Net-zero Nation: HVAC and PV Systems for Residential Net-Zero Energy Buildings across the United States
Wei Wu, Harrison M. Skye
This study compared the energy performance and initial cost of photovoltaic (PV) and heating, ventilating, and air-conditioning (HVAC) equipment for a residential net-zero energy building (NZEB), in different climate zones across the United States. We used an experimentally validated building simulation to evaluate various all-electrically-driven and commercially- available HVAC technologies. The HVAC accounted for 23.8 % to 72.9 % of the total building energy depending on the HVAC option and climate zone. Each HVAC configuration was paired with a PV system sized to exactly reach the net-zero energy target, so the economy was compared based on the initial PV + HVAC cost. Mechanical ventilation was considered with and without heat recovery; the heat recovery ventilator (HRV) saved a significant amount of energy in cold winter months and hot summer months, and the energy recovery ventilator (ERV) provided additional benefit for humid zones. The HRV was cost-effective in the cold northern latitudes of Chicago, Minneapolis, Helena, and Duluth, where energy savings reached 17.3 % to 19.7 %. In other climates, ventilation without recovery was more cost effective, by 1 % to 9 %, and sometimes even more energy efficient. The ERV was never the lowest cost option. A ground- source heat pump (GSHP) and an air-source heat pump (ASHP) were compared, where the GSHP provided significant energy savings, 24.3 % to 39.2 %, in heating-dominated climates (Chicago through Duluth). In warmer climates, the GSHP saved little energy or used more energy than the ASHP. The PV + HVAC cost was lower everywhere with the ASHP, though it is possible for colder climates that a carefully sized GSHP and ground loop could be cost-competitive. The energy and cost data as well as the required PV capacity could guide the HVAC and PV designs for residential NZEBs in different climate zones.