ZEH-Richmond's performance at year's end

So we have had a solid, representative year in our house now and we wanted to update its real-life performance. Our total energy bill for 2011 was $954, $532 for electricity and $422 for natural gas. The electric bill reflected the cost for heating, cooling, lights, appliances, etc. The highest monthly bill was $125 in the winter, while five months (the "shoulder" seasons in the spring and fall) were effectively "zero". Our natural gas bill reflected energy used to heat water, cook and operate the gas fireplace. The highest bill was $55 in the winter, while the lowest was $20 in the summer. We did make thoughtful attempts to run the house in an energy efficient fashion, opening & closing windows to take advantage of natural heating and cooling effects, and maintaining temperatures of 69day/68night (the geothermal system does not like big heat swings) in the winter and 76-78 in the heat of the summer. Our SRECs have turned out to be a bust. The initial contract we signed got "lost" in the system, and the replacement contract was only offered at a variable auction rate. The bottom subsequently fell out of the SREC market due to regulatory and political decisions that are too complex to explain here. As a result, we received a nominal $80 this year for SRECs, putting our net annual energy bill at $874. Given we have Watersense rated water fixtures and low flow toilets in the house, it is worth adding that our total annual water & sewage bill was $714. The lowest monthly bill was $31 and the highest was $90 (fall replanted lawn irrigation effect).So in sum, our average monthly energy bills were $73, our average water & sewage bill was $59 and our average total monthly utility bill was $132. In comparison, the average monthly energy bill for a (smaller) US home was approximately $180. We didn't make "zero", for a number of reasons I will address in a later blog, but I feel that a monthly energy bill for about the price of a dinner and a movie for the two of us is a pretty fair result!

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.

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.

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.