Introduction
There are many factors that affect human comfort in the internal built environment. Human comfort is affected by thermal factors; physical factors and personal factors. Another factor that can affect human comfort is sound of the environment around them. The final factor that affects the human comfort is the visual of the room and the light intensity. There are ways to measure the physical factors that affect human thermal comfort, the sound comfort and the visual comfort.
Thermal Factors
The average temperature inside a building is 19-21 degrees and outside is -1 degrees, but there are two different thermal factors that affect the temperature of the room and human comfort; they are physical and personal factors. The physical factors include; air temperature, mean radiation temperature, relative humidity and air velocity. The air temperature inside of a building will change depending on the temperature outside the building and the k-values of the materials used to build the walls and insulation. K-values are the values that all materials have which shows how good insulators the materials are, the lower the k-value the more affective the materials are at retaining heat. The u-value is what overall heat resistance of the materials are. Air temperature is also affected by the people inside the building and they activity they are doing. The mean radiant temperature also affects the human comfort; mean radiant temperature is the radiation that is coming into the building from windows and walls, balanced against the radiation given off by the human body. The relative humidity is another factor that affects the air temperature; the relative humidity is the percentage of water vapour saturation that is in the air. The final physical factor that affects human comfort is the air velocity; this is the movement of the air throughout a building or a room. This can be affected by the convection in the room, the warm air enters a room and rises to the ceiling, pushing the cold air downwards and draught also changes the air velocity, the cold air flows into the room and makes the temperature of the draught path colder that the room temperature.
Physical and Personal Factors
There are also personal factors that can affect the human comfort in a building, they include; age, gender, state of health, clothing and the level of activity. The age of a person greatly affects the temperature of a room; older people give off less heat then younger people. Gender is also a factor that affects the temperature given off by people, females give off less heat than males, and they give off 85% of what the male body gives off. The state of health of the person also affects the heat that they give off and the temperature of the room, a person who is sick or has an illness gives off less heat that a person who is physically healthy. The clothing you are wearing also affects the temperature that you need to be comfortable, depending on the weight of the clothing you will need different temperatures to feel comfortable e.g. swimwear 29 degrees, light clothing 25 degrees, suit, jumper 22 degrees, coat, glove, hat 14 degrees. The level of activity you are doing also affects the heat that you give off and the temperature needed to feel comfortable. Sleeping 70W, watching TV 115W, office 140W, factory work 265W, lifting 440W.
Audio / Sound Factors
The sound of the environment that a person is in greatly affects their comfort in the building. Sound is a form of energy that is transmitted in pressure waves and changes depending on the pressure of the air in the room. Sound is the vibration of the particles in a wave that send the particles in all directions and spread out; this creates a pattern of refraction and compaction. Sound has two different sources and types where it can originate from, they are impact/structure-borne sound and air-bourn sound. These are different as they are where the source of the sound comes from. Air-bone sound is sound which travels through the air before reaching a partition, meaning that the vibrations must have travelled through the air before they reach the partition. Main sources of air-borne noise are; voices, radios and musical instruments. Impact sound is vibrations that are generated on the partition and a continuous vibration can be classed as a series of impact noises in succession. Impact noise does not travel through air like air-borne noise does. The main sources of impact noise are; footsteps, slamming door and vibrating machinery. It is important to know the difference between impact and air-borne noise as the methods that are used to prevent them are very different. However a single source could generate both air-born and impact noise e.g. footsteps, on the floor below the origin the sound would be impacts as it is started on the partition, but in the room of the sound it travels through the it before reaching the partition making it both air-born and impact. Both types of sound have different ways of preventing, so different installations must be put in to insulate from the type of sound. Air-born sound can be prevented by mass of partitions e.g. thick walls as lightweight particles give very little resistance unless they are in layers. The main ways that impact sounds are prevented is by using vibration pads and soft covering on floors and walls. Sound reverberates, so if a sound suddenly stops the sound will not stop instantly. The time taken for the reverberation of a sound decays at different rates depending on the area of the exposed surfaces, sound absorption values of the materials used in the building, the distance between the surfaces and the sound and the frequency of the sound.
Visual / Lighting Factors
The final factor that affects human comfort is light intensity. If the light levels are too low or too high then it will not be as suitable. Light travels in rays and bounces off objects and into the eye. The rays cannot bend so they must go in straight lines, but light can be refracted through certain materials which can bend the beam slightly. The light needs to be the right intensity so that the eyes don’t have to strain too much if it is too dark or if the light is too bright it may blind. Light can be controlled by letting certain amounts of natural light through windows and also by the brightness of the artificial light from the light bulbs. Natural light can be controlled by using darkened windows and the artificial light can be controlled by having dimmers on the lights to change the intensity as the intensity of natural light changes. Glare can affect the human comfort, glare is a light intensity that is too high reflecting off a surface and reflecting into the eyes making it difficult to see detail or may cause visual discomfort.
