VENTILATION NATURAL VENTILATION FACTORS AFFECTING NATURAL VENTILATION Natural Ventilation Design Strategies Types of natural ventilation Stack Effect COURTYARD EFFECT PASSIVE COOLING TECHNIQUES Roof Pond MECHANICAL VENTILATION TYPES OF MECHANICAL VENTILATION SYSTEMS NATURAL INLET & MECH. EXTRACT MECHANICAL INLET & NATURAL EXTRACT Plenum System TYPES OF PLENUM SYSTEM NEED OF AIR CONDITIONING. SYSTEMS OF AIR CONDITIONING

1. HVAC SYSTEM
SUB : AD VIII
GROUP : OMKAR S. SHIVEKAR
:RAJESHWARI S PARAB
:BHAGYASHREE KHANDARE

2. VENTILATION
• Ventilation is the process of changing or replacing air in any
space to control temperature or remove any combination of
moisture, odors, smoke, heat, dust, airborne bacteria, or carbon
dioxide, and to replenish oxygen.
• Ventilation includes both the exchange of air with the outside as
well as circulation of air within the building.
• "Mechanical" or "forced" ventilation
is provided by an air handler and used
to control indoor air quality.
• Excess humidity, odors, and
contaminants can often be controlled
by replacement with outside air.
In humid climates much energy is
required to remove excess moisture
from ventilation air.

3. • 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.
• An important component of
natural ventilation is air changes
per hour: the rate of ventilation
through a room with respect to its
volume. For example, six air
changes per hour means that the
entire volume of the space is 10
MIN
• For human comfort, a minimum of
four air changes per hour is usually
targeted.

4. NATURALVENTILATION
• Natural ventilation is the process of supplying air to and removing
air from an indoor space without using mechanical systems. It refers
to the flow of external air to an indoor space as a result of pressure
differences arising from natural forces.
• Outdoor breezes creates air movement through the house interior by
“Push – Pull” effect of positive air pressure on the windward side
and negative pressure (suction) on the leeward side.
• To achieve good natural ventilation, openings should be provided
on opposite side.
• Natural ventilation also can be achieved by designing tall spaces in
building called as stacks.

5. FACTORS AFFECTING NATURAL
VENTILATION
The effectiveness of natural ventilation varies
based on:
• Dominant wind speed and direction
• Surrounding environment
• Building footprint and orientation
• Outdoor temperature and humidity
• Window sizing, location, and operable

6. Natural Ventilation Design Strategies
• Building location and Orientation
• Building form and dimensions
• Indoor partitions and layout
• Window typologies, operations, shapes and its
shading devices.
• Other apertures (Door, chimneys etc.)
• Construction methods and detailing
• External elements.

7. Types of natural ventilation
• WIND DRIVEN
• As winds blow across a building, it
hits the windward wall creating a
direct positive pressure.
• The wind then moves around the
building and finally leaves the
shielded wall with a negative
pressure (sucking effect).
• If openings on the leeward and
windward walls, fresh air will be
sucked through the openings on the
windward before leaving through the
sheltered wall openings so as to
balance pressure inside and outside
the building.

9. HOW VENTILATION WORKS

11. StackEffect

12. STACKEFFECT
•Stack effect is temperature induced.
•When there is a temperature difference between two adjoining
volumes of air, the warmer air will have lower density and be
more buoyant thus will rise above the cold air creating an
upward air stream.
•Forced stack effect in a building takes place in a traditional fire
place.
•Passive stack ventilators are common in most bathrooms and
other type of spaces without direct access to theoutdoors.

14. COURTYARD EFFECT
• Due to incident solar radiation in
courtyard, the air gets warmer and
rises up.
• Cool air from the ground level
flows through the louvered openings
of rooms surrounding a courtyard,
thus producing air flow.
• At night, the warm roof
surfaces get cooled by convection
and radiation.
• If this heat exchange reduces roof
surface temperature to wet bulb
temperature of air, condensation of
atmospheric moisture occurs on the
roof and the gain due to
condensation limits further cooling.

15. • If the roof surfaces are sloped
towards the internal courtyard,
the cooler air sinks into the
court and enters habitable
spaces / rooms through low
level openings, gets warmed up
and leaves the room through
higher level openings.
• Care should be taken that the
courtyard does not receive
intense solar radiation, which
would lead to conduction and
radiation heat gains into
building.

16. PASSIVE COOLING TECHNIQUES
• Evaporative Cooling :
•Technique in which outdoor air is cooled by evaporating water
before it is induced in the building.
•Heat of air is used to evaporate the water.Thus cooling the air.
• Evaporative cooling can be direct & indirect.
• Roof can be cooled with pond, wetted pads, spray and ceiling
transformed into cooling element that cools psace below by
convection and radiation without raising the humidity.
• Includes – water bodies, fountains, water curtains, wet jaalis, roof
ponding etc.

