Download - ISHRAE-PSNA Student Chapter Newsletter Department of ...psnacet.edu.in/mech_ish_2013-14.pdfISHRAE-PSNA Student Chapter Newsletter Department of Mechanical Engineering . Warm Greetings

Volume: 01-Issue: 01, August 2014

ISHRAE-PSNA

Student Chapter

Newsletter

Department of Mechanical

Engineering

Warm Greetings

Dear ISHRAEites, Students and Faculties

Addressing you all through this ISHRAE- PSNA Student

Chapter forum is a matter of immense pleasure and pride for me.

The Indian Society of Heating, Refrigerating and Air

Conditioning Engineers (ISHRAE), was founded in 1981 at New Delhi

by a group of eminent HVAC&R professionals. ISHRAE becomes

‘International Associate’ of the American Society of Heating,

Refrigerating and Air-conditioning Engineers (ASHRAE) in 1994.

ISHRAE-PSNA Student Chapter was inaugurated in August

2013 at our Department of Mechanical Engineering by a group of

eminent HVAC&R professionals, Faculties and Student members.

ISHRAE- PSNA Student Chapter mission is to protect the Environment,

improve Indoor Air Quality, help Energy Conservation, and provide

continuing education and career guidance to student members.

ISHRAE-PSNA student chapter of Mechanical Engineering

Department has been arranging various events such as seminars, quiz

contests, guest lectures, plant and site visits to enhance students

knowledge in the area of Heating ventilation and air conditioning,

energy conservation, environmental concerns.

I would like to bring out the details of the events that were

conducted in the ISHRAE-PSNA student chapter of Mechanical

Engineering Department during the period of August 2013 - 2014.

I express my sincere gratitude to our management, Principal,

Head of the Department, Faculties and students for their assistance in

ISHRAE-PSNA student chapter activities.

Best wishes and warm regards

Dr.G.R.Kannan

ISHRAE-PSNA Student Chapter-Department of Mechanical

Engineering

PSNA COLLEGE OF ENGINEERING AND

TECHNOLOGY

DEPARTMENT OF MECHANICAL ENGINEERING

ISHRAE-PSNA STUDENT CHAPTER -NEWSLETTER

August 2013-2014

Complied and Edited by Dr.G.R.Kannan; Publisher: PSNA College of Engineering and Technology

CONTENTS

Inauguration of ISHRAE-

PSNA Student Chapter

Guest Lecture

NCRAC-2013, IITM

Workshop at Anna

University

Design competition for

9th

Bry air Awards for

HVAC Excellence

Student Articles

CONVENER

Dr.G.R. Kannan

Dr.V.Paramasivam

ISHRAE-PSNA Student Chapter

Faculty Advisors

OFFICE BEARERS

Mr. P.M. Venkateswaran,

President

Mr. S.Venkat Sharma,

President-Elect

Mr. Milan Thapa, Secretary

Ms. Gaayathree, Treasurer

CHAPTER WORKING

COMMITTEE

Mr. R.V.Prasanth

Mr. Suresh

Mr. Bakhirathan Asokan

Mr. Rakesh.S

Mr. Upendra Sah Kalbar

Volume: 01- Issue: 01, August 2014

IISHRAE-PSNA STUDENT CHAPTER August 30, 2014

1

Bulletin board

Inauguration of ISHRAE-PSNA Student

chapter 2013-2014

Inaugural function of ISHRAE (Indian

Society of Heating, Refrigerating & Air-

conditioning Engineers) was held on

7th

August 2013 at our Sri Rangalakshmi

auditorium of PSNA College of engineering

and Technology. ISHRAE-PSNA student

chapter had been inaugurated with 60 student

members.

Office bearers and chapter working

committee members were selected and taken

oath for effective functioning of ISHRAE-

PSNA Student Chapter. The details of office

bearers and chapter working committee are

given below.

OFFICE BEARERS

Mr. P.M. Venkateswaran, President

Mr. S.Venkat Sharma, President Elect

Mr. Milan Thapa, Secretary

Mr. Gaayathree, Treasurer

CHAPTER WORKING COMMITTEE

Mr. R.V.Prasanth

Mr. Suresh

Mr. Bakhirathan Asokan

Mr. Rakesh.S

Mr. Upendra Sah Kalbar

Guest lecture

ISHRAE PSNA Student chapter was

conducted a Guest lecture titled as

Professional ethics for air conditioning

engineers by Mr. Shankar Rajasekaran-Zonal

Chair ISHRAE Southern Chapter, Chennai

on 07.08.2013 afternoon. The program was

attended by about 60 student members.

