Design Basis For AIR CONDITIONING SYSTEM of Control Room & Substation. CODES AND STANDARDS The design, manufacture, fabrication, installation and testing of equipment covered by this specification shall comply with latest edition of the appropriate equivalent international standards, all currently applicable statutes, regulations and safety codes in the locality where the equipment shall be installed. Minimum following standards or equivalent Indian / International standard shall be followed: 3.1 Refrigerator Reciprocating Compressors i) IS:660 Safety Code for Mechanical Refrigeration ii) iii) iv) ANSI-B 9.1 Safety Code for Mechanical Refrigeration ARI:520 Standard for positive Displacement Refrigeration Compressor & Condensing Units IS:2494 V-Belt for Industrial Purposes v) IS:3142 V-Grooved Pulleys for V-Belts vi) vii) IS:5222 Code of practice and measurement for testing refrigerant compressors ASHRAE-23-67 Methods of testing for rating positive standard displacement refrigerant compressor. 3.2 Water Cooled Refrigerant Condensers i) IS:2825 Unfired pressure vessels ii) ANSI-B-9.1 Safety code for mechanical refrigeration iii) IS:660 Safety code for mechanical refrigeration iv) IS:4501 Shell and tube type heat exchanger v) ASHRAE-22-72 Method of testing for rating water cooled refrigerant condensers 1
3.3 Refrigerant Chillers GUJARAT NARMADA VALLEY FERTILIZERS & CHEMICALS LTD i) ARI-480 Standard for refrigerant cooled liquid coolers remote type ii) ASHRAE-26 Method of testing for rating liquid coolers iii) IS:2825 Unfired pressure vessels iv) IS:4503 Shell and tube type heat exchanger v) ANSI-B-91 Safety code for mechanical refrigeration vi) ASME-SEC-VIII Unfired pressure vessels vii) IS:660 Safety code for mechanical refrigeration 3.4 Refrigeration Piping i) ANSI-B-31.5 Refrigeration Piping ii) IS:659 Safety code for air conditioning 3.5 Air Handling Unit (AHU) i) ASHRAE-33 Methods of testing for rating forced circulation air cooling and air heating coils ii) ARI-447 Standard for forced circulation air cooling and air heating coils iii) ANSI-B 9.1 Safety code for mechanical refrigeration iv) IS:659 Safety code for air conditioning v) IS:660 Safety code for mechanical refrigeration 3. 6 Horizontal centrifugal pumps i) IS:1520 Horizontal centrifugal pumps for clear, cold, fresh water ii) IS:5120 Technical requirements for roto dynamic special purpose pumps 2
iii) iv) IS:5639 Pumps handing chemicals and corrosive liquids IS:5659 Pumps for process water v) IS:6536 Pumps for handling volatile liquids vi) API-610 Centrifugal pumps for general safety services vii) HIS Hydraulic institute standards of USA 3.7 Air distribution system i) IS:655 Specification for Metal Air Duct ii) IS:277 Specification for galvanized steel sheet iii) IS:737 Specification for wrought aluminum and aluminum sheet and strip iv) ARI:210 Standard for unitary air conditioning equipment v) AIR-270 Standard for application, installation and services of unitary equipment vi) ASHRAE-37 Standard methods of testing for rating unitary air-conditioning and heat pump equipment 3.8 Filters i) BS:2831 Methods of test for air filters used in air conditioning and general ventilation ii) BS:3928 Sodium flame test for air filters (other than for Air supply to I.C. engines & compressors) 3
3.9 Thermal insulation for cold surface i) IS:3069 Glossary of terms, symbols and units relating to thermal materials ii) iii) IS:4671 Expanded polystyrene for thermal insulation IS:8183 Bonded mineral wool iv) IS:702 Industrial bitumen i) IS:4894 Centrifugal fans 3.10 Water piping i) IS:1239 Heavy class for sizes upto 150 mm dia Part I ii) API-5L-GRB Standard wall (ASA b.36.10) for 200 mm and above. 5.0 DESIGN BASIS 5.1 Selection of AC system For the AC system of the Control room & Substation, Air cooled Package Unit (Refrigerant R-407 # 2 Circuit), Scroll type Compressors with Microprocessor based Controller with Indoor & out Door units & other necessary services is to be designed, supplied, erected & commissioned. Spare 100 % spare Installed complete units are to be provided. 6.0 DESIGN CRITERIA: 6.1 Design Parameters a) Outside Design Conditions Season Summer Monsoon Winter DBT (deg.c) 48 28 18 The outside design temperatures are as follows: WBT (deg.c) 27.5 27 15 4
