Modelica-based modelling and simulation to support research and development in building energy and control systems

Abstract Traditional building simulation programs possess attributes that make them difficult to use for the design and analysis of building energy and control systems and for the support of model-based research and development of systems that may not already be implemented in these programs. This article presents characteristic features of such applications, and it shows how equation-based object-oriented modelling can meet requirements that arise in such applications. Next, the implementation of an open-source component model library for building energy systems is presented. The library has been developed using the equation-based object-oriented Modelica modelling language. Technical challenges of modelling and simulating such systems are discussed. Research needs are presented to make this technology accessible to user groups that have more stringent requirements with respect to the numerical robustness of simulation than a research community may have. Two examples are presented in which models from the here described library were used. The first example describes the design of a controller for a nonlinear model of a heating coil using model reduction and frequency domain analysis. The second example describes the tuning of control parameters for a static pressure reset controller of a variable air volume flow system. The tuning has been done by solving a non-convex optimization problem that minimizes fan energy subject to state constraints. Keywords: building simulationequation-based modellingrapid prototypingModelicacontrols Acknowledgements This research was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technologies of the US Department of Energy, under Contract No. DE-AC02-05CH11231. The author would like to thank Scott A. Bortoff at the United Technologies Research Center for his input to the controls design example and Philip Haves, Brian A. Coffey and Walter F. Buhl, all at the Lawrence Berkeley National Laboratory, as well as the anonymous reviewers, for their valuable feedback to the manuscript. Notes 1. For example, the statement Q1:=-Q2−Q3; is imperative and describes that Q1 is to be computed by assigning the sum of -Q2 and -Q3. A declarative statement may have the form 0 = Q1+Q2+Q3; which only describes how the three variables are related, but it does not specify what computer instructions need to be done to compute one from the other two. 2. Within the ASHRAE Technical Committee 4.7, the prospect of Modelica was already mentioned in 1998 when Sowell reported on this language. The committee reported that Modelica could eventually subsume NMF but it was decided to press for NMF and monitor the Modelica progress (Spitler Citation1998). 3. By hybrid differential algebraic systems of equations, we mean differential and difference equations that are coupled to continuous and discrete algebraic equations. An example is a chiller control that may be expressed as a state machine that is linked to a discrete time controller for a mechanically cooled building, which may be described by differential and algebraic equations. 4. The term k4 adds a penalty to f(·), if constraints are violated, that is increasing in k, for k ∊ ℕ.