NCRAC-IIT- Madras

Three students were attended

3rd

National conference on refrigeration and

air Conditioning (NCRAC-2013) at IIT

Madras, Chennai from 12.12.2013 to

14.12.2013. Selection of students for this

conference was purely on the basis of

technical quiz competition which was held in

our ISHRAE-PSNA Student Chapter.

The details of participants and their

photos, participation certificates are given

below:

3) Mr.P.M.Venkateswaran

1) Mr.P.Keerthi

2) Mr.S.Kumaraguru


2

Work Shop at Anna University

Two students were selected through a

Quiz competition related to heating

ventilation and Air conditioning at ISHRAE

Madurai Sub – Chapter. They were

participated in one day work shop on Basic

Air conditioning at Anna University, Chennai

on 04.01.2014. The details of selected

students are given below:

Student Participation on Design

competition of 9th

Bry air Awards

for HVAC Excellence

Five students were participated 9th

Bry

air Awards for excellence in HVAC & R

2013-14 which was held at New Delhi on

28.02.2014 with the title of solar energy

based air-cooled telephone booth using peltier

1) Mr.P.Keerthi

2) Mr.N.Madhukrishnaa


3

effect under the guidance of

Dr.G.R.Kannan, Associate Professor,

Department of Mechanical Engineering. The

details of participants are as follows:

1) Mr.S.Kumaraguru

2) Mr.P.Keerthi

3) Mr.K.Kirubakaran

Student Articles

1. History of Refrigeration- Mr.Milan Thapa, Secretary, Final Year

Refrigeration may be defined as the process

of achieving and maintaining a temperature

below that of the surroundings, the aim

being to cool some product or space to the

required temperature. One of the most

important applications of refrigeration has

been the preservation of perishable food

products by storing them at low

temperatures. Refrigeration systems are also

used extensively for providing thermal

comfort to human beings by means of air

conditioning. Air Conditioning refers to the

treatment of air so as to simultaneously

control its temperature, moisture content,

cleanliness, odour and circulation, as

required by occupants, a process, or products

in the space. The subject of refrigeration

and air conditioning has evolved out of

human need for food and comfort, and its

history dates back to centuries. The history

of refrigeration is very interesting since

every aspect of it, the availability of

refrigerants, the prime movers and the

developments in compressors and the

methods of refrigeration all are a part of it.

1.2. Natural Refrigeration

In olden days refrigeration was

achieved by natural means such as the use

of ice or evaporative cooling. In earlier

times, ice was either:

1. Transported from colder regions,

2. Harvested in winter and stored in ice

houses for summer use or,

3. Made during night by cooling of

water by radiation to stratosphere.


4

In Europe, America and Iran a

number of icehouses were built to store ice.

Materials like sawdust or wood shavings

were used as insulating materials in these

icehouses. Later on, cork was used as

insulating material. Literature reveals that

ice has always been available to aristocracy

who could afford it. In India, the Mogul

emperors were very fond of ice during the

harsh summer in Delhi and Agra, and it

appears that the ice used to be made by

nocturnal cooling.

1.2.1. Art of Ice making by Nocturnal

Cooling

The art of making ice by nocturnal

cooling was perfected in India. In this method

ice was made by keeping a thin layer of

water in a shallow earthen tray, and then

exposing the tray to the night sky.

Compacted hay of about 0.3 m thickness was

used as insulation. The water looses heat by

radiation to the stratosphere, which is at

around -55˚C and by early morning hours

the water in the trays freezes to ice. This

method of ice production was very popular in

India.

1.2.2. Evaporative Cooling

As the name indicates, evaporative

cooling is the process of reducing the

temperature of a system by evaporation of

water. Human beings perspire and

dissipate their metabolic heat by

evaporative cooling if the ambient

temperature is more than skin

temperature. Animals such as the

hippopotamus and buffalo coat themselves

with mud for evaporative cooling.

