air conditioning & hvac systems

Air Conditioning & HVAC Systems

Building Utility & Services

SyllabusAir Conditioning and HVAC systems: Conventional Systems and its types, HVAC Systems-Ventilation energy efficiency, air filtration and cleaning, Introduction to HVAC Industrial Standards, Heating for comforts- boilers and furnaces

Ventilation• It may be defined as supply of fresh

outside air into an enclosed space or the removal of inside air from the enclosed space. Ventilation may be achieved either by natural or artificial means.

Ventilation• Ventilation is essential for the following

reasons:• For Human respiration• To dilute air to prevent vitiation of body heat

and odors.• To remove product of combustion• To provide such thermal environment as will

assist in the maintenance of the heat balance of the body in order to prevent discomfort and injury to the health of the occupants

• To prevent suffocation condition in conference rooms, committee halls and cinema halls.

Ventilation

Functional Requirement of Ventilation

• Ventilation system provided for any building should meet the following functional requirements

• (a) Humidity• Air contains certain amount of water vapor or

humidity in it relative humidity is defined as the ratio of amount of water vapor if the air is saturated at the same temperature. Thus, the relative humidity of saturated air is 100 %. Relative humidity within the range of 30 to 70 % at the working temperature of 21 0C is considered to be desirable.

• For higher temperatures, low humidity and greater air movements are necessary for removing greater portion of heat from the body.

Humidity


Quality of Air • The air habitat room should never

contain more than 0.06 % of CO2, this can be achieved by proper ventilation


Effective Temperature • The general temperature difference between

inside & outside is kept not more than 8 0C. • The effective temperature, affects the human

body, is an index, which combines into a single value, the effect of air movement, humidity and temperature. This is a temperature at which a person will experience sensation of some degree of cold or warmth as in quite air fully saturated. The common value of effective temperatures in winter and summer are 20 0C and 22 0C

Effective Temperature


Air Changes per hour • The volume of outside air allowed into a room

in one hour compared with the volume of the room. Where people are working or living, in an enclosed space air has to be moved or changed to cause proper ventilation.

• The minimum rate of air change is one per hour while the maximum rate of change is sixty per hour.

• Air change per hour is the volume of outside air allowed in the room or enclosed space per hour compared to the volume of the room.


Recommended Values of Air Changes • The standard values of air changes are based on

control of body odor or the removal of products of combustion when no other contaminants are present in the air.

• Living room and bedrooms- Six air changes per hour.• Kitchen: Minimum three air changes to remove steam,

heat and smell and fumes generated in cooking and to prevent excessive rise of temperature and humidity.

• Kitchen – restaurants Minimum twelve air changes.• Bathroom and water closets: minimum six air changes

desirable after use.• Passages- No need as it is open.

Systems of Ventilation• There are two systems by which desired ventilation

can be obtained-• Natural and Artificial. • Natural ventilation is one which is effected by

the elaborate use of doors, windows, ventilators and skylights. It is suitable for residential buildings and small houses.

• Artificial ventilation is the one, in which some mechanical arrangements are made to increase the rate of airflow. This system is more useful for large buildings, assemblies, theatres etc. It involves the use of some mechanical equipment's offering effective air circulations.

Natural Ventilation

Artificial Ventilation

Systems of Ventilation• The following systems are

normally used- extraction system, plenum system, extraction-plenum and air –conditioning.

Systems of Ventilation• Natural Ventilation• The rate of ventilation by natural means

through windows or other openings depends upon.

• Direction and velocity of wind outside;• Size and disposition of opening (Wind Action)• Convection effects arising from temperature or

vapor difference between inside and outside the room;

• Difference of height between the outlet and inlet openings

Natural Ventilation

General Rules for Natural Ventilations

• The following rules are broadly followed for obtaining the efficient natural ventilation

• Inlet opening in the building should be well distributed and should be located on the windward side at a low level and outlet openings should be located on the leeward side near the top.

• When outlet serves also as inlets, they should be located at the same level.


• Inlet opening should be free from all obstructions- trees, buildings, signboards etc.

