Zero Energy Home Virginia:Solar PV-show me the money!

Everyone is always curious about the cost of solar PV and its "payback". So here's the numbers in black and white. The 4.2kW system cost $30,973 installed. The Commonwealth of Virginia gave us a rebate of $7189, and the Feds will give us a tax credit of $7135, resulting in a net cost of $16,649. We are selling the SRECs (Solar Renewable Energy Credits) for $200/yr. each (thanks to Cory, from olddominioninnovations.com, for brokering this) , for a total of approximately $800-1000 per year. The panels are generating from 11-25kWh per sunny day (less right now, with the shorter days & the sun lower in the sky; more come the long, high-in-the-sky days of early summer). So there it is, in black & white. I will leave it to each of you to decide how the "payback" looks to you, as the ways of calculating it are as myriad as the colors in the rainbow! All I know is that I love watching the digits in the Dominion Power digital meter get smaller!

Tightening up to Zero: the Blower Door test Blowout!

Creating a tight envelope is a critical goal in shooting for a zero energy home. And it is not enough to simply apply the correct techniques and materials, it is essential that we have a measure of their effectiveness. This is where the blower door test comes in. A blower door test is a diagnostic tool designed to test the air tightness of buildings.

A blower-door fan is sealed into an exterior doorway, all the house vents are temporarily sealed, and the calibrated fan blows air out of the house creating a pressure difference between the inside and outside, which draws air into all of the inadequately sealed cracks, holes and penetrations. A pressure sensing device is used to measure the rate of pressure change/leakage. The data is entered into a standardized formula and the number of Natural Air Changes per Hour (NACH) is derived. Typical production-built homes built under current building codes will score at about 0.5NACH or higher (one complete air change every two hours). A well built, near zero energy home aims for a score of 0.1-0.2NACH. EarthCraft Virginia officials, including Chuk Bowles, Technical Director (tending to the pressure monitor above) and KC McGurren, Executive Director, supervised the testing of our home this week.

As KC is indicating in the picture, the results were encouraging! We registered a score of 0.16NACH, reflecting approximately one complete air change every 6 hours, approximately 3 times tighter than a well built new conventional home! Mark Waring, our builder, said that he was very pleased with this performance, which reflects the tightest home he has built to date. This tightness will minimize the heating/cooling load, reducing the demand on the geothermal system and putting less draw on the solar PV array.

Zero in on Geothermal HVAC in Virginia

In a typical home, heating and cooling represents 56% of energy usage, the largest piece of the energy consumption pie. To strive for a zero energy home, it is logical to try to drive this heating and cooling load down as low as possible. Although we initially considered using solar thermal radiant heating, we soon abandoned this idea in favor of a geothermal heat pump in combination with solar PV. Solar PV is more "plug and play" than solar thermal, and when combined with geothermal, serves as one low energy solution to both heating and cooling needs, both of which are high demands in the temperate Virginia climate. A ground source geothermal heat pump uses the relatively constant temperature of the ground six feet below the surface, which in Virginia is estimated to be approximately 60 degrees, to heat or cool the home. An antifreeze solution is piped through loops in the ground where, depending on the season, heat is either absorbed and used to heat the home, or the unwanted heat from the home is expelled. As in a conventional heat pump, a compressor and an air handler are used to condense and distribute the heat exchange. A geothermal heat pump does not produce heat, but rather it extracts and moves heat. Where the most efficient gas furnace may approach 97% efficiency, a geothermal heat pump may approach 400% efficiency, in effect, extracting 4 units of heat energy for each unit of energy expended. Research suggests that a geothermal heat pump may result in energy savings of 69% over gas heat and 40% over air to air heat pump heat. Jim Satterfield of HVAC by JM LLC worked closely with our builder to assess our projected heating and cooling loads and recommended a 4 ton Comfort-Aire GeoMax2 split unit connected to 3200 feet of buried loop. The GeoMax2 is a rebranded Climatemaster Tranquility 27 Series, which has an EER rating of 16.6/23.7 and COP rating of 3.7/4.2, some of the highest ratings available. In comparison, Energy Star requirements for geothermal ground source heat pumps are 14.1 EER and 3.3 COP. The two stage compressor and variable speed fan coil contribute to the heightened efficiency while its reliance on R410-A refrigerant protects the ozone layer. The GeoMax2 includes a desuperheater, which uses excess heat to pre-heat your hot water, a nice added benefit. This a split unit, which means that the refrigerant/ compressor unit is seperated from the air handler unit, allowing them to more easily fit in the safety of the conditioned crawl space. The refrigerant/compressor unit is a small gray box about the size of a small bedside table. Once again, great things come in small packages!