Evaporative cooling has been used in India

for centuries to obtain cold water in summer

by storing the water in earthen pots. The

water permeates through the pores of

earthen vessel to its outer surface where it

evaporates to the surrounding, absorbing its

latent heat in part from the vessel, which

cools the water. It is said that Patliputra

University situated on the bank of river

Ganges used to induce the evaporative-

cooled air from the river. Suitably located

chimneys in the rooms augmented the

upward flow of warm air, which was

replaced by cool air. Evaporative cooling

by placing wet straw mats on the windows

is also very common in India. The straw

mat made from “khus” adds its inherent

perfume also to the air. Now-a-days desert

coolers are being used in hot and dry

areas to provide cooling in summer.

1.2.3. Cooling by Salt Solutions

Certain substances such as common

salt, when added to water dissolve in water

and absorb its heat of solution from water

(endothermic process). This reduces the

temperature of the solution (water+salt).

Sodium Chloride salt (NaCl) can yield

temperatures up to -20˚C and Calcium

Chloride (CaCl2) up to - 50˚C in properly

insulated containers. However, as it is this

process has limited application, as the

dissolved salt has to be recovered from its

solution by heating.

1.3. Artificial Refrigeration

Refrigeration as it is known these

days is produced by artificial means.

Though it is very difficult to make a clear

demarcation between natural and artificial


5

refrigeration, it is generally agreed that the

history of artificial refrigeration began in

the year 1755, when the Scottish professor

William Cullen made the first refrigerating

machine, which could produce a small

quantity of ice in the laboratory. Based on

the working principle, refrigeration systems

can be classified as vapour compression

systems, vapour absorption systems, gas

cycle systems etc.

1.3.1. Vapour Compression Refrigeration

Systems

The basis of modern refrigeration

is the ability of liquids to absorb

enormous quantities of heat as they boil

and evaporate. Professor William Cullen

of the University of Edinburgh

demonstrated this in 1755 by placing some

water in thermal contact with ether under a

receiver of a vacuum pump. The

evaporation rate of ether increased due

to the vacuum pump and water could be

frozen. This process involves two

thermodynamic concepts, the vapour

pressure and the latent heat. A liquid is in

thermal equilibrium with its own vapor at

a pressure called the saturation pressure,

which depends on the temperature alone.

If the pressure is increased for example in a

pressure cooker, the water boils at higher

temperature. The second concept is that the

evaporation of liquid requires latent heat

during evaporation. If latent heat is

extracted from the liquid, the liquid gets

cooled. The temperature of ether will

remain constant as long as the vacuum

pump maintains a pressure equal to

saturation pressure at the desired

temperature. This requires the removal of

all the vapors formed due to vaporization. If

a lower temperature is desired, then a lower

saturation pressure will have to be

maintained by the vacuum pump. The

component of the modern day refrigeration

system where cooling is produced by this

method is called evaporator.

The refrigeration effect is obtained in

the cold region as heat is extracted by the

vaporization of refrigerant in the

evaporator. The refrigerant vapour from

the evaporator is compressed in the

compressor to a high pressure at which its

saturation temperature is greater than the

ambient or any other heat sink. Hence when

the high pressure, high temperature

refrigerant flows through the condenser,

condensation of the vapour into liquid takes

place by heat rejection to the heat sink. To

complete the cycle, the high pressure liquid

is made to flow through an expansion valve.

In the expansion valve the pressure and

temperature of the refrigerant decrease. This

low pressure and low temperature refrigerant

vapour evaporates in the evaporator taking

heat from the cold region.

Fig 1. Vapour compression systems


6

It should be observed that the system

operates on a closed cycle. The system

requires input in the form of mechanical

work. It extracts heat from a cold space

and rejects heat to a high temperature heat

sink.

1.3.2. Vapour Absorption Refrigeration

Systems

John Leslie in 1810 kept H2SO4

and water in two separate jars connected

together. H2SO4 has very high affinity

for water. It absorbs water vapour and

this becomes the principle of removing the

evaporated water vapour requiring no

compressor or pump. H2SO4 is an

absorbent in this system that has to be

recycled by heating to get rid of the

absorbed water vapour, for continuous

operation. Windhausen in 1878 used

this principle for absorption refrigeration

system, which worked on H2SO4.