• Greatest flow per unit area can be achieved when inlet and outlet are equal in areas;

• Openings may be arranged to take advantage of constant and dependable stream of winds. In case of variables wind directions, openings have to be provided in all directions.

• The amount of outside air entering by natural infiltration through doors/ windows and other openings depend on direction and velocity of wind outside and /or convection effects arising from temperature or vapor pressure difference between inside and outside of the workroom.

Artificial Ventilation• Artificial ventilation involves the use

of some mechanical equipment's for effective air circulation.

• It is applied when natural ventilation is unsatisfactory in respect of quality, quantity and controllability.

• This system is costly but improves on the situation extraction (Exhaust), Plenum (Supply), extraction- Plenum and evaporative cooling and air conditioning.

Artificial Ventilation

Extraction System (Exhaust)

• It is based on creation of Vacuum in the room by exhaust the vitiated inside air by means of propeller type (exhaust) fans.

• The extraction of air from the room permits the fresh air to flow from outside to inside through openings (Windows). The system is more useful in removing smoke, dust, odors etc. from kitchen, toilets and industrial plants.

• The exhaust fans are not located near the windows openings to avoid short-circuiting of the air.

Extraction System (Exhaust)

Artificial ventilation• 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.

Plenum System

Artificial ventilationCelling Fans• Almost all types of houses and offices use

fan in bedrooms, living rooms and offices area.

• Variety of fans like ceiling, table mounted, and wall mounted, pedestal fans are available in the market. Air circulation by ceiling fans cover normal area of 9 to 10 sq. m. Ceiling fans are widely used in all premises for the purpose of ventilation. The ceiling fans are effective only over certain limited areas

Celling Fans

Artificial ventilation• Extraction –Plenum System• This is an extension of plenum

system in which extraction (Exhaust) fans are used for exit of the vitiated air from the rooms and fresh air supplied through system.

Extraction –Plenum System

Artificial ventilation• Evaporative Cooling• Evaporative cooling is used in the region

where high day temperature prevail with reasonably low humidity.

• This system may be employed effectively to lower the temperature of the air to near the wet bulb temperature.

• It produces an air supply cool enough to take care of the indoor sensible heat loads without exceeding the upper safe limits.

Evaporative Cooling

Artificial ventilationAir Conditioning • It is the process of treating air so to control

simultaneously its temperature, humidity, purity, and distribution to meets the requirement of the conditioned space.

• W.H. Carriers who is known as the ‘Father of Air Conditioning’ engineered and installed the first year around air conditioning system, providing for the the major functions of heating, cooling, humidifying and dehumidifying. He made use of air washers for controlling the dew point of air by heating or chilling recirculate water.

‘Father of Air Conditioning’

Air Conditioning

Air Conditioning• Carrier Presented ‘ Rational

Psychometric Formulae/ Related to the dry bulb, wet bulb, and dew point temperature of air with its sensible, latent and total heats and presented a theory of adiabatic saturation.

Air Conditioning• Moist air is the working

substance in air- conditioning system. It is a mixture of two gases dry air and water vapor.

• Dry air is a mixture of a number of gases and water vapor may exist in a saturated or supersaturated state. Dry air is considered as fixed part and water vapor is considered as the variable part.

Air Conditioning

Air Conditioning• Therefore, the air conditioning must be able

to vary the temperature and humidity of the air conditioning space according to the outside conditions. That means:-

• In hot arid regions it must reduce temperature and increase humidity;

• In hot-humid regions, reduce both temperature and humidity;

• In cold humid regions, increase both temperature and humidity

Air Conditioning

Air Conditioning• Air Circulation is the best system

of artificial ventilation in which provision is made for filtration, heating or cooling humidifying etc. Thus creating most comfortable conditions.

Air Conditioning• Air Conditioning helps in the following ways-

whether for comfort air conditioning or industrial air- conditioning;

• Preserving or maintaining health, and comfort of human beings;

• Comfortable entertainment in theatres, assembly halls;

• Journey on roads/ rails become comfortable.• Improving the quality of industrial products,

such as artificial silk, cotton cloth, etc.