The air handler is the same type of blower/ducting

system you have on your furnace.

But then lets not forget that buried loop I mentioned earlier. This involves 3200 feet of 3/4 inch high density polyethelene pipe buried in two 400 foot runs of trenches dug six feet deep and placed 10 feet apart. Suffice it to say that pretty much snaked over every available inch of our front, back and side yards. It looked like the mole from H_ll attacked our lot.

And in this case it was a big bright orange one!

Insulating our way to Net-Zero: Loose-Fill Cellulose

The last piece of the insulation puzzle is wet-spray cellulose's "poor relative", loose-fill cellulose. Loose-fill cellulose is made of up to 85% recycled paper and is sprayed dry with air, providing an R-value of 3.8 and blocking air leakage. Less expensive than both Icynene and wet-spray cellulose, our builder used it primarily in accessible, flat areas, sometimes using netting to hold it in place or offer support.

And the last piece of the insulation puzzle, would be fiberglass. To quote our builder, "in the inside walls for inexpensive sound insulation, that is the only place you will find fiberglass in one of my homes." He exaggerated a little, as he also used it (CertainTeed DRYRight) in the outside eaves, to form a barrier to spray the cellulose against. His opinion is that fiberglass is poorly suited to do its primary job, to provide insulation and to prevent air infiltration. To accomplish these tasks, the fiberglass must be installed perfectly, fitted precisely into all the nooks and crannies and sealed consistently around each and every opening and penetration. This is very time-consuming, labor intensive and challenging, as anyone who has attempted to apply fiberglass batt insulation can attest. It also tends to lose R-value across time and offers minimal thermal mass.

Insulating our way to Net-Zero: Icynene

Another integral part of creating a well sealed and insulated space involved the use of Icynene spray foam insulation. Icynene is a 100% water-blown insulation that sprays on as a liquid and immediately expands to 100 times its volume in soft foam that fills every crack and crevice while providing a flexible seal and a R-3.7 insulation value. It does not out-gas or emit any harmful fumes and it retains a stable R-value across time. It is an open cell foam, so it does not block the movement of water vapor. Icynene is a petroleum-based product (Icynene-R is a new product based on castor oil)that is a flame retarding material that will be consumed by flame, but contributes no fuel and will not sustain fire upon removal of the flame source. It must be covered by an approved thermal barrier, which our builder will accomplish by seperating it from living space with drywall.

More expensive than wet-spray cellulose, but less expensive than closed cell spray foam, our builder chose to selectively use it in hard to access or otherwise challenging areas, like the vaulted ceiling, where it clings tightly in place, helping form a continuous, insulating air barrier. Seven inches were sprayed along the roofline, for an R-25 insulation rating. EarthCraft specs say R-20 Icynene is equal to R-30 of fiberglass or cellulose on vaulted surfaces.

Note in the pictures that all ducting is being kept in conditioned space, increasing energy efficiency.

Insulating our way to Net-Zero: Wet Spray Cellulose

Our builder put a lot of thought into deciding what insulation to put where, balancing effectiveness against cost. One of his favorite products is wet-spray cellulose insulation, in this case from Applegate Insulation, a product that requires one fifth of the energy needed to produce an equivalent amount of fiberglass. Made from 85% recycled paper content, largely newspaper, and treated for fire and mold resistance with borate and with a dry adhesive, it is sprayed under pressure into the cavity with a small amount of water, completely filling all the nooks and crannies, reducing the flow of heat and virtually eliminating air infiltration. After completely filling the cavity, a rotating stud scrubber brush is run over the area, leveling it even with the tops of the studs. The cellulose will dry over the next 24 hours, becoming firmer to the touch. No dangerous outgassing is involved, as it does not contain any formaldehyde or respirable microscopic fibers.

