air-conditioning calculations - presentation

8/6/2019 Air-conditioning Calculations - Presentation

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Abstract


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ABSTRACT

The increasing demand for comfort air-conditioning

has brought with in the need for greater numbers of practical,

technical & sales personal who have should training

in basic principles and applications of modern air-conditioning.The technical information presented in this work is intended

to satisfy the immediate and fundamental concepts

in this work is intended to satisfy the immediate and fundamental

concepts and relevant principles in the field of air-conditioning.

The subject of air-conditioning has come

to stay with the universities in the country.


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The industries and commercial establishment are experiencing

the need of air-conditioning as an instrument and commercialestablishment are experiencing the need of air-conditioning

as in instrument of efficiency and increased output rather

than of comfort alone.

The practice of air-conditioning is making rapid strides

and its increase practical use has brought in new problems,

which is required to be tackled by scientific research.

As a thumb rule practice in air-conditioning do not lead to thorough

understanding or correct solution of new problems.

The project material has been prepared to help

to meet this by providing the fundamental process and procedures.


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For the completion of this project an easy and simple

methodology is adapted by preparing a met lab program to

generalize and making it simple for any multistory building

cooling/heating load estimation. For estimation

,first work sheets are prepared for different existing conditions.Then by using this program the total cooling/heating load

for the entire complex has been easily calculated .


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1-CHAPTER(Introduction)


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1. Definition ofAirConditioning:

Air conditioning is defined as the "the process of treating air so as to

control simultaneously temperature, humidity,cleanliness and distribution to meet the requirements

of the conditioned space."

As indicated in the definition, the important actions involved

in the operation of Air conditioning systems are:


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Temperature control- Room temperature is controlled to the pre

designed dry bulb temperature by cooling or heating room air.

Humiditycontrol Room air is controlled to

the pre designed relative humidity by humidifying or

dehumidifying the room air.Airfiltering, cleaningand purification Room air is cleaned

by removing dust and dirt from the air.

Airmovementandcirculation Air which is controlled

in temperature and humidity and cleaned is distributed

evenly throughout in a room. As a result, room air

can be maintained evenly in temperature humidity conditions.


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Temperature, humidity, cleanliness and distribution of air

are called "four elements of air conditioning". By controllingthese four elements, room air can be comfortably maintained

regardless of outdoor temperature. Should these four elements

can be replaced with the work of air conditioner, the room air is

drawn in the air conditioners, where dust and dirt are removed

from the air by the air filter (cleanness of air)and it is sent to evaporator,

where temperature of the air is reduced by evaporation of the

refrigerant (temperature), and at the same time, humidity in the

air is removed as condensation (humidity). As a result, the air

distributed from the air conditioner is cool and crisp and can

be distributed throughout the room by the evaporatorfan (distribution of air system). Such works are

repeated so as to perform air conditioning.


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1.1 COMFORTABLEAIR:

The heat and coldness that the men feel depend not only onair temperature (dry bulb temperature), but also on humidity

and distribution of air.

In addition the general comfortable zone air conditions

are within the comfortable zone, the room air is not always optimum.

For example, if temperature differs between indoor

and outdoor is nearly 10oC because room air controlled so asto be within this is my computer zone, one feels coolness

and heat strongly when he enters in and out of a room,

which makes him feel uncomfortable.

Such uncomfortable ness is called "cold shock" consequently,

it is important to control room air temperature so as notto feel "clock shock" during cooling by adjusting the thermostat.

The optimum temperature difference between indoor

and outdoor is from 3 to 6oC in consideration with health and economy.


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1.2. NEED OFACCURATEHEATLOAD ESTIMATION:

The primary function of air-conditioning is to maintain conditions that are:

Conductive to human comfort.

Required by a product, or process within 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 actualinstantaneous speak load requirement; type of

control is determined by the conditions to be maintained

during peak and partial load. Generally,

it is impossible to measure either the actual peak or

the partial in any given space; these loads must be estimated.


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2-CHAPTER

(CoolingandHeatingLoadConsiderations)


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2: PRELIMINARY CONSIDERATIONS:

The importance of accurate load calculations for air-conditioning design and selection of equipment can never

be overemphasized. In fact, it is on the precision and care

exercised by the designer in the calculations of the cooling

load for summer and the heating load for winter that a

trouble-free successful operation of an air-conditioning plant

after installation would depend.

An important consideration in this exercise is the date and

time for which these calculations are made. The date would

depend on the local climatic conditions. Although the longest

day in summer is June 21, hottest and most humid day may

occur in July. Similarly, the coldest day may occur inJanuary or even February instead of on December 21.


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Again, though the maximum temperature may occur outside

at 1or 2 p.m. the maximum heat gain of the room may occurat 3 or 4 p.m. due to the direct solar radiation through glass

on the west side, or even later due to the time lag for the heat

transfer through the structure.

