the Science and Engineering
The Delta T-90 house puts it’s resources in the right place: insulation. Insulation in the wall cavity, and insulation surrounding the wall cavity means both immediate and long-term savings. This conservation based approach is the cornerstone of any high-performance building project – reducing your energy loads means reducing the size and strain on mechanical and electrical systems. Reducing size and strain on mechanical and electrical systems meaning saving money in the near term and long term.
The structure of the roof was carefully considered for the snow loads experienced in our region and was an opportunity to fully integrate the photovoltaic array with the rectilinear form of the design. The photovoltaic array, lying flat on the roof, was intentionally sized to accommodate an average of one-hundred and twenty days of annual snow coverage.
The decision to integrate a thin-film amorphous CIGS photovoltaic array on the roof is a bold move, and one that effectively removes the ‘solar hardware’ from the visual presence of the house. The Delta T-90 house is ultra-energy efficient due to the 6kW building integrated PV Array and high performance building insulation. The occupants of the Delta T-90 House will enjoy zero utility costs from heating, cooling, and household electricity thanks to energy produced by the solar array.
Heat Recovery Ventilation
The Delta T-90 house uses a multi-unit system of synchronized, decentralized, through-wall, ductless units called Lunos e2 that use small fans and ceramic cores to provide continuous fresh air to the home. Three pairs of these units are distributed throughout the house. One pair is dedicated to the kitchen and living room, one pair is dedicated to the bathroom, and a third pair is dedicated to the bedrooms. These units have a 95% heat recovery capacity and a 20% to 30% humidity recovery. As a pair, one unit will bring in fresh air, while the other will exhaust stale air. The warm air being exhausted charges the ceramic core with heat. The fan in this unit then changes direction and fresh incoming air is pre-warmed. The corresponding unit that was formerly in intake mode switches to exhaust stale air. This 70-second cycle then repeats itself. The three units working together provide 75 cubic feet per minute (CFM) of fresh air to the house.
Space Heating and Cooling
A Mitsubishi air-source mini-split heat pump is the sole source of active heating and cooling in the Delta T-90 house. The annual total space heating demand is a little under 8.5 million BTU’s annually, and peak heat demand would not exceed 12K BTU’s. A single indoor unit, centrally located in the house, and one outdoor unit work to heat and cool air to distribute throughout the house to be utilized for space conditioning.
In an effort to reduce transmission losses, hot-water distribution within the 991 sq.ft. envelope occurs within a twelve foot line, or within 72 sq.ft. The Stiebel EltronTempra 20+ provides on-demand hat water and reduces stand-by losses in hot water delivery by 15% annually while allowing for hot water heating to arrive instantaneously when needed. The Tempra entirely replaces a water tank and automatically adjusts the flow of water to eliminate any temperature fluctuations.
The Delta T-90 team chose to use advanced double stud wall framing to take advantage of its three key benefits: less material waste, simpler and quicker construction processes, and improved insulation performance. By aligning the window and door openings with the framing members there is an insulation gain with a reduction in thermal bridging throughout the wall envelope. The roof joists, floor joists, and wall studs are vertically in line at 24 inches on center, which creates a simple, yet direct load path to distribute the roof live loads and dead loads uniformly to the ground. The roof construction is more than sufficient to support the average snow load of 60 pounds per square foot (psf), and accommodates for the lives loads of our bio-region.
Because the Delta T-90 Team is committed to creating a solar-powered design for Vermont, climate played a significant role in the design of our building systems. The structural system in the Delta T-90 House is unique for our traditional built environment. The double stud wall section allows us to have almost 12” of dense pack insulation. This system allows us to nearly eliminate thermal bridging and maximize R-Value for construction in our cold climate. By using engineered lumber, the Delta T-90 House is framed on continuous beams. This technology accommodates for our two structural modules and for transportation to Irvine, California from Vermont.
Air Tight Design
In 2013, many regard the historic Vermont farm house with deep respect, admiration, and sentimentality. Thousands of examples still exist from the 1800’s, and an industry surrounds their maintenance and survival. Many builders and architects cite the historic Vermont farmhouse’s survival due in part to a loose building envelope that allows moisture to breathe from interior to exterior, as well as exterior to interior. The drawback, of course, is lack of air tightness, severe heat-loss, and sometimes severely drafty interiors. Like the historic Vermont farmhouse, the Delta T-90 House maintains a vapor-permeable wall section from interior to exterior, as well as exterior to interior. With dense-packed cellulose fiber (packed to a density above 3.2lbs.cu./ft/), moisture vapor looses it’s vehicle (air movement) to migrate into wall cavities. In addition to this, vapor permeable house wraps and high performance tapes seal the Delta T-90 house and keeps the building draft-free. Now, what about air-circulation?
The Delta T90 house eliminates the footprint of mechanical systems and maximizes livable space. We are ensuring that the design will not be driven by mechanical systems, and we will utilize passive strategies to ventilate, day-light, and shade while regulating the air within the house. As high performance designs require the use of high performing products, we have chosen to use the Lunos e2 HRV, which is located within the exterior shell. Active heating and cooling will be provided via two 9000 BTU diffusers off of the Mitsubishi Mr. Slim heat pump.
Mitsubishi Air Conditioner Dual Zone Ductless Mini Split Heat Pump (a single 15,000 BTU Indoor Unit)
Also specified as the Mitsubishi Mr. Slim, this mini split ductless air-conditioning system is a quiet and efficient solution for heating and cooling. Used in applications worldwide, the Mr. Slim consists of three main components. The first, an outdoor ground mounted heat pump, that uses little energy to attract and condense air inside the house for heating and cooling. Next, an indoor ceiling mounted diffuser is linked to the outdoor unit by refrigerant lines that contain the condensed temperatures. By using the intake setting, the diffuser pulls in air from the inside of the space, filters it, and conditions it to be the desired temperature (whether warmer or cooler) and then disperses it throughout the space. The third component to The Mr. Slim HVAC system is a remote controlthat allows an occupant to set a comfortable temperature for that living space.
As one of twenty competitors in Solar Decathlon 2013, the Norwich University Delta T-90 Team has taken the position that high-performance solar-powered dwellings must become more widely available to households earning twenty percent below the median state income in Vermont. Toward this end, the Delta T-90 House streamlines mechanical, electrical, and building envelope systems in an effort to increase affordability, reduce primary energy demand, and reveal the poetic breath of high performance modern architecture.