FISIKA BANGUNAN 1
• THERMAL
Thermal comfort
The most commonly used indicator of thermal comfort is air temperature – it is easy to use and most people can relate to it. But although it is an important indicator to take into
account, air temperature alone is neither a valid nor an accurate indicator of thermal comfort or thermal stress. Air temperature should always be considered in relation to other
environmental and personal factors.
The six factors affecting thermal comfort are both environmental and personal. These factors may be independent of each other, but together contribute to a worker’s thermal comfort.
Environmental factors:
Air temperature
Radiant temperature
Air velocity
Humidity
Personal factors:
Clothing Insulation
Metabolic heat
The Six Basic Factors
Heat exchange of body
Gain
Met= metabolism
Cnd= konduksi/ bersentuhan dg benda panas
Cnv=konveksi/udara lebih panas daripada kulit
Rad=radiasi dari matahari, langit benda panas
Loss
Cnd=konduksi/ menyentuh benda dingin
Cnv=konveksi/ bila udara lebih dingin dari kulit
Rad=radiasi/ ke langit malam dan permukaan dingin
Evp=evaporasi/penguapan terhadap kelembaban dan keringat
Met-Evp ±Cnd ± Cnv ±Rad=0
kenyamanan termal
• 1.Pengertian kenyamanan termal
• 2.Kesetimbangan energi pada tubuh manusia
• 3.Faktor-faktor yang
mempengaruhi kenyamanan termal
• 4.Standar kenyamanan termal
• 5.laju pengeluaran energi
panas tubuh dari manusia ke
udara lingkungan
• Faktor – faktor yang mempengaruhi kenyamanan termal pada manusia :
• Temperatur udara lingkungan
• Radiasi dari atau ke lingkungan
• Kecepatan udara lingkungan
• Kelembaban udara lingkungan
• Insulasi pakaian
• Laju metabolisme
Thermal comfort
Environmental factors
Air temperature
This is the temperature of the air surrounding the body. It is usually given in degrees Celsius (°C) or degrees Fahrenheit (°F).
Radiant temperature
Thermal radiation is the heat that radiates from a warm object. Radiant heat may be present if there are heat sources in an environment.
Radiant temperature has a greater influence than air temperature on how we lose or gain heat to the environment. Our skin absorbs almost as much radiant energy as a matt black object, although this may be reduced by wearing reflective clothing.
Examples of radiant heat sources include: the sun; fire;
electric fires; furnaces; steam rollers; ovens; walls in kilns; cookers; dryers; hot surfaces and machinery, molten metals etc.
Air velocity
This describes the speed of air moving across the worker and may help cool the worker if it is cooler than the environment.
Air velocity is an important factor in thermal comfort because people are sensitive to it.
Still or stagnant air in indoor environments that are artificially heated may cause people to feel stuffy. It may also lead to a build-up in odour.
Moving air in warm or humid conditions can increase heat loss through convection without any change in air
temperature.
Small air movement in cool or cold environments may be perceived as draught. If the air temperature is less than skin temperature it will significantly increase convective heat loss.
Physical activity also increases air movement, so air velocity
may be corrected to account for a person's level of physical
activity.
• Konduksi Perpindahan panas melalui kontak langsung material. Kalor lingkungan contohnya dari dinding kayu yang terkena panas matahari ke tubuh manusia melalui kulit.
• Konveksi Perpindahan
kalor dari udara lingkungan ke tubuh manusia melalui udara atau hembusan angin.
Konveksi ke tubuh manusia
dapat terjadi apabila udara
lebih hangat daripada kulit
manusia.
• Radiasi Pancaran kalor langsung ke tubuh
manusia dari sinar matahari, atau udara lingkungan.
• Evaporasi Penguapan dari tubuh manusia
melalui keringat menuju
udara tak jenuh.
Thermal comfort
Humidity
If water is heated and it evaporates to the surrounding environment, the resulting amount of water in the air will provide humidity.
Relative humidity is the ratio between the actual amount of water vapour in the air and the maximum amount of water vapour that the air can hold at that air temperature.
Relative humidity between 40% and 70% does not have a major impact on thermal comfort. In some offices, humidity is usually kept between 40-70% because of computers. However, in workplaces which are not air conditioned, or where the climatic conditions outdoors may influence the indoor thermal environment, relative humidity may be higher than 70% on warm or hot humid days. Humidity in indoor environments can vary greatly, and may be dependent on whether there are drying processes (paper mills, laundry etc) where steam is given off.
High humidity environments have a lot of vapour in the air, which prevents the evaporation of sweat from the skin. In hot environments, humidity is important because less sweat evaporates when humidity is high (80%+). The evaporation of sweat is the main method of heat loss in humans.
When vapour-impermeable PPE is worn, the humidity inside the garment increases as the wearer sweats because the sweat cannot evaporate. If an employee is wearing this type of PPE (eg asbestos or chemical protection suits etc) the humidity within the microclimate of the garment may be high.
Personal factors
Clothing insulation
• Hambatan termal dari pakaian ditentukan oleh daya tembus kain, kekakuan dan ketat atau longgarnya pakaian.
• Nilai 1 Clo setara dengan 0,155 m2 K/W atau setara dengan penggunaan satu stel jas lengkap dengan dasi.
• Kondisi pakaian ini memungkinkan seorang dalam keadaan istirahat untuk mendapatkan keseimbangan termal pada temperatur 21 °C dengan ventilasi berkecepatan udara 0,1 m/detik.
Work rate/metabolic heat
• Metabolisme Tubuh manusia selalu
memproduksi panas terus- menerus sebagai sebuah kehidupan. Sumber energi panas didapatkan dari
makanan dan minuman.
Thermal comfort checklist
Use the table below to help you identify whether there may be a risk of thermal discomfort to your employees. Please note that this is a basic checklist and does not replace an adequate thermal comfort risk assessment. Read the descriptions for each thermal comfort factor, and tick the appropriate box. If you tick two or more ‘YES’ boxes there may be a risk of thermal discomfort and you may need to carry out a more detailed risk assessment.
Factor Description
Air temperature
Does the air feel warm or hot?
Does the temperature in the workplace fluctuate during a normal working day?
Does the temperature in the workplace change a lot during hot or cold seasonal variations?
Radiant temperature
Is there a heat source in the environment?
Humidity
Is there any equipment that produces steam?
Is the workplace affected by external weather conditions?
Are your employees wearing PPE that is vapour impermeable?
Do your employees complain that the air is too dry?
Do your employees complain that the air is humid?
Air movement
Is cold or warm air blowing directly into the workspace?
Are employees complaining of draught?
Metabolic rate
Is work rate moderate to intensive in warm or hot conditions? Are employees sedentary in cool or cold environments?
PPE
Is PPE being worn that protects against harmful toxins, chemicals, asbestos, flames, extreme heat, etc?
Can employees make individual alterations to their clothing in response to the thermal environment?
Is respiratory protection being worn?
What your employees think
Do your employees think that there is a thermal comfort problem?
