1 Environmental Thermal EngineeringLecture # 11 Min soo Kim Mechanical & Aerospace Engineering

2 Contents 1. Introduction 2. Equipments of Air Conditioning Systems3. HVAC Systems 4. HVAC Applications

3 Introduction

4 What is air-conditioning?The process of treating air to control simultaneously its temperature, humidity, cleanliness and distribution to meet the comfort requirements of the occupants of the conditioned space (“ASHRAE Handbook, Fundamentals, ” American Society of Heating, Refrigerating and Air-Conditioning Engineers)

5 Dehumidifying Operations in Air-ConditioningRelationship of the refrigeration and air-conditioning fields Air Conditioning Refrigeration Heating, Humidifying and Control of Air Quality Industrial Refrigeration, Including food Preservation, Chemical, and process industries Cooling and Dehumidifying Operations in Air-Conditioning

6 HVAC & R Heating Ventilating Air Conditioning Refrigeration

7 Heating Traditional Heating Systems Hearth, Franklin Stove, etc…Franklin Stove : Burning wood above a cold air duct heats air which then passes through baffles and is released through vents on each side of the stove Ondol (Korean) : floor radiant heating system

8 Heating Heating is the transfer of energy from a source to a spaceby following processes; - direct radiation - free convection Rate of sensible heating of air;

9 Ventilation Common contaminantsGases : carbon dioxide(CO2), carbon monoxide(CO), SO2, NO2 Volatile Organic Compounds (VOCs) Particulate Matter : soot, smoke, clay and bacteria, etc… Basic Methods to maintain good IAQ(indoor air quality) Source elimination or modification Use of outdoor air Space air distribution Air cleaning

10 Ventilation A typical ventilation system Conditioned Space Filter FanHeating Coil Cooling Conditioned Space Make-up outdoor air Exhaust (relief air) Supply air Return air Recirculated air

11 Carrier’s Centrifugal Chiller (1921)Air Conditioning W.H. Carrier Established Psychrometric Formulae (1911) Centrifugal Chiller (1921) -first practical method of air conditioning for large spaces Willis H. Carrier (1876~1950) 「TIME」 “King of Cool” 100 builders & titans of 20th century Carrier’s Centrifugal Chiller (1921)

12 Equipments of Air Conditioning System

13 Primary Equipments of HVACAir-Handling Equipment Heating Equipment Refrigeration Equipment Other Energy Saving Equipments - Thermal storage - Energy recovery - Solar energy - Geothermal

14 Air Handling EquipmentDuct Construction Air-Diffusing Equipment Fans Evaporative Air Cooling Equipment Humidifiers Air-Cooling and Dehumidifying Coils Desiccant Dehumidification

15 Air Handling Equipment

16 Duct Construction Duct system delivers a specific amount of air to each diffuser in the conditioned space at a specified total pressure. Duct construction is classified by application and pressure ; Residences ±125 Pa, ±250 Pa Commercial Systems ±125 Pa ~ ±2500 Pa Industrial Systems Any pressure

17 Duct Construction Pressure Drop in Duct Δp: Pressure drop [Pa]f: friction factor L: Length [m] D: Inner diameter of duct [m] Deq: Equivalent diameter [m] V: velocity [m/s] ρ: density [kg/m3]

18 Duct Construction Pressure Drop in Fittings Sudden Enlargement1 2 Sudden Contraction 1 2 1’

19 = radius of curvature/diameterDuct Construction Pressure Drop in Fittings Turns (90°) Ratio = radius of curvature/diameter Geometry factor Mitered 1.30 0.5 0.90 0.73 0.45 1.0 0.33 1.5 0.24 2.0 0.19

20 Duct Construction-cleaningDucts should be designed, constructed, and maintained to minimize the opportunity for growth and dissemination of microorganisms. Cleaning…

