PART C:
INSPECTION OF AIR CONDITIONING SYSTEMS
State Senior Mechanical Engineers/Mechanical Engineers are invariably called
upon to supervise air conditioning System on behalf of JKR Headquarters as well as for
their state projects. I wish to stress and emphasize that progressive inspection and
supervision of the project is a must and inspection is obvious as the ducts, chilled water
pipes, some of the valve and water pumps etc are insulated, and covered up and if this are
only inspected when the installation is completed, it is not possible to check the gauges,
class and type of material and equipment used.
2.
Therefore the following major items are to be checked against the specification as
and when they are delivered to site and in the process of being installed:
a) Air-conditioning, plant and its associated equipment
These are relatively simplier to check as the type model and size are stamped
on the machine and are factory built.
b) All Motors and Starters
The H.P as well as the RPM of the motors are to be checked. Contractors may
supply and install higher RPM than specified. For the same capacity, higher
RPM motor much cheaper, not so lasting and very noisy in operation.
Starters shall be of the following types to comply with TNB regulation:
i)
Up to 3 H.P motors – direct – on direct line
ii)
Above 3 H.P and up to 10 H.P motors star-delta or auto
transformer
iii)
Above 10 H.P motors – auto – transformer or secondary resistance
starters.
c) Air Handling Units:
If these are factory built, then it is relatively simplier to check but you will
have to ensure that they are not locally fabricated as the materials and
insulation used are usually of poor quality and the workmanship leaves much
to be desired.
d) Ducting
e) Chilled water and condenser piping
Obviously the gauge of GI sheets and the gauge and class of pipes used have
to be checked before these are insulated and covered up.
f) Supports and hangers
These should be of rugged construction so that each length of ductwork shall
be rigidly supported. Direct fastening of duct of support with screw are not
permitted.
g) Insulation
The type, thickness, thermal conductivity and density of the insulation are to be
checked against the specification. Generally for ductwork, 2” fiberglass
insulation a thermal conductivity not greater than 0.26 BTU/hr/sq.ft./°F and
density not less than 2 lb/cu.ft. are used. All ductwork within the plant room
shall have 2” cork insulation, and within the ceiling space below the roof or in
any vertical shaft, 2” fiberglass insulation is required. For the air handling unit,
the ductwork is insulated with 1” coporight or approved equivalent with vapour
seal. Obviously thinner thickness and lower density insulation is not acceptable.
h) Vapour Barrier
With the recent imposition of the Fire Regulations, double sided, fiberglass
reinforced, fire resistant aluminum foil are specified as against the single sided
aluminum foil previously used. Special attention should be paid as the price
difference can be as much as RM 0.20/sq.ft. Hence single sided aluminum foil
should not be permitted if double sided is specified.
i) Valve
These are applicable more for chilled water systems and generally our
specification calls for cast steel body type of valve below 3” with a working
pressure of 250 psi type & lower working pressure valves are not only below
specification but also the price difference will come to a few thousand dollars
for the large size of valves.
j) Chilled water and condenser water pumps.
Centrifugal water pumps with horizontally split casing, bronze impeller and
stainless steel shaft are specified and it must be ensured that cheaper types of
pumps e.g. vertically split casing, cast iron impeller and mild steel shaft are not
supplied and installed.
k) Cooling Tower.
In most cases Marley USA type of Cooling Towers or approved equivalent are
specified and accepted and the inspection present no serious problem. However
if locally fabricated Cooling Towers are accepted then a very stringent and
detail examination has to be made to check the quality of materials &
workmanship.
l) Automatic Controls.
You will have to ensure that the correct make and type of controls and their
associated equipment are supplied as offered in the specifications.
3.
The above are considered as the major items that should be progressively checked
and inspected. The salient feature and points are enumerated against the major items and
of course there are numerous other items and points to be considered and checked against
the specification and technical data as offered by the contractor. Not only the quality of
materials and equipment and their compliance to specification should be looked into but
also the standard of workmanship should be to the best engineering practices. The use of
sub-standard materials and equipment will lower the performance of the air conditioning
system and the design conditioning may not be achieved. Also the life of the plant and
equipment would be expected to be shorter than normal and maintenance cost in terms of
repairs and rectification will be comparatively higher. Therefore it is most essential to
have a proper progressive inspection of Air Conditioning systems for reasons stated
above and to safeguard government funds.
Air changes / HR – National Catalog
Home
Hotel
Restaurant
Theater
Kitchen
Bathroom & toilet
Living room
Ball room
Dining room
Kitchen
Corridor
Toilet
Dining room
Kitchen
Banquet hall
15
10
6
8
8
15
5
10
6
20
10
Auditorium
Corridor
Smoking room
Projection room
6
6
12
20
Industrial
plant
Ordinary
building
School
General working area
Printing area
Generator room
Office
Waiting room
Conference room
Exhibition hall
6
20
20
6
10
12
10
Chemical lab
Auditorium
Gymnasium
Library & classroom
6
6
8
6
Equipment selection
Water Cooled Packaged Unit
Compressor:
Total capacity
=
______ BTU/HR (CHECK SHC)
Evaporator Air
=
______ CFM
Entry wet bulb temp. =
______ °F
Condition temp.
