Efficiency calculation – Selecting the appropriate method
Methods – input values - conditions
Depending on the chosen method, certain input values and conditions must be known or determined. Often, comparative values are consulted for evaluating efficiency. The table provides an overview.
The choice of the specific method allows certain questions to be answered. Some possible questions include:
• What are the maximum costs of an energy modernisation measure with a given energy saving? (Break-even costs)
• What is the minimum amount of energy a measure should save for a given cost? (Break-even savings)
• After which period of time the expenses for the energy modernisation are balanced through the energy cost savings? (Payback period)
• Is it cheaper to save energy than to consume energy? (Equivalent energy price)
• Is the yearly burden after the modernisation (loan payment, low energy costs) lower than before the modernisation (high energy costs)? (Annuity)
Restricted choice of method
In principle, energy consultants, certificate issuers, building owners and investors are free to choose a method.
- Calculations in connection with applications for exoneration from requirements
Applications for exoneration from requirements are mostly based economic reasons. As far as the authorities in charge due to regional legislation have issued regulations about methods, these shall be followed. In accompanying studies to the Energy Saving Ordinance have proven the economic efficiency was proven using the “Amortisation Period”-method and assuming certain boundary conditions. Accordingly, any different economic situation in a concrete case (e. g. due to very high investment costs) should be calculated preferably using the same method and consistent boundary conditions.
- Indicators in energy certificates showing the economic feasibility of recommendations
If an (optional) indicator regarding the economic feasibility of modernisation recommended within the certificate shall be included on page 4 of the certificate, this should be done using a particular format. This requires estimating the payback period as well as the equivalent energy price (the cost per saved kWh of delivered energy).