Further, the application for which the building is intended to

be used would also govern the choice of time.F

or example,for an office building in winter that is not used at night, the

time for load calculations may be taken during the early hours

of the morning, although the maximum heating load may

occur at night. Similarly, an office building in summer may

have the maximum cooling load at 7 p.m. due to the time lag,

but since no occupants would be present at that time, thetime for load calculations may be taken as 4 or 5 p.m.


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The major components of load in buildings are due to the direct

solar radiation through the west glass, transmission through the

building fabric or structure and fresh air for ventilation. In the caseof applications such as theatres and auditoriums, the occupancy

load is predominant.

A detailed discussion of the solar radiation incident on a surface

and its transmission through glass has been given in the literature1.

F

urther, in literature2, we have studied the methods of calculatingheat transmission and infiltration through structures. These form the

components of load on the building from the external environment.

The internal and system heat gains or losses also form the major

components of other loads.

In this chapter, the methods for the evaluation of the above

mentioned and other individual loads are first presented, followedby a summary of all loads at the end along with an example and a

calculation sheet illustrating the procedure that is followed by

practicing engineers. In the first instance here cooling load

estimation is given followed by that of the heating load.


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2.1: INTERNAL HEAT GAINS: The sensible and latent heat gains

due to occupants, lights. appliances, machines, piping, etc., withinthe conditional space. form the components of the internal heat

gains.

2-2: Occupancy Load

The occupants in a conditioned space give out heat at a metabolic

rate that more or less depends on their rate of working. The relative

proportion of the sensible and latent heats given out, however,depends un the ambient dry bulb temperature. The lower the dry

bulb temperature, the greater the heat given out as sensible heat.

The values for restaurants include the heat given out by food as

well. It will be seen that the sensible heat (S) gain does not vary

much with activity, more and more heat being liberated as latent

heat (L) thus making up for total heat.

The usual problem in calculating the occupancy load lies in the

estimation of the exact number of people present.


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Table 2.1

:1 Heat liberated due to occupancy

Metabolic Heat liberated , W

------------------------------------------------------------------

Activity Rate Room dry Bulb temp. C

------------------------------------------------------------------

W 20 22 24 26

_____________________________________________

S L S L S L S L

Seated at rest 115 90 25 80 35 75 40 65 50

Office work 140 100 40 90 50 80 40 70 70

Standing 150 105 45 95 55 82 68 72 78

Eating in

restaurant 160 110 50 100 60 85 75 75 85

light work in

factory 235 130 105 115 120 100 135 80 155

Dancing 265 140 125 125 140 105 160 90 175


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2.3: Lighting Load

Electric lights generate a sensible heat equal to the amount of the

electric power consumed. Most of the energy is liberated as heat andthe rest as light which also eventually becomes heat after multiple

reflections.

Lighting manufacturers give some guidance as to the requirement of

power for different fittings to produce varying standards of illumination.

In connection with fluorescent tubes, it may be stated that the electric

power absorbed at the fitting is about 25 percent more than necessaryto produce the required lighting. Thus a 60 W tube will need 75 W at

the fitting. The excess of 15 W is liberated at the control gear of the

fitting.

As a rough calculation one may use the lighting load equal to 33.5

W/m2 to produce a lighting standard of 540 lumens/m2 in an office

space.

After the wattage is known, the calculation of the heat gain is done as

follows:

Fluorescent: Q= Total watts 1.25

Incandescent:Q= Total watts


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2.4: Appliances Load

Most appliances contribute both sensible and latent heats. The latentheat produced depends on the function the appliances perform, such

as drying, cooking, etc. Gas appliances produce additional moisture

as a product of combustion. Such loads can be considerably reduced

by providing properly designed hoods with a positive exhaust system

or suction over the appliances.

Electric motors contribution sensible heat to the conditioned space. Apart of the power input is directly converted into heat due to the

inefficiency of the motor and is dissipated through the frame of the

motor. This power is

Power (W) = (Input) (I -motor efficiency)

The rest of the power input is utilized by the driven mechanism for

doing work which may or may not result in a heat gain to the space.

These

depend on whether the energy input goes to the conditioned space

or outside it.


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Table 2:2 Appliance load, W

Appliance sensible latent

Coffee brewer 0.5 gal 265 65 329

Warmer 0.5 gal 71 27 98

Egg boiler 353 235 60

Food warmer /m of plate 1150 1150 2300

Griddle frying with frying

top of 46 cm *36 cm 912 500 1412

Toaster, 360 slices / h 1500 382 1882


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2.5: Piping,Tanks, EvaporationofWaterfroma FreeSurfaceandSteam

Heat is added to the conditioned space from running pipes carrying hotfluids due to heat transfer. On the other hand, cold pipes take away heat

from the space. Open tanks containing warm water contribute both sensible

heat and latent heat to the space due to evaporation.

