1. Introduction - Firenze University Press

4.3. Hierarchy for covering heat demand
Within each Time Slice, there are three different sources regarding utilities. The following
hierarchy [26, 27] should be followed in order to cover the heat demand:
i) Heat recovery should be maximised.
ii) The use of solar thermal energy via direct heat-transfer from collectors – immediately, when
available.
iii) Usage of the energy from the storage-indirect heat-transfer of solar thermal energy.
iv) A backup utility with constant availability is required.
Fig 8: Transferring solar heat from one combined TS to another [7, 27]
Integration using the direct transfer of solar thermal-energy within TS is then performed after heat
recovery. If there is unused heat from the solar-source, it is transferred to storage. The solar
thermal-energy can be unused for different reasons. One is a surplus and the other is a higher
demanded temperature than the temperature of the heat available from the solar-source. The stored
heat will be available in other TSs (Fig 8). This is an indirect way of using the solar thermal-energy.
When all the available solar thermal heat from the direct and indirect transfers is integrated, the rest
of the demand should be covered by those utilities with constant availability.
5. Case Study
5.1. Heat recovery
In this case study, the varying demand was presented by the batch process [7]. The streams are
presented in Table 1. The Time Slices from the heat demand were the starting and ending times of
the streams or changes in the loads for heat demand.
Stream No
and type
TS
[°C]
Table 1: Streams for Case Study [7]
TT
[°C]
305
CP
[kW/°C]
tstart
[h]
1 Cold 25 110 10 12 16
2 Cold 55 115 8 6 24
3 Hot 140 35 4 0 12
4 Hot 130 15 3 6 19
tend
[h]