Passivhaus versus Net-Zero Energy Buildings

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Passivhaus versus Net-Zero Energy Buildings

Not all houses are solar-ready — and PV ain’t pretty

Posted on Dec 10 2012 by mike eliason

The Passivhaus (or nearly zero energy building) vs. net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. debate has become an ongoing discussion that rears its nerdy head every few months. It really first took grasp shortly before Martin Holladay published his Net Zero versus Passivhaus blog. Recently, the topic has made its way into several conversations – and my arguments for nearly-zero-energy buildings (NZEBs) or NZEBs + renewables always spark a lively conversation. I was asked to put together a post collating my thoughts on why achieving Passivhaus should take priority over zero-energy buildings, or at least before adding renewables.

It may be worth mentioning that I view this as an apples v. brownies issue (I’ll leave you, dear reader, to decide which is which). On one hand, extreme comfort and consumption reduction (Passivhaus); on the other, energy production (which may or may not entail significant energy conservation measures). Passivhaus + renewables was an active (and lively) topic at the May 2012 Passivhaus conference in Hannover, Germany, and one of the more interesting aspects for me is where people fall on the spectrum – especially as it was a handful of Brits and Americans v. the remainder of the crowd on separating consumption and production.

As stated numerous times, significant energy reductions should be a priority (hence, Passivhaus). From an economic standpoint, I understand how a 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 makes sense for a home or business (albeit, a heavily subsidized one). However, a handful of zero-energy buildings in a sea of inefficiency does little in terms of actual CO2 reduction.

Instead, let’s be smart and have the foresight to retrofit (enerPHit!) and build an armada of efficiency (Passivhaus buildings, Minergie buildings, Living Building Challenge buildings – when Passivhaus!) and then, then! – once that’s been attained – let the energy companies do their thing (which they already do better than anyone else, anyway) to develop larger scale renewable projects, to decommission coal plants, and to green the damned grid.

This would have a far greater impact at lesser (collective) cost. It’s also on the radar for much of the European Union – where in the UK, addressing demand could cut up to 22 power stations, and where the Swiss are aggressively planning to reduce consumption by half (!) over the next 30 years.

Those aims, not coincidentally, parallel the goals of the incredibly ambitious Passive House Regions with Renewable Energies (PassREg) program. For those that don’t know, PassREg is yet another program where the leadership of the Passivhaus Institut has been superb. The program will leave the U.S. even further behind Europe. It’s literally the coolest thing since sliced bread, and makes me want to move back to Europe just so I can work on these, too.

The Passivhaus Institut states that PassREg will “… take a critical look the successful models employed by front runner regions, identifying the stakeholders involved, evaluating the driving factors and collecting appropriate solutions that might be applicable in other urban and economic contexts. In turn, the opportunities and existing barriers to the introduction and implementation of PassREg concepts in aspiring regions will be examined. Through PassREg, the wealth of knowledge that arises from this examination of the regions’ models as well as through the case studies of buildings in each region, known as beacon projects, will help aspiring regions to shape success models of their own and front runners to optimise what they already have...”

That’s not to say I abhor zero-energy buildings. We’d love the opportunity to crack open a few more Passivhaus buildings or zero-energy buildings here at Brute Force Collaborative. But if we’re going to shoot for zero-energy buildings, it really makes the most sense in terms of comfort and economics if paired with Passivhaus first.

Thus, I vote Passivhaus first…

It can be difficult for urban buildings and multifamily housing to reach zero energy

Even if achieving Passivhaus levels of efficiency, urban buildings and multifamily projects have proportionally smaller roof areas than detached housing, making it pretty difficult to achieve a zero-energy goal.

And that’s before Donald Trump blocks your solar access with a brass-bedazzled tower. Additionally, urban rooftops are typically utilized as a deck or HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. parking spot, which can interfere with incorporation of a rooftop PV array. +1 Passivhaus

Not all houses are “solar-ready”

Not all buildings are “solar-ready,” and enforcement/encouragement to make houses solar-ready can have some aesthetically dis-pleasuring consequences.

Do we really want to all have south-facing shed roofs? Who wants to live in that world? Not this guy! What if my gabled facades want to face east-west?

