Monday, December 15, 2008

Domestic Hot Water for Zero Energy Homes

Zero energy homes (ZEH's) in the near future will be simple, all electric, and supplemented with PV.

Hybrid PV/thermal solar collectors may be the best solution as costs come down. Sun Drum Solar is now offering a product. Dawn Solar also offers a building integrated hybrid PV roofing system. PVTSolar uses an air-based approach. When I worked at Solaron in the 80's, we abandoned air-based systems, and we were the world leader in air-based until that point. These are the only entries so far in the hybrid market sector. I expect to see more manufacturers enter the fray soon.

Whether or not a solar thermal DHW system is used, a grid-sourced backup water heater is required.
An affordable heat pump hot water heater (HPWH) is now on the market:

This type of system uses only 25%-35% as much electricity as a standard resistance water heater, making it the best choice for a ZEH without solar thermal.
Another bonus of these heat pumps is that they can supply "free" summer cooling for the house.

In the near future as costs stabilize, we'll learn if this $700 is worth it for a home with solar thermal or hybrid collectors. In Denver, a home with 100-150 ft2 of solar thermal or hybrid collectors probably won't need it. The $700 marginal cost would take too long to recoup because the solar is providing 90%+ of the domestic hot water load.

Wednesday, December 3, 2008

More on Advanced Wall Systems

Joe Lstiburek was at the EnergyStar Summit this week, and was ranting about the wall system we should be using in this climate. Bottom line - for less money than than the historical R-13 2x4 wall system, you can build a styrofoam sheathed R30 2x6 wall. Truly a no brainer.

However, there are two significant barriers to implementation:

1. Your framers, who have such a difficult time coping with wall systems that use LESS wood.

2. Your structural engineer, who wants OSB sheathing used everywhere.

One slight potential problem within the assembly, vapor condensation on the inside surface of the styrofoam, has been bothering me for a few years. Joe explained that this has been addressed in IRC 2009 with a climate zone prescriptive solution. It specifies the minimum R value for the external insulation to avoid condensation. This value is also a function of the stud cavity R value, but Building Science Corp. typically recommends 1.5 inches of taped external foam.

Thursday, October 30, 2008

What Ever Happened to Off-Peak Electric Rates?

In the 1970's, PSCO introduced off peak electric rates, which were designed to flatten their demand profile. At the time, a kwh used between 10pm and 6am was priced at less than a third of the cost of an on-peak kwh. If utilities can just tweak their customers usage habits thru rate schedules, they can really drop their capital costs. That is, they won't have to build that new power plant just to cover three week long spikes in demand.

Over the years, the PUC added many "cost adjustments" to the electric bill, which watered down the off-peak savings to be had. Eventually, all customers lost interest in the whole program and it was cancelled. These cost adjustments are multiplied by the kwh usage, and now account for around 66% of a residential electric bill. It didn't matter if all the usage was off-peak, these adjustments were still there in full. So, in 1980 if you were saving 2/3 of your bill with off-peak rates, by 2008, your savings would be 2/3 of the remaining 34%, or only 22%.

Sunday, October 12, 2008

Finally a Foolproof Toilet Fill Valve to Save Water

We had three brand-new toilets that leaked slightly, apparently through the flapper. Even if it wasn't a significant amount of water, or caused a noticeable increase in the water bill, it caused an unsightly red mold to grow. Even though the toilets are cleaned weekly, the mold can be seen as vertical stripes in the bowl wherever the leak runs down the sides of the bowl.

Anyway, Fluidmaster now makes a new fill valve that refuses to refill if there is a slow leak. As soon as the handle is jiggled, however, it will refill. So a tenant can use it just fine with minimal inconvenience, but the normally wasted water is saved.

This may increase your callbacks in new single family construction, but it's the perfect solution for buildings with maintenance staff.

Tuesday, October 7, 2008

H4H Redefined the State of the Art for Zero Energy Homebuilding

With NREL, Habitat for Humanity has built and tested the simplest Zero Energy home that I've seen to date. Lots to learn from the following final technical report:

Perhaps the most surprising lesson is the poor overall system efficiency of the solar thermal DHW preheat system. It shows that these systems may be hardly worth the effort. Ongoing maintenance for a system like this will further degrade the cost/benefit ratio for this subsystem.

Monday, October 6, 2008

NREL Denver Tour of Solar Homes

On Saturday, our East Wash Park home was on this year's Denver Tour of Solar Homes , sponsored by NREL.
Here's the blurb from the tour book:

Dickson Residence

This large house (4200 square feet) was completed in 2004 and is an updated version of the “Denver Square” design. The parcel was formerly a public service substation on three lots. The house uses a true direct gain passive solar design in that it has south facing glass and mass (concrete floors). Please note that the passive solar heating provides 90% of the space heating requirements – so much so that the radiant floor back up system is rarely used. If the owners were to do this again, they would install a less expensive backup system. In some places the concrete has been stained so that it is the actual floor. In other places, cork is laid over the concrete.