This can be calculated by knowing the rate of evaporation and energy

balance.

In industrial air conditioning, products have often to be dried. Thisinvolves the sensible heat gain to the space from the hot surfaces of the

dryer and the latent heat gain depending upon the drying rate. For these

calculations, knowledge of the heat and mass transfer coefficients is

essential.

When steam is entering the conditioned space, the sensible heat gain is very

little. It is equal to only the difference in the enthalpy of steam at the steam

temperature and the enthalpy of water vapour at the room dry-bulb

temperature. The main load is in the form of the latent heat gain. Thus

SHG = (kg/s) (tstcam- ti)(1.88)kW (2.1)

LHG = (kg/s) (2500) kW (2.2)


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2.6: Product Load

In the case of cold storages. the enclosures are insulatedwith at least 10 - 15 cm of thermocole and are almost

completely sealed. Thus, many of the loads present in

buildings for comfort air conditioning are either absent or

lessened in the case of cold storages. However, in

addition to the heat removed from products at the time of

initial loading, there is also the heat produced by the

commodities during storage. This heat of respiration

forms a sizable product load even at a storage

temperature of 0'C.At higher temperatures, it is more. The approximate rate

of evolution of heat by various products at different

temperatures.


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Table 2.3: Heat of respiration of products in J/kg per 24 hours

Product storage Temp.-----------------------------------------------------------------------0 C 4.4 C 15.6 C

Apples 312-1560 625-2810 2390-8215Bananas - - -Cabbage 1248 1770 4265Carrots 2183 3640 8420Cauliflower - 4680 10500Cherries 1352-1871 - 11440-13725Cucumbers - - 2290-6860

Grape fruit 416-1040 730-1350 2290-4160Grapes, American 624 1250 3640

Grapes, European 312-416 - 2290-2705Lemons 520-936 625-1975 2390-5200Melons 1350 2080 8840Mushrooms 6446 - -Onions 728-1144 830 2495Oranges 416-1040 1350-1665 3850-5405Peaches 936-1456Pears 728-936 - 9150-13725

Peas 8526-8733 13520-16635 40860-46265

Plums 416-728 935-1560 2495-2910Potatoes, immature - 2705 3015-7070Potatoes, mature - 1350-1870 1560-2705Strawberries 2807-3950 3745-7070 16220-21105Tomatoes, green 625 1145 6445Tomatoes, ripe 1040 1350 5820Turnips 1975 2290 5510


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2.7: Processload:

The procedure of calculating the cooling and heating load

for various industrial air-conditioning processes is specific

for each process. The requirements for the process may

involve the control of one or more of the following factors:

Regain of moisture content by hygroscopic materials, such

as cotton. silk, tobacco, etc., and the accompanying heatliberated.

Drying

load.

Rate of chemical and biochemical reactions.

Rate of crystallization, freezing, freeze-drying, etc.Sensible cooling load.

For details of these loads, one may refer to the ASHRAE

Handbook


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2.8: SYSTEM HEAT GAINS

The system heat gain is the heat gain (or loss) of an air-conditioning system

comprising its components, viz., ducts, piping, air-conditioning fan, pumps, etc.

This heat gain is to be initially estimated and included in the total heat load forthe air-conditioning plant. The same should be checked after the whole plant

has been designed

2.9: SupplyAirDuct Heat Gainand Leakage Loss

The supply air normally has a temperature of 10 to 15C. The duct may pass

through an unconditioned space having an ambient temperature of 40C. Thisresults in a significant heat gain till the air reaches the conditioned space even

though the duct may be insulated.

The heat gain can be calculated using the following expression

Q=UA (ta- ts) (2.3)

Where Uis the overall heat-transfer coefficient andA is the surface area ofthe duct system exposed to the ambient temperature ta.

As a rough estimate. a value of the order of 5 percent of the room sensible

heat may be added to the total sensible heat if the whole supply duct is

outside the conditioned space, and proportionately less if some of it is within

the conditioned space.


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It has been found that duct leakages are of the order of

5 to 30 percent depending on the workmanship. Air

leakages from supply ducts result in a serious loss of the

cooling capacity unless the leakages take place within

the conditioned space.

If all ducts are outside the conditioned space, a 10percent leakage is to be assumed which should be

considered as a complete loss. When only a part of the

supply duct is outside the conditioned space, then only

the leakage loss of this portion is to be included.

The fraction of 10 percent to be added in such a case isequal to the ratio of the length outside the conditioned

space to the total length of the supply duct.


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2.10: Heat GainfromAir-Conditioning Fan:

The heat equivalent of an air-conditioning fan horsepower is added as the

sensible heat to the system. If the fan motor is outside the air stream, the

energy lost due to the inefficiency of the motor is not added to the air. Thereare two types of air supply systems.

