VENTILATION AND AIR CONDITIONING SYSTEMS (H.V.A.C) - substation

 

Ventilation and Air Conditioning Systems
 
 SCOPE
  
   This specification mainly covers the design, manufacture, testing, delivery, and guarantee for ventilation and air conditioning systems of substation buildings.
 
   Detailed scope of supply includes, but not limited to, the items listed below.
 
-         Sizing of the air conditioning & ventilation system units in accordance with the essential loads and their characteristics required for ventilated and air-conditioned spaces.
 -         Provision of:-
 ·        Air conditioning system split units.
·        Air-handling units (AHU’S).
·        Air distribution system, ductworks and cover cladding.
·        Volume & fire dampers.
·        Grilles, diffusers, and fresh air intakes.
·        Filters.
·        Sound attenuators.
·        Electrical motors, power cables, control cables, conduits, and switchboards.
·        Ventilation & exhaust fans.
Although not within his supply, the supplier shall advise his requirements in respect of these items are at the tender stage.
 
 
 DEFINITIONS
 
      Air conditioning :
 The process of treating air so as to control simultaneously the temperature, humidity, cleanliness, and distribution to meet the requirements of the conditioned space.
 
  
    Comfort Zone:
 
Air-conditioned zones with specified values for temperature and humidity to release human stresses. Temperatures shall be  18C° - 26.6C° and relative humidity 40% - 60% accompanied by a suitable number of air changes.
 
   Minimum Fresh Air Admission
 
A minimum rate of provided fresh air inside the conditioned spaces (15-25 C.F.M) per person.
 
 
     Ventilation Rate
 
Number of air changes per hour (Ach/h) for all closed service areas, rooms, and switchgear.
 
        Noise Level
 The sound attenuation and vibration control equipment, associated with air conditioning and ventilation installation.
      Air Filteration
 Filters with different efficiencies equipped to fresh air intakes to keep inside rooms free from dust.
     Protection
 A contactor, manual reset, ambient insensitive overload protector is to be factory installed for each compressor.
 
    Volume Dampers
 Dampers to control and regulate the airflow in supply and extract ducts shall be provided in the specified positions.
  
    Fire Dampers
 A device, installed in an air distribution system, designed to close automatically upon detection of heat, to interrupt migratory airflow, and to restrict the passage of flame. A Combination of fire and smoke dampers shall meet the requirement of both.
 
  Guarantee
           
Is to cover the perfect mechanical operation of systems, perfect attainment of temperatures and humidities within specified design conditions, acceptable noise, and vibration levels and consumption of power.
 
    Temperature
 
The two most common thermometer scales are the Fahrenheit (F°) and the Celsius (centigrade) °C, absolute zero is that temperature where molecular motion stops and no more heat in the substance at this point.
 
   Calorie & B.T.U

B.T.U (British Thermal Unit) is the heat required to raise the temperature of one pound of water from 59°F to 60°F.
The term a calorie is commonly used which is the amount of heat required to raise the temperature of one gram of water one degree from 4°C to 5°C. Celsius conversion of calorie to British thermal unit (B.T.U) is as follow:
 
1 B.T.U           = 252 calorie.
1 B.T.U           = 1055 joule = 1.06 KJ.
1 kwh             = 3.6 Mj        = 10⁶ x 3.6j
            1-ton refrigeration (TOR)
            1 = 12000 BTU/hr
                = 3.516 kw.
 
   Hygrometer
           
Is an instrument used to measure the amount of moisture in the air, the hygrometer uses both a dry bulb thermometer and a wet-bulb thermometer, relative humidity can be found by using a chart named psychrometer.
 
   
    Dew Point
 
Dew point is the temperature below which water vapor in the air will start to condense, it is also the hundred percent humidity point. Dew point can be defined as the temperature at which moisture becomes saturated with water (100% relative humidity) with water vapor when cooled at constant pressure.
           
  Energy Efficiency Ratio  (EER)
Ratio of net equipment output capacity to the total rate of electric input under designated operating conditions
Is the efficiency of the air conditioner, or it is capable in (Btu/h) divided by the electrical input in watts. 
 
