hvacprogrammematerial-090703025103-phpapp02

8/12/2019 hvacprogrammematerial-090703025103-phpapp02

1/95

HEATING VENTILATION &

AIRCONDITIONING

SYSTEM DESIGN

FACULTY CO-ORDINATOR

NEERAJ SHUKLA


2/95

CONTENTS

PAGE NO.

1.0 INTRODUCTION AND OVERVIEW - 2

2.0 FUNDAMENTALS OF REFRIGERATION - 5

3.0 BASIC REFRIGERATION SYSTEM - 12

4.0 ELEMENTS OF PSYCHROMETRY - 16

5.0 APPLIED PSYCHROMETRY - 23

6.0 HEAT LOAD ESTIMATION - 33

.0 HEAT LOAD DATA SHEET ! TYPICAL CALCULATION - 4

".0 HEATING VENTILATION ! AIRCONDITIONING SYSTEMS - 52


3/95

1.0 INTRODUCTION AND

OVERVIEW


4/95

INTRODUCTION AND OVERVIEW

A simple definition of air conditioning is the simultaneous control of temperature,

humidity, air movement, and the quality of air in a space.

The use of the conditioned space determines the temperature, humidity, air

movement, and quality of air that must be maintained.

The primary function of air conditioning is to maintain conditions that are (1)

conducive to human comfort, or (2) required by a product, or process within a

space. To perform this function, equipment of the proper capacity must be

installed and controlled throughout the year. The equipment capacity is

determined by the actual instantaneous pea load requirements! type of control

is determined by the conditions to be maintained during pea and partial load.

"enerally, it is impossible to measure either the actual pea or the partial load in

any given space! these loads must be estimated.

The term #refrigeration$ may be defined as the process of removing heat from a

substance under controlled conditions. %t also includes the process of reducing

and maintaining the temperature of a body below the general temperature of itssurroundings. %n other words, the refrigeration means a continued e&traction of

heat from a body whose temperature is already below the temperature of its

surroundings.

'or e&ample, if some space (say in cold storage) is to be ept at 2 * (2+1 ),

we must continuously e&tract heat which flows into it due to leaage through the

walls and also the heat which is brought into it with the articles stored after the

temperature is once reduced to 2 * (2+1 ). Thus in a refrigerator, heat is

virtually being pumped from a lower temperature to a higher temperature.

According to second law of Thermodynamics, this process can only be

performed with the aid of some e&ternal wor. %t is obvious that supply of power

(say electric motor) is regularly required to drive a refrigerator. Theoretically, a


5/95

refrigerator is a reversed heat engine or a heat pump which pumps heat from a

cold body. The substance which wors in a heat pump to e&tract heat from a

cold body and to deliver to a hot body is called a refrigerant.

The refrigeration system is nown to the man since the middle of nineteenth

century. The scientists, of the time, developed a few stray machines to achieve

some pleasure. -ut it paved the way by inviting the attention of scientists for

proper studies and research. They were able to build a reasonably reliable

machine by the end of nineteenth century for refrigeration obs. -ut with the

advent of efficient rotary compressors and gas turbines, the science of

refrigeration reached the used for the cooling of storage chambers in which

perishable foods, drins and medicines are stored. The refrigeration has also

wide applications in submarine ships, aircraft and rocets.

Air conditioning has got wide range of applications and it is very much essential

in these days. Air conditioning is provided for some of the following reasons

1) To improve productivity in offices, factories by maintaining comfort

conditions for persons .

2) To maintain comfortable conditions for woring in hotels, labs, etc.,3) To avoid malfunctioning of some of the control panels in /lectrical *ontrol

-uildings.

4) To maintain over pressure inside the premises for avoiding outside (dusty)

air in to the room.

5) To create healthy atmosphere inside the room by supplying filtered air in to

the room.

6) To provide clean, filtered, healthy, comfortable conditions in hospitals etc.,


6/95

2.0 FUNDAMENTALS OF

REFRIGERATION


7/95

FUNDAMENTALS OF REFRIGERATION

0efrigeration is the process by which heat is removed from a low temperature

level and reected at a relatively higher temperature level. The Americans define

refrigeration in a somewhat different way, thus, refrigeration is the process by

which heat is removed from a place where it is not required and reected into a

place where it is not obectionable. This is not, strictly speaing, a proper

scientific definition, since it does not mae any mention of its temperature levels.

o process can be called refrigeration3 unless removal of heat is at a

temperature lower than the surrounding temperature.

-y nature heat always flows from one body to another body which is relatively at

a lower temperature. This law of nature cannot be altered by any means.

Transferring heat from a low temperature level to a high temperature level is

analogous to transferring water from a lower level to a higher level. %magine two

water tans, one located at the ground floor full of water and another empty,

located at the roof level of a building. %f water from the ground floor tan is to be

transferred to the roof tan, then the only thing to do is to bring a bucet, place it

at a level lower than the ground floor tan and allow the water to initially draininto the bucet according to the law of nature. The second step would be to lift

this bucet full of water to a level above the roof tan and now allow the water

from the bucet to drain into the roof tan according to the natural flow by gravity.

%n the foregoing process, we have used the bucet as the carrier and moved it up

and down, first to a level lower than the ground floor tan and then to a level

higher than the roof tan. eedless to add that in the process some mechanical

wor has been performed for lifting the bucet from the lower level to the higher

level.


8/95

Applying this analogy to the process of refrigeration, it is evident, that we require

a substance as the carrier of heat analogous to the bucet. This substance

should be first brought to a temperature which is lower than the low level

temperature so that heat from the low temperature level will automatically flow

into this carrier substance which has been brought to a still lower level of

temperature. After this carrier substance has been fully loaded with heat it has

got to be raised to a temperature which is higher than the high level temperature

so that heat from this carrier will automatically flow according to the law of nature.

The carrier substance referred to above is what is nown in refrigeration parlance

as refrigerant3. 4e shall now see what a refrigerant is really lie. All volatile

liquids including water have property whereby the temperature at which they

evaporate changes according to the pressure it is subected to. Tae water for

e&ample. At normal atmospheric pressure it boils at 155* (212'). 4hen the

water is subected to higher pressure its boiling temperature also becomes higher

than 155*. 6iewise, if the water is subected to pressures lower than the

atmosphere its boiling temperature also falls below 155*. %n fact water can boil

even at as low a temperature as 7* when it is ept in vacuum free of air. %n this

case the only pressure it will have above is its own vapour pressure. 8ifferent

volatile substances have different pressureboiling point characteristics. 'orrefrigeration purpose the most commonly used refrigerants are refrigerant 12 and

refrigerant 22. -y reference to a table giving the properties of these refrigerants

is will be seen that for each pressure there is a corresponding temperature at

which only the refrigerant will boil. %t goes without saying that at any given

pressure the temperature at which the liquid refrigerant boils is also the

temperature at which the refrigerant vapour would condense bac to liquid form.

