Causes of Discomfort in an Occupied Space - Term Paper Example

CAUSES OF DISCOMFORT IN AN OCCUPIED SPACE By: Course: Instructor: University, City, State: Date: I. CAUSES OF DISCOMFORT IN AN OCCUPIED SPACE Introduction The history of heating and cooling of buildings started during the pre-historic era. Cave dwellers were the first to create heating systems by making open fires to warmth themselves and their rock caverns. As civilization advanced, the Romans built the more advanced heating systems where they could operate furnaces under their buildings so that the hot gases could rise to the upper level rooms and warm them. The most challenging thing to designers was the provision of cooling in buildings than heating. Evaporative effects and the use of natural drafts were use in the early cooling systems and this technique is being revisited nowadays as modern engineers are drying to build better cooling systems that does not sustain heavy environmental cost. Researchers have come to understand that satisfaction with the thermal environment is not an easy thing. Our awareness of comfort is very much influenced many different variables like the characteristics of environment, activity level, cloths we ware etc. Environmental factors that researchers have identified other than the Dry Bulb Temperature which may cause discomfort in an occupied space includes and not limited to: a. Humidity b. Mean radiant temperature c. Air movement a. Humidity Humidity is also known as water vapour. This is the amount of moisture in air. Humidity is different from relative humidity. Relative humidity is a measure of moisture content of the air in relation to the maximum amount that air can hold at a given dry bulb temperature when saturated. Researchers have not really considered relative humidity to be of any vital importance in human comfort in an occupied space. This is because human body can adjust and tolerate a quite wider range of it (relative humidity) (Palonen et al., 1993). Humidity less than 40% will lead to complaints of dryness of skin and eyes and if it is more than 80%, human perspiration is uneasy. Palonen et al. (1993) further argued that thermal comfort can only be measured by the human’s body tolerance of dry bulb temperature, and not humidity. The experiment done by Palonen et al. (1993) concluded that “more humid air increases the tolerance of low temperature air and decreases tolerance of high temperature air”. Sling psychrometer (Hygrometer) is a simple instrument use to measure the humidity in the air. Sling psychrometer is made up of two mercury-filled glass thermometers mounted side by side on a frame. b. Radiation Thermal radiation does not depend on any intermediate medium and in this case, it will still happened across a vacuum as across an empty air space. Thermal radiation intensity depends on the total square of the distance between the point of the receiving surface and the point of origin. There is always an exchange of thermal radiant energy in an occupied space of four walls, a ceiling and a floor only if the surfaces have different textures and temperatures. For example if radiant heater used in in a cold room, the radiant heat will be exchanged with the walls, the ceiling, the floor and the occupants. After some time, someone may feel uncomfortable if his/her body starts to absorb excessive heat from the heater. Likewise, occupants may feel uncomfortable if the room surface they occupy is cold and their bodies radiate excessive heat to the surface. This was proven right by an experiment done by Li et al. (1993) when they investigated on different wall surface emissivities, that occupants were warm at air temperature of 10°C when the walls, a floor and the ceiling were sufficiently heated, and that they (occupants) were cool at air temperatures of 49°C when the surfaces were cooled. Therefore, depending on the worn and the activity, humans will feel more comfortable if the room they occupy is in the range of 18° to 27°C, and indoor surface temperatures should be 2.8°C below the dry bulb temperature. a. Air Movement Air movement is very important in replenishment of oxygen and the removal of odours in closed environments. However, air movement is known by researchers like Berglund and Fobelets (1987) (cited in ASHRAE, 2001) to cause discomfort if thermally neural environment is available. Toftum (2004) and Xia et al. (2000), in their experiments found out that sedentary subjects in closed environment find air movement to be unacceptable. They further found out that, air movement of less than 0.25 ms-1, depending on air temperature and humidity, are generally acceptable. The graph below can explain why low values of air speed are acceptable in winter than in summer. Air movement can be measured by using a hot wire anemometer to ascertain if comfort is compromised. The graph below shows a range of acceptable values for comfort. The Impact of Changes in Maximum U-Values Since 1980 King Herod live at the time when building controls was first introduced in the land and later pass the law, which stated that: “If a man constructs a building that will fall on someone else and kills this man, then this man should be killed too.” And since 1667, London Building Act laws have been laid down several times so as to make sure that all buildings were built to slow, if not to resist fire destructions. Since then, there have been several byelaws regarding to the safety of a building’s structure and on how a building can be constructed to resist fire. It was until 1985 when Building Regulations started to include the modern system of Building Control. In this system of building control, the primary concern was on how to build houses or closed spaces that can conserve energy efficiently and those that can have sound insulation and ventilation. During this period, some buildings were exempt from the building regulations e.g. small extensions, buildings for keeping animals, agricultural buildings etc. As time when by, people became aware of energy performance of buildings and they started calculation all building energy gains and loses. In many European countries, there are some requirements on the maximum energy transmission for every close occupied space components expressed in U-values. National U-value requirements for building an occupied space always tell the minimum requirements that do not mean anything about economic optimum. Due to the current sharp rise in energy prices, boundary conditions for putting a lot of insulation to buildings have considerably change. In fact, the European policymakers and regulators recommend U-values for building components. And far as the requirements of U-values, European policymakers and regulators concluded that: When comparing maximum U-values, climate protection and cost efficiency are not contradictory but can be well combined. Recommended maximum U-values in a building offer a room