Air ConditioningSummer Air Conditioning • In summer, outside temperature

is more, and hence cooling of air is required for greater comfort. The cycle of operations consists of air cleaning, air cooling, dehumidification and air distribution/ Circulation.

Summer Air Conditioning

Air ConditioningWinter Air Conditioning • In winter, outside temperature is

low and hence heating of air is required for comfort. The cycle of operation consists of air cleaning, air heating, and humidification and air distribution/ circulation.

Air Conditioning

Air ConditioningComposite Air Conditioning:• In this, the same air conditioning is

done throughout the year, irrespective of outside temperature.

Air ConditioningSystems of Air conditioning • All air conditioning systems can be

broadly classified in two categories- • Direct expansion systems ( DX

systems) and Chilled Water ( Indirect ) Systems.

Direct expansion systems ( DX systems)

Chilled Water ( Indirect ) Systems

Air ConditioningDirect Expansion System • It is the system where the refrigerant

is utilized to cool the air directly the common example are room air conditioners, packaged units, and central direct expansion plants.

Room Air Conditioner

• A room air conditioner is a factory made assembly designed unit for mounting on a window, through a wall,.

• It is designed to deliver conditioned air without ducts.

• It is the prime source of refrigeration and dehumidification and circulates and cleanses the air. It may also include means for ventilation and heating. Normal capacities of room air conditioners in KWH are 1 tonne to 10 tonne. Electrical consumption is a critical performance factor in air conditioning.

Room Air Conditioner• Purifying filters and de-odouring filters

are just some examples of the extra filters provided to convince consumers of the better performance and capacity to these filters. The function of the main filter is mainly to protect several components inside the system, of large particles that may get inside the appliance and damage it.

• The constant humming sounds of the AC, even if not very loud ( between 44 dB to 51 dB); can be quite annoying to the ear.

Room Air Conditioner• While Installing an air conditioner, its place

of installation is an important criterion, which affects the performance of the air conditioner.

• An AC should optimally distributed air with the same air speed and temperature in all points of the room. This allows for even cooling of the room.

• An AC should be located on shady side of the house or building and direct sunlight does not fall on AC as this reduces its efficiency. An AC should be protected from dust and rain.

Room Air ConditionerPackaged Air Conditioners• It comprises of a compressor, water cooled

condenser, evaporator and fan and all mounted in a sheet metal cabinet.

• They are ideally suited for residence, shops, banks, offices and some industrial applications. Window units are available up to a limited capacity.

• For large capacities floor mounted self-contained packaged units are made to meet to meet the requirements. They are normally mounted on a resilient pad, which prevents vibration of the compressor from being transmitted to the building. It is used for both comfort purpose as well as process control of temperature and humidity for manufacturing purposes.

Packaged Air Conditioners

Room Air ConditionerA split air conditioning System• It has a coil and fan inside the room and

the nosier components ( the compressor, fan and condenser) are on the outside.

• Split air conditioners are slightly more expansive to buy and install, but they are much quiter on the inside, more versatile than conventional types, and if you need air conditioning in more than one room, some models have an outside unit that can supply two or more fan/coils units on the inside.

A split air conditioning System

Air ConditioningIndirect Expansion • In this system chilled water is produced in the

refrigeration plant housed in the main plant room. Chilled water is then carried through insulated chilled water piping to air handling unit or fan-coil unit, where the return air and the fresh air mixture is filtered, cooled and dehumidified and then distributed to the conditioned space through galvanized iron and aluminum ducting and grills/ diffusers.

• The return air is brought back to the air handling unit through the annular space formed around the supply air duct and the false ceiling enclosure. Here it is mixed with the fresh air or ventilation air and then passed through the filters and the cooling coil.

Air Conditioning

Air Conditioning• There are two types of systems in

common use- using air for heating and cooling and using water and air. The former include fixed and variable air volume systems, while the latter include combined system using air for ventilation along with the coils at such zone for heating and cooling. The central air conditioning system consists of four main parts:

• Central plant; distribution system; terminal devices and controls.

Air Conditioning• In a fixed volumetric flow rate air

systems of heating and cooling an outside fresh air flows through the filter, cooling coil, humidifier and fan to the conditioned space.

