Comfort in a Very Cold Climate ra by Rachel Wagner ch el wagner

idespread attention is An example of such a first step is the

now finally being paid to 50% immediate reduction advocated The Skyline House in Duluth, Minnesota, was designed global warming, and many in the program Architecture2030, W and built to provide low-energy accomodations for homeowners want to know how they which was developed by architect Ed generations to come. can reduce their personal contribution Mazria. In this context, programs to greenhouse gas emissions. They such as Energy Star and LEED, as know that they must do much they are defined today, are inadequate use, most energy consumed in single- more than the often touted small solutions to the problem of creating family residences is used for heating, steps such as replace incandescent low-energy buildings. Rather, all cooling, and domestic hot water. In lightbulbs with compact fluorescents, new construction can and should cold climates, such as we have in or buy and use a programmable be designed to immediately reduce Minnesota, where I practice, heating thermostat. Homeowners look to consumption and emissions by 50% or consumes the most energy, so my architects, builders, and other design more compared to construction that efforts to reduce energy loads often professionals for information and just meets code, with the further goal focus on heating-associated numbers. recommendations. Therefore, building of creating buildings that reduce both and design professionals have the consumption and emissions by 75% to I find these three numbers opportunity, and the responsibility, 90% in the near future. most useful when quantifying and to offer approaches to building How will the home built today comparing design options: construction that reduce both energy rate in 40 years? Will it be easy to add

consumption and carbon dioxide (CO2) features that push it into even higher 1. peak heating load in British emissions. In professional practice, energy reductions? If the answer is to thermal units per hour per square the pertinent questions may be, How be yes, we need to build homes now foot; far can we go? and How soon can we with envelope and systems designs that 2. annual calculated consumption get there? As an architect who works greatly reduce the amount of energy in British thermal units per primarily in residential construction, needed for operation, and that take square foot per year; and 3. total I try to answer these questions with advantage of passive lighting, heating, household calculated annual every house I design and build. and cooling options. Building homes consumption in millions of British in this way will make it easier in the thermal units per year. Taking an Aggressive future to add technologies (such as First Step active solar-energy systems) that As the house design is developed, further reduce consumption of fossil I compare and modify the readily Buildings last. Many choices made fuels. available envelope design assemblies, in new construction today will have using an energy-modeling program. an impact on the environment for Targeting Energy Use There won’t necessarily be a single the next 100 years—much longer best assembly or component. But by than the impact of decisions made If the first step is to set a target comparing and quantifying different in many other industries. This is for energy use, the second step is to assemblies or components, I arrive at why it is so critical, first, to quantify quantify that target and to find the a desirable design solution. In doing the amount of energy used (and means to see that it is met. Calculated so, I consider many factors, including emissions generated) in building energy modeling is an essential tool climate, solar opportunity, budget, and operation, and second, to set targets for comparing assembly elements and regional materials and practices. I for reducing both. And this is also why systems design, and for quantifying have found REM:Design (REM stands an incremental, or staged, approach to their respective associated energy for Residential Energy Modeling) an reductions may not work well in the loads. Although miscellaneous affordable and easy-to-use program for building sector, unless that approach electrical loads represent a growing modeling houses. More recently, I was begins with an aggressive first step percentage of total household energy introduced to the Passive House PHPP

40 www.homeenergy.org Climate Solutions • Home Energy the goal of annual energy consumption for heating at about 10% of industry standard for new construction, and overall household energy consumption at about 15% to 20% of standard. This goal correlates well to the 75% to 80%

reduction in CO2 emissions called for by leading climate scientists. Thus was born the Skyline House. The client was a young family