The finished surface is quite smooth and spongy to the touch, and the 3.5" of cellulose provides an R-value of 13.3, which when added to the R-3 of the SIS (Dow Structural Insulated Sheathing) on the outside, results in an overall stable R-value of 16.3 for the walls. Our builder believes that the superior air sealing power and the added thermal mass provided by the wet spray cellulose make that R-value a conservative estimate. It is notable that contrary to initial impressions, wet spray cellulose is quite fire retardant, a result of both the fire retardants applied to the paper and its heavy oxygen-limiting density, providing up to a 50% increase in fire resistance. It is also a very good product with respect to air quality, as indicated by the American Lung Association of Virginia choosing to use it in it's Breathe Easy headquarters.

Richmond Virginia Zero Energy Home Progress & Appearance

It seems time to show how far the house has progressed and at the same time illustrate that a ZEH does not have to look unconventional. Placing the Schuco PV panels on the back of the south slanted garage roof aided in this outcome, as they are nearly unnoticeable from the street. I would add that the unusual ceiling planes of the pictured great room have caused Mark, our builder, a lot of thought in terms of where to set the boundary for the conditioned space, how to keep the HVAC ducting in those confines, and where to use loose cellulose versus spray foam insulation. It is becoming increasingly apparent how challenging it is to take the basic principles of a ZEH and translate them into a workable application.

Net Zero Energy Virginia Home and best practices...

As you tighten the envelope of the home, control of moisture becomes much more important, and standard practices become too low a target. the last thing you want is to have your tight envelope trapping wayward water. The dark material you see here coming up behind the brick is 30lb felt underlayment. Although the SIS already forms a vapor barrier, our builder, Mark Waring, prefers the redundancy of additionally installing the felt on top of the SIS.

The green material you see is GreenGuard® RainDrop® Housewrap.
RainDrop’s innovative drainage channels keep water out of the wall system. The channels won’t crimp, collapse, or flatten, ensuring water will drain no matter how tightly cladding is nailed to the wall. Because it’s not perforated, RainDrop resists air and water infiltration. Plus it breathes to allow moisture vapor to escape. With its high tear resistance and translucent design, installation is quick and easy with no job site waste. And it stays UV-stable up to 4 months. RainDrop is an ideal secondary weather barrier for fiber cement, vinyl, foam-backed vinyl, and wood sidings and meets the National, Standard, Uniform and International Building Code requirements for air barriers, moisture protection barriers and weather-resistive barriers. It is used on top of the SIS and behind any of the areas to be covered with shingling.

The window to a zero energy home, Richmond, VA style...

When it came to window choices, there was a lot to consider, because as you increase the tightness and the insulation level of your home, the glazing makes a greater impact on energy usage. And our particular home design has a lot of windows! Looking to the Efficient Windows Collaborative (EWC) for guidance, the 2009 Energy Star standards for Virginia suggested windows with a U-factor (the rate of non-solar heat loss or gain
through a whole window assembly) of .40 and a SHGC (the Solar Heat Gain Coefficient is the fraction of incident solar radiation admitted through a window) of <.40. But our EarthCraft builder reminded us that the EnergyStar standards were going to be tightened starting in 2010, so we set out in search of better windows. The new Virginia Energy Star standards are a U-factor of .32 and a SHGC of <.40, but few suppliers had windows available reflecting the new values yet. After some creative searching, Mark found us PlyGem MW Pro Series windows with a U-factor of .29 and SHGC of .25 for only $400 more than 2009 rated windows. These are vinyl clad PVC construction, 20 year, double pane, argon gas-filled, low-E glass windows with a Warm Edge technology ( the Warm Edge glass spacer system reduces thermal transfer around the glass perimeter by utilizing a unique U-shaped channel to separate glass panes and interrupt the natural flow of heat to cold). Hopefully the added insulation they provide will reduce the load on our geothermal HVAC system. We are hoping that the lower SHGC will work well, as we have a lot of southeast facing glazing on the back of our house, which because of solar sighting, has little shade in the summer, making excess heat gain in hot muggy Virginia a potential problem. Oh, and that door you see there, that is the Therma-Tru Classic-Craft® Mahogany(waiting to be stained) fiberglass front door, which is also EnergyStar rated. Have to have all the portals covered...

Solar PV arrives at the Virginia zero energy home!