4hether it is boiling or condensing all depends on whether it is receiving heat or

giving heat. 'or refrigerant purpose, therefore, we mae use of this natural

property of the volatile refrigerant. 'or e&ample, if the liquid refrigerant 022 is

by some means or other brought down to an absolute pressure of say 9:.+2 psi,

then this liquid is now in a position to boil at a temperature of 75'. %n order to

mae this liquid at low pressure boil, you will have to supply heat equivalent to


9/95


10/95

This brings us to a stage where we have to now the definition of certain terms

which are generally used in refrigeration parlance.

S#$%$'() T*+,*$%&*

'or any given refrigerant the temperature at which the liquid refrigerant would

boil (or conversely the refrigerant vapour would condense) when it is subected to

a certain pressure is defined as the saturation temperature corresponding to that

pressure. %t is obvious that at this temperature and pressure, refrigerant in liquid

and vapour form ept in a closed container would be in equilibrium with each

other.


11/95

S%-/((')

%n a lie manner if the liquid portion of the refrigerant is separated and completely

isolated from the vapour which is in equilibrium with it then any removal of heat

from this refrigerant would lower its temperature to a value below its saturation

temperature.


12/95

A'##$'/ C(+,&*'()

Any process which is performed without the addition of heat to or removal of heat

from the process is said to be an adiabatic process. *ompression of gaseous

refrigerant without addition or removal of heat is called adiabatic compression.

The pressure enthalpy diagram of a refrigerant has also lines showing adiabatic

compression. %t is, therefore, possible to find out the enthalpy and temperature of

the gas at various pressures during the course of compression.


13/95

3.0 BASIC REFRIGERATION

SYSTEM


14/95

BASIC REFRIGERATION SYSTEM

The various components which form part of a refrigeration system can be

described as followsB

E#,($(&

6et us start from the evaporator. 6iquid at high pressure has to be admitted into

the evaporator. %n order that this liquid may evaporate at low temperature, it is

essential that the liquid so admitted is simultaneously reduced in pressure. The

level to which the pressure has to be reduced of course is determined by the

temp. at which you want this liquid to evaporate. 'or e&ample, if you want

evaporation of refrigerant 22 at a temperature of 75', the absolute pressure

should be brought down to 9:.+2 psi or if the evaporation has to be at 15' the

absolute pressure should be brought down to :1.2> psi. The pressures indicated

above are the saturation pressures corresponding to the respective

temperatures. This pressure reduction is brought about by the use of what is

nown as an e&pansion valve. The e&pansion valve is ust a needle valve which

throttles the flow of liquid refrigerant thereby bringing about a pressure drop.

This e&pansion valve can also be hand operated, automatic or thermostatic.6iquid admitted into the evaporator now needs heat for evaporation. This head is

supplied by the air which is flowing over the evaporator coil. %n the process, the

air gets cooled and the liquid refrigerant evaporates.

C(+,&*(&

ow if you have got to ensure continuous evaporation at the same temperature,

it is very vital that the vapour evaporating in the coil is removed from it is as

rapidly as it is evaporating. Cnless this is done the evaporated vapour will build

up a pressure in the coil which would eep on rising. Any such rise in pressure

will naturally raise the evaporating temperature also since, the evaporation

temperature is higher and higher as the pressure increases. 0emoval of the

evaporator vapour is achieved by connecting the outlet of the evaporator to the


15/95

suction side of a refrigerating compressor.

=f course, the compressor has got to be si;ed so that it has got a volumetric rate

of displacement which matches with the evaporation rate. Thus the evaporation

pressure is maintained as steady and the liquid fed through the e&pansion valve

continues to evaporate at a steady temperature so long as heat for evaporation is

available at an equally steady rate from the air flowing over.

C()*)*&

The compressor compresses the vapour and discharges the same into the

condenser. %t is in this condenser that the high pressure hot gas delivered by the

compressor has to be condensed. 'or the purpose of condensing the gas it is

necessary that heat is removed from the hot gas. This removal of heat is

achieved by again creating an air flow over the condenser coil or water flow if

water cooled condensers are used. The heat given up by the refrigerant is

piced up by the air or water. The hot gas which has given up the heat naturally

condenses into liquid form at the same pressure. ow let us see how the

pressure builtup in the condenser coil it has got certain definite capacity to

transfer heat from within to the outside air or water for each degree oftemperature difference. 4e also now that for each 1b of refrigerant which has

got to be condensed into liquid form a definite capacity to transfer heat from

within to the outside air or water of refrigerant which has got to be condensed

into liquid form, a definite amount of heat, namely, the latent heat of

condensation has to be removed. %f in a refrigeration system the '22 circulation

is say, 1bsDminute, then the amount of heat which has got to be removed for

condensing this refrigerant gas is & latent heat. This means that the

temperature difference between the hot refrigerant gas within the condenser and

the air or water flowing over it should be such that the total amount of heat

transferred through the walls of the condenser tubes ust balances with the total

amount of heat which has got to be removed. The condensation rate would,

therefore, automatically balance with the compressor discharge rate as soon as


16/95

the temperature difference has been built up.

The pressure inside the condenser also which initially starts building up will attain

a steady level when the corresponding saturation temperature results in the

desired temperature difference for creating the desired heat transfer rate. This is

called the condesing temperature of the system. %t is obvious that if you use a

small si;e condenser the temperature difference has necessarily to be higher

and hence the condensing temperature and the corresponding pressure will also

have to be relatively higher.

R*/*'*&

A receiver is a pressure vessel which is used as a storage tan for the

condensed liquid refrigerant leaving the condenser. %t is from this receiver that

liquid is tapped and sent to the evaporator through the throttling device or

e&pansion valve. %t is not on all systems that we have a separate liquid receiver.

%n the case of systems having water cooled condensers, the shell of the

condenser itself serves as a storage vessel for the liquid refrigerant. %n smaller

systems even with air cooled condensers, it is possible to dispense with the useof a receiver if care is taen to charge the system with the correct amount of

refrigerant.

%n order that the various components forming part of a refrigeration system can

be designed, it is necessary to mae a more scientific study of the entire

operations. 'or this purpose we have to now the complete properties of the

refrigerant concerned when it is at gaseous form and also in liquid form. The

properties of each refrigerant are shown in what is called a Eressure /nthalpy

8iagram.


17/95


18/95

ELEMENTS OF PSYCHROMETRY

P/&(+*$&


19/95

temperature as well.

S#$%$'() L')*

The curved line on the e&treme lefthand side of the chart is what is called the

saturation line. *ondition of air represented by any point on this line is said to be

saturated air, which means that the air is having the ma&imum possible moisture

content in it. %t cannot hold any further moisture.

W*$ B% L')*

There are number of parallel slant lines which are called wet bulb lines. -y wet

bulb temperature what we really mean is the temperature of the air as recorded

by a thermometer with a wet wic on its bulb. Fou will also understand for the

moment that the air having a certain wet bulb temperature will have a definite

heat content although its dry bulb temperature may be anything.

R*#$'* H%+''$ L')*

4hen the air contains its ma&imum moisture content, we call it saturated air!

when it contains anything less than this ma&imum limit then it is not saturated air

because it has still capacity to have more moisture. 4e therefore, say that suchair is, say 5G saturated or ?5G saturated. Another term used to denote the

percentage saturation is relative humidity3. Thus it is one and the same thing

whether you say air is 5G saturated or air has got a relative humidity of 5G.

ote that we have used the word appro&imately3 because the strict scientific

definition of relative humidity is not nearly the comparison of moisture content. %n

fact relative humidity is defined as the ratio of the partial vapour pressure in the

air to the ma&imum vapour pressure that saturated air will have at this

temperature. @owever, for all practical purpose, this is equal to the ratio of the

actual moisture content present to the ma&imum moisture it can hold at that

temperature.


