THE POWER PLANT - CONDITIONING AND BUILDING VENTILATION

1- PURPOSE OF CONDITIONING & BUILDING VENTILATION SYSTEM

l  This system is commonly known as Heating, Ventilation & Air-conditioning (HVAC) System

l  HVAC system provides comfort for the human being.

l  HVAC system maintains the required inside temperature for different buildings, equipment, covering the entire power plant and associated auxiliaries / facilities.

2- WORKING PRINCIPLE OF  HVAC SYSTEM

l  It acts on the principle of reversed Carnot cycle.

l  Vapour is compressed isentropically in a compressor from a low pressure and low temperature to a higher pressure and high temperature and is passed through a condenser in which it is condensed at constant pressure.

l  The fluid is then expanded isenthalpically to its original pressure and is finally evaporated at constant pressure in an evaporator.

3- DESIGN CONDITION FOR AIR CONDITIONED AREAS

4- AIR CONDITIONING SYSTEM

l  The Central Air Conditioning system maintains a positive pressure to the building with respect to surrounding areas. And so, fresh air supply system will be applied in order to:

-          Provide a minimum fresh air to occupants for their health and comfort needs.

-          Maintain an overpressure to prevent the ingress of dust and sand.

-          Compensate for specific exhaust from toilet, kitchen etc.

l  The small room (For example electrical room in local electrical building, office in workshop or gate house) are air conditioned by Split air conditioner without humidity control. These rooms may not be maintained in a positive pressure.

l  The HVAC system is designed for continuous operation under all prevailing climatic and ambient conditions. And the verification of air quantities has to be based on a cooling load calculation considering external and internal heat gain and the room design condition as stated

l  Heating for Air Conditioned Areas with DX AHU and Reversible Air Cooled Condensing Unit, Split Air Conditioners, Packaged Air Conditioners will be done as below:

-          The fundamental of an air conditioning system is the use of a refrigerant to absorb heat from the indoor environment and transfer it to the external environment.

-          In the cooling mode, indoor units are supplied with liquid refrigerant. The amount of refrigerant flowing through the unit is controlled via an expansion valve located inside the unit.

-          When the refrigerant enters the coil, it undergoes a phase change (evaporation) that extracts heat from the space, thereby cooling the room. The heat extracted from the space is exhausted to the ambient air.

-          Whereas in the heating mode refrigeration systems can operate on reverse cycle mode enabling the absorption of heat from the external environment and using this heat to raise the internal temperature.

-          When in the heating mode, indoor units are supplied with a hot gas refrigerant. Again, the amount of hot gas flowing through the unit is controlled via the same electronic expansion valve.

-          As with the liquid refrigerant, the hot gas undergoes a phase change (condensation), which releases heat energy into the space. Thus heating is achieved to maintain the winter inside design temperatures.

-          If the temperature is not maintained through the heating mode, additional electric heater will be considered to maintain inside design temperatures.

l  Heating for the Non-AC areas is not envisaged.

l  Electronic steam humidifiers are provided to maintain the humidity in the air conditioned areas.

5- VENTILATION SYSTEM

l  Turbine Building

-          Supply air units equipped with intake louvers, pre filters, wall cowl, bird screen and sand / dust trap. The supply air is through supply air duct with motorized volume control damper, and air distribution by supply air grilles.

-          Exhaust through Roof extractors.

-          Heating is not envisaged in this area as the minimum temperature to be maintained is 7°C.

l  All the Ventilated Areas

-          Supply air louvers with pre filters and sand/dust trap.

-          Exhaust through exhaust fans with back draft dampers

l  In case of battery rooms, air handling unit and explosion proof exhaust fans are provided at a minimum, meeting all area classification requirements for gas emitted by batteries. All fans, ducting and grilles etc., in the battery room are given acid fume resistance anti corrosive paint and all motors will be of flameproof type.

l  Switchgear rooms, cable rooms, control rooms etc. are also provided with smoke exhaust fans.

l  In case of hydrogen generation plant explosion proof exhaust fans are provided at a minimum, meeting all area classification requirements.

l  The ventilation system in rooms containing a flammable or explosive material are automatically cut out under fire conditions. Ventilation systems in other rooms with automatic fire extinguishing systems are tripped and/or controlled in the local control panel and/or main control panel.

l  Toilets, Kitchen and pantry are supplied air and exhaust fans/exhaust hoods will evacuate all the supplied air (no recirculation is envisaged).

6- DETAIL OF HVAC SYSTEM IN THE PLANT

1) Central control building

2) Turbine building

3) GIS building & GIS control building

4) Administration building

5) Canteen building

6) Unit Switchgear building

7) Demineralization building

8) Air compressor building

9) Fire fighting pump house

10) Workshop building

11) Stores building

12) HRSG feed pump building

13) Fire fighting foam station

14) Cooling water pump station control building

15) Electro chlorination plant

16) Hydrogen generation building

17) Guard station

18) Diesel oil switchgear building

19) Hazardous storage building

20) Sea water desalination plant

21) Black start and emergency D/G building

22) Local dosing phosphate building

23) Lubricant storage building

24) Diesel oil pump house

7- OPERATION AND MAINTENANCE

l  The HVAC system can be started automatically / manually either from local control panel or centralized automatic regulatory/supervisory system located in control room.

l  The operation status as alarms, temperature, fault indication, status indication of each air  conditioning system will be in indicated and available at the local control panel or self-contained microprocessor / PLC based control panel.

l  The condensing unit compressor/s shall maintain the desired room temperature on the basis of input from temperature sensor and associated transmitters placed either in the return air path or in room.

l  Room RH control (wherever required) with the help of humidifiers (sensing the humidity) located in the return air path or in room.

l  The various HVAC systems are also interlocked with the fire alarm panel. The HVAC system shall be tripped automatically in case of fire by signal received from room mounted smoke detector through zonal fire panel and re-operated manually.

l  Smoke exhaust fan shall be started manually to remove smoke from the enclosed spaces. The smoke exhaust fan shall be capable of operation for 2 hours at 400°C and will be run by both normal and emergency power supply.

l  Inside room temperature for air conditioned areas shall be monitored properly to detect any equipment malfunction.

l  The HVAC equipment shall be checked properly for any undue noise or vibration.

l  Filter shall be cleaned and replaced properly as per O&M instructions.

l  Compressor oil level shall be checked properly.