The calculation methodology adopted in SolTerm, considers all solar thermal systems as pre-heat systems.

Simple schematic representation of the solar thermal system considered in SolTerm is given in Fig.2:

The main components of the system are:

• solar thermal collector characterized by the parameters: collector aperture area, zero-loss efficiency, heat loss coefficients determined according to EN 12975-2; section 6.1 (steady — state efficiency tests) [7]. The collector area is implemented by multiples of one collector and a data base of certified solar thermal collectors is integrated in the programme although the user can edit its own collector characteristics.

• collector loop including possibility to calculate pipe heat looses and efficiency of heat exchanger

• storage tank, characterized by its volume and heat losses coefficient

The energy delivered by the solar thermal system is a function of climate (climatic data base is included in the software tool) and by the load profile. A hourly load profile can be defined, as well as, week and week-end days and monthly load profiles.

The algorithm used, performs calculations in a simulation basis of the system behaviour in time steps on 10 min. Stratification of the storage tank is considered using an approach similar to the

one described in [6; chapter 8]. Transient behaviour of the system is not considered. The result of one simulation allows for the determination of:

a) monthly values of heat demand, i. e., Qsol, us, m, (calculated according to the load profile defined) where definition of load temperature and cold water temperature is included.

b) monthly values of energy delivered by the solar thermal system, i. e., Qsol, out, m The SolTerm version 5.0 was used in the comparison.

For comparison between the two methodologies, fixed values and procedures where adopted in SolTerm calculations in order to have input values as comparable as possible with the methodologie of EN 15316-part 4-3.

Since SolTerm allows for variations in Load profiles the option was to consider the same load profile seven days of the week with only one extraction between 17-18h.