Ventilation System

VENTILATION SYSTEM
Danish P, Imran, Qais, Simran, Mariyam, Afshan, Omkar, Ubed

VENTILATION SYSTEMS
VENTILATION SYSTEMS AND STRATEGIES
VENTILATION
o Ventilation is necessary in buildings to remove 'stale' air and replace it with 'fresh' air.
This helps to:
o Moderate internal temperatures.
o Reduce the accumulation of moisture, odours and other gases that can build up during
occupied periods.
o Create air movement which improves the comfort of occupants.
o Very broadly, ventilation in buildings can be classified as 'natural' or 'mechanical'.
o Mechanical (or 'forced') ventilation tends to be driven by fans.
o Natural ventilation is driven by 'natural' pressure differences from one part of
the building to another.
NEED FOR MECHANICAL VENTILATION
o The building is too deep to ventilate from the perimeter.
o Local air quality is poor, for example, if a building is next to a busy road.
o Local noise levels mean that windows cannot be opened.
o The local urban structure is very dense and shelters the building from
the wind.
o Air cooling or air conditioning systems mean that windows cannot be
opened
o Internal partitions block air paths.
Natural Ventilation
BENEFITS
o Better Indoor Air Quality.
o Helping to moderate internal
temperatures.
o Helping to moderate internal
humidity.
o Replenishing oxygen.
o Reducing the accumulation of
moisture, odours, bacteria, dust,
carbon dioxide, smoke and other
contaminants that can build up
during occupied periods.
o Creating air movement which
improves the comfort of occupants
Mechanical Ventilation
'Trickle ventilation’ or 'background' ventilation
can be necessary in modern buildings (which
tend to be designed to be almost completely
sealed from the outside to reduce heat loss or
gain), so that problems such
as condensation are avoided when openings
are closed.
'Mixed-mode' ventilation uses both
natural and mechanical ventilation, for
example, allowing the opening
of windows, but also providing a
mechanical air distribution system.
TWO BASIC TYPES

TYPES OF VENTILATION
1. EXHAUST VENTILATION
• Exhaust ventilation systems work by depressurizing the building. By
reducing the inside air pressure below the outdoor air pressure, they
extract indoor air from a house while make-up air infiltrates through leaks
in the building shell and through intentional, passive vents.
• Exhaust ventilation systems are most applicable in cold climates. In
climates with warm, humid summers, depressurization can draw moist air
into building wall cavities, where it may condense and cause moisture
damage.
• Exhaust ventilation systems are relatively simple and inexpensive to install.
Typically, an exhaust ventilation system is composed of a single fan
connected to a centrally located, single exhaust point in the house.
• A preferable option is to connect the fan to ducts from several rooms
(especially rooms where pollutants tend to be generated, such as
bathrooms).
• Adjustable, passive vents through windows or walls can be installed to
introduce fresh air rather than rely on leaks in the building envelope.
• However, passive vents may be ineffective because larger pressure
differences than those induced by the ventilation fan may be needed for
them to work properly.
• This can especially be of concern when bath fans, range fans, and clothes
dryers (which also depressurize the home while they operate) are run
when an exhaust ventilation system is also operating.
• Exhaust ventilation systems can also contribute to higher heating and
cooling costs compared with energy recovery ventilation systems because
exhaust systems do not temper or remove moisture from the make-up air
before it enters the house.

2. SUPPLY VENTILATION
• Supply ventilation systems work by pressurizing the building. They use a fan to
force outside air into the building while air leaks out of the building through
holes in the shell, bath- and range-fan ducts, and intentional vents.
• As with exhaust ventilation systems, supply ventilation systems are relatively
simple and inexpensive to install.
• A typical system has a fan and duct system that introduces fresh air into usually
one—but preferably several—rooms that residents occupy most (for example,
bedrooms, living room, kitchen). This system may include adjustable window or
wall vents in other rooms.
• Supply ventilation systems allow better control of the air that enters the house
than do exhaust ventilation systems. By pressurizing the house, these systems
discourage the entry of pollutants from outside and prevent backdrafting of
combustion gases from fireplaces and appliances. They also allow air introduced
into the house to be filtered to remove pollen and dust or to be dehumidified.
• Supply ventilation systems work best in hot or mixed climates. Because they
pressurize the house, they have the potential to cause moisture problems in cold
climates.
• In winter, the supply ventilation system causes warm interior air to leak through
random openings in the exterior wall and ceiling. If the interior air is humid
enough, some moisture may condense in the attic or parts of the exterior wall,
where it can promote mold, mildew, and decay.
• Like exhaust ventilation systems, supply ventilation systems do not temper or
remove moisture from the air before it enters the house. Thus, they may
contribute to higher heating and cooling costs compared with energy recovery
ventilation systems.

