HVAC Systems.ppt
- 1. HVAC SYSTEMS Presented by: BERNARDO M. TERROBIAS PME,PEE,RMP,EnP
- 2. 1.0 Brief Story about the Beginning of Air- conditioning by Willis de Havilland Carrier 2
- 3. 2.0 Some Important Definitions 2.1 Air-Conditioning – the control of temperature, humidity, cleanliness and motion of air in an enclosed space •For the comfort of the occupants of the space •For the treatment of diseases 3
- 4. •For the very exacting control of temperature and relative humidity, other than for comfort, in many manufacturing processes such as in pharmaceuticals, electronics and semiconductors, and many others •For preserving important documents, valuable paintings, and other valuable treasures against the ravages of environmental pollution and vagaries of the weather •For many, many other purposes 4
- 5. Air-Conditioning is made possible by refrigerating the AIR. 5
- 6. 2.2 Refrigeration - the process of absorbing heat where heat is unwanted, and discharging that heat where it is unobjectionable. 6
- 7. Aside from the mechanical components that produce refrigeration, another very important component is necessary, and this is the refrigerant. 7
- 8. Figure 1 8
- 9. Figure 1a 9
- 10. 2.3 Refrigerant – a chemical substance that has the characteristics of absorbing heat at a low pressure and temperature, and discharging that heat at a high pressure and temperature. 10
- 11. Figure 2 11
- 12. 2.4 Psychrometrics – a branch of physics that is defined as the science of moist air properties and processes which is used to illustrate and analyze air- conditioning cycles 12
- 13. The composition of dry air by volume is: 79.08% Nitrogen (N) 20.95% Oxygen (O) 0.93% Argon (Ar) 0.03% Carbon Dioxide (CO2) 0.01% Other Gases Dry air has the capacity of absorbing water vapor in amounts depending on the temperature of the air. Since the air around us is not really dry but is moist or it contains some water vapor, technically speaking, the air we breathe contains superheated steam. 13
- 14. Figure 3 14
- 15. 3.0 Sources of Air-Conditioning Loads or Heat Loads 3.1 Sensible Heat •Direct sunlight or solar heat •Transmitted heat due to temperature difference of the air between outside and inside across walls, glass windows, roofs and ceiling, and partitions •People, the sensible component of the heat they produce 15
- 16. •Lighting •Appliances such as computers, printers, motors, etc. •Outside air for ventilation, its sensible heat component due to its elevated temperature above room air •Air infiltration from the outside, its sensible component 16
- 17. 3.2 Latent Heat • People, the latent heat component of the heat they produce • Exposed water in the space • Steam • Air infiltration from the outside, its latent component 17
- 18. 3.3 Average Air Conditioning Loads of Various Spaces APPLICATION SQUARE METER PER TON 1. Residences: Living / Dining 20 – 22 Bedrooms 22 – 25 2. Offices: General Offices 20 – 22 Conference Room 12 – 14 3. Banking Areas 16 – 18 4. Theaters, Auditoriums 0.10 – 0.12 (ton/seat) 18
- 19. 5. Eateries: Fast Foods 8 – 10 Ordinary restaurant, Coffee shop, Canteen 10 – 12 Fine Dining 12 – 14 6. Classrooms, Training rooms 16 – 17 7. Shopping Centers; Dept. Stores Main Floors 16 – 18 Upper Floors 20 – 22 Grocery Store 20 – 22 19
- 20. 8. Hotels Main Lobby 17 – 19 Function Rooms 8 – 10 Banquet Hall / Ballroom 6 – 8 Guest Rooms 18 – 20 Rental Shops 16 – 18 9. Hospitals: Patients Room 20 – 22 Operating rooms / Delivery Rooms 6 – 8 ICU / Recovery Room 12 – 14 Laboratories 10 – 12 Emergency Room 10 – 12 Nurse Station 13 – 15 Doctor’s Clinic 13 – 15 20
- 21. 10. Manufacturing: Semi – conductors 8 – 10 Pharmaceuticals 8 – 10 Assembly areas & Light Manufacturing 8 – 12 11. Call Centers: Main Production Areas 15 – 16 Server room / LAN room 4 – 10 UPS room 8 – 10 Training room 16 – 17 21
- 22. 4.0 Types of Systems Two types of systems are in use: the direct expansion or the DX type and the chilled water type. 22
- 23. 4.1 DX System In the DX system, the refrigerant in the evaporator tubes cools directly the air flowing across the tubes. They are mostly used in small installations where the compressor, together with its condenser, is connected directly to an air handling unit or fan coil unit working together on a one-on-one basis. This has been the traditional DX system configuration. The room air-conditioner and the popularly known split type unit are DX type units. 23
