in making a coal plant infinitesimally cleaner, but fairly easy to invest in PVs. I choose to do that rather than to invest in a more expensive kitchen or car, just because it feels to me that it's the right thing to do, and it's within my personal sphere of influence.
It's true that a few boutique houses, either ZNE or PH, don't make a difference really. However, we can look at isolated cases, like parts of Austria, where the PH standard has made significant inroads into the new building stock. Whether it is the right target for a country with such diverse climates as the US is still an open question, but it represents an actual target, which has been sorely lacking in this country. My observation about people that I've trained in PH Consultant trainings is that taking the course forever changes their idea of what a building can be, and that ripple effect is more powerful than the one I've seen teaching people to do ZNE buildings.


4.
Fri, 01/07/2011 - 09:42

Edited Fri, 01/07/2011 - 10:32.

Nice Analysis
by Carl Seville, GBA Advisor

Helpful? 4

Thanks for the solid overview, Martin. I particularly liked this comment about PV: "Programs that encourage the installation of residential PV arrays draw investment dollars away from more logical investments (like improved air-sealing measures) which yield more energy savings per dollar invested." There has clearly been too much emphasis put on incentives for "things" like PV, geothermal, solar thermal, etc, while improving process and behavior have been all but ignored. This is mostly due to the fact that businesses can make more money by selling things than process, so they put their money into lobbying for thing incentives. The best evidence of this is the fact that the Home Star program, a good, although imperfect, set of incentives for high performance homes has languished while other incentives have succeeded.


5.
Fri, 01/07/2011 - 10:10

Edited Fri, 01/07/2011 - 10:16.

Response to Kristen Simmons and Marc Rosenbaum
by Martin Holladay, GBA Advisor

Helpful? 0

Kristen Simmons and Marc Rosenbaum,
Thanks to both of you for catching my error on the Passivhaus limit for space heating energy; I have corrected the text.

To clarify: 15 kWh/m²/year is the space heating energy limit; 10 W/m² is the recommended (but not required) power limit for the space heating system at the design temperature.

The correction of the typo, however, does not affect my basic argument, which remains as originally presented.


6.
Fri, 01/07/2011 - 10:28

Comment
by Mark Attard

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I would agree that Passive house does not preclude the use of PV or other renewable energy sources. Though the bottom line is, why make up for energy loss that is unnecessary? ROI must also include an analysis of the embodied energy of the products used. We know that there is a fair amount of embodied energy used in the production of PV panels not to mention the energy it takes to ship them. This embodied energy is an offset to the energy production of the panels. Depending upon the type of insulation used, the embodied energy in these products can be zero. There should also be life cycle considerations when choosing between building systems and materials. I feel much more confident that Passive house standards can obtain a 100 year plus building scenario with a greater carbon neutrality than net-zero housing.


7.
Fri, 01/07/2011 - 10:47

Response to Mark Attard
by Martin Holladay, GBA Advisor

Helpful? 0

Mark,
Although the embodied energy of insulation materials can be very low -- when it comes to purchased materials, cellulose insulation usually shines as the insulation material with the lowest embodied energy -- I've never seen an analysis that shows that an insulation material has zero embodied energy.

In an article in Home Power magazine, Justine Sanchez cited a 2006 study conducted by CrystalClear that calculated the estimated energy payback time (EPBT) for grid-connected roof-mounted PV systems. According to Sanchez, the study looked at the EPBT for PV systems, including balance of system (BOS) components (racks, inverters, wires, etc.) and assumed a system efficiency of 75%. “The study shows the EPBT for standard, single-crystalline module PV systems to be two years,” Sanchez writes. Systems using polycrystalline modules (produced with a casting method) had an even shorter EPBT at 1.7 years; modules produced with a ribbon method had EPBTs of 1.5 years.

The study used average solar data for southern Europe, estimated at 1,700 kWh/m2 [158 kWh/ft2] per year; average solar production in the U.S. is higher (1,800 kWh/m2 [167 kWh/ft2] per year), meaning the EPBT for U.S. installations shorter.


8.
Fri, 01/07/2011 - 12:03

It's clear
by markobmf

Helpful? 1

that the approach we follow that ultimately works best for our home and climate may be a hybrid or a custom approach and that a certification may be counterproductive. In CA solar PV keeps us out of higher rate tiers and has a marked effect on payback. It works well when our utilities have incentives to save rather than sell more power. Using Katrina as an example, solar PV could also help CA victims of a major earthquake weather a few weeks or months of no grid power if they have PV on their roofs.


9.
Fri, 01/07/2011 - 12:26

Using grid-connected PV during weather emergencies
by Martin Holladay, GBA Advisor

Helpful? 1

Mark Obmf,
I doubt if the average California homeowner has the wiring skills necessary to make use of their rooftop PV arrays in the event of a major earthquake or extended power outage.

