Case Study Las Vegas, Nevada By: Susan Farkas Chika Nakazawa Simona Tamutyte Zhi-ya Wu AAE/AAL 330 Design with Climate Professor Alfredo Fernandez-Gonzalez School of Architecture University of Nevada, Las Vegas Spring 2004
ABSTRACT Climate conditions vary throughout the world. Outdoor spaces, like building interiors, may require shading methods to provide comfortable areas for use. The importance of understanding the climate is integral to the effective design strategies needed to shade and cool these spaces The proposed study is an exercise for the AAE/AAL330 Design with Climate course at the University of Nevada, Las Vegas. It is an analysis of outdoor shading devices and cooling strategies at the Renaissance Center in Las Vegas, Nevada. By investigating a specific area within the complex area, the existing outdoor design strategies for shading and cooling can be studied for its effectiveness and alternate options can be suggested. In conducting the experiment, the intent is to compare the conditions within and surrounding an open courtyard, and to correlate these temperatures with the average activity level that occurs within and around the courtyards. By using various scientific tools such as the HOBO data logger, the data collected provides information of the space, the effectiveness of the comfort strategies, and how these spaces relate to the temperature vegetation, material and people activities. INTRODUCTION The desert climate of Las Vegas, Nevada can have extreme weather conditions throughout the year. Winters tend to be cool and windy, while summers temperatures reach 105º Fahrenheit (40º Celsius) from May through September with a few days exceeding 115º Fahrenheit (46º Celsius). Most of the annual 4 inches of rain fall occurs between January and March. Table 1 Average Las Vegas Temperature Chart
Table 2 Average weather in Las Vegas, Nevada High Temperature ( F / C ) Average Temperature ( F / C ) Low Temperature ( F / C ) Morning Humidity (%) Afternoon Humidity (%) Wind speed (mph) (meter/sec) Jan Feb Based on data reported by main weather stations Monthly Averages * Mar Apr May Jun Jul Aug Sep Oct Nov Dec 57 / 14 63 / 17 68 / 20 77 / 25 87 / 31 100 / 38 105 / 41 103 / 40 94 / 35 82 / 28 67 / 20 57 / 14 45 / 7 49 / 9 55 / 13 63 / 17 72 / 23 82 / 28 88 / 31 86 / 30 78 / 25 66 / 19 52 / 11 45 / 7 33 / 1 38 / 4 44 / 7 50 / 10 60 / 16 69 / 21 76 / 25 74 / 23 66 / 19 54 / 12 42 / 6 33 / 1 55 51 45 35 32 24 28 33 34 36 45 53 32 28 23 16 14 11 15 17 17 20 27 32 7.4 8.5 10.1 11 11 11 10.2 9.6 9 8.1 7.8 7.3 3.31 3.8 4.52 4.92 4.92 4.92 4.56 4.29 4.02 3.62 3.49 3.23 Wind Direction WNW WNW SW SW SW SW S SW SW WSW WSW WNW * Orange region denotes the month study was conducted. The Renaissance Center, located at the busy northwest corner between Eastern Avenue and Tropicana Avenue, is comprised of various buildings with two major architectural styles which were built in two major phases. The old portion, which consists of many small office areas linked by a series of courtyard, and the new portion, which consists of big office areas embellished by several courtyards, displays two architectural expressions of the Center. Photograph 1: Renaissance Center Both portions have outdoor courtyards which serve to link not only each building but also connect the two distinct built phases of the center. Both phases utilize the courtyards for circulation not only between the buildings, but also to link the two phases.
The Renaissance Center has a variety of interesting shading strategies used throughout the site. A large open main courtyard at the newer portion of the Renaissance Complex became the focus of this study. Situated in the newer phase of the complex, the concrete courtyard surrounded by grass and flanked with trees on one side, seems to be an inviting place for employees and visitors to enjoy the outdoors. The user friendly component of this space relies on the temperature and comfort level in and around the courtyard. Photograph 2: Open space courtyard The 20 ft. x 40 ft paved courtyard is comprised of two sections, each having 4 concrete block benches and is situated along the north-south axis. East of the courtyard, a one story office complex sits approximately 30 feet away with open space between. Several trees line the western part of the courtyard with a one story building just beyond. Parking areas are north and south of the courtyard, approximately 40 feet from the courtyard. Walkways on the east, north and south link the parking lots and office buildings to the courtyard. During the initial site visit, several questions arose about the courtyard including the following: Does the shading provided by the trees help to cool the courtyard? Does the vegetation help with cooling the area? What occurs in the areas outside of the courtyard? Based upon these questions and observations during this initial visit, the student research group hypothesized that the temperature and comfort level is cooler within the courtyard than outside of the courtyard. To test this hypothesis, equipment was placed in strategic areas to collect data pertaining to the temperature, humidity and air velocity. The results clearly supported the hypothesis statement - that the area within the courtyard was cooler than that of the outer perimeter area. Additionally, the air velocity was effective in evaporative cooling when temperatures became high. HYPOTHESIS The intent of this study is to examine the interior courtyard and its surrounding area and observe the characteristics of comfort levels achieved with air temperature, relative humidity and air velocity. The hypothesis is: The interior part of the courtyard, which is surrounded by trees on the western side, is cooler than the outer eastern and northern perimeter areas outside of the courtyard.
