When we say we need to build future friendly homes, this is what we mean. We designed and built this house to meet the rigorous Passive House standard, and our client chose to equip the home with the capacity to produce as much energy as it consumes on an annual basis – including the capacity to power an electric vehicle! It goes beyond Net Zero, it’s Net Positive!
This Passive House has been recognized for meeting two significant challenges. It is the first house in CT to be officially certified by the International Passive House Association AND it won 3 out of the 4 categories in the CT Net Zero Challenge, including being designated as the overall winner. These accomplishments reflect our intention to demonstrate that future friendly homes designed and built to be miserly in their use of energy are at the same time healthy, durable, and especially comfortable to live in. The icing on the cake is the ease with which these homes can completely satisfy all their domestic energy needs with on site sources of renewable energy. These homes are an inspired response to many challenges we are facing in this new century.
The genius of the passive house system is to slow energy loss to a trickle by managing the way the building loses energy through its surfaces and air leakages, and then capture ‘free’ gains from the sun and even the heat generated by people and devices in the home. With efficient lighting and Energy Star appliances it’s an easy step to add solar electricity to produce as much energy as it consumes on an annual basis. The resulting “energy balance” provides the building with exceptional comfort and health, simplified operation and dramatically lower operating costs.
|Conditioned Area||3561 SF|
|PV System||10.8 KW|
|Annual Heat Energy||1.46 Kbtu/sf/yr|
|HERS w/o PV||33|
In designing this home we evaluated the site to assure we had good solar access and oriented the building plan to capture solar energy on the roof and through the windows. We kept the shape simple but architecturally interesting by setting the garage and front porch off axis, adding a screen porch to the east, and working with the grade to nestle the house into the sloping terrain and get light into the finished areas on the lowest level. A two story central dining space with a dramatic open stair and stone clad wall adds excitement to the open plan. Then there are those iconic George Nelson pendant lights!
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The key to achieving Net Zero Energy performance can be summed up in this simple maxim: Reduce, then Produce. What this means is that if we can be miserly about the amount of energy the home requires to maintain comfort and meet occupant needs we can match that load with a rooftop solar array.
The energy “load” (the amount of energy required) for heating is both the largest AND the one we can reduce the most. The same efforts reduce the cooling load, though this is much smaller to begin with. After reducing these loads we focus on hot water. The client took on the challenge of constructing a solar hot water heating system, so all that is left is what is required to power the pump. Lighting is dramatically reduced by using LED lamps and we install the most efficient Energy Star appliances. This leaves the “plug loads” which power all our other “devices.” How much energy these require depends alot on how people use them.
The PV array that converts sunlight to usable electricity is sized to match these loads. For this house it is sized a bit larger, in anticipation of the purchase of an electric vehicle.
|Solar Hot Water||0.5||$26|
- Heating Savings 88.4%
- Cooling Savings 39.2%
- Hot Water Savings 96.4%
- Other Energy Savings 30.8%
Savings compared to a conventional Code Built equivalent of this home
The Home Energy Rating System (HERS) Index is the industry standard by which a home’s energy efficiency is measured.The projected annual energy costs for the home are compared to the projected costs for the HERS Reference Home to show projected annual energy cost savings. The reference home is the rated home reconfigured according to the 2004 Energy Code and federal minimum equipment efficiency standard and equals 100 on the HERS scale.
Capitalized Annual Savings
Capitalized Annual Savings are the net present value of the annual energy cost savings compared to the HERS Reference Home. This calculation uses the current market assumptions for energy cost inflation and the homeowner’s mortgage interest and a 30% marginal tax rate. It is a way to quantify the value of the avoided costs of energy for this versus a conventional home over 30 years. In other words, this is money you won’t need to spend on energy!
THE BUILDING’S PARTS
We construct the building with super-insulation on all SIX surfaces: Walls, Roof, and below the Slab. We are obsessive about air sealing to eliminate losses from air infiltration. We use high performing tilt turn triple glazed windows with large areas of glass on the south facade with “high solar heat gain coefficient” glass designed to capture the “free gains” from the sun (but shade them in the summer).
When we build like this we don’t need a complicated heat distribution system. We use high efficiency ducted minisplit heat pumps. The indoor environment is so stable that it maintains even temperatures with only this small amount of heat provided. A balanced heat recovery ventilation system assures constant fresh air at a rate optimized for health. The heat recovery assures very little energy is lost.
The owner took on the challenge of building his own solar hot water system including the storage tank. An on demand electric hot water heater is installed for backup, but is rarely needed. Finally the 10.8 KW PV System produces more energy than the house consumes on an annual basis. This home is “Net Positive!”
|Ceiling||Loose Fill Cellulose||R 83|
|Above Grade Walls||Dense Pack w/ Polyiso foam||R48|
|Foundation Walls||Dense Pack w/ Polyiso foam||R 43|
|Windows||Triple Glazed||R 7.6|
|Air Leakage||Blower Door Test||0.34 ACH50|
|Heating/Cooling||Mitsubishi 10.9 KBTU Ducted Minsplit||10 HSPF / 15 SEER|
|Solar Hot Water||DIY System|
|Ventilation||Zehnder Comfoair 350||84% Efficiency|
DRAWINGS AND PERFORMANCE ANALYSIS
These drawings show the floor plans, elevations and framing, and section details of the project. In addition there is the project’s Performance Analysis Report produced by our HERS Rater and Energy Star Certifier, Home Energy Technologies. Through the process of analysis and verification of this project the owner qualifies for rebates that amount to $10K, not including rebates and tax credits for the PV System.
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This Project won the Overall Grand Prize Winner in the energizeCT Zero Energy Challenge. It also won in for Lowest Overall HERS Score, Lowest HERS Index without renewables, Most Affordable, and Lowest Operating Cost! This video was produced to showcase the project and the features that contributed to that result. Program manager Enoch Lenge describe it as, “the most efficient house we have ever seen?”