- 24. Figure 4 24
- 25. More recently, however, due to advancements in the art and manufacturing technology, the so-called Variable Refrigerant Volume (VRV) or Variable Refrigerant Flow (VRF) units were introduced into the market and there are now several installations of this type worldwide including here locally. In this variation of the DX System, one compressor and condenser combination (or condensing unit) can be connected to several fan coil units. 25
- 26. Figure 4a 26
- 27. 4.2 Chilled Water System In the chilled water system, the refrigerant cools the water first and in turn, the water is circulated through several air handling units to cool the air. It is sometimes called “indirect system”. This type of system is found in large installations such as buildings, shopping centers, manufacturing plants, hospitals, schools, etc. 27
- 28. Figure 5 28
- 29. 5.0 Equipment 5.1 Compressors They are manufactured in either open type or hermetic construction. In the open type, the compressor and the drive motor are in separate enclosures and they are mechanically linked together through a flexible coupling. In the hermetic type, the compressor and the drive motor are in one single enclosure and they are linked together through a common shaft. 29
- 30. The common types are as follows: 5.1.1 Reciprocating Type It comes in either open or hermetic construction. It is manufactured from the smallest to about 150 tons capacities. In up to 10 tons capacities, they operate up to 3500 rpm. Larger sizes are designed to operate at 1750 rpm. They are used in either DX or Chilled Water Systems. 30
- 31. Figure 6 31
- 32. 5.1.2 Rotary Type This is a small compressor used mostly in refrigerators, room type air-conditioners, and car air-conditioners. It comes either in open or hermetic type construction. 32
- 33. 5.1.3 Centrifugal Type It comes in either open or hermetic construction. It has very few moving parts and it operates at high speeds, even up to 12000 rpm. In both cases, it comes factory-assembled together with its matching condenser and water chiller. Centrifugal chillers are manufactured in single sizes up to 1500 tons capacity for the hermetic unit and up to 10000 tons for the open type. They are used only in centralized chilled water systems. 33
- 34. Figure 7a 34
- 35. Figure 7b 35
- 36. Figure 7c 36
- 37. 5.1.4 Rotary Screw Compression This type of compressor has also positive displacement, just like the reciprocating type. On the other hand, just like the centrifugal type, it also has few moving parts. However, it operates only at 3500 rpm. It is manufactured in single sizes at up to 500 tons capacity. It can be used for either DX or Chilled Water Systems. It also comes in open or hermetic enclosures. It is the latter that is used more in air-conditioning applications. On the other hand, the open type is mostly used in low temperature refrigeration. 37
- 38. Figure 8 38
- 39. 5.1.5 Scroll Compressor This compressor is the latest development in compressor technology. It is also of the positive displacement type and has been found to be reliable. It comes only in hermetic construction. It can be used in DX or Chilled Water Applications. 39
- 40. Figure 9 40
- 41. 5.2 Condensers These usually come in two kinds, water-cooled and air- cooled. 5.2.1 Water-Cooled Condensers A water-cooled condenser consists of a bundle of tubes (usually copper) enclosed in a cylindrical steel shell with cast steel condenser heads at each end. Water flows inside the tubes and the hot refrigerant gas to be condensed is outside the tubes. Cooling water is recirculated through a cooling tower where the air- conditioning heat and heat of compression is finally rejected to the atmosphere. 41
- 42. Figure 10 42
- 43. 5.2.2 Air-Cooled Condensers An air-cooled condenser is constructed of copper tubes with aluminum fins to enhance heat transfer and increase the condensing surface. The tubes are arranged in rows and are assembled into a galvanized or corrosion- protected steel casing. Within the casing is a fan or a number of fans, depending upon the condenser size. The condenser assembly may be arranged for horizontal installation with the fans discharging air upward or for vertical installation with the fans discharging air horizontally. 43
