Monitoring, analysis, and evaluation of an owner-occupied net-zero energy house with solar photovoltaics and a hybrid heating system in cold-climate Ontario, Canada

The Strathroy House under investigation was designed and constructed to be a net-zero energy house (NZEH) using a hybrid Air Source Heat Pump (ASHP)-Natural Gas Furnace (NGF) HVAC system and solar photovoltaic (PV) panels. The objective of this study is to evaluate the home’s performance to determine whether it meets its NZEH design goals, and to identify the key factors that should be addressed to minimize or eliminate design discrepancies. A comprehensive energy audit, testing, and modelling analysis were conducted to investigate the performance of house energy demand and PV generation. The recently developed advanced Smart Dual Fuel Switching System (SDFSS) was installed and tested in the house to see its relative impact on the house’s energy performance. It was found that the differences in energy performance between the design and operational phases are caused by several factors, including higher-than-anticipated outdoor electric plug loads, underestimation of space heating and cooling requirements, lower-than-expected solar PV generation, and assumptions made during the initial design-stage HOT2000 modeling. Based on the analysis, the house was found to have a negative net-zero energy surplus as per the source-to-site ratios. It was concluded that even though the house meets the Ontario Building Code (OBC) and Energy Star standards requirements, it cannot be labeled as an NZEH. The data shows that discretionary loads, such as outdoor hot tubs, significantly contribute to the mismatch between electrical demand and generation. To address this issue, it is crucial to prioritize reducing discretionary load and optimizing operations. Expanding photovoltaic (PV) systems can be considered a secondary option, given space constraints and seasonal factors.