GLASS CURTAIN WALL EFFECTS ON THERMAL COMFORT AND COOLING ENERGY CONSUMPTION IN OFFICE BUILDINGS IN LOW-LATITUDE WARM CLIMATES.
facade performance, thermal comfort, energy efficiency, glass curtain wall
Facade design is a matter of great concern regarding the sustainability of buildings. In office buildings, all-glazed facades have become a common design solution regardless its environmental disadvantages. High-performance glazing systems are not a cost-effective option to Brazilian architects, hence the majority of glass curtain wall office building in Brazil, even in warm climates, has laminated glass panes without external shading devices. Such features are highly questionable for warm climates due to the huge amount of direct solar radiation and high U-value, affecting occupants’ thermal comfort. The higher operative temperature near facade´s perimeter zones could also demand for an air-conditioner adjustment to lower the set-point temperature in this zone, increasing cooling energy consumption. In many circumstances, this affects occupancy behavior that lead to drawbacks to the light environment, access view to the exterior or increasing of energy demand with artificial light during daytime. This thesis aims to evaluate the impact of office buildings´ all glazed-facades in low-latitude warm climates on occupant´s thermal comfort and energy use with HVAC systems. Research method is based on field measurements of air quantities carried out in six actual office buildings in Fortaleza/Brazil at centre and perimeter workspaces´ zones and simulation techniques. Simulations adopted a cell zone approach modelled according to typical Brazilian office buildings characteristics. A sensitivity analysis to test the thermal and energy performance of common façade´s design alternatives were done for a total of 10 cases. Thermal pictures were taken to identify the range of inner surface temperature, mainly from the glazing system, in order to compare than with field measurements’ and simulation´s results. Moreover, “walkthrough” observations done during field measurement period made possible to register a set of occupants´ behaviours to adapt themselves to the thermal and light environments’. Results showed that glass curtain wall facades has great potential to promote thermal discomfort at perimeter zones. They present a high inner surface temperature, enough to increase the mean radiant temperature and cause asymmetric thermal radiation. Even that, assessment of the thermal comfort using the PMV/PD index of actual cases predicted a thermal comfort condition at centre and perimeter zones. On the other hand, simulation results predicted thermal discomfort during occupied morning periods. Actually, there was a considerable mismatch between computer simulations results and field measurements regarding operative temperature calculation and evaluation of thermal comfort using the PMV/PPD index. Main causes for this are partially attributed to the occupants’ environmental adjustments, which are not usually modeled, and the main thesis limitations. Simulations’ sensitivity analysis demonstrated that common and, possibly, cheaper façade design solutions can improve thermal comfort conditions and reduce cooling energy consumption, as well provide better sound thermal and light environments.