ra with two children. They had a steeply

ch el wagner sloped site in Duluth, Minnesota, with spectacular views of Lake Superior, and they wanted to build a home geared toward generations of living to come. We defined three main environmental Roof overhang and a trellis structure manage the solar gain. goals for this project: longevity, low energy use, and sustainability, and Table 1. Environmental Goals for it can further reduce adopted a specific approach to achieve Skyline House Project energy consumption each of these goals (see Table 1). Goals Approaches Needed for heating. Post- Longevity Flexible design; single-floor occupancy interviews Obstacles living for adult occupants; durable of clients living in construction Low energy use Aggressive thermal envelope; houses constructed Like any good design challenge, passive-solar design; renewable using this process the project was not without obstacles. energy-integrated HVAC systems suggest that actual For the environmental goals set forth Sustainability Environmental approach to energy consumption above, the chief obstacles were climate, materials; adaptability to is often even less than site constraints, and the timing of changing circumstances the predicted energy the project. The climate in Duluth consumption. is often cold, with 9,800 heating degree-days per year. Solar exposure software program (developed by the One Solution: The Skyline (insolation) is fairly good at the site, Passive House Institute in Germany). House but it is sometimes compromised by The PHPP software is more difficult the Lake Superior’s cloud effect. Other to use than REM, largely because one As I mentioned earlier, two site constraints included the steep must enter an enormous amount of questions guide my practice: How far slope, and a narrow lot. In addition, data in order to obtain accurate results, can we go? and How soon can we get the best views were found at 30∞ to and because of the conversions from there? I was recently presented with a 45∞ east of south, which meant that imperial to metric units. However, the near-ideal opportunity to explore these the orientation best adapted to take very detailed reports that result make questions when I was asked to design a advantage of these views was not ideal PHPP an extremely useful tool for house with a low-energy envelope that for passive solar. Finally, since Skyline modeling very low-energy buildings. would significantly reduce energy use House was not initially conceived of It is worth noting that different and associated CO2 emissions. Near- as a Passive House project, the timing modeling programs produce different ideal because the project included a for designing to meet this goal was not results, and the most “real” data are client with a strong environmental ideal. PHPP analysis and modeling obtained from monitoring the actual focus and a comfortable budget; a site were only begun after construction energy consumption of a house. with good solar opportunities; and documents were under way. However, even if the modeled numbers a building program that fit readily are not exact, the process of setting into the naturally efficient form of Energy Modeling up a code-designed house for each a one-story house, with lower-level model gives me a valuable baseline living set into the ground. Partway into The 2,660 square foot house, which that I can use to compare with each the project, the clients and I decided has three bedrooms, two bathrooms, design variation. The solar-heating that we should try to design and build and an attached two-car garage, was component of a house is hard to model, this house so that it would meet the first modeled with REM:Design. When but with effective passive-solar design, Passive House Standard, which sets the calculation showed an estimated

Climate Solutions • Home Energy www.homeenergy.org 41 peak heating load of 8 British thermal changes was reduced units per square foot (a number that to 6.9 Btu per square roughly correlates to a 65% to 70% foot per hour. The final reduction in energy use compared to calculated heating loads a code-built house of the same design), in the Skyline House, the clients and I began the discussions with both REM:Design that led to us setting a goal for even and PHPP, correspond higher performance—the Passive to a reduction in

