heat ventilation and Air conditioning.pptx

Heat Ventilation Air conditioning Selection of Air Conditioning Systems

1. HVAC Air Conditioning System 21AE27 – Heat, Ventilation and Air Conditioning V. Kondusamy Assistant Professor, Department of Mechanical Engineering Karpagam College of Engineering

2. Introduction In order to maintain required conditions inside the conditioned space , energy has to be either supplied or extracted from the conditioned space . The energy in the form of sensible as well as latent heat has to be supplied to the space in winter and extracted from the conditioned space in case of summer. 21AE27 – Heat, Ventilation and Air Conditioning

3. A thermal distribution system is required to circulate the media between the conditioned space and the A/C plant to introduce the required amount of fresh air into the conditioned space (required Indoor Air Quality ( IAQ) can be maintained) 21AE27 – Heat, Ventilation and Air Conditioning

4. All air systems Air is used as the media to transfer energy from the conditioned space to the A/C plant . A ir is processed in the A/C plant and this processed air is then conveyed to the conditioned space through insulated ducts using blowers and fans. This air extracts ( or supplies in case of winter) the required amount of sensible and latent heat from the conditioned space. The return air from the conditioned space is conveyed back to the plant, where it again undergoes the required processing thus completing the cycle . No additional processing of air is required in the conditioned space. 21AE27 – Heat, Ventilation and Air Conditioning

5. All air system - Classification Single duct systems Dual duct systems Single duct systems: 1 . Constant volume, single zone systems 2. Constant volume, multiple zone systems 3. Variable volume systems Dual duct systems: 1. Dual duct, constant volume systems 2. Dual duct variable volume systems 21AE27 – Heat, Ventilation and Air Conditioning

6. Single duct, constant volume, single zone systems O utdoor air ( OD air) for ventilation and recirculated air ( RC air) are mixed in the required proportions using the dampers T he mixed air is made to flow through a cooling and dehumidifying coil, a heating coil and a humidifier using a an insulated ducting and a supply fan 21AE27 – Heat, Ventilation and Air Conditioning

7. Single duct, constant volume, single zone systems As the air flows through these coils the temperature and moisture content of the air are brought to the required values . Then this air is supplied to the conditioned space, where it meets the building cooling or heating requirements. 21AE27 – Heat, Ventilation and Air Conditioning

8. Single duct, constant volume, single zone systems 21AE27 – Heat, Ventilation and Air Conditioning

9. Single duct, constant volume, single zone systems The return air leaves the conditioned space , a part of it is recirculated and the remaining part is vented to the atmosphere . A thermostat senses the temperature of air in the conditioned space and controls the amount of cooling or heating provided in the coils so that the supply air temperature can be controlled as per requirement. 21AE27 – Heat, Ventilation and Air Conditioning

10. Single duct, constant volume, single zone systems A humidistat measures the humidity ratio in the conditioned space and controls the amount of water vapour added in the humidifier and hence the supply air humidity ratio as per requirement This system is called as a single duct system as there is only one supply duct , through which either hot air or cold air flows , but not both simultaneously. 21AE27 – Heat, Ventilation and Air Conditioning

11. Single duct, constant volume, single zone systems It is called as a constant volume system as the volumetric flow rate of supply air is always maintained constant . It is a single zone system as the control is based on temperature and humidity ratio measured at a single point. 21AE27 – Heat, Ventilation and Air Conditioning

12. Single duct, constant volume, single zone systems Z one refers to a space controlled by one thermostat. The single zone may consist of a single room or one floor or whole of a building consisting of several The cooling / heating capacity is regulated by regulating the supply air temperature and humidity ratio, while keeping the supply airflow rate constant . A separate sub-system controls the amount of OD air supplied by controlling the damper position. 21AE27 – Heat, Ventilation and Air Conditioning

13. Single duct, constant volume, single zone systems Since a single zone system is controlled by a single thermostat and humidistat , it is important to locate these sensors in a proper location, so that they are indicative of zone conditions 21AE27 – Heat, Ventilation and Air Conditioning

