Influence of slat-type blinds on energy consumption in office buildings

Highly glazed facades of commercial buildings are desirable from the point of view of architects, building owners, and building occupants because they create visual connections with the outdoors, offer the possibility for a naturally-lit workplace, and satisfy certain aesthetic desires. The physical properties of glass, however—even when part of the best current window systems—means that this form of environmental separation is highly vulnerable to thermal flux from and to the outdoor environment. The transmission of solar radiation to the perimeter spaces represents an important source of thermal influx, and is typically controlled with shading devices. At best, shading devices create a secondary thermal barrier between indoor and outdoor environments, which can lower energy consumption, decrease peak load, allow for smaller HVAC systems, and provide better occupant comfort. The physical influence of indoor blinds, though, is not always so straightforward. They tend to create two primary effects that operate in opposing directions in regards to energy consumption: (1) they reflect a portion of shortwave solar radiation entering the building back to the outdoors, and (2) they significantly increase the window surface area available for convective heat transfer, which can increase the convective fraction of solar gain, and potentially increase the magnitude of the instantaneous cooling load. For these reasons, the overall impact of interior blinds on equipment load and energy consumption is difficult to foresee. This study describes the results of experiments that tested various configurations of blinds in an outdoor test chamber that simulates conditions in a highly-glazed commercial office building. A simulation model that gives good agreement with experimental results was simultaneously developed. This model will allow retroactive parametric testing of blind parameters for the same given weather and internal load conditions.