Passive Passion

Passive Passion is a great 20 minute long documentary about the German Passive House energy efficiency standard.  It looks at the roots of the design standard in Germany, and gives a bunch of examples of implementations in Europe, from single family homes to row houses, apartment buildings, public housing, office buildings, etc.  Talks about what makes the standard work: airtight building envelopes, super insulation, no thermal bridging, heat recovering ventilation.  Also looks at a few builders and designers in the US trying to popularize these methods, and do it cost effectively.  Clearly it’s possible, we just have to decide to do it!

Empowerhouse: an affordable, net-zero Passivhaus in DC

The Empowerhouse is an affordable, net-zero Passivhaus design, that came out of the Solar Decathlon competition.  In collaboration with Habitat for Humanity, the team as built a duplex in the Washington DC area that is site net-zero, despite having the smallest solar array of any of the homes entered in the competition.  It was able to do this because it took a Passivhaus approach, aggressively minimizing all loads first, sealing the building nearly airtight, and super-insulating it.  They also integrated a rooftop garden and terrace.  By sharing the heat management equipment between the two relatively small units, they were able to reduce costs substantially.  All this means the low income residents will spend much, much less on energy over the lifetime of the building.  We need more affordable housing that looks like this.

When the River is Client

Design Explorations of the Lower Colorado River, a landscape architecture course taught by a friend of mine at Cal Poly, in which the Colorado River is taken to be the primary client, and human needs are assumed to be real, but secondary.  All we have left is gardening.  We might as well do a good job of it!

Google Street View for building energy efficiency

Essess is doing drive-by thermal imaging in high density urban areas across the US, hoping to target possible building energy efficiency opportunities.  Another company is using urban satellite imagery to choose the best rooftops for solar energy siting.  Big Brother may be watching you… but at least occasionally he’s got the right idea.

Location Efficiency and Housing Type

According to this EPA study, regardless of the type of housing, living in an area with good transit access saves more energy than building a “green home”. Of course, living in a mixed use, transit accessible apartment that’s also energy efficient uses the least energy, but it’s important to realize how limited the potential for cost-effective energy efficiency is in a sprawling suburban context.

Energy Efficiency and Economics at Walnut Mews

Our condo HOA had a meeting last fall, and somebody brought up selling the flat plate collectors on the roof that are part of our defunct solar thermal hot water system.  The 750 gallon cylindrical storage tank rusted out in 2003 after 20 years of service.  The outbuilding that houses it was basically built over the tank, so swapping it out for a new one would have meant either chopping the thing up in place with a cutting torch and building a new one on site, or removing the roof, which nobody was keen on.  Some plumbing got re-routed and the tank sits there still, derelict.  It was also mentioned that the main boiler for our hydronic district heating might be nearing the end of its days.  I volunteered to look into whether it would make economic sense to repair the solar thermal system, and what the options were for the boiler.

Given that flat plate solar thermal collectors generate an average of about 1kBTU worth of heat per day per square foot (according to the US EIA), and given that we have about 250 square feet of collecting area (nine 28 square foot panels), the current system ought to collect something like 250kBTU/day.  Our current boiler consumes 520kBTU/hr worth of gas, meaning that the solar thermal system could at best displace a half hour’s worth of operation each day.  Gas costs about $8/million BTUs, so the boiler costs about $4/hr to run.  If we assume optimistically that system losses are negligible, and that the boiler runs at least half an hour a day 250 days a year (it was only hooked up to the baseboard heating, not the domestic hot water) then the solar thermal system is capable of displacing something like $500 worth of gas each year.  This is a best case scenario though, since the hydronic system needs water that’s hotter than the flat plate collectors can make it (so the boiler will have to do some work to boost the temperature) and because the system losses are almost certainly non-negligible.

Still, $500/year might be a significant savings.  To know whether it’s really worthwhile, we need to know how much it will cost up front to get this savings, and how long we ought to expect to be able to collect it (i.e. what’s the system’s expected lifetime).  I got wildly varying estimates of the cost to get the system up and running again.  At the low end it was $5000, to leave the rusty tank where it is and put a collapsible storage bladder in the crawlspace.  At the high end it was $20,000 to remove the old tank and build a new spray-foam insulated stainless steel one in its place.  I used this calculator to sanity check my energy numbers above (which don’t seem crazy), as well as the estimates.  It suggests that all in, the total system cost including installation would be something like $28,000.  I suspect that a plastic bladder in the crawlspace wouldn’t be as efficient or as durable as the new stainless tank.  For the sake of argument, let’s say the cheap option will only last 5 years, and the expensive one will last 30 years.  The original tank lasted about 20 years.  Here’s what it looks like today:

Derelict Solar Thermal Storage Tank

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