17. Roof Pond :
• In this system a shallow water pond is provided
over highly conductive flat roof with fixed side
thermal insulation.
•The top thermal insulation is movable.
•The pond is covered in day hours to prevent heating
of pond from solar radiation.
• The use of roof pond can lower room temperature
by about 20°C. While keeping the pond open during
night the water is cooled by nocturnal cooling.
• The covered pond during the day provides cooling
due to the effect of nocturnally cooled water pond
and on other side the thermal insulation cuts off the
solar radiation from the roof.

18. ROOF POND :
• The system can be used for heating during the
winter by operating the system just reverse.
• The movable insulation is taken away during
day so the water of pond gets heated up by
solar radiation and heating the building.
• The pond is covered in night to reduce the
thermal losses from the roof and the hot water
in the pond transfers heat into building

19. MECHANICALVENTILATION
• DEFINITION - mechanical ventilation systems
circulate fresh air using ducts and fans rather
than relying on airflow through small holes or
crack’s in a home’s wall, roof or windows.
• These systems employ an electrically driven fan
or fans to provide the necessary air movement;
• They also ensure a specified air change and the
air under fan pressure can be forced through
filters.

20. BENEFITS OF USING
MECHANICAL VENTILATION
1. BETTER INDOOR AIR QUALITY – can remove
pollutants, allergens and moisture that can cause
mold problems.
2. MORE CONTROL – provide proper fresh air
flow along with appropriate locations for intake
and exhaust.
3. IMPROVED COMFORT – allow a constant flow
of outside air into the home and can also provide
filtration, dehumidification, and conditioning of the
incoming outside air.

21. TYPES OF MECHANICAL
VENTILATION SYSTEMS
1. Natural inlet and mech. Extract
(exhaust system)
1. Mechanical inlet and natural extract
2. Mechanical inlet and extract
3. Plenum system-
a) upwards
b) downwards
c) mixed

22. NATURAL INLET & MECH.EXTRACT
• Recommended for simplicity and economy.
• Amount of ventilation produced depends upon
Entry of
fresh air flow
air.
• The fan creates negative pressure on its inlet side,
and this causes the air inside the room to move
towards the fan, and the room air is displaced by
the fresh air from outside the room.
• Accomplished by propeller fans exhausting through
holes in the walls or by means of duct system.

24. NATURAL INLET & MECH.EXTRACT
• Use:- This is the most common type of system and is used for
kitchens, workshops, laboratories, internal sanitary apartments,
garages and assembly halls.
• ADVANTAGES:
1. Low on initial & maintenance cost
• DISADVANTAGES:
1) Doesn’t offer sufficient control over the condition of air
2) May cause draughts
• PRECAUTIONS TO BE TAKEN
1) Position of the air inlets in relation to the exhaust outlets
2) Ensure reasonable air at all points & Distance between
inlet and exhaust outlet

25. MECHANICAL INLET &NATURAL
EXTRACT
• It is essential with this system that the air is
heated before it is forced into the building.
• The system may be used for boiler rooms,
offices and certain
• types of factories.
• The air may be heated in a central plant and
ducted to the
• various rooms, or a unit fan convector may be
used.

26. • ADVANTAGES:
a)Reasonable control on air distribution, volume and
• velocity
b) Incoming air can be cleaned, washed or warmed
c) Heated air can re-circulated along with
sufficient fresh air
• for cost purpose
d)Air pressure within building is raised slightly
above the outside atmosphere prevent excess
air coming in & avoid draught
• DISADVANTAGES:
a) Control on distribution of air limited
b) Liable to short circuit when doors are opened

27. MECHANICAL INLET & EXTRACT
• This provides the best possible system of
ventilation, but it is also the most expensive
and is used for many types of buildings
including cinemas, theatres, offices, lecture
theatres, dance halls, restaurants, departmental
stores and sports centers.
• The system is essential for operating
theatres and sterilizing rooms.
• Where comfort is criteria, this provides total
control on input and extract.

28. • By providing smaller
capacity of extractor
fan than inlet fan a
positive pressure is
maintained in space
• This effectively keeps
out dust, draught and
noise.
• Requires windows to be
sealed properly and
swinging or revolving
doors

29. Plenum System
• In this system fresh
air is forced into the
room and the
vitiated air is
allowed to leave
through ventilators,
Air is Passed through
a fine gauge screen or
filter.
• A constant stream of
water is kept flowing
down the screen by
means of a blowing
fan. Thus all
impurities are
removed from the air,
and one can get fresh
air.

