Quick Reference -HVAC

Quick Reference -HVAC

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)
Rated Cooling Capacity (Kcal/Hr)	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
Longest side (mm)	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
Diameter of duct, mm	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	Remarks
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 Consumption	1.15 to 1.20	1	Annually extra expenditure of 15 to 20% in electricity bills in VRF system.
Security & Safety of Equipment & System	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 Benefits	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 system.
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 capacity	Its part load efficiency is good even at one – third of the rated capacity.