Ferdinand Carre invented aqua- ammonia

absorption system in 1860. Water is a

strong absorbent of NH3. If NH3 is kept in

a vessel that is exposed to another vessel

containing water, the strong absorption

potential of water will cause evaporation of

NH3 requiring no compressor to drive the

vapours. A liquid pump is used to increase

the pressure of strong solution. The strong

solution is then heated in a generator and

passed through a rectification column to

separate the water from ammonia. The

ammonia vapour is then condensed and

recycled. The pump power is negligible

hence; the system runs virtually on low-

grade energy used for heating the strong

solution to separate the water from

ammonia. These systems were initially run

on steam. Later on oil and natural gas based

systems were introduced. Figure 1.4 shows

the essential components of a vapour

absorption refrigeration system. In 1922,

Balzar von Platen and Carl Munters, two

students at Royal Institute of Technology,

Stockholm invented a three fluid system

that did not require a pump. A heating

based bubble pump was used for circulation

of strong and weak solutions and hydrogen

was used as a non-condensable gas to

reduce the partial pressure of NH3 in the

evaporator. Geppert in 1899 gave this

original idea but he was not successful since

he was using air as non-condensable gas.

The Platen-Munters refrigeration systems

are still widely used in certain niche

applications such as hotel rooms etc. Figure

2 shows the schematic of the triple fluid

vapour absorption refrigeration system.

Another variation of vapour

absorption system is the one based on

Lithium Bromide (LiBr)-water. This system

is used for chilled water air-conditioning

system. This is a descendent of

Windhausen’s machine with LiBr replacing

H2SO4. In this system LiBr is the absorbent

and water is the refrigerant. This system

works at vacuum pressures. The

condenser and the generator are housed in

one cylindrical vessel and the evaporator

and the absorber are housed in second

vessel. This also runs on low-grade energy

requiring a boiler or process steam.


7

Fig.2. Schematic of a triple fluid vapour

absorption refrigeration system

Reference

1. History of Refrigeration, IIT

Kharagpur

Student Article: 2

Role of Engineers in Air conditioning

System

Mr.P.Keerthi, Final Year

Air-conditioning is a process that

simultaneously conditions air; distributes it

combined with the outdoor air to the

conditioned space; and at the same time

controls and maintains the required space’s

temperature, humidity, air movement, air

cleanliness, sound level, and pressure

differential within predetermined limits for

the health and comfort of the occupants, for

product processing, or both. The acronym

HVAC&R stands for heating, ventilating,

air-conditioning, and refrigerating. The

combination of these processes is

equivalent to the functions performed by

air-conditioning.

An air-conditioning or HVAC&R

system consists of components and

equipment arranged in sequential order to

heat or cool, humidify or dehumidify, clean

and purify, attenuate objectionable

equipment noise, transport the conditioned

outdoor air and recirculate air to the

conditioned space, and control and maintain

an indoor or enclosed environment at

optimum energy use. The types of buildings

which the air-conditioning system serves

can be classified as:

• Institutional buildings, such as

hospitals and nursing homes

• Commercial buildings, such as

offices, stores, and shopping centers

• Residential buildings, including

single-family and multifamily low-rise

buildings of three or fewer stories above

grade

• Manufacturing and storing

buildings.

1.1.Air-Conditioning Project Development

and System Design

The goal of an air-

conditioning/HVAC&R system is to provide

a healthy and comfortable indoor

environment with acceptable indoor air


8

quality, while being energy efficient and cost

effective.

ASHRAE Standard 62-1989 defines

acceptable indoor air quality as “air in which

there are no known contaminants at harmful

concentrations as determined by cognizant

authorities and with which a substantial

majority (80% or more) of the people

exposed do not express dissatisfaction.” The

basic steps in the development and use of an

air-conditioning project are design,

installation, commissioning, operation, and

maintenance. There are two types of air-

conditioning projects: designbid and design-

build. A design-bid project separates the

design (engineering consultant) and

installation (contractors) responsibilities. In a

design-build project, the design is also done

by the installation contractor.