30. TYPES OF PLENUM SYSTEM
• UPWARD TYPE –
The air is thrown from floor level and vitiated air is
allowed to escape through vents provided at the
ceiling level.
• DOWNWARD TYPE –
The air is forced in room from ceiling level and
vitiated air is allowed to escape through vents
provided at the floor level or slightly above it.
This rather unnatural since the cold air is
introduced at higher level against the laws of
nature.

31. FAN
• Fans are classified according to the
direction of flow through the impeller:
• PROPELLER : Blades fix at the angles.
The main purpose is for free air from
openings in walls or windows but short
length of ducts. They can remove large
volumes of air. Low installation cost.
Propeller fan have broad blades will
move more air and quieter than fan with
narrow blades and running same speed.
• AXIAL FLOW: Air flows through the
impeller parallel to, and at a constant
distance from the axis. The pressure rise
is provided by the direct action of the
blades

32. FAN
• CENTRIFUGAL OR RADIAL
FLOW: Air enters parallel to the
axis of the fan and turns through
900 and is discharged radially
through the blades. The blade
force is tangential causing the air
to spin with the blades and the
main pressure is attributed to
this centrifugal force.
•CROSS FLOW: air enters the
impeller at one part of the outer
periphery flows inward and exits at
another part of the outer periphery

33. • PROPELLER FAN
• Does not create much air pressure
• Limited effect in ductwork
• Ideal for use at air openings in
windows and walls.
• Used in situations where there is
minimal resistance to air flow.
• Typical outputs are; up to 4 m3/s
and up to 250 Pa pressure.
• Fan efficiency is low at
about 40%.
• Suitable for wall, window and roof
fans where the intake and discharge
are free from obstacles.
• Can move large volumes of air.
• Low installation cost.

34. AXIAL FLOW FAN
• can develop high pressure
• Used for moving air through long sections of
ductwork
• The fan is integral with the run of ducting and does
not require a base.
• High volume flow rate is possible with this type of
fan with high efficiency, about 60% to 65%.
• Typical outputs are; up to 20 m3/s and up to 700 Pa
pressure.
• The fan is cased in a simple enclosure with the motor
housed internally or externally.

35. AIR CONDITIONING
• Air conditioning is the process of altering the
properties of air (primarily temperature and
humidity) to more favorable conditions.
• The control of these conditions may be
desirable to maintain the health and comfort
of the occupants, or to meet the requirements
of industrial processes irrespective of the
external climatic conditions

36. NEED OF AIRCONDITIONING.
• To create protective environment as against heat,
suitable for humans and sensitive machines (like
computers, telephone exchanges etc),
• Keeps working people enthusiastic in extreme hot/ cold
climatic conditions.
• To create protective environment as against humidity
Suitable for humans and sensitive machines
• To create protective environment as against noise,
solves noise problem for humans, working
environments, recording studios etc.
• To create protective environment as against fumes,
smoke and dust, to create healthy conditions for
humans

37. NEED OF AIRCONDITIONING.
• Increases life of sensitive machines. Helps to reduce
maintenance and cleaning work in residential units,
shops, displays etc.
• Life of furniture, curtains, upholstery increases
• Creates comfortable conditions for assemblies
(Auditoria, cinema halls, and conference halls etc.
where heat dissipation from crowds is very high.
• Delicate plant and machinery need AC to protect from
dust and temperature.
• The rating of commercial establishments goes up
(Hospitals,Cinema halls, Restaurants, hotels, shopping
complexes etc.)

38. SYSTEMS OF AIR
CONDITIONING
• ROOM AIR CONDITIONER:
Room air conditioners are suitable for rooms, office cabins,
small offices, shops etc. These are to be fitted on external wall.
Hence the possibilities of locating this type of unit in a room are
limited. The systems are available in 1, 1.5, 2, 3 tones etc. There
are inbuilt filters for filtering air.
• SPLIT AIR CONDITIONER:
The split air conditioner has a compressor and a condenser unit in
an external location. A chilled water pipe is carried from this unit to
the fan coil unit situated inside the room. The fan coil unit can be
located at any suitable point inside the room. It can be operated
with a remote control. Hence is very suitable for living rooms, bed
rooms, office cabins etc. The unit is available in the same numbers
of tonnage as the window unit. The “sweating” or condensation that
occurs at the fan coil unit must be carried away from the unit with
help of a pipe.

39. SYSTEMS OF AIR
CONDITIONING
• DUCTABLE UNIT
Ductable units are available in 7 ton onwards. These are units like
window units but the draft must be carried to different areas of the
establishment with help of a duct. This unit can be located in an
enclosure that has an external wall.
• FAN COIL UNIT SYSTEM:
Fan coil units are fitted to small size large number of units like
hotel guest rooms. It has a central compressor, condenser with
cooling towers and chiller system. The chilled water from chiller is
carried to the fan coil units located at various points. The sweating
of the fan coil unit must be taken care of.
• CENTRAL AC AND AHU:
This has a central compressor, condenser, cooling tower and chiller
unit. He chilled water is piped to various points where AHUs are
located. The AHUs supply conditionedair to assigned areas.

