Experimental analysis of an on demand external domestic hot water production system using four control strategies

In the paper, an experimental investigation on the performance of a space/water heating system using an on demand external domestic hot water production system (DHWPS) with different control strategies is reported. The tested DHWPSs consisted of a plate heat exchanger, a circulating pump, a flow switch and a thermostatic regulation valve. Four different control valves were considered in the analysis, comprising a 3-way mixing valve on the DHW-side, two different 2-way valves on the tank-side and a 3-way valve on the tank-side. Experiments have been performed heating the water in the tank up to 80 °C and considering DHW draw-off flow rates of 5, 10, 15 and 20 l/min at a set temperature of 45 °C. In the study the thermal behaviour of the four DHWPSs is analysed and compared, as well as its effects on the thermal performance of the tank during consumption operation. Results show that the control strategy of the DHWPS significantly influences the quality of the DHW supply and the thermal performance of the storage tank.