Quick Reference -HVAC


HVAC Power Consumption (IS 1391)

Cooling Capacity (Kcal/Hr)Maximum Power Consumption (KW)
1 kcal/Hr= 1.16278 watt


HVAC Noise Level (IS 1391)

Rated Cooling Capacity (Kcal/Hr)Maximum Noise Level (DBA)
4500 or less5868
5000 or more6270


Centrifugal Fans (As per CPWD)

TypeCharacteristicsTypical ApplicationsEfficiency (%)
RadialHigh pressure, medium flow, efficiency close to tube-axial fans, power increases continuouslyVarious industrial applications, suitable for dust laden, moist air/ gases72–79
Forward curved bladesMedium pressure, high flow, dip in pressure curve, efficiency higher than radial fans, power rises continuouslyLow pressure HVAC, packaged units, suitable for clean and dust laden air/ gases60–65
Backward curved bladesHigh pressure, high flow, High efficiency, power reduces as flow  increases beyond point of highest efficiencyHVAC, various industrial applications forced draft fans,79–83
Airfoil typeSame as backward curved type, highest efficiencySame as backward curved, but for clean air applications79–83


Axial Flow Fans (As per CPWD)

TypeCharacteristicsTypical Applications Efficiency (%)
PropellerLow pressure, high flow, low efficiency, peak efficiency close to point of free air delivery (zero static pressure)Air-circulation, ventilation, exhausts.45–50
Tube axialMedium pressure, high flow, higher efficiency than propeller type, dip in pressure-flow curve before peak pressureHVAC, drying ovens, exhaust Systems67–72
Vane axialHigh pressure, medium flow, dip in pressure-flow curve, use of guide vanes improves Efficiency exhaustsHigh pressure applications including HVAC systems78–85


Thickness of sheets for Rectangular Ductwork   (As per CPWD)

Longest side (mm)Minimum sheet thickness
For GSS For Aluminum
750 mm and below0.63 mm0.8 mm
751 mm to 1500 mm0.8 mm1 mm
1501 mm to 2250 mm1 mm1.5 mm
2251 mm & above1.25 mm1.8 mm
All ducts shall be fabricated either from Galvanized Sheet Steel (GSS) conforming to IS: 277 or aluminum sheets conforming to IS:737. The steel sheets shall be hot dip galvanized with MAT finish with coating of minimum 120 grams per square meter (GSM) of Zinc, GI sheets shall be lead free, eco friendly and Ro HS compliant


Thickness of sheet for Round Ducts (As per CPWD)

Diameter of duct, mmThickness of Sheet
For GSS For Aluminum
150 to 500 mm0.63 mm0.8 mm
501 to 750 mm0.8 mm0.8 mm
751 to 1000 mm0.8 mm1 mm
1001 to 1250 mm1 mm1.5 mm
1251 mm and above1.25 mm1.8 mm
All sheet metal connections, partitions and plenums required for flow of air through the filters, fans etc. shall be at least 1.25 mm thick galvanized steel sheets, in case of G.I. sheet ducting or 1.8 mm thick aluminum sheet, in case of aluminum sheet ducting and shall be stiffened with 25 mm x 25 mm x 3 mm angle iron braces.
Circular ducts, where provided shall be of thickness as specified in IS: 655 as amended up to date.
Aluminum ducting shall normally be used for clean room applications, hospitals works and wherever high cleanliness standards are functional requirements


Duct’s Associated Items

ApplicationDuct WidthAngle size
FlangesUp to 1000 mm35 mm x 35 mm x 3 mm
Flanges1001 mm to 2250 mm40 mm x 40 mm x 3 mm
FlangesMore than 2250 mm50 mm x 50 mm x 3 mm
BracingsUp to 1000 mm25 mm x 25 mm x 3 mm
BracingsMore than 1000 mm40 mm x 40 mm x 3 mm
Support anglesUp to 1000 mm40 mm x 40 mm x 3 mm
Support angles1001 mm to 2250 mm40 mm x 40 mm x 3 mm
Support anglesMore than 2250 mmSize and type of RS section shall be decided in individual cases
Hanger rods shall be of mild steel and of at least 10 mm dia for ducts up to 2250 mm size, and 12 mm dia for larger sizes
 All nuts, bolts and washers shall be zinc plated steel. All rivets shall be galvanized or shall be made of magnesium – aluminum alloy. Self tapping screws shall not be used.


Comparison of the VRF/ VRV systems with the Central Chilled water system (As per CPWD)

PointsVRF ACChilled Water
based AC
System BaseIt is Gas Base SystemIt is Water Base System
Peak Power Demand1.6KW/TR peak.
(Efficiency drastically reduces at high ambient)
1.3KW/TR Peak.
(IKW/TR<0.6 now for chilling units.)
Higher size & cost of Power Supply Capital Equipment like Transformers etc. & thus higher Cu losses in VRF system.
Annual Power
1.15 to 1.201Annually extra expenditure of 15 to 20% in electricity bills in VRF system.
Security & Safety of
Equipment &
Copper piping on
terrace & in building
MS pipingVRF system equipments/ materials prone to theft & damage by miscreants
Terrace SpaceAlmost 80% terrace is used for ODUs & Cu pipe & power cablesOnly Cooling Towers need to be installed at terrace.Problem of cleaning terrace & loss of water proofing also occurs over time.
Water ScarcityNo water requiredRegular Supply of Water required for condenser coolingMajor advantage in VRF system but, now STPs are generating water for meeting up to 75% of AC Plant demand. Water drift losses also being reduced by use of Geothermal Energy.
Air Quality of
Conditioned space
RH ,Co2, Bacteria, dust & other pollutants Control only to very
limited extent.
Full controlSick building syndrome is taken care of in Water based system with AHUs and demand based fresh air supply.
Service / Attending
to faults
Personnel have to go into the room. Problems of condensate dripping in rooms.Such problems
limited only in AHUs.
Long Term
Maintenance Expensive Low Cost Maintenance
Fire SafetyRefrigerant in system goes to all areas in building and is combustible at high temperatures, releasing toxic products of combustion.Only water in AHUs and Air only in rooms through ducts. Refrigerant is limited to only within the Chilling Units.Water based system is safer.
Life10 Years15-20 Years
ApplicationsHome or Small office with variable occupancy. More cost effective in room redundancy cases.Large office, continuously large air conditioning loads, proper controlled conditioning of  space.


Comparison of  VRF and VRV System (As per CPWD)

ApplicationVariable Refrigerant Flow (VRF) systemVRV System with Chiller based Air conditioners
Power ConsumptionsUp to 1.6 KW/TR of refrigeration.Up to 1.3 KW/TR of refrigeration.
ApplicationMost of the VRF units are designed at an ambient temperature of 36°C, and so its use would not be suitable if the system is used in places with hotter temperature.Customization in design of the Chiller
system can be done with respect
to ambient temperature
 Performance in Hot TemperatureIf the system is used at hotter place
then system de-rates.
This is not the case in chiller based
SpaceIt requires more space for its
outdoor unit as maximum size of outdoor unit available is 60 hp, so a large no. of outdoor units would be required to fulfill the requirement of 3500-4000 TR
It can be managed by a single plant room.
Designits design is very complexIts design is comparatively less complex
COPits CoP (Coefficient of Performance)
varies from 3 to 4.2; a higher CoP
implies greater efficiency
Its CoP varies from 5.4 (for 750 TR chiller) to 6.3 (for 1000 TR chiller)
EfficiencyIts part load efficiency is good if
used at more than 50 % rated
Its part load efficiency is good even at
one – third of the rated capacity.