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Optimizing Chilled Water Design in High-Rises in Hot, Humid Climates

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©2024 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 66, no. 1, January 2024. 

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Chilled water cooling systems consume nearly 50% of building energy required to meet cooling loads, especially in hot, humid climates.

Chiller COP can be improved with the optimal chilled water supply temperature, and significant amounts of system energy can be reduced. Similarly, chilled water distribution pumps designed with high temperature delta T will have less annual energy consumption compared to low delta T chilled water system design. The optimal chilled water supply temperature needs to be determined based on space dehumidification factor, since a high chilled water supply temperature leads to a decrease in the cooling coil latent load capacity and a potential increase in the size of cooling coils.

This study examined the impact of chilled water (CHW) supply temperature on the chiller’s efficiency, the effects of CHW temperature differentials on pump energy consumption and the most suitable CHW supply temperature for space dehumidification.

We consider a hypothetical office building model as a case study for optimizing the performance of the chilled water system in a high-rise 40 floor office building in Abu Dhabi (ASHRAE Climate Zone 1A,1B). The conditioned area of the office building is 58,000 m2 (624,306.8 ft2) with a mechanical floor on the 20th floor. Office space occupancy density is based on 1 person per 20 m2 (215 ft2) per ASHRAE Standard 62.1-2022.

The chilled water system is designed to meet the cooling load of the occupied spaces. Software was used to build a 3D geometry for a hypothetical office building and also used to run a thermal load and energy simulation.

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