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    Building and Conditioning Scalable, Affordable Net Zero Homes

    Nov. 23, 2023
    In the efficiency game, simplicity wins the race. This contractor provides "net zero for pennies".

    The "Holy Grail" of energy efficiency in home construction may be net-zero energy. To achieve this coveted title, a home must produce as much energy as it consumes in a calendar year, typically via solar or wind.

    “Net-zero has been an obtainable goal for decades, but almost always at a prohibitive initial cost,” said Tom Danielsen, founder of Danielsen Construction and Energy Management, in Altaville, CA.  “That’s what I’m working hard to change.”

    Danielsen has been a builder since 1990, and specialized in energy efficient construction in ‘04.  Now, after nearly two decades focused on reducing residential energy consumption, he’s developed what he calls “net-zero for pennies.”

    “Typically, achieving net-zero is exorbitantly expensive,” said Danielsen.  “I’ve spent the bulk of my career addressing that concern.”

    That’s not to say that Danielsen hasn’t built and retrofitted homes with multi-million dollar price tags.  He certainly has, and in the process he’s developed a reputation for reducing the energy consumption of structures large and small. But he’s always wanted to prove that by adopting net-zero as the goal early in the design process and keeping the project simple, the cost-per-square-foot difference between a traditional home and a net-zero home can be mere pennies, without sacrificing comfort or convenience.

    Danielsen’s territory - east of San Francisco by about 100 miles - falls in California Climate Zone 12, which experiences cooler winters and hotter summers than the Bay Area, for example.  Pair that with some of the highest utility costs nationwide, and you’d be hard pressed to find a better place to push the envelope on net-zero innovation than Calaveras County, CA.

    Pilot project

    In 2019, Danielsen was serving on the board of the Calaveras County Habitat for Humanity, a non-profit that helps people obtain safe, comfortable and affordable housing. His company has retrofitted many existing Habitat for Humanity houses with energy efficient upgrades.  But it wasn’t until more recently that Danielsen took control of a new construction project for the organization, with plans to definitively prove his “net-zero for pennies,” theory and, hopefully, use the home as a pilot project for many to come.

    Danielsen presented the Board with his idea to build an experimental home. The goal was to: a) prove that his net-zero construction method is replicable at scale b) prove that the home has a similar square-foot cost as traditionally-built homes and c) have an unbiased third-party measure the energy performance of the home. The Board agreed.

    “We build and retrofit homes with energy efficiency in mind all the time, but we’ve never had the opportunity to apply everything we’ve learned on a single project and gather persistent energy data,” said Danielsen. “That’s what this particular project allowed us to do.”

    Experience Applied

    “In any discussion of how to make a home efficient, the three main topics are inevitably the quality of the insulation, the way the house is air sealed, and the star of the show - the HVAC system,” said Danielsen.  “Each of these components relies on the other two.”

    Installing insulation properly is just as important as the quality of the insulation itself, according to Danielsen. He uses Owens Corning L77 BIB (blown in blanket) insulation in the ceilings (R-40) and walls (R-21). Spray foam, he says, generates too many VOCs in the occupied space, and batt insulation doesn’t perform well.  He installs AMSCO low-E 366 glazed, argon filled vinyl windows.  When it comes to framing, two-by-six is more than sufficient, so long as the outside corners are “open.”

    “When most people think about air sealing, their mind goes to the weather stripping around the front door,” he said.  “This is important, but the critical areas are those that can’t be accessed once construction is finished; the plumbing cutouts, framing cavities, the bottom frame-plate to the subfloor, wiring inlets and register exchanges.  This is where blower door air sealing tests are won or lost.”    

    A Different Take on Ductwork

    “We’re big believers in Fujitsu heat pump technology,” said Danielsen.  “That doesn’t make us unique, but how we size and install them does.”

    Danielsen uses Right-Suite design software to calculate the load for each room in a house, giving him an accurate load for the whole house, but just as importantly, a load for each room, which he uses later to size and balance ductwork.

    “Most design software defaults to a 1.30 modifier, automatically oversizing the capacity of the heat pump,” said Danielsen.  “We bring our modifier down to 1.10. I want the heat pump to run 24/7.”

    Danielsen explains that heat pumps - or any HVAC equipment for that matter - don’t reach full efficiency until they’ve been running for 10 or 15 minutes. An oversized unit that constantly cycles on and off never operates at its full potential. 

    Danielsen explains that heat pumps - or any HVAC equipment for that matter - don’t reach full efficiency until they’ve been running for 10 or 15 minutes. An oversized unit that constantly cycles on and off never operates at its full potential.  As a result, he sizes his systems for design conditions and no more. 

    “Our approach to installing slim-duct systems is really just best practice, but some companies don’t use the same level of detail that we do,” said Danielsen.  “As a result, they sacrifice efficiency.”

    “Our ductwork layout is always a radial design,” he continued.  “We run duct directly from the plenum to point of use. Legs start at the plenum, never branching off another supply. This makes balancing a breeze.”

    He also explained that by placing registers on interior walls and using a very short return, a natural convection current occurs. Because the systems run 24/7, the delta-T remains under 23°F, regardless of the season. As a result, air in the room doesn’t stratify.  Air temperature readings at the floor and ceiling show a differential of 2°F or less.

    “Air should move at 400-600 CFM, generating very little friction and conductive loss,” said Danielsen.  “Air should move as fast as possible without creating much friction.”

    Finally, sealing and burying the ductwork is more important than many people think.  anielsen likes to see 100% of the ductwork covered by insulation, but sometimes it’s just not possible. They cover everything they can. Once duct sealant is applied to the entire duct system, Danielsen typically sees five percent or less duct leakage to the outside. 

