Scholarly record
THE AIR TEMPERATURE PROFILE ABOVE THE NON-GREEN AND GREEN FLAT ROOF OF LARGE BUILDING AND ITS IMPACT ON THE ENERGY EFFICIENCY OF ROOFTOP HVAC UNIT
Abstract
Two variants of roof construction were compared. It is a non-green roof and the extensive green roof. The analysis of surface temperature of flat roof was provided by the simulation in DesignBUILDER v7. The surface temperature of extensive green roof was lower up to 28 K in comparison with the non-green roof. The results from DesignBUILDER were used as data input for the CFD model in ANSYS CFX. The results from CFD model showed that the outside air temperature close to the surface of non-green roof can rise to 3.7 K in comparison with surrounding air. If the electric heat pump (in cooling regime) works with higher air temperature on the condenser, the energy efficiency ratio of device can decrease up to 10 %. In the case of the green roof with lower surface temperature, the air temperature close to the surface of green roof can increase by 1.3 K in comparison with surrounding air temperature. So, the energy efficiency ratio of heat pump (in cooling regime) can decrease up to 3 %. So, we can decrease the consumption of electric energy for heat pump (in cooling regime) up to 7 % in summer in comparison with energy consumption of heat pump installed on the non-green roof. The proper position for HVAC units placed on the roof should be at least 0.75 - 1.0 m above the roof. From this level the influence of higher external surface temperature of roof on the surrounding air temperature is negligible.
Publication details
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