The house is joined to the building next door, which originally contained battery storage for the Denver Tramway system. Now the building houses an office and shop area.

The house is built using SIPs (structural insulated panels). In getting the permits for the house, the Denver plan review and inspection departments added eight months of delay in getting a building permit, according to the owner, because of their inexperience with SIPS. Greenprint Denver may be helping to alleviate the problems like this.

An interesting note is that three of the stained glass windows in the house were designed by a relative of Frank Lloyd Wright.

Passive Solar Features


Mass of 2” of concrete on the floor

Trees planted on the east and west for shade control

Photovoltaic Panels

3.3 kW system

Grid tied

Utility bill has decreased $55 per month since installation

Thermal Envelope / Thermal Comfort

Insulated above code with SIPS

Low-e windows

Interior and exterior shades

Evaporative cooling (unique indoor cooler)

Expanding foam insulation around windows and outlets

Zoned heating

Night setback thermostats

Radiant floor backup heating system


Some CFL lights

Motion sensors or timers in the mudroom and garage


6” thick SIPS walls

Thermal breaks at entry doors and perimeter of entire foundation

Pre-plumbed for solar thermal collectors

Lightweight Metal shingles


Energy Star rated

Sealed combustion boiler/hot water heater

Transportation / Lifestyles

Hybrid SUV

50% of all errands are done by bicycle

Light rail is used once a week



Vegetable gardening

Re-Use / Salvaged Materials / Recycle

Reclaimed brick

Reused existing building and converted into a home office from its original purpose

Unique Features

Homeowner trained in solar during the energy crisis of the 70’s

Homeowner holds patents for pneumatic fittings, valves, and a nose hair trimmer

Green Features

EPS insulation

Stained concrete floors

Reused an entire building and converted into a home office

No particle board was used

Steel roof

Cork floor

Water Features

Low flush toilets (5 out of 5)

Low flow shower heads (3 out of 3)


Drip irrigation

REC’s and Windsource

On demand hot water system: “Doorbells” in each bath summon hot water without wasting it

Sunday, October 5, 2008

A little bit of nice publicity from the WPP....

Sunday, September 28, 2008

My First Electric Vehicle

Prices for low end Electric Bikes recently came down another notch, so I snapped one up.
It's fun, and really solves the problem of getting too hot when bicycling around town. You can let the electric motor do all the work on the way to a meeting, and arrive relatively fresh. It has pedals and a seven speed derailleur, so there is always the opportunity for exercise. The small 15-mile range has never been an issue, most bike trips are shorter than that. However, for $100, you can add a second battery to double the range, or to quick-swap batteries like a cordless drill.

Wednesday, August 13, 2008

GM Will Provide Electric Cars Soon or Die

OK, you gotta keep your old clunker running 2-3 more years until the GM Volt is released.

Current estimates have the Volt going about 40 miles before a little gas engine kicks in to increase range. Five more years of battery development will increase range enough to wean us from gas entirely.

As we all have hoped, technology will get us out of this mess, and please note that the free market economy is what encourages innovations. Government incentive programs should be used sparingly. Case in point, the laws that encouraged ethanol production have affected food prices. It's hard to predict unintended consequences, and the free market is smarter than any of us.

Start Learning about V2G (vehicle to grid)

The oil needed for transportation is probably the nation's #1 issue right now. The solution is now being fleshed out, and it's simple, elegant and involves your home.

I'll give the executive summary:

1. Forget Hydrogen powered cars.
2. Forget Natural gas powered cars.
3. Forget ethanol powered cars.

Daily driving trips will be done with an electric car that plugs into the grid at home, work or anywhere. Today's grid can already handle this growing demand, but it must become a smarter grid. Digital powerline signals will meter your electricity usage wherever you plug in. The V2G part comes into play during those demand peaks. All the electric cars that are plugged in during those times will be called upon to put electricity back on the grid, thereby avoiding any potential brownouts.

The reason electricity wins is because it is TEN TIMES cheaper than gas per mile driven. Wind electricity is already cheaper than coal, PV electricity promises to be even cheaper than that.

To learn more, google "V2G" The links change daily.

Of course the solution for the long-distance freight industry has been obvious for 150 years. Trains will replace trucks, a perfect reversal of the 20th century. Electric trucks will be developed to distribute the freight on a local basis.