METHODS Date: Data was collected from four sources in and around the courtyard on March 22, 2004 between 9 am and 5 pm. Location: Renaissance Center open courtyard in new phase. Equipment: Four Hobo Data Sensors by Onset, Inc. These measure temperature (T) and relative humidity (RH). The collected data can be downloaded to a computer spreadsheet program for further analysis. VELOCICALC Plus Meter by TSI, Inc. Using a single probe (Pitot tube), this handheld instrument simultaneously measures logs various ventilation parameters. Once collected, this data can be downloaded to a computer spreadsheet program. For this study, the Velocicalc Plus Meter was used to measure air velocity (V). Equipment Placement: Four HOBO data loggers were secured to the tops of 2 posts that were rods that were placed in the following four locations in and around the courtyard: HOBO 1: Inside the sitting area of the courtyard HOBO 2: Along the eastern walkway outside the courtyard HOBO 3: Along the northern walkway outside the courtyard HOBO 4: North of the courtyard near parking area Additionally, the Velocicalc Plus Meter was taken to each HOBO location to measure the air velocity at 15 minute intervals.
Once collected, the data was downloaded and plotted to show correlations of temperature and comfort levels. A final analysis was compiled to show the results. Monitoring the Shade: Trees and buildings can provide shading and create cooler areas. Hourly photographs of the four HOBO locations were taken by the student researchers. The objective was to have visual data to track the shade in the designated areas of study. To prove the hypothesis, the study was conducted using methods of physical measurements and calculations. The physical measurements included: Table 3 EQUIPMENT & METHOD OF MEASURING DATA EQUIPMENT MEASUREMENT UNIT INTERVAL METHOD HOBO Data Logger Temperature ( T ) F every 5 minutes Automatic Relative Humidity ( RH ) % every 5 minutes Automatic Velocicalc Plus Meter Air Velocity ( V ) m/s every 15 minutes Digital Camera Shading every 1 hour Student Researcher Student Researcher Once the information was gathered and downloaded, analysis of the data followed. The ASHRAE Thermal Comfort Program was used to calculate the Standard Effective Temperature Index for the adjusted shift in thermal comfort of the area. SHADING RESULTS Photographs were taken every hour at the top of the hour to track the shading within the designated space. The photographs resulted in showing the times that the HOBO areas were shaded: Table 4 SHADING TIME TABLE LOCATION HOBO 1 HOBO 2 HOBO 3 HOBO 4 TIME AREA WAS SHADED 10AM - 5 PM 2PM - 5 PM 1PM - 5 PM 5 PM
TEMPERATURE Meteorological data for March 22, 2004 was reported at Las Vegas McCarran International Airport (approx. 5 miles from Renaissance Center): Table 5 Las Vegas 30 Year Temp. Averages & Records March Monthly Average/Records March 22, 2004 Normal High (F / C) 68 / 20 70 / 21 Normal Low (F / C) 44 / 7 45 / 7 Record High (F / C) 91 / 33 87 / 31 Record Low (F / C) 23 / -5 32 / 0 Mean (F / C) 56 / 13 58 / 14 Normal Precip (in) 0.4 0 The collected Hobo data was downloaded and a graph was prepared to show the relationship between the four locations. Table 6 Temp (F) 140 Temperature: March 22, 9:00am - 5:00pm 120 100 80 60 40 20 0 9:00 AM 9:25 AM 9:50 AM 10:15 AM 10:40 AM 11:05 AM 11:30 AM 11:55 AM 12:20 PM 12:45 PM 1:10 PM 1:35 PM 2:00 PM 2:25 PM 2:50 PM 3:15 PM 3:40 PM 4:05 PM 4:30 PM 4:55 PM HOBO 1 HOBO 2 HOBO 3 HOBO 4 time and day
HUMIDITY According to the Hobo data, the humidity of the positions were almost the same. Table 7 RH (%) 45 Relative Humidity: March 22, 9:00am - 5:00pm 40 35 30 25 20 15 10 AIR VELOCITY 5 0 9:00 AM 9:25 AM 9:50 AM 10:15 AM 10:40 AM 11:05 AM 11:30 AM 11:55 AM 12:20 PM 12:45 PM 1:10 PM 1:35 PM 2:00 PM 2:25 PM 2:50 PM 3:15 PM 3:40 PM 4:05 PM 4:30 PM 4:55 PM HOBO 1 HOBO 2 HOBO 3 HOBO 4 time and day The air velocity for each HOBO location indicates random and inconsistent numbers. Table 8 Air Velocity 400 Air speed (feet/min) 350 300 250 200 150 100 50 hobo 1 hobo 2 hobo 3 hobo 4 0 9:00 9:45 10:30 11:15 12:00 12:45 13:30 14:15 15:00 15:45 16:30 Time
