Energy Use in a Net Zero Home

posted by Lee Grutchfield, AIA

When I am talking to people about the idea of a “net-zero” home, I will sometimes say that we are now able to build houses that use no energy.  In reality, it is more appropriate to say that the houses create as much energy as they use over the course of the year. This is done by harvesting the sun’s energy, through the use of photovoltaic and solar hot water systems, as well as passive solar heat gained through south facing glass.  Often the next question will be, “How much energy can I use, and still have a net zero house?”

While there is no set answer to that question, I thought I would share a case study from a recently completed home in the South Farms development in Hinesburg, Vermont.  The house has approximately 1,800 square feet of heated living space, and utilizes a geothermal well for primary heat, with wood stove back up.

Energy use projection in kWhrs/yr: 

Refridgerator 383
Dishwasher 82

Microwave 50
Clothes Washer 153
Clothes Dryer 104
TV 50
Computer 20
Stereo 20
Lights 250
Garage Door Opener 50
Water Well Pump 100
Heat Recovery Ventilation 220
Central Vac 60
Domestic Hot Water 400
Phantom loads 100
Heat Pump 1,800

Total Load 3,842 kWhrs/yr

Energy production from PV panels generate 4,352 watts, which will give a total gain of 4,787 kWhrs/yr.

In this scenario the local power company will owe the owner $179.00 at the end of the year for excess power that is fed into the utility grid.