Hybrid air-hydronic HVAC performance in a residential net-zero energy retrofit

While the United States is no longer the global leader in primary energy consumption, it still represents a significant percentage of global consumption. Residential buildings account for 22% of U.S. national primary energy consumption. Research efforts improving efficiency of existing U.S. homes will have opportunity to greatly impact national energy consumption by addressing a significant energy savings potential. Driving towards net-zero energy buildings provides an ideal scenario where homes produce all energy demands on-site. A joint research project, the ReNEWW House, captured an approach of renovating a home to net-zero energy. An efficient and advanced, hybrid air-hydronic HVAC system was installed. During the first heating season, excessive heat pump short-cycling occurred from improper buffer tank controls by default manufacturer settings. Modifications to the temperature control strategy recorded lower energy use through an improved heating system effectiveness. Results were collected over two heating seasons from in-field measurements. During the first heating season, the heat pump used 5440 kWh of electricity at annual heating degree day (HDD) of 6080 °F-day. The second season measured 3920 kWh of electricity at annual HDD of 4800 °F-day. The effectiveness for the heating season increased from 0.89 kWh/°F-day for the first season to 0.82 kWh/°F-day for the second.