   Coefficient of Performance (COP), heating
 
Ratio of the rate of heat delivered to the rate of energy input, in consistent units, for a complete heat pump systems under designated operating conditions.
 
   Psychomotor Chart
 
            A graphical representation of the thermodynamic properties of moist air.
 
 CLASSIFICATION
 
       Ventilation and air conditioning shall be classified as suitable for “ standard or particularly adverse” conditions as defined below:
 
 
   Equipment for standard service conditions
 
Such equipment shall be suitable for conditions as specified in the table (1) the atmosphere shall be regarded as corrosive with fine dust.
 
   Equipment for particularly adverse service conditions
 
Such equipment shall be suitable for conditions where the atmosphere is not only corrosive with fine dust, but also shall be considered in addition as having particular site adverse.
 
            This climate must be considered when select fans type.
 
Conditions such as coastal salt fog, or other contaminants where applicable, such designation shall be indicated and details table (1).
 
      For proper operation of substation and in consideration of the climatic and structural conditions, HVAC system shall be designed in two systems as follows :
 
      Ventilation system combined with overpressure system for switchgear, workshop, indoor transformers, and cable basements/galleries to prevent dust from entering these places at doors and /or windows. Overpressure shall not exceed 3.5 mm water column.
 
Negative pressure system can be designed according to purchaser recommendations and the instructional buildings should be dustproof, and self-closing doors with filter screens.
 
This system shall be mainly used for battery rooms, stores, toilets, and kitchens.
 
   Air conditioning split units shall be designed to provide air to conditioned spaces to meet specified performance requirements. The units are classified to be package units or mini-split type units according to EETC recommendations.
 
Air conditioning shall be provided for all areas requiring temperature control. This system shall be mainly used for offices, Control rooms, PLC rooms, and metering rooms. Outdoor ventilation air shall be introduced into the air conditioning system to satisfy the occupancy ventilation requirements.
 
   The ventilation system shall keep the temperature less than ambient by DT equals 5°C.

 REQUIREMENTS
 
         Environmental Conditions
 
   The environmental conditions of general application and detailed in the following:-
 

Parameter	Value
Maximum ambient temperature	47°C *
Maximum 24hr. average ambient temperature	30.1°C
Minimum mean daily temperature	-5°C
Relative humidity	0-100%
Atmosphere	Corrosive, fine dust.

Table (1)
Note:   This table is valid altitude (0-1000m)
   Maximum temperature shall be in accordance with substation location   
   in Egypt.
* For Cairo zone
      All outdoor locations are subjected to sand storms, consequently, all equipment shall be proof against ingress of sand.
 
      The air conditioning  system shall be designed to be capable to maintain inside the conditioned spaces the following conditions:-
 
-           Ambient conditions                        Summer                     Winter
 
Dry bulb temperature          35°C                           10°C
Wet-bulb temperature         26.6°C                         8°C
-           Inside Conditions
All conditioned zones to be for comfort with the following inside conditions:-
 
Summer                     Winter
Dry bulb temperature          23.6°C ^{- 2°C}                                         22.2°C^+2°C
Relative humidity                50% R.H ^+5%                                      45%^+5%
 
                       
     System Parameters:
 
The system the parameter shall be adequate to operate driven equipment without motor overload under all operating conditions and loads throughout the capacity range of equipment . Motors shall be capable of delivering full rated output operating at a voltage deviating by 5% from the rated voltage at rated frequency.
 
The system will be connected to power supply rated 380/220 +5% volts, 50Hz, three-phase, four-wire with solidly earthed neutral.
 
Interlocks shall be provided in case of outbreak of fire and operation of fire detection and signaling system.
 
      Quality Assurance :
 
   Applicable codes and standards
 
The air conditioning and ventilation systems in this specification shall comply with the latest editions of relevant publications of international standards or American standards and codes of practice.
 
Ventilation and air conditioning shall comply with:-
 
-    EUS: Electricity Utility specification.
-         ASHRAE: American Society of heating, refrigerating, and air
    conditioning engineers.
-         NFPA: National fire protection association
   NFPA –90A “installation of air conditioning and ventilation system”
-         IEC: Standard.
-         SMACNA: Specifications for sheet metal ductwork issued by heating
    & ventilating contractor association.
-         ASTM: American society of testing material.
-   NEBB         : National Environmental balancing bureau.
 
