Impact of vegetation layer on external heat transfer characteristics

The object of research is a natural physical model of a green roof, which is a fragment of the surface layer of soil with landscaping in the form of a grassy layer on top of the substrate. The climate type is Dfa according to the Köppen classification. Method. Field thermal tests of the object were carried out by the "additional wall" method in the transition (autumn) period of the year. All control tests were performed within 5 days, recording parameters every 5 minutes. The equipment provides high measurement accuracy: for heat flow is plus minus 6%, for temperature is plus minus 0.2%. The measurement process was under control. Results. It has been experimentally established that fluctuations in heat flux and temperature on the surface with the plant layer are complex, due to daily cycles. It has been proven that the plant layer noticeably smoothes the temperature wave formed due to external air temperature fluctuations. The coefficient of smoothing of temperature fluctuations is 2.5–3.0; therefore, the surface layer of the substrate and the vegetable layer are in the zone of active fluctuations. It was experimentally confirmed that the air temperatures at different measurement points almost coincide, which excludes the influence of other factors on the temperature regime of the studied fragment. For the first time, the value of the external heat transfer coefficient (from external surface to external air) for green surface is 14.6 W/(sq.mxK) was established. The external heat transfer resistance for green surface exceeds the standard value by 1.7 times. This can be explained by the fact that vegetation creates additional resistance to convective heat transfer compared to surfaces without landscaping. The obtained results make it possible to more accurately calculate the external heat transfer of landscaped roofs.