First of all, their grid-tie inverters will be useless, because grid-tie inverters require power from the grid to operate. So their rooftop PV arrays will only produce DC, not AC.

Most grid-tied arrays now produce higher voltages than the old 12-V DC systems of the 1980s, so these California homeowners won't be able to use their rooftop arrays to power any appliances from their recreational vehicles (most of which run on 12 V DC).

So, in order for these homeowners to be prepared for the Big One, they need to buy and install:
1. A transfer switch that disconnects their rooftop array from their grid-tie inverter.
2. An off-grid inverter that matches the voltage of their rooftop array.
3. A large battery bank so that they can have some electricity at night.

Those items will cost at least $5,000. But if they buy and install all that stuff, they'll have lights on when the Big One hits. Unless, of course, their home is seriously damaged by the earthquake.


10.
Fri, 01/07/2011 - 12:39

scrutiny is good and . .
by J Chesnut

Helpful? 1

Martin,
Your scrutiny in this comparison leads to better informed professionals. This contributes to better decisions and combining the strengths of both approaches.

As a designer I obviously gravitate towards Passivhaus. The reason being that designers see value in a well developed concept and energy modeling tool that allows the leveraging of free AND DIRECT passive solar gains to radically reduce energy required for heating. This is not just a matter of adding insulation; it is the coordination thru design of the thermal envelope, orientation of the building, and fenestration.

Many designers have the luxury to work on custom homes where cost-effectiveness does not necessarily dictate the design of the home. I imagine builders tend towards net-zero energy because the bottom line is the driving factor.

Say we were to argue which is the best approach for a "more sustainable" future. In this context maybe cost-effectiveness needs to be understood as a reflection of CURRENT conditions and as a requirement may tend to uphold the status quo.

The Passivhaus limits should be scrutinized and understood and changed if beneficial. Although there is a cache to a fixed and branded concept. There is a niche market for Passivhaus design because, like LEED, for the consumer it is 'well-packaged'.


11.
Fri, 01/07/2011 - 12:52

Passivhaus retrofits vs new construction
by J Chesnut

Helpful? 1

When you end with an example of retrofit work trying to meet Passivhaus this is not the best way to argue that Passivhaus is not cost effective.

Passivhaus represents holistic design of an orientated thermal envelope. Retrofitting a building not designed to these principles is a completely different exercise than new construction.


12.
Fri, 01/07/2011 - 12:54

Edited Fri, 01/07/2011 - 12:56.

PHPP is good
by Martin Holladay, GBA Advisor

Helpful? 0

J,
Concerning your statement, "As a designer I obviously gravitate towards Passivhaus. The reason being that designers see value in a well developed concept and energy modeling tool that allows the leveraging of free AND DIRECT passive solar gains to radically reduce energy required for heating."

You're right -- PHPP (the Passivhaus spreadsheet) is an extremely useful tool.

Of course, most designers of superinsulated houses and net-zero-energy houses also consider (and take advantage of) passive solar gains, even when these designers don't use PHPP.


13.
Fri, 01/07/2011 - 13:02

fair point, how can we do it?
by J Chesnut

Helpful? 0

I think that it’s sensible to use the cost of PV as an upper limit or “reality check” when considering the cost of any envelope improvement. It’s a useful way of reining in an out-of-control designer who’s about to go over the cliff.

This is a sensible exercise and in the interests of the client. Don't know if I would go as far as to set it as the upper limit but it does offer the reality check context.

When I think how this can properly be accomplished the designer will need to know the performance of the thermal envelope at different insulation levels to compare prices with solar installation bids.
I can imagine how to accomplish this using the PHPP energy modeling software. Are you aware of other methods of measuring the performance of proposed thermal envelopes at different insulation levels accounting for passive solar gains?


14.
Fri, 01/07/2011 - 13:17

Energy modeling software
by Martin Holladay, GBA Advisor

Helpful? 0

J,
The field of energy modeling software is a huge one, and hard to get a handle on or keep up to date with.

The U.S. Dept. of Energy lists 345 energy modeling programs on its Web site:
http://apps1.eere.energy.gov/buildings/tools_directory/subjects.cfm/page...

Just considering the software programs with "Solar" in the title, I notice SolaCalc, Solar-5, SolArch, and SolarShoeBox. But a great many residential energy modeling programs -- the majority, I think -- make an attempt to account for solar gains. Obviously, that includes the hundreds of programs that don't happen to have "solar" in their title.


15.
Fri, 01/07/2011 - 14:55

Reduce the demand
by Andrew Henry

Helpful? 0

Martin,

To keep things 'pleasant' we need to reduce carbon emissions as close to zero by 2050, which means we are going to undergo (hopefully) a profound transformation in our energy supply. This challenge, to me at least seems best met by doing all we can to reduce our energy demand.