3. BALANCED VENTILATION
• Balanced ventilation systems, if properly designed and installed, neither
pressurize nor depressurize a house. Rather, they introduce and exhaust
approximately equal quantities of fresh outside air and polluted inside air,
respectively.
• A balanced ventilation system usually has two fans and two duct systems. It
facilitates good distribution of fresh air by placing supply and exhaust vents
in appropriate places.
• A typical balanced ventilation system is designed to supply fresh air to
bedrooms and common rooms where people spend the most time. It also
exhausts air from rooms where moisture and pollutants are most often
generated, such as the kitchen, bathrooms, and the laundry room.
• Like both supply and exhaust systems, balanced ventilation systems do not
temper or remove moisture from the air before it enters the house.
• They do, however, use filters to remove dust and pollen from outside air
before introducing it into the house.
• Also, like supply ventilation systems, outdoor air may need to be mixed with
indoor air before delivery to avoid cold air drafts in the winter. This may
contribute to higher heating and cooling costs.
• Balanced ventilation systems are appropriate for all climates; however,
because they require two duct and fan systems, they are usually more
expensive to install and operate than supply or exhaust systems.

4. ENERGY RECOVERY SYSTEM
• Energy recovery ventilation systems usually cost more to install than other
ventilation systems. In general, simplicity is key to a cost-effective
installation. To save on installation costs, many systems share existing
ductwork.
• Complex systems are not only more expensive to install, but often they are
also more maintenance intensive and consume more electric power. For
most houses, attempting to recover all of the energy in the exhaust air will
probably not be worth the additional cost. Also, these types of ventilation
systems are still not very common. Only some HVAC contractors have enough
technical expertise and experience to install them.
• In general, you want to have a supply and return duct for each bedroom and
for each common living area. Duct runs should be as short and straight as
possible. The correct size duct is necessary to minimize pressure drops in the
system and thus improve performance. Insulate ducts located in unheated
spaces, and seal all joints with duct mastic.
• Also, energy recovery ventilation systems operated in cold climates must
have devices to help prevent freezing and frost formation. Very cold supply
air can cause frost formation in the heat exchanger, which can damage it.
Frost buildup also reduces ventilation effectiveness.
• In addition, energy recovery ventilation systems need to be cleaned regularly
to prevent deterioration of ventilation rates and heat recovery, and to
prevent mold and bacteria from forming on heat exchanger surfaces.

MECHANICAL VENTILATION- CATEGORIES
Mechanical ventilation systems are frequently applied to commercial buildings, workshops, factories, etc. where the air change requirements are
defined for health and welfare provision.
THERE ARE THREE CATEGORIES OF SYSTEM
NATURAL INLET AND MECHANICAL EXTRACT MECHANICAL INLET AND NATURAL EXTRACT MECHANICAL INLET AND MECHANICAL EXTRACT
o Used for kitchens, workshops, laboratories,
internal sanitary apartment ,garages and
assembly halls.
o The fan creates negative pressure on its inlet side,
and this causes the air inside the room to move
towards the fan.
Section through kitchen
Natural inlet
Inside air passes through canopy
Fan (which removes warm air from room)
o The air heated before it forced into the
building.
o Used for boiler room, offices and factories.
o Air is heated in central plant and ducted to the
various rooms.
Section through boiler room
Heated air goes inside
cooled air removes out
o This provides best possible system of ventilation.
o Used for cinemas, theatre, offices, lecture
theatres, dance halls, restaurants etc.
o The both inlet and outlet are mechanically
operated.
Section through theatre
Inlet (cool air goes inside)
Outlet (warm air removes out)
Extract grills under the seating
Extract fans above the slab or ceiling

