How to Build Your
Oregon Net Energy Home

Net Energy Homes (NEH), sometimes called Zero Energy Homes, are exceptionally energy efficient homes with installed renewable energy generation systems that either make the house energy self-sufficient, or put more energy on the electrical grid than they take from it on a yearly basis. Good NEH design practice makes use of green design principles and materials, so that the house provides a healthy indoor environment with a minimized environmental footprint. Net Energy Home design and detailing are quality and building science-driven, rather than building code minimums-driven.

Architecture
A Net Energy Home takes building efficiency to a new, higher standard, but it can look just like the house next door. Synergistic economies in well-designed buildings can keep additional costs to a minimum- perhaps less than the cost of those granite countertops! A key architectural design philosophy is to keep the house small; what kind of house would you build if you knew energy costs would more than quadruple in the next ten years?

Passive Solar: Any NEH makes optimal use of the local climate and established passive solar design principles to provide the maximum amount of “free” energy. See the Oregon Office of Energy page on Solar Space Heating.

Super Insulation and Tight Construction: A NEH must be super-insulated, built nearly airtight, and have high quality windows. A key design philosophy is to put your money into the envelope: because it only gets built once, and everything else can be easily changed later. For most Oregon climates, design for R-values of R45+ in the roof, R30+ in the walls, R38+ in framed floors, and continuous R10+ foam underneath slabs. Windows should have U-values below .33, except for designed-in south-facing solar glazing that may have a U-value below .45 and night insulation. It is not difficult to keep the Design Heating Load below 6-8 Btu/Hr per square foot, even east of the Cascades. Keep the thermal and pressure envelopes aligned and seek a natural air exchange rate of less than .20 ACH.

Green Building: A NEH makes use of non-toxic, low-embodied energy, durable, recyclable, local materials, and minimizes the environmental footprint of the building process through time. See the Leadership in Energy and Environmental Design (LEED) standards at the United States Green Building Council, for an excellent compilation of green building criteria.

Pattern Language: A building’s efficiency through time relies on it being comfortable, attractive, affordable, and durable. Using design principles demonstrated in books such as A Pattern Language (Christopher Alexander, et al) will help insure that people will enjoy living in their Net Energy Homes for centuries to come.


Renewable Energy Systems
Provide large, unshaded areas of south facing roof for solar thermal and photovoltaic panels, and chases, conduits, and access for piping and wiring from the roof to the mechanical room. A detached garage can provide additional roof area and PV balance-of-system space. If sufficient renewable power is available, an all-electric house may be a good design choice. See the Energy Outlet information sheets on renewable power.

Solar Thermal: Install a solar water heating system sized to the home. Some climate zones in Oregon will support space heating with solar thermal.

Photovoltaics, Wind, or Microhydro: For an on-grid NEH, install the largest renewable electric power generation system the site and budget allow; at least 3KW for PVs. Provide additional roof area and install over-sized wiring or modular electrical design to accommodate future system expansions.


Heating, Ventilation, and Cooling
In the NEH the heating loads are minimal; heat through the ventilation ducts using the water heater and a fan coil. Most components of the mechanical system are serving more than one purpose, making this an economical mechanical package. See the Energy Outlet information sheet Net Energy Home Integrated Mechanical System Diagram.

Heat Recovery Ventilators & Heating: Building a tight envelope necessitates a mechanical heat recovery ventilation (HRV) system, both for fresh air and retention of ventilation air heat. Use the HRV distribution ducts for the heating system as well. (Most NEHs will have heating airflows below 300 cfm.) Keep the galvanized steel ductwork entirely inside the conditioned envelope, and provide for return air movement. Some homeowners may call for a high-efficiency sealed-combustion gas heater or high mass woodstove to provide a hot spot to stand next to.
Water Heaters & Waste Heat Recovery: Any high efficiency water heater can be used in the NEH system; a heat pump model if electric, a tankless modulating burner or condensing gas model if natural gas or propane. (Do not use any atmospherically vented gas appliance!) The solar thermal system provides a storage tank that may simplify some system integration issues.

Passive Cooling & Evaporative Cooling: Most locations in Oregon have a 30 degree F day-to-night summer temperature difference, making cooling by nighttime ventilation the best efficiency option. Provide for opening windows low and high in the building to facilitate natural convective cooling. If mechanical cooling is necessary, most Oregon locations can use a direct or direct/indirect evaporative cooler.

On Paybacks
It is common to question the “cost-effectiveness” of building envelope and mechanical system upgrades, despite the fact that no other components of the house are expected to pay for themselves! Aside from the fact that it is expensive and difficult to upgrade the envelope after the house is completed, there are two ways to answer this concern:

1. “Simple payback” calculations use the billed cost of energy with an optimistic cost increase factor in the payback equation. Because “externalities” (the normal and environmental costs of doing business that are shifted onto the public sector) are left out of most calculations, Americans pay far more for their energy use in taxes and other costs than they pay in their utility bills. The simple payback equation is based on incorrect information and returns inaccurate results.
2. Why not look at energy efficiency upgrades as desirable and essential elements of a good house? The only reasonable use for simple payback figures is to help prioritize a list of efficiency choices.

Copyright Alan Van Zuuk