Elimar Frank

A unified model for the simulation of oil, gas and biomass space heating boilers for energy estimating purposes. Part I: Model development

A unified model for the simulation of oil, gas, pellet and wood chip space heating boilers for energy estimating purposes has been developed based on a literature review and laboratory measurements on four different boilers. The model includes the influence of space heating return temperature, power modulation and condensation gains on the flue gas losses of the boiler, the simulation of a thermal boiler capacitance including its heat losses during standby and operation, and the ability to calculate carbon monoxide emissions and electricity use dependent on power modulation and number of burner starts. Some of the new features of the presented boiler model are the unification of models for oil, gas and biomass boilers into one model, and the combination of steady state calculation for the flue gas to water heat transfer with an explicit solution for the time dependent temperature change of the boilers thermal capacitance.

A unified model for the simulation of oil, gas and biomass space heating boilers for energy estimating purposes. Part II: Parameterization and comparison with measurements

A semi-physical model for the simulation of oil, gas and biomass space heating boilers has been parameterized based on measurements on nine different boiler units and simulation results have been compared to results obtained from measurements in steady state and transient operation. Although the agreement between simulated and measured boiler efficiencies was within the range of measurement uncertainties in most cases, model improvements are expected to be possible concerning the heat capacitance modelling in cycling on/off operation as well as influences of start and stop behaviour on the overall efficiency. It is found that electricity consumption during cycling on/off operation of small pellets or oil space heating boilers may have a significant influence on the overall energy balance of these units. This influence increases strongly with decreasing heat load and increasing number of on/off cycles.

A Transient Immersed Coil Heat Exchanger Model

The aim of this paper is to present a transient one-dimensional (1D) radial immersed coil heat exchanger model that accounts for the effect that geometry and operating conditions have on heat transfer performance. Insights gained through its use in both an analysis of experimental data and an implementation in the simulation environment TRNSYS are shown and discussed. While variation in the external convection coefficient of immersed coil heat exchangers has little effect on the annual solar fraction of a generic solar domestic hot water system, variation in collector side flow can influence the solar fraction as great as ±5%, in particular low collector side flow improves stratification inside the store.