Every zero energy home needs a renewable power source and ours consists of 20 Schuco SPV 210 panels supplied by Dereck McAvoy of Midsouth Building Supply. These monocrystalline panels are some of the more efficient ones available, rated at PTC/STC 91.5%, indicating that they in effect, under real world conditions, produce very close to their advertised power rating. They are warrantied to produce at least 80% of their initial output for 25 years. They are on the List of Eligible SB1 Guidelines CompliantPhotovoltaic Modules for the Go Solar California program, one of the longest established and most respected state solar programs. They were installed on the back face of the south facing garage by SunFlower Solar and connected to a SMA Inverter SB 5000us attached to the inside wall of the garage, that wirelessly sends production data to my laptop. The inverter, warrantied for 10 years, converts the DC output to AC and feeds it to the house with the excess going back into the Virginia Power grid with the help of a grid-tie connection to their net metering program. This program allows two way metering, so that excess power can flow into the grid, and needed power (ie. at night) can be drawn out. The arithmetic sum is carried over a 12 month period. If you produce excess power it can be carried forward; if you fall short, it can be subtracted from that sum (or you pay a bill). Any excess that is not used in a 12 month period is donated to the grid, and you get warm fuzzy feelings for your kindness to humanity. All of this now sounds very simple, and the panels look neat and clean. Let me tell you, pulling this together was not simple, neat or clean. It took many hours of active research, several false starts, a motivated, thoughtful builder, and several solar resource experts to make this happen. More on this later.

ZEH, SIS, and other energy-friendly acronyms to know

The envelope of the house is rapidly developing, so its time to highlight a few key products. The house will have an exterior sheathing of a new product from Dow, Styrofoam SIS (Structural Insulated Sheathing). Winner of the 2009 Green Product Awards from Building Products Magazine, STYROFOAM SIS™ Structural Insulated Sheathing from Dow combines a structural layer, a moisture barrier, and foam insulation, providing R-values of 3.0 at ½ inch or 5.5 at 1 inch. Made of up to 80 percent post-consumer recycled content by weight, STYROFOAM SIS™ Brand Structural Insulated Sheathing is ENERGY STAR-qualified. And, at one-third the weight of OSB†, it is easier to handle and quicker to install. One judge summed up the products benefits as, "This appears to be an excellent product, providing wall bracing, energy performance, and the potential for weatherization all in one. The labor savings alone is huge." Our builder chose to use the 1/2 inch product, after an analysis revealed relatively little energy gain for the thicker product in our build (rule of diminishing returns). The panels are nailed or stapled in place to the outside of the studs and the seams are taped with WEATHERMATE™ Construction Tape (2-7/8" wide) .

WEATHERMATE Construction
Tape is pliable, ensuring a tight
seal, even at extremely low

temperatures. The oriented
polypropylene backing is
formulated with a UV-treated
film to help resist degradation
from exposure to sunlight.

The garage is not insulated, but covered with WEATHERMATE™ Plus – Housewrap to serve as an air and moisture barrier. It is significantly superior in water resistance, air porosity, vapor permeability and tear resistance than the more commonly used Tyvek. It also possesses prolonged UV ray resistance, allowing it to be exposed up to 120 days before significantly degrading (hopefully our garage will not test that limit).

ZEH Virginia, its all in the little things

Building a green ZEH is not one big thing, but a series of many little things. Our builder is using AdvanTech subflooring, a product offered by Huber with a 50 year guarantee that shows significant improvement over both OSB and plywood in stiffness, strength and water resistance, while using no added formaldehyde and meeting the Sustainable Forestry Initiative (SFI) Standard. This produces stiffer, quieter floors while minimizing outgassing. The piece of light blue material you see sticking out from the block in the lower picture is a foam gasket that serves as an air sealing measure along the uneven block and brick. It also is a moisture break to keep water from migrating to the wood from the foundation. The aim of maintaining an extremely tight "envelope" with respect air and moisture infiltration is a guiding principle that directs innumerable building product choices and practices when constructing a zero energy home. Mark, our builder, is shooting for the lowest HERS rating house in Virginia, so each of these decisions is made with efficiency and best practice in mind.

