Introduction

HVAC (heating, ventilation, and air conditioning) is the technology of indoor and vehicular

environmental comfort. HVAC system design is a subdiscipline of mechanical engineering,

based on the principles of thermodynamics, fluid mechanics, and heat transfer. HVAC is

important in the design of medium to large industrial and office buildings such as

skyscrapers and in marine environments such as aquariums, where safe and healthy building

conditions are regulated with respect to temperature and humidity, using fresh air from

outdoors.

Heating

A heater is an object that emits heat or causes another body to achieve higher temperature. In

a household or domestic setting, heaters are usually appliances whose purpose is to generate

heating .Other types of heaters are Ovens and Furnaces. Heaters exist for all states of matter,

including solids, liquids and gases. There are 3 types of heat

transfer: convection, conduction and radiation. The opposite of a heater (for warmth) is an air

cooler used to keep the user cooler than the temperature originally surrounding them. There

are many different types of heating systems. Central heating is often used in cool climates to

heat houses and public buildings. Such a system contains a boiler, furnace, or heat pump to

warm water, steam, or air in a central location such as a furnace room in a home or

a mechanical room in a large building. The use of water as the heat transfer medium is known

as hydronics.

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. It is one of the most important factors

for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building

may be divided into mechanicaland natural types.

Air Conditioning

Air conditioning and refrigeration are provided through the removal of heat. Heat can be

removed through radiation, convection, or conduction. Refrigeration conduction media such

as water, air, ice, and chemicals are referred to as refrigerants. A refrigerant is employed

either in a heat pump system in which a compressor is used to drive thermodynamic

refrigeration cycle, or in a free cooling system which uses pumps to circulate a cool

refrigerant (typically water). Free cooling systems can have very high efficiencies, and are

sometimes combined with seasonal thermal energy storage so the cold of winter can be used

for summer air conditioning. Common storage mediums are deep aquifers or a natural

underground rock mass accessed via a cluster of small-diameter, heat exchanger equipped

boreholes. Some systems with small storages are hybrids, using free cooling early in the

cooling season, and later employing a heat pump to chill the circulation coming from the

storage.

Components of HVAC

1. 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.

2. The Heat Exchanger

Heat exchangers reside in the housing of every furnace unit. When the furnace is activated by

the thermostat, the heat exchanger begins to function as well. Air is sucked into the heat

exchanger, either from the outside or from a separate duct that pulls cool air out of the

building’s rooms. This type of duct is called a cold air return chase. When the cool air comes

into the heat exchanger, it is quickly heated and blown out through the ducts to be dispersed

into the building. If the furnace operates on gas, the heating is accomplished by gas burners.

If it uses electricity, it is done via electric coils.

3. The Evaporator Coil

Like heat exchangers, evaporator coils are also part of the furnace unit. However, they serve

the opposite function to that of heat exchangers. They are also attached to a different part of

the furnace. Instead of being within the furnace housing, 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. The internal design of an evaporator coil resembles that of a car’s

radiator. Evaporator coils are connected to the HVAC system’s condensing unit, which is

typically located on the exterior of the building.

4. 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.

5. 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 aluminum or copper.

They are designed to be durable and functional under extreme temperatures.

6. 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.

7. 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.

8. 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.

Principles of Thermodynamics in HVAC application

Heat Transfer

Heat is a form of energy. Every object on earth has some heat energy. The less heat an

object has, the colder we say it is. Cooling is the process of transferring heat from one

object to another. When an air-conditioning system cools, it is actually removing heat and

transferring it somewhere else. This can be demonstrated by turning on a Spot Cooler and

placing one hand in front of the cold air nozzle and the other over the warm air exhaust.

You will feel the action of the transfer of heat.

Sensible and Latent Heat

There are two forms of heat energy which are sensible heat and latent heat.Sensible heat

is the form of heat energy which is most commonly understood because it is sensed by

touch or measured directly with a thermometer. When weather reporters say it will be 90

degrees, they are referring to sensible heat.Latent heat cannot be sensed by touch or

measured with a thermometer. Latent heat causes an object to change its properties. For

example, when enough latent heat is removed from water vapor (steam or humidity), it

condenses into water (liquid).If enough latent heat is removed from water (liquid), it will

eventually freeze. This process is reversed when latent heat is added.

Change of State

An object that changes from a solid to a liquid or liquid to vapor is referred to as a

change of state. When an object changes state, it transfers heat rapidly.

Humidity

Moisture in the air is called humidity. The ability of air to hold moisture directly relates

to its temperature.

The warmer air is, the more moisture it is capable of holding. Relative humidity is the

percentage of moisture in the air compared to the amount of moisture it can hold. A

moisture content of 70°F air with 50% relative humidity is lower than 80°F air with 50%

relative humidity.When the humidity is low, sweat evaporates from your body more

quickly. This allows you to cool off faster. High humidity conditions do not allow sweat

to evaporate as well because the air is at its maximum capacity.Humidity is also a form

of latent heat. When air contains more humidity, it has more latent heat.

Refrigerants

Refrigerants are substances used by air conditioners to transfer heat and create a cooling

effect. Air-conditioning systems use specially formulated refrigerants designed to change

state at specific temperatures providing optimum cooling.Portables use a refrigerant

called R-22 or HCFC-22. HCFC stands for hydrochlorofluorocarbon. This is currently

the most common refrigerant used by air-conditioning systems.

Latest Technology in HVAC Application

Chilled Beams

Chilled beams can offer facility managers energy-efficient alternatives to standard air

conditioning systems in retrofits, renovations or new construction.