Much of the existing housing stock doesn’t have the roof area, orientation, or solar access to make a zero-energy building feasible, whereas updating to enerPHit or near-enerPHit levels may not be entirely difficult. Pushing the existing housing stock to the level of zero energy with rooftop PV is so difficult, it’s only been attempted by a few projects.

Furthermore, obstacles like trees (and power poles, overhead wiring) can seriously affect the output of a PV array (even when bare in winter, as Marc Rosenbaum recently attested). Whereas, trees are a pleasant thing to look at in a warm, comfortable Passivhaus, and can provide shade from overheating in summer. +1 Passivhaus

Passivhaus buildings need a smaller PV array

Achieving Passivhaus levels of efficiency is one of the surest ways to ensure your PV array doesn’t have to spill over the boundaries of the building.

This is true for homes and commercial buildings. As we noted a few years back, the Bullitt Center’s PV array could have avoided intruding into the public domain had the building met Passivhaus. The amount of PV needed for North American Passivhaus homes to become zero-energy buildings is pretty small, especially compared to what's necessary in solar-deficient Central Europe.

In looking at some of the Building America projects incorporating PV, in nearly every case, a Passivhaus would have resulted in significantly less PV than what was utilized (!). The PV arrays for many net-zero projects are much larger than would be needed for a worst-case Passivhaus, and significantly larger than an aggressively efficient Passivhaus.

Instead of having PV bleeding out over the entire roof and adjacent garage, you could conceivably get by with just adding PV on your garage. +1 Passivhaus

Retrofit projects could be cheaper if they aimed for PH + PV

When you have an existing project that could be considered solar-ready – e.g., one with a generous south-facing roof or a large enough flat roof – it may actually be less expensive to achieve Passivhaus/enerPHit and add renewables than to just add lots of PV.

Those existing projects in the U.S. that have been able to achieve zero-energy status seemingly do it on the backs of large tax credits and incentives (as was the case for the Grocoff Net Zero project: $49,000 out of pocket, $43,000 incentives/credits!). In a brief breakdown of their numbers, an EnerPHit-type reduction actually would have resulted in avoiding the ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures. ($21,000), and a “Passivhaus + PV” system would have been anywhere from 33% to 59% smaller. Even tripling the insulation/airsealing cost, adding minisplits and $100/sq. ft. Passivhaus-certified wood windows, the Grocoffs would have spent much less money to achieve ZEB – which by the way could have allowed those generous tax credits and incentives to be spread around to more projects and have even greater economic and environmental impacts. +1 Passivhaus

New buildings could be cheaper with the PH + PV approach

We’ve looked at this on a couple of buildings here in the Northwest that aimed or are aiming to be zero-energy buildings. Two of the more high-profile ones (Bullitt, zHomes) could have actually saved quite a bit of money (through PV/mechanical costs) by achieving Passivhaus first.

We’ve been stating this for years, as have others in the Passivhaus community – but I think we’re finally at the point where the cost to achieve Passivhaus is exceeded by the reduction in PV costs through meeting Passivhaus. Onion Flats Rowhouses in Philladelphia ($129/sf!), which took the PH + PV approach, are a terrific example of this (see Image #1, above).

For the Salem Passivhaus, the size of the needed PV array would only be 2.8 kWp (PHPP) – 3.8 kWp (actual) – to offset the energy consumed. In Germany, where installed PV prices are even lower than the U.S., the emphasis is still on “Passivhaus first, then renewables.” They’ve been doing this in solar-deficient Austria, Switzerland, and Germany for a decade now.

They’ve even surpassed net-zero through the incorporation of Passivhaus: Passivhaus + renewables = Plusenergiehaus (a.k.a. producing more than consuming) – and this was also a large focus at the Hannover conference.

As the cost to achieve Passivhaus in the States drops due to familiarity, smarter designs, smarter Passivhaus integration, and the use of affordable and locally manufactured products (pretty please!) – this will be even more true. +1 Passivhaus

PV ain’t pretty

Yup, like semantics, aesthetics count. The nasty array on the banal house below isn’t even an extreme example.