14. Single duct, constant volume, multiple zone systems Designed for large buildings with varying heating/cooling needs . A single system handles multiple zones economically . Air is pre-conditioned to a minimum/maximum temperature and humidity . Constant air volume supplied to each zone's reheat coil . Zone thermostat adjusts reheat coil temperature based on load . Operates using electricity or hot water. 21AE27 – Heat, Ventilation and Air Conditioning

15. Single duct, constant volume, multiple zone systems 21AE27 – Heat, Ventilation and Air Conditioning

16. Single duct, variable air volume (VAV) systems Air is cooled and dehumidified in a cooling coil (CC ). Variable air volume supplied to each zone based on load . Zone dampers control airflow, regulated by zone thermostats . Supply air temperature remains constant; flow rate varies . Optimized for energy efficiency and comfort in diverse zones. 21AE27 – Heat, Ventilation and Air Conditioning

17. Single duct, variable air volume (VAV) systems Advantages: Lower cooling energy consumption by avoiding excessive cooling and reheating. Reduced fan power due to lower airflow rates under low loads. Significant energy savings, especially in perimeter zones with variable solar and outdoor temperature loads. Challenges: Ventilation, indoor air quality (IAQ), and air distribution issues at low zone loads. Difficulty in precise humidity control. Balancing dampers can be complex with varying airflow rates. Combining with terminal reheat helps maintain minimum airflow for ventilation and distribution. 21AE27 – Heat, Ventilation and Air Conditioning

18. Dual duct, constant volume systems Supply air fan splits airflow into two streams : Cold Stream: Cooled and dehumidified (~13°C) via cooling coil. Hot Stream: Heated (~35–45°C) via heating coil. Separate ducts for cold and hot air streams . Mixing box adjusts proportions of hot and cold air for each zone . Zone thermostats control mixing to meet specific load requirements . Constant airflow volume to zones; supply air temperature varies with load. 21AE27 – Heat, Ventilation and Air Conditioning

19. Dual duct, constant volume systems 21AE27 – Heat, Ventilation and Air Conditioning

20. Dual duct, constant volume systems Advantages: Constant airflow ensures proper indoor air quality (IAQ) and air distribution. Allows simultaneous cooling in some zones and heating in others. Highly responsive to zone load variations, enabling precise control of conditions. Disadvantages : Requires more space due to dual duct design for cold and hot air streams. Less energy efficient due to simultaneous cooling and heating. Energy efficiency can be enhanced by: Shutting off the cooling coil in low outside temperatures. Shutting off the heating coil in hot weather and adjusting air mixing . 21AE27 – Heat, Ventilation and Air Conditioning

21. Dual Duct, Variable Air Volume Systems Similar to dual duct constant volume systems but with variable airflow . Mixing boxes adjust airflow rates based on zone load requirements . Airflow decreases as zone load drops, maintaining energy efficiency . Allows precise temperature and airflow control for each zone . Combines the flexibility of VAV systems with dual duct functionality. 21AE27 – Heat, Ventilation and Air Conditioning

22. Out door air control in All air system Outdoor air is essential for ventilation and is controlled by a sub-system in all-air systems. Exhaust, re-circulated, and outdoor air dampers work in unison to balance airflow. Outdoor airflow rate typically equals exhaust airflow rate, ensuring mass balance. When outdoor air damper opens, re-circulated air damper closes, and vice versa. Minimum outdoor air (10-20% of supply airflow) is maintained during extreme temperatures: Below -30°C or above 24°C. Outdoor air percentage increases as outdoor temperature rises: From -30°C to 13°C, outdoor air increases gradually. 100% outdoor air used when the temperature is between 13°C and 24°C. This method helps reduce annual energy consumption while ensuring comfort. 21AE27 – Heat, Ventilation and Air Conditioning

