Performance assessment of seawater cooled chillers to mitigate urban heat island

Abstract

Urban heat island (UHI) phenomenon, nowadays accentuated by global warming, is growing its negative influence on urban resilience, building energy budget and human comfort during summer. To reduce UHI effect, mitigation strategies are normally focused on actions related to urban design like the use of high reflectivity surfaces and increase of vegetation. But, as concerns building anthropogenic heat, the benefits of a possible reduction of the heat released by air conditioning systems to neighborhoods are often underestimate. An effective solution consists in transporting the heat emitted by chiller condensers elsewhere by using water as heat transfer fluid. The systematic use of seawater to cool chillers in an urban area of a coastal city was investigated. The modification of the UHI phenomenon was studied as well as the consequences on building cooling demands and chiller performances assessed in dynamic conditions. Urban weather files in presence of different types of chillers were elaborated by Urban Weather Generator model. Building cooling demands in the area were evaluated by using archetype modeling approach and EnergyPlus model. The algorithm adopted to assess chiller performances takes into account also the effect of part load working condition. The comparison of seawater cooled chillers technology versus the more diffuse use of air cooled chillers highlights a significant UHI effect reduction which reaches 57% during the night. As regards cooling demand increment caused by UHI, with seawater cooled chillers it is reduced of 58%. In the end, thanks to lower demand and higher chiller efficiency, seawater cooling chillers achieve an energy saving of 23.5%. Therefore this solution can foster the urban resilience and sustainability with an increasing contribution in front of the future climate scenario. Therefore, the introduction of a district cooling network is an important UHI mitigation strategy and its feasibility would have to be always verified between the possible actions.