Net Zero doesn't do enough to reduce the demand, it makes up for the buildings energy demand with on site renewables, whereas Passive House focuses on the demand.

More importantly there is a temporal disconnect with NZE between the buildings peak demand and it's renewable electric generating capabilities peak supply. A disconnect you have pointed out with PV for those wanting to live off-grid. Buildings', in heating climates, peak demand is in the winter when there is very little electricity produced from PV. So with NZE you can end up with buildings with higher energy demands (assuming the NZE didn't meet Passive House) and no way to make up for that higher demand because it's winter.

Hypothetically, say a northern jurisdiction mandates that all new buildings be NZE. That jurisdiction could well end up with a much higher winter energy demand compared to a jurisdiction that mandated Passive House. It would have to import supply from other jurisdictions to make up for that demand in winter. The flip side is that the NZE jurisdiction may also have to 'give away' energy in the summertime as it produces far more than the jurisdiction needs.

As for retrofit's, J Chestnut was right in pointing out the use of a Passive House retrofit as an example of costs. I didn't think it was a valid example for comparison.
As well, (this is off topic) I question whether retrofits are worth the bother financially. I recall reading one article pointing out that economically it made more sense to tear down the existing building and start again. Then the design constraints for achieving Passive House, or whatever the goal is are greatly reduced.

Finally, with respect to Passive House ACH targets being overly ambitious, whether or not the ACH target can be met in new construction seems to be an issue that is best resolved by good design practices rather than heroic implementation efforts. From the Passive House examples that GBA has showcased, good design seems to have dealt with the goal of meeting the ACH targets.

Respectfully,

Andrew


16.
Fri, 01/07/2011 - 14:56

Apples and oranges
by Lucas Durand - 7A

Helpful? 0

Martin,
From the point of view of conservation of resources, I think your argument makes a lot of sense. A "reality check" should be part of any project.

I have noticed that ROI (ie: a comparison of monetary investment vs energy return) is often the only approach used to make the required comparisons.
While certainly useful in many cases, it is not clear to me that ROI is the best way to understand where certain thresholds lie. Comparisons seem to become very complicated due to cost variations which are not universally applicable across the land.
In an earlier comment, Mark Attard said:

ROI must also include an analysis of the embodied energy of the products used.

I agree with Mark in the sense that I think a better understanding of embodied energy could provide a more accurate "picture" while also possibly being a less complicated shortcut to understanding conservation in building.

There is a sort of "ROI" that compares energy inputs to energy return and is known as EROEI (Energy Return On Energy Invested).
EROEI has the advantage of balancing comparisons between dissimilar components (like PV panels and insulation) by eliminating the variable monetary aspects and focusing strictly on the net energy return.
By focusing on EROEI, "reality checks" by comparing the cost of insulation to the cost of PV might be side-stepped all together by direct analysis of (for example) the net energy return of increased foam thickness or the net energy return of a PV installation.
Obviously, an EROEI analysis requires accurate data on life-cycle energy use of all components considered in the analysis. Obtaining a comprehensive dataset could be a challenge.
A software program similar to PHPP could be used to run such analyses.
What do you think?


17.
Fri, 01/07/2011 - 15:05

Response to Andrew Henry
by Martin Holladay, GBA Advisor

Helpful? 0

Andrew,
All good points; thanks for your thoughtful post.

Anyone contemplating a new-home construction project has several goals to juggle. Often the best house for the planet is not the same as the best house for the homeowner's budget.

Weighing these competing goals can be tricky. (Moreover, many homeowners can't afford to choose a best-for-the-planet design if that option is significantly more expensive than the best-for-my-budget design.)


18.
Fri, 01/07/2011 - 15:09

Response to Lucas Durand
by Martin Holladay, GBA Advisor

Helpful? 0

Lucas,
I'm not sure whether it will ever be possible to develop a software program that can accurately and usefully integrate "energy return on energy invested" data into residential design.

For example, mud and straw homes, if their walls are sufficiently thick, will probably have excellent "energy return on energy invested" numbers. Does that mean that all homes should have walls built of mud and straw?

Perhaps -- but there are so many variables in the equation that it's hard to see how your proposed metric would be integrated with other requirements.


19.
Fri, 01/07/2011 - 15:37

I see your point.
by Lucas Durand - 7A

Helpful? 0

I suppose my proposal was more aimed at making certain specific choices within a specific project...
For instance: "am I really saving anything by going to 12 inches of XPS instead of staying at 6 inches?"
Maybe 12 inches is what would be required for PH certification, but that doesn't necessarily mean there is going to be a net energy advantage to getting that certification which was a point I think you were trying to make in your blog.
I think EROEI has a lot to offer in these types of comparisons although when its application is most appropriate may be a bit fuzzy.


