Direct heat flux sensing for window shading control in passive cooling systems

Abstract

Greenhouse gas emissions from space cooling are expected to double globally by 2050, giving urgency to the development of low-carbon cooling methods. Solar heat gain through windows is a leading contributor to cooling loads, and accordingly, operable shading strategies have been established that respond to numerous environmental parameters, including solar radiation, illumination, time of day, and indoor and outdoor air temperature. While these have shown excellent performance, optimal setpoints are typically specific to climates, seasons, and spaces, preventing development of controls with consistent effectiveness across varying conditions. Here we investigate an alternative parameter, window surface heat flux, in which a universal setpoint of 0W/m2 identifies transitions between window heat gain and loss. Examination of heat flux signals acquired with low-cost sensors first revealed the associated noise to be consistent but too great for control application. Representative noise characteristics were then used to construct noisy signals for simulations, allowing evaluation of noise mitigation by digital filtering methods and signal persistence requirements. Strikingly, shading controlled by the resulting output reduced window heat gain by 54–78% in six contrasting climates, comparable to or exceeding the performance of established approaches, indicating that heat flux sensing is now an outstanding candidate for shading control in passive cooling systems.