Sure, there are a few projects with building-integrated PV, as well as a few zero-energy projects, that incorporate attractive PV installs (next post!) – half of them are Passivhäuser. But let’s be honest: most PV installations are an aesthetic abomination.

PV arrays tend to be rather crude, don’t work well with certain roof types (mansard! hip!) – and if the roof angle ain’t where it should be for optimal performance, racking the panels up or down on a tilted array just makes the installation look worse.

This goes doubly for solar-hot-water installations, which except in certain applications don’t really make economic sense anymore, anyway (as Martin Holladay claims, solar thermal is dead!).

I just don’t get the appeal of looking at roof-mounted PV arrays, when they’re usually so poorly installed that even the aesthetically ridiculous spoiler on a VW Beetle looks light years better. +52 Passivhaus

Passivhaus wins on the embodied energy argument

As we’ve blogged (and the Passivhaus Institut and others have shown), the additional embodied energy required to hit Passivhaus is nominal, and is recouped in a few years at most (or less – if using natural materials).

Whereas, studies on the embodied energy payback of PV systems are on the order of nearly a decade (or more) once accounting for the structure, inverterDevice for converting direct-current (DC) electricity into the alternating-current (AC) form required for most home uses; necessary if home-generated electricity is to be fed into the electric grid through net-metering arrangements., and location/orientation/system efficiency. +1 Passivhaus

Passivhaus wins on the quantity of rare earth minerals required

You can build a Passivhaus almost entirely without rare earth minerals, but a photovoltaic panel?

Not so much. If mountaintop removal is environmentally devastating, if the tar sands are an environmental desecration – should we really give rare earth minerals a pass because iPhones and androids are überkůl? +1 Passivhaus

A Passivhaus is a resilient house

Resilient buildings have been getting a lot of (deserved) attention lately, thanks to Alex Wilson’s latest venture. In a lot of respects, this is. A certified Passivhaus should have few issues with durability (part of the reason for the extreme airtightness).

A grid-tied PV won’t keep you warm at night during a blackout. Roger Lin’s Arlington Passivhaus lost power for nearly two insanely hot and muggy days last summer. How’d the house perform? Extremely well: “While the outdoor temperature was 92 degrees, the basement was a comfortable 73 degrees. First floor was a warm but not unpleasant 81 degrees. Second floor was 79 degrees… Insulation really works. First, all the insulation in the walls and roof is effectively isolating the indoor environment from the outdoor elements, slowing down the effects of extreme outdoor temperature changes, i.e. after 40 hours of power loss, the first floor only warmed up by 6 degrees (75°F -81°F) and second floor by 2 degrees (77°F-79°F).”

And, as Greg Duncan recently tweeted, the “Winter of ‘extreme storms’ is new norm. Passivhaus ensures comfort from drafts, cold; resilience against outages and respite from loud winds.”

Whether it’s holding in heat, keeping the heat at bay, or reducing external noise, Passivhaus bests a zero-energy building in nearly every case. Another way to think about it: Don’t like living next to that loud street or in that airport approach? Maybe you could use your solar panel as a sound barrier! +1 Passivhaus

Zero-energy buildings are not bound by Quality Control

Finally, and I think this is one of the most important reasons, Passivhaus (at least in Europe) is much revered for being the “quality control” standard (despite PHIUS’s ridiculous proclamation to the opposite).

Recently, a costly zero-energy building wasn’t built well, and during the monitoring process, it became clear there were performance issues. This Living Building, the Tyson Living Learning Center, required an envelope audit – less than six months post-construction!

Shooting for Passivhaus would not only have saved them the headache of the audit, it would also have saved some serious coin. The Center as a “worst-case Passivhaus” would have reduced the amount of PV required by two thirds (!) compared to what eventually was installed/needed to meet LBC.

This debacle led to our critique of the Living Building Challenge program, which we actually support and would love to see heavily adopted – just in conjunction with Passivhaus. +1 Passivhaus

So fix yer damn U-values!

Focus on your air sealing. And build a stunning Passivhaus.

Because then – without any horrendous, oversized, budget-busting photovoltaics slapped on top – your house can truly be a very, very, very fine house!

Mike Eliason is a designer at Brute Force Collaborative in Seattle, Washington.


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Image Credits:

  1. Onion Flats