scope:

This supplement to the guideline VDI 2077 applies to the consumption-based billing for heating systems in which, for design-inherent reasons, a considerable amount of the heat to be supplied to the consumer units is lost through pipes, but usually remains unaccounted-for. Such heating systems are, in particular, vertical single-pipe heating systems with non-insulated trunk lines and, e.g., horizontal single-pipe heating systems of the Rietschel- Henneberg type (non-insulated ring line, see Bibliography). It is irrelevant, from the technical point of view, if the piping in question is exposed or inwall. The heat loss through these pipes may have a significant impact on the accuracy of heat cost allocation.

This guideline gives recommendations for reducing the heat loss through pipes and specifies methods for considering the heat loss through pipes in heating-costs billing so as to avoid or reduce cost distortions.

The methods are not intended to make up for any shortcomings in system engineering (such as insufficient hydraulic balancing, high supply temperatures or pump pressures, lack of insulation, etc.). Where technically feasible and economically reasonable, these shortcomings should be eliminated in order to achieve optimised operation. For details see Section 6.

The consumption-based share in the heating costs (usually 50 % to 70 % according to the German Heating Costs Billing Ordinance) depends on the devices of the specific metering system used. In many cases, these devices are heat cost allocators installed on radiators. However, part of the useful heat is lost, particularly through non-insulated or insufficiently insulated heating pipes running through the rooms to be heated (heat loss through pipes), and is not metered. This non-metered portion of heat for space heating causes cost shifts within the billing unit. The same effect is caused by non-metered heating of individual spaces (e.g. shared facilities such as staircases or drying rooms).

These costs shifts are characterised by the fact that users exhibiting above-average consumption within the billing unit are billed a consumptionbased charge higher than the equivalent cost of the metered heat portion that they have used for space heating. Users whose consumption is below average are then allocated an inadequate share. This effect may become more evident on completion of building renovation measures, particularly those for energetic enhancement of the building envelope (thermal insulation). Similar cost shifts that are not due to heat loss through pipes but, e.g., to high expenses for the provision of heat, are not covered by this guideline. It is planned to deal with this issue in the guideline VDI 2077 Part 2.

The following methods are intended to compensate for, or reduce, the aforementioned cost shifts which, according to the standards EN 834 und EN 835, must be considered as significant. The methods are applicable to the calculation and consumption- based allocation of the heating costs incurred by using hot-water central-heating systems. They mainly refer to single-pipe heating systems.