Indoor environmental quality

Indoor environmental quality:
From the occupant point of view, the ideal situation is an indoor environment
that satisfies all occupants (i.e. they have no complaints) and does not
unnecessarily increase the risk or severity of illness or injury. Both the satisfaction
of people (comfort) and health status are influenced by numerous
factors: general well-being, mental drive, job satisfaction, technical competence,
career achievements, home/work interface, relationship with others,
personal circumstances, organizational matters, etc. and last but not least
environmental factors, such as
• IAQ: comprising odour, indoor air pollution, fresh air supply, etc.;
• thermal comfort: moisture, air velocity, temperature;
• acoustical quality: noise from outside, indoors, vibrations;
• visual or lighting quality: view, illuminance, luminance ratios, reflection;
• aesthetic quality.
Although there is rich scientific literature and the reports of several
national experiences on this subject, a uniform set of criteria for the countries
of Europe has not yet been defined.
Currently, in several standards and guidelines, human indoor environmental
requirements for spaces are expressed by physical and chemical
indicators (temperature, Decibel, Lux, CO concentration, etc.) (CEN, 1998;
ASHRAE, 2004a; ISO, 2005). Although required levels in those standards
and guidelines are met, it can be concluded from several studies that the
IEQ as experienced by occupants is not always acceptable and sometimes
is even unhealthy, causing health and comfort problems (Bluyssen et al.,
1995). This mismatch is due to several reasons:
• the relationship between objective measurement and human assessment
is not known for all physical/chemical parameters. No consensus model
is available for air quality. For light, recent findings show that brightness
of the surroundings is the key element and not only the illuminance
(Light & Health Research Foundation, 2002).
• even if established models for separate subjective issues exist [e.g. thermal
comfort (Fanger, 1972) and noise], the holistic effects of all separate
physical/chemical factors are still largely unknown.
Besides the physical/chemical indicators, other indicators are being
used such as the percentage of dissatisfied occupants, productivity numbers
(Clements-Croome, 2002), sick leave, estimated life expectations
(Carrothers et al., 1999) and even the number of deaths related to a BRI.
However, the determination and use of these indicators has not been documented
in guidelines or standards.
In several spaces (cars, space industry and buildings), health complaints
and comfort problems are strongly related to the available methods of ventilation.
This relation has been shown, for example, by the increased risk of
infectious disease transmission (recirculated air), sources in heating, ventilating
and air-conditioning (HVAC) systems causing an overall distribution
of unwanted pollutants (Bluyssen et al., 2003), and stagnant zones and
draught (insufficient ventilation effectiveness). Complaints are in general
related to air quality, thermal comfort and noise parameters.

ASHRAE Comfort Zones

ASHRAE Comfort Zones
Based on results of research conducted at Kansas State University and at other institutions,
ANSI/ASHRAE Standard 55-1992 specified winter and summer comfort zones to provide for the
selection of the indoor parameters for thermal comfort . This chart is based upon an
occupant activity level of 1.2 met (69.8 W/m2). For summer, typical clothing insulation is 0.5 clo,
that is, light slacks and short-sleeve shirt or comparable ensemble; there is no minimum air speed
that is necessary for thermal comfort. Standard 55-1992 recommended a summer comfort zone with
an effective boundary temperature ET*  73 to 79°F (22.5 to 26°C) at 68°F (20°C) wet-bulb as its
upper-slanting boundary and dew-point temperature 36°F (2.2°C) as its bottom flat boundary. If the
clothing insulation is 0.1 clo higher, the boundary temperatures both should be shifted 1°F (0.6°C)
lower. Rohles et al. (1974) and Spain (1986) suggested that the upper boundary of the summer
comfort zone can be extended to 85 or 86°F (30°C) ET* if the air velocity of the indoor air
can be increased to 200 fpm (1 m/ s) by a ceiling fan or other means.
The winter comfort zone is based upon a 0.9-clo insulation including heavy slacks, long-sleeve
shirt, and sweater or jacket at an air velocity of less than 30 fpm (0.15 m/s). Standard 55-1992 recommended
a winter comfort zone with an effective boundary temperature ET*  68 to 74°F (20 to
23.3°C) at 64°F (17.8°C) wet-bulb as its slanting upper boundary and at dew-point 36°F (2.2°C) as
its bottom flat boundary.
Indoor air parameters should be fairly uniform in order to avoid local discomfort. According to
Holzle et al., 75 to 89 percent of the subjects tested found the environment within this summer
comfort zone to be thermally acceptable.
ASHRAE comfort zones recommend only the optimal and boundary ET* for the determination
of the winter and summer indoor parameters. For clothing insulation, activity levels, and indoor air
velocities close to the values specified in Standard 55-1992, a wide range of indoor design conditions
are available.