Friday, May 30, 2008

Obvious Need for Smart Metering

Some sort of weird incentive program has been approved by the PUC. From the Denver Post article:

"Under a new incentive plan approved by the commission, Xcel could recover from ratepayers all costs for programs that encourage customers to use energy more efficiently. Xcel also could receive bonuses if it meets certain targets." Is it just me, but isn't this some kind of circular logic? Here's another way to say it, and it's hard to believe the Post can write this with a straight face: "Xcel will recover from ratepayers all costs for programs that encourage ratepayers to use less." Auugghhh!

How about a rate-based incentive program? That's how the rest of our economy works. You are charged the cost of a service plus a profit. The amount of profit is determined by the market price.

Since Xcel is a monopoly, the market price is set by the PUC. Therefore the market price should be the cost plus the 10% profit that Xcel is allowed by law.

The problem is that the rate structure doesn't reflect actual costs.

The smart metering initiative will solve this problem, so incentive programs like this are unnecessary because normal economic laws of the marketplace will naturally encourage conservation and alternative energy.

Friday, May 16, 2008

Home Tour a Huge Success

The turnout for the Wash Park Home Tour was the biggest ever. We weren't allowed to stay around during the tour, so if anyone has further questions about the home, feel free to call Kevin at 720 435-5909

Sunday, April 27, 2008

Solar Home on the Wash Park Home Tour

Our personal residence, a "solar Denver Square", built in 2004, is on this year's East Wash Park Home Tour.

This annual event is the biggest fundraiser for Steele Elementary.

Things to look for:
1. High SGHC glass used on the south side.
2. "Poor man's terrazo" diamond-ground and stained concrete floors for thermal mass.
3. Rare indoor swamp cooler that serves as a humidifier in the winter.
4. Infloor radiant heat.
5. On demand hot water.
6. Near-zero exterior maintenance.
7. Low-water landscaping.



“The Substation House”



Green Features

  1. Site is at the south end of the block which allowed unrestricted access to the sun. (little to no shading)

  1. Passive Solar : Large window area on the south walls of the house. The interior temperature swings somewhat because of the heat gain from the sun. After a sunny day the living room temperature will be 68, and early in the morning, it will be 64. A room temperature of 65 feels quite comfortable because the house isn’t drafty and the walls and windows are relatively warm compared to older homes.

  1. Minimized window area on east, north, and west. On the north, to save heat in winter, on the E & W to reduce heat gain in summer and shoulder seasons. Most of the E & W windows are shaded for the same reason.

  1. South window glazing is a special low-e coating with a high solar heat gain coefficient (SHGC) to maximize heat gain in winter. This keeps the space heating cost to $20/month for the main house in the 4 coldest months.

  1. Stained concrete floors provide thermal mass to “save up” daytime heat until nighttime. This process is unregulated and occurs naturally and automatically. 2” thick concrete was poured on the first and second floors. The basement slab is 6” to prevent cracking due to somewhat expansive soil. Similarly, the concrete floors help keep the house cool on hot summer afternoons

  1. Large window well on the south side provides more heat and light than usually found in a basement.

  1. Structural Insulated Panels (SIPs) used for wall and roof construction. SIPs can be described as stressed-skin foam panels. They provide a high R-value and ensure a tight heated envelope (reduced unwanted air leakage). Having a SIP roof and no conventional attic trusses make the attic livable space for very low cost.

  1. Unique indoor-mounted evaporative cooler uses 5 times less energy than A/C for summertime cooling. The airflow is reversed thru the cooler in winter, using the HEPA air filter, thereby serving as the humidifier. The indoor location of the evaporative cooler allows easier maintenance. Denver is one of the best places on the continent for evaporative cooling.

  1. Medium-high efficiency boiler for the in-floor radiant back-up heat and domestic hot water. The boiler is “direct vent” to eliminate the possibility of CO entering the house. The combustion air is sucked in directly from the outside, and blown outside after combustion. The radiant in-floor heat system was installed by Advanced Hydronics. Because the home uses such little backup space heat, this boiler was the best choice at the time.

  1. 3.3 KW photovoltaic system mounted on the garage roof feeds power back on to the grid when it is generating more electricity than the home is using.

  1. The pre-existing red brick building was saved and re-purposed as the home office/shop. (It still has poor energy performance, but a brick insulation retrofit experiment is ongoing. This is a city-wide problem needing a solution ASAP.) Side note: this building was originally built in the late 40’s to store a huge bank of lead-acid batteries. These batteries were part of the electrical grid for the Denver Tramway system.

