Assignment Ac-system1

7/29/2019 Assignment Ac-system1

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2012

Thermal system design

assignmentSubmitted to: Dr.Demiss A.

Alemnew EbabuAka

M E K E L L E U N I V E R S I T Y , G R A D U A T E P R O G R A M - E N E R G Y T E C H N O L O G


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Thermal system design assignment

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Assignment -1-

Design of ventilation system .

The Restaurant shown below is to be maintained at a constant environmental temperature of

22o

C for a plant operation of 12 hours per day.The Restaurant area is on the ground floor of anSingle storey building located at 51.7

oNThe internal construction is lightweight partitions,

concrete hollow slab floors and suspended ceilings.it was desired to design a ventilation system

for the restaurant.

the following ste[ps are neccesary to be carried out the plan view of the restaurant is shown

belaow

Calculate Ventilation rates. Decide on number of fans and grilles/diffusers. Draw scale layout drawing and Position fan(s). Lay out ductwork. Lay out grilles and diffusers. Indicate flow rates on drawing. Size ductwork Size fan Size grilles and diffusers

14.0 m

7.7

9.5

FemaleToilet

MaleToilet

Receptio

Entranc

10.0Lobby

Restaurant

3.5

Kitchen

2.7m

Cold

Store

Prep.

Room

PLAN

South

Height of wall to

eaves

Height of

ceiling at


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Fig: the elevation plan view

Table: ventilation system design data for occupancy, building category and exterior structure

dimensions

Sn.

Design data for the restaurant

1 Occupants 70

2 Infiltration 1.0 ACH

3 Outside air temperature 28oC.

4 Area of window 2.8 m2

5 Total area of glass 28.0 m

2

6 Area of glass facing South 28.0 m2

7 Area of wall facing South 28.0 m2

8 Floor area 140 m2

9 Room volume 623 m3

10 Building classification lightweight, fast response

building

South


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Ventilation requirements;

In this design it is proposed to ventilate the kitchen, the preparation room and the restaurant

and toilets separately using 4 exhaust fans the position of the fans its to be decided after the

longest path for which the maximum pressure drop occurs is determined the supply fan should be

as far as possible from the restaurant to avoid noise creation

All rooms the cheaper alternative is an extract system with replacement air coming in through

doors and operable windows. Fans should be located in accessible positions; in the corridor,

above ceilings. In-duct axial flow fans take up less space than centrifugal fans. Possible use of

wall mounted fan in Food Prep. Room. Upward with diffusers installed in suspended ceilings.

Use separate extract systems so that smoke will not spread from room to room through ducts.

Consider fire dampers in ducts. Fans are positioned as far away from Conference room and

restaurant as possible. Choose fans from catalogue with decibel levels less than 85dB if possible.

ventilation requirements for restaurant rooms

Room or building type Recommended fresh air

supply rate

Recommended total air

supply rate(ACH)

Restaurant

Kitchen 10

Female toilet 8

Male toilet 8

Table: restaurant rooms ventilation requirements as recommended by the Table B2.3 (CIBSE

1986).


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.

Table: calculated ventilation rates for the rooms suggested requiring ventilation

The next is to calculate the fresh rate this was done by assuming that the outdoor air supply per

person should suit for a heavy smoking area this is because of the possibility that heavy smokers

may arrive as consumers at restaurants. And since we are dealing with restaurants it is fair to

assume a heavy smoking area with a recommended air supply rate per person of 24 liters per

second. Therefore similarly like the ventilation requirements and assuming a peak of70 persons

the outdoor fresh air supply was found to be 1680

Table: recommended outdoor air supply rates.

