Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Tham khảo tài liệu 'refrigeration and air conditioning 3e episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 234 Refrigeration and Air-Conditioning Figure 23.5 Basic CIBSE psychrometric chart Courtesy of the Chartered Institution of Building Services Engineers A further property which is shown on the psychrometric chart is the specific volume of the mixture measured in cubic metres per kilogram. This appears as a series of diagonal lines at intervals of 0.01 m3. 23.7 Effects on human comfort The human body takes in chemical energy as food and drink and oxygen and consumes these to provide the energy of the metabolism. Some mechanical work may be done but the greater proportion is liberated as heat at a rate between 90 W when resting and 440 W when doing heavy work. A little of this is lost by radiation if the surrounding surfaces are cold and some as sensible heat by convection from the skin. The remainder is taken up as latent heat of moisture from the respiratory tissues and perspiration from the skin see Table 23.2 . Radiant loss will be very small if the subject is clothed and is ignored in this table. Convective heat loss will depend on the area of skin exposed the air speed and the temperature difference between the skin and the Figure 23.6 Psychrometric chart Air and water vapour mixtures 235 236 Refrigeration and Air-Conditioning Dry bulb Figure 23.7 Reading the CIBSE psychrometric chart ambient. As the dry bulb approaches body temperature 36.9 C the possible convective loss will diminish to zero. At the same time loss by latent heat must increase to keep the body cooled. This too must diminish to zero when the wet bulb reaches 36.9 C. In practice the human body can exist in dry bulb temperatures well above blood temperature providing the wet bulb is low enough to permit evaporation. The limiting factor is therefore one of wet bulb rather than dry bulb temperature and the closer the upper limits are approached the less heat can be rejected and so the less work can be done. 23.8 Climatic conditions Figure 23.8 shows the maximum climatic conditions in different .
