Improved Conduction Transfer Function Coefficients Generation In Trnsys Multizone Building Model

Abstract

Many building energy performance simulation programs (including TRNSYS) use the Conduction Transfer Function (CTF) method to compute 1-D transient heat conduction through multi-layer slabs. Problems have been reported with the current CTF implementation in the TRNSYS multizone building model, especially during the CTF coefficients generation. These problems are related to heavy and highly insulated slabs and short time-step simulations (less than 15-minute time-step). This paper describes the implementation of a new CTF coefficients generation method in the TRNSYS building preprocessor (TRNBuild). The efficiency and the types that cause problems are presented and discussed, including a full house model for a net-zero energy renovation project. STATE OF THE ART The CTF method has been implemented in many BPS programs (including TRNSYS and EnergyPlus) to model 1-D transient conduction heat transfer through building slabs. It was introduced by Mitalas and Stephenson (1971) and consists in time series which allow to compute the inside and outside surface heat flows (𝑞̇𝑠iand 𝑞̇𝑠𝑜) from current and past values of surface temperatures (Tsi and Tsₒ) and past values of heat flows themselves: 𝑛𝑏 limitations of this method are also discussed.