21 Air Diffusing EquipmentRequirements of air distribution; The flow rate must compensate for the net heat loss or gain in the space The velocity must not be higher than m/s in the occupied regions of the room There should be some motion of air to breakup temperature gradients in the room (warm air at the ceiling and cold air at the floors)

22 Air Diffusing EquipmentLinear Louver diffuser Types of Supply Air Outlets Grille and Register Outlets Linear Slot Outlets Ceiling Diffuser Outlets Perforated diffuser Ceiling Diffuser Outlets Linear Slot diffuser

23 Fans Fan is an air pump that creates a pressure difference and causes airflow. Types of Fans Centrifugal Fan Axial Fan

24 Centrifugal fans Centrifugal Fans Air enters the fan- Turns and moves into the blades - Enters the scroll Produce pressure from; - Centrifugal force created by rotating the air - Kinetic energy imparted to the air

25 Backward-inclined Backward-curvedCentrifugal fans Centrifugal Fans Type Figure Characteristics Airfoil Highest efficiency of all centrifugal fan designs. 10~16 blades of airfoil contour curved away from direction of rotation. Deep blades allow for efficient expansion within blade passages. Air leaves impeller at velocity less than tip speed. For given duty, has highest speed of centrifugal fan designs Backward-inclined Backward-curved Efficiency only slightly less than airfoil fan. 10~16 single-thickness blades curved or inclined away from direction of rotation. Efficient for same reasons as airfoil fan.

26 Centrifugal fans Type Figure Characteristics Radial Forward-curvedHigher pressure characteristics than airfoil, backward-curved (inclined) fans. Curve may have a break to left or peak pressure and fan should not be operated in this area. Power rises continually to free delivery. Forward-curved Flatter pressure curve and lower efficiency than the airfoil, backward-curved (inclined) fans. Do not rate fan in the pressure curve dip to the left of peak pressure. Power rises continually toward free delivery. Motor selection must take this into account

27 Performance characteristicsCentrifugal fans Centrifugal Fans – Performance Curves Type Performance curves Performance characteristics Airfoil Highest efficiencies occur at 50 to 60% of wide open volume. This volume also has good pressure characteristics. Power reaches maximum near peak efficiency and becomes lower, or self-limiting, toward free delivery. Backward-inclined Backward-curved Similar to air foil fan, except peak efficiency slightly lower.

28 Performance characteristicsCentrifugal fans Centrifugal Fans – Performance Curves Type Performance curves Performance characteristics Radial Higher pressure characteristics than airfoil and backward-curved fans. Pressure may drop suddenly at left of peak pressure, but this usually causes no problems. Power rises continually to free delivery. Forward-curved Pressure curve less steep than that of backward-curved fans. Curve dips to left of peak pressure. Highest efficiency to right of peak pressure at 40 to 50% of wide open volume. Rate fan to right of peak pressure. Account for power curve, which rises continually toward free delivery, when selecting motor.

29 Axial Fans Produce pressure from the change in velocity passing through the impeller

30 Axial Fans Axial Fans Type Figure Characteristics Propeller TubeaxialLow efficiency. Limited to low-pressure applications. Usually low cost impellers have two or more blades of single thickness attached to relatively small hub. Primary energy transfer by velocity pressure. Tubeaxial Somewhat more efficient and capable of developing more useful static pressure than propeller fan. Usually has 4~8 blades with airfoil or single-thickness cross section. Hub is usually less than half the fan tip diameter.

31 Axial Fans Vaneaxial Good blade design gives medium-to high- pressure capability at good efficiency. Most efficient of these fans have airfoil blades. Blades may have fixed, adjustable, or controllable pitch. Hub is usually greater than half fan tip diameter.

32 Performance characteristicsAxial Fans Axial Fans – Performance Curves Type Performance curves Performance characteristics Propeller High flow rate, but very low-pressure capabilities. Maximum efficiency reached near free delivery. Discharge pattern circular and airstream swirls. Tubeaxial High flow rate, medium-pressure capabilities. Performance curve dips to left of peak pressure. Avoid operating fan in this region. Discharge pattern circular and airstream rotates or swirls. Vaneaxial High-pressure characteristics with medium-volume flow capabilities. Performance curve dips to left of peak pressure due to aerodynamic stall. Avoid operating fan in this region. Guide vanes correct circular motion imparted by wheel and improve pressure characteristics and efficiency of fan.

