Ventilation-system-通风系统-英文-百科

Ventilation (architecture)

An

air handling unit

is used for the heating and cooling of air in a central location

(click on image for legend).

Ventilating

(the

V

in

HVAC

) is the process of

indoor air quality

(i.e. to control temperature, replenish oxygen, or remove moisture, odors, smoke, heat,

dust, airborne bacteria, and carbon dioxide). Ventilation is used to remove unpleasant smells and excessive

moisture, introduce outside air, to keep interior building air circulating, and to prevent stagnation of the

interior air.

Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It

is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for

ventilating a building may be divided into

mechanical/forced

and

natural

types.

[1]

is used to control indoor air quality. Excess

humidity

, odors, and

contaminants can often be controlled via dilution or replacement with outside air. However, in humid

climates much energy is required to remove excess moisture from ventilation air.

Kitchens

and bathrooms typically have mechanical exhaust to control odors and sometimes humidity.

Kitchens have additional problems to deal with such as smoke and grease (see

kitchen ventilation

). Factors

in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent

size) and noise level. If ducting for the fans traverse unheated space (e.g., an attic), the ducting should be

insulated as well to prevent condensation on the ducting. Direct drive fans are available for many

applications, and can reduce maintenance needs.

Ceiling

fans

and table/floor fans circulate air within a room for the purpose of reducing the perceived

temperature because of evaporation of perspiration on the skin of the occupants. Because hot air rises,

ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the

ceiling to the floor. Ceiling fans do not provide ventilation as defined as the introduction of outside air.

Natural ventilation

is the ventilation of a building with outside air without the use of a fan or other

mechanical system. It can be achieved with openable windows or

trickle vents

when the spaces to ventilate

are small and the architecture permits. In more complex systems warm air in the building can be allowed to

rise and flow out upper openings to the outside (

stack effect

) thus forcing cool outside air to be drawn into

the building naturally through openings in the lower areas. These systems use very little energy but care

must be taken to ensure the occupants' comfort. In warm or humid months, in many climates, maintaining

thermal comfort

solely via natural ventilation may not be possible so conventional

air conditioning

systems

are used as backups. Air-side

economizers

perform the same function as natural ventilation, but use

mechanical systems' fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air

when appropriate.

Contents

1 Definition

1.1 An example of closed

2 Necessity

3 Types of ventilation

4 Ventilation rate

5 Ventilation standards

6 Ventilation equipment

7 Natural ventilation

8 Demand- controlled ventilation

9 Local exhaust ventilation

10 Ventilation and combustion

11 Smoking and ventilation

12 Problems

13 Air Quality Procedures

14 See also

15 References and notes

16 External links

ventilation

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Definition

Ventilation

is the intentional movement of

air

from outside a building to the inside.

Ventilation air

, as

defined in

ASHRAE

Standard 62.1

[2]

and the

ASHRAE Handbook

,

[3]

is that air used for providing acceptable

indoor air quality

. It mustn't be confused with

vents

or

flues

; which mean the exhausts of clothes dryers and

combustion equipment such as

water heaters

,

boilers

, fireplaces, and wood stoves. The vents or flues carry

the products of combustion which have to be expelled from the building in a way which does not cause

harm to the occupants of the building. Movement of air between indoor spaces, and not the outside, is

called

transfer air

.

This article

may need to be rewritten entirely to comply with Wikipedia's

quality standards

, as Reason is explained in the talk page.

You can help

.

The

discussion page

may contain suggestions.

(May 2010)

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An example of closed ventilation

In commercial, industrial, and institutional (CII) buildings, and modern

jet aircraft

, return air is often

recirculated to the air handling unit. A portion of the supply air is normally exfiltrated through the building

envelope or exhausted from the building (e.g.,

bathroom

or

kitchen

exhaust) and is replaced by outside air

introduced into the return air stream. The rate of ventilation air required, most often provided by this

mechanically-induced outside air, is often determined from

ASHRAE Standard 62.1

for CII buildings, or

62.2

for low-rise residential buildings, or similar standards.

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Necessity

When people or animals are present in buildings, ventilation air is necessary to dilute odors and limit the

concentration of

carbon dioxide

and airborne pollutants such as dust, smoke and volatile organic

compounds (VOCs). Ventilation air is often delivered to spaces by mechanical systems which may also heat,

cool, humidify and dehumidify the space. Air movement into buildings can occur due to uncontrolled

infiltration

of outside air through the building fabric (see

stack effect

) or the use of deliberate

natural

ventilation

strategies. Advanced air filtration and treatment processes such as

scrubbing

, can provide

ventilation air by cleaning and recirculating a proportion of the air inside a building.

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Types of ventilation

?

Mechanical or forced ventilation

: through an

air handling unit

or direct injection to a space by a

fan

. A local exhaust fan can enhance infiltration or natural ventilation, thus increasing the ventilation

air

flow rate

.

?

Natural ventilation

occurs when the air in a space is changed with outdoor air without the use of

mechanical systems, such as a fan. Most often natural ventilation is assured through operable windows

but it can also be achieved through temperature and pressure differences between spaces. Open

windows or vents are not a good choice for ventilating a basement or other below ground structure.

Allowing outside air into a cooler below ground space will cause problems with humidity and

condensation.

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Mixed Mode Ventilation

or

Hybrid ventilation

: utilises both mechanical and natural ventilation

processes. The mechanical and natural components may be used in conjunction with each other or

separately at different times of day. The natural component, sometimes subject to unpredictable

external weather conditions may not always be adequate to ventilate the desired space. The mechanical

component is then used to increase the overall ventilation rate so that the desired internal conditions

are met. Alternatively the mechanical component may be used as a control measure to regulate the

natural ventilation process, for example, to restrict the air change rate during periods of high wind

speeds.

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Infiltration

is separate from

ventilation

, but is often used to provide

ventilation air

.

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Ventilation rate

The

ventilation rate

, for CII buildings, is normally expressed by the volumetric flowrate of outside air being

introduced to the building. The typical units used are cubic feet per minute (CFM) or liters per second (L/s).

The ventilation rate can also be expressed on a per person or per unit floor area basis, such as CFM/p or

CFM/ft

?

, or as

air changes per hour

.

For residential buildings, which mostly rely on

infiltration

for meeting their ventilation needs, the common

ventilation rate measure is the number of times the whole interior volume of air is replaced per hour, and is

called

air changes per hour

(

I

or

ACH

; units of 1/h). During the winter, ACH may range from 0.50 to 0.41 in

a tightly insulated house to 1.11 to 1.47 in a loosely insulated house.

[4]

ASHRAE now recommends ventilation rates dependent upon floor area, as a revision to the 62-2001

standard whereas the minimum ACH was 0.35, but no less than 15 CFM/person (7.1 L/s/person). As of 2003,