ROOMS volume(m3) Recommended (ACH) ventilation rate (m3/hr) ventilation rate(m3/

kitchen 217 35 7595 2.10972

preparation room 47.25 10 472.5 0.1

male toilet 84 8 672 0.18666

female toilet 140 8 1120 0.31111

restaurant 980 10 9800 2.72222

12064.5 3.3

Level of Smoking

Outdoor air supply rate

(liter/s per person)

No smoking 8

Some smoking 16

Heavy smoking 24

Very heavy smoking 36


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CALCULATING THE FRESH AIR RATE

occupants outdoor supply air(heavy smoking l/s/person) fresh air rate(l/s)

70 24 1680

Table: calculated outdoor air supply rate

Duct sizing

The recommended velocity for main duct and branch ducts for restaurants are 7.5m/s and 5m/s

respectively therefore by choosing a square duct with aspect ratio of 1 we can determine the

nearest standard sizes of the ducts and the following standard sizes were obtained for the main

duct and the branching ducts to the rooms which require ventilation.

As shown on the table below the main duct area is 0.45m2and the branching duct are also shown

by considering a square duct the nearest standard sizes were determined for the rooms kitchen,

preparation room ,restaurant and toilets respectively

Table: standard size duct selection

Branching ducts(m2) Main duct area(m2) Square duct size(m)

Nearest

std.size(mm)

0.421944444 0.446833333 0.649572509 300*300mm

0.02625 0.162018517 150*150mm

0.037333333 0.193218357 150*150mm

0.062222222 0.249443826 150*150mm

0.668455932

500mm*500mm(std.)


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Design tool duct sizer

BuildingAir Velocity (m/s)

Main Duct Branch

Domestic 3 2

Auditoria 4 3Hotel bedroom, Conference hall 5 3

Private office, Library, Hospital ward 6 4

General office, Restaurant, Dept. store 7.5 5

Cafeteria, Supermarket, Machine room 9 6

Factory, Workshop 10-12 7.5


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As t can be seen from the results of the duct sizer air at 370c and 23% relative humidity at 1

atm is assumed the results were found to be consistent with spreadsheet results moreover the

velocity pressure and the static pressure losses were found to be 0.749pa/m and 31.5pa for the

dynamic losses therefore the total head loss is given by

Total head loss= velocity pressure loss+ static head loss.

To compute the total pressure loss it is first necessary to identify the index run that is the longest

path of the duct work layout a suitable duct layout system is proposed next which roughly

identifies the longest path for which the highest pressure drop occurs and which is late used as a

selection criteria for the fan sizing.

Figure; rough duct layout system for the main and branching for the whole building to estimate

the index run.

The duct layout can be laid out as shown above to roughly estimate the index run from the

supply side of the fan therefore the maximum run could be the duct system from the fan position

at the reception site to the branch duct for the preparation room which runs half the perimeter of

the whole building so it is estimated as 22m.


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the next step is therefore to estimate the total static head loss for the index run which enables to

select the appropriate fan type by using the flow rate already obtained for their and the total

pressure earlier the pressure loss length was found as 0.79pa/m which gives

Total static pressure loss across the index run=22*0.79=31.5pa

Total pressure loss=static head loss dynamic head loss=49pa

from the calculations and from the table above showing the standard duct size selection

unequal size of branching ducts with duct dimensions ranging from150mm*150mm-

300*300mm were selected and 500mm*500mm standards size square duct were chosen .the

total pressure loss that the supply fan must overcome is found to be 49pa

Fan selection

Given the total pressure drop along the index run and the air flow rate for the main supply duct it

is possible to choose the appropriate fan from available catalogs from the above design

calculations the operation criteria was found to be 12064m3/hr and 49pa.

Table; fan performance curves for various models obtained from catalog


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the fan performance curve for the model 634-b model is suitable for the air flow rate and total as

as shown by the red lines corresponding to the flow rate and total pressure losses obtained from

calculations 12604m3/hr and 49pa.

Table; product specification of fans type cc 630

For more comprehensive design one can look at the power requirements and noise conditions by

referring to the specifications provided in the above table the model we have chosen has a noise

generation of71db which is acceptable for the restaurant compared to 85db limit.


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Documents

Assignment Ac-system1