20.
Fri, 01/07/2011 - 15:40

situational
by 5C8rvfuWev

Helpful? 1

@ Andrew Henry

I'm not at all equipped to debate the subject, but if checks and balances is the focus of this blog and great discussion, I cringed when you made your comment (which I recall you said was Off topic):

> I question whether retrofits are worth the bother financially. I recall reading one article pointing out that economically it made more sense to tear down the existing building and start again. Then the design constraints for achieving Passive House, or whatever the goal is are greatly reduced.

If we are going to speak of "durability" and "sustainability" and "recycling" I can't see that a blanket statement on "tear it down" works very well. I don't mean to be as obvious as this becomes -- but doesn't the renovation or rebuild or remodel of a structure depend on a wide range of variables?

Indeed, there are some that the neighbors would probably help destroy. I however was the "looney tunes" in my neighborhood once upon a time and took down two decaying NE barns to use in a house.

I doubt you meant the statement the way I took it, but again decisions on what to do need to be decided through 'checks and balances.' Or so I'd think.

Respectfully,
Joe Wilson


21.
Fri, 01/07/2011 - 15:47

Further response to J Chesnut and Andrew Henry
by Martin Holladay, GBA Advisor

Helpful? 0

To J Chesnut and Andrew Henry,
J Chesnut wrote: "When you end with an example of retrofit work trying to meet Passivhaus this is not the best way to argue that Passivhaus is not cost-effective."

Andrew wrote: "As for retrofits, J Chestnut was right in pointing out the use of a Passive House retrofit as an example of costs. I didn't think it was a valid example for comparison."

Actually, I'm going to disagree with you here. I think that any honest designer of a cold-climate Passivhaus building will admit that, even for a new construction house, you end up using insulation levels that cost more than PV.

That's why Katrin Klingenberg ended up with 14 inches of sub-slab foam at her Illinois house.

That's why Rachel Wagner ended up with R-60 sub-slab foam and R-40 foundation walls on her not-quite Passivhaus building in Duluth, Minn.

That's why the Waldsee Biohaus in Minnesota ended up with 16 inches of sub-slab insulation and R-55 basement walls.


22.
Fri, 01/07/2011 - 15:54

I really Enjoyed This Post
by Edgar Lopez

Helpful? 0

It is certainly a topic that requires further study and discussion but I do favor the Passivhaus standard for the following reason:

- Resilience: passive systems such as insulation are simple, long lasting and the article mentioned, virtually maintenance free.

Each additional inch of insulation saves less energy the the previous one but each inch still bears the same cost. This diminishing-returns view is a little narrow. Depending on the type of insulation and location of installation, each additional inch can contribute towards improving air-sealing and reducing thermal bridging.

Other than lasting longer than a PV system, Passivhaus-amounts of insulation reduce the size requirement for the heating system... there's more savings there.

In my opinion Passivhaus just makes achieving Net Zero really easy. Is it possible to lump the cost of a Passivhaus certified home and some renewable energy into the mortgage?


23.
Fri, 01/07/2011 - 16:07

Response to Edgar Lopez
by Martin Holladay, GBA Advisor

Helpful? 0

Edgar,
If three builders get together -- one who follows the tradition of superinsulation, one who builds net-zero-energy homes, and one who builds Passivhaus buildings -- all three will agree that lots of insulation is good.

The question is simply, "When do I stop?" It's not an easy question to answer.

In general, I believe that it is true that insulation lasts longer than PV modules. But that isn't always true. The Claudia King project (mentioned in the blog) is a renovation of a 1975 house. When the walls were opened up, it was discovered that the 35-year-old insulation (admittedly, fiberglass batts -- we all know what they are worth) was deteriorated and rodent-infested. All of the wall insulation had to go into the Dumpster.

Meanwhile, my oldest PV module (from 1980) is working fine -- I'm sure it will last longer than the fiberglass batts in the King home. The PV module hasn't required any maintenance, other than snow removal (which is optional).


24.
Fri, 01/07/2011 - 16:46

PH v ZEB
by mike eliason

Helpful? 1

i don't see them as mutually exclusive or competing - PH makes achieving zero-energy buildings w/ significantly reduced cost and area of PV arrays possible.

add in the comfort factor of a Passivhaus, and i think that only makes it more favorable approach towards ZEBs.

the other nice thing about PHPP is that you can calculate the amount of PVs needed to be plus energy and even carbon negative building.

there are a few projects that come to mind combining both, specifically rolf disch's solarsiedlung/sonnenschiff in the freiburg (DE's) vauban district.