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P2- Describe how each factor is measured
There are methods that are used to measure the physical factors that affect human thermal comfort. To measure the physical factors, the instruments that are used are; thermometers, globe thermometer, hygrometer and anemometer. A thermometer is a device that is used to measure the temperature of a room, a thermometer includes a liquid that rises as the temperature does and on the side a scale that measures the temperature in °C and degrees °F. A globe thermometer is a device that measures radiant heat and consists of a thermometer sensor with a bulb located at the middle of a black copper bulb. The globe thermometers units’ of measurement are °C. This can be used to calculate the mean radiant temperature providing that you know the air velocity and temperature. A hygrometer is an instrument that is used to measure that saturation of water vapour in the air of the surrounding environment. This instrument relies on the pressure, temperature, mass and mechanical or electrical change. By calibrating the device and calculating the other factors the humidity can be worked out. It measures its units in percentages. An anemometer is a device used to measure the speed of wind, but there is also an anemometer that measures the pressure of wind, it consists of three or four cups that revolve around a shaft at different speeds depending on the wind temperature and pressure. They are measure in meters per second.
Sound is measured using a sound level meter, this instrument analyses the sound that it picks up and uses electronics to convert the sound onto a digital scale. Sound level meter can pick up sound instantly or can be used to pick sound up over time and the average can be calculated.
The intensity of light in a room can be measured using a light meter. The light meter woks using an electrical current which is generated by photosensitive electrons that detect the amount of light hitting the surface. This causes the electrons to react depending on the amount hitting the surface and is then converted into an electrical reading.
P3- State acceptable values for each factor
Each measurement has a range of acceptable values that affect the human comfort is the environment. The suitable range for temperature in a room is from 19°C- 21°C. This is also the same value with a globe thermometer. The acceptable value for the humidity of a room ranges from 40%-60%.
The units of measurement that sound is calculated in is decibels and the suitable range in a workplace is from 135dB-137dB maximum.
Light intensity is measured using Lux, the acceptable values for the intensity of light is 50- 100Lux.
M1- Produce clearly worked, accurate answers for different calculations relating to human comfort in the internal environment
1) Calculate the U-value of a cavity wall with a 102.5mm thick brick outer leaf, 45mm of clear cavity, 50mm of fibre insulating board, 115mm of lightweight concrete block inner leaf and 15mm of dense plaster finish.
Brickwork – 0.84
Cavity – 0.13
Fibre insulting board – 0.05
Concrete, lightweight – 0.19
Plaster, dense – 0.50
0.1025 + 0.05 + 0.115 + 0.015 + 0.13 =0.13 + 0.05 = 2.06728696742
0.84 0.05 0.19 0.50
1 = 0.483725779
2.06728696742
U-value = 0.48W/m²K
2) Compare the U-values of a single-glazed window made up of one sheet of 14mm glass with a double-glazed window made up of two sheets of 28mm glass with a 20mm air gap between them. Comment on the difference in U-values and its effects.
Glass – 1.022
Cavity – 0.13
Single-glazed = 0.014 + 0.13 + 0.05 = 0.19369863013
1.022
1 = 5.162659127
0.19369863013
U-value = 5.16W/m²K
Double-glazed = 0.028 + 0.028 + 0.13 + 0.13 + 0.05 = 0.36479452054
1.022 1.022
1 = 2.741269249
0.36479452054
U-value = 2.74W/m²K
The single-glazed has a higher U-value compared to the double-glazed. The difference in the U-value is 2.42; this makes a big difference in the insulation or resistance of heat. The higher U-value has less resistance and is a better insulator, so heat can easily escape. However the double-glazed has more resistance and cannot conduct the heat as well.
3) An un-insulated wall has a U-value of 0.92W/m²K. If insulation board is added to the construction, what minimum thickness of this board is needed to reduce the U-value to 0.34W/m²K? The conductivity of the insulation board is 0.028W/mK.
0.0565 + 0.92 = 2.93785714286 0.028
1 = 0.34048348655
2.93785714286
U-value = 0.34W/m²K
Insulation board = 56.5mm
4) A dwelling is 6m long by 4.5m wide by 2.4m high. In the walls, there are two windows, each 1m by 0.6m and a large door 2m by 0.8m. The construction has the following U-values:
Windows – 4.8
Door – 3
Walls – 2.3
Roof – 0.15
Floor – 3
The inside environmental comfort temperature is 19°C while the outside air temperature is -1°C. The volumetric heat specific capacity of the air is 1300J/mK. There are 1.5 air changes per hour. Calculate the total rate of heat loss for the dwelling.
