Step it up from Earth Day to Energy Independence Week

Here’s a great idea from Graham Wright, PHIUS Senior Scientist and Chair of the PHIUS Technical Committee. We hope you’ll take up the challenge.

So, Earth Day was great, and everything. And the Earth Hour there.

Energy Independence Week. It's fun, it's patriotic, and we're virtually certain Stephen Colbert would approve.

Energy Independence Week. It’s fun, it’s patriotic, and we’re virtually certain Stephen Colbert would approve.

But let’s be real, Earth Day doesn’t challenge you to actually do anything in particular, and while Earth Hour does, that is vanishingly little  — one hour out of 8760 is addressing like 0.01% of the problem. After how many years now of Earth Day, what do you say we step the game up?

I call it Energy Independence Week. The idea is that, you extend the 4th of July holiday to a full week, during which you observe these three rules:

1. Use no grid electricity.
2. Burn no fossil fuels.
3. Make no trips to the grocery store.

It’s patriotic and fun. Like a staycation. You’ve got the charcoal grill out anyway. Notice that it’s twice as good even as “1% for the planet” in a couple of ways.

A) it’s 1 out of 52 instead of 1 out of 100, and
B) it’s not just a sacrifice concentrated on you for a diffuse benefit to the planet – it increases your own resilience.

I did this in 2008, a few months before I ever heard of passive house. But I like how it ties in – because of the time of year, it focuses attention on avoiding overheating, not a bad thing. (You will be fine if your passive house is not designed too hot. 😉 And it’s forgiving to the many of us who do not yet live in passive houses; this would be a much harder challenge yet in the winter, in most places.

At the time, I was living in rural Minnesota in a straw bale cottage, so heating and cooling wasn’t a problem. I got by with one solar panel and one battery for electricity. That was enough to run the well pump and my laptop. You don’t need much lighting in Minnesota that time of year. Instead of hot showers I swam in the river, which was a short bike ride away. It’s like camping but, you’ve got all your books or shoes with you.

Your challenges may vary. On rule 3 there, stocking up ahead of time is ok, preparations are part of the idea here. One of the other preparations I made was for irrigation — at the time I was trying to keep a bunch of discount hazelnut seedlings alive in the baking sun. I figured my little panel could not generate enough electricity to run the well pump for that, so I set up a big water barrel so I could gravity feed the orchard. Yeah, I faked it by filling it from the well ahead of time; ideally it would have been a real rain barrel all along.

Again, learning stuff like this is part of the fun. So, I hope you’ll take up the challenge and start planning now. And please, share your strategies, tactics, and experiences in the comments section here at the Klingenblog.

The Anchoring Passive House Principle: Equal In – Equal Out

We are glad that this topic of local climate-specific refinement of the passive house standard has sparked such a lively debate and discussion. Clearly there is a lot of interest in the topic! That’s really good.

I’d like to take this opportunity to explain why our proposal to make passive house accommodate North American climate variations does not challenge the standard’s core principle.

We consider the passive house standard’s anchoring principle to be its commitment to comfort through near-perfect balancing of losses and gains. To date, meeting this goal has required minimizing peak load (the worst case scenario of heat loss on the coldest day of the year) to approximately 1 W/ft².  At this peak load only a very small back-up space conditioning source is needed to keep comfortable.

The original idea of this balancing act — and of the peak load target of 1 W/ ft²  — pre-dates the European passive house standard by more than 20 years. The peak load target was first introduced in the U.S. inaugural model energy code in 1975 (a code created as a result of the oil embargo in 1973). Today’s IECC commentary explains the principle very simply: If you have a room that is 100 ft² in area, and that room has a 100 watt light bulb in it, you are meeting your peak load requirement and don’t need a separate heating system.

Of course this is a very simplified way to describe the conceptual anchor of passive house, the light bulb being a placeholder for the sum of the internal energy sources matching the losses through the envelope, including ventilation losses. Equal in – equal out.

Now let me explain why we do not consider the 15kWh metric as either a magic number or an anchoring principle, but rather as a derivative of that peak load assumption. The 15 kWh/m²yr (or 4.75 kBTU/ft²yr) annual heat demand metric is used to identify the amount of heating energy consumed over the period of one year.

That 15kWh figure was derived for the German climate from the peak load target figure (1 W/ft².). It so happens that Darmstadt, Germany is one of the climate sweet spots where limiting heat loss to that 1 W/ft² (10 W/m²) threshold is possible with relatively reasonable and cost-effective amounts of insulation. Germany’s climate is called “moderately cold” for a reason. The delta T is not that great. Heating is the only climate issue that needs to be addressed. That makes the design process — relatively speaking — easy and clear-cut as there are no additional conditions, such as cooling needs or dehumidification, to consider.

We know the design recipe components necessary for building a European passive home envelope that keeps heat loss smaller or equal to our internal gains, or, in other words, meets the 1 W/ft² (10 W/m²) peak load criterion: we calculate the required amount of superinsulation; we use high quality windows, we assume airtightness at 0.6 ACH50…

In Central Europe, we reach the 1 W/ft² (10 W/m²) peak load target with an approximate insulation level of 14 inches of R-4 for a well-oriented, compact single family home. A practical and attainable scenario — in Darmstadt.

From the specs for that same house, we can calculate the total energy usage for heating over the period of one year based on the climate-specific heating degree days. For the Darmstadt climate, that annual heating demand calculates to approximately 15 kWh/m²yr or 4.75 kBTU/ft²yr. No rocket science. Simple energy balancing.

Therefore we do not consider the annual heating demand (15 kWh/m²yr ) as a fixed and given part of the “functional definition” of a passive house,. It is a consequence of designing to meet the peak load criterion of 1 W/ft² (10 W/m²) in the particular Central European climate.

The 15 kWh figure is a good median starting point for passive designs, as it is derived in a median type climate — median delta T, median length of time when heating is required — where the peak load balancing act is fulfilled almost perfectly. But this is only one specific climate with one specific combination of climate characteristics. This 15 kWh criterion will need to flex as the delta T and amounts of heating degree days change and the underlying principles are applied in different, more extreme climates that deviate significantly from the median base line climate of Central Europe.

Aside from heating, the existing standard is limited even further when we factor in additional North American climate issues such as cooling and dehumidification.

To reiterate:

  • We consider the passive house standard’s anchoring principle to be its commitment to comfort through near-perfect balancing of losses and gains.
  • To date, meeting that balance has meant minimizing peak loads to approximately 1 W/ft².  In Central Europe, that happens to pencil out to the 15kwh average consumption figure.

But, we will demonstrate in a future blog post that achieving that peak load goal (and therefore the 15kWh max threshold figure) is next to impossible in some climates, and definitely not practical. Because the peak load of  1 W/ft² doesn’t apply everywhere, neither can the 15kWh.

Other building science experts, Including Marc Rosenbaum, agree that the current standard has limitations, and offer their own ideas about addressing the issue. (Check out Marc’s proposal for New England.) The good news is that despite all these reasonable challenges to the notion of a single standard, the design principles still hold true, and the peak load target remains a useful tool as a benchmark — even if not an absolute in every single climate zone.

As we develop the specifics of our proposal, we look forward to discussion and debate among all interested and knowledgeable parties. Combined with the growing body of data we’ve accumulated from passive house projects that have been built around the continent, we believe we can introduce the flexibility that will make fundamental passive house principles mainstream practice.

In the meantime, look for more on lessons learned, climate complexity and how to possibly refine annual heating and cooling demands while maintaining the underlying physics principles in upcoming blog posts. Stay tuned!!