In addition to the performance characterisation in the European standard EN 12976-1 many requirements are set up regarding safety, reliability and durability of thermal solar systems. Their objective is to ensure that the systems operate reliably, even under extreme conditions such as heavy snow or wind loads or extended stagnation periods during the summer. In addition, also the documentation of the system and the installation and operation manuals have to fulfil certain requirements in order to ensure a correct installation and operation by installer and owner, respectively.

2. System performance according to ISO 9495-5 (DST-Method)

The thermal performance of factory made systems is determined according to EN 12976-2 either by applying the DST-method (DST = Dynamic System Test, ISO 9459-5 /3/) or by using the CSTG — method (CSTG = Complete System Testing Group, ISO 9459-2 /2/). For both test procedures, the whole thermal solar system is installed on a test facility and operated under natural climate conditions according to well defined test sequences. The aim of both test procedures is to determine the annual system performance for specified reference conditions on the basis of short term tests.

The DST-Method can be applied for thermal solar systems with and without auxiliary heating. It is therefore the most relevant test method for ‘typical’ factory made solar domestic hot water systems used in northern and middle Europe. The aim of the DST test is to determine a set of parameters which allows, in combination with a numerical model, a detailed description of the thermal behaviour of the system. These parameters are determined by means of parameter identification based on measurements which are recorded during the operation of the system on a test facility. The annual performance of the system can be predicted by using the numerical system model and the parameters determined from the system test. The DST test method is standardised in ISO/DIS 9459-5 and has been developed over many years. Its comprehensive validation was realised among others within a project supported by the EU (Bridging the Gap, Contract No. SMT4-CT96-2067 /4/). It could be shown that the DST method is able to give re-producible results for a wide range of various types of solar domestic hot water systems at different climatic conditions and locations.

Today, every system configuration of a solar domestic hot water system (DHW) has to be tested by an accredited testing laboratory in order to obtain the Solar Keymark certification. Often, companies offer a product line of their solar DHW systems, which are identical with regard to their design and only differ in their collector and storage dimension. Due to the relatively cost — and time-intensive procedure of the testing it is no longer acceptable for the companies to test each system type of a product line. Hence, it is desirable to have a calculation tool that is able to predict the thermal performance of the whole product line without the need to test each of the system configurations.

At ITW, such a procedure for the extrapolation of performance test results for one tested solar domestic hot water system to systems of the same type but differing in size was developed within the Solar Keymark II project (Large open EU market for solar thermal products) financed by Intelligent Energy — Europe (IEE) under grant number EIE/05/052/SI2.420194. Related to this procedure also a software tool named DHWScale was developed by ITW. The procedure is based on the assumption

that the thermal performance of solar DHW systems which are part of a product line is similar, because they are based on the same design principles. Hence, the thermal performance of systems of the same product line can be described as a function of size.