Sustainable Building Operation Using Simulation - Low Energy Cooling for Sustainable Buildings - page 228

For the implementation of such a model-based control system, online simulation
models of the building and the plants have to be developed and validated against
measurement data. The main question which has to be considered and clarified is
the necessary level of modelling detail to meet the required accuracy for the planned
control implementation. Are dynamic models required? How simple can a dynamic
model be? Which time steps are required for the planned control action etc.? These
are the questions to be answered. In the case of the building, detailed static calculation
methods according to DIN EN 832 or DIN V 18599 can be used for calculating the
energy demand of the building in monthly or, with small adjustments in the calculation
methods, even daily mean values. For shorter periods in time steps of 1 hour the
building dynamic caused by the internal mass has to be considered. This requires
more or less detailed dynamic building simulations. In a first approach the following
simple model, based on an extension of the steady-state calculation methods, has been
developed and tested.
6.2.2 Communication Infrastructure for the Implementation
of Model-Based Control Systems
For the implementation of a model-based control system a software interface to the
installed BMS is required. Such software can run on a PC separate from or parallel to
the BMS and can be located on site or centrally in the office of an energy management
agency. In any case, the measured data and setpoints collected by the BMS need to
be transferred to the model-based control system. The possible solutions for the data
transfer strongly depend on the installed BMS and the available interfaces. In the eas-
iest case the BMS provide an interface which transfers the measured data directly to a
socket server (e.g. DataSocket or OPC server). If the BMS provides only an interface
which loads the measured data into a database on the PC, then additional database
reader and writer software is necessary to read the necessary data from the database
and write it to an online server. For the transfer of measured data to the online simula-
tion models, a socket client (reader) and a corresponding server have to be installed on
the PC which is connected to the BMS and to an Internet/modem connection. Socket
clients (reader and writer) have to be installed on a PC at the energy management
agency as well. The client reads the necessary measurement data via the Internet or
modem connection from the socket server running on the PC which is directly con-
nected to the BMS on site and passes the data to the online simulation tools running
on the PC at the energy management agency. The simulation results are then written
back to the server running on the PC on site. Additionally, the calculated output per-
formance is compared with the measured performance of the building. If the deviation
between measurement and simulation exceeds a certain threshold, additional warning
messages and control actions can be written back to the socket server running on the
PC on site. DataSocket and OPC are provided by National Instruments amongst others.