SECTION 5a.
UNDERSTANDING THE MONTHLY PLOTS





By plotting the months on the psychrometric chart, it becomes much easier to visualize the climatic conditions for each month. By visual inspection alone we will determine some key facts about the climate.

Remember though, that the plottings represent only the dry-bulb temperatures and corresponding relative humidities. They do not, as yet, take into account, wind conditions or solar access or available thermal radiation. These factors too, affect thermal comfort as perceived by the human body. Before we assess bio-climatic needs, we will look at how factors like air movement or solar access affect thermal comfort.

Check out the 'SlideAnimation' below.





















We will assess bioclimatic needs by determining the conditions of underheated period, overheated period, radiation received, wind speeds, relative humidity and required shading. Out of these, the underheated and overheated period and relative humidity can be determined from the psychrometric chart itself.

To find conditions of wind speeds, we will look at the 'Monthly Average Hourly Surface Wind Speeds [mph]'. The hourly readings from the climatic data are put together in the table below by groups of readings for day and night. 12 hours each are averaged together to give average daytime and nighttime wind speeds in mph (miles per hour) which are then converted to m/s (meters per second).

Monthly Average Hourly Surface Wind Speeds [mph] for Tucson
Hr JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
6:00 5.0 3.0 1.0 2.0 7.0 10.0 15.0 7.0 6.0 11.0 9.0 6.0
7:00 5.0 3.0 7.0 1.0 10.0 10.0 9.0 6.0 5.0 8.0 9.0 6.0
8:00 6.0 7.0 6.0 5.0 10.0 9.0 7.0 5.0 5.0 9.0 8.0 7.0
9:00 7.0 7.0 9.0 10.0 9.0 8.0 7.0 5.0 5.0 8.0 7.0 8.0
10:00 5.0 3.0 10.0 5.0 6.0 9.0 7.0 5.0 5.0 5.0 7.0 6.0
11:00 2.0 0.0 13.0 1.0 5.0 10.0 6.0 5.0 6.0 5.0 8.0 5.0
12:00 0.0 3.0 3.0 9.0 5.0 10.0 8.0 6.0 7.0 11.0 8.0 3.0
13:00 2.0 5.0 9.0 10.0 10.0 9.0 11.0 6.0 10.0 16.0 7.0 2.0
14:00 3.0 3.0 7.0 23.0 6.0 7.0 13.0 7.0 14.0 7.0 6.0 1.0
15:00 5.0 10.0 13.0 21.0 14.0 6.0 10.0 8.0 17.0 9.0 6.0 0.0
16:00 6.0 5.0 10.0 25.0 10.0 6.0 0.0 11.0 14.0 10.0 9.0 2.0
17:00 8.0 3.0 14.0 17.0 14.0 6.0 11.0 14.0 11.0 5.0 13.0 3.0
Ave for
Daytime		 mph 4.5 4.33 8.5 10.75 8.75 8.33 8.66 7.08 8.75 8.66 8.08 4.08
m/s 2.01 1.93 3.80 4.80 3.91 3.72 3.87 3.16 3.91 3.87 3.61 1.82
18:00 9.0 3.0 13.0 15.0 11.0 7.0 14.0 17.0 8.0 17.0 16.0 5.0
19:00 8.0 3.0 7.0 7.0 13.0 11.0 13.0 13.0 8.0 10.0 13.0 5.0
20:00 6.0 3.0 5.0 14.0 10.0 15.0 15.0 10.0 7.0 9.0 9.0 6.0
21:00 5.0 3.0 5.0 14.0 10.0 20.0 15.0 6.0 7.0 6.0 6.0 7.0
22:00 6.0 5.0 3.0 15.0 8.0 20.0 7.0 6.0 8.0 6.0 6.0 6.0
23:00 8.0 6.0 7.0 2.0 8.0 20.0 8.0 6.0 9.0 6.0 7.0 5.0
24:00 9.0 7.0 6.0 2.0 5.0 20.0 11.0 7.0 10.0 8.0 8.0 5.0
1:00 5.0 9.0 5.0 6.0 8.0 7.0 13.0 5.0 7.0 3.0 9.0 6.0
2:00 6.0 3.0 7.0 3.0 6.0 8.0 13.0 5.0 8.0 7.0 11.0 9.0
3:00 7.0 9.0 7.0 2.0 7.0 8.0 5.0 5.0 9.0 5.0 13.0 10.0
4:00 6.0 5.0 10.0 6.0 9.0 9.0 13.0 5.0 8.0 7.0 12.0 9.0
5:00 5.0 3.0 8.0 6.0 8.0 10.0 13.0 6.0 7.0 6.0 10.0 7.0
Ave for
Nightime		 mph 7.5 4.91 6.91 7.66 8.58 12.91 11.66 7.58 7.91 7.5 10.0 6.66
m/s 3.35 2.19 3.09 3.42 3.83 5.77 5.21 3.39 3.53 3.35 4.47 2.97

The averaged hourly daytime and nighttime air movement velocities are compared against the bio-climatic assessment chart above. A similar process is followed for the assessment of solar radiation during daytime. The values are obtained for average monthly solar radiation during daytime in W/m².

