Load Matching, Grid Interaction, and Advanced Control - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 319

Implementing a strategy consisting of an MPC algorithm, or based on an
MPCalgorithm,isnotnecessarilyadifficulttask.Oncethemodelisinplace,
a solver tool will be able to find the value of the “control variables,” such as
cooling/heating power, ventilation rates, or valve positions. An alternative
pathistoobtainappropriaterulesbasedontheresultsoftheMPCalgorithm
under numerous scenarios (May-Ostendorp et al. , 2011).
6.4 Development of Models for Controls
The control engineering community has carried out significant research
efforts on MPC for buildings in recent years. In these studies, simple linear
models have been the most common approach (Deng, Barooah, and Mehta,
2012; Goyal and Barooah, 2011; Gyalistras and OptiControl Team, 2010;
Oldewurtel et al. , 2010a). Simple linear models are, of course, not new in
the thermal modeling of building components or whole buildings. However,
their usefulness for advanced control applications makes it relevant to
revisit these models from a different, control-oriented perspective.
Simple models with a reduced number of parameters provide some
advantages for the application of advanced control strategies: insight,
flexibility, computational efficiency and, above all, ease of formulation and
implementation.
This section presents a brief introduction for building engineering
specialists to the use of linear models for advanced controls, as well as the
different incarnations that linear models might take. This text is not aimed
as an exhaustive discussion on building physics or control engineering.
Instead, the objective is to provide a bridge for building engineers to the
language and methodologies used in controls.
6.4.1 Building Components: Conduction Heat Transfer
Conduction transfer functions (CTFs), proposed decades ago (Stephenson
and Mitalas, 1971), are z -transform transfer functions that significantly
facilitate the calculation of conduction through opaque building envelope
components. CTFs are presented in depth in Chapter 2 . CTFs play a very
important role in ASHRAE's heat balance (HB) and the radiant time series
(RTS) methods (ASHRAE, 2009). Different algorithms exist for the
calculation of coefficients in CTFs (Spitler, Fisher, and Pedersen, 1997).