One Watt House™ FAQs:
1.   What is a One-Watt-House?
2.   How are One-Watt-Houses heated?
3.   What does a One-Watt-House cost compared to the average building?
4.   How do One-Watt-Houses relate to Energy Star, LEED and Zero-Energy-Houses?
5.   What is the availability of key components of One-Watt-Houses™ in North America?
6.   How does One-Watt-House efficiency compare with conventional US home construction?
7.   What is in it for communities, governments and energy policy?
8.   What do occupants say about air quality, comfort and level of satisfaction of inhabitants of One-Watt-Houses?
9.   What about building maintenance and longevity?
10.   Can windows be opened in a One-Watt-House™?
11.   Can the One-Watt-House concept be used in any US climate zone? Are any design changes necessary?
12.   How does a One-Watt-House look compared to the average American house?
13.   What design tools and engineering resources are needed to design and build a One-Watt-House?
14.   How is a One-Watt-House project executed?
15.   Is a One-Watt-House green aside from its energy efficiency?
16.   What is heat load, heat energy and total energy?
     
What is a One-Watt-House™?

One-Watt-Houses are designed to use no more than One Watt per square foot in heat and eliminate the need for conventional heating systems. In addition, a One-Watt-House use no more than 10kWh (34kBtu) per square foot in primary energy. These targets are inspired by the German Passivhauses.

One-Watt-Houses reduce the total energy demand of a building by 60 - 80% relative to average Mid-West buildings. To help understand these values, 20 x 100Watt light bulbs supply enough heat for a 2,000 sq .ft. home during the coldest day of the year. Consequently, most active heating and cooling equipment can be eliminated.

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How are One-Watt-Houses heated?

One-Watt-Houses are heated and cooled passively most times of the year. The necessary added heat during climate extremes can supplied with a variety of low load solutions. A fundamental design goal of One-Watt-Houses is simplicity:
The extra investment in insulation, windows and other passive house components is rewarded with savings in mechanical systems. Furnaces are not needed. Instead, we can use a on-demand water heater, heat pumps, solar thermal or other sources for both space heat and domestic hot water needs. CTI analyses available energy sources, heat load and the house system as a whole to determine the optimal HVAC solution for the building.


(Contact CTI for detailed questions on heating and cooling solutions in your location)

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What does a One-Watt-House cost compared to the average building?
The incremental, added cost for a One-Watt-House ranges from 10% to 20%. More money is spent on super windows and insulation, but less is spent on mechanical equipment. Even at this price difference, One-Watt-Houses are the most economical building type when considering the total cost of ownership during the life of a building. If the energy cost increases faster than the cost of capital, as it has over the last few years, the amortization of extra investments in efficiency will be further accelerated. One-Watt-Houses are not just better houses, good for the environment they are also good investments considering our uncertain energy future.
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How do One-Watt-Houses relate to Energy Star, LEED and Zero-Energy-Houses?

Energy Star is a broad initiative established by the Department of Energy to promote energy efficient appliances, devices and buildings. Any building which is 15% more efficient than the local reference building can achieve an Energy Star rating. One-Watt-Houses are 60 - 80% more efficient than average - raising the bar significantly.

LEED (Leadership in Energy and Environmental Design) is a growing standard for "green building" in the US within which Energy Efficiency is one of many aspects. It looks at the building process comprehensively and attempts to improve site selection, material choices, transportation, and other building attributes. One-Watt-House™ and LEED are complementary - in fact we can help LEED to be more effective. Other, non-energy criteria of LEED should be applied where possible. We do believe that energy efficiency takes priority, considering the related resource, climate and political challenges of this century.

Zero-Energy-Buildings supply enough renewable energy to neutralize the on-site demand of a building. If the building is not based on a very high level of energy efficiency, it will require major investments in renewable energy features. A One-Watt-House prioritizes first on energy efficiency investments to minimize energy load.  Starting with a super efficient, passive building will significantly lower the need for active systems.

Additional investments can go into super efficient refrigerators, cars, and other household items to further lower one's carbon foot print.

What are the system requirements that make One-Watt-House™ possible?

Component One-Watt-House™ requirement US Mid-West typical
Windows
[Btu / sq ft hr deg F]
U max. = 0.14 U max. = 0.35
Insulation
[sq ft hr deg F / Btu]
R min. = 40 - 60 R min = 13
Air-tightness
[Air exchange per hour
at 50PA pressure]
ACH50 = 0.6 ACH50 = 6
Heat-Recovery-Ventilation Min. Efficiency = 85% Not needed
Window energy balance Net. Gain Net. Loss
(Rough comparison only)

It is important to keep in mind that insulation of One-Watt-Houses™ forms an entirely enclosed thermal envelope. Thermal bridges are minimized to achieve the 1W/sq ft heat load requirement.
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What is the availability of key components of One-Watt-Houses™ in North America?

