• Martin Frandsen
  • Jakob Vind Madsen
The energy use for domestic hot water (DHW) production in non-residential buildings has in many years been neglected in the research and development of energy efficient buildings. As energy use for space heating, ventilation, and lightning has been reduced, the energy share for DHW production has increased. With today’s focus on energy efficient buildings, the DHW systems must not be left behind the other fields to get the holistic approach to energy efficient building. To develop more energy efficient DHW systems more knowledge is needed regarding draw-off duration, flow rates, and temperatures from different draw-off types. This master thesis presents high resolution measurement results in two office and educational buildings, which show that the three DHW systems only utilize 3.4, 5.9, and 7.5 % of the total energy used for DHW production. Above 85 % of the total energy use is lost from the circulation circuit to secure a high hot water temperature close to the draw-off point. Temperature measurements at the draw-off points yet show that a significant share of the heat is lost from connection pipes. Draw-off durations are 56 and 47 % of the time below 10 s at washbasins and kitchen sinks, respectively. The measurements at 15 draw-off points give essential knowledge of consumption patterns for washbasins, kitchen sinks, and service sinks in non-residential buildings. This knowledge can contribute to developing energy efficient DHW systems and new types of DHW productions. The measurements are furthermore used to validate two simulation models of two existing DHW systems in Modelica. Modelica is used for detailed modeling of the dynamic behavior of the DHW systems when high resolution draw-off profiles are imported to the simulation model. The simulation models are validated with measured energy use from the DHW production and measured hot water flow rates and temperatures at the draw-off points. With the calibrated model, a sensitivity analysis shows that the most influential parameters for a DHW system are the insulation thickness, pipe diameter, and circulation flowrate. From the results of the sensitivity analysis, these three parameters are improved individually, and in a combined optimization. The combined optimization contains changes as; reducing the internal pipe diameter from 19.6 mm to 10 mm, at some locations increasing the insulation thickness from 20 mm to 40 mm, and reducing the activation time of the circulation pump. The results are among others; maximum waiting time reduced from 21.2 s to 3.2 s, total DH use reduced by up to 53.1 %, and the average tapped hot water temperature is 5◦C higher. Furthermore, the simulation show potential in using Modelica for detailed simulation of DHW systems. With the presented knowledge in this master thesis, the use of detailed simulation for designing energy efficient DHW systems for new buildings is moving closer.
Publication date10 Jun 2021
Number of pages213
ID: 414373244