    Got the Green Goods

    None of the changes Danielsen implements are radical, but each small improvement builds on the next, adding up to substantial energy savings.  That said, a tight building envelop, correctly-sized HVAC, smart ductwork design and robust insulation are only half the equation.  Selecting and properly installing the correct appliances and systems is the other half.

    The home does not have battery storage capacity.  Rather, the solar array feeds the power grid during the day, and draws from it at night.

    After getting the green light from the Board at Habitat for Humanity, Danielsen had a conversation with a local solar company, Technical Specialty Solutions.  They offered to donate an eight-panel, 2.76 kW solar array that was installed on the 1,250 square-foot house. 

    The home does not have battery storage capacity.  Rather, the solar array feeds the power grid during the day, and draws from it at night.  The donated solar array would nearly cover all the power used in the home.

    The heat pump installed on the project is a single-zone 12,000 BTU/h Fujitsu H-Series 12LUAS1, offering up to 21.5 SEER.

    “We install Fujitsu heat pumps for a variety of reasons,” said Danielsen.  “First, I feel like they heat extremely well.  Second, if there’s a problem, there’s never a problem.  Their tech support and warranty is the best in the business.  Their local support is also outstanding.”

    Danielsen sources all of his heat pumps at Johnstone Supply’s Stockton branch. 

    “Mark Whitlock, at Johnstone is absolutely brilliant,” said Danielsen.  “Smart, times ten to the power of eight.  He’s helped with small things and even big things, like designing a VRF system at a massive church.  I feel lucky to be working with both Johnstone and Fujitsu.”

    To round out the equipment list at the Habitat pilot project, Danielsen installed a 50-gallon Ruud heat pump water heater.

    Dream team

    Danielsen Construction and Energy Management was under the gun from the Habitat director to stay on budget.  The original design for the home called for a 60,000 BTU/h gas furnace and three-ton air conditioner.  Danielsen’s heat pump design trimmed 50 percent from the HVAC cost, allowing more money to be invested in other areas, primarily insulation. 

    Over the course of the nine-month project, Danielsen worked with his team of four installers, Alejandro Rodriguez, Hamberto Espino, Will Ibarra and Jose Rodriguez.  All of them have worked for Danielsen for over a decade, some nearly two decades. 

    “I can’t give these guys enough credit,” said Danielsen. “They do phenomenal work, and really see the value in what we strive to accomplish.”

    As home construction drew to a close, one more key player came on the scene. Torsten Glidden is a contractor for the U.S. Department of Energy’s Building Technologies Office and is the technical lead on their Home Energy Score program. His reputation as a fair and impartial inspector provided the perfect finish to the team.

    Glidden was instrumental to implementing the SiteSage energy monitoring equipment that would ultimately tell the whole story of the home’s energy performance.  The system was installed on the home’s main breaker panel, allowing real-time data collection from every circuit in the home.

    The Experiment

    Once the house was complete and occupied, an important part of the experiment was to encourage the occupants to make their home comfortable year-round.  There were no restrictions on energy use. Danielsen wanted all the appliances in the home to be used in a manner congruent with the average American household. 

    “Accurately monitoring all-electric homes is far easier than monitoring a home with gas,” said Danielsen.  With Torsten’s guidance over a year of data collection, we had very specific numbers to compare against Pacific Gas & Electric’s (PG&E) annual utility data for the property.”

    The data collected by the SiteSage system corroborated what appeared in PG&E’s annual True-Up bill: extremely low household power utilization. While the utility bill confirmed the overall power consumption and solar array generation, the energy monitoring system provided the real insight. 

    The Results

    Over the course of the year, the small solar array produced 4,571 kWh.  Not surprisingly, the water heater consumed the most power, followed by the heat pump, the dryer, the refrigerator and so on. 

    “We can see that the Fujitsu system operates continuously, using between 400 and 600 Watts during the winter, and between 600 and 800 Watts in the summer,” said Danielsen.  “Over the course of the year, keeping the home comfortable required a little more than double the energy it took to operate the refrigerator.  That’s amazing.”

    Over the course of the year, the small solar array produced 4,571 kWh.  Not surprisingly, the water heater consumed the most power, followed by the heat pump, the dryer, the refrigerator and so on. 

    When the utility’s annual True-Up bill became available, all electric consumption in the home was portrayed in dollar values, adjusted for the power generated by the solar array.

    The homeowner’s annual energy expense was $574.  Domestic hot water production cost was $159, heating and cooling accounted for $128, and the dryer consumed $76 worth of power. 

    “In the state of California, an average utility bill runs about $375 per month,” said Danielsen.  “Here in Calaveras County, with relatively hot summers and cold winters, the average home utility cost is at least that. It costs less to power this house for a year than the average home in California for two months!”

    The energy data collected and verified by Glidden and PG&E are in line with what Danielsen has seen on most of his construction projects over the past decade.  Once provided the data, board members at Habitat for Humanity could hardly believe the numbers were real. 

    “What I find most encouraging is that we’re not doing anything crazy here, and even if the solar array hadn’t been donated, this house would have cost roughly the same as a traditional home” said Danielsen.  “There were no ultra-expensive building materials or methods used.  We installed basic equipment, employed best practices and added a small photovoltaic array.  In fact, if we’d have added one more panel to the array, the annual energy cost would have been less than zero, making this a true net-zero property.”

    The ability to build net-zero homes at scale for roughly the same cost as ‘regular’ houses changes everything,” he continued.  “It gives people the choice between buying nearly identical homes at a very similar cost, except one home will have no utility bills and a dramatically reduced environmental footprint.”