With all care that has to be taken with respect to the assumptions and simplifications made, the following results become obvious:
- An individual dwelling – in effect a single-family home – causes losses worth around 40 cents annually.
- 100 homes cause losses not as high as 100 times, but only as 20 times as much, worth about EUR 8 in total, i. e. 8 cents per dwelling.
- The dwellings “with electrical warm water supply for bath and shower purposes” exhibit lower losses (also see the plot Fig. 6) than the dwelling without (Fig. 7).
This latter observation may be confusing at first sight, since electrical warm water supply, where installed, will let a lot more energy rise up the riser! The calculation is based on a practical example (4796 kWh/a instead of 2903 kWh/a at a long-term average over 20 years) with an additional consumption of 65%, which means a plus of about 2/3 on top of the electricity bill of the home without electrical warm water supply. However, the “electrical warm water supply for bath and shower purposes” takes into regard the current intake of a direct instantaneous electric water heater (to be installed immediately at the construction stage or to be refurbished later on), which is capable of heating the water just as quickly as it flows. This requires installed capacities between 18 kW and 27 kW. While such a high power is needed for just a few minutes per day, the requirements for larger conductor cross sections are the same as would be for permanent load. Over the rest of the day, this larger cross section then reduces the losses.
As an overall result, it can be stated that the riser may just be missed out of this consideration right from the start. Even if the mentioned guesswork should be by a whole magnitude in error, this would not change anything about the result. This being so, the estimate is quite likely to be still too high, since all risers have been calculated as being loaded with the entire current drawn by the building. In fact, every storey takes away its part of the load, and the last section is loaded only more with the current of two flats. So one ought to calculate with half the load as a mean or, alternatively, with half the real length, neither of which was done here. Despite this inaccuracy, which lays the estimate “onto the safe side”, the riser losses turned out to be negligible here. Hence, the force to design the conductors to the peak of the occurring load is not really a cost driver but rather a piggy bank, viewed across the lifespan, adding erection and loss costs! The riser need not be optimized anymore because it has already been energy optimized, although not for energy efficiency but other – compelling – reasons.