Vic I. Hanby

MODEL-BASED CONTROL OF RENEWABLE ENERGY SYSTEMS IN BUILDINGS

This paper describes a research project concerned with the problem of supervisory control of systems that combine a range of heat sources with active and passive thermal storage. The work is based on a prototype building that includes a ventilated photovoltaic array, solar air and water heating, a biomass-fired boiler, and a stratified thermal store. The supervisory control problem is, for each source, whether to deploy the received energy directly into the building, store it for later use, or reject it to the environment. These decisions are currently made by a building management system programmed with a complex, arbitrary set of rules and setpoints. The considerable number of operational states means that such a control system is very difficult to commission. Analysis of the data for the early stages of building operation indicate strongly that it is unlikely optimal use is being made of the renewable energy sources with this approach. The objective of this research is to investigate the potential effectiveness of replacing the rule-based control scheme with one based on a combination of a building/system model with an optimization algorithm. The existing building, plant, and control systems were modeled using a commercial simulation environment and calibrated against measured data from the building. A period of swing-season operation was used to compare the existing control with that based on an optimal approach. Results indicate that significant improvements in system operation are possible but also that significant improvement in execution time will be needed for any future online deployment.

Methodologies for the generation of design summer years for building energy simulation using UKCP09 probabilistic climate projections

Design summer years representing near-extreme hot summers have been used in the United Kingdom for the evaluation of thermal comfort and overheating risk. The years have been selected from measured weather data basically representative of an assumed stationary climate. Recent developments have made available ‘morphed’ equivalents of these years by shifting and stretching the measured variables using change factors produced by the UKCIP02 climate projections. The release of the latest, probabilistic, climate projections of UKCP09 together with the availability of a weather generator that can produce plausible daily or hourly sequences of weather variables has opened up the opportunity for generating new design summer years which can be used in risk-based decision-making. There are many possible methods for the production of design summer years from UKCP09 output: in this article, the original concept of the design summer year is largely retained, but a number of alternative methodologies for generating the years are explored. An alternative, more robust measure of warmth (weighted cooling degree hours) is also employed. It is demonstrated that the UKCP09 weather generator is capable of producing years for the baseline period, which are comparable with those in current use. Four methodologies for the generation of future years are described, and their output related to the future (deterministic) years that are currently available. It is concluded that, in general, years produced from the UKCP09 projections are warmer than those generated previously. Practical applications: The methodologies described in this article will facilitate designers who have access to the output of the UKCP09 weather generator (WG) to generate Design Summer Year hourly files tailored to their needs. The files produced will differ according to the methodology selected, in addition to location, emissions scenario and timeslice.

Simulation study on a domestic solar/heat pump heating system incorporating latent and stratified thermal storage.

Both solar and heat pump heating systems are innovative technologies for sustaining ecological heat generation. They are gaining more and more importance due to the accelerating pace of climate change and the rising cost of limited fossil resources. Against this background, a heating system combining solar thermal collectors, heat pump, stratified thermal storage, and water/ice latent heat storage has been investigated. The major advantages of the proposed solar/heat pump heating system are considered to be its flexible application (suitable for new and existing buildings because of acceptable space demand), as well as the improvement of solar fraction (extended solar collector utilization time, enhanced collector efficiency), i.e., the reduction of electric energy demand for the heat pump by management of the source and sink temperatures. In order to investigate and optimize the heating system, a dynamic system simulation model was developed. On this basis, a fundamental control strategy was derived for the overall co-ordination of the heating system with particular regard to the performance of the two storage tanks. In a simulation study, a fundamental investigation of the heating system configuration was carried out and an optimization was derived for the system control, as well as the selection of components and their dimensioning. The influence of different parameters on the system performance was identified, where the collector area and the latent heat storage volume were found to be the predominant parameters for system dimensioning. For a modern one-family house of 120 m2 living area with a specific annual heat demand of 60 kWh/(m2 a) for both heating and domestic hot water, a solar collector area of 30 m2, and a latent heat store volume of 12.5 m3 are proposed for the location of Wuerzburg (Germany). In this configuration, the heating system reaches a seasonal performance factor of 4.6, meaning that 78% of the building’s and users’ heat demand are delivered by solar energy. The results show that the solar/heat pump heating system can give an acceptable performance using up-to-date components in a state-of-the-art building.

Development of Optimal Design of Solar Water Heating System by Using Evolutionary Algorithm

There are growing initiatives to promote renewable energy in Hong Kong, particularly for solar energy. In order to encourage wider application of centralized solar water heating system for high-rise residential buildings, it is important to pursue an optimal design to get significant energy-savings potential. In this regard, system optimization would be useful because it can relate to a number of design variables of the solar water heating system. The objective function is to maximize the year-round energy savings by using the solar heating against the conventional domestic electric heating. For the methodology of optimization, evolutionary programming, one of the paradigms of the evolutionary algorithm, was applied. From the optimization results, it is suggested that the solar collectors can be installed onto the external shading devices as an integrated architectural feature, since the optimal tilt angle is 21 deg and relatively flat. The optimal surface azimuth is southwest 16 deg, instead of due south. For the engineering design, both the optimal values of calorifier storage capacity and pump flow rate show that the calculations from normal design practice may not achieve an optimal performance.

A Dynamic Multinode Model for Component-Oriented Thermal Analysis of Flat-Plate Solar Collectors

A mathematical model of a flat-plate solar collector was developed on the basis of the physical principles of optics and heat transfer in order to determine collector’s component temperatures as well as collector efficiency. In contrast to many available models, the targeted use of this dynamic model is the detailed, theoretical investigation of the thermal behaviour of newly developed or adjusted collector designs on component level, for example, absorber, casing, or transparent cover. The defined model is based on a multinode network (absorber, fluid, glazing, and backside insulation) containing the relevant physical equations to transfer the energy. The heat transfer network covers heat conduction, convection, and radiation. Furthermore, the collector optics is defined for the plane glazing and the absorber surface and also considers interactions between them. The model enables the variation of physical properties considering the geometric parameters and materials. Finally, the model was validated using measurement data and existing efficiency curve models. Both comparisons proved high accuracy of the developed model with deviation of up to 3% in collector efficiency and 1 K in component temperatures.