ZEH design blueprint

Where did the design of this ZEH house come from? Good question. A lot of tiresome searchs on the internet uncovered a few rare nuggets. The first and in many ways the most fruitful was the Zero Energy Home section of Toolbase Services: the Home Building Industry's Technical Information Resource. This site has a wonderful article titled Seven Steps to a ZEH that is the closest thing to a ZEH "blueprint" out there. Links to scientifically monitored zero energy homes, like the Tuscon's Zero Energy Home were invaluable not just for the data they included, but the encouragement they provided that this is indeed a practical, achievable goal. Given we became interested in the combination of solar PV and geothermal HVAC after tossing around ideas with our builder, Mark Waring, finding the series of articles titled Energy efficiency, SIPS, geothermal, and solar PV used in near zero-energy house was like striking gold, as it documented and evaluated a series of homes using this exact combination. In looking for books on the topic, the pickings were slim. Ed Begley's Guide to Sustainable Living served as good primer for general energy-efficiency ideas, while Got Sun? Go Solar by Ewing and Pratt was a practical, content-rich guide to utilizing solar PV as part of a ZEH effort. The Renewable Energy Handbook, Revised Edition by Kemp offered a broader exploration of alternative energy alternatives. Toward a Zero Energy Home by Johnston & Gibson is a very recent release whose greatest value may be its descriptive "Case Studies" of 13 near ZEHs. Two magazines that offered some help were Solar Today Magazine and HomePower Magazine, the former focused on solar power, but from a wide ranging perspective, while the latter is more focused on real world applications of renewable energy, including solar, and yielded needed product information. In the end, working with our builder who was already experienced in building energy efficient homes, pulling ideas from a variety of sources, and considering and ruling out some promising but impractical combinations, we embarked on an informed leap of faith. Time will tell how much of a leap, and we work with our builder on a weekly basis to continue to hone and fine tune the design, in search of that elusive "zero."

Starting the envelope

The foundation walls are up and the workers are laying the 2" Dow Styrofoam Scoreboard insulation against the walls. This forms the continuous insulation (R-10) and moisture barrier along the masonry wall that is vital to our conditioned crawl space. It takes the place of any insulation that would normally be against the floor. The joints between pieces are sealed with expanding spray foam sealant, creating the continuous barrier. There will be a vinyl strip below the installed insulation that we will seal the floor vapor barrier to, once the house is dried in. It is already clear in watching the workers, that while thoughtful design and product choice are important in reaching the desired energy goals, correct application and attention to detail is equally important. It is noted that Dow STYROFOAM products are CFC Free, they do not contain fully halogenated chlorofluorocarbons (CFCs) regulated by the United Nations Environment Program (UNEP) in the Montreal Protocol.

An enlightening experience...

In striving for an zero energy home, once your heating and cooling load has been reduced through a tight, well insulated house envelope and geothermal heating/cooling system, your appliances and lighting become a proportionally more significant issue. In looking to reduce lighting energy demands, the use of more energy efficient, long lasting CFLs and LEDs becomes paramount. In recently searching for lighting fixtures designed specifically for these types of bulbs, we found the local "pickings" to be sparse and expensive. Searching online was somewhat more successful, with sites like arcadianlighting.com, lightingdirect.com and tcpi.com offering more choice of fixtures, and maxlite.com, earthbulb.com, creelighting.com, junolightinggroup.com, superbrightleds.com and edgelighting.com offering access to quality bulbs at reasonable prices. We have decided to primarily go with CFLs in conventional CFL-compatible (read: hides the bulb) fixtures, while using longer lasting but more expensive LEDs in key recessed lighting and undercabinet locations. We plan to use cooler color bulbs (5000K)in closets and dressing areas, where their greater accuracy is useful. In the remaining areas, we will be using warmer bulbs (2700K) bulbs for their flattering glow. Part of being a successful "early adopter" is having a high frustration tolerance and a healthy dose of initiative, imagination and stubbornness. It is sometimes tempting to simply yield to the easy, available and less immediately expensive answer, but that will rarely get you to your goal. Plus we plan to enjoy the projected 34 years of use of those little LEDs.

A Greener Foundation

When we visited the build site this week, we saw cement trucks and a tall pumper (the tall River City boom in the picture) busy pouring our foundation. In talking with our EarthCraft builder, we learned that he is using fly ash concrete, a form of concrete which replaces some of the cement in the mixture with fly ash, the fine powdery residue from coal combustion. This produces a concrete that is stronger, more durable and easier to work with and diverts that fly ash generated by our coal-fired power plants from ending up in our landfills. Fly ash containing concrete mixes can receive LEED credit under the guidelines established by US Green Building Council. In the vein of there being nothing new under the sun, a form of volcanic fly ash concrete was used by the Romans in building the Coliseum and the first domestic use of fly ash concrete was in 1929 in the construction of the Hoover Dam.

