Static study of traditional and ring networks and the use of mass flow control in district heating applications

• Published in: Applied thermal engineering 2013-05, Vol.54 (2), p.450-459
• Main Authors: Kuosa, Maunu, Kontu, Kaisa, Mäkilä, Tapio, Lampinen, Markku, Lahdelma, Risto
• Format: Article
• Language: English
• Subjects: Applications; Applied sciences; Control systems; District heating; District heating and refrigerating; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Flow rate; Heat transfer; Heating, air conditioning and ventilation; Mass flow; Mass flow control; Mathematical analysis; Mathematical models; Networks; Outdoor; Ring network; Space heating. Hot water; Static study; Theoretical studies. Data and constants. Metering
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2013.02.018

District heating (DH) systems are an inseparable part of the infrastructure in many countries. Today more attention is being paid to energy savings, efficiency improvements, and the replacement of fossil fuels by renewable energy. Research in the field of DH is focused on the supply of areas with low heat demand and low-energy buildings and on an increased share of heat being produced from renewable energy sources. New DH systems are expected to remain competitive in the future. In this study a new DH concept is proposed which is based on mass flow control. The DH system using mass flow control is meant for the concept of a ring network technology where mass flow rates in consumer substations are controlled by pumps with inverters to improve heat transfer. It will replace the traditional DH network and control in which water flow is throttled by control valves. The new control system will enable new temperature curves to be adopted for supply and return temperatures and more significant temperature cooling. First, a new topology and control method is presented. This ring network and the method used to control the flow rate of the primary supply water and its temperature are compared with the traditional technology. This method clearly shows the benefits of the DH applications under consideration. Second, these benefits are demonstrated by mathematical modelling. A simulation model is developed to study the area heating of six single-family houses and two apartment buildings. The static operation on the primary side of the networks is investigated for the most common outdoor temperatures. The numerical results are compared to those achieved with the traditional technology. The new flow rate is 46%, the pressure loss 25%, and the pumping power 12% of their former values in the pipes. The heat losses increase slightly with higher outdoor temperatures. The return temperature is lowest with the new technology. In the future the equipment that consumers will have will be more intelligent. The new technology that is presented allows consumers to adjust their energy consumption more easily by means of fast feedback on outdoor and room temperatures. ► Novel DH technology is proposed based on ring network and mass flow control. ► Network has equal pipe lengths and pumps at substations instead of control valves. ► New supply and return temperatures are received and greater temperature cooling. ► The flow rate, the pressure loss, and the pumping power are diminished i