INDOOR DESIGN CONDITIONS

INDOOR DESIGN CONDITIONS

Indoor design parameters are those that the air conditioning system influences directly to produce a

required conditioned indoor environment in buildings. They are shown below and grouped as follows:

1. Basic design parameters

_ Indoor air temperature and air movements

_ Indoor relative humidity

2. Indoor air quality

_ Air contaminants

_ Outdoor ventilation rate provided

_ Air cleanliness for processing

3. Specific design parameters

_ Sound level

_ Pressure differential between the space and surroundings

The indoor design parameters to be maintained in an air conditioned space are specified in the

design document and become the targets to be achieved during operation. In specifying the indoor

design parameters, the following points need to be considered:

1. Not all the parameters already mentioned need to be specified in every design project. Except

for the indoor air temperature which is always an indoor design parameter in comfort air conditioning,

it is necessary to specify only the parameters which are essential to the particular situation

concerned.

2. Even for process air conditioning systems, the thermal comfort of the workers should also be

considered. Therefore, the indoor design parameters regarding health and thermal comfort for the

occupants form the basis of design criteria.

3. When one is specifying indoor design parameters, economic strategies of initial investment

and energy consumption of the HVAC&R systems must be carefully investigated. Design criteria

should not be set too high or too low. If the design criteria are too high, the result will be an excessively

high investment and energy cost. Design criteria that are too low may produce a poor indoor

air quality, resulting in complaints from the occupants, causing low-quality products, and possibly

leading to expensive system alternations.

4. Each specified indoor design parameter is usually associated with a tolerance indicated

as a _ sign, or as an upper or lower limit. Sometimes there is a traditional tolerance understood

by both the designers and the owners of the building. For instance, although the summer

indoor design temperature of a comfort air conditioning system is specified at 75 or 78°F

(23.9 or 25.6°C), in practice a tolerance of _2–3°F (_1.1 – 1.7°C) is often considered

acceptable.

5. In process air conditioning systems, sometimes a stable indoor environment is more important

than the absolute value of the indoor parameter to be maintained. For example, it may not be necessary

to maintain 68°F (20°C) for all areas in precision machinery manufacturing. More often, a

72°F (22.2°C) or even a still higher indoor temperature with appropriate tolerance will be more

suitable and economical.

