Energy and Buildings 43 (2011) 2973–2987 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me p age: www.elsevier.com/locate/enbuild Thermal comparison between ceiling diffusers and fabric ductwork diffusers for green buildings Anthony Fontanini, Michael G. Olsen, Baskar Ganapathysubramanian ∗ Department of Mechanical Engineering, 2100 Black Engineering, Iowa State University, Ames, IA 50010, USA a r t i c l e i n f o Article history: Received 12 February 2011 Received in revised form 18 June 2011 Accepted 3 July 2011 Keywords: Green buildings Ductwork Thermal management Computational fluid dynamics High performance computing Fabric ducting a b s t r a c t Continuously increasing energy standards have driven the need for increasing the efficiency of buildings. Most enhancements to building efficiency have been a result of changes to the heating/cooling sys- tems, improvements in construction materials, or building design code improvements. These approaches neglect the way in which air is dispersed into individual rooms or in a building – i.e., the ducting system. This opens up the possibility of significant energy savings by making ductwork systems lighter and better insulating while ensuring cost effectiveness. The current study explores this idea by comparing the performance of conventional ductwork with recent advancements in fabric-based ductwork. We focus on the transient behavior of an on/off control system, as well as the steady state behavior of the two ductwork systems. Transient, fully three dimen- sional validated computational (CFD) simulations are performed to determine flow patterns and thermal evolution in rooms containing either conventional or fabric ductwork. This analysis is used to construct metrics on efficiency. A number of different flow rates are examined to determine the performance over a range of operating conditions. Transient finite volume simulations consisted of over 13 million degrees of freedom for over 10,000 time steps. The simulations utilized HPC (High Performance Computing) for the large scale analysis. The results conclusively show that fabric ducting systems are superior to the conventional systems in terms of efficiency. Observations from the data show that fabric ducting systems heat the room faster, more uniformly, and more efficiently. The increase in performance demonstrates the potential benefits of moving away from conventional systems to fabric systems for the construction of green buildings: particularly in conjunction with adaptive control systems. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The design of efficient building systems is necessary for meeting increasing energy standards. This trend pushes designers to create green buildings. Numerous strategies are available for increasing the energy efficiency of buildings: energy collection systems such as solar power cells can decrease the energy load in the building [1], solar water heating systems can preheat water to cover a large fraction of the heating demand [2], and materials such as aerogels and phase change materials (PCMs) can help increase the ther- mal resistance of building envelope components [3,4]. Control and supervision of heating ventilation and air conditioning (HVAC) sys- tems can optimize the task of efficiently moving the energy through the building [5,6]. In addition, architectural design can create spaces that are both aesthetically pleasing and energy efficient [7]. Each of ∗ Corresponding author. Tel.: +1 515 294 7442; fax: +1 515 294 3261. E-mail address: baskarg@iastate.edu (B. Ganapathysubramanian). these approaches have aided in decreasing the amount of energy needed to operate green buildings. Most energy saving systems used in green buildings have neglected a significant component of HVAC systems, the duct- work system. Conventional ductwork systems comprised of sheet metal ductwork and diffusers have a number of features that can adversely affect their performance. The conduction of heat through the sheet metal leads to a loss in energy as the air is dispersed in the building. Coatings can be added to the ductwork to make them less conductive, but the coatings lead to additional costs in the sys- tem. Moreover, the ductwork is heavy, and needs extra parts for support. Most importantly, the non-homogeneous nature of the airflow generated by diffusers leads to non-uniformities in heat- ing/cooling causing discomfort. Finally, placement of conventional diffusers becomes a significant design decision in the effort to min- imize local hot/cold spots and unpleasant drafts within the space. Recent advances in ductwork technology has shown promise towards enhancing building efficiency. Fig. 1(b) shows a ventila- tion system where an insulating fabric ductwork has been used to transport air to desired locations within the building, thus limiting 0378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2011.07.005