1-Draw-through system

In the draw-through system, the fan is drawing air through the cooling coil

and supplying it to the conditioned space. This is the most common system.

In this system, the fan heat is in addition to the supply air heat gain. The

heat should therefore be added to the room sensible heat.2-Blow-through system

In the blow-through system, fan blows air through the cooling coil before

being supplied to the conditioned space. In this system, the fan heat is

added after the room to the return air. Thus the fan heat is a load on the

cooling coil. The heat should therefore be added to the grand total heat.

The fan efficiencies are of the order of 70 percent for central airconditioning plant fans and about 50 percent for package air-conditioner

fans.

The fan horsepower depends on the quantity of air supplied and the

pressure rise. The supply air quantity in turn depends on the dehumidified

rise, which is of the order


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of 8 to 14C. The fan total pressure depends on the

system pressure loss which comprises the pressure

drop through the duct-work, grilles, filters, cooling, etc.

Once the supply air-rate and pressure developed are

known, the fan power can be calculated. But these

cannot be known until the load calculations have been

completed. Hence the procedure is to initially assume

fan heat between 2.5 and 7.5 percent of the room

sensible heat and check the value after the design hasbeen completed


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2.11: ReturnAirDuct Heatand Leakage Gain:The calculation of the heat gain for return air

ducts is done in exactly the same way as for

supply air ducts. But the leakage in this case is

that of the hot and humid outside air into the duct

because of suction within the duct. If the ducts

are outside the conditioned space, an in leakage

up to 3 per cent may be assumed depending on

the length of the duct. If there is only a short

connection between the conditioning equipmentand the space, this leakage may be neglected


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2.12: Heat GainfromDehumidifierPumpand Piping:

The horsepower required to pump water through the dehumidifier

adds heat to the system and is to be considered like that of other

electric motors.

For this purpose pump efficiencies may be assumed as 50percent

for small pumps and 70 percent for large pumps.

The heat gain of dehumidifier piping may be calculated as apercentage of the grand total heat as follows:

(i) Very little external piping: 1 % of GTH

(ii) Average external piping: 20%of GTH

(iii) Extensive external piping: 4% of GTH.

Note: Percent Addition to Grand Total Heat: It is to be noted that all

heat gains after the room are not to be added to room heat gains but

to the grand total heat load that directly falls on the conditioning

equipment. These include the return air duct heat


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and leakage gain, dehumidifier pump power, dehumidifier

and piping losses, as out- lined above and the fan

sensible heat in the case of the blow-through system.

2.13: Safety Factor

Safety factor is strictly a factor of probable error, in the

estimation of the load. For the purpose, additional 5

percent heat should be added to the room sensible and

latent heats.


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3-CHAPTRER

(BUILDING SURVEY)


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Introduction


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Abha, the city in kingdom of Saudi Arabia is situated at

18.23 N latitude and 42.65E longitudes in the south west of the

kingdom.

Its height from sea level is 1,500meter. Here the weather

condition is very good. The average temp. round the year is

about 26 C.So throughout the year, it is very comfortable. But

due to global change in weather condition the weather is

becoming sour andhot .Forhuman comfort we need to air-

condition our residential and commercial places. For the air-

conditioning we have selected the workshop complex of

Mechanical Engg. Department of KKU, ABHA.


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3. BUILDING SURVEY:

An accurate survey of the load components of the space to

be air-conditioned is a basic requirement for a realistic

estimate of cooling and heating loads. The completeness

and accuracy of this is my computer survey is the veryfoundation of the estimate, and its importance cannot be

overemphasized. Mechanical and architectural drawings,

complete field sketches and in some cases, photographs

of import aspects are part of a good survey. The following

physical aspects must be considered.


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3.1:Orientation ofbuilding Location of the space to nbr air conditioned with

respect to:Compass points sun and wind effects.

Nearby permanent structures shading effects.

Reflective surfaces water, sand, parking lots etc.

3.2:Use ofspace (s) Office, hospital, department store, specialty shop,

machine shop, factory, assembly plant etc.

3.3:Physical dimensions ofspace (S) Length, width and height.

3.4:Ceilingheight Floor to floor height, floor to ceiling, clearance between

suspended ceiling and beams.

3.5:Columnsandbeams Size depth also knee braces.

3.6:Construction materials Materials and thickness of walls, roof, ceiling,

floors and partitions and their relative position in the structure.

Surrounding conditions Exterior color of walls and roof, shaded by adjacent

building or sunlit. Attic spaces invented or vented. Surrounding space

conditioned or unconditioned temperature of non conditioned adjacent

spaces such as furnace or boiler room and kitchens, floor on ground, crawl

spaces, and basement.


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3.7:Windows Size and location wood or metal sash, single or

double hung. Type of glass single or multipane. Type of shading

device. Dimensions of reveals and overhangs.