AIR CONDITIONING

AIR CONDITIONING
Air conditioning is a combined process that performs many functions simultaneously. It conditions
the air, transports it, and introduces it to the conditioned space. It provides heating and cooling from
its central plant or rooftop units. It also controls and maintains the temperature, humidity, air
movement, air cleanliness, sound level, and pressure differential in a space within predetermined
The term HVAC&R is an abbreviation of heating, ventilating, air conditioning, and refrigerating.
The combination of processes in this commonly adopted term is equivalent to the current definition
of air conditioning. Because all these individual component processes were developed prior to the
more complete concept of air conditioning, the term HVAC&R is often used by the industry.
COMFORT AND PROCESSING AIR CONDITIONING
SYSTEMS
Air Conditioning Systems
An air conditioning, or HVAC&R, system is composed of components and equipment arranged in
sequence to condition the air, to transport it to the conditioned space, and to control the indoor environmental
parameters of a specific space within required limits.
Most air conditioning systems perform the following functions:
1. Provide the cooling and heating energy required
2. Condition the supply air, that is, heat or cool, humidify or dehumidify, clean and purify, and
attenuate any objectionable noise produced by the HVAC&R equipment
3. Distribute the conditioned air, containing sufficient outdoor air, to the conditioned space
4. Control and maintain the indoor environmental parameters–such as temperature, humidity,
cleanliness, air movement, sound level, and pressure differential between the conditioned space
and surroundings—within predetermined limits
Parameters such as the size and the occupancy of the conditioned space, the indoor environmental
parameters to be controlled, the quality and the effectiveness of control, and the cost involved determine
the various types and arrangements of components used to provide appropriate characteristics.
Air conditioning systems can be classified according to their applications as (1) comfort air
conditioning systems and (2) process air conditioning systems.
Comfort Air Conditioning Systems
Comfort air conditioning systems provide occupants with a comfortable and healthy indoor environment
in which to carry out their activities. The various sectors of the economy using comfort air
conditioning systems are as follows:
1. The commercial sector includes office buildings, supermarkets, department stores, shopping
centers, restaurants, and others. Many high-rise office buildings, including such structures as the
World Trade Center in New York City and the Sears Tower in Chicago, use complicated air conditioning
systems to satisfy multiple-tenant requirements. In light commercial buildings, the air conditioning
system serves the conditioned space of only a single-zone or comparatively smaller area.
For shopping malls and restaurants, air conditioning is necessary to attract customers.
2. The institutional sector includes such applications as schools, colleges, universities, libraries,
museums, indoor stadiums, cinemas, theaters, concert halls, and recreation centers. For example,
one of the large indoor stadiums, the Superdome in New Orleans, Louisiana, can seat 78,000 people.
3. The residential and lodging sector consists of hotels, motels, apartment houses, and private
homes. Many systems serving the lodging industry and apartment houses are operated continuously,
on a 24-hour, 7-day-a-week schedule, since they can be occupied at any time.
4. The health care sector encompasses hospitals, nursing homes, and convalescent care facilities.
Special air filters are generally used in hospitals to remove bacteria and particulates of submicrometer
size from areas such as operating rooms, nurseries, and intensive care units. The relative humidity in a
general clinical area is often maintained at a minimum of 30 percent in winter.
5. The transportation sector includes aircraft, automobiles, railroad cars, buses, and cruising
ships. Passengers increasingly demand ease and environmental comfort, especially for longdistance
travel. Modern airplanes flying at high altitudes may require a pressure differential of
about 5 psi between the cabin and the outside atmosphere. According to the Commercial Buildings
Characteristics (1994), in 1992 in the United States, among 4,806,000 commercial buildings having
67.876 billion ft2 (6.31 billion m2) of floor area, 84.0 percent were cooled, and 91.3 percent
were heated.
Process Air Conditioning Systems
Process air conditioning systems provide needed indoor environmental control for manufacturing,
product storage, or other research and development processes. The following areas are examples of
process air conditioning systems:
1. In textile mills, natural fibers and manufactured fibers are hygroscopic. Proper control of humidity
increases the strength of the yarn and fabric during processing. For many textile manufacturing
processes, too high a value for the space relative humidity can cause problems in the spinning
process. On the other hand, a lower relative humidity may induce static electricity that is harmful
for the production processes.
2. Many electronic products require clean rooms for manufacturing such things as integrated circuits,
since their quality is adversely affected by airborne particles. Relative-humidity control is
also needed to prevent corrosion and condensation and to eliminate static electricity. Temperature
control maintains materials and instruments at stable condition and is also required for workers who
wear dust-free garments. For example, a class 100 clean room in an electronic factory requires a
temperature of 72 _ 2°F (22.2 _ 1.1°C), a relative humidity at 45 _ 5 percent, and a count of dust
particles of 0.5-_m (1.97 _ 10_5 in.) diameter or larger not to exceed 100 particles/ ft3 (3531 particles
/m3).
3. Precision manufacturers always need precise temperature control during production of precision
instruments, tools, and equipment. Bausch and Lomb successfully constructed a constanttemperature
control room of 68 _ 0.1°F (20 _ 0.56°C) to produce light grating products in the
1950s.
4. Pharmaceutical products require temperature, humidity, and air cleanliness control. For instance,
liver extracts require a temperature of 75°F (23.9°C) and a relative humidity of 35 percent.
If the temperature exceeds 80°F (26.7°C), the extracts tend to deteriorate. High-efficiency air filters
must be installed for most of the areas in pharmaceutical factories to prevent contamination.
5. Modern refrigerated warehouses not only store commodities in coolers at temperatures of
27 to 32°F (_2.8 to 0°C) and frozen foods at _10 to _20°F (_23 to _29°C), but also provide
relative-humidity control for perishable foods between 90 and 100 percent. Refrigerated storage
is used to prevent deterioration. Temperature control can be performed by refrigeration systems
only, but the simultaneous control of both temperature and relative humidity in the space can only
be performed by process air conditioning systems.