33 Psychrometric Chart Cooling, Humidification and Dehumidification

34 Evaporative Air Cooling EquipmentAn evaporative cooler produces effective cooling by combining a natural process - water evaporation - with a simple, reliable air-moving system. Fresh outside air is filtered through the saturated evaporative media, cooled by evaporation, and circulated by a blower wheel

35 Evaporative Air Cooling EquipmentAdvantages - Substantial energy & cost savings - Reduced peak power demand - Improved indoor air quality - Life cycle cost effectiveness - Easily integrated into built-up systems - Environmental benign

36 Wetted-Drum Humidifier Power Wetted-Element HumidifierHumidifiers Wetted-Drum Humidifier Residential Humidifiers Power Wetted-Element Humidifier Pan Humidifier Atomizing Humidifier

37 Humidifiers Humidifiers – Load calculationFor ventilation systems having natural infiltration For mechanical ventilation systems having a fixed quantity of outside air H = humidification load, kg/h V = volume of space to be humidified, m3 R = infiltration rate, air changes per hour Qo = volumetric flow rate of outside air, kg/h Wi = humidity ratio at indoor design conditions, kg(water)/kg(dry air) Wo = humidity ratio at outdoor design conditions, kg(water)/kg(dry air) S = contribution of internal moisture sources, kg/h L = other moisture losses, kg/h Ρ = density of air at sea level, 1.2kg/ m3

38 Air-Cooling and Dehumidifying CoilsFluid inside the coil - Water and Aqueous Glycol Coils - Direct-Expansion Coils (refrigerant inside) Coil design: Extended surface (finned) cooling coil - most popular and practical

39 Desiccant DehumidificationThe use of chemical (or physical) absorption of water vapor to dehumidify air and reduce the latent cooling load in a building HVAC system Advantage Reduces cost of cooling Improves product quality for companies with moisture sensitive products Improves occupant comfort Increases overall cooling capacity of existing cooling equipment Reduces the amount of conventional cooling and elective demand Improves indoor quality by reducing airborne bacteria and fungus

40 Desiccant DehumidificationTraditional System Dehumidification was achieved by lowering the temperature of the air. Large energy required because air is over-cooled. Rotary Dehumidification Unit Desiccant dehumidification flows air from the building over a porous material that attracts moisture. The porous material attracts moisture until it is saturated and can hold no more. Warm air is then passed over the desiccant and the moisture is released and exhausted to the outside

41 Desiccant Dehumidification1: Process air "ON" 2: Filter 3: Rotor 4: Process air fan 5: Process air "OFF" (Dry air) 6: Regeneration air "ON" 7: Filter 8: Heating elements 9: Drive motor 10: Regeneration air fan 11: Regeneration air "OFF" (Wet air)

42 Heating Equipment Boiler FurnaceResidential In-Space Heating Equipment

43 Boilers Basic Classification of Boilers: working pressure and temperature Medium & High- Pressure Boiler Low-Pressure Boiler Pressure : 100~200 kPa (Water) 1,100 kPa (Steam) Temperature : 120°C Steam Boilers / Water Boilers

44 Boilers Fuel Used: coal, fuel oil, gas / electricity- Other Classifications: Fuel Used: coal, fuel oil, gas / electricity Construction Material: cast-iron, steel, copper, stainless steel, etc… Condensing/Non-condensing Boilers: Condensing fuel gas in the boiler Etc Boiler classifications are important to the engineers because they affect performance, first cost and space requirements.