TYPES OF MECHANICAL VENTILATION SYSTEMS
AHU(AIR HANDLING UNIT)
AIR CONDITIONING SYSTEM HEATING,VENTILATION, AIRCONDITING SYSTEM
VAV AND VRVV
SYSTEM
Window Air Conditioning
System
Split Air Conditioning
System
Centralised Air
Conditioning System
Packaged Air Conditioning
System
Advantages of a central AC system:
o It cools all the rooms connected to ducts at
once, thus creating a cooler & regulated
environment around the house in minimum
time.
o Since cool air is circulated in all rooms,
humidity is reduced around the house, making
the overall environment more comfortable.
Advantages of Window AC system:
o Window units are typically less costly and
cheaper to operate
o Simple to install
o Easy to maintain
o Do not take up your floor space
Advantages of Packaged AC system:
o Saving Interior Space.
o Easy, Streamlined Maintenance.
o Easy Installation.
o Lower Utility Bills.
o Reliability and Versatility.
o Heating and Cooling a Large Space.
Advantages of a Split AC system:
o No ductwork needed to install
o operation of the split system is simple
o Split air conditioning units function with great
quietness
o Other than providing full control of the air
conditioner, most of the split air conditioner
has an additional heating capability.
o Cost Effectiveness
o Many split systems models will purify the air
entering

AIR CONDITIONING SYSTEM
• WINDOW AIR CONDITIONING SYSTEM
• SPLIT AIR CONDITIONING SYSTEM
• CENTRALIZED AIR CONDITIONING SYSTEM
• PACKAGED AIR CONDITIONING SYSTEM
CENTRALIZED
AIR
CONDITIONING
SYSTEM
It is the most efficient method to manipulate and ensure the building thermal comfort.
REFRIGERATION
CYCLE
AIR
CYCLE
An air conditioner is a system that is used to cool down a space by removing heat from the space and moving it to some outside area. The
cool air can then be moved throughout a building through ventilation.
Refrigeration cycle is the process of
removing heat from one place to
another
Air cycle is a process to distribute
treated air into the room that needs
to be conditioned.
COMPONENTS OF THE SYSTEM

COMPONENTS OF THE SYSTEM
Component study through a case study – java mall
• 8 storeys of shopping mall
• 4 storeys of basement car parks
The building is conditioned by –
1. Chilled water air handling units (AHU)
2. Fan coil untis (FCU)
3. Air cooled split unit
AHU at first floor
Round diffuser at ceiling
Split AC for MDF and fire control room
AC make up tank (water tank) at roof level
Cooling tower on roof level
Chiller plant room- 6th lvl
AHU at every alternate floor
Control unit and water pump

HVAC & AHU- AIR CHANGE
Fresh Supply Air Rates
Typical Air Changes Per Hour
NOTE: An air change is how many times the air enters and exits a room from the HVAC system in one hour. Or, how many times a room would fill up with the air from the supply
https://www.contractingbusiness.com/service/article/20868246/use-the-air-changes-calculation-to-determine-room-cfm
Use the Air Changes Calculation to Determine Room CFM
CFM gives the value of AHU required
in Ton

AIR CONDITIONING SYSTEM HEATING,VENTILATION, AIRCONDITING SYSTEM VAV AND VRV SYSTEM
Although passive measures will improve thermal comfort, air-conditioning may still be required
for maintaining comfort conditions
HAVC equipment can be reduced by
following proper operation and
maintenance procedures as these
increase the life of equipment and
enhance energy savings by optimizing
operational performance.
Both direct expansion (DX) and central
systems are used for cooling buildings.
Heating systems are required to ensure
comfort winter, especially in colder
climates.
Low energy comfort systems like ground
source heat pumps, radiant cooling,
evaporative cooling, desiccant cooling
and trigeneration systems can reduce
energy use significantly as they use waste
energy
Energy use of HVAC systems can be
reduced by careful design and sizing of the
system, choosing appropriate technology
and system controls, and optimizing the
delivery of HVAC systems.

GREEN ROOF
INTRODUCTION
A green roof system is an addition made to the roof of an existing building
for growing flora. Depending on the type of green roof you install, the
plants may be modular or have drainage layers. However, all green roofs
include a few important features, such as waterproofing and root
repellent, to keep the structure safe and undamaged.
There are two primary forms of
green roofing:
Intensive
Semi intensive
Extensive.
These are differentiated by the
amount of vegetation utilized.
WORKING
Both green roofs utilize a layering system, which establishes a base for the
planters through the use of various soils, mats, and other materials to
retain the nutrients while forcing out any waste by-products. Through
these layers, a soil profile is mimicked, thus creating a drainage process
that allows liquid to be filtered through safely while also nourishing the
plants.