1.2 Mechanical Engineer’s Responsibilities

The normal procedure in a design-bid

construction project and the mechanical

engineer’s responsibilities are

1. Initiation of a project by owner or

developer

2. Organizing a design team

3. Determining the design criteria and

indoor environmental parameters

4. Calculation of cooling and heating

loads

5. Selection of systems, subsystems,

and their components

6. Preparation of schematic layouts;

sizing of piping and ductwork

7.Preparation of contract documents:

drawings and specifications

8. Competitive biddings by various

contractors; evaluation of bids; negotiations

and modifications

9. Advice on awarding of contract

10. Monitoring, supervision, and

inspection of installation; reviewing shop

drawings

11. Supervision of commissioning

12. Modification of drawings to the

as-built condition; preparation of the

operation and maintenance manual

13. Handing over to the property

management for operation

Reference

1. Wang, S.K. and Lavan, Z. “Air-

Conditioning and Refrigeration”

Mechanical Engineering Handbook Ed.

Frank Kreith Boca Raton: CRC Press

LLC, 1999.

Student Article: 3

Heating, Ventilation Air conditioning

Mr.S.Kumaraguru, Final Year

One of the most important decisions

regarding a new home is the type of heating

and cooling system to install. Equally critical

is the heating and cooling contractor

selected, as the operating efficiency of a

system depends as much on proper

installation as it does on the performance

rating.

Keys to obtaining the design

efficiency of a system in the field include:

• Sizing and selecting the system for the

heating, cooling, and dehumidification load

of the home being built

• Correct design of the ductwork or piping

• Proper installation and charging of the

HVAC unit

• Insulating and sealing all ductwork or

piping


9

1.1 Types of HVAC Systems

There are two primary types of central

heating systems - forced-air systems and

radiant heating systems. Most new homes

have forced-air heating and cooling systems -

either using a central furnace and air

conditioner or a heat pump.

Figure 1 shows that in forced-air systems

a series of ducts distribute the conditioned

heated or cooled air throughout the home.

The conditioned air is forced through the

ducts by a blower, located in a unit called an

air handler. Most homes have three choices

for central, forced-air systems: electric

resistance heat or fuel-fired furnaces with

electric air conditioning units or electric heat

pumps, which can be either air-source or

ground-source (geothermal). The best system

for each home depends on many factors -

cost, comfort, efficiency, annual energy use,

availability, and local prices for fuels and

electricity.

When considering a HVAC system for a

residence, remember that energy efficient

homes have less demand for heating and

cooling, so substantial cost savings may be

obtained by installing smaller units that are

properly sized to meet the load. Because

energy bills in more efficient homes are

Return Plenum Filter should be in a

convenient location Refrigerant Lines

Heating Source Blower Supply Plenum

Branch Duct Trunk Duct Evaporation Coil

Condensate Line 124 lower, higher

efficiency systems will not provide as much

annual savings on energy bills and may not

be as cost effective as in less efficient

houses.

1.2 Multiple HVAC Zones

Larger homes often use two or more

separate heating and air conditioning units

for different floors or areas. Multiple

systems can maintain greater comfort

throughout the house while saving energy

by allowing different zones of the house to

be at different temperatures. The greatest

savings come when a unit serving an

unoccupied zone can be turned off.

Rather than install two separate

systems, HVAC contractors can provide

automatic zoning systems that operate with

one system. The ductwork in these

systems typically has a series of

thermostatically controlled dampers that

regulate the flow of air to each zone.

Although somewhat new in residential

construction, thermostats, dampers, and

controls for zoning large central systems

have been used for years in commercial

buildings.

If your heating and air conditioning

subcontractor feels that installing two or

three separate HVAC units is needed,

have them also estimate the cost of a

single system with damper control over

the ductwork. A single, larger system


10

running longer is usually more efficient

than separate systems.

Such a system must be carefully

designed to ensure that the blower is not

damaged if dampers are closed to several

supply ducts. In this situation, the blower

still tries to deliver the same air flow as

before, but now through only a few ducts.

The reduced air flow creates back pressure

against the blades of the blower and may

cause damage to the motor. There are three

primary design options:

1. Create two zones and size the ductwork

so that when the damper to one zone is

closed, the blower will not suffer damage.

The higher pressure can possibly damage the

duct work as well, but that will not be

noticed.2. Install a manufactured system that

uses a dampered bypass duct connecting the

supply plenum to the return ductwork. The

control system always allows the same

approximate volume of air to circulate.3.

Use a variable speed HVAC system. Because

variable speed systems are usually more

efficient than single-speed systems, they will

further increase savings.