   Alternative Codes and Standards
 
The supplier may propose alternative codes and standards provided it is demonstrated that they give an equivalent of quality as referenced codes and standards. Acceptability of any alternative codes or standards is at the discretion of the purchaser.
 
  Precedence of Codes and Standards
 
In cases of the conflict between this specification and any of the referenced codes and standards, the following order of precedence shall apply:-
-         This specification.
-         EUS specification.
-         IEC recommendations.
-         Referenced codes and standards.
-         Acceptable alternative codes and standards.
 
     Design
 
   Design Conditions
 
-  Heating, ventilating, and air conditioning system (HVAC) shall be designed and installed to provide an  environment suitable for personnel and equipment operation. The system shall maintain the levels of temperature, humidity, air  pressurization and exhaust as required by the equipment.
 
-  Positive pressure for switchgear, rooms, cable basement, workshop, corridors, and staircases shall be sufficient to prevent dust from entering through doors and windows.
 
-   Negative pressure is required for battery rooms, kitchen, store, and toilets. Both cases of positive negative pressures shall keep the number of air changes per hour according to the table (2) with considering referenced codes and standards and their precedence
All mechanically ventilated spaces should be served by both supply and exhaust fans.
 
 -  Air conditioning systems shall be sized no larger than 115% of the total cooling load at design conditions.
 
 
   

Space	Relative humidity (R.H)	Air change per hour (Ach/h)	Temperature (°C)
(A) Ventilated Spaces
Switchgear rooms	<90%	According to calculations with respect to temperature conditions	According to items 3.2.3 and 4.5.13
Transformer rooms	<90%
Battery room	N/A
Battery charger room	50%
Basement/cable gallery	<90%
Kitchen, toilets	<90%
Other indoor places.	50%
(B) Air Conditioning Spaces
Control room	50%	N/A	24-2
Office	50%	N/A	24-2
Relay and metering room	50%	N/A	24-2
AC/DC distribution room.	50%	N/A	24-2
Communication room	<90%	N/A	24-2

Table (2)
 
 Noise Levels
 
The sound attenuation and vibration control equipment, associated with air conditioning and ventilation installation shall; be selected to ensure that the noise level do not exceed 60 dB.
 
   Fabrication
 
-         Fans. shall be centrifugal, high efficiency designed for the delivery of large air volume at moderate pressures.
 
-         Ventilating and exhaust fans shall have a specified SP with a maximum speed (r.p.m) selected according to referenced codes and standards.
 
-         Fans shall be driven c/w motors mounting plates, pulleys, flexible connections for outlet flanges, anti-vibration mounting…etc.
 
-         The capacities of the fans hall are in accordance with the design calculations. Fans shall have the direction of rotation or discharge direction arrangements to suit space conditions.
 
 
-         All fresh air (ventilating) fans shall be supplied and installed c/w sand trap louvers, pre-filter, and bag filter section at fan inlet. Filter average synthetic dust weight arrestance shall not be less than 85%.
 
-         All fan housings shall be “double skin” acoustically treated for quiet operation. Fans are to be driven with a v-belt drive. Sheaves shall be adjustable ration type and shall be sized to give the required fan speed with the motor sheaves at about the middle of its range of adjustment.
 
-         Fan housing shall be rigidly built, braced, and acoustically installed. Bearings shall be self-aligning and prevent leakage of oil or grease. Sups or oil chambers must be provided in assessable positions outside of the dust connections for easy lubrication.
 
-         There shall be at least two belts, capable of carrying the entire load when one belt broke.
 
-         Operation of exhaust fans shall be synchronized with that of the corresponding ventilating fans.
 
-  All fans shall fulfill the specified requirements without producing excessive noise anywhere in the building.
 
-         Fan wheels shall have ample strength and be statically and dynamically balanced.
 
-         Batteries room’s exhaust fans shall be provided by an explosive proof type motor.
 