House Standard. energy use of about ra The client was interested in the 75% compared to use ch el wagner Passive House approach, and excited for a house of the same about the prospect of improving the size and design in the design to a level that might achieve same location, built to Passive House certification. The house Minnesota code. (See was modeled using the PHPP software “Skyline House Basics.”) A stone dining terrace abuts the west facade. package used for Passive House design The design relies on a and certification. The PHPP process very high performance starts with specific energy consumption envelope and passive-solar heating to warm air to the upper level via the targets, regardless of climate, and sums lower annual loads. Heat and domestic ventilation system. all envelope component and primary hot water are delivered with a whole- energy loads using specific building house combination system using a Ventilation Strategies location climate data. solar-thermal storage system with gas- The detailed and extensive fired backup. A geothermal ventilation Passive House Standards require modeling approach led to some air tempering system optimizes the mechanical ventilation with heat changes in envelope design, with use of renewable energies. Finally, recovery. This is considered best the goals of approaching the Passive an airtight wood stove with direct- practice in any case where the house House Standard of 4,750 British combustion air supply provides is very tight and minimum use of thermal units per square foot per another means of using a renewable year. Already-aggressive insulation fuel source to contribute to meeting levels were increased in the ceiling, the home’s heating needs. Skyline House Basics in the walls, and under the slab. The Modeled Energy Loads for Heating goal for airtightness was increased, HVAC and Plumbing and geothermal tempering loops 1. Peak heating load = 5.9 British were added to the design to preheat Water for heating and plumbing thermal units per hour per square the incoming air for the mechanical is stored in two tanks. An 80-gallon foot. 2. Annual calculated consumption ventilation system. tank holds domestic hot water, and a = 7,266 British thermal units per Since the attempt to meet the 275-gallon tank is used for thermal square foot per year. Passive House Standard began well storage. A 48-tube (120 square foot into the design process, I was unable ) evacuated solar thermal array first 3. Total household calculated annual to make a few possible changes (in heats the water in the smaller tank. consumption = 19.3 million British particular to site orientation) that When water in this tank reaches the thermal units per year. might have made meeting these set temperature, the solar thermal requirements easier. In addition, the energy is diverted to the larger tank. Design Basics recently translated software package The thermal energy stored in the • One-story house with lower-level contained some confusing language larger tank can be transferred to the walk-out that may have contributed to my domestic hot water tank or used for • 1,540 gross square feet per floor entering data incorrectly. Nonetheless, space heating. The water from the • 1,330 conditioned square feet the PHPP software proved a valuable domestic hot water tank runs through per floor (total 2,660 conditioned tool, and it helped guide the decisions the on-demand water heater, which square feet) needed to create an ultralow-energy acts as a boost when the system needs • Attached two-car garage house in a very cold climate. The a rise in temperature. One distribution • Three bedrooms, one on the upper level, two on the lower level PHPP-calculated energy for heating on loop from the thermal storage tank • Two full bathrooms, one up and one the Skyline House is 23 kilowatt-hours provides hydronic floor heat on the down per square meter—or 7,266 British lower level and to the upper-level • Stacked levels, no cantilevers thermal units per square foot—per year. bathroom. A second loop distributes • Bathroom and plumbing clustered The peak load with the PHPP-inspired and close to the mechanical room

42 www.homeenergy.org Climate Solutions • Home Energy Window Detail and Framed Wall ra ch el wagner

Insulated fiberglass window frames with triple- pane glazing allow solar gain and prevent heat loss.

energy is desired. Controlled, whole- house mechanical ventilation creates a healthy indoor environment with the least energy penalty during the heating season. The Skyline House to standard practice. Extra attention air changes per hour at 50 Pascals. has a whole- house, balanced heat was paid during construction to Construction was completed at the recovery ventilation (HRV) system airtightness, and to maintaining end of 2007, so comprehensive real-life with a high- efficiency HRV unit. Fresh the integrity of the defined thermal energy data will not be available until air is delivered to all living spaces and boundary. The contractor and the after the 2007-2008 heating season. exhausted from bathrooms and kitchen. energy and building performance In the future, actual energy use will An independent makeup air system consultant stayed in communication, be compared to modeled energy was installed to balance the kitchen and most potential problem areas use. I expect my clients—and their range exhaust. were identified before detailed work children and grandchildren—will be Two geothermal loops of PEX was done in those areas. A smooth comfortable in this house for many tubing filled with a mixture of water and successful construction process decades to come. and propylene glycol, one deep under was made possible by ongoing H e the house slab and one underground communication between the trades outside the house, connect to a water- and the design and performance Rachel Wagner is a partner at Wagner to-air heat exchanger in the outdoor air consultants. The general contractor Zaun Architecture, which is based in duct of the HRV to provide ventilation knew why envelope performance Duluth, Minnesota. air tempering. This system pre-warms goals had been set so high, and he ventilation air in winter and pre-cools understood the client’s priorities. it in summer. Passive- solar design and He set the tone and the expected For more information: good cross-ventilation reduce the need level of performance for all of the for air conditioning. subcontractors, and he helped The energy and building performance coordinate a process designed to consultant for the Skyline House was Getting the Details Done facilitate excellence. Conservation Technologies. The Airtightness was tested with a general contractor was J & R Sundberg Most of the construction methods blower door test, with a measured air Construction. To learn more about and materials used in the Skyline infiltration of .12 cubic feet per minute other Wagner Zaun projects, visit House required only minor alterations per square foot at 50 Pascals, or .93 www.wagnerzaun.com.

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