1 Scope This International Standard specifies the assumptions, boundary conditions, equations and validation tests for a calculation procedure, under transient hourly conditions, of the internal temperatures (air and operative) of a single building zone No specific numerical techniques are imposed by this International Standard. Validation tests are included in Clause 7. This International Standard does not contain sufficient information for defining a procedure able to determine the internal conditions of special zones such as attached sun spaces, atria, indirect passive solar components (trombe walls, solar panels) and zones that the solar radiation may pass through. For such situations different assumptions and more detailed solution models are needed (see Bibliography in ISO/TR 52016 2). A calculation procedure for specific application areas (e.g. energy need for heating and cooling, internal temperature, design heating and cooling load) including specific assumptions and input data for those applications is given in ISO 52016 1.