  The work presented in this paper relates to a small scale district heating
network heated by a gas fired CHP. In most common situations, such a CHP is
heat driven operated, meaning that the CHP will switch on whenever heat is
needed, while not taking into account the demand of electricity at that time.
In this paper however, an active control strategy is developed, aiming to
maximize the profit of the CHP, selling its electricity to the spot market. The
CHP will therefore switch on at moments of high electricity prices.
Nevertheless, since there never is a perfect match between the demand of heat
and the demand of electricity, a thermal energy storage is included in the
network to overcome the difference between supply and demand of heat in the
network. In this study, three different storage concepts are compared: (1) a
central buffer tank next to the CHP; (2) small storage vessels distributed over
the different connected buildings; and (3) the use of the thermal mass if the
buildings as storage capacity. Besides the development of the control
algorithms based on model predictive control, a simulation model of the network
is described to evaluate the performance of the different storage concept
during a representative winter week. The results show that the presented
control algorithm can significantly influence the heat demand profile of the
connected buildings. As a results, active control of the CHP can drastically
increase the profit of the CHP. The concept with the distributed buffers gives
the best results, however the profit for the thermal mass concept is only
marginally smaller. Since in this latter case no significant investment costs
are needed, the conclusion for this case study is that the use of thermal mass
of buildings for demand side management in district heating systems is very
promising.
