Using computer climate generator versus conventional lapse rate to model skyscrapers

The values of temperature and humidity at the top of skyscrapers are different from those near the ground. Thus, different mechanical systems, air flow rates, and other design parameters are required for such tall buildings. Conventional air temperature reduces linearly with increasing altitude, or lapse rate, of −6.5 °C/km. This study examines how the conventional lapse rate in a hot and humid region differs by using a computer-based climate generator in Dubai at an altitude of 600 m, we address three issues: whether the conventional lapse rate is always a good indicator of the climate profile, whether building design conditions change with altitude, and by how much the predicted energy consumption changes with altitude. Our first conclusion is that the conventional lapse rate may not always be a good indicator of the climate profile. The lapse rate is influenced by humidity. When humidity is low, the lapse rate tends to be higher and can reach up to −9.8 °C/km under adiabatic conditions. Conversely, when humidity is high, and as temperature drops with increasing elevation, condensation occurs and releases heat of vaporization, which warms the air and reduces the lapse rate. Under certain conditions, temperature inversion can occur, and the temperature above the ground may be higher than the temperature at 600 m altitude. Our second conclusion is that the linear lapse rate is not always a good predictor of design conditions. During the summer, there is a tendency to underestimate the lapse rate due to low relative humidity. In contrast, during winter, there is a tendency to overestimate the lapse rate due to low temperatures and high relative humidity. Last but not least, the linear lapse rate is not always a good indicator of energy consumption. Based on simulations, we found that differences in the lapse rate and the air density influenced the energy consumed by the air conditioning system in an office building. Specifically, between altitudes of 11 and 600 m, the energy consumption differed by approximately 5%.