Ventilation (architecture)
An air handling unit is ud 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 "changing" or replacing air in any space to provide high indoor air quality (i.e. to control temperature, replenish oxygen, or remove moisture, odors, smoke, heat, dust, airborne bacteria, and carbon dioxide). Ventilation is ud to remove unpleasant smells and excessive moisture, introduce outside air, to keep interior building air circulating, and to prevent stagnation of the interior air.他陶醉了
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]
"Mechanical" or "forced" ventilation is ud 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 grea (e 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 noi level. If ducting for the fans traver 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 purpo of reducing the perceived temperature becau of evaporation of perspiration on the skin of the occupants. Becau hot air ris, ceiling fans may be ud 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 u of a fan or other mechanical system. It can be achieved with openable wi
ndows 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 ri 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. The systems u 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 ud as backups. Air-side economizers perform the same function as natural ventilation, but u mechanical systems' fans, ducts, dampers, and control systems
to introduce and distribute cool outdoor air when appropriate.
edit Definition
Ventilation is the intentional movement of air from outside a building to the inside. Ventilation air, as defined in ASHRAE[2] and the ASHRAE Handbook,[3] is that air ud for providing acceptable indoor air quality. It mustn't be confud 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 cau harm to the occupants of the building. Movement of air between indoor spaces, and not the outside, is called transfer air.
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edit An example of clod ventilation婚庆网
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 for CII buildings, or for low-ri residential buildings, or
similar standards.
edit Necessity
When people or animals are prent 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 (e stack effect) or the u
of deliberate natural ventilation strategies. Advanced air filtration and treatment process such as scrubbing, can provide ventilation air by cleaning and recirculating a proportion of the air inside a building.
edit 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.成长的力量
▪Natural ventilation occurs when the air in a space is
changed with outdoor air without the u of mechanical
systems, such as a fan. Most often natural ventilation is
乖乖熊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 bament or other below ground structure. Allowing outside
air into a cooler below ground space will cau problems with humidity and condensation.
▪Mixed Mode Ventilation or Hybrid ventilation: utilis both mechanical and natural ventilation process. The mechanical and natural components may be ud in conjunction with each other or parately 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 ud to increa the overall ventilation rate so that the desired
炒股基本知识internal conditions are met. Alternatively the mechanical
component may be ud as a control measure to regulate the natural ventilation process, for example, to restrict the air change rate during periods of high wind speeds.
office97▪Infiltration is parate from ventilation, but is often
ud to provide ventilation air.
edit Ventilation rate
The ventilation rate, for CII buildings, is normally expresd by the volumetric flowrate of outside air being introduced to the building. The typical units ud are cubic feet per minute (CFM) or liters per cond (L/s). The ventilation rate can also be expresd on a per person or per unit floor area basis, such as CFM/p or CFM/ft², 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
怎样快速减大肚子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 hou to 1.11 to 1.47 in a looly insulated hou.[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, the standards have changed to an addition of 3
CFM/100 sq. ft. (15 l/s/100 sq. m.) to the 7.5 CFM/person (3.5 L/s/person) standard.[5]
edit Ventilation standards
▪In 1973, in respon to the 1973 oil crisis and
conrvation concerns, ASHRAE Standards 62-73 and 62-81)