1.3 Air Conditioning Equipment

Air conditioners and heat pumps work

similarly to provide cooling and

dehumidification. In the summer, they extract

heat from inside the home and transfer it

outside. In winter, a heat pump reverses this

process and extracts heat from outside and

transfers it inside. Both systems typically use

a vapor compression cycle, which is

described in Figures 3 and 4. This cycle

circulates a refrigerant - a material that

increases in temperature significantly when

compressed and cools rapidly when

expanded. The exterior portion of a typical air

conditioner is called the condensing unit and

houses the compressor, which uses most of

the energy, and the condensing coil. The

inside mechanical equipment, called the air

handling unit, houses the evaporator coil, the

indoor blower, and the expansion or throttling

valve. The controls and ductwork for

circulating cooled air to the house complete

the system.


11

1. Cold, liquid refrigerant circulates through

evaporator coils. Inside air is blown across

the coils and is cooled. This warms and

evaporates the refrigerant. The cooled air is

blown through the ductwork. The refrigerant,

now a gas, flows to the outdoor unit.

2. The compressor (in the outside unit)

pressurizes the gaseous refrigerant. The

refrigerant temperature rises, but remains a

gas.

3. Fans in the outdoor unit blow air across the

hot, pressurized gas in the condensing coil.

The refrigerant cools and condenses into a

liquid.

4. The pressurized liquid flows inside to the

air handling unit. It passes through an

expansion valve, where its temperature drops

as it vaporizes. The refrigerant flows to the

evaporator coil and the process starts over.

The exterior, air-cooled condensing

unit should be kept free from plants and

debris that might block the flow of air through

the coil or damage the thin fins of the coil.

Ideally, locate the condensing unit in the

shade. However, do not block air flow to or

from this unit with dense vegetation, fencing

or overhead decking.

1.4 Ventilation and Indoor Air Quality

All houses need ventilation to

remove stale interior air and excessive

moisture. There has been considerable

concern recently about how much

ventilation is required to maintain the

quality of air in homes. While there is

substantial disagreement on the severity of

indoor air quality problems, most experts

agree that the solution is not to build an

inefficient, “leaky” home. Because make-

up air is brought in at outside

temperatures, it often requires more

energy to condition the home. However,

the ventilation may reduce energy use by

removing excess humidity. With humid

environment, though, the outside air will

typically be more humid than the inside

air.

Research studies show that

standard houses are almost as likely to

have indoor air quality problems as energy

efficient ones. Most building researchers

believe that no house is so leaky that the

occupants can be relieved of concern about

indoor air quality. They recommend

mechanical ventilation systems for all

houses.

The amount of ventilation required

depends on the number of occupants and

their lifestyle, as well as the design of the

home. The ASHRAE standard,

“Ventilation for Acceptable Indoor Air

Quality” (ASHRAE 62) recommends that

houses have 0.35 natural air changes per

hour (nach) or 15 cubic feet per minute of

ventilation per occupant.

Older, drafty houses can have

infiltration rates of 1.0 to 2.5 nach.


12

Standard homes built today are tighter and

usually have rates of from 0.5 to 1.0 nach.

New, energy efficient homes often have

less than 0.35 nach.

Infiltration is not a successful means

of ventilation because it is not reliable and the

quantity of incoming air is not controllable.

Air leaks are unpredictable, and infiltration

rates for all houses vary. For example, air

leakage is greater during cold, windy periods

than during muggy, hot weather. Thus,

pollutants may accumulate during periods of

calm weather even in drafty houses. These

homes will also have many days when

excessive infiltration provides too much

ventilation, causing discomfort, high energy

bills, and possible deterioration of the

building envelope.

Reference

1.dnr.louisiana.gov/assets/TAD/buildersguide

2. ASHRAE: American Society of Heating,

Refrigerating and Air-Conditioning Engineers

www.ASHRAE.org.

Student Article: 4

Thermoelectric Refrigeration Systems

Mr.K.Kirubakaran, Final Year

A refrigeration effect can also be achieved

without using any moving parts by simply

passing a small current through a closed

circuit made up of two dissimilar materials.

This effect is called the Peltier effect, and a

refrigerator that works on this principle is

called a thermoelectric refrigerator.

