Passive flow monitoring in heating system networks
This work deals with a "passive flow monitoring" technique which can be used to help determine the energy used by a building's heating system. The thesis first highlights the background and importance of energy monitoring in buildings. This work points out that energy monitoring is an important feature in the running of buildings today. In the past, the energy crisis in the 1970's made people aware of how important it was to have knowledge of how buildings consume energy. More recently, environmental issues have reinforced the importance of gaining good quality information on energy use in buildings. This thesis investigates the use of combined port flow characteristics/control signal relationships for three port control valves to predict system water flow rate in heating systems. A laboratory test rig was built and a range of three port valves were tested. A series of combined port flow characteristics/control signal relationships were developed from measurements from the test rig. Curve fit models were then applied to these relationships in the form of polynomial equations. Where practical relationships could not be measured for a valve, a theoretical valve model was derived. In order to validate the polynomial regression model and the mathematical model, the test rig was modified to take into account practical heating system characteristics. A series of flow characteristic results were produced from the modified test rig so that the performance of the two models (empirical and mathematical) could be evaluated. It was found that the empirical model performed well in predicting combined port flow ratios with RMS errors ranging between 2.73% and 6.54%. The mathematical model gave overall prediction errors between -2.63% and +9.25% which compare favourably with the performance of some flow meters. The work then goes on to present an energy use algorithm which incorporates the valve model (empirical or theoretical) for use in BEMS.