Volume of room = 6 × 4.5 × 2.4 = 64.8m³
Air change rate = 1.5
Volumetric specific heat for air = 1300J/mK
Temperature difference = 20°C
64.8 × 1.5 × 1300 × 20 = 702W
1
Rate of heat loss = 702W
5) Calculate the reverberation time for a hall which has a volume of 2000m³ and a sound absorbing area of 350m².
0.16 × 2000 = 0.91428571428
350
Reverberation time = 0.91s
6) A hall has a volume of 4000m³ and a reverberation time of 1.6 seconds. Calculate the amount of extra absorption (m²) required to obtain a reverberation time of 1 second. Comment on how the length of the reverberation time has an impact on activities.
4000 × 0.16 = 400
1.6
Extra absorption = 400m²
The length of reverberation time can have an impact on activities. Depending on the reverberation time may have a large effect on it. If the activity is a speech then the reverberation time needs to be lower. The ideal reverberation time for speech is 0.5 – 1 second. However, of the activity involves music then the reverberation time can be higher as the ideal reverberation time for music is 1.5 – 2 seconds.
7) Calculate the wavelength of sound in air at 40Hz.
340 = 8.5
40
Wavelength = 8.5
8) Calculate the illumination in lux (lx) at a desk in a room where there is a requirement for a 5% daylight factor. The external sky has been measure at 7300 lx.
7300 × 5 = 365
100
5% = 365lx
D1- Analyse, in both qualitative and quantitative terms, the basic factors that affect human comfort
In a building the human comfort can be affected by the temperature in the room, the light intensity and the sound levels in the room. If any of these are higher or lower than the acceptable values then the people might not be able to work to the best of their abilities or concentrate. The use of ventilation, the need and the relation to heat loss. The partitions used and the relation to sound and heat transfer.
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To make sure that the temperature in a room is constantly within the right values the ventilation and heating up of the new air has to be constant. This is so that the temperature changes cannot affect the workers in the office; if the temperature levels are changing constantly it can affect work rate and ability. Temperature can change quickly by being in a draft or the convection as the hot air rises and the cold air is pushed down. When the room is hot this can also increase the humidity in the room, when the humidity gets high it can make perspiring difficult. This makes the quality of the work that will be done lower and also makes the experience of the worker worse. The temperature can also be too low as well. If the temperature is too low then this will also have a negative effect on the work that will be done. When they are too cold it will cause shivering which will make working harder, if typing or writing.
The sound in a room also affects the human comfort. If the noise level in a room is too high then the workers would be uncomfortable. If the sound is increased then this will make hearing much more difficult. This would also make listening to others harder and also following spoken instructions much more difficult to follow out. This could also have a permanent effect of the persons hearing and may partially or completely deafen them. this means that the quality of the work would not be done as well and may also not be done to the standard wanted due to a possible hearing disability.
The amount of light in a room is also a factor that also affects human comfort. If the light levels are too high in a room then the worker may be unable to see well or if light is reflecting off surfaces into their eyes this may irritate the workers. This may also cause partial blindness or permanent blindness. The contrast in lights if they are working at a computer may also hurt their eyes due to straining them to see a screen or paper. However, if the light levels are too low this may also have a negative effect as well. If the light levels are too low this will also cause straining on the eyes and difficulty seeing. Also the contrast of lights in certain areas may have a harmful effect on the eyes of the workers. If the light on the screen is too bright compared to the inside and natural lighting then this could also hurt their eyes.
Another factor which may affect human comfort would be the altitude that they are working at. If they are at a high altitude then there may be a lack of oxygen or knowing that they are high may make the workers feel nauseated and sick. At high altitudes people may experience increased bladder activity, decreased appetite, insomnia, swelling of hads, feet and knees and breathlessness.
Ventilation is also needed in a working environment. If there is no ventilation then the room would have an insufficient supply of oxygen and exchange for fresh air. If the room is also too hot this will cause the room to be stuffy and will have a very bad effect on the workers. The ventilation can be shafts and windows. Windows will also allow light into the office so that the light levels will not be too low and this will also allow a large amount of oxygen into the offices.
The partitions that are used in an office may be good and bad. The partitions could be too thin and you may be able to hear through the partitions, this could be distracting for workers and depending on the thickness of the partition, it may trap in too much heat or let too much heat escape making it difficult to work in conditions that aren’t correct.
If an office has a large amount of natural light this can be good for the workers as they will feel like they are in a natural environment, also allowing enough fresh air at a constant temperature, however if it is very dark outside then it might make the workers feel colder and if it is too bright then it may make them feel too hot. This could be avoided by having curtains or blinds, which will also trap heat in if it is a cold day and keep the cold out.
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