Adaptive model-based advanced natural ventilation control strategy for mixed-mode residential buildings in Japan

Abstract

The mixed-mode (MM) ventilation strategy combines natural ventilation (NV) with conventional mechanical heating and cooling systems to improve energy efficiency while maintaining thermal comfort. The energy-saving effect of an MM building depends on integrating and coordinating operable windows with air-conditioning systems. Existing studies on fixed-threshold model-based NV control methods provide limited guidance, as the thermal comfort of occupants is adaptive to the outdoor environment. The adaptive approach in ASHRAE Standard 55–2020 advocates a shift to a variable comfort threshold. Researchers have developed NV strategies using this adaptive approach, but the NV operation time is reduced to increase the comfort ratio, which may overlook its potential. An adaptive approach is required for appropriate control.

This study develops an advanced adaptive model-based NV control strategy with a higher NV rate and energy-saving rate for residential MM buildings. The optimized NV threshold maximizes energy savings while satisfying high comfort rates (percentage of hours falling within comfort zone to total hours). To examine strategy performance, three existing methods (fully mechanical, fixed-threshold NV, and variable-threshold NV control methods) were selected and compared in eight regions of Japan with different energy-saving classifications. Four metrics (system operating rate, heat load, energy consumption, and comfort rate) compared the proposed and existing method performances. The simulation results demonstrated that the proposed strategy showed the highest NV runtime, with an improvement of 27.8 % to 58.1 %, significantly reduced the HVAC energy consumption by 188.8 to 692.5 kWh compared to fully mechanically controlled homes, and provided excellent thermal comfort, achieving up to 95.5 %, thereby offering practical benefits for residential buildings.