Heat transfer correlations for low approach evaporative cooling systems in buildings

• Published in: Applied thermal engineering 2009-01, Vol.29 (1), p.105-115
• Main Authors: Costelloe, B., Finn, D.P.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chilled ceilings; Cooling towers; Devices using thermal energy; Energy; Energy. Thermal use of fuels; Evaporative cooling; Exact sciences and technology; Free cooling; Heat exchangers (included heat transformers, condensers, cooling towers); Heat transfer; Low energy cooling; Theoretical studies. Data and constants. Metering; Thermal performance
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2008.02.005

The experimental performance of an open industrial scale cooling tower, utilising small approach temperature differences (1–3 K), for rejection of heat at the low water temperatures (11–20 °C) typical of chilled ceilings and other sensible air–water heat dissipation systems in buildings, is examined. The study was carried out under temperate maritime climatic conditions (3–18 °C wet-bulb temperature range). Initially a theoretical analysis of the process at typical conditions for this climate was conducted, which indicated that a water to air ( L/ G) mass flow rate ratio of less than 1.0 was required for effective operation. Consequently for these low L/ G ratios, the thermal performance of the experimental tower was measured and correlated. A new correlation is proposed which shows a significant increase in the NTU level achieved, for the required L/ G ratios (0.3–0.9). As the cooling tower in this application is predominantly a mass transfer device under summer conditions, the evaluation of the total volumetric heat and mass transfer coefficient (kg a s −1 m −3) is of particular relevance and is also determined.