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41
cessive heat loss from the body to the environment, as would be experienced
during occupation of a glasshouse through seasonal variations.
4). Percentage saturation should be in the range 40-70%.
5). Maximum air velocity at the neck should be 0.1 m/s for a moving-
air temperature of 20 °C d.b. Both hot and cold draughts are to be avoided.
Data are available for other temperature and velocity combinations.
6).Variable air velocity and direction are preferable to unchanging values
of these variables. This is achieved by changes in natural ventilation from pre-
vailing wind, movement of people around the building, on-off or high-low
thermostatic operation of fan-assisted heaters or variable-volume air-
conditioning systems.
7). The minimum quantity of fresh air for room use that will remove
probable contamination from smoking, for example, is 10.41/s per person.
8). Mechanical ventilation systems should provide at least four air
changes per hour to avoid stagnant pockets and ensure good circulation.
9). Incoming fresh air can be filtered to maintain a clean dust-free internal
environment.
10). The difference between room air temperatures at head and foot levels
should be no more than 1 °C.
11). Ventilation air quantity саn be determined by some other controlling
parameter: removal of smoke, fumes or dust, solar or other heat gains and dilu-
tion of noxious fumes.
Block B
Lexical exercises
I. Answer the questions:
1. Where are thermocouples used? What are their advantages?
2. How can heat leakages due to inadequate thermal insulation and
damaged pipes or cables be detected?
3. What is the function of environmental temperature?
4. Explain the meaning of the terms «olf» and «decipol». How are olf
and decipol used in the design of ventilation systems?
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