45 Boilers Condensing BoilersHot exhaust gases condense and lose much of their energy to pre-heat the water in the boiler system

46 Boilers Wall-Hung Boilers Small residential gas fired boiler

47 Boilers Electric Boiler Packaged Fire-Tube boiler - No combustion- Electrode is immersed in the boiler water Packaged Fire-Tube boiler

48 Boilers Boilers - Terminology in Korean flue tube-smoke tube boiler수관 보일러 flue tube-smoke tube boiler forced circulation boiler water tube boiler once-through boiler tubular boiler, smoke tube boiler packaged boiler convection boiler double ended boiler supercharged boiler monotube boiler 패키지 보일러

49 In-Space Heating EquipmentNot for the central heating system Room Heater

50 Furnace Wall Furnace Heating Furnace- Part of the structure of building - Supplying heated air by natural/forced convection Heating Furnace - Air is heated directly by the hot gas of combustion

51 Other Energy Saving Equipments- Thermal storage - Energy recovery - Solar energy - Geothermal energy

52 HVAC Systems

53 Air-Conditioning SystemsSchematic of a typical commercial air -conditioning system

54 HVAC System - SelectionOn selecting a system, the followings are to be considered; System constraints Cooling load, Zoning requirements, Heating and ventilation Architectural Constraints Size and appearance of terminal devices, acceptable noise level, Space available to house equipment and its location relative to the conditioned space, acceptability of components into the conditioned space Financial Constraints Capital cost, Operating cost, Maintenance cost

55 HVAC System Central System Decentralized SystemPrimary equipments are located in a central plant Energy efficient Lower maintenance & operating cost Decentralized System Primary equipments are located throughout the building First cost is very low

56 All Air Systems An all-air system provides the conditioned space with;Sensible heating and humidification Sensible and latent cooling All-air systems can be classified into 2 categories; - Single duct system Dual duct system or Constant air volume system Variable air volume (VAV) system

57 All Air Systems AdvantagesMaintenance is performed in unoccupied areas (centrally located). No drain piping or power wiring or compressors in occupied areas. Systems can include options such as; Air-side economizer, heat recovery, winter humidification Simple seasonal changeover Simultaneous cooling and heating in various zones. Disadvantages Additional duct space is required. Air-balancing may be difficult in large systems. Close coordination is needed between designers and installers to assure good accessibility to terminal units.

58 All-Air System (Single duct)

59 All Air Systems VAV SystemKeep the air temperature constant and vary the air supply volume. Easy to control, energy efficient and fairly good room control. Poor ventilation under low load conditions Difficult humidity control under widely varying latent loads

60 All Air Systems VAV System

61 All Air Systems Dual duct SystemThe dual-duct system employs two air ducts to supply cold air and warm air to a mixing terminal unit which proportions the cold and warm air in response to a thermostat located in the conditioned space Systems with terminal volume regulation are self-balancing. Zoning of central equipment is not required. Instant temperature response No seasonal changeover is needed Higher initial cost Does not operate as economically as other systems.

62 All Air Systems Dual duct System

63 All Air Systems Reheat SystemReheat system heats the supply air whenever the cooling load is below the maximum. This is applied where spaces have wide load variations, high latent loads, or where close control of both temperature and humidity is required. High operating cost Energy inefficient

64 All Air Systems Reheat System

65 All Air Systems Multizone System (central)The multi-zone system applies to a relatively small number of zones served by a single, central air-handling unit. Different zone requirements are met by mixing cold and warm air through zone dampers at the central air handler in response to zone thermostats

66 All Air Systems Multizone System (central)

67 Air and Water Central SystemsThese systems distribute both air and hot/cold water to terminal units in the conditioned spaces. The air and water is cooled and heated in a central mechanical room. Advantages The use of water greatly reduces the size of the air ducts. The air-handling system is also much smaller. Provides positive ventilation All zones can be individually controlled. Zone cooling and heating needs are satisfied independently. Disadvantages High operating cost Design for the intermediate season operation is critical Changeover is complicated and requires trained operators Controls are more complicated than for all-air systems Terminal units require frequent in-space maintenance Humidity cannot be tightly controlled.

