For most of the climates mankind inhabits, heating ventilation and air conditioning (HVAC) systems are a basic necessity for maintaining constant and comfortable indoor temperature. Currently, residential buildings account for 20% of total energy consumption in the United States, with single family detached houses accounting for 77% of residential site energy consumption. Crucially, over 50% of this residential consumption is due to HVAC systems. Homes and residences have generally used constant air volume systems, in contrast to the well-controlled variable air volume (VAV) systems used in commercial buildings. These VAV systems can save energy by directing conditioned air to different occupied zones in the home as needed. While multizone VAV systems in single family houses have been economically inaccessible in the past, recent technological developments in building automation controls and the Internet of Things (IoT) can enable homeowners to retrofit their existing HVAC systems into VAV systems, warranting further investigation into the energy savings potential of such systems. Past residential VAV system research mostly involved simulations and measurements of singular case study houses over short periods of time.
Although products available in the market promise 15%-25% energy saving for VAV retrofitted HVAC systems, there is a need for further modeling since the figures provided are based on limited modeling and testing scope; typically looking at a house in a single location for times periods less than a year. On this account, Daniel B. Lu from the New York University and Professor David M. Warsinger from the Purdue University, proposed to expand on existing singular case studies by simulating the energy usage of representative houses of two different sizes and across various climates over an entire year. Their work is currently published in the Journal of Building Engineering.
In their approach, a baseline model was first created with floor area, room numbers, interior room geometry, internal load schedules, and HVAC system representative of a typical US single family house using data aggregated from the Energy Information Administration and other sources. A second model was then created matching the baseline, but with the single zone Constant Air Volume (CAV) system replaced by a multizone VAV system, where each zone had its own occupancy-based thermostat schedules to dictate zone supply vent damper positions accordingly. In addition, a pair of CAV-VAV models was made for each of the seven International Energy Conservation Code climate zones in the US. Overall, a total of twenty-eight energy models were simulated to compare these two systems in energy and energy cost savings.
The authors found the average size house models yielded 24%–42% source energy savings while large house size models have 18%– 35% source energy savings, with houses in cooling dominant climate saving relatively more. In general, the reported results were seen to indicate greater energy savings potential for single family homeowners considering VAV retrofits in cooling climates and areas with higher cost of electricity.
In summary, the study used representative energy models of two different house sizes, with estimates of individual room sizes, to expand on existing case studies and further examine energy savings potential for single family homes across seven US climate zones over an entire year. Remarkably, the results indicated that the VAV system could significantly reduce source energy and energy costs due to lower fan and cooling energy usage. In a statement to Advances in Engineering, Professor David M. Warsinger said their research work offered valuable insights on VAV systems; and that future research should focus on the payback analyses of single family VAV system implementations and its sensitivity to occupant behavior.
Daniel B. Lu, David M. Warsinger. Energy savings of retrofitting residential buildings with variable air volume systems across different climates. Journal of Building Engineering; volume 30 (2020) 101223.