Wow.. it's going to really happen!!

Seeing the cleared lot offered a stark example of the application of the theory of unintended consequences combined with the principle of compromise. We knew that to get adequate solar exposure to our PV array mounted on the garage roof, that we would need to take most of the trees down. We positioned the array on the lot to maximize solar exposure, but it still required that we clear most of the mature oaks that might have otherwise been spared. That left us with a rather bleak picture, and took most of our privacy away. We took heart in the knowledge that Mark, our builder, had recycled all of the cut wood to the lumber mill, for mulch, pulpwood and lumber. I believe that is part of the EarthCraft building guidelines. In looking at the back of the cleared lot, and thinking of how to gain some privacy without creating problem shading, I realized that in the future there may be a place for solar-sensitive landscape design (ie. now what can I plant back there that will provide cover and not grow more than about 15 feet high?).

ZEH: it's a system

In 1990 we built what was for its time, an energy efficient, all brick home. It included some 6 inch walls, extra insulation, a Lennox pulse gas furnace, low-flow toilets (they are forever clogging), low-E windows, and south facing glass. The rumor around our Richmond neighborhood was that we were from Vermont, and did not know how to build for the more temperate climate. Fast forward 20 or so years. My wife found a lot with river access closer to her office, so it's time for an encore, to build our single level (out of deference to aging knees) "retirement" home. Out of concern for the generations to come, for minimizing monthly bills and for an outlet for our creative expression, the notion of building a zero energy home (ZEH) emerged. After a bit of study, it becomes clear that a ZEH is not a single feature or advantage, but rather a set of complementary features which form an efficient system. That sytem consists of creating a home with a tight, well insulated envelope, minimizing the energy loads in that envelope, and adding a renewable energy source. Sounds simple, but as you move forwards it gets complicated quickly. In an email to a interested relative, I described the basics of our proposed ZEH as:

...it is basically designed as a single story home, with some bonus rooms upstairs...it will be all brick with a semi-detached garage (the why of that comes later)...the walls will be R16 and the attic R38...the walls will use wet spray cellulose and the attic loose cellulose...a conditioned crawl space...we are also using a new product on the outside of the stud walls, Dow Styrofoam SIS, (structural insulated sheathing) which will be taped, forming an air/vapor barrier, an extra layer of insulation, a shield against thermal bridging of the studs, and a structural element...pretty cool...with respect to the R levels, they are more than sufficient for our climate, as the wet spray cellulose significantly increases the thermal mass of the house... along with the tightness of the house (we aim for less than a .20 Natural Air Exchanges per Hour blower door result and a less than 4% of floor area served leakage to outside duct test result; an ERV will be installed for ventilation), the increased thermal mass may even eliminate the need for a setback thermostat, as the temperature of the house should remain incredibly stable...we are going to look into cool roofs/radiant heat barriers, but setting up the heating/coolng "firewall" at the attic floor may be more cost effective....

...we are looking at double pane, vinyl clad, low E, argon windows, with U value of .33 and SHGC of.30...we are looking into a new model with a U below .30, getting a price difference on that...

...Caroma (the reviews say they never clog) 1.28/0.8 dual flush toilets to save water...

...the HVAC system is proposed to be a Comfortaire GeoMax2 geothermal heat pump of 4 ton capacity with desuperheater rated @ 23.7/16.6 EER & 4.0 COP...hot water will be pre-heated by the desuperheater and then go to a 98% efficient Navien tankless condensing water heater with a built in recirculation pump & mini buffer tank for a digital timer controlled recirculation loop to prevent the dreaded "cold water sandwich" you can get with tankless water heaters...the solar grid-connected PVC array will consist of 20 Schuco Monocrystalline 210 panels (4.2kW) and a SunnyBoy inverter mounted on a true south oriented garage roof...

We will begin to look at each of these features as the build progresses, analyzing their benefits and potential assets and seeing how they may complement (and hopefully not compromise) the "system". Stay tuned.