Thermal Performance of Balconies and Floor Slabs Study – Update #2 Weather analysis
Published by Irina Susorova
We have the first batch of monthly data from the City Hyde Park (CHP) weather station we installed in February!
Our first task was to compare the local micro-climate conditions at the CHP weather station against standard Chicago weather conditions recorded by two major weather stations located at O’Hare International Airport (O’Hare) and Midway Airport (Midway). Cyclone Energy Group’s research team plotted ambient air temperature, relative humidity, and wind speed over a period of one week (February 5th to 11th, 2016). The airport weather data for that period were based on the information from Weather Underground website (www.wunderground.com). Note that the airport measurements are 7-9 minutes ahead of the CHP station data.
Our observations for that one week in February showed that ambient air temperature and relative humidity at all three locations were generally very similar. This finding is not surprising as the distance between all stations is less than 20 miles with no big changes in terrain. The average air temperature at the CHP station (27ºF, 65% RH) is however 3ºF warmer than at O’Hare station (24ºF, 70% RH) and 1ºF warmer than at Midway station (26ºF, 63% RH), which can be explained by the CHP station’s proximity to Lake Michigan with its warming effect.
Meanwhile, wind observations from the CHP station look very different than the airports’ ones. The factors that affect wind speed are the elevation at which it is measured and site physical conditions. Wind speeds are generally lower close to the ground and increase with the height. At the same time, wind speed depends on physical characteristics of the surrounding terrain (natural topography, vegetation, adjacent structures) – decreasing in densely built urban centers and increasing in the open terrain.
Winds in Chicago are predominantly from the northwest direction in winter and are on average 10-12 mph. Our observations for that one week in February showed that the prevailing wind direction measured by the CHP station is from the northwest with the average wind speed of 3.6 mph (maximum of 12 mph), which is lower than the wind speed observations from both airports during the same period. Although the CHP weather station is located at a higher elevation (761 ft.) than the weather stations at O’Hare Airport (673 ft.) and Midway Airport (623 ft.), it is surrounded by clusters of tall buildings, making the station somewhat less exposed to wind.
We also thought that it would be interesting to trace any global change in Chicago weather by comparing the recent observations from both airports with the 30-year mean weather data for the same locations (from Typical Meteorological Year TMY3 files). The recently-measured weather parameters are noticeably different from the TMY3 data. Some variability can be observed in wind speed, which is natural when it comes to analyzing such a highly unpredictable weather parameter; however, the overall wind speed fluctuations stay in the same range as the 30-year data. The 30-year mean ambient air temperature is lower than the recent data; however, it is difficult to explain such a large difference between the two TMY3 files from stations located relatively close to each other.
Stay tuned for more updates and our findings!