41. OUTDOOR COMPONENTS

42. THE FURNACE
• The furnace unit is typically
fairly large, requiring its own
space within a building.
• It is often installed in the
basement, in the attic, or in a
closet.
• The furnace pushes the cold or
hot air outward into the ducts
that run through every room in
the building.
• Throughout the ducts, there
are vents that allow the warm
or cool air to pass into rooms
and change their interior
temperature.

43. THE EVAPORATOR COIL
• evaporator coils are part of the furnace
unit. they serve the opposite function to
that of heat exchangers.
• They are also attached to a different
part of the furnace.
• they are installed inside a metal
enclosure that is affixed to the side or
the top of the furnace.
• Evaporator coils are activated when
cool air is needed. When triggered, the
evaporator coil supplies chilled air,
which is then picked up by the furnace
blower and forced along the ducts and
out through the vents.
• Evaporator coils are connected to the
HVAC system’s condensing unit, which is
typically located on the exterior of the
building

44. THE CONDENSING UNIT
• The condensing unit is installed outside
the building, separate from the furnace.
• Inside the condensing unit, a special kind
of refrigerant gas is cooled through the
exchange of heat with the air outside.
Then, it is compressed and condensed into
liquid form and sent through a tube or a
line made of metal.
• This tube runs straight to the evaporator
coil. When the liquid reaches the coil, a
series of small nozzles spray the liquid,
lowering its pressure and allowing it to
resolve back into gaseous form.
• During the evaporation of liquid to gas,
heat is absorbed, causing a sudden drop in
temperature and supplying cold air for the
furnace blowers.
• The refrigerant gas is then sent back
outside to the condensing unit, and the
process is repeated again to generate
additional cold air

45. THE REFRIGERANT LINES
• The refrigerant lines are the metal tubes that carry the liquid to the
evaporating coil and return the gas to the condensing unit.
• Refrigerant lines are usually made from aluminium or copper.
• They are designed to be durable and functional under extreme
temperatures.

46. THE THERMOSTAT
• The thermostat controls the function of the
furnace. It is directly connected to the
furnace and includes temperature-sensing
technology as well as user controls.
• A thermostat is usually positioned
somewhere within the building where it can
easily discern temperature and remain
accessible to users.
• A large building may have more than one
thermostat to control different areas of the
structure.
• The inhabitants of the building can manually
set the thermostat to a certain temperature.
• If the air in the room or building is too cold,
the heat exchanger kicks in and blows heat
through the vents.
• If the room is too warm, the condensing unit
and evaporator coil start to function, and the
air conditioning system sends cool air
throughout the building or to one particular
section of the building.

47. THE DUCTS
• Heating ducts are put in during the construction of a home or a building.
• They are often run through the ceiling.
• In each room, at least one rectangular opening is cut into the duct so that
a vent or vents can be installed.

48. THE VENTS
• Vents are usually rectangular in
shape. They are placed in the ceiling,
with their edges corresponding to
the opening in the duct above.
• As warm or cool air pours through
the ducts, vents allow it to disperse
into the rooms below.
• Vents are usually made of metal,
which can handle a wide range of
temperatures.
• The vent is comprised of a
rectangular edge or frame, within
which is a series of thin metal slats.
The slats are angled to channel the
air downward.
• Some vents also include a manual
control that lets users angle the air
toward a different part of the room
depending on their preference.

49. TYPES OF FURNACES
• Furnaces can be divided into two main categories:
1. Single stage furnaces
2. Two-stage furnaces.
• Both types of furnaces are further distinguished by their
performance ratings.
• The chart below explains the function of performance ratings.
• In furnaces with 80% or +92%efficiency, any energy that is not
captured by the ducts is lost, usually through the furnace housing or
through vents leading to the outside of the building
Efficiency Rating Meaning
80% efficiencY Ducts collect and reuse 80 percent
of the generated heating or cooling
energy
92% efficiency or higher Ducts collect and redistribute 90
percent of the energy created by the
furnace unit

50. HVAC DESIGN FOR HEALTHCARE
FACILITIES
The most effective means of controlling contaminants,
odor and indoor air pollution is through ventilation,
which requires simultaneous control of number of
conditions:
1. Air change rates
2. Pressure gradient appropriate with class of isolation
3. Appropriate air distribution in the compartments
being air conditioned.
4. High quality air filtration including absolute filtration
5. Precise temperature and humidity control ensuring
maintenance of the intended microclimate

51. • Ventilation for Acceptable Indoor Air Quality or
otherwise in the absence of any specified supply
air change/hour following guidelines may be
used:
• For the space to be maintained under negative
pressure exhaust 10 to 15 percent more air than
the supply.
• For the space to be maintained under positive
pressure, exhaust 10 to 15 percent less air than the
supply air.

