By DAVE BRACH, AIA, CPHC May 27, 2012
I still remember the first time I met with Joe Turner and Rebecca Guymon to discuss a new home they wanted to build in the Millcreek area of Salt Lake City. In retrospect, I must have sounded like a real killjoy.
A custom home is not like a car or a sofa, I told them. You can’t take it for a test drive or lounge around on it in the showroom before you decide to buy it. And it’s not like a computer or smart phone — you can’t upgrade it or download the latest app to keep it on the cutting edge.
Rather, the process of designing and building a sustainable house doesn’t involve instant gratification. Instead, it requires months of decision-making and communication among the owners, the architect and the contractor, and the owners may not fully appreciate the true character and performance of the home until years down the road.
Despite my brutal honesty — or perhaps because of it — they asked me to help them create their dream home.
Decisions Large and Small
Luckily, the couple had very few preconceived notions about the perfect home. This was immensely helpful in preparing them to face the daunting task ahead of them and in keeping them from getting bogged down in all the critical choices required to keep the project moving.
As a veteran of many new homes and remodels, I knew that there are a million choices that go into each project, from the biggest picture questions of how many square feet to build to the smallest details like where to locate the silverware drawer. In this respect, Joe and Rebecca’s project was no different from any other. At times they were overwhelmed with choices — floor plan layout preferences, exterior finish options, color schemes, tile samples, lighting fixtures and on and on and on.
But one fundamental choice was surprisingly easy to make — they decided to build their new home to the rigorous Passive House energy standard. Early in the design process, I introduced them to the idea of the Passive House Certification, which is a voluntary energy consumption standard administered by the Passive House Institute US and the Passive House Institute in Germany.
Unlike traditional passive solar buildings, a Passive House has very strict measurable air-tightness criteria, as well as rigorous calculable energy consumption requirements for annual heat demand, annual cooling demand, heating and cooling loads and total annual energy demand. The architect or designer must develop a climate-specific design using the energy modeling software in the Passive House Planning Package (PHPP) to fine-tune building components in order to make the design affordable to build.
In addition to extremely low energy use, the core goals of Passive House design are thermal comfort and excellent indoor air quality. By eliminating thermal bridges and using airtight construction techniques, a Passive House maintains uniform interior surface temperatures even when outdoor temperatures are extreme. A dedicated energy recovery ventilation system ensures clean, healthy indoor air.
The owners questioned how much it would increase costs to achieve these goals.
To address their concern, I used the PHPP computer energy model to optimize insulation levels in the walls, under the slab and in the roof. I also chose a simplified build- ing form, employed optimal value engineer- ing framing techniques and used standard methods and materials to keep costs down. The result was that the house achieved the Passive House standard and cost only about $9 per square foot more than business-as-usual code construction. Given this modest cost increase, and the fact that upgrading the energy efficiency of the home in the future would be impractical, expensive and disruptive, the owners agreed that Passive House was a sensible investment.
Making a (Passive) House a Home
But energy efficiency doesn’t make a house a home, and the owners had a clear vision for how their new abode could accommodate and enhance their lifestyle. Topping their wish list were a generous space on the ground floor for entertaining; indoor and outdoor dining; an open plan with lots of diffuse natural daylight; a simple and logical flow of spaces; views of the beautiful Wasatch mountains; and a clean, uncluttered aesthetic. As the design materialized, it became clear that the choice to build a Passive House dovetailed nicely with the owners’ practical and intangible requirements.
At first, however, these requirements did not seem to synchronize with the site. Although certainly not the tiniest of urban lots, the .19-acre, slightly sloping parcel forced us to adapt the vision to some challenging existing conditions. Orienting the long axis of the house east toward the street wasn’t an option, because that would practically guarantee excessive summertime overheating and sever the sense of connectedness and movement between the green public space in front and the private garden in the back. In addition, the mature silver maple tree on the north side of the front yard pushed the driveway to the south, but also became a perfect way to shade the east side of the house from the hot morning sun in the summer.
The initial schematic design for the structure — dubbed the “Breezeway House” — had a roofed passageway, open at the front and back, connecting the low-profile flat-roof garage on the south to the two-story shed roof home to the north. This “out- door room” would connect the front yard, backyard, garage and main living spaces. In short, it would be the central organizing spatial element uniting the disparate places on the property — the departure point that gives clarity to moving in and out of the building.
I know architects always blame zoning ordinances for screwing up their design intentions, but this time it was true. Local zoning rules don’t allow an open-air breezeway between a house and an attached garage, so the breezeway became an entry vestibule but retained its initial intended role as the lynchpin of the design. And the name stuck — “Foyer House” just doesn’t have the same ring to it.
Reduced Demand, Renewable Supply
The Passive House standard results in an extremely energy-efficient building. This reduction in heating and cooling loads allows designers to use innovative systems to meet the reduced demand.
The heart of the Breezeway House’s heating system is a 120-gallon TiSun solar hot water tank that supplies the domestic hot water (DHW) system and the hydronics. The tank has about 110 gallons of hydronic water storage, with another 10 gallons of DHW storage in a stainless steel heat exchanger.
