Quick Reference -HVAC (Part-1)

HVAC Power Consumption (IS 1391)

Cooling Capacity (Kcal/Hr) Maximum Power Consumption (KW)
3000 1.65
4S00 2.3
6000 3.1
7500 3.6
9000 4.4
1 kcal/Hr= 1.16278 watt

HVAC Noise Level (IS 1391)

Rated Cooling Capacity (Kcal/Hr) Maximum Noise Level (DBA)
Indoor Outdoor
4500 or less 58 68
5000 or more 62 70

Centrifugal Fans (As per CPWD)

Type Characteristics Typical Applications Efficiency (%)
Radial High pressure, medium flow, efficiency close to tube-axial fans, power increases continuously Various industrial applications, suitable for dust laden, moist air/ gases 72–79
Forward curved blades Medium pressure, high flow, dip in pressure curve, efficiency higher than radial fans, power rises continuously Low pressure HVAC, packaged units, suitable for clean and dust laden air/ gases 60–65
Backward curved blades High pressure, high flow, High efficiency, power reduces as flow  increases beyond point of highest efficiency HVAC, various industrial applications forced draft fans, 79–83
Airfoil type Same as backward curved type, highest efficiency Same as backward curved, but for clean air applications 79–83

Axial Flow Fans (As per CPWD)

Type Characteristics Typical Applications  Efficiency (%)
Propeller Low pressure, high flow, low efficiency, peak efficiency close to point of free air delivery (zero static pressure) Air-circulation, ventilation, exhausts. 45–50
Tube axial Medium pressure, high flow, higher efficiency than propeller type, dip in pressure-flow curve before peak pressure HVAC, drying ovens, exhaust Systems 67–72
Vane axial High pressure, medium flow, dip in pressure-flow curve, use of guide vanes improves Efficiency exhausts High pressure applications including HVAC systems 78–85

Thickness of sheets for Rectangular Ductwork   (As per CPWD)

Longest side (mm) Minimum sheet thickness
For GSS  For Aluminum
750 mm and below 0.63 mm 0.8 mm
751 mm to 1500 mm 0.8 mm 1 mm
1501 mm to 2250 mm 1 mm 1.5 mm
2251 mm & above 1.25 mm 1.8 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, mm Thickness of Sheet
For GSS  For Aluminum
150 to 500 mm 0.63 mm 0.8 mm
501 to 750 mm 0.8 mm 0.8 mm
751 to 1000 mm 0.8 mm 1 mm
1001 to 1250 mm 1 mm 1.5 mm
1251 mm and above 1.25 mm 1.8 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

Application Duct Width Angle size
Flanges Up to 1000 mm 35 mm x 35 mm x 3 mm
Flanges 1001 mm to 2250 mm 40 mm x 40 mm x 3 mm
Flanges More than 2250 mm 50 mm x 50 mm x 3 mm
Bracings Up to 1000 mm 25 mm x 25 mm x 3 mm
Bracings More than 1000 mm 40 mm x 40 mm x 3 mm
Support angles Up to 1000 mm 40 mm x 40 mm x 3 mm
Support angles 1001 mm to 2250 mm 40 mm x 40 mm x 3 mm
Support angles More than 2250 mm Size 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)

Points VRF AC Chilled Water
based AC
System Base It is Gas Base System It is Water Base System
Peak Power Demand 1.6KW/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 1.20 1 Annually extra expenditure of 15 to 20% in electricity bills in VRF system.
Security & Safety of
Equipment &
Copper piping on
terrace & in building
MS piping VRF system equipments/ materials prone to theft & damage by miscreants
Terrace Space Almost 80% terrace is used for ODUs & Cu pipe & power cables Only Cooling Towers need to be installed at terrace. Problem of cleaning terrace & loss of water proofing also occurs over time.
Water Scarcity No water required Regular Supply of Water required for condenser cooling Major 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 control Sick 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 Safety Refrigerant 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.
Life 10 Years 15-20 Years
Applications Home 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)

Application Variable Refrigerant Flow (VRF) system VRV System with Chiller based Air conditioners
Power Consumptions Up to 1.6 KW/TR of refrigeration. Up to 1.3 KW/TR of refrigeration.
Application Most 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 Temperature If the system is used at hotter place
then system de-rates.
This is not the case in chiller based
Space It 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.
Design its design is very complex Its design is comparatively less complex
COP its 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)
Efficiency Its 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.
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