We should first clearify whether we discuss about cost-optimum or cost-efficient minimum EP requirements. In the case of cost-optimum, the requirements will be dynamic, because of the ever changing boundary conditions like prices, inflation rates, etc. Costs can regionally or seasonally differ even within a country. As we speak about minimum reqiurements, we should in my mind concentrate on cost-efficient requirements, which have to respect national boundary conditions as construction tradition, life style and others.
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