The hot water from the hydronic system runs through a heating coil in the ventilation air stream to heat the house and through pipes embedded in the floor of the foyer to provide backup heat to the entry vestibule during extremely cold weather.
Very hot (160o F/71o C) hydronic fluid surrounds and continually heats the 10 gallons of water stored in the heat exchanger, acting as an on-demand heater for domestic hot water. A second heat exchanger at the bottom of the tank connects to two TiSun solar thermal collectors on the roof.
A Passive House is airtight, so an energy recovery ventilator (ERV) is mandatory to ensure that pollutants and moisture do not build up in the home. The overall efficiency and energy consumption of the ERV is critical to meeting the stringent requirements of the Passive House standard. We chose an ERV with an efficiency of 93 percent at 200 cubic feet per minute (cfm), which means that only 7 percent of the heat in the home’s air is lost in the exhaust.
In addition, we installed a simple geothermal heat exchanger in the incoming ventilation airstream, which is connected to 800 feet of HDPE “slinky” tube buried about five feet below the ground behind the home. A glycol solution flows through the buried tubing and through a copper heat exchanger in a loop, which takes heat from the earth in the winter months and boosts the temperature of the fresh air going into the ERV.
The water from the solar tank is circulated through a water-to-air heat exchanger inline with the ERV system, and this 200 cfm of fresh air heats the entire house, except for the backup radiant tubing in the entry area. A CO2 sensor monitors occupant activity and modulates the ERV ventilation rate. If the heat demand trumps ventilation needs, the ERV speeds up to meet the heat demand.
The cooling system is an indirect-direct evaporative cooler ducted to all the cooling load spaces in the house. Unlike single-stage evaporative coolers, this unit runs air through an indirect heat exchange mechanism that removes heat from the air without adding moisture, resulting in drier air and better occupant comfort. When cooling is called for, a motorized damper opens, allowing cool fresh air to flow into the building from the cooler, which is located outside. Two motorized window openers allow an exit path for exhaust air.
For the sake of simplicity, the owners decided to forgo natural gas service. For food preparation, they use an induction cooktop, and the electric resistance element in the solar storage tank provides space heat when the passive solar design and the solar hot water system cannot provide enough heat. In addition, because electricity is relatively expensive in Salt Lake City and is generated by burning coal, we installed a 2.2-kilowatt photovoltaic (PV) solar electric system to begin to balance on-site energy consumption with energy production.
The Breezeway House’s relatively high electricity use results from the decision to cook and heat with electricity. Thanks to the modular nature of a PV system, the owners can add modules in the future to supply that electricity if they choose. In the meantime, they can enjoy their beautiful, comfortable home secure in the knowledge that building a state-of-the-art Passive House was a smart choice that will serve them well far into the future.
Dave Brach is a licensed architect, contractor, carpenter, cabinet maker, woodworker, rock climber, fly fisherman, mountain biker, hiker, skier and overall worshipper of the high desert climate. Originally from the Midwest, he studied anthropology at Notre Dame and architecture at the University of Illinois Chicago. In 2004, he moved to Utah to be close to the mountains.
Breezeway House Project Details
Owners: Joe Turner and Rebecca Guymon
Architect: Dave Brach, AIA, CPHC, Brach Design Architecture, brachdesign.com Contractor: Mark Fisher, Fisher Custom Building Inc.
Size: 2,800 square feet (260 square meters) of “treat- ed floor area” (a Passive House term analogous to “finished floor area”), 3,200 square feet (297 square meters) measured from the exterior
Construction cost: $450,000
Date Completed: November 2009
Basement floor, R-41
Basement wall, R-35
Window glass area in square feet (square meters)
North, 43 (4)
East, 54 (5)
South, 151 (14)
West, 54 (5)
Average window total unit heat transfer coefficient (U-value), U-0.18 (R-5.6) Solar heat gain coefficient (SHGC)
0.51 on south side
0.31 on others
Solar Electric System
2.2-kW photovoltaic system
10 REC Solar Inc. 220-watt modules
National Renewable Energy Laboratory’s PV Watts calculator estimates that a 2.2-kW system in Salt Lake City will produce about 3,000 kWh AC annually. The Passive House energy-modeling tool predicts a total energy consumption (heat demand, cooling demand, hot water demand, miscellaneous household electricity) of 105 kWh per square meter (9.76 kWh per square foot) per year, or 27,090 kWh per year source energy and 10,030 kWh (27,090/2.7) site energy.
Solar Hot Water System
Two TiSun solar thermal flatplate collectors, 77 square feet (7 square meters) 120-gallon (454-liter) TiSun solar hot water tank
An electric resistance element in the solar storage tank provides space heat to supplement the passive solar design and the solar hot water system. The foyer floor includes backup hydronic radiant heat for periods of extreme cold.
OAsys two-stage 40 SEER evaporative cooler, ducted separately from the ventilation system
Energy Recovery Ventilator
UltimateAir RecoupAerator 200DX