20/95


21/95

D* P(')$

4e have seen that at any given temperature air has a ma&imum limit of moisture

holding capacity when it is said to be saturated. 'or e&ample from the

psychrometric chart we can see that +5' saturated air can hold a ma&imum of

115 grains per 1b of dry air. All temperatures above +5', air with the same

moisture content will be, say 95G, >5G etc., saturated depending on what its dry

bulb temperature would be. %f air with this moisture content and at temperature

higher than +5 is cooled down, then its condition will move along the hori;ontal

115 grains line, till the temperature falls to +5'. +5' and 115 grains D 1b as we

have seen corresponds to saturated condition. This is the temperature at which

air with 115 grains of moisture D 1b will begin to shed its moisture by condensing

if you continue to cool the air. This temperature is called the 8/4 E=%T of the

air. eedless to add, it is the moisture content which determines the dew point.

All you have to do is to move hori;ontally on the psychrometric chart and read

the temperature where you intersect the saturation line.

E)$#,

4e were ust now referring to the wet bulb as line of constant heat content of air.

/nthalpy is ust another term used in place of heat content3. =f course, theenthalpies represented here are all values for samples of air containing 1 lb of

dry air.

The amount of moisture content in the air is generally e&pressed in terms of

grains of moisture per 1b of dry air. 'or your information, grain is a weight

measure. +555 grains mae 1 lb. 4hen we say that the moisture content is 125

grains, what we mean is there is 1 lb, of dry air containing 125 grains of moisture.

The total weight of this moist air would, therefore, by 1 H 125D+555 lbs I 1.51+1

lb. At any temperature there is a limit to the ma&imum moisture holding capacity

of air. This limit is something definite and does not alter e&cept under different

atmospheric pressures. At higher and higher atmospheric pressure the moisture

holding capacity at any given temperature becomes less and less.


22/95

At any temperature when air contains the ma&imum amount of moisture it is said

to be saturated air. 4hen air has attained saturation at any given temperature, it

is impossible to add any further moisture in vapour form.


23/95

S(&$ D*7')'$'()

D&-% T*+,*$%&*

The temperature of air as registered by on ordinary temperature.

W*$-% T*+,*$%&*

The temperature registered by a thermometer whose bulb is covered by a wetted

wic and e&posed to a current of rapidly moving air.

D*,(')$ T*+,*$%&*

The temperature at which condensation of moisture begins when the air is

cooled.

R*#$'* H%+''$

0atio of the actual water vapor pressure of the air to the saturated water vapor

pressure of the air at the same temperature.

S,*/'7'/ H%+''$ (& M('$%&* C()$*)$

The weight of water vapor in grains or pounds of moisture per pound of dry air.

E)$#,

A thermal property indicating the quantity of heat in the air above an arbitrary

datum. %n -TC per pound of dry air. The datum for dry air is 5 ' and, for

moisture content, :2 ' water.

E)$#, D*'#$'()

/nthalpy indicated above, for any given condition, is the enthalpy of saturation. %t

should be corrected by the enthalpy deviation due to the air not being in the

saturated state. /nthalpy deviations in -TC per pound of dry air. /nthalpy

deviation is applied where e&treme accuracy is required B however, on normal air

conditioning estimates it is omitted.


24/95

S,*/'7'/ V(%+*

The cubic feet of the mi&ture per pound of dry air.

S*)'* H*#$ F#/$(&

The ratio of sensible to total heat.

A')+*)$ C'&/*

6ocated at 95 ' db and 5G rh and used in conunction with the sensible heat

factor to plot the various air conditioning process lines.

P(%) (7 D& A'&

The basis for all pyschrometric calculations, remains constant during all

psychrometric processes. The drybulb, wetbulb, and dewpoint temperatures

and the relative humidity are so related that if two properties are nown, all other

properties shown may then be determined. 4hen air is saturated, drybulb,

wetbulb, and dewpoint temperatures are all equal.


25/95

5.0 APPLIED PSYCHROMETRY


26/95

APPLIED PSYCHROMETRY

6et us now see how the various air conditioning procedures will be represented

on a Esychrometric chart.

1. S*)'* H*#$')

-y sensible heating, we mean adding heat to air whereby the entire heat

added goes to raise the temperature of the air. %t is obvious that in such a

process there is no change in the moisture content of the air. %n other

words, during sensible heating process the air retains a constant moisture

content and accordingly, its condition will move on a hori;ontal line

corresponding to its constant moisture content.


27/95

4. C((') #) D*%+''7')

*ooling and dehumidifying is ust the reverse of heating and humidifying.

=n a psychrometric chart such a process will also be represented in the

same manner as for heating and humidifying, the only difference being the

arrows representing the direction of movement of conditions would be ust

reverse.

5. E#,($'* C((')

/vaporative cooling is the process by which air is simply subected to a

spray of recirculated water ust as in the e&periment described earlier, the

only difference being, we do not provide an infinite number of spray bans

as in the e&periment. The chamber with the bans of spray is called an Air

4asher. Air so subected would of course tend to get saturated and

change out at a temperature equal to its wet bulb temperature. @owever,

since we do not provide adequate number of spray bans to completely

humidify, the air comes out not at 155G humidity but somewhat lower than

that. eedless to say, since this process is adiabatic, the air has constant

enthalpy throughout the process and hence its condition moves along the

line representing its wet bulb temperature.

P/&(+*$& # A,,'* $( A'&/()'$'()')

%t now remains for us to study psychrometry as applied to air conditioning

process. 4e will only see for the present what the heat load form is lie

and also the various sections into which it is divided. %t is only after you

understand this that you will be in a better position to understand

psychrometry as applied to air conditioning.


28/95

4hen a space is maintained at a temperature below the atmospheric

temperature surrounding the space, then there is a transfer of heat from

outside into the conditioned area, which tends to raise the inside

temperature unless this heat is removed as fast as it enters this space.

Then you have heat or any other appliances which may be in the space.

All such heat which are either transmitted into the room or generated from

within due to occupants and appliances which tend to raise the inside

temperature are termed as room sensible heat. %n the lie manner, the

occupants within the room also release moisture from their body into the

room. There may be other sources inside the conditioned area which add

up more moisture into the atmosphere. %f the space has not only to be

maintained at a particular temperature, but also to be held within certain

limits of relative humidity, then it is necessary that such moisture gain

inside the room should also be removed ust as rapidly. -y removal of

moisture what we have really mean is condensing this moisture from the

air and discarding it outside. 'or condensing the moisture, you have to

remove the latent heat of vaporisation of water.


29/95

%n heat load, there is one more source which contributes to the room

sensible and room latent heat loads. This is on account of infiltration of

fresh air directly into the conditioned space and bypass of certain amount

of fresh air that is normally taen into the system through the air handling

apparatus. The form is designed so that the room sensible heat, latent

heat and the additional load due to outside air, not forming part of room

load are all calculated separately.