The above designs outside temperatures are established based on climate data of the nearest weather station. b) Inside Design Conditions The internal design conditions in various areas to be maintained are as follows: 22 0C ± 10C DB and 50% ± 5% RH for AC areas of control room and adjoining rooms. 240C ± 10C DB and 50% ± 5% RH for Switchgear room. The Air-conditioning spaces shall be maintained at positive pressure to avoid any infiltration of dust. 6.2 All the equipments of Air Conditioning system shall be designed for continuous duty. 6.3 In Air conditioning system the return air shall be through ducts and use of plenum space for return air may be avoided. 6.4 Automatic (motorised) fire dampers for supply air ducts and fusible link type fire dampers for return air ducts shall be provided at locations where ducts pass through walls and floors for ease of isolation, maintenance and as well as for emergency operations. The operation of these automatic dampers shall be interlocked with the fire alarm system and shall also be possible manually from the remote control panel. 6.5 For maintenance of chilling units, AHU s (Air Handling Units) etc. chain pulley block of suitable capacity shall be provided in the AC plant rooms and AHU rooms. The design of room is such that, dismantling / replacement of part is possible with out removal of any near by equipment / structure & with sufficient place around it. 6.6 Design Chilled water flow shall not be less than 0.7 Cu.m/hr per TR air-conditioning load and design cooling water flow shall not be less than 1 Cu.m /hr per TR air-conditioning load. 6.7 Coil face area of Air Handling units shall be designed considering a face velocity of not more than 2.5 m/sec. Velocity of water flow shall be limited to 2.5 m/sec and for gravity flow the same shall be limited to 1.5 m/sec. The air distribution system shall be sized to have a constant frictional drop along its length and velocity through ducts shall not exceed 7.5 m/sec 6.8 For pumps, continuous motor rating (at 50oC ambient) shall be at least ten percent (10%) above the maximum load demand of the pump in the entire operating range. For fans, compressors and blowers continuous motor rating (at 50oC ambient shall be at least ten percent (10%) above the maximum load demand of the fan, compressors, blower at the design duty point. Wherever belt drives are used the belts shall be sized for 150% of the rated power and there shall be minimum of two belts per drive. 6.9 Noise level within the air conditioned space shall be restricted to 35 45 NC level with suitable acoustic attenuation (with duct silencer/ acoustic insulation etc.). 5
6.10 A margin of 25% is considered over the total heat load while arriving at the air conditioning capacity. 6.11 The following building constructional details have to be considered for preliminary cooling load calculations: All external walls are of 230mm thick brick construction with external plaster 20mm thk, internal plaster 12mm thk, 6mm thk plaster below RCC slabs. Roofs and floors are of RCC slabs. Ceiling of AC spaces are insulated with under deck insulation of 50 MM thk.. The building is RCC framed structure. 7.0 SALIENT FEATURES OF THE EQUIPMENT 7.1 The evaporator shall be cleanable shell and tube water heat exchange containing refrigerant circuits constructed from integral seamless copper tubes. The shell casing shall be made of MS plates fusion welded. The shell casing and heads shall be insulated. Evaporator capacity equal to the total refrigeration capacity required, designed as per ASME Section-VIII /TEMA Class-C standards. The evaporator shall be designed with at least 2 C super-heat under rated designed condition. The average tube velocity and fouling factor shall be 2.5 m/sec and 0.000013 (hr C- mm2)/kcal respectively. 