COMFORT ZONE Combining the hourly data of temperature (T), relative humidity (RH) and air velocity (V) and placing them into the ASHRAE Thermal Comfort Program, the Standard Effective Temperature Index was calculated. This index permits the comfort level to shift upward in the psychometric charts (Table 9) The shift changes the average comfort level of 83º F to move upward to 86º F, primarily as a result of the evaporative cooling from the air velocity that occurs at various times of the day. Table 9 PSYCHOMETRIC CHARTS HOBO 1 HOBO 2 Outside comfort zone from 1pm 2pm Outside comfort zone from 11am 2pm HOBO 3 HOBO 4 Outside comfort zone from 10am - 2pm Outside comfort zone from 10am 4pm
ANALYSIS During the data collecting, each student researcher was assigned to spend 2 3 hours at the courtyard between 9am and 5 pm. While collecting data throughout the day, noticeable temperature changes were felt as the day progressed. Within the courtyard, under the shade, the temperature remained cool and comfortable, while outside the courtyard the temperature felt warmer and less comfortable. SHADING HOBO 1 Shading from the morning hours of 10 am and onward kept the area cooler with the highest temperatures occurring at 1pm HOBO 2 Shade occurred in the mid afternoon hours of 2 pm onward. This caused higher temperature conditions from 11 am 2 pm. HOBO 3 Shade began to fall upon this area from 1pm onward, with the temperatures dropping only after 3pm. HOBO 4 This area was exposed to the sun throughout the entire study period, from 9am 5pm. Temperatures rose dramatically to over 100º F as early as 10am and remained extremely hot until 4pm. The HOBO Data Loggers collected a broad range of temperature and relative humidity values. The temperature data resulted in a quick analysis and understanding. The temperature graph (Table 6) displays the varied values that each HOBO collected. The following analysis can be made: VALUES HOBO 1 - These values were dramatically different as the distance to the other HOBOs became greater. The values between HOBO 1 and HOBO 4 were the most extreme. HOBO 2 The values were fairly similar to HOBO 1 and HOBO 3. HOBO 3 The values were somewhat similar to HOBO 1 and HOBO 2. HOBO 4 These values were much higher than the rest of the HOBOs. RELATIVE HUMIDITY The relative humidity values were fairly constant inside and surrounding the courtyard throughout the day, averaging 22.5%, +/- 0.5 %. The dryness of the desert climate supports the consistency that this would be relatively constant. AIR VELOCITY Velocicalc Plus Meters measured the air velocity at each HOBO location. The rate of speed (m/s) helped to create a cooler comfort zone during the hot times throughout the day. While some hours had temperatures exceeding 83º F that is normally the maximum comfort level, the air velocity permitted temperatures ranging from 83º F - 86º F to become an effective temperature comfort level.
CONCLUSIONS The collected data and analysis supported the hypothesis that the inside courtyard was cooler in temperature and had a more comfortable level while the areas outside the courtyard were warmer and less comfortable. The temperature analysis showed that there is a difference in temperature range between the HOBO locations due to the placement. The shading by the trees on the western side also helped to cool the areas that became shaded. The relative humidity was consistent in all locations and did not have as much effect on the cooling and comfort level as the shading did. Finally, the air velocity played a major role by creating evaporative cooling and permitting temperatures exceeding the 83º F to also become within the ranges of the comfort zone in the psychometric charts. The information gathered and analyzed during this study can provide information for most of the mild months of weather conditions at the Renaissance Center. Further studies may be conducted during hotter months (May September) which can help to understand how the courtyard can be best utilized throughout the year. It may also be helpful to collect data for longer periods of time to establish more precise information. REFERENCES (Las Vegas Climate Data) http://www.city-data.com/city/las-vegas-nevada.html http://www.greatlasvegashomes.com/las_vegas_climatechart.htm http://www.intellicast.com/ http://www.wunderground.com/