@ere, we have used the term -ypass3. Fou must understand what

e&actly the meaning of the term -ypass3 is. 'or removing sensible heat

and latent heat at the same rate at which they are being gained within the

conditioned space, conditioned air is admitted within this space at a

predetermined temperature and humidity condition such that this air would

absorb the room sensible and room latent heat loads and in the process

attain a final condition which is e&actly equal to the condition to be

maintained in the room. This is achieved by continuously drawing from

within the room certain amount of air and adding to it a certain percentage

of fresh air for ventilation and cooling and dehumidifying this mi&ture in a

cooling coil. %t is this treated air, which is supplied bac into theconditioned area. =n account of some free passages in between the fins

and tubes a small percentage of the air comes out on the other side of the

coil without undergoing any change. %t is this, which we terms as bypass

of air. As far as the portion of the air, which is actually recirculated from

the room is concerned, bypass will have no influence on the ultimate

result. %t only means that some air has been withdrawn from the room and

ust put bac into the same room without any change in its condition either

upward or downward. -ut, what really influences is the bypass of the

fresh air, which is also passed through the cooling coil along with the re

circulated air.


30/95

brought down to the room condition. The general formula for arriving at

the e&act air quantity isB

cfm I I

@owever, you must realise it is not merely the selection of the condition of

the supply air that is important. 4e have also to consider how air can be

cooled down to the selected condition in a cooling apparatus. %n a cooling

coil in which air is cooled, there is no practical means of ensuring that the

air leaving the coil would be at the e&act temperature and humidity

condition corresponding any condition selected by us on the sensible heat

factor line. @owever, there is one temperature and humidity condition

which is very easy to eep under control. This is the condition which lies

not only on the sensible heat factor line but also on the saturation line on

the psychrometric chart. %n other words, if the sensible heat factor line is

e&tended till it meets the saturation line, then the condition represented by

the point of intersection of these two lines is the one condition which can

be under our control. This temperature is called apparatus dew point.

B,# F#/$(&

The problem becomes a bit more complicated because in every cooling

coil there is always a small percentage of the total cfm which escapes

totally untreated. 4hen outside air taen into the system bypasses the

coil, it will tend to raise the room temperature and humidity conditions

above the desired level. %t is, therefore, necessary to tae into

consideration the effect of bypass right at the time of maing the heat load

calculations.


31/95

PSYCHROMETRIC FORMULAS

A. AIR MI8ING E9UATIONS :O%$((& #) R*$%&) A'&;

tmI (1)

hmI (2)

4mI (:)

B. COOLING LOAD E9UATIONS

/0


32/95


33/95


34/95

cfmda I (71)

cfmsa I (72)

cfmsa I (7:)

cfmsa I (77)

cfmba I cfmsa cfmda (7)

ote B cfmdawill be less than cfmsaonly when air is physically bypassed

around the conditioning apparatus.

cfmsa I cfmoaH cfmra (7?)

H. DERIVATION OF AIR CONSTANTS

1.59 I .227 L

4here .227 I


35/95

1:. I


36/95


37/95

HEAT LOAD ESTIMATION

I)$&(%/$'()

The primary obective is to provide a convenient consistent, and accurate method

of calculating heating and cooling loads and to enable the designer to select

systems that meet the requirements for efficient energy utili;ation and are also

responsive to environmental needs.

The ability to estimate loads more accurately due to changes in the calculation

procedure provides a lessened margin of error. Therefore, it becomes

increasingly important to survey and chec more carefully the load sources, each

item in the load and the effects of the system type on the load. This tightening up

on the hidden safety factors occurs for a number of reasons. There is greater

emphasis, by standards and codes, on si;ing equipment closer to the e&pected

loads, as determined by outside design weather conditions. Also the suggested

indoor design temperatures are now usually + ' for cooling and +2 ' for

heating. %nstalled lighting levels are being reduced and the calculations are using

lighting loads closer to the actual loads. All of these factors require that the

designer introduce any margin of safety by a positive action, rather than rely on

an assumed hidden margin.

P%&,(* (7 L(# C#/%#$'()

6oad calculations can be used to accomplish one or more of the following

obectives B

7) Erovide information for equipment selection and @MA* system design

8) Erovide data for evaluation of the optimum possibilities for load reduction.

9) Eermit analysis of partial loads as required for system design, operation

and control

These obectives can be obtained not only by maing accurate load calculations

but also by understanding the basis for the loads. There a brief description of

cooling and heating loads are included.


38/95

P&')/',* (7 C((') L(#

%n airconditioning design there are three distinct but related heat flow rates, each

of which varies which varies with timeB

10) @eat "ain or 6oss

11) *ooling load or @eating 6oad

12) @eat /&traction or @eat Addition 0ate

@eat "ain, or perhaps more correctly, instantaneous rate of heat gain, is the rate

at which heat enters or is generated within a space at a given instant of time.

There are two ways that heat gain is classified. They are the manner in which

heat enters the space and the type of heat gain.

The manner in which a load source enters a space is indicated as followsB

13)


39/95

%f a constant humidity ratio is to be maintained in the enclosure, then water vapor

must be condensed out in the cooling apparatus at a rate equal to its rate of

addition in the space. The amount of energy required to do this is essentially

equal to the product of the rate of condensation per hour and the latent heat of

condensation. This product is called the latent heat gain.

As a further e&ample, the infiltration of outdoor air with a high drybulb

temperature and a high humidity ratio, and the corresponding escape of room air

at a lower drybulb temperature and a lower humidity ratio, would increase both

the sensible heat gain and the latent heat gain of the space.

The proper design of an airconditioning system requires the determination of the

sensible heat gain in the space, the latent heat gain in the space, and a value for

the total load, sensible plus latent, of the outdoor air used for ventilation.

The sensible cooling load is defined as the rate at which heat must be removed

from the space to maintain the room air temperature at a constant value. The

summation of all instantaneous sensible heat gains at a specific time does not

necessarily equal the sensible cooling load for the space at that time. The latentload however is essentially an instantaneous cooling load. That part of the

sensible heat gain which occur by radiation is partially absorbed by the surfaces

and contents of the space and is not felt by the room air until sometimes later.

The radiant energy must first be absorbed by the surface that enclose the space

such as walls and floor and by furniture and other obects. As soon as these

surfaces and obects become warmer than the air some heat will be transferred

to the air in the room by convection. The heat storage capacity of the building

components and item such as walls, floors and furniture governs the rate at

which their surface temperatures increase for a given radiant input. Thus, the

interior heat storage capacity governs the relationship between the radiant

portion of the sensible heat gain and how it contributes to the cooling load. The

thermal storage effect can be important in determining the cooling equipment


40/95

capacity.

The actual total cooling load is generally less than the pea total instantaneous

heat gain thus requiring smaller equipment than would be indicated by the heat

gain. %f the design is based on the instantaneous heat gain, the rest of the

system may be oversi;ed as well.

@eat e&traction rate is the rate at which heat is removed from the conditioned

space. ormal control systems operating in conunction with the intermittent

operation of the cooling equipment will cause a swing3 in room temperature.

