Hydraulic network simulation

The present report summarises the work done within the IEA-Annex 10: Building System Simulation Work. The subtask consists of simulating a water radiator heating system as a whole coupled with the building using design data as input and using measured data for verification of the predictions. Altogether three participants carried out the exercise: University of Stuttgart (IKE), Polytechnic Torino (PI) and Technical Research Centre of Finland (VTT). In addition some contribution was given by the University of Liege (ULg). The exercise had three stages: hydraulic balance, thermal balance, and plant simulation coupled will the building. The participants used different hydraulic and energy balance calculation methods. Based on the hydraulic simulations it was found that a water radiator network can be dimensioned with a "quick" method, i.e. the wanted flow rates are obtained without precise pressure drop calculation. The quick dimensioning method requires loose pipe-dimensioning and high pressure loss at radiator valves. During some operating conditions the pressure drop of radiator valves may exceed 1 - 15 kPa which cause unintended noise problems. Pressure condition can be kept relatively constant by using by-pass or differential pressure control valves and thus the noise problems can be eliminated. Thermal balance analysis showed the importance of flow control devices in stabilising the network hydraulically. Heat emission of the network was also influenced by the flow control devices: the narrower the proportional band of by-pass valves the smaller the deviation of heat emission and flow rates of the radiators from the wanted values. In the plant simulation the heat distribution network of the La Chaumiere Building was coupled with multi-zone simulation of building. The dynamic behaviour of the network was studied for a two weeks winter period. Based on these calculations it was concluded that the use of by-pass or pressure differential valves has not a great energy saving potential (1 - 4 %), but they should be used to stabilise the network hydraulically. The models developed within IEA-Annex 10 work for simulating the hydronic heating system coupled with the building was found to be reasonable and accurate enough to analyse the energy saving potential and influences of the components on the thermohydraulic performance of the water radiator heating system.