Paper Conference

Proceedings of Building Simulation 2021: 17th Conference of IBPSA


Quantification of the cost of oversizing cooling installations in a case study under construction in Vietnam

Pedro Marques, Mathias Vandecasteele, Kien Le Trung, Wim Boydens
Studiebureau Boydens, Belgium

Abstract: In countries where energy regulation is rather lax and young, the HVAC design team might lack the incentive to do a careful sizing of the heating and cooling loads in a building. Instead, predefined values in watts per square meter, generous “safety factors” or a combination of both are used. Oversizing of HVAC installations occurs more often than one would expect - upon site visits in Vietnam, installations with several chillers are observed running one chiller only. In such cases, oversizing did not necessarily translate into malfunctioning on site, for the building occupants felt no issues, as there is no difference in comfort between an oversized installation and a rightly sized one. However, such design practice will unquestionably end up in a higher capital investment, lower plant efficiency, higher energy and maintenance costs when compared to a more carefully designed installation. It is difficult for the project manager to assess the gap between the necessary and installed power for several reasons, ranging from internal (team technical experience) to external (common industry practice). Hence, for most projects little to no action is taken in this regard. However, it would not be difficult to convince the investor if he is informed of the total cost of this problem. The main difficulty is related to the lack of signs of discontentment: • The HVAC designer delivered a system that provides air conditioning as requested, and “better installing too much than not enough”. • The building manager has no major problems running the system. If one chiller goes out of service, plenty of backup is available. • The design team technical knowledge is insufficient to assess the issue, either because the team lacks experience, or because technical experience comes from analogous designs. • No regulation is enforcing the reporting and benchmarking of the efficiencies of the cooling plant, or the general building consumption. In this case study, the final HVAC plans from a local MEP designer were placed under the magnifier and benchmarked against calculation-based cooling load sizing. An IESVE model was created for this office building for that effect; dynamic thermal simulations helped assessing the reality of the sizing results. These values were finally converted into capital cost, energy cost and maintenance cost, so that the connection between choice and cost is finally achieved.
Keywords: oversizing, dynamic simulations, cooling installations
Pages: 3400 - 3401