Monthly Average Hourly Solar Radiation on Hz Surface [BTU/ft²] between 6 am - 5 pm for Tucson
Hr JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
6:00 0.0 0.0 3.0 25.0 58.0 55.0 21.0 15.0 8.0 0.0 0.0 0.0
7:00 3.0 9.0 57.0 104.0 133.0 129.0 93.0 86.0 67.0 41.0 15.0 5.0
8:00 48.0 82.0 133.0 182.0 208.0 204.0 174.0 164.0 143.0 112.0 72.0 44.0
9:00 108.0 151.0 203.0 247.0 269.0 264.0 237.0 232.0 210.0 174.0 129.0 99.0
10:00 159.0 206.0 256.0 280.0 311.0 306.0 280.0 181.0 259.0 222.0 175.0 147.0
11:00 193.0 241.0 287.0 266.0 334.0 328.0 305.0 299.0 286.0 245.0 201.0 161.0
12:00 207.0 256.0 299.0 236.0 339.0 330.0 314.0 287.0 289.0 247.0 204.0 144.0
13:00 199.0 249.0 288.0 167.0 328.0 315.0 302.0 260.0 274.0 229.0 186.0 109.0
14:00 169.0 217.0 256.0 125.0 298.0 280.0 269.0 232.0 238.0 188.0 147.0 76.0
15:00 120.0 167.0 203.0 102.0 248.0 227.0 220.0 194.0 179.0 129.0 94.0 45.0
16:00 61.0 101.0 133.0 61.0 180.0 160.0 161.0 136.0 106.0 62.0 35.0 17.0
17:00 7.0 28.0 59.0 30.0 104.0 95.0 90.0 67.0 33.0 2.0 0.0 1.0
Ave for
Daytime		 BTU/ft²h 106.1 142.2 181.4 152.0 234.2 224.5 205.5 179.4 174.3 137.5 104.9 70.6
W/m² 33.65 45.08 57.50 48.20 74.24 71.15 65.16 56.86 55.25 43.60 33.25 22.39

Comparing the radiation data against bio-climatic assessment chart, we determine solar, thermal radiation needs.

Tabulating all the analyses in a concise format, we find the following:

Bio-climatic Needs Table
CONDITIONS FOR TUCSON JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
N D N D N D N D N D N D N D N D N D N D N D N D
Temperature (°C) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downless.gif (900 bytes) upless.gif (893 bytes) upmore.gif (892 bytes) upmore.gif (892 bytes) upmore.gif (892 bytes) upmore.gif (892 bytes) upmore.gif (892 bytes) upmore.gif (892 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes)
Radiation                        
Relative humidity upmore.gif (881 bytes)   downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) upmore.gif (892 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) downmore.gif (883 bytes) upmore.gif (892 bytes) upless.gif (893 bytes) upmore.gif (892 bytes) upless.gif (893 bytes) downmore.gif (883 bytes) upmore.gif (892 bytes)   upless.gif (893 bytes)
Air Movement
Shading                   upmore.gif (892 bytes)   upmore.gif (892 bytes)   upmore.gif (892 bytes)   upmore.gif (892 bytes)   upmore.gif (892 bytes)            
N = Night; D = Day; upmore.gif (881 bytes) = Significantly higher than comfort; upless.gif (893 bytes) = Not Significantly higher than comfort;
downmore.gif (883 bytes) = Significantly lower than comfort; downless.gif (900 bytes) = Not significantly lower than comfort;
Air movement velocities in m/s; = Comfort condition; BLANK = N/A


Inferences from Visual Inspection and the Bio-climatic Needs Table:
i) January, February, March, April, November and December are months which are substantially or less significantly underheated. While some of the daytime heating requirements can be taken care of by the sun, thermal radiation, either from systems heated up during the day or independently has to be supplanted for comfort.
ii) January, Feburary, November and December are months when relative humidity is low during the day and increases during the night but on the whole, the climate would be cold and dry. To counter the dryness, humidification might be needed.
iii) The months of March, April and May are transitional months from winter to summer. March and April will have cooler nights. May will have warm to moderately hot days with comfortable nights and low relative humidity.
iv) The month of June is the hottest month where the temperature would hit over 37.78°C (100°F). Relative humidity will still be as low as 15% so this is the month and even the nights for the most part will be warmer than comfortable. October is similar but less extreme.
v) The months of August, July and September are the months with a high relative humidity and temperature and hence, are thermally the most uncomfortable.


Next, we will look at thermal comfort strategies that can bring the monthly plots within thermal comfort. We will also learn under what conditions does one work better over the other and what might be their architectural expressions.




©1998-2008 Peyush Agarwal. All rights reserved. Contact peyusha AT hotmail DOT com for comments.
You may freely download, distribute, copy and use the Website in whole or in parts, as long as credit is cited alongwith.