Where air-conditioning is essential: Raising a yellow flag ten times - where wet bulb globe temperature under shaded outdoor shelter fails to refresh adapted healthy individuals

Eric Laurentius Peterson 

Concerning the modern paradigm shift to insulate building envelopes with the ambition to improve winter comfort without demand for heating, unintended problems can arise in summer as insulation traps heat and humidity from cooking and occupants’ respiration. So, we should consider outdoor living areas, covered from sun and rain, but openly alfresco - such as verandas. The current work extends on a counterfactual approach to designing air-conditioning that considered passive and low energy alternatives. That research found air-conditioning is desirable on days when conditions exceed 25.6°C daily maximum wet-bulb globe temperature in shade (WBGTs) – referred to as a “white-flag” day (Wsd). Furthermore, access to cool shelter becomes a necessity for a greater proportion of the population if maximum outdoor WBGTs exceeds 29.4°C – referred to as a “yellow-flag” day (Ysd). Global mapping highlights practical limits of passive and low energy alternatives to air-conditioning, but lack of weather stations overlook urban heat islands. Accepting that there may be poorly designed dwellings prone to dangerous overheating that demands active cooling while neighbouring parks and gardens may provide passively cool relief – the current work broadly identifies observed and forecasted limits of shaded outdoor living areas as an effective refuge. Analysis of weather stations’ annals (1988-2020) of threshold-days are globally mapped, classified by annual exceedance. Standard deviations of interannual variability are added to long term averages, compared with standard estimate of error added to linear regression intercept at the last year – to estimate days white- and yellow-flag conditions in shade were exceeded in hotter years (WsD† and YsD†). Finding where WsD† exceed 10 days per “hot” year but Ysd had not, thence these 4661 locations are now reanalysed with respect to accessible observations during the 50 years through 2024 and projected to 2050. The number of locations exceeding thresholds generally increased, while local exceptions are detailed in supporting material. Air-conditioned shelters are needed by more vulnerable people, while passive and low energy solutions should be delivered whenever practical so that electricity networks are not overloaded.