Freezing from the heat: Building overcooling in Qatar

Abstract

Qatar has the unfortunate reputation of the country with the highest per-capita carbon emissions in the world, 15% of which is due to space cooling demand. We investigate the extent to which this demand is driven by ‘overcooling’ in non-domestic buildings, that is low indoor set-points resulting in wasted energy and cold thermal discomfort. Using a recently developed overcooling metric, ISO 7730 compliant sensors and occupant survey data comprising 2,472 responses from eight morphologically diverse office buildings, we find that 32% of occupants can be classed as uncomfortably cold. Our analysis implicates the application of the ‘international’ ASHRAE 55 thermal comfort standard in the observed overcooling. Using computer models of the studied buildings, we find that this overcooling is responsible for 27% of their cooling energy demand, translating to 4% of national cooling energy demand and 2% of carbon for all non-domestic buildings. Thus, a simple upward adjustment of set-point temperatures by ∼ 2°C in non-domestic buildings would greatly improve comfort and reduce energy consumption and carbon emissions without changing the building or its systems. This suggests an urgent need for a new localised thermal comfort standard, with wider regional applicability due to similar culture and climates. Practical application Eliminating building overcooling yields in a notable reduction of 8.5% of cooling energy demand for every 1°C increase in the indoor setpoint temperature. This reduction results in an average of 32.3 kW·h/m2/yr in a typical office building in Qatar. A comfort temperature of 24.9°C is suggested which is on average of 1.5°C warmer than the currently applied indoor temperature setpoint, resulting in substantial cooling reductions and increased thermal comfort. In practice, raising the indoor setpoint temperature by 2°C could prevent building overcooling, improve indoor thermal comfort and reduce cooling energy demand across in warm climates.