Профессиональное развитие будущих инженеров-строителей средствами иностранного языка: Лексический практикум по английскому языку. Трубникова Н.В. - 59 стр.

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and precool the incoming outside air to save energy. Such heat exchangers are

around 55% efficient, which is not as good as recirculation.

Humidification

In winter, incoming fresh air with a low moisture content can be humidi-

fied by steam injection, banks of water sprays, evaporation from a heated water

tank, a spinning disc atomizer or a soaked porous plastic sponge. A preheater

low-pressure hot-water coil usually precedes the humidifier to increase the wa-

ter-holding capacity of the air. This also offsets the reduction in temperature of

the air owing to transference of some of its sensible heat into latent energy,

which is needed for the evaporation process.

A temperature sensor in the humidified air is used as a dew-point control

by modulating the preheater power to produce air at a consistent moisture con-

tent throughout the winter. For comfort air conditioning, the room percentage

saturation will be 50% ± 10%. This permits a wide range of humidifier per-

formance characteristics.

The humidification process often follows a line of constant wet-bulb tem-

perature. The water spray temperature is varied to alter the slope of the line on

the psychrometric chart. The preheating and humidification stages have been

omitted, as close humidity control is deemed not to be needed in this case.

Some reheating of the cooled and dehumidified air will be necessary be-

cause of practical limitations of cooling coil design. Part of the boiler plant re-

mains operational during the summer. Reheating can be avoided by using a

cooling coil bypass which mixes air and air to produce the correct supply condition.

Air temperature profile

The recommended upper limit for the room environmental temperature

for normally occupied buildings is 27°C (CIBSE, 1986, Section A8). The ex-

ternal design air temperature for comfort in offices in London (CIBSE, 1986,

table A2.22) may be chosen as 29 °C d.b., 20 °C w.b. Higher outdoor air tem-

peratures occur. The indoor limit of 27 °C will be exceeded in naturally venti-

lated buildings in the United Kingdom and in warmer locations (Chadderton,

1997a, chapter 3). The elevation of indoor temperature above that of the out-

door air is caused by a combination of the infiltration of external air, solar ra-