GREEN ROOF
Green roof temperatures can be 30–40°F lower than those of conventional roofs and can reduce city-wide
ambient temperatures by up to 5°F.1,2 In addition, green roofs can reduce building energy use by 0.7%
compared to conventional roofs, reducing peak electricity demand
A good green roof system can also help reduce space conditioning loads on
your building. Evapotranspiration is a natural process where plants create a
thermal barrier on the roof of your building. This thermal layer can help reduce
cooling loads of your HVAC system during hot weather.
Evapotranspiration (ET) is the sum of water evaporation and
transpiration from a surface area to the atmosphere.
Case study – Commercial space ,Spain
the average annual temperature is 23.0 ◦C
during the day and 13.8 ◦C
at night.

GREEN ROOF

GREEN ROOF
Reduces the ambient
temperature
Plants absorb sunlight, 50% is
absorbed and 30% reflected; so
this helps to create a cooler and
more pleasant climate.
Increases solar panel
efficiency
A green roof reduces the
temperature on the roof.
Thanks to this cooler roof, the
efficiency of solar panels is
higher and so you reduce
your total energy costs.
Increases biodiversity
The Sedums, herbs, grasses or
host plants that are included in
the a green roof promote the
habitat of birds, butterflies and
insects, especially in the city
environment which is mainly
concrete and asphalt.
Creates fire-resistant layer
Plants naturally contain a lot
of moisture. With a green
roof you create a natural fire-
resistant layer on your house
or office building.
Provides a rainwater
buffer
A green roof absorbs rain
water by the water
buffering in the plants,
substrate and drainage
layer
DISADVANTAGES
o Insurance for green roofs is important, due to the potential of
droughts or unforeseen storms, but also is expensive.
o The weight of the green roof may result in liability issues if
the pressure of it causes sagging.
o Any damage the plants might do to the building, such as the
roots growing into the shingles, will result in costly repairs.
DESIGN STANDARDS
1. Location factors
- Regional and local climate.
- Volume of rainfall.
- Amount of sunlight.
- Exposure - strength of wind, amount of
frost and snow.
2. Structure factors
- Load capacity of the roof.
- Pitch of the roof.
- Shading and rain shadow from adjacent structures
- Hot/cold air emissions from air conditioning units and
other equipment.
- Height of parapet walls.
- Safe access to install and maintain the green roofs.
3. Vegetation
-Depth of substrate required by plants.
- Drought tolerance of plants.
- Shade tolerance of planting.
- Other habitat creation and environmental
issues.
ADVANTAGES

GREEN ROOF
VANCOUVER CONVENTION CENTRE

GREEN ROOF
FB HQ BY FRANK GEHRY ARCHITECTS

DOUBLE GLAZING
DEFINITION
o The Double Skin Facade is a system consisting of two glass skins placed in such a way that air flows in
the intermediate cavity. The glass skins can be single or double glazing units with a distance from
200mm up to 2 meters.
o For protection and heat extraction reasons during the cooling period, solar shading devices are placed
inside the cavity. However, due to the additional skin, a thermal buffer zone is formed which reduces
the heat losses and enables passive solar gains.
PURPOSE
o The purpose of the double skin facades, has often been to reduce the high temperatures in the
building behind during the summer and to lower the heat losses during winter compared with a glazed
single skin facade.
o Other improvements, which can be achieved are aesthetics, preheating of ventilation air, sound
protection, night cooling etc.
COMPONENTS
The following figure shows
the components of a
double skin facade.
1. Exterior glazing.
2. Interior glazing.
3. Structural frame.
4. Operable sun shade
5. Sun shade canopy.
6. Upper operable
ventilation
7. Maintenance
catwalks
Louvers placed inside a cavity Louvers from internal side

DOUBLE GLAZING
The air buffer works as a barrier to heat loss.
Sun-heated air contained in the cavity can
heat spaces outside the glass, reducing the
demand for indoor heating systems.
The cavity can be vented outside the building to mitigate solar gain and
decrease the cooling load. Excess heat is drained through a process
known as the chimney effect, where differences in air density create
a circular motion that causes warmer air to escape from top.

