The authors investigate the effect of the coating of various internal blinds on the operative room temperature in an office space. It is very important to correctly evaluate the impact of solar protection and daylight/glare systems on building comfort, and the resulting influence on human behaviour. Many building energy simulation programmes consider the Mean Radiant Temperature (MRT) independently of the actual emissivity of the internal surfaces. This approximation is acceptable for normal constructions with emissivity close to 1, but leads to considerable errors if low-emissivity paint or coatings are used. Starting from the theory of the net-radiation in a grey enclosure, the authors evaluate the MRT, assuming that the incoming flux and the radiated flux are the same. This method is based both on an ESP-r integrated whole-building-simulation programme and on an analytical method which allows for the correct evaluation of the thermal radiant field induced by considering the presence of surfaces with low-e coatings. The method can be used either ‘stand-alone’ for comparisons of different facade variants or within a building simulation. The simulations carried out indicate that when an ‘absorptive blind’ surface faces outwards, the summer temperature can be reduced by about 1 K at a position close to the facade.