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Comfort and Health Indoor
Environmental Quality
Comfort involves: control of temperature, humidity, air mo
radiant sources interacting with the occupants
Not everyone can be made comfortable by one set of cond
Oder, dust, noise, and vibration are additional human comf
Nonenvironmental factors such as dress and the activity le
occupants must be considered
A well-designed HVAC system manages to keep these vari
within specified limits set by customer, building codes, and
engineering judgment
Engineers are challenged to utilize all of the available infor
tools to design systems that provide a comfortable environ
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Comfort PHYSIOLOGICAL consideration
The amount of heat generated and dissipated by the huma
considerably with activity, age, size, and gender
The body has a complex regulating system acting to maint
body temperature of about 98.6 f (36.9 C)
Thermal balance with environment = comfortable
ANSI/ASHRAE standard 55-1992 specifies the thermal Env
Conditions for Human Occupancy as conditions in which 8
of the occupants will find the environment thermally accep
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Comfort PHYSIOLOGICAL consideration
The environmental factors that affects thermal comfort are
The dry bulb temperature of the surrounding air
The humidity of the surrounding air
The relative velocity of the surrounding air
The temperature of any surfaces that can directly view
the body and thus exchange radiation
The personal variables that influence thermal comfort areclothing
Animal and human body temperatures are controlled by a
that involves metabolism, blood circulation near the surfac
respiration, and heat and mass transfer from the skin
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Comfort PHYSIOLOGICAL consideration
The energy generated by a person’s metabolism varies wit
Met is a unit to express the the metabolic rate per unit of barea 1 met = 18.4 Btu/(hr-ft 2 ) (58.2 w/m 2 )
The average adult is assumed to have an effective surface
transfer of 19.6 ft 2 (1.82 m 2 ) and will dissipate approximate
(106 W)
Clothing insulation is described as a single equivalent un
over the whole body
Clo is a unit for clothing insulation 1 clo = 0.88 (F-ft2-hr)/B
C)/W]
A heavy two-piece business suit with accessories has an i
value of about 1 clo, whereas a pair of shorts has about 0.
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Environmental comfort indices
Temperature: is easily measured as air or dry bulb tempera
Humidity: can be described, for a given pressure and dry btemperature
Air motion: can be determined from measurement or predi
theories of fluid mechanics
Radiant exchange: between person and surroundings
Surroundings do not surround a person but occur on osides
Computation involves the angle factor or configuration
The basic index used to describe the radiative conditio
the mean radiant temperature
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Environmental comfort indices
Vernon ’ s globe thermometer is the most common instrume
determine the mean radiant temperature
The mean radiant temperature can calculated as:
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Environmental comfort indices
Other indices have been developed to simplify description o
thermal environment and to take in account the combined e
or more factors
The Effective Temperature: i s the temperature of an environ
relative humidity that results in the same total heat loss from
in the actual environment. It combines the humidity and the
into single index
The Operative Temperature: is the average of the mean radiaambient air temperature
The humid Operative temperature: is the temperature of a u
environment at 100% relative humidity in which a person los
total amount of heat from the skin as in the actual environm
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Environmental comfort indices
The Heat Stress Index: is the ratio of the total evaporative he
required for thermal equilibrium to the maximum evaporativ
possible for the environment, multiplied by 100, for steady-s
conditions, and with the skin temperature held constant at 9
The Wet Bulb Globe Temperature:
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Environmental comfort indices
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comfort conditions
ASHRAE sensation Scale
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comfort conditions
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comfort conditions
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comfort conditions
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comfort conditions
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comfort conditions
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The basic concern of iaq
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Common contaminants
Carbon Dioxide CO 2
Carbon Monoxide (Co)
Sulfur oxides
Nitrous oxides
Radon
Volatile Organic Compounds (VOCs)
Mycotoxins (Mold Poisons)
Particulate Matter
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METHODS TO CONTROL HUMIDITY
Humidity is a significant parameter in comfort
Low relative humidity and the dry effect on nose and bronchial linings
increased incidence of disease
High relative humidity encourages condensation and growth of harmfu
such as mold
Indoor air relative humidity must be kept around 50%
Moisture must be removed (dehumidification) when cooling and added(humidification) when heating
The condensed liquid should not be blown into the supply duct
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METHODS TO CONTROL HUMIDITY
Methods to control humidity:
Lower the supply temperature low enough to remove the required a
moisture and then reheat that air back to a temperature required to
space cooling load
Reduce fan speed (reduce air flow) or bypass some of air around the
Use surface or liquid desiccants to remove water chemically from hu
makeup or recirculated air. Desiccants are particularly useful in HVA
where:
When heating steam should be injected in air stream rather than sprayi
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METHODS TO CONTROL contaminants
Four methods to control gaseous or particulate contaminants and main
Source elimination or modification
Use of outdoor air
Space air distribution
Air cleaning
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sources Elimination or modificatio
The most effective method for reducing contaminant- operates directl
this method specifies exactly what building materials and furnishings a
allowed in the buildings
Design and construction should be such that water can not condense o
building
Elimination of smoking within the buildingNo paints, solvents, cleaners, and volatile compounds within the buildi
outdoor intake
Cleanup of mold and fungus
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use of outdoor air
Outdoor air is use dilute
contaminants within a space
Supply air is the air delivered to theconditioned
Ventilation air is the portion of
supply air that is outdoor air plus
any recirculated air that has been
treated for the purpose of maintain
acceptable IAQ
Makeup air is outdoor air supplied
to replace exhaust air and
exfiltration
Infiltration and exfiltration air
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use of outdoor air
The contaminant concentration in space can be calculated as
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use of outdoor air
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use of outdoor air
Occupied Zone is the region within
an occupied space between the
floor and 72 inch (1800mm) above
the floor and more than 2 ft (600
mm) from the wall or fixed air –
conditioning equipment
Occupied Zone must be maintained
at a nearly uniform condition.
Some fraction S of the supply air
bypasses and does not enter the
occupied zone
Effectiveness Eoa is the fraction of
outdoor air entering the system
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use of outdoor air
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use of outdoor air
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Indoor Air quality procedure
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Indoor Air quality procedure
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Indoor Air quality procedure
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filtering: particulate removal
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filtering: particulate removal
Efficiency measures the ability of the air cleaner
to remove particulate matter from an airstream
(Fig 4-8)
The smaller particles are the most difficult tofilter
The air-flow resistance is the loss in total
pressure at a given flow rate
Air flow resistance is an important factor in
operating costs for the system since it is directlyrelated to fan energy requirements
The pressure loss at any required rate of flow Q
can be determined by
Where the subscript r stands for rated conditions
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filtering: particulate removal
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filtering: particulate removal
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filtering: particulate removal
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filtering: particulate removal
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filtering: particulate removal
filtering: particulate removal
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