-         All fan systems shall be controlled by the main control board (MCB). Fans shall shut down when the main control board receives a signal from the fire alarm system.
 
  Ventilation and air conditioning
 
   Control / Relay room, PLC room, and offices
 
-         Temperature and humidity control are required.
-         Control / relay room , PLC room and offices shall be air-conditioned by split-type air conditioning units.
 
 
-         Air conditioning units shall be sized so that the space temperature does not exceed the above mentioned requirements of each area (table 2).
-         One split unit extra shall be provided for the control/ relay room for the emergency cases and as a substitute.
 
   Other areas in Control Building
 
-         All other areas in the control building, except battery room, store, WC and kitchen will be ventilated by fresh air be ducted to various rooms or zones from filtered air supply fan units located on the control building’s roof.
-         At least two filtered air supply fan units will be provided, each unit be capable to carry the cooling full load to increase overall system reliability. The second unit shall be interlocked with the running unit so that it will automatically started upon failure of the normally running unit.
 
 11KV hall & AC/DC room
 
-         Temperature control is required, this can be done by mechanical. Ventilation filtered air supply fan units, or by split types air conditioning units for substations located in the Upper Egypt zone.
-         Ventilation rate shall be sized so that the space temperature does not exceed the manufacturer’s maximum allowable temperature for the 11 kV switchgear and AC/DC equipment.
-         In case of ventilating the 11 kV shall be split type air conditioning units, on split extra shall be provided for emergency cases.
 
 Auxiliaries Transformers,  Corridors
 
-         Temperature control is required, this can be done by mechanical ventilation by supplying air from the filtered air supply fans units.
-         No ductwork be installed within or beneath slab on grade floor.
 
  Battery Room
-         Temperature and chemical concentration control is required.
-         The battery room shall be ventilated by means of two exhaust fans.
-         It is important to maintain the average ambient room temperature not less than 25°C (77°F).
-         Fans are arranged so that one is operating at full flow and the other is on stand-by. An airflow sensor shall be installed to initiate an alarm when the running fan becomes inoperative and the stand-by fan will be automatically started upon failure of the normal running fan. Each fan shall have an independent failure alarm.
-         Fans shall be located at the highest level in the room and all exhaust air shall be discharged outside the building.
-         Exhaust fans used shall be provided by an explosion-proof type motor. Fan motors must be outside the battery room.
 
  Workshop & Battery Charger Room
 
-         Temperature control is required, this can be done by mechanical ventilation either by using motor powered fans (gravity ventilation) or filtered air supply fan units.
 
  WC. Kitchen & Store
 
-         Temperature and odors control are required.
-         Kitchen, WC, and store shall be provided with sufficient ventilation by means of exhaust fans.
-         Louvered doors shall be used.
-         It is important to maintain the ambient room temperature at least 5°C below the outside ambient temperature.
 
  Sheet Metal Duct Work

 -  The duct shall be installed straight and smooth the inside with neatly finished joints. Connections are to be free from vibration under all operating conditions.
 
-         All spaces around the ducts shall be filled where they pass through walls or partitions so that no holes are left. The materials used for this purpose shall be equal in fir-resistant qualities to the construction through which the ducts pass. Care shall be taken to prevent transmission of floor vibration to ducting.
 
-         No ductwork will be outside the building.
 
-    The ductwork dimension is shown on the drawings shall represent the net free internal size exclusive of all linings.
 
-   Elbows for conventional ductwork shall have approved radio aerodynamically correct running vanes. All fittings shall be constructed for minimum pressure drop and noise generation at the selected air velocity.
-   A substantially constructed manual damper of the butterfly or multiple blade type shall be provided in every branch duct. Each damper shall be equipped with a locking quadrant of heavy construction and must be connected to a mechanically operated tripping system that holds then open against a spring during normal operation, the tripping mechanism must be achieved by a fire system.
 
-         Shop drawings for ductwork shall be made by the supplier after actual job measurements are obtained. These drawings shall indicate the coordination with piping and other mechanical and electrical services installed. Shop drawings shall be submitted for approval.
 
