Zero Energy Homes

The basic of a zero net energy home is that its produced energy is equal to or greater than it consumes. The ability of the house to be zero-energy is primarily dependent on three elements:

  1. Advanced shell design
  2. Super high efficiency heating system
  3. Photovoltaic power generation

The three elements work in unison and are required to create as much energy as is consumed in a viable economic package. The design team was committed to using easily replicable construction techniques that could be accomplished for not more than 115% of conventional construction cost. A key element of uniqueness to the Rose house is that in addition to demonstrating technical innovation, it is all about affordable and appealing design that is accessible to the general population.

The advanced shell design serves to minimize the heating and cooling requirements of the home. A Structurally Insulated Panel System (SIPS) is used for the roof. A Staggered Stud System is used at the walls with recycled blown cellulose insulation (R-25) allowing continuous insulation around the studs and providing a breathable vapor barrier. Special foundation insulation details minimize temperature changes.

The Super High Efficiency space conditioning system uses less than half the energy of a conventional system while providing fresh air and eliminating the need for a furnace in favor of a solar heat pump. The heat pump gathers energy from the back of the PV collectors and generates energy as hot water. A 120 gallon thermal storage tank A clearstory bank of windows provides generous day-lighting and natural stack effect ventilation instead of air conditioning.

The 3.3KW Photovoltaic Array of Sharp solar PV panels is a grid tied system that provides more energy than required at times and less than required in others. The grid acts as a big electrical storage bank that is required to make the house function properly. During start-up of motors and electrical equipment much more than 3.3 KW is required and the grid provides that extra capacity.

As seen by the following diagram, overall during the year, the house will supply more energy to the grid than it has consumed. Since all appliances and the heating systems work on electrical energy the house is a Zero-Net Energy house. Solar PV power is the blue contribution below the line and the various household loads are above the line.

The diagram is a computer model of this house. The WEB site will show a daily and accumulated graph of. The actual energy delivered by the photovoltaic grid and the household energy loads.

The Cost of a Zero-Net Energy Home

The first cost of a "zero" net energy home can be reduced to near that of a typical house. Some of the component cost savings were possible because of new energy recovery technologies, and low-cost, yet sophisticated programmable controls. The majority of the cost savings however, came from a design that gets multiple benefits from each feature. These design elements and their relative cost savings will be presented.

Envelope design with highly insulated staggered stud wall system allows loads to be met with airflow rates provided by the fresh-air ventilation system.

Use of a heat pump for domestic hot water heating, space heating and space cooling.

Use of an energy recovery ventilator to provide humidity-optimized fresh air and serve as a primary driver for the heating coil, energy recovery and economizer function.

Use of concrete slab construction to serve as thermal storage both passively (direct gain) and actively (heat pump).

Use of PV array to provide a source of waste heat, reduce cooling loads and improve roof life, in addition to providing all of the annual energy requirements for the house.

Final costs for all system components will be presented and compared to current conventional residential construction. Preliminary results indicate that the additional costs of the house from these features will be less than 15% - including the net cost of the PV system after incentives and tax credits.

Oregon Zero Energy Home Base House

The following is a description of the "Base House" which is used to for evaluation purposes the solar heat pump system in Oregon. The design allows for good solar access both on the roof and as a passive solar design. Maximum roof area for solar measures 36 feet wide by 12 feet tall for (431 ft2).

ZEH Base House Design

Heated Floor Area 1900 ft2
Total Glazing Area 394 ft2
Passive Solar Glazing Area 225 ft2
Potential Solar Roof Area 500 ft2
Total Solar Resource Fraction 100 %
Water Heating .93 EF electric
Space Heating Heat Pump SEER 13
Heat Recovery Water 60% GFX
Air 80% ERV
Appliances Energy Star Clothes Washer
Energy Star Dishwasher
Energy Star Refrigerator
Lighting Fluorescent (90%)
Other Plug Loads 1000 kwh/yr
Phantom loads 200 kwh/yr

Construction Details

These are just base starting point assumptions.

ZEH design Code design

Walls U-0.045 various U-0.060 2x6 stud w/R21
Roof U-0.027 conditioned attic U-0.027 attic w/R30
Floor U-0.025 micro-basement U-0.032 ventilated crawlspace w/R25
Windows U-0.330 vinyl low-e, argon U-0.400 vinyl low-e
Solar Windows U-0.300 SHGC > 0.60, w/NI none
Doors U-0.200 U-0.500
Infiltration 2.0 ACH50 7.0 ACH50
UA overall 270 Btuh/F 360 Btuh/F

Loads and Consumption

Portland Medford Redmond

Design Temp (F)
Design Load (Btu/hr)
Heating (kWh/yr)
Cooling (kWh/yr)
DHW (kWh/yr)
Appliances (kWh/yr)
Lighting (kWh/yr)
Other Plug (kWh/yr)
These Values are +/- 20%