Study on the second-order transfer function models for dynamic tests of flat-plate solar collectors Part II: Experimental validation Jie Deng a,b , Xudong Yang a,⇑ , Pengsu Wang a a Department of Building Science, Tsinghua University, Beijing 100084, PR China b Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, PR China Received 29 September 2013; received in revised form 28 July 2014; accepted 25 January 2015 Communicated by: Associate Editor Hans-Martin Henning Abstract In order to validate the accuracy levels of three forms of transfer function models (TFMs), dynamic thermal performance tests of a flat-plate solar air collector with louvered fin structure are conducted. Model coefficients in the TFMs are constructed by strict error analysis and the weighed least square (WLS) method. Comparing with the experimental data, it is verified that the three forms of TFMs perform well and have the similar level of accuracy. It is further demonstrated that, the second-order differential TFMs have the same accuracy as the reduced first-order differential models with the present temperature measurement accuracy using thermocou- ples. Whilst the collector thermal storage quantities of the second-order differential terms in the TFMs are very small. In order for the second-order TFMs to perform better in the dynamic tests, the measured accuracy of temperatures should be improved. Otherwise, the combined standard uncertainties of the second-order differential terms of temperatures could be larger than the second-order differential terms of temperatures and the second-order terms in the three forms of TFMs would become meaningless. Ó 2015 Elsevier Ltd. All rights reserved. Keywords: Flat plate solar collector; Dynamic thermal performance; Transfer function model 1. Introduction In the companion paper, the second-order transfer func- tion model (TFM) in terms of the collector heat removal factor F R is presented for dynamic tests of flat-plate solar collectors (Deng et al., 2015). The equivalent relationships among the three different forms of TFMs (TFM by Hou, 2005; ITFM by Kong et al., 2012b, TFM based on F R ) are elucidated. The ITFM by Kong et al. (2012b) is expressed as Eq. (1) below (Eq. (7) in the companion paper). Eq. (2) (Eq. (16) in the companion paper) shows the TFM based on F R . And Eq. (3) gives the equivalent form of the TFM developed by Hou (2005). The TFM by Eq. (2) based on F R is equivalent to the ITFM by Eq. (1) according to energy balance. The TFM by Hou (2005) is equivalent to the ITFM by Kong et al. (2012b) as well as the TFM based on F R when the working fluid inlet temperature rate of change is small enough. Furthermore, the methodology of constructing the model coefficients in the TFMs is elucidated, based on error ana- lysis and the weighed least square (WLS) method. Q u ¼ _ m f c f ðT fo  T fi Þ¼ F 0 ðsaÞ en K hb ðhÞA a G b þ F 0 ðsaÞ en K hd ðhÞA a G d þ s cu ðm f c f Þ d 2 T f d s 2 ðmcÞ e dT f d s  s cu  _ m f c f  dT fo d s  dT fi d s    F 0 A l ðU L þ wU w ÞðT f  T a Þð1Þ http://dx.doi.org/10.1016/j.solener.2015.01.045 0038-092X/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +86 10 6278 8845; fax: +86 10 6277 3461. E-mail address: xyang@tsinghua.edu.cn (X. Yang). www.elsevier.com/locate/solener Available online at www.sciencedirect.com ScienceDirect Solar Energy xxx (2015) xxx–xxx Please cite this article in press as: Deng, J., et al. Study on the second-order transfer function models for dynamic tests of flat-plate solar collectors Part II: Experimental validation. Sol. Energy (2015), http://dx.doi.org/10.1016/j.solener.2015.01.045