To assess the suitability of solar collector systems in which polymeric materials are used versus those in which more traditional materials are used, a case study was undertaken. In this case study a solar heating system with polymeric solar collectors was compared with two equivalent but more traditional solar heating systems: one with flat plate solar collectors and one with evacuated tube solar collectors. To make the comparison, a total cost accounting approach was adopted. The life cycle assessment (LCA) results clearly indicated that the polymeric solar collector system is the best as regards climatic and environmental performance when they are expressed in terms of the IPPC 100 a indicator and the Ecoindicator99, H/A indicator, respectively. In terms of climatic and environmental costs per amount of solar heat collected, the differences between the three kinds of collector systems were small when compared with existing energy prices. With the present tax rates, it seems unlikely that the differences in environmental and climatic costs will have any significant influence on which system is the most favoured, from a total cost point of view. In the choice between a renewable heat source and a heat source based on the use of a fossil fuel, the conclusion was that for climatic performance to be an important economic factor, the tax or trade rate of carbon dioxide emissions must be increased significantly, given the initial EU carbon dioxide emission trade rate. The rate would need to be at least of the same order of magnitude as the general carbon dioxide emission tax rate used in Sweden. If environmental costs took into account not only the greenhouse effect but also other mechanisms for damaging the environment as, for example, the environmental impact factor Ecoindicator99 does, the viability of solar heating versus that of a natural gas heating system would be much higher.

There is a need for accurate and readily available information about theoptimization, economics, and environmental impacts of combi-heating systems.Accordingly, the authors have developed TRNSYS-based software called Flexifuel thatincludes a TRNSED application for calculating the annual system performance ofcombi-heating systems involving any combination of heat pumps, flat or vacuumtube solar collectors, pellet burners, electric auxiliary heaters, and heatstorage tanks. Selection of less complex software systems and types reduces thesimulation time without significantly affecting the accuracy of the results.Annual performance data for a system can be simulated in from one to twominutes. Comparison of accumulated theoretical and measured performance dataover the time period for a full-scale test plant with heat pumps and solarcollectors showed that simulation errors were below 5%.

To assess suitability ofsolar collector systems with polymeric materials versus those with moretraditional materials such as metals a case study was undertaken within theframework of Task 39 of the IEA Solar Heating and Cooling Programme. In thisstudy one solar heating system with polymeric solar collectors were comparedwith two equivalent but more traditional solar heating systems, one with flatplate collectors and one with evacuated tube solar collectors. Life Cycle Assessment(LCA) results obtained clearly indicated that the polymeric solar collectorsystem is the most favourable as regards climatic and environmentalperformance. In terms of climatic and environmental costs per solar heat collected,the differences between the three kinds of collector systems, however, aresmall when compared with existing energy prices. In the choice between arenewable heat source and a heat source based on the use of a fossil fuel,which was also analysed in the present study, the conclusion was that forclimatic performance to be an important economic factor, the rate of carbondioxide emission must be considerably increased above the level given by thepresent EU carbon dioxide emission trade rate. The rate would be at least ofthe same order of magnitude as the general carbon dioxide emission tax rateemployed in

Sweden.An alternative to an increase in the EU carbon dioxide emission trade ratewould be to introduce a tax system based on environmental cost, making use ofe.g. Ecoindicator99, to include also other impacts on the environment not justthe greenhouse effect.

In design, control and installation of combined heating systems with solar energy utilization various tools are required in assuring rationality and cost effectiveness. A project was therefore initiated to develop such tools involving (a) building of a full scale plant for tests of combined heating systems containing solar collectors, pellet boilers, heat pumps and heat stores, (b) evaluation of system performance for some combined heating systems with varying control strategies through measurement, and (c) development of a user-friendly data soft ware tool for evaluating system performance of the kind of combined heating systems studied.

Results so far include building of the test plant and start of measurements of system and component thermal performance making use of the test plant. A TRNSYS deck of the system has been designed, and will be used for further investigations. From the results it can be concluded that user-friendly TRNSED data software would be possible to accomplish for calculation of thermal performance but also of economy, and climatic performance of combi-heating systems to best serve the needs expressed by the industrial partners of the project.

A DoE investigation using factorial and response-surface designs to analyze a solar–pellet combisystem in Sweden to optimize the system based on energy cost was performed. The same approach was also used to examine collector output energy. Investigated parameters were: building heating load, hot tap water consumption, collector flow rate, tank size, collector area, and estimated wood pellet cost. Cost- and performance-based regression equations were derived for optimal collector area and tank size for a range of buildings, providing tools for individual building solar combisystem sizing and optimization. Tank set-point temperature and estimated future pellet price were subjected to sensitivity analysis, and the influence of solar collector parameters and tank insulation level on profitability was investigated. The results indicate that a larger than expected collector area would be profitable due to inflation and the future price of pellets, and that tank size is less important to system profitability. However, tank insulation and set-point temperature were highly significant.