______ 105°F
=
Refer catalogue 50BA page 4 & 5
HP required
Cooling Tower:
Total Heat Rejection
=
______ TR x 15000 BTU/HR
Quality of water required
=
______ TR x 15000 US GPM
500 x ∆ t
=
______ x 0.83 IGPM
=
______ temp. difference
=
______ 7.5°F or 10°F (for chilled water)
∆t
Cooling Tower Fan Motor (refer catalogue)
Evaporator Fan
Static Head of system:
Duct
=
0.1
100
x
______ length
Coils (4 rows)
Bends and fittings
Supply Air Grille
Return Air Grille
Filters
=
=
=
=
=
=
TOTAL:
10% Safety factor =
Grand Total:
Refer Catalogue:
Unit No.
CFM
External Static Pressure (above)
RPM}
Required
BHP}
HP
=
BHP
0.06
0.15
0.15
0.15
0.15
____
________
Water Pump
Water quantity (USG PM) – Above
Pipe diameter
Frictional Losses
5’ H20/100 ft.
Floor length of pipe
Height length of pipe
(No. of) Elbow Equivalent length
(No. of) Gate Valve
=
=
=
=
Total Length: ________________
Frictional Losses
=
total length x 5/100
Static head of pipe (cooling tower)
Condenser Pressure Drop (refer catalog)
Safety Factor 10%
Total:
(Take to nearest 5 or 10)
IGPM =
Ft. Head (Above)
BHP =
IGPM x Ft. Head
33000 x 2
HP
=
BHP x 1.25
Velocity
=
550 fpm
=
=
=
= _________________ (ft. head)
x
10lb
Gallon
x
100
70
x
Coils
CFM =
__________ supply air
Area
cfm
550
=
Cooling Tower:
i)
Recirculated water quantity =
ii)
Evaporation Losses
iii)
Windage Losses GPM
GPM =
w
=
bw
TR x HRF x 24 = TR x 1.25 x 24
temp. rise of water
temp. rise of water
TR x HRF x 24 = TR x 1.25 x 24
HFG
1050
0.2% H2O Quantity
100
80
iv)
Bleed of = windage GPM =
bw
USGPM (windage losses)
4.25-1
vi)
Bleed of GPM
=
USGPM – USGPM
bw
w
b
vii)
Make Up ( USGPM *)
=
USGPM + USGPM + USGPM
e
w
b
viii)
Storage Tank
=
IGPM x HRS
s
Electrical Energy Consumption
Cost
=
[ total HP x 0.746 x HRS x DAYS x 0.12 ]
=
[ 0.8 x ( Compressor HP + Evap. Fan HP + Cooling Tower Fan HP +
Water Pump HP )] x 0.746 x HRS x DAYS x 0.12
Load (tons)
Quantity (USGPM) x (Temp. Rise °F) x Specific Head x Specific Gravity
0.15”
0.15”
0.15”
Bends and Fittings
Supply Air Grille
Return Air Grille
=
=
=
Ducts
x Length of Duct
100 ft.
0.1 in
Filters (2”)
=
Coils (4 Rows)
=
Add 10% for safety factor
0.12”
0.37”
Return Air Grille
Area x velocity
Velocity of air
=
=
cfm
500;600;700 ft/min
Table of Grille
CFM
Neck Size
Base Size
≤ 300
10” x 10”
301 - 400
12” x 12”
401 - 500
14” x 14”
501 - 600
16” x 16”
601 - 700
18” x 18”
CHILLED WATER COOLING COIL
14” x 14”
16” x 16”
18” x 18”
20” x 20”
22” x 22”
Determine Job Requirements:
Given, Grand Total Heat
=
Air Quantity
=
Max. Coil Face Velocity
=
Entering Air Temp
=
Leaving Air Temp
=
Entering Water Temp
=
Water Flow Rate
=
Max. Water Pressure Loss
=
Approx. Coil Size
=
Min Coil Face Area:
Required Min. coil face area =
cfm
Coil face velocity
Coil Face Velocity:
Actual Face Velocity
=
cfm
Tabulate coil face velocity
Water temp. Rise (WTR) = ∆ t
WTR =
GTH
500 x GPM
Actual Water Velocity (WV)
Assume a 6 – pass, full (28) circuit coil
Actual WV =
GPM x 1.18
Coil circuit
Actual Leaving Air temp. (t1) - °F and GTH Removal
GTH =
Rated MBtuh/ft² x tabulated coil face area
Static Head for Fan
AHU fan
Duct length (ft) x 0.1 = x”
Static Head
= x” + 1.2 x 10%
= y”
Exhausts Fan
Duct length (ft) x 0.1 = y”
100
Static Head
= y”+ 0.3 + 10%
= z”
~ Cooling Tower Lower than package must put a butterfly valve so that when switch off
the unit no water will flow suck to the cooling tower as to make the pipe empty.
Exhaust Fan
=
(volume)
60
=
- (Air Change) CFM
=
total CFM x 144
550
=
x
=
TAO x 144
550
=
x Sq.ft.
S.A friction
=
0.1
R.A friction
=
0.05
1 l/m
=
0.035 CFM
R.A.G
F.A.G