There, the room air temperature is constant only at those rare times when the

heat e&traction rate equals the cooling load. *onsequently, the computation of

the heat e&traction rate gives a more realistic value of energy removal at the

cooling equipment than does ust the instantaneous value of the cooling load

provided the control system is simulated properly. The determination of the heat

e&traction rate must include the characteristics of the cooling equipment and the

operating schedule of thee equipment, in addition to the various sources of

cooling load.

%f the equipment is operated some what longer before and after the pea load

periods, and D or the temperature in the space is allowed to rise a few degrees at

the pea periods during the cooling operation (floating temperature), a reduction

in the design equipment capacity my be made. A smaller system operating for

longer periods at times of pea loads will produce a lower first cost to the

customer with commensurate lower demand charges and lower operating costs.

"enerally, equipment si;ed to more nearly meet the cooling requirements result

in a more efficient, better operating system particularly when is at a partially

loaded condition.

Csually a fraction of the sensible heat gain does not appear a cooling load, but

instead is shifted to the surroundings. The fraction 'cdepends upon the thermal


41/95

conductance between the room air and the surroundings. %t may be also

considered as a adustment factor which results when the load components as

superimposed.

The adustment factor, 'cis calculated by the following equation.

'c I 1 5.52 T

4here Tthe unit length conductance between the room air as surroundings in

-tu D (hr. ft2'), is given by

T I 1D6'(C4A4H CowAowH CcAc)

4here

6' I 6ength of the e&terior walls of the room, ft.

C I Cvalue of room enclosure element (subscript w for window, ow

for outside wall and c for corridor), -tu (hr. ft2')

A I Area of the specific element

%f the cooling load component has already been obtained by the technique used

in this manual, multiply that result by the calculated 'cfactor.

The adustment factor should be used only for individual small spaces or ;ones.

%t is not to be used for bloc loads nor for industrial applications.

D'*&'$ (7 C((') L(#

8iverting of cooling load results from not using part of the load on a design day.

Therefore diversity factors are factors of usage and are applied to the

refrigeration capacity of large airconditioning systems. These factors vary with


42/95

location, type, and si;e of applicant and are based entirely on the udgment and

e&perience of the engineer.


43/95

"enerally, diversity factors can be applied on loads from people and lights! there

is neither 155G occupancy nor total lighting at the time of such other pea loads

as pea solar and transmission loads. The reductions in cooling loads from

nonuse are real and should be accounted for.

%n addition to the factors for people are lights a factor should also be applied to

the machinery load in industrial buildings. 'or instance, electric motors may

operate at a continuous overload, or may operate continuously at less than the

rate capacity or may operate intermittently. %t is advisable to measure the power

input whenever possible! this will provide a diversity factor. %t is also possible to

determine a diversity factor for a large e&isting building by reviewing the

ma&imum electrical demand and monthly energy consumption obtained from the

utility bills.

P&')/',* #) P&(/*%&* 7(& C#/%#$') H*#$') L(#

The pea heating requirements may occur either at night during unoccupied

hours or in the morning picup period following a shutdown. Therefore a number

of calculations are helpful in maing a proper equipment selection and system

design.

I)7(&+#$'() R*


44/95

21)


45/95

'or transmission of heat through a barrier, the motive force corresponding to M3

is temperature difference between the two sides of the barrier. The formula for

rate of heat transmission per hour @ isB

@ I A & C & (T)

4here T is the temperature difference in ' and A is the area of the barrier in

sq.ft. and C is the overall heat transmission coefficient e&pressed in

-TCD@rD


46/95

fluid) which clings on to the barrier surfaces. This resistance is more when the

air is still and is relatively less when there is wind velocity. 6ie thermal

conductivity, the heat transmission capacity of a film is e&pressed as the rate of

heat of transfer in -TCD@rD


47/95


48/95


49/95

in tables, based on the nature of their activities in the room.

24) 6ightsB 6ighting is generally specified in terms of watts per sq.ft.

The total watt has to be converted into -TCD@r by multiplying by

conversion factors.

25) AppliancesB /lectrical, gas burners, steam generation, etc.

26) /lectric PotorsB Applies generally in some of industrial

applications. This load will have to be properly analysed by

discussion with user and appropriate diversity factors should be

applied for estimating the actual load. *onvert the @E into -TCD@r.

4e shall now briefly lay down the procedure for heat load estimating with

e&planations wherever required.

1. *ollect architect$s drawings for the building giving all details and

dimensions of walls, floors, windows, etc. %f such drawings are not

available, survey the place and get the particulars.

2. 'or every application, there are certain things which the ultimate user has

to specify. These areB

27) Temperature N humidity conditions to be maintained inside the space

and tolerance.

28) =ccupancy K i.e. ma&imum no. of people liely to occupy the space

and the nature of their activity.

29) 6ighting load and other internal source of heat generation.

30) Eeriod of operation K e.g. 9 a.m. to + p.m. or 15 a.m. to 9 p.m. etc.

31) 'or industrial application you require also the @E load in the

conditioned space and diversity factor thereon.

32) Pinimum ventilation required.

3. O%$'* D*') C()'$'()


50/95

33) 'or comfort air conditioning application, use the mean ma&imum 8-

temperature N the 4- temperature which occurs simultaneously with

the assumed 8-.

34) 'or industrial applications where temperatures and humidities are to

be maintained within very close tolerance through the year, tan the

ma&imum 8- and the simultaneously occurring 4- temperature.

7. 'or all applications mae a second load estimate for monsoon conditions.

. 'or applications where the conditioned spaces are spread over very vast

floor areas, divide the entire area into convenient ;ones and mae load

estimates.


51/95

?. =ccupancy %n certain applications a diversity factor may have to be used

even in respect of occupancy. /&amples areB =ffice areas where a

separate conference room is also provided. The conference room may be

designed for a large number of people. -ut you must reali;e that it is

mostly the people in the office who go into conferences and hence any

occupancy in the conference room brings about an equal reduction in the

occupancy in other areas of the office.


52/95


53/95

TYPICAL DIVERSITY FACTORS FOR LARGE BUILDINGS

:APPLY TO REFRIGERATION CAPACITY;

DIVERSITY FACTOR

PEOPLE LIGHTS

=ffice 5.+ to 5.>5 5.+5 to 5.9

Apartment, @otel 5.75 to 5.?5 5.:5 to 5.5

8epartment storage 5.95 to 5.>5 5.>5 to 1.5

%ndustrial 5.9 to 5.> 5.95 to 5.>5


54/95

'resh air requirement 2.5 air changes D hr.

or

15 *'P per person

8esign conditionsa indoor +5 ' Q 2 ' 8-T ! G Q G 0@

b =utdoor 15: ' 8-T ! 92 ' 4-T


55/95

U - FACTOR CALCULATIONS

#. E=,(* W#

Total resistance 0T I 0oH L101H L202H L:0:H 0i

I 5.2 H 12. & 5.2 H 2:5 & 5.2 H 12. & 5.2 H 5.?9 2 2 2

I 2.>+ hr. ft2. ' D-TC

=verall heat transfer *oefficient

I 1R I 1R 0T 2.>+

I 5.::+ -TC D hr. ft2. '

. P#&$'$'()

0T I 0iH L101H L202H L:0:H 0i


56/95

I 5.?9 H 12. & 5.2 H 2:5 & 5.2 H 12. & 5.2 H 5.?9 2 2 2

I :.75 hr. ft2. ' D-TC


I 1R I 1R 0T :.75

I 5.2>7 -TC D hr. ft2. '

/. R((7 *=,(* $( %)

0T I 0iH L101H L202H 0i

I 5.2 H 15 & 5.2 H 5 & 7.5 H 5.>2 2 2

I 15.:+ hr. ft2. ' D-TC


I 1R I 1R0T 15.:+


57/95

I 5.5>? -TC D hr. ft2. '


58/95

".0 HEATING> VENTILATION !