3.8:Doors Location, type, size and frequency of use.

3.9:Stairways, elevatorsand escalators Location, temperatureof space if open to unconditioned area. Horse power of machinery,

ventilated or not.

3.10:People Number, duration of occupancy, nature of activity, any

special concentration at time, it is required to estimate the number of

people on the basis of square feet per person, or on average traffic.


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3.11:Lighting Wattage at peak. Type incandescent, fluorescent,

recessed, exposed. If the lights are recessed, the type of airflow over the

lights, exhaust, return or supply, should be anticipated. At time, it is requiredto estimate the wattage on a basis of watts per sq. due to lack of exact

information.

3.12:Motors Location, nameplate and brake horsepower and usage. The

latter is of great significance and should be carefully evaluated. The power

input to electric motors is not necessarily equal to the rated horsepower

divided by the motor efficiency. Frequently these motors may be operating

under a continuous overload, or may be operating at less than rated capacity.

It is always advisable to measure the power input whenever possible. This is

my computer is especially important in estimates for industrial installations

where the motor machine load is normally major portion of the cooling load.

3.13:Appliance, business machines, electronicequipment Location,

rated wattage, steam or gas consumption, exhaust air quantity installed or

required and usage. Avoid pyramiding the head gains from various

appliances and business machines. For examples, a toaster or a waffle iron

may not be used during the evening, or the fry kettle may not be used during

moming, or not all business machines in a given space may be used at the

same time.


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3.14:Ventilation CFM per person, CFM per Esq. ft. Scheduled

ventilation (agreement with purchaser) Excessive smoking, floor

orders, code requirement. Exhaust fan-type, size, speed, and CFM

delivery.

3.15:Thermalstorage includes system operating schedule (12,

16 or 24 hours per ay. Specifically during peak out door conditions,

permissible temperature swing in space during a design day, rugson floor.

3.16:Continuous orintermittentoperation Whether system be

required to operate every business day during cooling season, or

only occasionally, such as churches and ballrooms. If intermittent

operation, determine duration of time available for precooling or pull

down.


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4-CHAPTER

(DESIGN CONDITIONS)


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4. DESIGN CONDITIONS:

Since the need of air conditioning is primarily a function of

our body's reaction to the climate, we will begin our study

of load estimating by looking at outdoor and indoor designconditions. Establishing these conditions for a specific

application, locality, and time will fix the magnitude of

head gain or loss essentially establishes the potential for

head to flow and can be equated to establish the voltage

for an electrical circuit.


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:OUTDOORDESIGNCONDITIONS:1.4There are several sources of data that can be secured to establish outdoor

design. Three common ones are.

ASHRAE Handbook ofFundamentals.

Engineering Weather Data.

Carrier System Design Manual.

Each source contains data based on average weather conditions available at thetime of publication.

It is commonly acknowledged that ASHRAE has come to be regarded as the

industry standard when it comes to outside design data for abha. ASHRAE data

is based on detailed records from official weather stations of the abha. Weather

Bureau, abha.

To illustrate the outdoor design data is taken from carrier system design manual.New Delhi will be used to illustrate the values published.


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:USEOFOUTDOORSDESIGNCONDITIONS2.4

Summerdesign condition inABHA(KINDOMOFSAUDIARABIA)

Summer DB34oC

Summer WB21oC Daily Range12oC

:INSIDEDESIGNCONDITIONS:3.4

The human body considers itself comfortable it can maintain an

average body temperature between 360C and 37.70C. To accomplish

this is my computer body exchanges heat with its environment by

evaporating body fluids and


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exchanging heat thru stable body temperature, and the mindperceives itself as comfortable when body temperature can

easily maintained. It becomes the task of air-conditioning to

maintain the environment around the body within this is my

computer comfort zone of conditions.

The following variables, all of which affect the ability of bodyto exchange heat with surrounding and perceive itself

comfortable.

Surrounding Dry Bulb Temperature

Surrounding Relative HumiditySurrounding Mean Radiant Temperature

Surrounding Air Velocity


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: DESIGNCONDITIONS4.4

At this point we have sufficient information to complete the

design portion of the calculation sheet form for ourworkshop complex building in the department of

Mechanical Engineering ,KKU ,Abha . Assuming we are

going to do a block load for our selected building for May

at 4 P.M. the outdoor design conditions from table 1 has

been determined to 340C DB and 21oC WB. Plotting thispoint on the psychometric chart results in finding a

corresponding 74 GR/LB moisture content of the air.

Considering the ASHRAE comfort zone, let's pick inside

design conditions of 22 oC DB and 50% RH (relativehumidity). The difference between outdoor air DB of 34oC

and room (indoor) DB of 22oC IS 12oC. This indicates for

each CFM of outdoor air entering the building for

ventilation purposes, the OA must be cooled 12oC.


