Report – ENVR110 – A Study of the Relationship of Relative Humidity and Temperature

A Study at Camosun College, Lansdowne Campus of the Relationship of Relative Humidity and Temperature

Jenny Kendrick, Geoff Kerr, Stefan Martensson, Kate Musto

ENVR 110, Camosun College

November 20, 2009

Introduction:

Relative humidity is a ratio expressed as a percentage of the moisture in the air to the moisture it would contain if it were saturated at the same temperature and pressure (Oxford Concise Science Dictionary, 2006).  The maximum amount of water vapor that can be contained in the air is dependent on temperature.  A given volume of warm air can hold more water vapor before it precipitates than colder air can. Factors that influence relative humidity include: altitude, cloud cover, pollution, air temperature, regulated temperature in buildings and wind.

For this study, we have chosen three unique locations at Camosun College Lansdowne campus: the smoking area located outside of Ewing Building, the showers of the men’s locker room in Young Building, and a book shelf on the second floor of the library.

The three sites we chose have unique factor influencing relative humidity.  The smoking area may be influenced by the presence of people and their habit, smoking.  Because this area is sheltered, and there was little wind on the day the data was recorded, the data logger was not exposed to strong wind.  Because it is outside, and the measurements were taken in late October, the air temperature is expected to be lower at this location than the others.  Due to the low temperature, and our proximity to the ocean, we predict that the relative humidity be quite high in this location.

The other two locations are inside, and so are expected to be warmer.   Due to the warmer temperature, these locations should have lower relative humidity.  However, due to the running water in the shower, we predict that there should be enough moisture in the air to cause this location to have the highest relative humidity of the three.  As for the library, we predict that the relative humidity will be lowest of all the locations due to the books absorbing some of the water vapor in the air.
Method and Materials:

For this experiment, a HOBO data logger was used to measure temperature and relative humidity at ten second intervals.  The software used for the HOBO Data Logger was BoxCar 4.3. Microsoft Excel 2007 was used to graph the data.

As stated earlier, the locations on Camosun College Lansdowne Campus used for the experiment were the smoking area located outside of Ewing Building, the showers of the men’s locker room in Young Building, and a book shelf on the second floor of the library.  Data was collected for approximately sixteen minutes at each of the three sites.

Results:

The following graph shows that the relative humidity was highest at the smoking area outside of Young Building and lowest in the library.

Graph 1 – Measurement of Temperature and Relative Humidity vs. Time at Three Locations on Camosun College Lansdowne Campus.

The average relative humidity recorded during the entire time at the smoking area was approximately 56-57%.  The maximum and minimum relative humidity recorded were approximately 64% and 44% respectively.  The mode, or most common value of relative humidity recorded at this location was 68.2%.  The average temperature recorded in the same time frame was 13.7°C.  The maximum and minimum temperatures recorded were approximately 18.45°C and 11.7°C respectively.  The mode value for temperature at this location was 12.21°C.

The average relative humidity recorded during the entire time at the showers was approximately 50-51%.  The maximum and minimum relative humidity recorded were approximately 63% and 44% respectively.  The mode value of relative humidity recorded at this location was 47.3%.  The average temperature recorded in the same time frame was 16.3°C.  The maximum and minimum temperatures recorded were approximately 18.57°C and 12.16°C respectively.  The mode value for temperature at this location was 17.9°C.

The average relative humidity recorded during the entire time on the library book shelf was approximately 42%.  The maximum and minimum relative humidity recorded were approximately 50% and 38% respectively.  The mode value of relative humidity recorded at this location was 39.2%.  The average temperature recorded in the same time frame was 19.4°C.  The maximum and minimum temperatures recorded were approximately 20.8°C and 16.62°C respectively.  The mode value for temperature at this location was approximately 20.6°C.


Discussion:

In general, areas of lower temperature had the highest relative humidity, and areas of higher temperature had the lowest relative humidity.  Though the lowest relative humidity was recorded in the library as predicted, the highest relative humidity was recorded at the smoking area, not the showers.  We predicted that the showers would have the highest relative humidity because of the high amount of moisture that would be expected in the air due to the running water, but we underestimated the effect that temperature would have on the relative humidity.  Because the temperature of the air at the smoking area was approximately six to ten degrees Celsius colder than the other areas, the saturated vapor pressure of the water in the air was lower.  In the equation used to calculate relative humidity, the saturated vapor pressure of water is the denominator, and the partial pressure of water vapor in the air is the numerator.   Therefore because the saturated vapor pressure is lower for the water in the colder air outside at the smoking area, the partial pressure of the water vapor in the warmer air in the shower would need to be considerably higher than that in the smoking area to yield a higher relative humidity value.

Some possible sources of error include heat sources (such as people) or drafts in close proximity to the data logger, and insufficient time spent at each location.  As is seen on the graph, the temperature and relative humidity continue to rise or fall as the temperature of the data logger itself adjusts to the temperature of each new location.  The data only begins to “flatten out” for the points on the graph correlating to the last minute or so at each location.  The results would have been more accurate if more time had been spent collecting data after the logger reached the same temperature as its surroundings.

Even though some trends are exhibited at each of the three locations, our data is inconclusive and more sampling, with longer intervals needs to be done to verify exact measurements of the three sites.

Conclusion:

Our findings suggest that relative humidity is inversely related to temperature.

References:

Oxford Concise Science Dictionary. (2006).

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