HISTORICAL DEVELOPMENT

HISTORICAL DEVELOPMENT

The historical development of air conditioning can be summarized briefly.

Central Air Conditioning Systems

As part of a heating system using fans and coils, the first rudimentary ice system in the United

States, designed by McKin, Mead, and White, was installed in New York City’s Madison Square

Garden in 1880. The system delivered air at openings under the seats. In the 1890s, a leading consulting

engineer in New York City, Alfred R. Wolf, used ice at the outside air intake of the heating

and ventilating system in Carnegie Hall. Another central ice system in the 1890s was installed in

the Auditorium Hotel in Chicago by Buffalo Forge Company of Buffalo, New York. Early central

heating and ventilating systems used steam-engine-driven fans. The mixture of outdoor air and return

air was discharged into a chamber. In the top part of the chamber, pipe coils heat the mixture

with steam. In the bottom part is a bypass passage with damper to mix conditioned air and bypass

air according to the requirements.

Air conditioning was first systematically developed by Willis H. Carrier, who is recognized as

the father of air conditioning. In 1902, Carrier discovered the relationship between temperature and

humidity and how to control them. In 1904, he developed the air washer, a chamber installed with

several banks of water sprays for air humidification and cleaning. His method of temperature and

humidity regulation, achieved by controlling the dew point of supply air, is still used in many industrial

applications, such as lithographic printing plants and textile mills.

Perhaps the first air-conditioned office was the Larkin Administration Building, designed by

Frank L. Wright and completed in 1906. Ducts handled air that was drawn in and exhausted at roof

level. Wright specified a refrigeration plant which distributed 10°C cooling water to air-cooling

coils in air-handling systems.

The U.S. Capitol was air-conditioned by 1929. Conditioned air was supplied from overhead

diffusers to maintain a temperature of 75°F (23.9°C) and a relative humidity of 40 percent during

summer, and 80°F (26.7°C) and 50 percent during winter. The volume of supply air was controlled

by a pressure regulator to prevent cold drafts in the occupied zone.

Perhaps the first fully air conditioned office building was the Milan Building in San Antonio,

Texas, which was designed by George Willis in 1928. This air conditioning system consisted of one

centralized plant to serve the lower floors and many small units to serve the top office floors.

In 1937, Carrier developed the conduit induction system for multiroom buildings, in which recirculation

of space air is induced through a heating/cooling coil by a high-velocity discharging

airstream. This system supplies only a limited amount of outdoor air for the occupants.

The variable-air-volume (VAV) systems reduce the volume flow rate of supply air at reduced loads

instead of varying the supply air temperature as in constant-volume systems. These systems were introduced

in the early 1950s and gained wide acceptance after the energy crisis of 1973 as a result of

their lower energy consumption in comparison with constant-volume systems. With many variations,

VAV systems are in common use for new high-rise office buildings in the United States today.

