PhD Thesis - Energy Systems Research Unit - University of Strathclyde

The dotted lines in Figure 3.2 represent the location of the controlling sensors. Thecontrol strategies adopted for the whole building and individually on each componentare explained in more detail in Section 3.2.3.The CHP component model used in the plant network to provide heating andelectrical power is the one calibrated in the IEA Annex 42 project [11], andrepresents a 5.5 kW el / 12.5 kW th IC engine by Senertec Dachs [12, 13]. Although theunit is intended to run on Natural Gas, in this research the unit was assumed to runon Liquefied Petroleum Gas (LPG) as Natural Gas is absent from the Maltese fuelmix. The system was assumed to be grid connected, enabling both export and importof electricity. The recycled ‘waste heat’ stored in the hot water storage tank, wasrecovered from the engine’s cooling system and the combustion exhaust gases. Tocover for any shortfalls in the heat supply, an auxiliary boiler with ‘On’/‘Off’ control(developed by Hensen in [14]) was connected in parallel to the CHP unit.The hot water storage tank was connected via a water pump to both the domestic hotwater storage tank feeding the hot water supply of the entire building, and theventilation system. In case of the ventilation system, depending on the type of spaceconditioning demand required, the hot water was fed either to the absorption chilleror directly to the heating coils. Separate ventilation supply ducts were used to supplyeach individual apartment, with each duct containing its own cooling and heating coil.The flow could be manipulated so as to permit control of the individual apartmenttemperatures. For further details, Appendix ‘C’ shows the physical and thermalcharacteristics of the main components used in the plant network.The plant network topology used was the same for both the 3 household and the 6household models. Preliminary simulations performed showed that the same plantnetwork topology (including cooling coils, heating coils and ancillaries sizing) couldbe used satisfactory for both building models provided that, the plant controls wereadjusted to take into consideration the different (time-sensitive) thermal demands ofthe two buildings. Considering the higher demand in terms of hot water, the hotwater storage tank in the 6 household building was however enlarged to 0.5m 3 .99