• The system is more useful for factories, hotels, assembly halls, and big residential buildings where it is un-economical to install separate units for each rooms.

Air Conditioning• The main components of this system are the same as

direct expansion system but a chiller is the additional item. The system has the following components….

• Compressor• Condenser• Chillers• Air handling unit with chilled water coil and/or

fan coil unit or chilled water air washers.• Cooling tower;• Chilled water and condenser water pumps sets;• Air distribution ducting and grills.

Air Conditioning

Heating for Comfort• In cold region, it is necessary to keep

warmth in the building; therefore some artificial measures need to be taken.

• The primary sources of heat for buildings heating-systems are fossil fuels, natural gas, and various grades of fuel oils and coal.

• Electricity is used under certain circumstances for heating in commercial buildings including perimeter zone heating and service water heating.

Heating for Comfort• The heating plant produces heat and

distribution systems like ducts, fans and pumps, terminal devices and auxiliary equipment distributed to the intended places. The equipment that produces heat are furnace, boilers and furnaces, heat pumps, heat exchangers, etc.

Heating for ComfortFurnaces• Furnaces are used to heat air streams that are

used for heating the interior of buildings. Boiler are pressure vessels used to transfer heat produced by burning a fuel to a fluid. The most common fluid used for this purpose in buildings is water liquid or vapor.

• The key distinction between furnace and boiler is that air is heated in furnace and water is heated in the boilers. The fuel used for producing heat in boilers and furnace include natural gas (i.e. methane),propane, fuel oil, wood, coal and other fuels.

Heating for Comfort

Heating for Comfort• Modern furnaces use forced convection to

remove heat produced within the firebox from its outer surface. The up-flow design is used in fully sized mechanical rooms where sufficient floor –to ceiling space for the connecting ductwork.

• Down-flow furnace works in reverse, airflows, downward as it is heated by passing over the heat exchanger. This design is used in residences without basements or in upstairs mechanical spaces in two story buildings.

• In addition to natural gas, liquefied propane gas (LPG) and fuel oils can be used as energy source for furnaces.

Heating for ComfortBoilers • A boiler is a device made from copper, steel

or Cast-Iron to transfer heat from a combustion chamber to water in the liquid phase, vapor phase or both.

• Boilers are classified both by the fuel used and by the operating pressure. Fuels include fuel oils, woods, coal refuse drive fuels, and electricity. Boilers produce either hot water or stream at various pressures. Stream produces by boilers is used in buildings for space heating, water heating and absorption cooling's.

Boilers

Heating for Comfort• Boilers for buildings are classified as – low

pressure and high pressure boilers.Low pressure boilers • Steam boilers with operating pressure below 100

kPa and hot water boilers with pressure below 1000 kPa, temperature are limited t 120 0C.

High pressure boilers• Steam boilers with operating pressure above 100

kPa and hot water boilers with pressure below 1000 kPa, temperature are limited to 120 0C

HVAC Standards• ISHRAE • The Indian Society of Heating,

Refrigerating and Air Conditioning Engineers (ISHRAE), was founded in 1981

• ISHRAE’s primary objective is the advancement of the art and sciences of Heating, Ventilation, Air Conditioning, Refrigeration Engineering & other related Building Services.

HVAC Standards

HVAC StandardsThe codes, regulation as detailed below shall be followed in this contract :-• Safety code for air-conditioning (revised)

amendment 1 : IS 659 : 1964 (reaffirmed 1991) • Safety code for mechanical Refrigeration : IS

660 : 1963 (reaffirmed 1991) • Air-cooled heat exchangers (amendment 1) : IS

10470 : 1983 (reaffirmed 1991) • Packaged Air-conditioner(amendment 1991) :IS

8148 : 1976 (reaffirmed 1991)

HVAC StandardsSafety Codes • The following IS codes shall be

followed: • Safety code for mechanical

refrigeration : IS 660 • Safety code for air conditioning : : IS

659

References

Building Services: S.M. Patil Internet Websites http://ishrae.in/

http://ishrae.in/

http://ishrae.in/

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