Fig 1. Working Principle

In 1821 the German physicist T.J.

Seebeck reported that when two junctions of

dissimilar metals are kept at two different

temperatures, an electro motive force (emf) is

developed, resulting in flow of electric

current. The emf produced is found to be

proportional to temperature difference. In

1834, a Frenchmen, J. Peltier observed the

reverse effect, i.e., cooling and heating of two

junctions of dissimilar materials when direct

current is passed through them, the heat

transfer rate being proportional to the current.

In 1838, H.F.E. Lenz froze a drop of water by

the Peltier effect using antimony and bismuth

(it was later found that Lenz could freeze

water as the materials used were not pure

metals but had some impurities in them). In

1857, William Thomson (Lord Kelvin)

proved by thermodynamic analysis that

Seebeck effect and Peltier effect are related

and he discovered another effect called

Thomson effect after his name. According to

this when current flows through a conductor

of a thermocouple that has an initial

temperature gradient in it, then heat transfer

rate per unit length is proportional to the

product of current and the temperature. As the


13

current flow through thermoelectric material

it gets heated due to its electrical resistance.

This is called the Joulean effect,

further, conduction heat transfer from the hot

junction to the cold junction transfers heat.

Both these heat transfer rates have to be

compensated by the Peltier Effect for some

useful cooling to be produced.

For a long time, thermoelectric

cooling based on the Peltier effect remained

a laboratory curiosity as the temperature

difference that could be obtained using pure

metals was too small to be of any practical

use. Insulating materials give poor

thermoelectric performance because of their

small electrical conductivity while metals

are not good because of their large thermal

conductivity. However, with the discovery of

semiconductor materials in 1949-50, the

available temperature drop could be

increased considerably, giving rise to

commercialization of thermoelectric

refrigeration systems.

Fig. 2. Schematic of a thermoelectric

refrigeration system

Figure 2 shows the schematic of the

thermoelectric refrigeration system based

on semiconductor materials. The Russian

scientist, A. F. Ioffe is one of the

pioneers in the area of thermoelectric

refrigeration systems using semiconductors.

Several domestic refrigerators based on

thermoelectric effect were made in USSR as

early as 1949.

However, since 1960s these systems

are used mainly used for storing medicines,

vaccines etc and in electronic cooling.

Development also took place in many

other countries. In USA domestic

refrigerators, air conditioners, water coolers,

air conditioned diving suits etc. were made

using these effects.

System capacities were typically

small due to poor efficiency. However some

large refrigeration capacity systems such as

a 3000 kcal/h air conditioner and a 6 tonne

capacity cold storage were also developed.

By using multistage temperatures

as low as 145oC were obtained. These

systems due to their limited performance

(limited by the materials) are now used only

in certain niche applications such as

electronic cooling, mobile coolers etc.

Efforts have also been made to club

thermoelectric systems with photovoltaic

cells with a view to develop solar

thermoelectric refrigerators.

Reference

1. Refrigeration and Air Conditioning-IIT

Kharagpur Notes

https://www.scribd.com/doc/25369918/Refrigeration-and-Air-Conditioning-IIT-Kharagpur-Notes

https://www.scribd.com/doc/25369918/Refrigeration-and-Air-Conditioning-IIT-Kharagpur-Notes


14

Student Article: 5

Current Trends in Low-Energy HVAC

Design

Mr. Milan Thapa, Secretary, Final Year

Throughout the 20th century, trends

in HVAC design have been determined

largely by technological advances and energy

costs. Engineers have always sought to find

new ways to ensure occupant comfort, but

the level of attention devoted to finding

innovative ways to reduce energy use has

fluctuated over the last few decades. When

energy costs have risen, energy efficiency

has become a priority; when they have been

low, it has been less of a design driver. This

article identifies several trends which are

being used to reduce energy use in

commercial buildings. The trends to be

considered include decoupling of ventilation

and heating/cooling, designing systems for

optimal efficiency, increased analysis in

system design, and total building integration.

This article is not intended to be a technical

argument or justification for selection of one

system against another. Many technical

articles are available for more complete

handling of each of the trends.

1.2 Decoupling of Ventilation and

Heating/Cooling

The current movement in HVAC design

toward the decoupling of ventilation and

heating is in some ways a return to the past.

