For evaluating investment options I have studied project appraisal methods since the 1970s, also exploring the domain of social cost-benefit analysis. The central mathematical operator in such methods is discounting nett cash flows. As simple this straightforward operator functions, as complex can practical applications grow when societal decisions of wide and long-term scope are considered. One faces quickly Kant's ethical imperatives when weighing choices between nuclear power and climate change risks. Formal decision methods fall short in providing answers on such societal issues. Understanding the methods well and getting familiarity for their use when their use is appropriate, will contribute to one's participative and decision making capacity.

During some years I was teaching a course on formal decision making based on notes and books by e.g. R. Howard, H. Raiffa, Bierman, Bonini & Hausman. When I was studying more environmental risks, the analysis was extended with Risk Assessment Methods (V. Covello & M. Merkhofer). On occasions I also have given lectures to non-economists on economic decision making tools (discounted cash flow analysis, cost-benefit analysis), and I applied the theory in a number of investment choices (district heating, cogeneration, electric power expansion).

In 2010 the methodology was applied on deciding the energy performance endowment of buildings (at the moment of new constructions or fundamental retrofits). The emphasis on the aspect "endowment" is important. Under realistic expectations about climate change and climate change policies in the coming years the theory of investment shows that one can better invest immediately in the most advanced efficiency measures (choose or lose) instead of getting locked in an inferior quality building that lasts for a few decades.