Effect of an on/off HVAC control on indoor temperature distribution and cycle variability in a single-floor residential building

This paper investigates an influence of an intermittent on/off operation of the air-conditioning (AC) equipment on the indoor temperature distribution, air flow and a cycle variability within a single-floor medium-size residential house. The analysis is performed using a recently developed and well validated computational tool based on a Computational Fluid Dynamics (CFD) method, coupled with conjugate heat transfer simulations within a three-dimensional model of a solid building envelope, and an HVAC on/off control model. The importance of including unsteady minute-level dynamic effects associated with the cycling of AC equipment into the energy and thermal analysis of residential and commercial buildings was recently recognized. Despite that, there were no studies that examined the effect of on/off cycling on the physics of the air mixing during both cooling and heating stages of the AC cycle, and how these unsteady interactions effect both the energy consumption and its variability, and the indoor thermal environment linked to a thermal comfort of the building occupants. The current paper focuses on analyzing the duration and variability of the cooling and heating cycles and their effect on the temperature distribution inside a residential house. It is found that both heat transfer from the walls, and turbulent intermittency of the indoor air affect the duration of the cooling and heating cycles. It is demonstrated that a central air system controlled by a single thermostat placed in the hallway results in a consistent overcooling of the interior spaces. These findings are important for the considerations of the electric grid management, and for the improvement of HVAC systems design and control.