25.
Fri, 01/07/2011 - 16:54

Edited Sat, 01/08/2011 - 12:13.

Response to Mike Eliason
by Martin Holladay, GBA Advisor

Helpful? 0

Mike,
Here in colder regions of the U.S., Passivhaus designers are NOT finding that "PH [the Passivhaus standard] makes achieving zero-energy buildings with significantly reduced cost and area of PV arrays possible."

The least-cost path to building optimization -- basically the net-zero-energy or BeOPT path -- results in thinner insulation (in cold climates) than the Passivhaus approach. As I showed in my earlier blog on this topic, Can Foam Insulation Be Too Thick?, Passivhaus levels of insulation often exceed the cost of PV.


26.
Fri, 01/07/2011 - 17:12

PH in cold climates
by J Chesnut

Helpful? 0

Here in colder regions of the U.S., Passivhaus designers are NOT finding that "PH makes achieving zero-energy buildings with significantly reduced cost and area of PV arrays possible."

Passivhaus built in cold climates are still in a prototype phase. There is still some room to bring down costs within the PH approach. Of course solar rebates are a variable subject to change also.

I'm on a third PH design, the current design for a ~2800 sf home. We were surprised in our initial calculations that we could move from an ~R70 (for a carbon neutral operations home @ 1940sf) wall to a ~R45 wall and meet the standard. I wonder if there is a tipping point in the size of home where PH overtakes net-zero in cost effectiveness even in cold climates.


27.
Fri, 01/07/2011 - 17:17

colder regions
by mike eliason

Helpful? 0

that might be true, i haven't taken a stab at anything colder than zone 5 ON PHPP - though that might be an interesting undertaking.

also, in terms of net zero, are we talking source or site?


28.
Fri, 01/07/2011 - 17:30

Site or source energy?
by Martin Holladay, GBA Advisor

Helpful? 0

Mike,
In the U.S., most definitions of net-zero-energy homes refer to site energy, not source energy.

Needless to say, you can use any definition you want.


29.
Fri, 01/07/2011 - 18:05

PH retrofit vs new construction
by J Chesnut

Helpful? 0

Actually, I'm going to disagree with you here. I think that any honest designer of a cold-climate Passivhaus building will admit that, even for a new construction house, you end up using insulation levels that cost more than PV.

I don't doubt this Martin and I wasn't disagreeing with you here.
My point is there is a big distinction between the financing of a new construction to meet PH versus trying to convert an old home.
Deep energy retrofits in general cannot be reasonable financed but someone who can afford to hire an architect for a custom home can with adequate solar exposure attain a design that meets the PH standard within a custom home budget.


30.
Fri, 01/07/2011 - 18:33

It depnds on your purpose
by Zane Selvans

Helpful? 0

Which approach makes sense depends on what your driving goal is. Most builders are just trying to minimize up-front costs and create a superficially attractive building that conforms to current lending requirements and won't result in their being sued down the road. A custom home builder with a client taking a long-term financial view will do some upgrades -- much better insulation than code requires, heavier copper in the wiring, a tighter envelope than most buildings, and good windows, but almost never any on-site generation (depending on available subsidies). The financial sweet spot seems not to be code, nor net-zero, nor PH. Net-zero is a nice simple aesthetic goal, but it doesn't necessarily require a particularly efficient building if you've got money (or subsides) to burn on PV, and it doesn't take into account the embodied energies of your materials, and if what you care about is climate, then low-energy materials and the lowest possible grid-tied load really matter. Afternoon solar power can effectively offset natural gas peaker plants, but if you're on a coal-based grid, all the electricity you draw at night (or throughout the winter) puts emissions up, and they don't come down no matter how much solar power you generate. My understanding of the PH standard was that it grew out of the same conversations that generated the Swiss 2000W society initiative. If we want to run our civilization on renewable energy, then with 7-9 billion people, we each get at most about 2000W to work with, which means our buildings need to pretty much take care of their own energy demands.

Saul Griffith does a great job of laying this view of energy out in his talk Climate Change Re-calculated.


31.
Fri, 01/07/2011 - 18:51

Edited Fri, 01/07/2011 - 18:51.

Response to Zane Selvans
by Martin Holladay, GBA Advisor

Helpful? 0

Zame,
I don't know why you have concluded, "Net-zero is a nice simple aesthetic goal, but it doesn't necessarily require a particularly efficient building if you've got money (or subsides) to burn on PV."

I have never yet seen a net-zero-energy building that didn't have a very low level of air leakage, very high levels of insulation, and high performance windows.

It just wouldn't make financial sense to build a building that was "not particularly efficient" and then buy a PV array 3 times larger than necessary -- simply because the designer was too lazy to build a good shell. It just doesn't happen, because your hypothetical approach is much more expensive than the normal way (a very efficient building with the smallest possible PV array).