52. ROOM PRESSURE CONTROL
• If the building pressure is allowed to become
negative due to supply filters being loaded,
supply fans running too slow, humid and dirty air
can be drawn into the building through cracks
and openings.
• Building room pressure gradient is achieved by
controlling the quality and quantity of intake and
exhaust air, maintaining differential air pressures
between adjacent areas, and designing patterns
of airflow for particular clinical purposes.

53. INFECTION-CONTROL AND
VENTILATION REQUIREMENTS FOR
“AII” ROOMS
1.The airborne infectious isolation rooms are designed to
maintain negative pressure.
2. Maintain continuous negative air pressure no less than2.5 Pa
in relation to the air pressure in the corridor. This is
accomplished via a separate exhaust system sized to remove
at least 15% more air than that of the supply system.
3. Monitor air pressure periodically, preferably daily, with audible
manometers or smoke tubes at the door (for existing AII
rooms), or with a permanently installed visual monitoring
mechanism.
4. Provide ventilation to ensure >12 ACH for renovated rooms
and new rooms, and >6 ACH for existing AII rooms, when
supply or exhaust air filters are at their maximum pressure
drop.

54. 5. Recirculation of exhausted air is discouraged, from
rooms. The exhaust air should be directed to outside,
away from air-intakes and populated areas.
6 However, where recirculation may be deemed acceptable
in some circumstances, HEPA filters (99.97% @ 0.3µm
DOP) capable of removing airborne contaminants on the
supply side must be incorporated.
7. The disposal of effluents should not create a hazard to
persons outside or the staff maintaining these systems.
8. Consider UVGI fixtures on or near the ceiling to irradiate
upper room air. Note that UVGI, may be used to augment
HEPA filters, but cannot be used in place of HEPA filters,
as their effectiveness on airstreams is limited.

55. 9. The supply air should be located such that clean air is first passed
over the staff/other occupants and then to the patient.
10. Insider patient room, the supply air should be from the ceiling
diffuser located at the perimeter near to the entry and the
exhaust air should be drawn at lower levels approximately 6
inches above the floor in the room.
11. Exhaust air ducts should be independent of the building’s common
exhaust air system to reduce the risk of contamination from back
draught.
12. Locate the exhaust fan at a point in the duct system that will
ensure the duct is under negative pressure throughout its run
within the building.
13.. Ensure supply air ducts are independent of the building’s common
supply air system. If sharing of supply ducts with other isolation
rooms is unavoidable, provide the ducts with terminal HEPA filters
(or other failsafe back draught prevention system). Install a high
efficiency bag filter as a pre-filter to protect the HEPA filter.

56. 15. Design the supply air and exhaust systems to be of a constant
volume system. Variable air volume (VAV) systems are NOT
recommended.
16. A monitoring system should be provided to signal any
malfunction
Properly constructing windows, doors, and intake and exhaust
ports
Maintain plasterboard ceilings that are smooth and free of
fissures, open joints, and crevices
Sealing all penetrations on the walls above and below the ceiling
Monitoring for leakage and making any necessary repairs

57. EMERGENCY ROOMS AND RECEPTION
AREAS
• In public areas of a health care facility such as an
emergency room, reception and waiting areas,
persons with undiagnosed active infection can
come in contact with and infect others prior to
examination and treatments. The likelihood of
airborne contaminants leaving these rooms is
reduced by keeping these rooms under NEGATIVE
• pressure, relative to surrounding areas. Air is
exhausted from these rooms either directly to the
outside or through high efficiency particulate air
(HEPA) filters.

58. INFECTION-CONTROL AND
VENTILATION REQUIREMENTS FOR
OPERATING ROOMS
1. Maintain positive-pressure ventilation with respect to
corridors and adjacent areas; maintain >15 ACH, of which >3
ACH should be fresh air.
2. Filter all recirculated and fresh air through the appropriate
filters, providing 90% efficiency (dust-spot testing) at a
minimum.
3. In rooms not engineered for horizontal laminar airflow,
introduce air at the ceiling and exhaust air near the floor.
4. Do not use ultraviolet (UV) lights to prevent surgical-site
infections.

59. DIRECTIONAL CONTROL OF AIRFLOW
• The design principle of pressurization control
is to exhaust air from those areas which have
the greatest contamination potential, and
allow air to be staged, or cascaded, from
progressively cleaner areas. Figure below
illustrates the basic principle of cascading
airflows from clean areas to relatively
contaminated areas.