Plenty of envelope and wall solutions are available in the US: most common are light wood frame and loose fill insulation. Structured Insulated Panels (SIPs), a sandwich of OSB panels and foam insulation, offer a good alternative. Extra attention is needed when selecting windows, heat recovery ventilators, doors, and other components to complete the super insulated envelope. For example, a typical One-Watt-House window uses 3 panes of glass with an Ar or Kr gas and one or two coats of heat reflective coating (low E).

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How does One-Watt-House efficiency compare with conventional US home construction?

comp chart

One-Watt-Houses typically achieve HERS® ratings between 30 and 42. (A newly built local reference building - build excactly to meet IBC 2004 - scores a HERS® 100)

HERS: Home Energy Rating System - a nationally reckongized system for rating homes. The system is also basis for determining Energy Star® and LEED® credits and is the only rating system endorsed by the IRS. A HERS 100 is an exactly average local reference building complying with the International Building Code 2006.

Please also refer to http://www.natresnet.org/

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What is in it for communities, governments and energy policy?
Sustainable buildings are part of sustainable communities. If One-Watt-Houses are adopted on a broad scale, new power stations and investment in the power grid are not needed and resources can be spent on improving existing ones. Investments in super efficient houses in Germany have created more jobs per invested dollar than other strategies (15 man years per $1 Million investment). A One-Watt-House takes more craftsmanship on-site, more local resources and more vendors supplying higher engineered components than a conventional home; therefore it is an excellent tool for communities to generate growth.
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What do occupants say about air quality, comfort and level of satisfaction of inhabitants of One-Watt-Houses?
Few people in doubt the higher level of comfort along with improved air quality in One-Watt-Houses. The empirical data on CO2 , CO and VOC levels has convinced skeptics that controlled, continuous fresh air supply makes for healthier houses. Old house odors are removed and temperature differences throughout houses are minimal when compared with the average building. No more uncomfortable thermal drafts, hot and cold spots, uncomfortable cold surfaces in winter, and related condensation issues. We recommend letting the ventilation system run on low speed year around.
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What about building maintenance and longevity?
When houses become more passive, less systems require less maintenance and replacement. Because building material is kept at even temperatures and condensation due to thermal bridging is minimal, One-Watt-Houses™ last longer and generate a greater return on investment than the average building.
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Can windows be opened in a One-Watt-House™?
Yes, they can like in any other house.  Keep in mind that fresh and warm air is also supplied via the ventilation system.
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Can the One-Watt-House™ concept be used in any US climate zone? Are any design changes necessary?
Yes, the laws of heat loss and gain work the same everywhere. What must be adjusted are insulation levels, window types, etc.  Local climate, including humidity, cooling loads, traditional local building constrains all enter the design process when customizing the One-Watt-House. 
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How does a One-Watt-House look compared to the average American house?
Architects can still creatively design buildings.  Guidelines for compactness, southern vs. northern windows are embraced by most architects once they understand the benefits. Most typical house designs in US can be modified to be a One-Watt-House.
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What design tools and engineering resources are needed to design and build a One-Watt-House™?
Energy simulations, systematic analysis of component options and an iterative design process are used to reduce risk and ensure success.
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How is a One-Watt-House™ project executed?
Many details of walls, foundations, insulation, windows and HVAC differ from the common practice of contractors. Therefore, full-service architecture, engineering and construction support is highly recommended with a mutual education process that includes local building departments, component vendors, contractors, and design professionals to ensure success. Building projects are most successful when all tasks are well coordinated and everyone works as a team.
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Is a One-Watt-House™ green aside from its energy efficiency?
Decisions for all building components such as wall paint, kitchen appliances, paving material, etc. can be done in an environmentally friendly and healthier way. We are experienced in Green Building and the LEED rating system ensuring a complete and thorough approach to sustainability.
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What is heat load, total energy and primary energy?

The maximum heat load describes how much heat is lost and must be supplied in a building at the time of climate extremes to insure indoor comfort. For Chicago, the design load is 0°F. Because a One-Watt-House™ loses its heat much slower in those extremes, temperature lows and peaks are less noticeable. Heat Load is a dynamic measure and expressed in Watts or Btu/hr .


Total on-site energy demand includes all fuels & forms of energy supplied: electricity, natural gas, propane, etc. typically over one year and is measured in kWh, Btu, Therm, per conditioned floor area etc.

Primary Energy (PE) is the amount of energy the power plant needs to process in order to balance the total on-site energy demand.  It includes inefficiencies during generation, distribution and transformation of energy.  The total Primary Energy of a building depends largely on the local power supply structure and the Primary Energy conversion factors. The national average Primary Energy conversion factor is about 3.

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