-         All ductwork shall be cross braced to guarantee rigidity and stability of sheet metal.
 
    Duct Work And Fittings Materials
 
-         All ductwork and fittings shall be constructed of galvanized metal and in accordance with (SMACNA).
 
    Flexible Connections
 
-         Suitable flameproof flexible connections shall be furnished and installed on all suction and discharge connection units, for preventing the transmission of vibration through the ducts to occupied spaces.
 
-         Flexible connections shall be of suitable weight and composition for the static pressure developed.
 
    Access Doors in Sheet Metal Work
 
-         Where necessary in ductwork, casing, or sheet metal partitions suitable access doors and frames to permit inspection operation and maintenance of all valves, controls, volume, and fire dampers, filters, sprays, bearings, traps of other apparatus concealed behind the sheet metal work shall be provided. All such doors shall be double construction, of not less than 10/10 mm (no. 20 gauge) sheet metal and shall have sponge gaskets around their entire perimeter and electric light in a watertight type failure shall be provided.
 
  
    Mini-Split Type Units
 
-         Mini-spilled air conditioning units with exposed high wall/ceiling evaporator blower units shall be used for air conditioning of offices, control room, protection room, AC/DC distribution room and communication room.
 
-         One split unit extra shall be provided for the control room for emergency cases.
 
-         All mini-split units shall be heat – pump type.
 
-         Evaporator/blower units for exposed units shall be finished in attractive slim cabinets to blend with interior décor of rooms.
 
 Filter For Ventilation And Air-conditions System 
 
-         Filters with high efficiency shall be used to reduce the dirt content of the air supplied to the different areas and to keep equipment in a clean environment.
-         Filters percent efficiency shall be determined by the dust spot test specified in ASHRAE standard 52.
-         Filters shall be a drawer washable type and re-used.
 
 ELECTRICAL WORK

 
      The HVAC supplier shall furnish & install main control board, as described hereinafter as well as supply & install all electrical & control cables between the control board and their respective HVAC unit.
 
    On /Off electrical isolator shall be push-button type.
 
   All enclosures for MCB. Shall be sheet metal with 1.5 mm at least thickness for enclosure 2mm for doors.
 
     Electrical motor shall have adequate to operate driven equipment with 110% nameplate power without overload and shall be rated for continuous operation.
 
      The electrical motor shall have class (F) insulation with 80°C continuous temps. rise & electrical motor shall be IP55 protection degree.
 
           Power, Control Cables
 
   All wiring for connection to motor shall be conductor electrolytic annealed tinned copper and stranded wire.
 
     In the multi-core cables. Cable shall be played on galvanized cable trays.
 
    Wires and cables for the power circuits shall be rated for 0.61/1KV and shall comply with IEC 60227.
 
            Main Control Board (MCB)
 
    MCB shall be supplied with a sheet metal enclosure with 1.5 mm thick. for panels, 2mm for doors.
 
   MCB shall accommodate the various electrical & control components as specified hereinafter.
 
     HVAC supplier shall submit before any supply of MCB complete wiring and submittals for approval.
 
      MCB shall contain at least (and not limited) the various components: main incoming circuit breaker, branches circuit breakers & contactors. Push-button, selector switches, indicator lamps for each run-stop, for HVAC equipment, amperemeter, voltmeter and any necessary components shall be required.
 
      MCB enclosure protection category shall be (IP 55).
 
 
        Earth Bonding
 
All piping and ducting shall be electrically earthed, throughout its length in accordance with EUS specification E27, IEC standard, and reference standards.
 
 TESTING AND INSPECTION
 
 Before operating the system, perform these steps:-
 
1-   Obtain as-built design drawings and specifications and become thoroughly acquainted with the design intent.
 
2   Obtain copies of approved shop drawings of all air handling equipment, outlet (supply, return, and exhaust), and temp. control diagram.
 
  
3-   While the system from the system AHUs to terminal units to determine the variation of installation from design.
 
 
4-  Check filters and dampers ( both volume and fire) for correct and locked position and temp. control for completeness of installation before starting fan.
 
 
5-   Prepare report test sheets for fans and outlets.