60. • In the above diagram,a
facility is depicted which
has offices
and isolation rooms,
separated by corridors
and other areas
• Air is supplied to the areas, usually offices, maintained at the
greatest positive pressure (marked with a ‘++’), and exhausted from
the areas maintained at the negative pressure (marked with a '- -').
Transfer air (exfiltration/infiltration) is identified with blue arrows.
The unlabeled rooms in the diagram above could be laboratories,
which usually have independently operating exhaust hoods or
separate ventilation systems.

61. AIR DISTRIBUTION
• In conventional air conditioning, filtered air is typically
distributed from the ceiling, with
• return air is collected from the ceiling on the other side of
the room.
• In special situations in health care facility (e.g., operating
rooms, delivery rooms, catheterization laboratories,
angiography rooms, HEPA-filtered rooms for
immunesuppressed patients) the direction of air movement
needs to be controlled. The air is introduced from ceiling
registers on the perimeter and is returned or exhausted
through registers located at least 6 inches above the floor.
This arrangement provides a downward movement of clean
air through the breathing and working zones to the
contaminated floor area for exhaus

62. • Figure below shows the introduction of low velocity air near the ceiling at the
entrance of the room, flowing past the patient, and exhausted or returned close to
the floor at the head of the patient bed. An airflow pattern is thus established
which helps to move microorganisms from the point of patient’s expulsion to the
exhaust / return air terminal to prevent health care workers or visitors from
inhaling the bacteria.
• Non-aspirating diffusers (typically perforated face) are recommended. These
diffusers entrain large amounts of air, achieve good mixing, prevent updrafts and
provide a laminar flow of air that will flush the isolation room of unwanted
airborne particles.
• The diffuser should be placed away from patient bed, preferably near the point
where a health care worker or visitor would enter the room.
• Do not place diffuser immediately over the patient bed as it would result in
• uncomfortable drafts projected directly at the patient.

63. HIGH EFFICIENCY PARTICULATE AIR
(HEPA) FILTERS
• HEPA filters have a minimum initial efficiency of 99.97% for
removing particles 0.3 microns in size
• HEPA filters should be used:-
1. On the supply air distribution of the protective rooms.
2. On the return air of the infectious isolation rooms when the air is
recirculated within the space in order to increase ACH while
reducing the total exhaust requirements. Ideally the infectious
isolation rooms should be designed for 100% fresh air and
exhaust.
3. On the exhaust of the infectious isolation rooms and local exhaust
hoods when exhausting air to the outside is not practical or when
the exhaust is located near a potential air intake. (Refer note
below)
4. When the HVAC system configuration dictates recirculation of air
from the isolation room to other parts of the facility.

64. ODOR CONTROL
• There are several areas within a health care
facility where odors or gaseous contaminants are
common. Some of these contaminants may only
be nuisance or comfort related, while others may
represent a threat to personal health.
• Fumes and smells can be removed from air by
chemical processes such as “gas sorption” which
control compounds that behave as gases rather
than as particles

65. LABORATORIES AND SPECIAL
PROCEDURE ROOMS
• Laboratories and special procedure rooms that are known
to contain toxic and hazardous contaminants are typically
designed under negative pressure to prevent these gases
from spreading throughout the facility.
• Examples of these areas include cytology labs where
xylene and toluene may be part of the process,
• X-ray film processing areas, infectious materials in waste
(including regulated medical waste), steam sterilizers, areas
using high-level disinfectants or morgues, where formalin
may be used.
• These chemicals are both irritants and carcinogenic. Such
areas typically employ 100% pass-through ventilation
where no air is recirculated within the facility

66. LOCKER ROOM, TOILET, AND SHOWER
SPACE VENTILATION
• The ventilation of locker rooms, toilets, and shower spaces
is important in removing odor and humidity.
• Legal minimum requirements should be consulted when
designing these facilities
• In toilets recommended rates of exhaust ventilation are 10
ACH or 2cfm /sq-ft whichever is higher. Supply air may be
introduced through door grilles
• Do not transfer more than Public toilets and congregate
baths do require ducted supply air up to 8.5 air changes per
hour maximum.
• The balance air should be drawn from the corridors to
maintain negative pressure and to ensure exhaust of 10 air
changes per hour.

67. TYPE OF HVAC SYSTEM - ISOLATION
ROOMS AND CRITICAL EXAMINATION
ROOMS
• For the critical areas such as isolation rooms,
intensive care units and operating rooms, critical
diagnostic and examination rooms, consider only
the centralized HVAC system encompassing “all
air systems”.
• All air systems can be classified as
1. single-zone
2. multi-zone
3. dual-duct
4. reheat systems

68. SINGLE-ZONE SYSTEMS:
• Single-zone systems serve just one zone
having unique requirement of temperature,
humidity and pressure. This is the simplest of
all air systems. For this type of system to work
properly, the load must be uniform all through
the space, or else there may be a large
temperature variation.

