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HEATING AND VENTILATION


Positioning of the polyurethane shells.


units, central Variable Refrigerant Volume (VRV)-systems and direct expansion air handlers, as well as water, mini-chillers for generation of local cooled water, and air- cooled chillers for central chilled water generation. The central hot and cold-water systems


worked best, although they had a higher initial cost. Due to the simplicity and robustness of the systems, the maintenance cost was much lower. The energy efficiency of cold and heat generation was greater, and thus the operating costs were lower. Finally, it was observed that the terminal equipment lasted an average of 25 years, compared to direct expansion equipment that lasted an average of 10 years. Furthermore, due to the nature of the water systems, the central and terminal units can be replaced by any equipment independent of brand and manufacture, which is very important in Uruguay – a country that does not have access to constant commercial representation of brands and stock of components. Taking these considerations into


account, the plan for the new areas was to utilise a central chilled water system, with a cooling plant composed of three air- cooled chillers of 150 refrigeration tons – each provided by the brand Trane within the ERTAF-line, and a central hot water system generated in a water/steam plate exchanger, where the steam is generated


Corrosion due to condensation on rubber insulated pipe.


by dual fuel/GLP boilers already in operation in the building, with a surplus capacity to cover the heat consumption of the new areas. For the selection of the material of pipes and insulation of the distribution systems of hot and cooled water, the different facilities that existed in the building were evaluated, analysing the performance and state of conservation over the years. The use of thermoplastic pipes was ruled out since significant wear was observed in hot water plastic pipes within less than 10 years of service, whereas Schedule (Sch) 40 seamless steel pipes showed a greater resistance against wear and corrosion, as evidenced by the fact that the heating pipes had been in service for 40 years without apparent problems. This was not the case with the


seamless steel pipes for chilled water. Although the interior was kept in good condition, the accumulation of steam condensation on the outer surface of the pipe caused a major deterioration through oxidation, due to poor insulation, even in temporary pipes that were installed during the construction phase in a period as short as two years. This failure in the insulation of chilled water pipes was due to several factors: l In the case of insulated pipes formed by polystyrene foam shells, with a steam barrier made of polyethylene


film and galvanised sheet lining, as exterior protection, no guarantee can be provided that the vapour barrier itself secures the tightness against the pass of steam.


l In the overlaps of the polyethylene film the concentrated and condensed steam on the surface of the pipe results in corrosion of the pipe because of oxidation. Although the polystyrene foam has a good index of thermal conductivity, because it must be executed on site with preformed shell parts, the continuity of the insulation cannot be achieved due to cavities generated, resulting in condensation.


l The protection of galvanized or stainless-steel sheet does not have the mechanical robustness to withstand impacts and therefore, the protections were broken and left the insulation and the vapour barrier exposed to rainwater and UV-rays. This completely deteriorated the pipe insulation function.


l In the case of pipes with elastomeric rubber insulation, the insulation ended up falling off mainly due to the low quality of the work carried out. The edges between the different pieces were made with contact cements or with specific tape overlaps, generating points of discontinuity in the insulation that caused condensation on the surface of the pipe, resulting in oxidation.


Mould in stainless steel jacket joints due to condensation. 48


Chilled water secondary circuits manifold and buffer tank. IFHE DIGEST 2020


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