for improvement if required. II. POTENTIAL PROBLEMS ASSOCIATED WITH CONSTRUCTING “AIRTIGHT BUILDINGS” Some of the problems associated with “Airtight Buildings” are that; when there is inadequate thermal comfort in the room, it may lead to health problems to the young children and the older people occupying it because they have weak thermoregulatory systems (Heyman, 2005). As per the Institute of Medicine (2004), cold houses are more often than not, likely to be damp, and as a result, it will lead to the built up of moulds, that can cause respiratory symptoms. A part from negative effects on occupant’s well-being, it is energy consuming. Also “Air tight Buildings” has also been cited to have cause poor performance on housing stocks to buildings that were built before 1978 when minimum level of insulation was introduced for all new constructions. Other problems caused by “Airtight Buildings” include allergies and Sick Building Syndrome (SBS). III. INTERNAL HEAT GAINS (IHG) The sources of internal heat gains (IHG) include and not limited to: 1. People 2. Lights 3. Equipment a. Electrical plug loads b. Processes such as cooking Internal gains from occupants, equipment and lighting are the main sources of internal heat gains in closed occupied space. IHG for electrical and lightning equipment can only be calculated if the number of fixtures and its types are known. On the other hand, IHG for people and non-residential buildings can only be approximated because it has different level of activities. In non-residential or commercial buildings, IHG loads are estimated because these buildings can be under-used or over-used or may be used for purposes that were not design for. But in the case of small buildings like offices, lighting loads have been reduced because it has been built or equip with efficient equipment and lighting loads. Latent heat from equipment or from people that is added to the space is just an example of instantaneous cooling load. Any sensible heat generated or emitted by interior heat sources like equipment, people and lights are generally considered as time-consuming cooling load. But when external heat sources like the solar radiation heat enters to and occupied space, say through a transparent window, it is absorbed by the surroundings of that enclosed space. For example, if solar heat falls on a moist surface, a metal, room air or water inside a room, heat transfer will also take place by radiation, convection, conduction and evaporation as demonstrated by the figure below. As the surroundings get warmer because of solar radiation, the heat is then released into the surrounding air space, thus increasing the temperature of the mentioned occupied space. Once the room temperature starts to rise, the control system (thermostat) is triggered to start cooling the room. Another alternative of reducing heat gain in a room is by using modern day fluorescent lighting which has the same light levels as that of regular home lamps. These kind of efficient lights are much less expensive and they emit very little unwanted heat indoors. Just in case there is a lot of thermal heat radiation in the summer season, external shading devices can use to reduce heat gain in the room (Vechaphutti, 2001). External shading do a better job in keeping homes cool than internal window coverings. Internal coverings are known to reduce heat gains by 15%, whereas external shading can reduce heat gains by as high as 85% (Yu, 2010). If shading is fitted, it should be far enough from the window so as allow enough space for air circulation. Heat exchange processes between a building, internal and the external environment IV. USE OF NC-NR CURVES IN THE SPECIFICATION OF NOISE LEVELS IN OCCUPIED SPACES. Noise Criterion (NC) was first recognized in the United States of America for assessment of noise in an occupied space. Noise Rating Curves (NR) are commonly use in European countries. There are two factors that an occupant may considers when deciding if a background noise is acceptable or not. First is how an occupant perceived the loudness of the noise in relation to the everyday activities; and if is noticeable, then it is more likely to cause complaint and distraction. The second factor is the sound quality of the noise in the background. If there is some kind of roar, hiss, rumble or throb, this may lead to complaints of stress and is said to be unbalanced. NC/NR was established to determine the appropriate (acceptable) indoor environment for hearing protection and speech communication. The noise assessment graphs like the one below are plotted at suitable sound pressure levels at different frequencies depending on different sound pressure levels. The room and the use of that room determine the acceptable sound pressure level. NC/NR number is use to obtain each curve and every curve is obtained for its own different type of use. NC comprises a set of criteria curves that can extend from 60 to 7500 Hz. The NC/NR curves are used to explain the range at which octave band spectra should not exceed in order to meet acceptance in occupied spaces. The European Union has laid down some regulations and policies that are aimed at preventing the risks of workers being exposed to noise. Council Directive 86/188/EEC has laid down some directives and terms for employers to make sure that daily personal exposure of an employee be minimized. Regular audiometric test should be done to all employees in compliance with the conditions and standards laid down by ISO 6189. Also, governments should recommend on threshold limit values (TLV) as far as occupational noises are concerned. References ASHRAE (2001). Fundamentals Handbook (SI) - Chapter 8 Thermal Comfort. American Society of Heating, Refrigeration and Airconditioning Engineers, Atlanta. Heyman, B., Harrington, B.E., Merleau-Ponty, N., Stockton , H., Ritchie, N. and Allan, T.F. (2005). Keeping warm and staying well. Does home energy efficiency mediate the relationship between socio-economic status and the risk of poorer health? Housing Studies 20, 649-64. Institute of Medicine. Committee on Damp Indoor Spaces and Health (2004). Damp indoor spaces and health. Executive Summery. National Academies Press, Washington, DC. Li, Y., Sandberg, M. and Fuchs, L. (1993). Effects of thermal radiation on air flow with displacement ventilation: an experimental investigation. Energy and Buildings, 19, 263-274. Palonen, J., Seppanen, O. and Jaakkola, J.J.K. (1993). The effects of air temperature and relative humidity on thermal comfort in the office environment. Indoor Air, 3, 391-397. Vechaphutti, T., 2001. Simulation of Heat Gain through Building Envelope for Buildings in Hot Humid Climates . Buildings, 2002(1). Yu, W.Y.W. et al., 2010. The Comparative Analysis on the External Shading Application Effect of Residential Building. EProduct EService and EEntertainment ICEEE 2010 International Conference on, p.1-4. Read More