In large space buildings such as check-in halls and departure halls in airports, the envelope is dominated by glass facades, skylights, and metal ceilings. A radiant floor is an effective sensible heat removal terminal due to its direct longwave radiant heat exchange with high-temperature wall surfaces and absorption of solar radiation. The emissivities of metal ceilings and many advanced materials (e.g., low-e coating) in large spaces range from 0.2 to 0.9, markedly different from that of traditional building materials (0.9-0.95), which affects the indoor longwave heat exchange. Moreover, the number of transient solar radiation incidents on the floor surface can vary tremendously, resulting in remarkable differences in cooling capacity of the radiant floor, e.g., from 30 to 40 W/m(2) to more than 100 W/m(2). In this paper, a new simple calculation method for longwave radiant heat exchange that considers emissivity is proposed, and the location and duration of transient solar radiation through skylights and side windows in large spaces are depicted quantitatively. Based on this new method, a typical case study is presented, in which the cooling capacity of a radiant floor in the large spaces of an airport is calculated. The case study also showcases designs of radiant floors in large spaces with different material emissivity and transient solar radiation values. (C) 2015 Elsevier Ltd. All rights reserved.