Area of FSV UK Prague in Jinonice with low-cost heating and cooling

A new library has been designed as a four-story building, assigned the role of a visible landmark from many directions. The structural system of the building consists of a spatial truss steel construction supplemented with beams and ceiling joists. The ceilings are made of reinforced concrete. The new library building impresses from a distance not only with its shape but mainly with its façade. It features a glazed lightweight outer shell supplemented with a light filter from the outside. In fact, it is a perforated shell made of gold-colored expanded metal mesh. This achieved an attractive appearance on one hand, while also creating a barrier against direct sunlight and preventing overheating of the building on the other. The motif of the outer shell, which creates the impression of a lace veil over the building, is not merely decorative; it draws inspiration from the graphic elements of the historical emblem of Charles University. In the new building, in addition to a representative foyer and café, students will find an extensive space (over 2000 m²) for meetings and studying, including the necessary library. "Long discussions about how the building should function energetically led to fundamental priorities that then became a springboard for the final design of the technological solution. Emphasis was particularly placed on the ecological nature of the building and its energy efficiency. Modern buildings need a powerful brain that can intelligently and meaningfully manage many systems while reflecting an environmentally friendly approach. At the same time, we architects wanted to design a building whose interior environment would be more contemplative, somewhat closed off from the surroundings, yet open to beautiful views of Prague," explains Ing. arch. Miroslava Tylšová, co-author of the architectural design. This laid the groundwork for the idea of designing a building with tempered concrete ceilings. "In my view, this is a technology of the future that we have already practically tested on several projects, proving how elegantly it works," adds Miroslava Tylšová.

Pre-cooled Ceiling oBKT

The energy-efficient system of tempered (pre-cooled) concrete ceilings is provided by REHAU. It essentially involves a surface radiant transfer of heat, or cold, from the pipe system to the concrete ceiling slab and then into the interior. Imagine it like the effect of a church, where the natural accumulation of heat or cold from strong stone walls is utilized. In the case of the new library building, the oBKT solution was used. This means that the RAUTHERM SPEED pipes made of cross-linked polyethylene type PE-Xa with a diameter of 14 × 1.5 mm were placed in a double meander under the lower reinforcement of the concrete structure. Consequently, they are closer to the lower edge of the concrete core, which effectively means providing higher cooling performance, faster response, and a change in surface temperature (about 2 °C per hour) compared to the BKT (Beton Kern Temperierung) system, where the pipes are located in the middle of the concrete ceiling slab. The source of heat/cold is a heat pump located on the roof of the existing reconstructed building, supplemented by gas boilers if necessary. In the entrance hall and café, the system is combined with underfloor heating. Active ventilation is utilized by opening windows and skylights with night pre-cooling of the concrete ceiling. The thermal loss of the building was determined to be 147 kW, while the gain for the entire building was set at 150 kW. The calculation of thermal losses was processed for an outdoor temperature of –12°C, while the heated space was calculated for a winter temperature of +22°C and a summer temperature of +26°C. It is also worth noting that the entire interior space is ventilated by a central recuperation unit. To achieve the required hygienic minimum air exchange of 25 m³/h per person, while respecting minimum operating costs, the building is equipped with automatically opening windows. All technological elements are controlled with the help of a central Building Management System (BMS) with visualization and control via a web interface.

REHAU and Environmental Responsibility

The systems of surface ceiling heating/cooling benefit from the principle of radiant heat and cold transfer, representing a highly economical yet effective solution. The system is primarily hidden within the concrete structure, so it does not obstruct anywhere, and operates at lower temperatures (hence a low-temperature system) when correctly regulated, leading to maximum energy savings. Additionally, in cooling mode, people inside are not exposed to unnecessary noise (as with traditional air conditioning), and they do not have to face temperature fluctuations or drafts, which, especially on hot days, can cause health issues like colds for many individuals. Allergy sufferers and asthma patients naturally also warmly welcome this advanced technology. However, it is also crucial to adopt a maximally environmentally friendly approach. The new library building of the Faculty of Social Sciences of Charles University in Jinonice is currently awaiting its grand opening and the arrival of the first students. This project is another in a series where the BKT (oBKT) system from REHAU contributed to the idea of building a modern, largely self-sufficient low-cost building.

www.rehau.cz

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Investor: Faculty of Social Sciences, Charles University, Prague 5 Jinonice
Architecture: Ing. arch. Miroslava Tylšová, Ing. arch. Judita Fischerová, Ing. arch. Miloš Fischer
Construction realization: OHLA ŽS, a.s.