ChapmanBDSP, Abu Dhabi
Historically, the biggest challenge in chilled-water system design for high-rise buildings was high static pressure related to height of the water column in the chilled water distribution circuits. This problem was efficiently resolved with introduction of plate heat exchangers, enabling multiple pressure breaks that keep maximum pressure in a system within acceptable limits. However, a small “price” in terms of chilled water temperature increase (around 1°C) must be paid on every heat exchanger / pressure break. With building height records being consistently broken, and approaching 1 kilometer, a new challenge has arisen. The challenge is to bring chilled water at a sufficiently low temperature to the point of cooling demand, which can be far from the point of cooling energy/chilled water generation. Low temperature at point of cooling demand (the air handlers of fan coils) is crucial to enable effective heat transfer to cope with high cooling-load demand. This is particularly important for latent components of cooling load, as the latent capacity of cooling coils significantly decreases along with the increase of chilled-water supply temperature.
Two approaches can be adopted to resolve this problem. The first approach is to install chillers somewhere high in the building, so that the distance between the point of CHW generation and furthest point of utilization would be reduced, and somewhat similar to a tall building application. An alternative approach to this problem is to implement low-temperature chillers, utilizing glycol to eliminate the risk of freezing. This presentation analyzes the pros and cons of either of the two options, and provides recommendations on which option should be adopted in design of modern supertall buildings.