7.2 Steel Structure The complete condensing / chilling units shall be mounted on steel structure and shall be provided with necessary vibration isolators. 7.3 Chilled Water Pumps These shall be either horizontally split casing type centrifugal pumps and shall have CI casing and bronze impeller. The pumps shall be direct driven and mounted on a common base frame with motor. The operating speed of the pump should not exceed 1500 rpm. 7.4 Air Handling Unit (AHU) Each AHU shall consist of Casing, Fan section, cooling coil section, damper section, steel frame with vibration isolators (minimum efficiency of 85%) for the complete AHU, Isolation dampers at the suction and discharge of each AHU, Pre filter at the suction and fine filter (microvee type) and absolute (HEPA type) filters (wherever applicable) at the discharge of each individual AHU, and heater section in the common discharge of AHU. The efficiency of the pre filters shall be 90% down to 10 microns and efficiency of fine filters shall be 99% down to 5 micron size. The efficiency of the absolute filters shall be 99.97 % down to 0.3 micron. Automatic Fire dampers to be provided for isolation of the system during emergency at common supply air (AHU outlet) from each AHU and Fusible link type fire dampers to be provided for isolation at common return air ducts (inlet to AHU) The casing of AHU shall be double skin construction. Double skin sandwich panels (inside and outside) shall be fabricated using minimum 0.63 mm (24g) Galvanised sheet steel, with 25 mm thick 6
polyurethane foam insulation of minimum 38 Kg/cm3 density in between. Suitable reinforcements shall be provided to give structural strength to prevent any deforming/buckling. Cooling coil shall be of seamless copper tubes with aluminium fins and shall be provided with suitable drains and vents connections. Fan Section: a) Fan impeller : Forward/ backward curved blade & centrifugal type. b) Impeller material : Mild steel spray galvanised with minimum zinc deposition conforming to Class 275 of IS:277. c) Fan casing : GI sheet steel of minimum thickness of 3 mm d) Fan bearings : Self aligning type, permanently lubricated, heavy duty with a design life of 10,000 operating hours. e) Operating range : Fans to be designed to operate within 9% and 25 % of the system throttling line. f) Critical speed : First critical speed of rotating assembly shall be at least 25% above the operating speed. g) Drive : Motor driven, with removable belt guard. One common set of electrical strip heater package of suitable capacity complete with humidistat, safety thermostat, heater box with insulation etc for monsoon reheat mounted inside the A/C plenum/duct. 7.5 Air distribution system a) Rectangular duct: Stainless steel (SS) ductwork shall be fabricated from stainless steel sheet confirming to IS 6911. b) Entire supply air duct will be thermally insulated. c) First 5m of A/C supply air ducting from AHU outlet will be acoustically insulated. d) The supply air ducting will be designed based on equal friction method to have an initial velocity not exceeding 7.5m/s. e) Supply air grilles/supply air diffuser will be with volume control damper and will be made up of GI sections. f) Return air grilles/ Return air diffuser will be without volume control damper and will be made up of aluminium with powder coating. g) Neck velocity for supply air diffuser/grille and return air diffuser/grille will be 3 m/s (max) and 2.5 m/s (max) respectively. 7
