Air Conditioning System-1

1. Air Conditioning System-1 Created by: David Chadderton Email: dchadder@ncable.net.au

2. Introduction • Refrigeration system for ducted air conditioning systems • Understand how the heat removal and rejection system functions • Thermodynamic principles in action

3. Heat Removal from a Building • Explanations of, • Refrigerant cycle • Heat absorbed from occupied areas • Condenser cooling • Cooling tower • Typical temperatures

4. Overview • Lowering the internal air temperature against a warmer external climate, requires the use of a refrigeration cycle heat pump • Mechanical systems are used

5. Vocabulary • Compressor – energy source • Evaporator – cools the chilled water • Cooling coil – cools the indoor air • Condenser – rejects heat into water • Cooling tower – rejects heat to atmosphere • TEV – drops refrigerant pressure • Refrigerant – phase-change fluid, non-CFC

6. This is the air conditioning air handling unit, AHU, where the air is filtered, cooled and blown through ducts to the conditioned rooms Outside air at 27oC and above is brought into the building and mixed with returned air from the rooms at 24oC Chilled water air cooling coil lowers the supply air to around 15oC

7. Air handling unit Conditioned supply air ducted to rooms, 15oC to 24oC in summer, 24oC to 30oC in winter Hot water air heating coil raises supply air to required condition, 15.0oC to 24oC in summer Supply air fan, usually a centrifugal fan, blows conditioned air through the ducts to the conditioned rooms.

8. Chilled Water System to the AHU The evaporator shell and tube heat exchanger cools water from 12oC to 6oC and removes heat from the incoming air and the recirculated air from the rooms, to cool the building. 12oC chilled water return 6oC chilled water flow Chilled water pump

9. Chilled Water System to the AHU Room air temperature sensor Chilled water flow control valve and driving motor Electronic valve controller

10. Chilled Water Pump Control Chilled water flow control valve and driving motor Electronic variable frequency drive, VFD or VSD (speed) to reduce pump speed as valve closes, saves energy.

11. Refrigeration Provides Cooling Warmed refrigerant vapour at 20oC is sucked back into the compressor Refrigeration compressors, two reciprocating piston compressors, screw or centrifugal, are the power source for the refrigeration system, electric motor driven. Building Services Engineering, 4th edition

12. Refrigeration Plant Compressors are noisy, located in Plant Room or on roof deck, on mass concrete base, separated from floor by a layer of cork or rubber. Building Services Engineering, 4th edition

13. Refrigerant Provides Cooling Thermostatic expansion valve reduces refrigerant pressure, forming flash vapour and liquid to pass to evaporator Evaporator 5oC refrigerant, HFC134a or other non chlorinated fluorocarbon, with zero ozone depletion potential, ODP.

14. Refrigerant Provides Cooling Shell and tube refrigerant condenser provides warm, 29oC liquid refrigerant to the TEV TEV Evaporator

15. Condenser Function The compressors raise the pressure of the refrigerant vapour to 10.0 bar (1.0 bar = 1.0 atmosphere, approx.) and around 60oC. This hot gas is condensed to liquid in the shell of the condenser. TEV Condenser

16. Condenser Function The cooled liquid refrigerant at 29oC and 10.0 bar passes to the TEV. TEV Condenser

17. TEV Function The TEV drops the pressure rise created by the compressor. Liquid refrigerant at 29oC and 10.0 bar passes through the resistance of the TEV to 5oC liquid at 4.0 bar, with some flash vapour. TEV Condenser

18. Evaporator The cold refrigerant liquid at 5oC is fully evaporated into vapour as it passes through the tubes of the evaporator and rises to 20oC prior to the compressor inlet.. TEV Evaporator Condenser

19. Condenser Cooling Now you understand the complete refrigeration cycle. The missing part is how to reject heat from the condenser, i.e. cool the building and system. Where does it go to? TEV 5oC 20oC Evaporator 50oC 60oC Compressor 29oC Condenser 20oC

20. Condenser Heat Removal • The heat must be rejected to the outside air, or into the ground. • Wet cooling tower • Dry air cooling coils • In-Ground pipes • Waste heat exchanger TEV 50oC 29oC

21. Cooling Tower Outside air enters the cooling tower at up to 35oC db, 21oC wb, blown through by an axial or centrifugal fan. Condenser cooling water is circulated from the condenser, removing heat from the building, condensing refrigerant into liquid. 29oC Refrigerant vapour enters at 50oC 35oC Refrigerant liquid leaves at 29oC Condenser

22. Cooling Tower Water distributor Condenser cooling water is automatically dosed with biocide chemical to control bacteria. The tower is emptied, cleaned and re-dosed at 3 monthly intervals or whenever it is contaminated. 29oC Refrigerant vapour enters at 50oC 35oC Refrigerant liquid leaves at 29oC Condenser

23. Air- Cooled Heat Exchanger Condenser cooling water 29oC A finned tube heat exchanger remains dry on the outside to minimise contamination of the outside air. Six axial fans on this sketch. Located on the roof plant deck, discharging waste heat to the outside air. Refrigerant vapour enters at 50oC 35oC Refrigerant liquid leaves at 29oC Condenser

24. What have we learned? • Indoor air at 27oC is cooled by a chilled water coil at 6oC to 15oC • Refrigerant at 5oC cools the chilled water • Compressor raises refrigerant to 50oC • Refrigerant is condensed at 29oC • Liquid refrigerant evaporates at 5oC, returns to compressor • Condenser water cooled by outside air

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