23-05-2012, 10:03 AM
Mapping and analyzing Ventilation system in University building
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Abstract
The Threshold Limit Value for 8-hour time-weighted-average exposures to CO2 is 5,000 ppm. Currently, the American Society of Heating, Refrigeration, and Air-conditioning Engineers recommends a minimum office building ventilation rate offices of 10 Ls-1 per person, corresponding to an approximate steady state indoor concentration of 870 ppm based on the assumptions that outdoor CO2 is 350 ppm and indoor CO2 generation rate is 0.31 Lmin-1 per person. The purpose of this project is to study the current state of ventilation system in 2 computer rooms of MDH university building. We will measure carbon dioxide concentration and temperature variations inside these rooms. At the moment, the system is working as on/off control. We will investigate that whether this kind of control is effective or not. We will also take into account all kinds of heating sources available in the room in different positions and climatic conditions.
In this project, we measure the room temperature and carbon dioxide contained in room by using thermocouple and carbon dioxide transmitter respectively. This data is collected and recorded by using data logger and easy view program. The last step is to make graphs for the measurements in the room to see the variations in different parts of the room and then analyze them to make some recommendations for the existing operating conditions.
Introduction
All closed places need ventilation. Ventilation system is the system that is used for exchanging indoor air with outdoor air for reduced moisture, odor, and other pollutants and is used for controlling indoor air temperature. To ensure enough ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. says that “the living area should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per minute (cfm) per person, whichever is greater”. (WHOLE-HOUSE VENTILATION SYSTEM). This can be illustrated in the figure shown below:
Background and Literature review
Any combination of temperature and relative humidity falling within comfort zone is expected to maintain comfortable conditions for majority of occupants. Unless otherwise specified, inside condition of 24 °C 1 °C, 50 – 60 % RH (RH is Relative humidity) and air movement of 4.5 to 7.5 m/min are satisfactory for comfort cooling applications. (Aphornrathana,2007)
2.1 Ventilation in air conditioning space
Ventilation of outdoor air with the air already in the building can be divided into two broad classifications: Ventilation and Infiltration. (Aphornrathana, 2007)
Ventilation air is the air used to provide acceptable indoor air quality. Ventilation of certain amount of outside fresh air into the air conditioned space is also absolutely necessary, to replace the oxygen consumed and to dilute the concentration of carbon dioxide and pollutants like bacteria, fungus growth, viruses, cigarette smoke, carbon monoxide from outside air, hydrocarbons from building material, and etc. These contaminants in the air can cause health problems. Therefore, it is necessary to reduce the contaminations’ level within safe limits. (Aphornrathana, 2007)
Infiltration air is the flow of outdoor air into the building through cracks and other unintentional opening and through the normal use of exterior doors for entrance and egress. Infiltration is also known as air leakage into the building. (Aphornrathana, 2007)
2.2 Heat transfer to the air conditioning space
The air inside the air conditioning space receives heat from
-Heat transmission through walls, ceilings, floor and windows.
-Solar radiation through glass windows.
-Lightings.
-Equipments.
-People.
Discussion and Conclusion
Most people have some idea about ventilation in general terms but are not so sure of its importance in daily life. Ventilation is basically a process of removing bad air and supplying in fresh air containing the necessary ratios of the gases present in air for a normal breathing, either by natural or mechanical means. Ventilation removes indoor air pollutants and thereby improves the quality of indoor air. Indoor air pollutants may include tobacco smokes or fumes, unpleasant smells, dust particles, volatile organic compounds and many others. Moreover, the main purpose of the ventilation is to remove excess carbon dioxide, the accumulation of which causes suffocation and it becomes difficult for the inhabitants to breathe in. Ventilation system also controls the indoor air temperature, thus providing an environment where the people can live comfortably.
The ventilation system of MDH building is being controlled centrally. It was being complained that the system is not working properly in some parts of the building and feeling of discomfort is observed which includes increase in temperature and suffocation. So, it was a dire desire that some study must be conducted in order to understand the reason for it. Our group was given the opportunity to investigate and analyze the ventilation system of two of the computer labs and see the main causes of the discomfort. The measurements were made for the winter as well as spring season, but the main focus was the spring season, as the outside temperature is higher and also the breathing rate during spring is comparatively more.