Ellen Kathrine Hansen of VKR Holding in Denmark spoke in early November at UC Berkeley about her work implementing the Active House vision—creating buildings that combine energy efficiency with the use of renewable energy systems to create a positive energy balance, that provide a superior level of indoor comfort and health, and that generally tread very lightly on the environment throughout the building’s lifecycle. Hansen was project director on two Active House buildings, a single-family house in Aarhus, Denmark dubbed “Home for Life” and a daycare center named “Solhuset”.
Above photo courtesy of VKR Holding
The Active House concept seems to build on the Passive House approach by emphasizing optimal design, orientation, and high-performance materials to minimize energy use, but also stresses the use of renewable energy and incorporates intelligent control systems to move shading systems and open or close windows in response to varying climate conditions. Daylighting to minimize lighting energy use and natural ventilation are key features, although most houses also rely on mechanical ventilation with heat recovery during the winter for good indoor air quality.
Home for Life is oriented south, and 40 percent of the building envelope is devoted to windows. A weather station on top of the roof, combined with CO2, humidity, and temperature sensors in every room, ensures that the house is coordinated with and responds to the ever-changing weather. The south-facing windows are double-pane to boost passive solar gain, while all the other windows are triple-pane. The home’s window placement facilitates natural ventilation whenever the weather permits. Hansen used Velux’s Daylight Visualizer, which is downloadable for free, to assist with window design.
Data loggers were used to measure energy performance, indoor air quality, and the outdoor environmental conditions. The architectural team examined the measurements on a monthly basis to commission and optimize the systems. In the first year, the household’s energy use was higher than expected. The team attributed this increase partly to the building being not as airtight as it should have been; repairs were undertaken, and all the accessible leaks were air sealed. The other contributing factor to this unexpected energy bump was that the residents set the temperatures higher than the modeled settings—the pesky occupants messing with perfection again. As Hansen noted, finding a balance between automated control and residence control is important.
Other lessons from the first year included comments from the residents about how much they liked the daylight and fresh air. Indeed, the occupants had to be coaxed into closing the windows and relying instead on mechanical ventilation once the temperatures started dropping. The house suffered a bit from a surfeit of south-facing window, because the solar gain was a little excessive. The architectural team realized that some of the glass area should have been shifted to the north side to get more daylight in the winter. Finally, use of high-thermal-mass materials indoors would help to stabilize the temperature in all seasons.
The lessons learned from Home for Life were applied to the design of the Solhuset daycare center. The north-facing triple-glazed roof windows have a lower pitch than the south-facing double-glazed roof windows to maximize daylight throughout the year. This strategy has been successful, as very little energy is used for lighting. The south-facing windows were selected to have a high solar heat gain coefficient and also feature external sun shades to cut the gain in summer. Concrete inner walls help to regulate indoor temperatures. Energy production for the building comes from a variety of renewable sources, including from photovoltaics, solar thermal, geothermal, and a heat pump.
Details about this project and many other Active Houses can be found at www.activehouse.info.
