Case study of a high efficiency home
The PowerHouse home in Newton, IA was designed and built with energy efficiency in mind. The main technology being studied is ZeroNet's "super envelope" design, which incorporates expanded polystyrene bonded with a fiber-reinforced concrete coating on each side. The highly insulated walls and roof of the PowerHouse should reduce heating and cooling energy consumption by up to 50% throughout the year while the sophisticated HVAC equipment will improve air quality and human comfort by reducing pollutants inside the residence.;Research Goals. (1) Evaluate building envelope performance with regards to design heating and cooling loads; (2) Estimate the annual performance using a commercially available computer program simulation and compare it to actual performance; (3) Simulate the annual performance of a traditionally build home and compare it to the PowerHouse; (4) Monitor and analyze end-use electrical consumption for various HVAC and domestic equipment and appliances; (5) Evaluate the performance of the home as a whole using sub-metered data to calculate a performance index; (6) Compare the PowerHouse home's annual energy performance index with various other homes and government indexes; (7) Find ways of improving the performance of the installed mechanical systems.;The design heating and cooling loads where calculated to be 31,659 Btu/hr and 24,828 Btu/hr, respectively. These design loads where calculated using the ASHRAE approved method outlined in the 2005 Fundamentals Handbook (ASHRAE, 2005).;The simulated annual energy consumption of the HVAC equipment was 18,217 kWh. The home actually consumed 19,167 kWh, so the simulation was fairly accurate. The annual energy consumption of a 2x6 built home of the same design was estimated to be 25,899 kWh. The 2x6 home uses 42% more energy for heating and cooling than the PowerHouse. This extra energy use equates to over 575 per year of extra utility bills. Considering a modest 2% fuel inflation rate, over a ten year period the ZeroNet design would save over 6,300. The higher U-value of the exterior walls and roof and the increased infiltration rate are the main factors contributing to the extra energy use.;In 2005, the PowerHouse consumed a total of 35,480 kWh of electricity. This corresponds to an energy intensity of 28.8 kBtu/ft2. According to the Energy Information Administration (EIA, 2004), in 2001 the average energy intensity of a single-family detached home in the Midwest was 49 kBtu/ft 2 (EIA, 2004). Thus, the PowerHouse home represents a 41% improvement in energy intensity than the average.;Detailed monitoring conducted from January, 2005 thru December 2005 showed that there are several steps that could be taken to lower the annual energy consumption of the Powerhouse home. The domestic hot water system has large standby losses due to a recirculation system that keeps hot water at all the taps in the home. While the home was unoccupied and no hot water was being used, the domestic water heater consumed over 500 kWh per month. A clean air system integrated into the air handling unit relies on the fan running at low speed 100% of the time, even when there are no loads, to circulate air and carry away heat from the ultraviolet bulb fixture.;Overall the PowerHouse was performing as expected. The detailed monitoring showed that there were still ways to greatly reduce the overall energy use. Utilizing a geothermal system's higher coefficient of performance, the HVAC cost could be cut by over 60%. The domestic hot water load would also be supplemented by a de-superheater included with most heat pumps. The PowerHouse was already performing better than average, so applying these upgrades would make it all that much better.