23. All Air system Advantages: Energy Conservation: Effective use of outdoor air for energy savings. Precise Control: Maintain temperature within ±0.15°C and humidity within ±0.5%. Simultaneous Cooling & Heating: Dual duct systems allow easy changeover between seasons. Consistent Air Distribution: Ensures good room air distribution and ventilation across varying loads. Building Pressurization: Easily achieved in all-air systems. Flexible Air Conditioning Plant Location: Plant can be positioned away from conditioned spaces, reducing noise and offering flexible filtration options . 21AE27 – Heat, Ventilation and Air Conditioning

24. All Air system Disadvantages: Space Requirement: Occupies more space, reducing available floor area, challenging for high-rise buildings. Difficult Retrofitting: Space constraints can make retrofitting difficult. Air Balancing Issues: Balancing air, especially in VAV systems, can be complex. Applications: Suitable for both comfort and industrial air conditioning. Ideal for buildings with multiple zones requiring individual control (offices, hospitals, hotels). Essential for environments needing precise conditions (clean rooms, computer rooms, operating theatres). 21AE27 – Heat, Ventilation and Air Conditioning

25. All water systems All water systems use water to transfer thermal energy between the conditioned space and the air conditioning plant. Cooling: Cold water circulates when cooling is needed. Heating: Hot water circulates when heating is required. Ventilation: Treated outdoor air is supplied separately for ventilation. Types of All Water Systems: 2-Pipe System: Application: Used for either cooling or heating, but not both simultaneously. Components: One supply pipe for cold or hot water. One return pipe for water flow back to the coil. Control: Flow rate controlled by a flow control valve, managed by zone thermostat. Note: Requires separate system for ventilation air. 21AE27 – Heat, Ventilation and Air Conditioning 21AE27 – Heat, Ventilation and Air Conditioning

26. All water systems 4-Pipe System: Application: Can provide both heating and cooling simultaneously. Components: Two supply pipes (one for cold water, one for hot water). Two return pipes (one for each water type). Operation: Cold and hot water mixed as needed depending on the zone load. Return: Separate return streams for cooling and heating coils 21AE27 – Heat, Ventilation and Air Conditioning

27. All water systems Heat Transfer Methods: Convection: Heat transfer via air movement (fan coil units, convectors). Conduction: Direct heat transfer through material (radiators). Radiation: Transfer through electromagnetic waves (radiators). Types of Heat Transfer Equipment: 1. Fan Coil Units (FCU): Components: Finned tube coil, fan, air filter, drain tray, controls. Cooling Function: Cold water circulates through the coil, fan blows air over it, cooling and dehumidifying the room air. Heating Function (Optional): Heating coil can be added (electric or hot water/steam). Control: Airflow can be adjusted via damper or fan speed, controlled manually or automatically by room thermostat. Note: Does not provide ventilation; a separate system is needed. A version with ventilation is called a unit ventilator . 21AE27 – Heat, Ventilation and Air Conditioning

28. All water systems Fan Coil Units (FCU): 21AE27 – Heat, Ventilation and Air Conditioning

29. All water systems 2. Convectors: Components: Finned tube coil for hot or cold fluid. Operation: Heat transfer occurs through natural convection (no fan). Application: Commonly used for heating, rarely for cooling. 3. Radiators: Components: Coils that transfer heat primarily through radiation. Operation: Some heat transfer via natural convection. Application: Widely used for heating, now also used for cooling in certain systems. 21AE27 – Heat, Ventilation and Air Conditioning

30. All water systems Advantages: Compact Thermal Distribution: Requires less space compared to all-air systems. Smaller plant size due to the absence of large supply air fans. Individual Room Control: Offers precise control for each room while retaining central system benefits. Energy Efficiency: Low-temperature hot water allows the use of solar or waste heat for winter heating. Retrofitting Capability: Suitable for both new buildings and existing structures. Flexibility: Simultaneous cooling and heating possible with 4-pipe systems. 21AE27 – Heat, Ventilation and Air Conditioning

