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HVAC Power Consumption (IS 1391) |
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| 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 | |
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HVAC Noise Level (IS 1391) |
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| Rated Cooling Capacity (Kcal/Hr) | Maximum Noise Level (DBA) | |
| Indoor | Outdoor | |
| 4500 or less | 58 | 68 |
| 5000 or more | 62 | 70 |
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Centrifugal Fans (As per CPWD) |
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| 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 |
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Axial Flow Fans (As per CPWD) |
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| 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 |
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Thickness of sheets for Rectangular Ductwork (As per CPWD) |
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| 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 | ||
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Thickness of sheet for Round Ducts (As per CPWD) |
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| 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 | ||
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Duct’s Associated Items |
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| 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. | ||
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Comparison of the VRF/ VRV systems with the Central Chilled water system (As per CPWD) |
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| 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. |
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| 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. | |
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Comparison of VRF and VRV System (As per CPWD) |
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| 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. |
View more at https://electricalnotes.wordpress.com/2019/12/01/electrical-thumb-rules-hvac/.
Published by Department of EEE, ADBU: tinyurl.com/eee-adbu