h) Fire dampers with 90 minutes fire rating will be provided in the AC supply air duct and return air passage crossing wall, floor slab and return air opening in order to isolate the respective AHU in the event of fire. The solenoid of fire damper will be of continuous rating and will remain energized in normal condition to effect opening of damper and will be de-energized to close in the event of fire. 7.6 Piping and Fittings a) Piping for Chilled water, Heavy grade-is:1239 or Condenser water of AC equivalent up to 150 mm NB System & Circulating water IS:3589 or Equivalent for pipes beyond 200 mm NB with a minimum thickness of 6 mm. b) Drain piping Same as (a) above & galvanised as per IS: 4736. c) Refrigerant piping: Copper tubes as per IS: 2501 (Copper material as per IS: 191 hard copper grade). d) Fittings: i) The steel fittings shall conform to ASTM A234 Gr WPB and dimensional standard to ANSI B 16.9/ANSI B16.11 / Equivalent for sizes 65 NB and above. ii) ii) For sizes 50 NB and below, the material shall conform to ASTM A-105. iii) All steel flanges shall be of slip on type and shall conform to ANSI B 16.5 iv) For pipe sizes above 350 NB, fabricated fittings from sheets of adequate thickness may be used. v) The bend radius in case of miter bends shall be minimum 1.5 times the nominal pipe diameter and angle between two adjacent sections shall not be more than 22.5 deg and shall be as per BS:2633/BS:534. v) Fittings, flanges and pipe joints of refrigerant piping shall conform to ANSI B31.5. 7.7 Valves a) Valves shall have full sizes port and suitable for horizontal and as well as vertical installation. b) Valves for regulating duty shall be of globe type suitable for controlling throughout its lift. c) Gate, Globe and stop check valves shall have bonnet back seat to facilitate easy replacement of packing with the valves in service. d) All safety/relief valves shall be so constructed that the failure of any part does not obstruct the free discharge. 8
e) Manual gear operators shall be provided for valves of size 250 NB and above. f) All valves with rising stem shall have position indicators. g) All valves shall be provided with locking arrangement. h) The refrigerant line valves shall have steel or brass body with TEFLON gland packing. The construction of disc shall be either globe or angle type. The valve seat shall have white metal lining or equivalent. i) All water line valves shall be of Cast Iron body for sizes 65 NB and above conforming to IS: 780 and Gun Metal construction for sizes less than 65NB conforming to IS: 778. Cast Iron parts shall conform to IS: 210 Gr FG 260. 7.8 Thermal and Acoustic insulation 7.8.1 Application a) All surfaces to be insulated both thermally and acoustically shall be thoroughly cleaned, dried and an adhesive (CPRX compound of Shalimar Tar Products or Equivalent) be applied @ 1.5 kg/sqm on the surface. b) Insulation material (either expanded polystyrene foam or Glass Wool / Mineral wool /Glass fibre or Equivalent) shall be struck to the surface. All the joints shall be sealed with bitumen. c) Insulation mass to be covered with 500 gauge polythene sheet with 50 mm overlaps and sealing all joints on hot side. d) Insulation Finish of types specified under shall be provided thereafter. 7.8.2 Type of Insulation and Finish ------------------------------------------------------------------------------------------------------------ Sl. Surface Insulation Insulation no. Material Form ------------------------------------------------------------------------------------------------------------ 1 Supply & return Resin bonded Roll /Slab air duct of AC Glass wool 2 Refrigerant Expanded Pipe sec. (Suction and Polystyrene liquid lines) or Mineral wool 3 AHU drain pipe Expanded - Pipe sec Polystyrene OR Mineral wool 9
OR resin bonded glass wool. 4 AHU casing Expanded As per and conden- polystyrene manufasate pan or mineral ctors std. wool or resin bonded glass wool. 5 Chilled water - do - Pipe section piping Valves & specialities 6 Chiller - do - Slab 7 Chilled water - do -` - do pumps 8 Expansion tank - do - Slab/section & associated Pipe piping 9 Acoustic insu- Glass Slab 25 lation of duct wool & AHU room ------------------------------------------------------------------------------------------------------------ 8.8.3 Specification for insulation shall be as follows: - ------------------------------------------------------------------------------------------------------------ Insulation Material Code Thermal Density (min) Conductivity Kg/m3 (mw/cm/oc ------------------------------------------------------------------------------------------------------------ Resin bonded mineral IS: 8183 0.49 at 50oC 24 (For thermal wool/glass wool/equivalant insulation) Mineral wool pipe section IS: 9842 0.43 at 50oC 81 Expanded polystyrene IS: 4671 0.37 at 50oC 15 10 48 (For acoustic Insulation) 48 (For AHU room Acoustic insulation) ------------------------------------------------------------------------------------------------------------ Note : Expanded polystyrene shall be of self extinguishing type (Type 2 of IS:4671)