31. All water systems Disadvantages: Higher Maintenance: Increased maintenance demands in conditioned spaces compared to all-air systems. Condensate Drainage Issues: Potential for mess and health risks if condensate water stagnates. Can be mitigated by central ventilation handling dehumidification. Ventilation Challenges: Positive ventilation depends on wind and stack effects when using open windows or apertures. Humidity Control: Difficult to maintain precise humidity control during summer using chilled water valves . Applications: Ideal for buildings requiring individual room control: Hotels Apartment buildings Office buildings 21AE27 – Heat, Ventilation and Air Conditioning

32. Air water systems Dual Medium System: Primary air and secondary water are used to achieve desired indoor conditions. Air and water are cooled or heated in a central plant. Primary Air: Constant volume supplied to meet ventilation needs and latent cooling load. Cooled and dehumidified during summer; humidified during winter. Secondary Water: Circulates to offset sensible cooling or heating loads in conditioned spaces. Avoids condensation issues as water handles only sensible cooling. 21AE27 – Heat, Ventilation and Air Conditioning

33. Air water systems 21AE27 – Heat, Ventilation and Air Conditioning

34. Air water systems System Components: Central plant for air and water treatment. Ducts and fans for air distribution. Pipelines and pumps for water circulation. Room terminal units (e.g., fan coil units, induction units, or radiant panels). Room Terminal Units: Fan Coil Units: Similar to those in all-water systems, handle secondary water for temperature control. Induction Units: Use medium- to high-pressure primary air to induce airflow of secondary air through coils for heating or cooling. Mixed primary and secondary air is supplied to the room. Radiant Panels: Use water to provide thermal comfort through radiant heat exchange. 21AE27 – Heat, Ventilation and Air Conditioning

35. Air water systems Features : Primary air addresses ventilation needs without requiring separate systems. Combines the benefits of central plant efficiency with localized control 21AE27 – Heat, Ventilation and Air Conditioning

36. Air water systems Advantages: Efficient Zone Control: Room thermostats manage secondary water flow or air, enabling economic individual zone control. Simultaneous Cooling & Heating: Primary air and secondary water can handle both requirements simultaneously. Space-Saving: Less primary air required compared to all-air systems, reducing duct space. Reliable Ventilation: Ensures positive ventilation under all conditions. Dry Coil Operation: Avoids latent heat transfer in cooling coils, preventing odor, fungal growth, and extending coil life. Heating Efficiency: Secondary air and coils can heat spaces in winter without primary air. Simplified Maintenance: Easier servicing of indoor units compared to all-water systems. 21AE27 – Heat, Ventilation and Air Conditioning

37. Air water systems Disadvantages: Complex Operation: Requires dual control systems for air and water. Limited Application: Generally suitable for perimeter zones only. Coil Maintenance Issues: Secondary water coils may accumulate dirt if room unit filters are inadequate. Primary Air Limitations: Constant primary air supply prevents shutting down for unoccupied spaces. Condensation Risk: Abnormally high latent loads can cause condensation on secondary cooling coils. 21AE27 – Heat, Ventilation and Air Conditioning

38. Air water systems Primary Applications: Buildings with Large Sensible Loads: Ideal for structures with high cooling or heating requirements without significant latent load. Spaces Without Strict Humidity Control Needs: Not suitable for environments requiring close humidity management. 21AE27 – Heat, Ventilation and Air Conditioning

39. Unitary refrigerant based systems Systems consist of self-contained air conditioning units with individual refrigeration cycles. Factory-assembled and tested for reliability and compliance with standards . Types and Configurations: Window Air Conditioners: Cooling capacities: 0.3 TR to 3.0 TR. Single package unit with evaporator and condenser coils, hermetic compressor, fans, filter, and controls. Mounted on window sills or through walls. Split Air Conditioners: Separate indoor and outdoor units. Indoor unit: Evaporator, expansion device, air filter, and evaporator fan. Outdoor unit: Compressor, condenser, and condenser fan. Ductable Systems: For larger spaces; can use air-cooled or water-cooled condensers. Cooling capacities can go up to 100 TR. Heat Pumps: Provide both cooling and heating capabilities depending on seasonal requirements . 21AE27 – Heat, Ventilation and Air Conditioning