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:LOAD COMPONENTS:5.4

The load components are one of the two general types:

SensibleLatent

result when heat entering the conditioned space causes:ASensible Load1.5.4

a dry bulb temperature increase.

result when moisture entering the space causes theALatentLoad:2.5.4

humidity to increase. A load component may be all sensible, all latent or a

combination of two.Additionally load components can be classified into one of the following three

categories.

SKIN LOAD

INTERNAL LOADS

OTHER LOADS

Skin loads originate from heat sources outside or external to the conditionedspace. Internal loads have their sources within the space itself. Other Loads

occur from head gains or losses associated with moving cool fluids to and from

the conditioned Space design conditions.


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:SKINLOADS:3.5.4

:SOLARGAINTHRUGLASS:6.4The sun rays pass through the glass windows as radiant

energy and are absorbed within the space. Solar head gain

typically reduced by the space. Solar heat fain is typically

reduced by the use of internal or external-shadin g devices,

reveals, overhangs or shadows cost by adjacent buildings.:SOLARAND TRANSMISSIONGAINTHRUWALLS1.6.4

AND ROOF:

Heat is caused to flow through external wall and roofs by

two sources:Sun rays striking the external surfaces.

The high outdoor air temperatures.


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:TRANSMISSIONTHRUGLASS, PARTITIONS,2.6.4

CEILINGAND FLOORS:

When an adjacent area is at a temperature higher than thespace to be air conditioned, heat will flow through windows,

ceilings, partitions, or floors by means of transmission.

:INFILTERATION:3.6.4

Wind blowing against the side of building causes the

outdoor air, which is higher in temperature and moisturecontent, to infiltrate thru the cracks around doors and

windows. This results in localized sensible and latent heat

gains.

;VENTILATION:4.6.4Should ventilation air for odor removal be introduced directly

into the space, it will appear as load in the space. It could be

considered as forced infiltration and would result in localized

sensible and latent heat gain.


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4.7:INTERNAL LOADS:

:PEOPLE:1.7.4

The human body through metabolism generatesheat within itself and releases it by radiation,

convection, evaporation from the surface, and by

convection and evaporation in the respiratory tract.

The amount of eat generated and released dependson surrounding temperatures and the activity level

of the person. Both sensible and latent heat loads

will enter the space.

:LIGHTS:2.7.4Illuminates convert electrical power into light and

sensible heat. Lighting is either fluorescent or

incandescent.


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:LIGHTS:2.7.4

Illuminates convert electrical power into light and sensibleheat. Lighting is either fluorescent or incandescent.

:EQUIPMENT:3.7.4

Within the conditioned spaced powered equipment can

produce localized sensible and / or latent loads. Such

devices would include calculators, computers, motors,popes, tanks, or product from a process.

:ROOMLOADS:4.7.4

The room includes the entire space inside the building.

Adding all the sensible loads together results in the roomsensible heat gain (RSH). Similarly, the sum of all the latent

heat gain (RLH). Finally the sum of RSH and RLH is the

room total (RTH).


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SUPPLYAIRSIDE::OTHERLOADS8.4

If there was no heat gained or lost between the coil of the air

handling unit and supply air terminal, the temperature of theair leaving the coil would be the same as that of the air

entering the room. In a real system the following losses

exists.

:SUPPLYDUCTHEATGAIN:1.8.4Should be supply air duct pass thru a space whose

temperature is higher than that of the air being transmitted, a

sensible heat gain will be experienced.

:SUPPLYDUCTLEACKAGELOSS:2.8.4

The supply air is transmitted under to the room. Dependingon the quantity of ductwork installation, leaks at the joints will

exits to some degree resulting in a loss of sensible as well as

latent capacity.


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:SUPPLYAIRHEAT:3.8.4

In air handling units whose fan is located downstream of the coil, the

does the work on the air resulting in a sensible heat gain to supply air.

In addition the motor losses could show up on the supply air of themotor is located on the air stream.

:BYPASSED OUTDOORAIR:9.4

Because the coil is not a perfect device, a position of the entering air

passes through the coil completely unaltered in temperature or

humidity, resulting in a sensible and latent loss of supply air.4.10: EFFECTIVE LOADS:

Adding the supply air sensible losses to the RSH results in air load

laving the coil referred to as effective room sensible heat (ERSH). In

similar manner latent losses of the supply air plus RLH results in

effective room latent heat by the coil. These loads are referred to as

effective since both the coil leaving air temperature and humidity levelmust effectively be lower than conditions required at the room on order

to:

Absorb the losses along the way and

Absorb the room loads


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4.11: EQUIVALENTTEMPERATURE DIFFERENCE:

Heat flow though an exterior wall is due to the combined effect of twoheat sources:

Sun's rays striking the wall resulting in solar insert gain.

