HERS Rating: 57% Improvement over Code (What is a HERS rating?)
Projection: 80% Improvement over Code
- load calculations from HVAC engineer of the highly efficient geo-thermal system together with infrequent usage of the system due to the Owner's preference for the designed natural ventilation
- ceiling fans
- CFL Energy Star and low-wattage LED fixture
- all Energy Star appliances
- ERV (what is an ERV?)
- Rainwater collection pumps
- Photovoltaic production contributing to Net Usage
Actual: 85% Improvement
- One year of energy bills logged and added up
Rainshine's actual energy consumption for 2010, the first full year of occupied operation, is remarkable.
The 2008 HERS (Home Energy Rating System) rating projected only a 57% improvement over code for RainShine. Not pleased with the HERS rating we chose to conduct our own calculations and projected usage averaging $71.22 per month, an 80% improvement over a code compliant house.
We were confident in our numbers and knew HERS did not consider a variety of factors contributing to energy consumption. Among them:
1. The microclimate of the house
2. The extensive passive solar feature such the overhanging eaves, light shelves and east/west windows located to reduce solar gain through screening from existing trees.
3. The critical factor of the willingness of the clients to live a sustainable life in a sustainable house.
To prove our calculations we tracked the house's actual occupied energy consumption and photovoltaic production for 2010. Average gross utility cost per month was $48.57, an 85% improvement over code. A few more photovoltaic panels and the house would be net zero.
The most disappointing result from our survey was photovoltaic production. Our calculations were based on a site specific calculation provided by the manufacturer who estimated (conservatively according to them) generation of 7,500 kWh/yr. Only 3,155 kWh were generated in 2010, less than half of the projection and a shortfall of $740 for the year and an average of $60 per month. If the PVs had performed up to snuff the house would easily be net zero.
Conclusion: energy projections can be, as we all know, misleading and every house should be tracked to determine actual energy consumption. In general we were delighted with Rainshine's real-life performance. Rainshine proves how energy efficient thoughtfully combining site features, orientation, passive solar design concepts with active systems can be (even when incorporating major areas of glass). Kudos to the owner and design team!
Throwing features and systems at house designs in order to improve energy performance is, as I suspect HERS is necessarily dumbed down to do, wasteful and counterproductive. As in Rainshine an energy efficient house should look like an energy efficient house, not a neo-eclectic mishmash with energy features screwed in/tacked on a sideways compromising manner.