DOUBLE GLAZING
CLASSIFICATION OF DOUBLE SKIN FACADE SYSTEMS
There are different types of classification for double skin facades. Double skin facade has been used for several envelop function such as optimization of
natural lighting and better ventilation system, and thermal and acoustic insulation . The classification figure out here is based on the mode of working of a
facade presenting 3 categories which are independent on another.
THE TYPES OF VENTILATION
It is related to the different types of driving forces ventilation of the cavity between
two glass facades. The ventilation of the cavity can be natural, fan supported or mechanical . There are three kind of ventilation in double glass facade:
Natural ventilation Hybrid ventilation Hybrid ventilation includes both natural and
mechanical ventilation in which we use
mechanical ventilation when natural
ventilation is not sufficient or it cannot work
properly.
Double-glazed windows could save 50% of
entire building loads, 0.2% on power
consumption, 12.4% on overall households'
energy consumption.
Reducing your heat loss or gain by up to 30%
when compared to single-glazed windows.

EVAPORATIVE COOLING (Role of water body in Structure)
o Over the years, traditional wisdom has supported the idea of a water body such as pond, lake or a fountain to provide cooling effect to the surrounding
environment. This effect lowers the indoor air temperature – a widely known concept of evaporative cooling. Evaporative cooling lowers the indoor air
temperature thus lowers the energy cost for air-conditioning in buildings. However, evaporative cooling is mostly effective in hot and dry climate where the
humidity is low.
Air is in direct contact with the cooling media, water, in direct evaporative cooling. The most
commonly used methods are water bodies and water sprays.
o Pools, ponds and water features immediately outside windows or in courtyards
can pre-cool air entering the house. As water evaporates it draws large amounts
of heat from surrounding air.
o In public buildings, water in pools and fountains can be used as a cooling element
along with cross-ventilating arrangement of openings.
Passive down draught
towers catch hot
ambient air through
wind scoops at the
top. This air is cooled
either through
mechanical systems
like nozzle sprays or
through passive
systems like water
filled vessels.
o Cooling towers The cooling tower may be used to evaporate, precool ventilation air for one or
more air handling units (AHU), reducing the load on the mechanical cooling system.
Evaporative coolers can replace mechanical cooling in hot-dry climates. In composite climates
evaporative cooling systems can be used to reduce HVAC system use during early summer
months when the temperatures are high and humidity is low.

EVAPORATIVE COOLING (Role of water body in Structure)- Indirect Method
Schematic diagram of a multistage evaporative cooling system.
The mechanism involves sensible and latent
cooling of air with water. Direct evaporative
cooling is most effective when the outside
condition is dry and below the desired
conditions. Indirect evaporative system is used
during the seasons when little or no
humidification is required i.e. when outside air
humidity is within a comfortable range.

VEGETATION (Role of vegetation in Structure)
Vegetation can be used for shading, altering the microclimate and modifying the wind direction.
Selecting the appropriate variety of plantation and it's placement are key factors that determine how
well the vegetation will serve its intended purpose.
Creepers are flexible shading devices for
verandahs and interior space.
Deciduous trees are the best for shading parts of the building
that need sun in the winter and shade in the winter
Trees and shrubs create different air flow patterns, provide shading and keep the surroundings cooler in warm weather. Vegetation can be used for energy
conservation in buildings in the following ways:
o Shading of buildings and open spaces through landscaping
o Roof gardens (or green roofs)
o Shading of vertical and horizontal surfaces (green walls)
o Buffer against cold and hot winds
o Changing direction of wind

o VAV, variable air volume, systems work by varying the airflow in a
building at a constant temperature, which is the opposite workings of
a CAV system that varies the temperature at a constant airflow.
o For larger commercial buildings, whether it be a five-story office
building or a shopping mall, this is a pronounced advantage as it
allows better temperature control.
o With buildings of these sizes, individual control is a necessity and
accomplished via a main VAV/airbox, zones, ductwork, and dampers.
o How this works is that the supply air temperature remains constant,
and the airflow rate fluctuates to accommodate the loss-and-gain
heating patterns of each connected zone.
VAV
System
Working
Diagram
COMPONENTS
Variable Speed
Exhaust Fan
Pre Heating Coil Cooling Coil Terminal Unit
Variable Air Volume (VAV) SYSTEM

