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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The (HVAC) Elephant in the Room

A look at the difficulties of getting good HVAC design in high performance homes.  Most HVAC professionals are not familiar with the design requirements of very energy efficient homes with tight envelopes.  Most rules of thumb and the very basic modeling that is done in support of sizing the systems implicitly assume a “code” home… which is the least efficient house you can build without getting sued.  Oversized systems cause different problems than undersized ones, but they’re still significant problems.  As high performance homes become more common, more people are running into these issues.  Better contractor, builder, and homeowner education is needed.

Toward a Zero Energy Home by David Johnston and Scott Gibson

I’ve been looking, apparently in vain, for a good book (that’s not in German!) detailing Passive House building and modeling techniques.  The best I’ve been able to do so far is Toward a Zero Energy Home, and it must have been pretty good, since I read it cover-to-cover in less than 24 hours.  It’s not particularly dense or detailed, but it was a nice quick overview of low energy building systems, with lots of pretty pictures, and a dozen case studies from all over North America, including a couple right here in Boulder.

Refurbished with passive house components, kindergarten in Estonia Valga

The goal that the authors have chosen to highlight — “Net Zero” — means that the buildings in question produce as much energy as they consume on an annually averaged basis.  This necessarily means that they all have some on-site production, wind, PV, solar-thermal hot water, etc.  However, to keep such projects reasonably cost effective, it’s necessary to focus first on energy efficiency measures.  Most important among these is a very tight building envelope, much more insulation than code requires, and appropriate glazing for passive solar gain.  Then the internal power loads need to be minimized, by using energy efficient appliances and LED or CFL lighting.  Only after doing all that is it financially worthwhile to start adding on-site renewable generation, capable of meeting the overall annual energy demands of the dwelling.  Financially worthwhile, that is, if you have already decided that you want to create a Net Zero building.

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German Passive House building robots

A short video from German home fabricator Hanse House.  They do both stock and custom homes, but both are fabricated off-site.  The video shows their production facility, and some of the techniques for putting together a building in pieces.  It’s pretty awesome.  Half robotic assembly line, and half humans, building to what’s essentially a CAD specification, with pipes and wires already laid in place within the structural elements before it gets loaded on the truck that takes it off to the building — or rather assembly — site, where the foundation awaits:

And here’s a time-lapse of one of their Passive Houses being assembled on-site:

I wonder if they do multi-family buildings too.  What it would take to get a facility like this operating in Boulder County?  Other than a rebound in the housing industry of course.

Boulder’s Passive Aggressive Building Standards

Usually when people say that “better is the enemy of good enough”, they’re pointing out that striving for perfection can be a distraction from just getting the job at hand done.  There are other dynamics that involve these concepts too.  As social animals, we tend to judge ourselves against those around us.  Once our basic needs have been satisfied, our relative wealth or deprivation often becomes more important to us than our absolute level of well being.  We have little concept of how much is enough.  This can lead to the familiar runaway acquisitiveness (keeping up with the Joneses) when there is a well established (or constructed…) social norm favoring consumption.  Less obviously, it can also lead to an inappropriate lack of ambition when faced with an objective task that is not supported by widespread social norms.

Over the last couple of years Boulder has upped its building energy efficiency standards.  The new permitting regime requires buildings to perform better — net of on-site generation like photovoltaics — than the 2006 international building codes (IBC).  Smaller dwellings (< 3000 square feet) have to use 30% less energy than the baseline.  Medium homes (3000-5000 sq ft) need to do 50% better, and large ones (> 5000 sq ft) have to beat it by 75%.  Obviously this is an improvement over the previous situation, but in comparison to what is possible, and what is necessary to combat climate change, it’s actually pretty unimpressive.  Homes of all sizes built to the Passive House standard use 80-90% less energy than the baseline code, and they do it without counting any on-site power generation against the building’s energy consumption, whereas the HERS index that is used in the Boulder code does count on-site generation.  This is an important distinction, because the atmosphere doesn’t cancel out your nighttime coal-fired emissions with the solar electricity that you sell onto the grid during the day.  All it cares about is the total amount of CO2 released.

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Links for the week of December 9th, 2010

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Links for the week of December 3rd, 2010

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Thoughts on the TVAP and Junction Place Village

Boulder Transit Village Before and After

Boulder has about 100,000 citizens, and about 100,000 jobs.  Of course, a lot of us aren’t working.  Some of us are climbing bums; some of us are four years old; and some of us are climbing bums staying home to take care of four year olds.  50,000 people commute into Boulder every day to work, and about 10,000 leave the city to go work somewhere else, for a net influx of roughly 40,000 workers, making up for those of us too old, young, lazy, or busy to have a so-called “real job.” (The kind you tell the IRS about).  That’s a lot of people moving around, and a lot of lonely driving, since around 2/3 of those commuters are in single occupancy vehicles.  If only there were more places to live in Boulder, especially more places that service employees could afford, maybe so many people wouldn’t need to move around.  This is how the story goes anyway, and while it’s not quite that simple, I think it’s close to true given the 5:1 ratio of in vs. out commuters.

One of the few remaining large tracts of low-density land within Boulder’s borders is the light industrial area between 30th St. and  Parkway, straddling the Pearl Parkway, between Valmont and Arapahoe.  The northern portion of that area is now slated for redevelopment, following the 2007 Transit Village Area Plan (TVAP).  The general idea of the plan seems to be to create an eastern downtown locus, and to eventually have an urban spine running through central Boulder along Pearl St. and Pearl Parkway, from 9th St. all the way out to Foothills Parkway, and to ensure that transportation within this urban core is functional by de-emphasizing the use of private cars and providing excellent connectivity to the rest of the city via transit, foot, and bike.  Additional regional mass transit connections are also planned to this eastern core, including both BRT and rail.  As a human powered urbanist, this idea sounds great to me, and much better than the ocean of asphalt and big boxes that 29th St. unfortunately turned into.  I’d love for Boulder to accept the role of being a small city rather than a big town, while aggressively enforcing the existing well-defined geographical boundaries, and avoiding high-rise buildings.  If we can pull that off, then we will have an interesting, beautiful city of intrinsically human scale, and I can’t think of a nicer kind of place to live.  I haven’t been around for the years of debate leading up to the present situation, instead being preoccupied with graduate school, and unsure whether I would be staying long enough to actually see anything actually get built.  But now I plan to be here, have the time to pay attention, and am interested to see what happens.

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Links for the week of September 28th, 2010

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