First developed in Norway in 1975, the technology has been used successfully throughout

commercial applications in Europe for at least 20 years, according to ASHRAE. But chilled

beams are just starting to see more use in the United States as an alternative to conventional

systems.

Chilled beams are hydronic HVAC components that circulate chilled or heated water. Such

systems use pumps to move water instead of using fans to move air and they run more quietly

than conventional cooling systems, according to

Thermostat with built-in Wi-Fi connectivity

Figure shows the U.S. General Services Administration (GSA).

The icomfort Wi-Fi® thermostat gives you total remote comfort control. It makes it easy for

you to adjust your home's temperature and save energy from anywhere in the world, using a

smartphone, tablet or laptop.

Dual-fuel comfort

Dual-fuel system offers the perfect combination of efficiency and comfort with two energy

sources an electric heat pump and a gas furnace.

What makes this system so ideal is that it seamlessly alternates between the two energy

sources, depending on outdoor conditions. A heating and cooling system all in one, the heat

pump functions as both of heating and cooling system, reducing gas fuel consumption. On

extra cold days the gas furnace becomes the primary heat source, ensuring maximum comfort

is maintained.

Sustainable Solution:

1) Reflective Coatings

Reflective coatings come in a wide variety of paints, membranes, and textures to reflect solar

and ultraviolet heat. The use of reflective coating can reduce interior temperatures of a

building 7 to 10 degrees and has a life expectancy of ten times that of normal paint. Using

reflective coatings will reduce energy needed to cool homes, offices, and shopping centres.

Energy star reflective coatings are composed mainly from acrylic or urethane. Reflective

coatings should be applied by a certified contractor because they might require special

surface preparation, repair of leaks or damaged areas and proper selection of materials.

Reflective Roof Coatings

You can lower cooling costs and extend roof life by putting a light coloured coating (also

called cool-coating system) over an existing roof. Reflective roof coatings can provide a

water tight surface as well as reflecting heat and reducing heat transfer to the inside of the

building. This extends the life of HVAC systems and reduces maintenance costs.

Reflective coatings are measured in terms of their albedo. The higher the albedo of a surface,

the more heat it reflects and the better its performance in reducing interior temperatures.

Typical coating costs can vary from $0.50 to $1.50 per square foot depending on quality of

coating and roof condition. Reflective coatings are categorized by the IRS as restoration, not

capital improvement, allowing deduction of its expense in one year instead of amortization

over the life of the roof.

Reflective Roof Coating Benefits

The use of reflective coatings on roof surfaces is a simple solution to increase building

endurance and save money. Below is a list of possible benefits:

Reduces interior temperature by 7-10 degrees

Reduces roof surface temperature by 20 to 60 degrees

Extends life of HVAC systems

Reduces energy consumption

Can reduce the size of original HVAC design system

Creates a more comfortable interior environment

Can be applied over almost any roof surface

Extends life of roofing systems

Easier installation when compare to other alternative surface materials

Wide variety of colours to choose from

The reflectiveness of the coating have be measured by test methods ASTM E424-71, E903-

96, C1549-04, E1918-97 or a solar spectrum reflectometer, and have a minimum reflectivity

of 75%. The U.S.

2) Roof Gardens and Energy Savings

Helps to keep cities warm in winter, the urban heat island makes cities and towns sweltering

hot in summer, which means air-conditioners and other cooling equipment have to work

harder and longer. The resulting spike in energy demand puts a real strain on electrical grids,

and can send summer energy bills through the roof.

A roof garden, however, can ease the burden on homes and commercial buildings. A study by

the National Research Council of Canada found that an exposed roof can get as hot as 158

degrees F on a sunny day; an identical roof, when covered by a green, shady roof garden,

stays relatively cool at just 77 degrees F.

This cooling effect resulted in big energy savings. According to the Canadian report, the

average daily energy demand for air-conditioning with the bare roof was 6.0 to 7.5 kWh

(20,500-25,600 BTU). But the shade plants in the rooftop garden reduced the heat flow,

thereby reducing the average daily energy demand to less than 1.5 kWh (5,100 BTU) -- a

savings of over 75 percent.

The Architectural Benefits of Green Roofs

In addition to energy savings, roof gardens have a beneficial effect on roofs themselves. Most

roofs, exposed as they are to sun, wind, snow and rain, go through rather large variations in

temperature. These extreme temperatures cause the roof membrane to shrink in cooler

weather, and expand in hot weather.

All this shrinking and swelling takes a toll on the roof, shortening its lifespan -- but rooftop

gardens can help. In the Canadian research noted above, the bare roof experienced daily

temperature fluctuations of 83 degrees F; the roof gardens reduced this variation to just 22

degrees F. When the city of Roanoke, Va., installed a green roof on its municipal building --

at a relatively low cost of $123,000 -- it added 20 to 60 years to the life of the current roof.

Roof Gardens and Storm water Management

Another big advantage to roof gardens is their ability to manage rainfall, making it cleaner

while also reducing its quantity, thus easing the burden on local storm sewer systems.

When the Canadian researchers compared the runoff from a bare roof and a rooftop garden,

the difference was astounding: The roof garden reduced the amount of runoff by 75 percent,

and delayed the run-off time by 45 minutes. For wastewater systems that routinely discharge

raw sewage after a rainstorm, this finding is big news.

3) Windows

As by own assumption we have thought about implementing an extra criteria that we come

out with which is Heat film as it has better thermal resistivity compared to Solar film.