68 Air and Water Central Systems

69 Air and Water Central SystemsThe room terminals Induction unit Room fan-coil units : usually used Radiant panels

70 All Water Central SystemsThe space cooling is performed by chilled water circulated from a central plant to air handling or terminal units. Heating water is supplied through the same or a separate piping system. Advantages Water is a more energy and space efficient method. Recirculation of air is unnecessary. First cost is often less than for other central systems Individual zone temperature control Disadvantages Some maintenance must be performed in occupied areas. No humidification is provided. Seasonal change over is required No positive ventilation is provided unless wall openings are used

71 All Water Central Systems

72 All Water Central SystemsA fan-coil unit consists of a finned tube coil, a filter and a fan section. The fan recirculates air continuously

73 Direct Expansion SystemsDirect expansion of refrigerant - without the chilled water cooling medium These units are designed for comfort cooling and delivery of conditioned air to a room either without ducts or with very short ducts

74 HVAC Applications

75 Comfort Applications Residences Retail FacilitiesCommercial and public Buildings Places of Assembly Domiciliary Facility Educational Facilities Health Care Facilities Surface Transportation Aircraft Ships

76 Industrial ApplicationsIndustrial Air Conditioning Enclosed Vehicular Facilities Laboratory Systems Engine Test Facilities Clean Spaces Data Processing System Areas Printing Plants Textile Processing Photographic Materials Environmental Control for Animals and Plants Drying and Storing Farm Crops Air Conditioning of Wood and Paper Products Facilities Nuclear Facilities Ventilation of the Industrial Environment Mine Air Conditioning and Ventilation Industrial Exhaust Systems

77 Residences Single-Family Residences Multifamily Residences HeatingHeat Pumps Furnaces Hydronic Heating Systems (Boilers) Air Conditioners Unitary Air Conditioners Evaporative Coolers Humidifiers Air Filters Central Forced-air Systems Hydronic Central Systems Through-the-wall units Water-Loop Heat Pump Systems

78 Residential Heating & Cooling SystemsForced Air Hydronic Zonal Most Common Energy Sources Gas Oil Electricity Resistance Heat Pump Heat Distribution Medium Air Water Steam Refrigerant Heat Distribution System Ducting Piping Piping or None Terminal Devices Diffusers Registers Grilles Radiators Radiant panels Fan-coil units Included with product

79 Retail Facilities Even small stores often have large frontal glass areas which could result in high peak solar effects. High heat loss can also occur on cold, cloudy days. Single-package rooftop units are most commonly used on 1 and 2 story buildings for heating and cooling service.

80 Retail Facilities Duct SystemDuct velocities should be kept low (800 to 1,200 fpm) to minimize any noise. Lights, displays and other ceiling-suspended obstacles require attention as they can interfere with air distribution An ample outside air intake duct should also be provided and dampers installed for proper air balance and ventilation

81 Office Buildings Weather, occupancy, lighting, and floor loads (computers, printers, copiers, and other office machinery) are the big energy users. Building shape, design, and orientation can also have a major effect on energy use.

82 Office Buildings Systems Rooftop cooling unit Heat pumpsSeparate VAV unit Central condenser water loop, etc…

83 Office Buildings DuctsThe outdoor air quantities are needed for suitable indoor air quality. However, a constant minimum volume of ventilation air is needed for VAV units depending upon occupant requirements.

84 Domiciliary Facility SystemsConstantly operational, but not necessarily occupied at all times.  Individual room control of the HVAC system. Relatively high domestic hot water use over short periods of time, several times a day. Load characteristics are well defined at design stages, without need for future expansion.

85 Libraries and Museums SystemsHVAC systems run year-round (cooling systems can easily run up to 5,000 hours a year or more)  Heavy-duty long-life equipment required All equipment should be vibration and sound isolated.  Mechanical rooms should be located as remotely as possible to minimize the cost of acoustic and vibration isolation