69. MULTI-ZONE SYSTEMS:
• Multi-zone systems are used to serve a small
number of zones with just one central air
handling unit. The air handling unit for multi-zone
systems is made up of heating and cooling coils in
parallel to get a hot deck and a cold deck. For the
lowest energy use, hot and cold deck
temperatures are, as a rule, automatically
changed to meet the maximum zone heating (hot
deck) and cooling (cold deck) needs. Zone
thermostats control mixing dampers to give each
zone the right supply temperature.

70. DUAL-DUCT SYSTEMS
• Dual-duct systems are much like multi-zone
systems, but instead of mixing the hot and
cold air at the air handling unit, the hot and
cold air are both brought by ducts to each
zone where they are then mixed to meet the
needs of the zone. It is common for dual-duct
systems to use high-pressure air distribution
systems with the pressure reduced in the
mixing box at each zone

71. REHEAT SYSTEMS
• Reheat systems supply cool air from a central air handler as
required to meet the maximum cooling load in each zone.
• Each zone has a heater in its duct that reheats the supply air
as needed to maintain space temperatures.
• Reheat systems are quite energy-inefficient and have been
prohibited by various codes.
• Energy may though be saved through the recovery of the
refrigeration system's rejected heat and the use of this heat to
reheat the air

72. AIR HANDLING EQUIPMENT SIZING
CRITERIA
• The air handling equipment must be sized in accordance with
the following guidelines
1. LOAD CALCULATIONS: Heat gain calculations must be done in
accordance with the procedure outlined in the latest ASHRAE Handbook of
Fundamentals. The calculations performed either manually or with a
computer program.
2. The calculated supply air shall be the sum of all individual peak room air
quantities without any diversity.
3. SAFETY MARGIN: A safety factor of 5 percent shall be applied to the
calculated room air quantity to allow for any future increase in the room
internal load.
4. The adjusted supply air shall be, thus, 5 percent in excess of the calculated
supply air.
5. AIR LEAKAGE: The air leakage through the supply air distribution
ductwork shall be computed on the basis of the method described in the
SMACNA Air Duct Leakage Test Manual. The maximum leakage amount
shall not exceed 4 percent of the adjusted supply air.

73. 7. Equipment Selection: selection of the supply air fan,
cooling coil, preheat coil, energy recovery coil (if any),
filters, louvers, dampers, etc., shall be based on the
supply fan capacity,
• A psychrometric chart shall be prepared for each air-
handling unit. Make sure heat gains due to the fan
motor and duct friction losses are taken into account
for sizing cooling coils.
8. Air Distribution:
• The main supply air ductwork shall be sized to deliver
the supply air fan capacity,.
• The individual room air distribution system including
supply, return, exhaust air ductwork, air terminal units,
reheat coils and air outlets/inlets shall be sized and
selected on the basis of the adjusted supply air volume,

74. Air Handling Units Specifications
• The following key elements need to be addressed when procuring
these units.
1. Specify the cabinet construction with stainless steel or galvanized
steel sheets polyester-coated both from the inside and outside.
Ensure cabinet framework is constructed from aluminum profiles
for increased rigidity.
2. Specify a layer of non-flammable mineral wool between the inside
and outside sheets for the cabinet casing.
3. Specify oblique floors for the air handling unit, tubs for the cooling
units and drip channels made of stainless steel construction. Specify
vacuum seal P-trap on the drain pan.
4. Specify all edges and offsets to be filled with fungicidal silicon
certified for hygienic applications in health care facilities which
precludes formation of the microbe expansion centers.
5. Specify provision for pressure gauges on the filter section casing of
AHU along with audible alarm. This is to confirm that NO air stream
will elude filtration, if openings are present because of filter
damage or poor fit.

75. 6. Specify access and inspection openings with the lighting elements
installed in covers of the sections for humidification, filtration, heat
exchangers and fans.
7. Specify modular construction with all the subunits to be assembled
in a manner enabling their washing from all sides. All subunits and
materials shall be resistant to commonly used disinfecting agents.
8. Specify a drum fan with an inspection flap and an outflow pipe
which enables the drum cleaning OR a centrifugal and axial-flow fan
with an open rotor.
9. Specify driving motor manufactured in the IP class, enabling washing
and disinfection.
10. Specify multistage filtration with minimum of MERV 14 final
filtration installed in plastic frames and mounted in frameworks
made of resistant materials. The filters shall be provided with
differential pressure gauge and pollution level indicators.
11. Specify UV bactericidal lamp ensuring disinfection of the
recirculated air.
12. Specify cable glands providing connection of motors and the
lighting system, ensuring the appropriate tightness and cleanliness
class