32.
Fri, 01/07/2011 - 19:19

My list of what I like that works today
by aj builder, Upstate NY Zone 6a

Helpful? -2

http://www.passivehouse.us/passiveHouse/PassiveHouseInfo.html

http://www.aaepassivesolar.com/low-energy.html

http://www.minnesotagreenhomebuilder.com/docs/Amaris%20Wall%20Section.pdf

Google Natural Building http://en.wikipedia.org/wiki/Natural_building

I am leaning toward what I have done, which is get the solar details as right and as passive as the site allows. Get the ACH down low, which I do now. Use continuous insulation as much as possible no matter what insulation chosen. I am OK with all kinds of insulation, it just depends on the design, budget and the desired level of going natural and truly sustainable.


33.
Fri, 01/07/2011 - 20:20

PV in an earthquake - from Outback
by markobmf

Helpful? 0

Martin,

This seems cost effective and user friendly and by no means an obscure brand or technology. I understand your objections but an analysis for my circumstances in the bay area really make PV on my roof a great solution.

"SmartRE is the revolutionary Smart Renewable Energy solution from OutBack Power, bringing you simplified grid-tie solar with back-up power for residential and small commercial applications. Designed with an emphasis on ease of installation, a SmartRE solution installs and operates similarly to basic grid-tie solar inverters but with the unique additional benefit of providing UPS quality battery back-up during utility outages. An integrated ultra-fast AC transfer switch guarantees that even sensitive back-up loads, like computers, never know when a utility outage occurs. Recommended AGM batteries are maintained and charged by an innovative OutBack multi-stage charging process. This valuable feature assists in providing reliable back-up power and will help extend your battery life up to 10 years."


34.
Fri, 01/07/2011 - 21:38

Payback
by Steve Landau

Helpful? 0

In all this discussion, the quote from the article comes back to me as most disingenuous.

"By adding more insulation — ....... Assuming that heat is supplied by a ductless minisplit heater with a COP of 2.0, the extra insulation would have a simple payback period of about 58 years."

Insulation and the shell easily would last 58 years. I can't see the compressor in a Minisplit lasting more than 15. So you would need to buy 3 minisplit systems, and 2 PV systems to last that 58 years.

Passive, is passive, no compressors, no PV panels or wires outside to rot n the UV and weather of the sun. PH only needs a small fan inside, protected for ventilation.


35.
Fri, 01/07/2011 - 22:42

Edited Fri, 01/07/2011 - 22:46.

Less is more
by aj builder, Upstate NY Zone 6a

Helpful? 0

KISS, keep it simple rules... Less is more..... Hard to argue with what Steve posted. Things like replacing the inverter 10 times in 58 years, and a well build superinsulated home may be just getting broken in. We can build homes that last for centuries if we want to. We can chose where to live so that less is needed to live at the chosen location.

One thing is for sure, the planet will not have trillions of humans some day. There has to be a limit to human population on Earth at least. No one really knows how many of us this planet can handle. But there is a limit and we need to stop adding humans by enacting a one child per law worldwide. This law is way more important than this blog's "which is better" debate.

No human to house and the debate.. is moot. Save the planet, get your tubes cut.


36.
Fri, 01/07/2011 - 23:30

airtightness
by Garth Sproule

Helpful? 0

Martin
Another great blog.
You said "Finally, almost all wood-framed homes with air leakage rates of 2 or 3 ach50 are doing fine, with no evidence whatsoever of structural damage."
I have no doubt that this is true. But the reason that they are "doing fine" is quite likely because of the excessive heat flux through the structure which drying the assembly. Is it not true that as the insulation level goes up, the potential for moisture problems increases because there is much less heat flux? So the requirement for extreme airtightness varies with the amount of heat flow??

Dr Joe writes about this here
http://www.buildingscience.com/documents/insights/bsi-028-energy-flow-ac...


37.
Sat, 01/08/2011 - 06:42

Response to Steve Landau
by Martin Holladay, GBA Advisor

Helpful? 0

Steve Landau,
You wrote, "Insulation and the shell easily would last 58 years. I can't see the compressor in a Minisplit lasting more than 15. So you would need to buy 3 minisplit systems..."

So? All Passivhaus buildings have heating systems. Here in the U.S., the most common heating system for the Passivhaus buildings I've seen is a ductless minisplit system. But it's possible to use other heating systems.

I used the example of the most common heating system used here because it's the most realistic. Choose another heating system if you want, and my basic argument doesn't change. Every Passivhaus building has a heating system! And you're right -- that equipment will eventually need to be replaced, just as it must in any building.

Concerning the fact that insulation generally (but not always) lasts longer than PV, I already conceded that point several times in my article.