AIRCONDITIONING SYSTEMS


59/95

HEATING> VENTILATION ! AIRCONDITIONING SYSTEMS

A. AIR CONDITIONING SYSTEMS

Airconditioning is defined as the simultaneous control of temperature,

humidity, quality and movement of air in a conditioned space or building.

An air conditioning system is therefore, defined as an arrangement of

equipment which will air condition a space or a building. Thus, a complete

air conditioning system includes a means of refrigeration, one or moreheat transfer units, air filters, a means of air transport and distribution, an

arrangement for piping the refrigerant and heating medium, and controls

to regulate the proper capacity and operation of these components.

The items outlined above are considered to be the components of a

complete air conditioning system.

There has been a tendency by many designers to classify an air

conditioning system by referring to one of its components. 'or e&ample,

the airconditioning system in a building may include a dual duct air

transport arrangement to distribute the conditioned air and is then referred

to as a dual duct system. This classification maes no reference to the

type of refrigeration, the piping arrangement or the type of controls.

'or the purpose of classification, the following definitions will be usedB

A) A'&/()'$')') %)'$is understood to consist of heat transfer surface

for heating and cooling, a fan for air circulation, means of cleaning the air,

a motor, a drive, and a casing.


60/95

A *7-/()$#')* #'&/()'$'()') %)'$ is understood to be an

airconditioning unit that is complete with compressor, condenser, controls,

and a casing.

A) #'& #)') %)'$ consist of a fan heat transfer surface, a motor, a

drive and a casing

A &*+($* air handling unit or a &*+($* air conditioning unit is a unit

located (%$'*of the conditioned space which it serves.

The most common types of refrigeration machines, classified according totheir type of operation are (1) mechanical compression, (2) absorption and(:) vacuum.

Apart from the above types the airconditioning system are generally

clarified is to following categoriesB

1. 4indow (room) airconditioners

2.


61/95

reciprocating, rotary or centrifugal in which the cooling effect as well as

the heat reected is used to furnish cooling or heating to the air

conditioning units, either simultaneously or separately.

R*/',&(/#$') (& &($#& /(+,&*(& can be used in systems that

circulate the refrigerant through remote direct e&pansion heat transfer

surfaces. Alternately they can be used in conunction with a water chilling

heat e&changer, to produce chilled water for circulation through remote

heat transfer surfaces that cool and dehumidify the air.

C*)$&'7%# &*7&'*$'() machines are generally not suitable for

circulating and e&panding the liquid refrigerant in remote heat e&changes

surfaces. *entrifugal machines are therefore used only to chill water or

brine for circulation through remote heat e&change surfaces.

A(&,$'() +#/')* cycles are similarly to mechanical compression

machine cycles only to the e&tent that both cycles evaporate andcondense a refrigerant liquid. They differ in the mechanical compression

cycle use purely mechanical processes, while the absorption cycle uses

physiochemical processes to produce the refrigeration effect.

V#/%%+ &*7&'*$'() machines, such as steam et and water vapor

units, are seldom used in modern airconditioning systems.


62/95

1. R((+ A'&/()'$'()*&

This is the simplest form of an air conditioning system. %t has a

hermetically sealed motor compressor assembly, an air cooled condenser

coil, an evaporator coil, condenser fan and evaporator fan. %t has a

capillary tube in place of an e&pansion valve for metering refrigerant flow

to the evaporator. 0oom air conditioners are generally made of capacities

ranging from :D7 ton to 11D2 tons suitable for operation on 2:5 M, single

phase, 5 cycles supply. %t is completely factory assembled and can be

straightaway plugged into power supply when installed.

A,,'/#$'()

"enerally used for small office rooms, shops and residential rooms where

the where the load will generally be within 11D2 tons.


63/95

2. P#/?#* $,* #'& /()'$'()*&

These are larger versions of 0oom Air *onditioners e&cept that they are

generally made with watercooled condensers. They can also be made

with air cooled condensers either built in with the pacage or for remote

installation. They are generally made in capacities ranging from to 15

tons. Cnits with water cooled condensers require condenser water

circulating system and cooling tower. The units may also require e&ternal

duct wor for air distribution. This unit operates on 755 M, phase, 5

cycles supply.

A,,'/#$'()

These units are most ideal where the load is between to 25 tons.


64/95

when diesel engine is used. They are generally with watercooled

condensers even though they can also be built with aircooled

condensers.

A,,'/#$'()

The 8L system of *entral Elant is perhaps the most widely used system

for medium loads between 25 and 155 tons. %t can be used for almost all

types of application.

A#)$#*

The 8L system is perhaps the most efficient of all system from a thermo

dynamic point of view since the heat transfer is directly between the

conditioned air and the refrigerant. The open type compressors used for

these systems have built in capacity controls to tae care of load

fluctuations. Elants of any capacity can be built with 8L systems using

multiple compressors, condensers and evaporators. Although it is

preferable to eep each compressor with its condenser and evaporator as

a single unit, these plants can also be built with interconnection between

them on the refrigerant side.


65/95

involve installation of the plant on upper floors where vibration and other

problems have to be effectively tacled in order to eliminate transmission

of vibrations to the occupied ;ones. *ost wise also, such individual

systems in each floor may prove to be much higher.

4. C*)$ ,#)$ - C'* W#$*& S$*+

A central chilled water system is made up on one or more water chilling

plants. /ach water chilling plant may be built with either one or two

compressors to wor with one or two chillers (8L chiller or shell and tube

flooded chiller) and one or two water cooled condensers. /ach such

water chilling unit is field assembled on structural framewor with the

necessary refrigerant pipes so as to mae a compact assembly. 4here

such multiple water chilling units are used, they are generally

interconnected on the water side both in the condenser circulating system

and chilled water circulating system.

A,,'/#$'()

Pultiple water chilling units with reciprocating compressors are generallysuitable for multistoreyed office buildings where the load is between 155

and :55 tons. @owever, there is no bar against using more number of

water chilling units with reciprocating compressors even for loads higher

than :55 tons. 'or loads e&ceeding :55 tons. 4ater chilling units with

centrifugal compressors would be preferable.

5. C'* W#$*& 7(& P&(/* C((')

A#)$#*

The best advantage of a chilling water system in that the *entral Elant can

be installed in as remote a location as desired from the conditioned areas.