Variable Refrigerant Volume (VRV) SYSTEM
o VRV is a technology that alternates the refrigerant volume in a
system to match a building’s precise requirements.
o Only a minimum amount of energy is required for a system to
maintain set temperatures, and ensure that it automatically shuts
off when no occupants are detected in a room.
o This unique mechanism achieves more sustainability in the long run,
as end users save on energy costs while reducing their system’s
carbon emissions.
VRV System Working Diagram
COMPONENTS
Heat Exchanger/ Out Door Unit 4 –Way Valve
64 INDOOR UNITS CONNECTED TO 1 OUTDOOR UNIT

CASESTUDY
UNNATI OFFICE
Location Greater NOIDA
Occupancy Type Office, Private
Typology New Construction
Project Area 3,740 m
2
Date of Completion 2018
The Unnati Office Building is the regional headquarter (North) for Gainwell
Commosales Pvt. Ltd., part of a larger 5 acre campus. It is the first building in
India to be certified Platinum under LEED v4 BD+C : NC rating in 2018. The
building performs 59% better than a conventional office building in the region,
and 40% of the building energy consumption is met through on site renewable
energy generation.

CASESTUDY
PASSIVE STRATEGIES
Landscaping
The landscape is a mix of existing and new vegetation. 30% of
the site is un-built, of which 25% is covered with shrubs and
trees. Only native vegetation has been planted to reduce
irrigation water volume as well as pump energy. Treated waste
water is used for irrigation.
Daylighting
90% of the office spaces, including the core and service areas,
receive uniformly distributed daylight. This can be attributed
to the form, central courtyard, shallow floor plates,
appropriate sizing and distribution of openings. All the
windows have box shading that prevents glare.
Orientation
The three-storey building is a cuboid with a central courtyard. It is oriented
northeast-southwest, with the core areas distributed in the east and the west
orientations. Passive design strategies have been integrated with the building
design.

CASESTUDY
Ventilation
o A design ventilation rate of 30% additional outdoor air over ASHRAE
Standard 62.1-2010 enhances indoor air quality and occupant comfort.
o Passive design features reduce the total diversified AC load to 208 kW for
3740 m2 (80 tons for 33,500 ft2).
Building Envelope and Fenestration
o Climatically responsive façade concepts, including green wall and shading on
all windows, protect the interiors from direct sun and reduce heat gain.
o All external surfaces, including the walls, roof and foundation, are insulated
(using polysterene panels) on the exterior.
o Truss reinforced insulated concrete panels (TRIC) used for the exterior walls
are 25 mm concrete (AAC), 60 mm expanded polystyrene (EPS), and 25 mm
concrete (AAC), and 10 mm plaster.
o The green roof insulation materials are 13 mm extruded polystyrene
insulation and a 300 mm layer of green roof soil substrate.
o Window-to-wall ratio (WWR) is 30%, which helps ensure maximum
daylighting potential with minimum solar heat gains.
o High performance envelope insulation leads to 54% reduction in energy use
(compared with the ASHRAE/ IESNA Standard 90.1-2010 baseline).
o High performance double-glazed windows provide improved protection
against sunlight with integrated motorized blinds and shading (efficient
glazing balancing low thermal conductivity and shading coefficient).

CASESTUDY
ACTIVE STRATEGIES
Optimized Energy Systems / HVAC system
o The building has a hybrid HVAC system which is a
combination of water-cooled air handling units and
ceiling-embedded radiant cooling system.
o Cooling load distribution of the system is such that 55%
of the load is met by the radiant cooling system and 45%
by AHUs. Total
o cooling load for the project is around 90 TR for which 2#
80 TR screw chillers (1 Working + 1 Stand-by) are
provided.
o Based on indoor design conditions of 24°C and 55%
relative humidity, the room dew-point temperature is
12°C and chilled water is supplied at a temperature 7°C
to avoid any condensation on surfaces.
Indoor Air Quality
o Dry outdoor ventilation air is supplied through an
externally mounted unit that dehumidifies the air before
it is supplied to occupied space. This dry outdoor air acts
as primary air to the chilled beams.
o The air quality is monitored inside the entire building
with help of CO2 sensors which provide an audible alarm
o The DOAS system starts at 8 a.m. to remove moisture
that builds up during unoccupied hours and brings down
the temperature to desired level before office start-up.

Ventilation System

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