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This study is focused on the feasibility of using energy performance contracting (EPC) for the retrofit of two apartment buildings constructed using precast concrete technologies in Slovakia decades ago. The retrofit packages were defined, and their suitability for EPC was evaluated through discounted payback. The uncertainties in the profitability calculations were covered by designing five possible economic developments and defining input ranges instead of just single inputs. The measures in the technical systems were shown to be more feasible than the retrofit of the building envelopes. The potential to finance the selected measures for technical systems through EPC was further evaluated. It was shown that, for at least one of the two buildings studied, the EPC was recommended only for the economic developments with a notable increase in energy prices compared to the baseline that referred to the situation before the Covid-19 pandemic. In the best case, the payback was four years for one building and seven years for the other; thus, both were potentially suitable for EPC. However, for a complex retrofit, the EPC must be combined with a different funding source to also finance other retrofit measures.

• Construction rules were studied for wall and ceiling systems suitable for retrofit. • Adding insulation was not necessary with insulating core even for low wall thickness. • Increase in output per 1 cm of pipe spacing was maximal at 6 cm. • A dense spacing maximized the system output per energy input. • A metal fin attached to a pipe in insulation led to the highest output. The application of radiant heating and cooling systems in building retrofit could facilitate the use of renewable energy sources in existing buildings. This research focused on adapting the design of a ceiling and wall system with pipes underneath the surface and a wall system with the pipe embedded in a bricklayer. These systems are suitable for installation in retrofitted rooms, but the findings are also applicable to new buildings. Heat transfer was computed using a validated numerical model. With a conductive core, insulation thickness of up to 3 cm was appropriate for an internal wall. With an insulating core, insulation was not necessary even if the core was only 15 cm thin. The increase in output per 1 cm of pipe spacing was maximal at 6 cm. Spacing below 3 cm was inefficient. A dense spacing maximized the system output per energy input by creating a uniform surface temperature, while also shortening the response time. Attaching a metal fin to a pipe in plaster increased the output by as much as reducing the pipe spacing from 10 to 6 cm (14 W/m2, i.e. 20%). Attaching a metal fin to a pipe embedded in insulation for a compact design led to the highest output of all cases studied. Placing the pipe in a brick layer added to a conductive wall did not increase the heat storage capacity of the wall. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water-based wall systems for heating and cooling and thermal barriers are reviewed. • A classification scheme is proposed for heating/cooling systems and thermal barriers. • Benefits and drawbacks are summarized, design recommendations are provided. • Alternating between heating, cooling, and thermal barrier is perspective operation strategy. • Incorporating PCM in the wall and use in building retrofit are research opportunities. This study reviews water-based wall systems for space heating and cooling and thermal barriers (TB) for the reduction of buildings' thermal load. The review gives a general overview of the research and groups it into subtopics that are discussed in detail. For space heating and cooling, the subtopics entail thermal performance, thermal comfort, renewable energy sources, use for building retrofit, and combination with phase change materials (PCM). For TB, especially the working principle, types and designs, and performance are discussed. A classification system is proposed separately for wall heating and cooling systems and TB based on the designs found in scientific literature. Benefits and drawbacks are summarized, and design recommendations are provided for the wall systems. It was shown that in certain cases, radiant wall systems can be preferable to radiant floors and ceilings, but further comparisons would be useful to provide conclusive evidence. For TB, the studies uniformly declare that TB reduce buildings' thermal loads and energy demands. Few studies focused on the economic and environmental aspects of using TB. Most of the studies about TB are based on calculations. Measurements to quantify the benefits of TB under real operation and refine the conditions under which various types of TB are feasible are lacking. Enhancing the wall performance by PCM in the active layer, application of the wall systems in building retrofit, and alternating between the functions of heating, cooling, and TB present the biggest research opportunities and challenges. [ABSTRACT FROM AUTHOR]