%n fact, they can even be built in a remote plant room with chilled water

piping either underground or overhead running to all the ;ones where air


66/95

handling units are installed. This system provides ma&imum fle&ibility in

operation since the air handling units serving individual ;ones can be cut

off from the chilled water circulating system whenever air conditioning is

not required in any particular ;one.


67/95

basis of 155G fresh air.


68/95

. S/&* C'*&

0efer to figure showing single line diagram of refrigeration cycle for the

above and for piping schematics. /ach vertical screw compressor

discharges hot, high pressure gas through a discharge service valve (A)

(or chec valve in multiple compressor units) into the condenser, where it

condenses outside tubes, reecting heat to cooling tower water flowing

inside the tubes. The liquid refrigerant drains to the bottom of the

condenser and e&its into the economi;er feed line.

The refrigerant flows through the economi;er feed ball valve (-), dropping

its pressure, causing it to flash. %t then flows into the flash economi;er

tan (*) which is at an intermediate pressure between condenser and

evaporator, liquid is centrifugally separated from the flash gas and the

liquid drains to the bottom of the tan, e&its via the economi;er drain line,

and passes through the economi;er drain ball valve (8). -oth economi;er

ball valves are actuated by a modutrol motor (C) that adusts flow to

maintain an appropriate refrigerant level in the evaporator, determined by

a liquid level float switch (M).

'rom the drain line, liquid refrigerant flows into the flooded evaporator,

where it boils, cooling the water flowing inside evaporator tubes. Mapor

from the boiling refrigerant flows up the suction pipes through a shutoff

valve (/) (optional), suction chec valve (') and suction filter (") (inside

compressor) into the compressor where it is compressed and starts cycle

again.

Mapor flows from the top of flash economi;er into the compressor at the

vapor inection port, which feeds it into the compressor part way through

the compression process. *hec valve (@) prevents bacflow at

shutdown in multi compressor units. Al compressors operate in parallel on

a common evaporator and condenser.


69/95


70/95


71/95


72/95

The use of ice storage to minimi;e pea energy usage is not a new or

e&perimental idea. %t has been used for years on applications with short

pea energy usage such as churches, meeting facilities and theaters. =n

these applications, however, the longer pea uses were handled by

conventional rooftop cooling or water chilling D air handling systems.

ow, however, there is renewed interest in a broad use of ice maing and

storage systems by both users and utility companies as the best way of

offsetting rising demand loads and resulting utility cost increases.

%ce storage systems can not only cut operating costs substantially, but

they can also reduce capital outlays when systems are properly applied

for both new and e&isting buildings and commercial and industrial types.


73/95

F% S$(* O& P#&$'# S$(*@

Two load management strategies are possible with ice storage systems.

4hen utility rates call for complete load shifting, a conventionally si;ed

chiller can be used to shift the entire load into offpea hours. This is

called a full storage system and is used most often in e&isting building

renovation or retrofit applications using e&isting installed chiller capacity.

%n new construction, a partial, storage system is usually the most practical

and cost effective load management strategy. %n this load leveling

method, the chiller is si;ed to run continuously e&cept for scheduled

preventive maintenance down time. %t usually charges the ice storage

tans at night and cools the load directly during the daytime pea hours

with help from stored cooling capacity.

This will greatly reduce the installed chiller capacity and its required capital

e&penditure, as well as the demand charge for electricity to run the chiller

during utility peaing periods. Typically reductions can be 5 percent or

more.

H( $* I/* S$(* S$*+ W(&?

A common ice storage system is a modular, insulated tan. Tans are

typically available in several tonhour rated si;es. Typically at night a mild

concentration of glycolwater solution (typically 2 percent ethylene glycol

based industrial coolant such as 8ow *hemical *ompany 8owtherm


74/95

Typical schematic flow diagrams for a partial storage system are shown in

figure1N2. At night, the waterglycol solution circulates through the chiller

and the ice ban heat e&changer, bypassing the air handling coil that

supplies conditioned air to occupied building spaces. 8uring the day, the

solution is cooled by the ice ban from 2 ' to :7 '. A temperature

modulation valve set at 77 ' in a bypass loop around the ice ban permits

a sufficient quantity of 2 ' fluid to bypass the ice ban permits a sufficient

quantity of 2 ' fluid to bypass the ice ban, mi& with the :7' fluid, and

achieve the desired 77 ' temperature. The 77 ' fluid then enters the coil,

where it cools air from appro&imately + ' to '. The fluid then leaves

the coil at an elevated temperature (appro&imately ?5') and enters the

water chiller where it is cooled ?5' to 2 '.

%t is important to note that while maing ice at night, the chiller must cool

the water glycol solution down to 2? ', rather than producing 77 ' water

required for conventional air conditioning systems.

*hillers with aircooled condensing also benefit from cooler outdoor

ambient dry bulb temperatures to lower the system condensingtemperature at night.

The temperature modulating valve in the bypass loop has the added

advantage of providing e&cellent capacity control. 8uring mild

temperature days, typically in the spring and fall, the chiller will often be

capable of providing all the necessary cooling capacity for the building

without the use of cooling capacity from the ice storage system. 4hen the

building$s actual cooling load is equal to or less than the chiller capacity at

the time, all of the system coolant will flow through the bypass loop as

shown in fig.:


75/95


76/95


77/95


78/95

DUCTING DESIGN

The satisfactory distribution of conditioned air requires a well designed and

energy efficient air transport system with appropriate ducts and fans plus air

treatment and control devices.

The various method of duct designs, proper fan selection and control and

methods of air distribution system control for acceptable comfort and air quality in

the conditioned spaces are some of the points to be discussed.

The various methods of duct designing are

a. *onstant Melocity method

b. /qual friction method

c.


79/95

b. @igh velocity above 255 to 555 fpm

ormally return air systems for both low and high velocity supply air systems are

designed as low velocity systems. The velocity range for commercial and factory

comfort application is as followsB

1. *ommercial comfort airconditioning low velocity upto 2555 fpm.

ormally between 155 and 1955 fpm.

2. 'actory comfort airconditioning low velocity upto 255 fpm. ormally

between 1955 and 2255 fpm.

P&*%&*

Air distribution systems are divided into three pressure categories! low, medium

and high. These divisions have the same pressure ranges as *lass %, %% N %%% fans

and indicatedB

1. 6ow pressure upto :S inch wg class % fan

2. Pedium pressure from :S to ? S inch wg class %% fan

:. @igh pressure from ? S to 12 S inch wg class %%%

These pressure ranges are total pressure, including the losses through the air

handling apparatus, ductwor and the air terminal in the space.

The choice of design method depends almost entirely upon the si;e of the

ductwor installation.


80/95

equal friction method.

%n designing ductwor, a new term called unit friction3 will be utili;ed which

means the friction loss per 155 ft of duct wor equivalent length.