76. INSULATION
• The dew-point temperature of the air surrounding the
cooler ducts and pipes could easily be higher than the
surface temperature of the ducts and pipes.
Condensation will occur when this happens. If the
ducts and piping happen to be in the ceiling space, the
condensate can drip onto a surface that is loaded with
mold food (ceiling tiles, dry wall boards, insulation,
plywood, etc.) and all of the necessary elements are
there for mold growth.
• Care must be taken to ensure that the supply air ducts,
the chilled water lines (supply and return) and the
refrigerant lines are well insulated with non-flammable
mineral wool.

77. NOISE CRITERIA
• 1. The noise level should be restricted to 35 NC level for all
patient rooms, operating rooms (major or minor),
diagnostic rooms, audio suites, examination rooms,
conference rooms, large offices, lobbies and waiting areas.
• 2. The noise level should be restricted to 40 NC level for all
small private offices, nursing stations, auditoriums,
treatment areas, corridors, pharmacy and general work
rooms.
• 3. The noise level should be restricted to 45 NC level for all
laboratories, Dining, Food Service/Serving , Therapeutic
Pools
• 4. The noise level should be restricted to 50 NC level for all
gymnasiums, recreation

78. DUCT SIZING CRITERIA
• Duct systems should be designed in accordance with the general rules
outlined in the latest ASHRAE Guide and Data Books, SMACNA Manuals
and Design Guide Section of the Associated Air Balance Council Manual.
• 1. Supply duct system, with total external static pressure 2 inches – w.g
and larger, shall be designed for a maximum duct velocity of 2500 fpm for
duct mains and a maximum static pressure of 0.25 inch-w.g. per 100 ft
duct length. Static pressure loss and regain shall be considered in
calculating the duct sizes. Size supply branch ducts for a maximum duct
velocity of 1500 fpm.
• 2. All other duct systems such as return and exhaust, including branch
ducts, shall be designed for a maximum velocity of 1500 fpm for the duct
mains and a maximum static pressure of 0.10 inch- w.g. per 100 ft duct
length, with the minimum duct area of 48 sq in ( or 8 in x 6 in) size.
• 3. Indicate Duct Static Pressure Construction Classification according to
SMACNA (1/2", 1", 2", 3" and 4") on drawings

79. HVAC EQUIPMENT LOCATION AND
INSTALLATION
• Equipment shall be located to be accessible for installation,
operation and repair. Mechanical spaces shall be of suitable size to
permit inspection and access for
• maintenance, and to provide space for future equipment when
required.
• The effect that equipment noise or vibration might have on areas
adjacent to, above, and below equipment shall be considered.
Design shall comply with specified room sound ratings.
• Location of equipment remote from sound sensitive areas should
be emphasized.
• Make provisions for all necessary stairs, cat walks, platforms, steps
over roof mounted piping and ducts, etc., that will be required for
access, operation and maintenance. Access to roofs by portable
ladder is not acceptable

80. HVAC system impact on generator size
• HVAC systems have a significant impact on the
emergency power system of a hospital.
• The connected load of the HVAC equipment
can range from 3 to 6 W/sq ft in an acute care
facility.
• This is generally 50% to 60% of the entire load
on the emergency generator plant.

81. CONCLUSION
Class – P: Positive Pressure
Areas (e.g. Protective
Environment)
Class – N: Negative
Pressure Areas (e.g.
Airborne Infection
Isolation)
Pressure differentials > 2.5 Pa (0.01 in-water
gauge
> 2.5 Pa (0.01 in-water
gauge)
Air changes per hour (ACH) >12 > 12 (for renovation or new
construction)
Filtration efficiency Supply 99.97% @ 0.3µm
DOP
Exhaust – None required
Supply 90% dust spot test
Exhaust – 99.97% @ 0.3µm
DOP
Room airflow direction Out to the adjacent area In to the room
Clean-to-dirty airflow in
room
Away from the patient
(high risk patient or
immunesuppressed
patient)
Towards the patient
(airborne disease patient)
Ideal pressure differential >8 Pa > 2.5 Pa

82. • Pa = Pascal, a metric unit of measurement for pressure
based on air velocity; 250 Pa equals 1.0 inch water gauge.
• DOP = Dioctylphthalate particles of 0.3 µm diameter.
Understanding the role of a hospital in the community
during an emergency situation where normal power is
not available and determining what functions within the
hospital must remain operational in that emergency are
the basis for many of the HVAC design decisions on a
project. The right decisions will ultimately provide the
hospital with a safe and reliable HVAC system.