Prior to the widespread use of cooling for

buildings, perimeter radiation of some form

was typically used for heating, with operable

windows providing ventilation.

Following World War II, use of air

conditioning became more common, mainly

driven by prosperity and the manufacturing

boom. Early air conditioning systems

combined heating, ventilation, and air

conditioning into a single system, delivered

by the building’s central fan and air

distribution network. This fan system

typically delivered a mixture of outdoor air

for ventilation along with warm or cool air to

meet the building’s temperature requirements.

Larger buildings would have separate systems

or zones for interior and perimeter spaces.

In more extreme climates, a perimeter

heating system may also have been installed

or reheat coils provided on ducts serving

perimeter spaces. As prices soared during the

energy crisis of the 1970s, engineers looked

for a way to reduce costs and improve space

comfort conditions. One solution, dual duct

systems, provided warm air through one duct

and cool air through another. The air would

then be mixed at the zone level to provide

appropriate temperature supply air for the

zone’s needs, typically at constant volume.

Dual duct systems allowed buildings to be

divided into many more zones while using a

larger central fan system. Dual duct systems

also eliminated the need to re-heat air at the

zone level resulting in less re-heat energy and

reducing the piping network throughout the

building.

In one common example, a dedicated

outside air system (DOAS), the airflow

provided by the fan system is limited to the

code-required ventilation component. The

DOAS air handling unit provides heated and

de-humidified air for ventilation and is

frequently provided with some form of heat


15

recovery component such as enthalpy transfer

wheels, “run around” coils or heat pipes to

further reduce energy consumption by

utilizing building exhaust air to

pre-condition the ventilation air.

A DOAS system typically provides

20% or less airflow than what would be

provided at peak cooling periods utilizing a

VAV system. With a DOAS system, the

heating and cooling requirements for the

space are met through a water-based system.

Since water has a much higher capacity for

energy transfer than air, the amount of

energy required to deliver the heating and

cooling is greatly reduced, while pump

energy is somewhat increased.

A side benefit of the reduced air

quantity is smaller ductwork, which decreases

the cost of the ventilation system and,

potentially, the building’s required floor-to-

floor height. DOAS systems are typically

paired with passive chilled beams, radiant

heating/cooling, or fan coils.

When applying DOAS and chilled

beam systems (shown in Figure 1), the

designer must be careful to pay attention to

how the air is distributed to the space and

how heating is accomplished. In buildings

with low heating needs, the ventilation air

may be able to provide adequate heating. In

buildings with higher heating requirements,

supplemental heating systems such as

perimeter baseboard may be required. It is

critical that the ventilation air reach the

occupied breathing zone. For this reason,

DOAS systems are frequently configured to

deliver the air with a displacement strategy at

low level.

Fig. 1. Passive chilled beam system diagram

Fig 2. Active chilled beam diagram.

A second type of decoupled system

could be considered a hybrid model. Active

chilled beams (shown in Figure 2) deliver

both ventilation and heating/cooling services,

but induced air at the chilled beam delivers

most of the heating and cooling while the air

handling unit provides only a portion of the

requirements. The primary airflow for an

active chilled beam system is more than that

of a DOAS/passive chilled beam system

because the active chilled beam utilizes the

primary air to induce room air across the coil


16

in the beam. The static pressure in the

primary air system may also be higher than

that of a DOAS system. Similar to the

DOAS/passive chilled beam system,.

We analyzed a simple 20-story

building to compare the DOAS/passive

chilled beam system and the active chilled

beam system to an ASHRAE standard 90.1

baseline VAV system. The results of the

study are reflected in Figure 3.

Fig 3: Fan energy comparison

The pictures of low energy HVAC

design are given for easy understanding

Reference

1. Robert l. Tazelaar, Pe, Leed Ap,Current

trends in hvac design –National Science

Foundation work shop, 2013.

Volume: 01-Issue: 01, August 2014

Published:

Department of Mechanical Engineering, PSNA College of Engineering and Technology

Kothandaraman Nagar, Dindigul -624622, Tamil Nadu,

www.psnacet.edu.in

Download - ISHRAE-PSNA Student Chapter Newsletter Department of ...psnacet.edu.in/mech_ish_2013-14.pdfISHRAE-PSNA Student Chapter Newsletter Department of Mechanical Engineering . Warm Greetings

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