25. A Zero Energy Prefabricated ADU for New Zealand

Human activities threaten the sustainability of energy and environmental resources. One route to alleviate this is that all buildings need to be zero energy in operation. This paper discusses the results of simulating the energy use of a prefabricated accessory dwelling unit (ADU) for different construction scenarios in Wellington, New Zealand. The aim is to see whether it is possible given the construction constraints to achieve zero energy for space conditioning. The simulation was first done using ALF 3.2 software, developed specifically for New Zealand conditions. Changes in each scenario relate to using different thicknesses of Structural Insulated Panels (SIPs) for walls and roof and considering different types of floor, together with different heating regimes. Using ALF 3.2 a total of 36 different scenarios were simulated to see how much energy the ADU needs during a year and where the main sources of energy loss and gain occur. The next stage was running the simulations while adding different degrees of thermal mass to selected designs to see the effect of mass on the ADU energy consumption. The last stage was amending the size of windows in the best performing designs in order to find the best balance between gains and losses through them. Simulation results showed that heating the whole ADU to 16 °C all day and using 165 and 215 mm SIPs panels for walls and roof, respectively, with the ADU sitting on a 150 mm insulated concrete slab delivers the best result, being very close to zero energy for space conditioning.