Master's Thesis Meike Voß


Creation of a district energy concept for existing multi-family homes

In a case study of a larger apartment compound, this paper presents a concept for retrofitting the energyproviding
system of existing residential buildings. For this purpose, eight retrofit scenarios are defined
and compared with the pre-existing condition of the compound (“base scenario”). The key ecological
and financial data are calculated with a view to identifying the scenario which optimally reconciliates
ecological objectives with financial constraints. All scenarios are defined as financially sustainable
where the costs of retrofit may be recovered from the savings owing to the retrofit. In the foreground of
the paper is the search for a scenario where a retrofit may be financed without recourse to payments
from the apartment owners in excess of their payments in the base scenario.
In two scenarios, the retrofit is confined to retrofitting the technical energy-providing structure. In one
of these scenarios, the pre-existing decentralized technical structure is rehabilitated, and in the other
scenario, the pre-existing structure is replaced by a central structure for the entire compound that couples
the production of power with the production of heat. In the other scenarios, the retrofit of the technical
structure is linked to the retrofit of the buildings comprising the compound.
The key data concerning energetics are calculated pursuant to the “Energy Savings Directive” (“EnEV”)
2009, and the key economic data are calculated in terms of annuities (“Annuitätenmethode”). In a first
conservative financial analysis, prospective developments and assumptions are disregarded. Under this
approach, three scenarios qualify as financially sustainable – the two scenarios confined to retrofitting
the technical structure and one scenario linking the retrofit of the technical structure to a retrofit of the
In a second step, assumptions regarding inflation of relevant prices and hypothetical costs of maintaining
the pre-existing structure are included in the calculations. Now, seven of the eight scenarios appear to
be financially viable. All calculations illustrate the financial superiority of a central energy-providing
structure over a decentralized. The results of calculations with prospective assumptions vs. the results
without such assumptions also suggests that the financial viability of retrofits tends to improve over
The best ecological results are achieved in the scenario shifting the central technical structure from gas
to biogas and linking that structure to a retrofit of the buildings. These results make the entire investment
into the retrofit eligible for lending by the German Bank for Reconstruction (“KfW”) at a preferential
rate and for outright subsidy. This subsidies in turn makes the scenario financially viable. Ecological
objectives are thus optimally reconciled with financial constraints by a central energy-providing structure
based on biogas. Facilitating such a retrofit financially, fiscal support achieves its political purpose.
Optimal reconciliation of ecological objectives with financial constraints must be facilitated by a concept
planning retrofitting with a view to fine-tuning the retrofit of the technical structure to the retrofit
of the buildings. Project finance models may best be suited for implementing such a concept.
The results of this study illustrate the advantages of retrofitting in the framework of an over-arching
master plan over piecemeal retrofits.