38.
Sat, 01/08/2011 - 06:51

Edited Sat, 01/08/2011 - 06:53.

Response to Garth Sproule
by Martin Holladay, GBA Advisor

Helpful? 0

Garth,
You wrote, "Is it not true that as the insulation level goes up, the potential for moisture problems increases because there is much less heat flux?"

Yes. I wrote about that phenomenon here: How Risky Is Cold OSB Wall Sheathing?

You wrote, "So the requirement for extreme airtightness varies with the amount of heat flow?"

Actually, the likelihood of moisture accumulation varies with a great number of factors. In addition to the heat flow, these factors include:
- the outdoor temperature
- the indoor temperature
- the indoor relative humidity
- the pressure difference between the indoors and outdoors
- the size of the hole and the rate of air flow
- the type of materials exposed to these conditions.

Most experts would NOT agree with you that well-insulated homes with 2 ach50 experience "excessive heat flux." (Of course, the R-value of the building assemblies as well as the airtightness are important factors in determining whether heat flux is "excessive.")


39.
Sat, 01/08/2011 - 07:02

More on off-grid inverters
by Martin Holladay, GBA Advisor

Helpful? 0

Mark Obmf,
Your suggested solution is the same as mine. If a homeowner wants to buy a transfer switch, and an inverter designed to work off-grid, and to buy and maintain a large battery bank, then it's possible to have a PV system that works when the grid is down.

I still maintain that my estimate for the extra cost for this system -- at least $5,000 more than a system without battery backup -- is about right.

So we both agree. However, it's important to point out that very few California homeowners who have installed PV have forked over the $5,000 or more for such a system.


40.
Sat, 01/08/2011 - 09:24

Bang for Your Buck
by Shane C

Helpful? 0

It seems to me that both the PH design and Net-zero design are attempting to achieve the same goal, albiet different paths of getting there. I think they compliment each other. I think the comparison between PV arrays or more insulation is apples to oranges. Insulation conserves Heat or cool air in the home. PV generates electricity. Heat savings are measured in BTUs, Electrical savings are measured in KWHs.
All I know is Electric costs way more to heat a house than Hydronic, air, or wood.
I think the net-enrgy input into a material produced is a valid consideration. Its like Ethanol. It takes 95k BTUs to produce to get a fuel that produces 65k BTUs. Its a negative return.
Martin, you say "With a good energy modeling program, it’s easy to do the math; if the cellulose saves more than 160 kWh per year, it’s a good investment compared to PV."
It would be safe to say that it costs more to produce electricity than it does to heat your home.
When looking at dollars, I see people drivin around in cars that they bought for 40k-80k dollars. The value of new car drops as soon as you leave the lot. Is this a good investment? no.
PV arrays and lots of insulation complement each other, the trick is finding the sweet spot for both.

Also, Martin in your article you say a 1kwh system


41.
Sat, 01/08/2011 - 10:27

Response to Shane C
by Martin Holladay, GBA Advisor

Helpful? 0

Shane,
You wrote, "All I know is electric costs way more to heat a house than hydronic, air, or wood."

Actually, it depends. If you heat with electricity using an air-source heat pump (a ductless minisplit unit), the cost can be comparable to other fuels. That's why most U.S. Passivhaus buildings are being heated with electricity (usually using a ductless minisplit).


42.
Sat, 01/08/2011 - 11:08

Heat Flux
by Garth Sproule Zone 7B

Helpful? 0

Martin
You wrote "Most experts would NOT agree with you that well-insulated homes with 2 ach50 experience "excessive heat flux."
Do you think that "most experts" believe that homes that are insulated to today's building code levels are considered "well-insulated"? I live in Zone B where a nominal R20 wall will meet code. This wall probably has a whole wall R value of less than R12 in our climate. I am no expert, but I think that R12 is waaay to little.


43.
Sat, 01/08/2011 - 11:16

More
by Garth Sproule Zone 7B

Helpful? 0

I want to add that the nominal R20 walls that I referred to in my previous post, are probably very durable walls and will easily tolerate 2 or even higher ACH rates and probably higher indoor RH levels as well. But they are durable mainly due to the amount of energy flowing out through the walls. Am I wrong here?


44.
Sat, 01/08/2011 - 11:57

R-12 and R-20 walls
by Martin Holladay, GBA Advisor

Helpful? 0

Garth Sproule,
I'm sorry if my previous posts weren't clear.

This discussion in this blog refers to net-zero-energy houses and Passivhaus buildings. In making comparisons between these two design approaches, I'm working with the basic assumptions I listed in the second paragraph of the blog: "Both types of buildings aim to reduce the amount of energy used for space heating or cooling by designing envelopes with a low rate of air leakage, thick insulation, and high-performance windows."