8.8.4 Acoustic Insulation All ducts up to a distance of 5 meters from AHU and outlet shall be acoustically lined from inside with 25 mm thick resin bonded mineral wool and 30 gauge perforated aluminium sheet having 5 mm dia perforation at 8 to 10 mm centre-to-centre distance. Insulation shall be fixed on wooden frame of 600 x 600 mm dimension. 8.8.5 Polythene sheet shall be applied over the outer surface of insulation before applying perforated aluminium sheet. Application of acoustic insulation shall be inline with Cl. 8.8.1 above. 8.8.6 In case of external insulation, Aluminium sheet (22 gauge) cladding, properly stitched all joints need to be provided over the external surface. 8.9 Material of construction 8.9.1 Condenser (Horizontal shell & tube type water cooled). Standard: IS-4503/ ASME/ TEMA i) Shell Carbon Steel ii) Tube 18 G integrally finned Copper iii) Head ends Carbon Steel iv) Tube sheet Materials Carbon Steel v) Baffle plate Carbon Steel vi) Tube support plate Crbon Steel 8.9.2 Chiller (Horizontal shell & tube direct expansion type) Standard: IS-4503/ASME/TEMA i) Shell Carbon Steel l ii) Tube 18 G integrally finned Copper iii) Head ends Carbon Steel l iv) Tube sheet Material - Carbon Steel l v) Baffle plate - Carbon Steel vi) Tube support plate - Carbon Steel 8.9.3 Air Handling Unit 11
i) Casing Galvanized Steel (16 G) ii) Impeller Galvanized Steel iii) Shaft Carbon Steel iv) Material of tube Seamless Copper (27 G) v) Material of fins Aluminium 8.9.4 Centrifugal Pumps (Condenser water and Chilled Water pumps) i) Impeller - CS ii) iii) iv) Pump shaft Carbon Steel C-45.IS-1570 or class -IV IS-1875 Casing Cast Steel Wearing ring Cast Steel v) Shaft Sleeve Hardeneed Cast Steel vi) Base plate Cast Steel 8.9.5 Air distribution system: Ducting : SS Diffuser : GI section Grille : GI section VCD blade & frame : 16 G GSS Fire damper blades and frame : 16 G GSS Louver frame : 16 G GSS Louver blade : 20 G GSS 9.0 CONTROL & INSTRUMENTATION FOR AC SYSTEM: PLC/microprocessor based Local Control Panel (LCP) shall be provided for the monitoring & control of air conditioning system. Redundancy shall be provided for the Main processor (hot redundant), Network interface module, communication cable and power supply of the PLC/microprocessor system. The LCP shall house HMI operator interface for control, monitoring & operation of the air conditioning system. All indications & alarms shall be displayed on this. Necessary and suitable field instruments(as illustrated in the P & ID as minimum), interconnecting cables, junction boxes, local panels etc. required for the complete, safe and reliable operation of the system shall be provided. 12
All Temperature elements shall be duplex type by default. Thermo wells shall be provided in various locations of the system to enable to take readings during performance testing. All field instruments shall be located in accessible/vibration free locations and clearly visible range for all readable instruments. Annealed tinned copper (ATC), multi strand, twisted multipair, screened, armored FRLS grade cables are envisaged for both signal and control. Safety earthing and electronic earthing shall be separate. All panels housed in non air-conditioned area shall be under protection class of IP-54. IP-42 shall be considered for panels mounted in air-conditioned environment. IP-65 protection class shall be considered for Field instruments. 13