40. Unitary refrigerant based systems Key Features: Compact design for single or multiple conditioned spaces. Cooling capacity controlled via: Compressor on-off cycling. Adjustable fan speeds for modular control. Condensate management via trays or drain pipes. Applications: Residential buildings, small offices, hotels, and spaces with isolated cooling needs. Suitable for retrofits or where ducted systems are impractical. 21AE27 – Heat, Ventilation and Air Conditioning

41. Unitary refrigerant based systems 21AE27 – Heat, Ventilation and Air Conditioning

42. Unitary refrigerant based systems Remote Condensing Unit: Houses compressor and condenser (air-cooled or water-cooled). Indoor Unit: Contains: Evaporator : Plate fin-and-tube type. Blower : Circulates air through ducts. Air Filter : Removes dust and debris. Drain Tray : Manages condensate water. Duct connections for supply and return air. Integrated Design Option: Entire refrigeration housed in one package. Includes water line connections and air duct provisions. 21AE27 – Heat, Ventilation and Air Conditioning

43. Unitary refrigerant based systems 21AE27 – Heat, Ventilation and Air Conditioning

44. Unitary refrigerant based systems Cooling Capacities: Ranges from 5 TR to 100 TR. Air Handling: Can provide air conditioning to: A large room. Multiple small rooms via ducting. Control Systems: Simple thermostat-based on/off control (smaller units). Advanced microprocessor control for larger systems with: Multiple compressors. Variable air volume (VAV) control. Optional Features: Heating Coils: Combined with evaporators for seasonal flexibility. Outdoor Air Supply: Provision for ventilation. Applications: Large rooms like auditoriums or banquet halls. Multiple small rooms, e.g., offices or commercial complexes. 21AE27 – Heat, Ventilation and Air Conditioning

45. Unitary refrigerant based systems Advantages Ease of Control: Simple and cost-effective individual room control. Occupants can adjust air distribution easily. Manufacturer Assurance: Guaranteed performance due to factory-assembled and tested units. Quick and Simple Installation: Minimal time and effort required for setup. User-Friendly Operation: Does not require specialized operators for day-to-day functioning. Cost-Effective: Lower initial investment compared to central systems. Retrofitting Compatibility: Ideal for existing buildings due to compact floor space requirements. 21AE27 – Heat, Ventilation and Air Conditioning

46. Unitary refrigerant based systems Disadvantages Limited Flexibility: Pre-matched components restrict customization of air flow, condenser, or evaporator sizes. Higher Energy Usage: Power consumption per ton of refrigeration (TR) is typically higher than central systems. Humidity Control Challenges: Precise control of space humidity is difficult. Noise Concerns: Higher noise levels in the conditioned space compared to central systems . 21AE27 – Heat, Ventilation and Air Conditioning

47. Unitary refrigerant based systems Disadvantages Ventilation Limitations: Limited capability for fresh air ventilation. Aesthetic and Compliance Issues: Less visually appealing; often meets appliance standards rather than building standards. Temperature Fluctuations: Room temperatures may swing when on-off control mechanisms are used. Limited Air Distribution Control: Fewer options for modifying air circulation within the space. Shorter Equipment Life: Relatively reduced lifespan compared to central air conditioning systems. 21AE27 – Heat, Ventilation and Air Conditioning

48. Unitary refrigerant based systems Applications Suitable for locations where stringent temperature and humidity control is not required. Commonly used in: Individual rooms. Hotels, classrooms, and offices. Shopping centers and nursing homes. Ideal for retrofitting in existing buildings with space constraints. 21AE27 – Heat, Ventilation and Air Conditioning