  1. The SIP construction allowed the easy finishing of the attic space, providing a very useful 3rd floor bonus room. (Conventionally built homes have vented attics, which are hot in summer, and cold in winter, and the single largest cause of heat loss and heat gain.) Design flaw #1: Kevin’s experience with finished attics led him to believe that the 3rd floor wouldn’t need any heat. The assumption was that the heat from below would migrate up. It turned out that the house is comfortable at only 65F, so very little heat migrates up at that low of a temperature, and the third floor needs some heat at times.

  1. Exterior below grade basement/foundation insulation. This is a really important detail that is rarely done correctly in new construction. The result is the basement zone stays at 64 degrees in the winter without any heat from the boiler.

  1. No wood or gas fireplaces. Although we like the ambiance of fireplaces, any room with a fireplace would overheat quickly in this house.

  1. Hot water “D’mand” pump. In each bathroom, the doorbell button summons hot water to the fixtures by turning on a pump for a few seconds. This is much quicker than turning on the faucet or shower and waiting for hot water to reach it. This also saves lots of water. This type of demand system is considered superior to timed recirculation systems that waste heat when hot water isn’t called for in the bathrooms.

  1. Note on “passive solar cooling”: In the summer, the large double doors on the third floor can be opened at night along with the basement windows. Although over 1000 cubic feet per minute of air then naturally flows up through the house, it’s still not enough cooling effect for the two hottest months of summer. Denver’s climate has changed enough to generally require active cooling.

  1. Low maintenance items:

a. Brick and stucco exterior.

b. 75 year stone coated steel shingles. They are much lighter and more hailproof than solid roof tiles.

c. Minimal painted exterior wood surfaces

d. Concrete floors have no maintenance, only cleaning.

e. Minimal roof penetrations mean fewer future roof leaks, and less air leakage. There is no fake chimney that is still put on most new homes. The joint between a chimney and the roof is the single largest source of roof leaks.

f. Low maintenance landscaping, wood mulch for weed control

18. Low Water Landscaping: Although there is a bluegrass play area, the rest of this large lot uses xeriscaping and a drip system for irrigation. Summertime water usage is usually under 10,000 gallons per month.

Thursday, March 13, 2008

Smart Metering Coming to Boulder

In previous posts, I have emphasized the need for "smart meters". In a move that was secret until today, Xcel Energy has announced plans for an even more ambitious program called the "smart grid".

They have chosen Boulder for the pilot program.

Saturday, March 1, 2008

Cheap Photovoltaics Mean Easy Zero Energy Homes

Let's see, there are at least two photovoltaic manufacturers in Colorado that promise $1.00/watt thin film PV panels "soon". If you add maybe $4.00/watt for installation, and subtract the rebates, which are at least $4.50/watt, it means your PV investment will be almost free, and it wipes out your electricity bill of $50-$150/month.

By any measure, this is a good investment. Think about it for a minute, and you'll conclude that your new zero energy home should be ALL ELECTRIC. It goes against today's conventional wisdom, but things are changing fast. The reason is simply that there is currently no method for a residential building to make natural gas and put it "back on the grid". In the summer, you'll have excess electricity production, but Xcel pays you retail for it. You can't do that with solar thermal either.

It can also be shown that Zero Energy homes with no solar thermal or natural gas appliances are simpler and cheaper to construct, so it's win-win all around.

Monday, February 4, 2008

Green Politics in Denver

I'm personally not a big fan of traditional green politics, like passing laws that favor evaporative coolers over conventional A/C. (This happened in Denver recently) In most cases, market forces combined with lots of consumer education will produce the best results. "Unintended consequences" often result from poorly thought out laws (just ask Jared Polis). All other things being equal, fewer laws are better than more laws for many reasons. High on that list of reasons is the need for fewer lawyers.

Chris Nevitt, Denver's "greenest" city councilman, however, informed me of an interesting law passed by the city of Berkeley, CA. If you own a home and want to put photovoltaic solar on the roof, find a contractor and get a bid. The city will pay for it, then add the cost to your property tax bill to be paid over time.

With a financing scheme like that, there really aren't any barriers to PV ownership. The yearly savings on your electricity bill is instantly larger than the property tax increase.

Saturday, January 12, 2008

PassivHaus Report

This report, from the CEPHEUS project, should change your mind about many aspects of homebuilding.

I'll try to boil down the most important points in the report in regard to green building in Denver and Colorado:

1. If the walls are superinsulated, if excellent windows are used, and air infiltration is minimized, there may be no need for a heating system per se.

2. A house this tight does need ventilation, and a good way to precondition this air is through a buried tube. The common fear of mold in this tube shouldn't be a problem in Colorado.

3. An 80% effective air to air heat exchanger should be employed to recoup the heat from the stale air being exhausted from the house.

4. Eliminating the thermal bridging commonly seen in stud walls is highly important.

5. A superinsulated home automatically means a very uniform temperature distribution, and increased comfort.