0egardless of the duct design method chosen by the air transport system

designer, the final design and duct layout will liely result from the use of

computeri;ed duct design and drafting programs available that are based on

algorithms from the A THEATERS>PUBLIC BUILDINGS

INDUSTRIALBUILDING

=utdoor air intaes1 55 55 55

'ilters1 25 :55 :5

@eating coils1,2 75 55 ?55

*ooling coils1

75 55 ?55Air washers1 55 55 55

'an outlets 1555 1?55 1:55 2555 1?55 2755

Pain ducts2 +55 >55 1555 1:55 1255 1955

-ranch ducts2 ?55 ?55 >55 955 1555

-ranch risers2 55 ?55 +55 955

Pa&imum velocities, 'EP

=utdoor air intaes1 955 >55 1255

'ilters1 :55 :5 :5

@eating coils1,2 55 ?55 +55

*ooling coils1 75 55 ?55

Air washers 55 55 55

'an outlets 1+55 155 2255 1+55 2955

Pain ducts2 955 1255 1155 1?55 1:55 2255

-ranch ducts2 +55 1555 955 1:55 1555 1955

-ranch risers2 ?5 955 955 1255 1555 1?55

1These velocities are for total face area, not the net free area B other velocities in


81/95

table are for net free are

2'or low velocity systems only.

1>? American society of heating, refrigerating and airconditioning engineers,

inc. reprinted by permission for A


82/95

To properly design a water piping system, the engineer must evaluate not only

the pipe friction loss by the loss thru valves, fittings and other equipment. %n

addition to these friction losses, the use of diversity in reducing the water quantity

and pipe si;e is to be considered in designing the water piping system.


83/95

P',* F&'/$'() L(

The pipe friction loss in a system depends on water velocity, pipe diameter,

interior surface roughness and pipe length. Marying any one of these factors

influences the total friction loss in the pipe.

Post air conditioning applications use either steel pipe or copper tubing in the

piping system.

*harts enclosed are for schedule 75 pipe upto 27 inch diameter. *hart shows

the friction losses for closed recirculation piping systems and for once thru D

open recirculation piping systems.

These charts show water velocity, pipe or tube diameter, and water quantity, in

addition to the friction rate per 155 ft of equivalent pipe length. nowing any two

of these factors, the other two can be easily determined from the chart. The

effect of inside roughness of the pipe or tube is considered in all these values.

The water quantity is determined from the airconditioning load and the water

velocity by predetermined recommendations. These two factors are used toestablish pipe si;e and friction rate.

W#$*& V*(/'$

The velocities recommended for water piping depend on two conditions!

1. The service for which the pipe is to be used.

2. The effect of erosion.

The design of the water piping system is limited by the ma&imum permissible

flow velocity.


84/95

R*/(++*) W#$*& V*(/'$

SERVICE VELOCITY RANGE

:FPS;

Eump discharge 9 12

Eump suction 7 +

8rain line 7 +

@eader 7 1

0iser : 15

"eneral service : 15

*ity water : +


85/95

B. VENTILATION SYSTEM

=utdoor air that flows through a building either intentionally as ventilation

air or unintentionally as infiltration (and e&filtration) is important for two

reasons. 8ilution with outdoor air is a primary means of controlling indoor

air contaminants and the energy associated with heating or cooling this

outdoor air is a significant, if not a maor, load on the heating and air

conditioning system. 'or ma&imum load conditions, it is essential to now

the magnitude of this air flow to properly si;e equipment! for average

conditions, to properly estimate average or seasonal energy consumption!

and for minimum conditions, to assure proper control of indoor

contaminants. %n larger buildings, it is important to now ventilation

effectiveness. nowledge of smoe circulation patterns can be crucial in

the event of fire.

Mentilation occurs by two means, natural and forced, atural ventilation

can be classified as (1) infiltration or (2) controlled. Panually controlled

natural ventilation is the ventilation from operable windows, doors or other

openings in the buildings envelope. The latter is an important means of

ventilation in residences in mild weather when infiltration is minimal or inwarm climates to avoid air conditioning costs.

'orced ventilation is mandatory in larger buildings where a minimum

amount of outdoor air is required for occupant comfort. Air contaminant

measurement technology has advanced to include alternate methods

designed to assure that indoor air quality meets specified conditions.

These methods permit the amount of outdoor air to vary according to the

actual requirements of occupants in the space.


86/95

This chapter focuses on envelope or shelldominated buildings! i.e.,

residences or small commercial buildings in which the energy load is

determined by the construction and performance of the building envelope.

The physical principles discussed also apply to large buildings. @owever,

in large buildings, ventilation energy load and indoor air quality conditions

depend more on ventilation system design that on building envelope

performance.

V*)$'#$'() R*


87/95

T,* (7 V*)$'#$'()


88/95


89/95


90/95

R*


91/95


92/95

U I (cf)*vAv (2)

4here

U I Air flow m:Dhr

A I 'ree area of inlet openings, m2

4ind speed, mDs

*v I /ffectiveness of openings (*v) is assumed to be 5.5 to

5.?5 for perpendicular winds

cf I *onversion factor, :?55

%nlets should face directly into the prevailing wind direction. %f they are not

advantageously placed flow will be less than in the equationB if unusually

well placed flow will be slightly more. 8esirable outlet locations are (1) onthe leeward side of the building directly opposite the inlet (2) on the roof.

V*)$'#$'() #) I)7'$$'()

%n the pressure area caused by a flow discontinuity of the wind, (:) on the

adacent to the windward face where low pressure areas occur, (7) in a

monitor on the leeward side, () in roof ventilators or (?) by stacs. 0efer

to *hapter 17 for a general description of wind on a building.

F( C#%* T*&+# F(&/*

%f there is not significant building internal resistance, the flow caused by

stac effect isB

U I (cf)AWh(T1K T5)DT1X1D2

4hereU I Air flow, m:Dhr

A I 'ree area of inlets or outlets (assumed equal), m:

@ I @eight from lower opening to E6, m

T1 I Average temperature of indoor air in height h,

WIt(deg.c)H2+:.1X


93/95

T5 I Temperature of outdoor air,

cf I *onversion factor, including a value of ?G for

effectiveness of openings! this should be 5G if conditions

are not favourable (cf I 15:?5)

The height h is the distance from the lower opening to the neutral pressure

level.

N#$% V*)$'#$'() G%'*')*


94/95

+. =penings with areas much larger than calculated are sometimes

desirable when anticipating increased occupancy or very hot

weather. The openings should be accessible to and operable by

occupants.


95/95

9. 4hen both wind the stac pressures act together, even without

interference, estimated resulting airflow is not equal to the two flows

separately. 'low through any openings is proportional to the

square root of the sum of the squares of the two flows calculated

separately.

C. FORCED VENTILATION

This involves forced supply systems, forced e&haust systems or both,

depending on the requirements.

This is done by fans of various types, including propeller fans, a&ial flow

fans and centrifugal fans. Eropeller fans are generally wall mounted type

and cater to small capacity D small pressure static requirements. A&ial

fans can either be duct mounted or wall mounted type and cater to

medium capacity requirement.

*entrifugal fans, which are a separate topic by themselves, cater to a wide

range of capacity and static pressure requirements.

The later two types of fans can be hooed up to a supply or e&haust duct

system. They can also be hooed up to an air washer D fanfilter system.

'orced ventilation systems can also be classified into dry or wet systems.

8ry systems involve the use of fans alone or with filter bans for dust

Documents

hvacprogrammematerial-090703025103-phpapp02