Analysis of the effect of heat column generation on energy performance of split AC units in high-rise residential buildings

Abstract

In recent high-rise residential building constructions, air-cooled split-type air conditioners are popular due to their cost-effectiveness and installation flexibility. However, placing outdoor units in restricted building re-entrants creates heat columns along the height of the building. This phenomenon adversely affects energy efficiency and contributes significantly to the overall power consumption of the A/C units. I recent years, the escalating use of air conditioners due to global warming highlights the substantial energy dedicated to space cooling. Hence, improving air conditioning efficiency is vital in managing end-user electricity consumption. This research examines split air conditioning performance in a tropical high-rise residential building, focusing on heat column generation in re-entrants. The study assesses system efficiency under different loads and outdoor temperatures. A numerical framework was developed to optimize condenser layouts, allowing simulation of various scenarios. By analyzing outdoor wind conditions, individual usage, and room cooling loads, the research aims to predict the impact of heat columns generation on Split A/C performances in high rise residential buildings. The study reveals that elevated ambient temperatures in re-entrants significantly degrade performance due to heat column effects. CFD simulations demonstrated that condenser placement and re-entrant geometry critically influence temperature distribution, with upper-floor units experiencing severe accumulation, causing COP reduction up to 62% and elevating consumption by 75%. Simulations showed that under no-wind conditions, locating units 1.5 m from the exterior wall minimized heat column buildup, while 2.0 m proved optimal at 2 m/s outdoor wind conditions. Introducing a perforated slab improved thermal management, lowering peak temperatures from 64°C to 59.5°C at no-wind conditions. The findings underscore strategic importance in optimum layout of outdoor units in re-entrants to enhance efficiency and reduce costs, providing insights for architects and engineers. This study contributes insights into factors influencing heat column strength and emphasizes the mathematical framework for optimizing condenser arrangements.