Outside air temperature higher than the inside temperature resulting in

transmission thru the wall.

Since the wall has mass, the storage, affect of wall makes the flow of

heat through it time related. Determination of actual amount of eatsentering the space is therefore a rather complex calculation. To get a look

for the movement of heat thru wall under these circumstances a look at

time related temperature profiles across a wall is beneficial. Assume air

temp. on both sides of a walls maintained at 23.88oC. With no sun

shining on the wall temp thru wall is constant. As sun shines on wall,radiant energy is converted to heat at surface to outdoor air and into wall.

With time the surface temp. rises as well as temp in the wall, as heat

flows into wall and then on to the interior.


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With continued sun shining on the wall, a steady state heat

flow situation will occur where amount of energy striking thesurface equals the amount of heat given off to outdoor air

plus the amount of heat entering the interior. When sun

cease to shine on the wall, stored energy in wall continues to

flow to the outside and inside until temp. Throughout the wall

equalizes. Whether the sun is shining on the wall heat isalways flowing in two directions. Transmission heat flow thru

wall behaves in a manner similar to solar flow of heat. As the

outdoor temperature rises-causing heat to flow into wall. If

outdoors temp. remained at 34oC for a long time a steady

state heat transfer condition would exist. Under this condition

heat entering the indoor space would define by equation:

Q = U*A* (Temperature Difference)


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Should the outdoor air temp. fall quickly,

energy stored in wall quickly flow outward inboth directions . Under these conditions the

flow of heat is no longer steady state and

above equation no longer applies. Since the

solar intensity striking the outside air

temperature is continually changing, simple

heat transmission equation cannot be used.

The equivalent temperature difference is afactious number used to describe the flow of

heat thru the wall at a given point in time.


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4.12: INFILTRATION, VENTILATIONAND EXHAUST:

Infiltration is leakage of untreated outdoor air through porous exterior

walls, floors, roofs etc. the amount of leakage is not controllable by theoccupants in the building, and can results in rather large heat gains or

losses.

The rate of which the leakage takes place is dependent upon the

pressure differential across the exterior surface. The pressure difference

is in turn caused by wind velocity, difference in air density, orpressurization caused by mechanical supply and exhaust systems.

Due to the tremendous variability in building geometry, wind patterns,

and construction quality, accurate evaluation becomes the task of the

designer to use his educated judgment based on the information

available to provide for this potential load source.

The following text provides a partial in sight into this phenomenon,however, further research by the reader is necessary to properly

evaluate infiltration-particularly in tall building (i.e. those over 30 m high).


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:VENTILATION:13.4

The introduction of outdoor air for ventilation of conditionedspaces is necessary to dilute odors given off by people,

smoking, or other internal air contaminants. Local codes

usually determine the minimum amount of ventilation

required, and may be specified either as CFM / person or

CFM/Ft2 of net floor area.It is customary to minimize the amount of outdoor air

introduced into the space since this can result in a

substantial heating or cooling load. With high-energy costs

this can translate into significant operating costs. The

people density of the building is 50 sq. ft. / person/ as we

know that 15 CFM / Person is a good minimum ventilation

rate. Thus the building requires.


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:EXHAUST:14.4

Codes require that some odour producing areas in a building

must be positively exhausted. Such area would be toilets orkitchen hoods over grilles. This does not mean that extra

outdoor air must be supplied for the purpose of exhausting.

Room air in most cases is perfectly satisfaction for exhaust

requirements.

:AIRCHANGE:15.4As the example building is a shopping complex application,

therefore 1 air change is given in order to maintain the proper

air composition in the conditioned space.

:: INTERNALHEATGAIN16.4

Within the conditioned space people, lights, generate sensible

loads, powered equipment, and appliances. Internal latent

load sources are recorded further down the load calculation

sheet .


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:PEOPLE:1.16.4

Heat is generated within the human body by

oxidation commonly called metabolic rate. Thisheat is carried to the surface of the body and

dissipated by:

Radiation from the body to the surrounding colder

surfaces.Convection from the body and respiratory tract to

the surrounding air.

Evaporation of moisture from the body surface and

in the surrounding air.from the carrier system design manual shows

average dissipation of Sensible and latent heat

from people at different level of activity.


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:LIGHTS:2.16.4

Lights generate sensible heat by the conversion of electrical power into

light and heat. The heat is then dissipated by radiation to the surroundingsurfaces, by Conduction into adjacent materials, and by convection to the

surrounding air. Lights are typically specified as lamp watts/ Ft2 of floor

area.

Incandescent lights convert approximately 10% of the power input into

light. The rest appears as heat within the bulb. The heat then makes its

way into the space 80% by radiation and 10% by conduction andconvection florescent lights are more commonly used in commercial

buildings. About 20% of the input power(E) is converted to light by

florescent bulbs thus they are more efficient than incandescent lights.

