Development of a new laboratory evaporation measurement device as decision support for evaporation-optimized building

• Published in: Building and environment 2011-12, Vol.46 (12), p.2552-2561
• Main Authors: Starke, P., Wallmeyer, C., Rölver, S., Göbel, P., Coldewey, W.G.
• Format: Article
• Language: English
• Subjects: Applied sciences; Buildings. Public works; Computation methods. Tables. Charts; Concretes; Devices; Evaporation; Evaporation measurement; Evaporation rate; Exact sciences and technology; Humidity; Laboratory method; Materials selection; Mathematical analysis; Measurements. Technique of testing; Structural analysis. Stresses; Urban development; Urban evaporation; Urban surface material; Vapour
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/j.buildenv.2011.06.010

A new laboratory evaporation measurement device (LEMD) was developed to estimate the evaporation rates of urban surface materials. Here, evaporation is induced by means of a constant heat input and airflow. The evaporation can be measured using two different methods concurrently. Method 1 is based on a balance, which measures the mass loss over time. In method 2 the water vapour transport in the air is measured by humidity sensors thus enabling the calculation of the evaporation rate. Test measurements show a sensitivity of method 2 against influences from the environment, therefore, method 1 was used for subsequent measurements. With the assistance of the LEMD, an estimation of the evaporation rates for different materials was determined within a short period of time and with low costs. First measurements were carried out at 29 different urban surface materials. The main focus was placed on pervious concrete materials. In general, a more evenly distributed evaporation from pervious concrete was observed. It was possible to select pervious materials with anticipated higher evaporation rates for a subsequent field test. Especially two-layered pervious materials with a fine grained top layer and a coarse grained bottom layer show the highest laboratory evaporation rates. Furthermore, very low evaporation rates (even lower as from impervious materials) were observed for pervious materials with coarse grained aggregates. If these results can be verified in the field, it will be possible in future to regulate the urban water balance through the targeted deployment of different types of water-permeable pavements. ► We developed a device to measure evaporation rates in the laboratory. ► The device was tested and validated by two independent working measurement methods. ► Pervious concrete samples (fine-, coarse grained and 2-layered) were measured. ► Lowest evaporation on coarse grained, highest on 2-layered pervious concrete. ► Urban evaporation rates can be regulated by the use of special pervious concrete.