In general, cold-climate net-zero energy homes usually have R-20 foundation insulation, R-40 wall insulation, and R-60 ceiling insulation, along with triple-glazed windows. There are exceptions, of course, but this is the type of building I'm talking about.

I wasn't talking about R-12 or R-20 walls. That's a whole different kettle of fish.

I think that a net-zero-energy building with these specs can perform well (without structural damage) with 2 ach50, as long as the design is intelligent. Of course, 0.6 ach50 is better, and I admire builders who attain that goal. But I don't think there is much evidence that 1 ach50 buildings or 2 ach50 buildings, if intelligently designed, are suffering structural failures due to the fact that their air leakage rates are higher than 0.6 ach50.


45.
Sat, 01/08/2011 - 21:01

Edited Sun, 01/09/2011 - 06:21.

Passivhaus
by Green Mountain Realty

Helpful? -1

We are a green home builder and an eco green realtor here in Asheville NC. We sell green homes and build custom green homes for clients and will always argue that it is far wiser to spend more money on super insulating and sealing the envelope more vs. installing a ton on Pv on the home to offset energy costs. Just our opinion as degreed engineers, and certified green home builders here in Asheville.


46.
Sun, 01/09/2011 - 16:49

Neighborhood PV vs. Large Scale Renewables
by Kevin Dickson

Helpful? 0

Thanks Martin for another blog post that shakes up the conventional wisdom.

I think you overlooked a few minor advantages of neighborhood PV:

1. Transmission losses - - Although grid-tied PV needs a functioning grid, most of the PV kilowatthours generated at a PV-equipped house stay in the neighborhood and aren't diminished by transmission losses which are usually quoted at 30%.

2. Autonomy - - Let's say you are building a spec house that you want to have low net energy usage. If you install PV, you have added value, but if instead you donate money to the local wind farm, there isn't currently a way for you or your buyer to recoup that money.

3. Utility power outage avoidance - - Once PV market share reaches a crucial point, the local utility will see the potential of outage avoidance that distributed PV inherently has. At that point they will start providing that $5k upgrade you describe, because they can do it much cheaper. Utilities receive big rewards for reducing outages.

In Colorado, Xcel is required by law to reach 30% renewable energy by 2020. Neighborhood PV is one of the top 3 ways this will happen, partly because it's easy and incremental compared to larger, more cost effective but cost intensive measures.

Is a Renewable Energy Standard an artificial incentive? Of course it is, but until a carbon tax is implemented, there is no other incentive to reduce the use of fossil fuel.


47.
Sun, 01/09/2011 - 16:57

ZEB walls
by mike eliason

Helpful? 0

martin,

i put together a 1400 sf, 3 BR project for indianapolis that was designed to meet Passivhaus, which utilizes less insulation than the above mentioned R-20 foundation, R-40 wall , and R-60 roof. here in Seattle - it's possible to get away with even less (I realize we're not 'cold').

migrating the project's climate to toronto while upping envelope to R-20/R-40/R-60, and verification just misses PH standard at 5.20kBTU/ft2a. a slight bump to R-28 under slab, and verification shows 4.69kBTU/ft2a.

so i think, given the proper design, it might be possible to achieve PH in colder climates without significantly more insulation than the net zero approach mentioned. also, a larger multi-family project should be able to achieve PH in colder climates with even less insulation than a single family (again, if properly designed).


48.
Sun, 01/09/2011 - 17:12

Response to Kevin Dickson
by Martin Holladay, GBA Advisor

Helpful? 0

Kevin,
Thanks for pointing out some advantages of distributed generation, especially PV. These are real advantages (although transmission losses are far lower than 30%) -- usually advantages to the utility, not the homeowner, although advantages none the less.

If the day ever comes when local utilities subsidize the installation of large battery banks in private homes, as you predict may happen, this will not be an unalloyed day of joy for homeowners. Battery banks contain lead and acid; they regularly lose water vapor and need to be topped up with distilled water on a routine basis; they get corroded terminals which need to be cleaned and tightened; and they have to be replaced every 6 to 10 years.

In short, these battery banks are a pain in the butt. I know that because I live with one.


49.
Sun, 01/09/2011 - 17:16

Response to Mike Eliason
by Martin Holladay, GBA Advisor

Helpful? 0

Mike,
Thanks for sharing encouraging specs from your projects. That's good news.

It's always good to hear of Passivhaus projects that don't cost too much money or require outlandish amounts of insulation. Let's hope that such projects become more common.


50.
Sun, 01/09/2011 - 17:46

Purpose of PV?
by Greg Duncan

Helpful? 0

What is the purpose of the grid-tied PV for most projects? Is it a financial investment or is it used as an offset for moral or marketing reasons?


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