20% of the power input (E) is dissipated by convection and conduction to

the space. Additionally, 20% of the input power is generated as heat in theballast of the lamps. The above values very from manufacturer to

manufacturer and more efficient lights significantly reduce the ballast loss.

Generally, however, the following equations are used to give a good

approximation of the heat gain to the space.


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TYPE:HEATGAINTOTHESPACE:

FLORESCENT:BTUH / WATT413.3X25.1RATED LAMP WATTS xINCANDESCENT:BTUH / WATT143.3RATED LAMP WATTS X

1.25 ACCOUNTS FOR BALLAST HEAT GAIN


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:STORED EVERGYFROMLIGHTS:3.16.4

The radiant energy from lights has the potential to be

stored in the mass of the building and appear as a load

later in the space. This is the same process that occurswith solar radiant energy.

It is normal practice to neglect the storage impact when

calculating the space load due to lights. Most comfort

applications result in less than 2% reduction in the load,and therefore, storage is neglected. The basic reason

behind this practice is as follows:

Carpeting is widely used. The primary target for radiant

energy from the lights is the floor. Carpet insulates the

floor from the radiant light rays. The radiant energy strikesthe carpet and is converted into heat. The heat is then

dissipated almost immediately into the space. Only a small

portion of the energy is stored in the floor.


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Unless the air conditioning equipment is run for an hour or two beforethe light are turned on, the mass of the building will already be

saturated with stored heat from the night before, therefore, as light

heat is observed in the mass, the equivalent amount of energy is

almost simultaneously released to the space:

In order to see a significant reduction in heat of lights due to storage

the following Condition should be present.The air conditioning equipment should be run longer then 12 hours per

day to remove solar energy from the mass of the building, and also

reduce or eliminate morning pull down loads.

The lights should be turned on 1 (preferably 2) hours after the air

conditioning equipment in the morning. Determining the storageimpact can be done by the use of tables 12 in the carrier system

design manual.


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:BYPASSED OUTDOORAIR:17.4

Since the cooling coil is not a perfect heat exchanger device, some of

the air entering the coil passes through the coil untreated. This

represents a loss air leaving the coil must overcome before entering the

room. It is a load equivalent to an infiltration load in the room, and iscalculated in that manner. The percentage of air (expressed as a

decimal) that passes through the coil untreated is referred to as the

bypass factor and is typically figured at 0.5. it is really a function of the

type of the coil and equipment used. A more accurate value can be

assigned, as the designer becomes more familiar with cooling coil used

in air conditioning equipment.


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:EFFECTIVEROOMSENSIBLEHEAT(ERSH):18.4

Adding the supply duct sensible losses to the room sensible

heat (RSH) results in a load known as the effective room

sensible heat (ERSH). This load is used in determining theCFM of air required across the cooling coil the air must be

effectively higher than the normal quantity to absorb the

room load and the losses encountered along the way from

the cooling coil to the room.


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4.19: LATENT LOADS:The latent counterparts of infiltration, internal loads are

now calculated order to determine the room latent heat

(RLH) and effective room latent heat (ERLH). Vapor

transmission is one new load source encountered.:VAPOURTRANSMISSION:20.4

Water vapor flows thru building structures, resulting in a

latent load whenever a vapor pressure difference exists

across the structure. The latent load from this source is

usually insignificant in comfort application and need beconsidered only in low or high dew point applications.


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Water vapor flows from high to lower vapor pressure at rate determined by the

permeability of the structure. Further details on this subject can be found in the

carrier system design manual.

For the air conditioning the available plan of the workshop complex building of

Mechanical Engineering,KKU,ABHA,KINDOM OF SAUDI ARABIA has been

selected for cooling load calculation .The plan of the complex as shown in

fig.1.The other details for the building are taken as below.

Building located at 18.2o N Latitude, the following data are given

Plaster on inside wall=1.25 cmOut side wall construction=20 cm concrete block

=10 cm brick veneer

Partion wall construction=33 cm brick

Roof construction=20 cm RCC slab with 4 cm asbestos cement board

Floor construction=20 cm concrete

Densties, brick=2000kg/ mConcrete=1900kg/m

Plaster=1885kg/m

Asbestos board=520kg/m


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Fenestration (weather-stripped, =2mx1.5m glasses loose fit

lU=5,9wm k

doors 1.5mx2 m wood panels

U=.63w m k

out door design condition =34C DBT,22C WBT

Indoor design condtion 25 DBT, 50% RHDaily rang 220C TO 34 C =12 C

Occupancy=200

Light 15000 w fluorescent

4,000 w tungsten

Assume bypass factor of cooling coil =0.15

Find room sensible and latent heat load and also the grand total heat load .

air-conditioning calculations - presentation

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