Because of the rapid development of space technology after the 1960s, air conditioning systems

for clean rooms were developed into sophisticated arrangements with extremely effective air

filters. Central air conditioning systems always will provide a more precisely controlled, healthy,

and safe indoor environment for high-rise buildings, large commercial complexes, and precisionmanufacturing

areas.

Unitary Packaged Systems

The first room cooler developed by Frigidaire was installed about in 1928 or 1929, and the “Atmospheric

Cabinet” developed by the Carrier Engineering Company was first installed in May 1931.

The first self-contained room air conditioner was developed by General Electric in 1930. It was a

console-type unit with a hermetically sealed motor-compressor (an arrangement in which the motor

and compressor are encased together to reduce the leakage of refrigerant) and water-cooled condenser,

using sulfur dioxide as the refrigerant. Thirty of this type of room air conditioner, were built

and sold in 1931.

Early room air conditioners were rather bulky and heavy. They also required a drainage connection

for the municipal water used for condensing. During the postwar period the air-cooled model

was developed. It used outdoor air to absorb condensing heat, and the size and weight were greatly

reduced. Annual sales of room air conditioners have exceeded 100,000 units since 1950.

Self-contained unitary packages for commercial applications, initially called store coolers, were

introduced by the Airtemp Division of Chrysler Corporation in 1936. The early models had a refrigeration

capacity of 3 to 5 tons and used a water-cooled condenser. Air-cooled unitary packages

gained wide acceptance in the 1950s, and many were split systems incorporating an indoor air handler

and an outdoor condensing unit.

Packaged units have been developed since the 1950s, from indoor to rooftops, from constantvolume

to variable-air-volume, and from few to many functions. Currently, packaged units enjoy

better performance and efficiency with better control of capacity to match the space load. Computerized

direct digital control, one of the important reasons for this improvement, places unitary packaged

systems in a better position to compete with central hydronic systems.

Refrigeration Systems

In 1844, Dr. John Gorrie designed the first commercial reciprocating refrigerating machine in the

United States. The hermetically sealed motor-compressor was first developed by General Electric

Company for domestic refrigerators and sold in 1924.

Carrier invented the first open-type gear-driven factory-assembled, packaged centrifugal chiller

in 1922 in which the compressor was manufactured in Germany; and the hermetic centrifugal

chiller, with a hermetically sealed motor-compressor assembly, in 1934. The direct-driven hermetic

centrifugal chiller was introduced in 1938 by The Trane Company. Up to 1937, the capacity of centrifugal

chillers had increased to 700 tons.

During the 1930s, one of the outstanding developments in refrigeration was the discovery by

Midgely and Hene of the nontoxic, nonflammable, fluorinated hydrocarbon refrigerant family

called Freon in 1931. Refrigerant-11 and refrigerant-12, the chlorofluorocarbons (CFCs), became

widely adopted commercial products in reciprocating and centrifugal compressors. Now, new refrigerants

have been developed by chemical manufacturers such as DuPont to replace CFCs, so as

to prevent the depletion of the ozone layer.

The first aqueous-ammonia absorption refrigeration system was invented in 1815 in Europe. In

1940, Servel introduced a unit using water as refrigerant and lithium bromide as the absorbing solution.

The capacities of these units ranged from 15 to 35 tons (52 to 123 kW). Not until 1945 did

Carrier introduce the first large commercial lithium bromide absorption chillers. These units were

developed with 100 to 700 tons (352 to 2460 kW) of capacity, using low-pressure steam as the heat

source.

Positive-displacement screw compressors have been developed in the United States since the

1950s and scroll compressors since the 1970s because of their higher efficiency and smoother rotary

motion than reciprocating compressors. Now, the scroll compressors gradually replace the reciprocating

compressors in small and medium-size refrigeration systems. Another trend is the development of

more energy-efficient centrifugal and absorption chillers for energy conservation. The energy consumption

per ton of refrigeration of a new centrifugal chiller dropped from 0.80 kW/ton (4.4 COPref)

in the late 1970s to 0.50 kW/ton (7.0 COPref) in the 1990s. A series of rotary motion refrigeration