- 44. Figure 11 44
- 45. 5.2.3 Cooling Towers Cooling towers are mechanical draft, where atmospheric air is forced through the tower fill surface with fans, usually of the propeller type. The fill or heat transfer surface, thru which the water drips down, is made of wood slats or plastic material. Cooling towers are either of the counter flow type or cross-flow type. 45
- 46. In the counter flow type, the cooling air enters at the bottom of the fill and flows upward thru it in strict counter flow against the water that drips down. In the cross-flow type, the cooling air enters at the sides horizontally and flows at right angle with the dripping down water. In most cases, the towers are induced draft, meaning, the fans are installed at the top of the tower structure sucking the cooling air thru the fill. 46
- 47. In the forced draft tower, the fans are installed at the lower side of the tower to force the cooling air thru the fill. Forced draft fans can only be adapted in counter flow towers. The configuration of the cooling towers may either be rectangular or circular. Fans are either driven thru gear reducers or belts and pulley combination. 47
- 48. Figure 12 48
- 49. 5.2.4 Fluid Coolers or Chillers They are constructed almost similarly as water cooled condensers, shell and tube. There are two types of fluid coolers: the dry expansion type and the flooded type. 49
- 50. a. Dry Expansion Type The evaporating refrigerant in the dry expansion type is inside the tubes and the liquid to be cooled is outside the tubes. A thermostatic expansion valve with several small distributor tubes distributes the expanding refrigerant to the tube bundle of the cooler. This type of cooler is common to small chiller packages. 50
- 51. Figure 13 51
- 52. b. Flooded Type The tubes in the shell in the flooded type are submerged in a liquid refrigerant and cooling is affected with the evaporation of the refrigerant that is subjected to the suction of the compressor. The liquid refrigerant level inside the shell is controlled by a float valve. The fluid or water to be cooled flows inside the tubes. This type of cooler is standard in large chiller packages. 52
- 53. Figure 7a 53
- 54. 5.3 Equipment Selection In air conditioning and refrigeration systems there are two modes of condensing; air cooled and water cooled. Both modes have their own advantages and disadvantages. A. Reciprocating and Scroll Compressors 1. Air cooled condensing is usually employed in small installations like window type units and packaged units of sizes up to 30 tons capacity in single model. For air conditioning levels, the specific compressor input is 1.60 kw/ton. These type of unit lend itself to totally independent energy metering and its is popular with condominium developers and owners. For high rise buildings, however, with very limited machine spaces, the air cooled condensers pose some serious problems on unit locations to prevent condenser air short circuiting. 54
- 55. 2. Water cooled condensing has the principal advantage of better efficiency resulting lower average specific energy input of the compressor at about, 0.90 kw/ton. These units are used mostly in central type installations. Both air cooled and water cooled units can be employed in either direct expansion and chilled water systems. 55
- 56. B. Centrifugal Units These are the most efficient units with an average power input of 0.55 kw/ton at air conditioning levels. They come in single sizes from 150 to 10,000 tons capacity. They can only be used in chilled water systems. The centrifugal compressor has excellent capacity unloading characteristics. 56
- 57. C. Screw Type Units This is a relatively new type of compressor. It is a cross between the reciprocating and centrifugal compressor. It has positive displacement like the reciprocating and has good capacity modulation like the centrifugal machine. It can be air cooled or water cooled and it can be used for either direct expansion or chilled water systems. It comes in sizes from 40 tons to 750 tons capacity. Its power input is about 0.75kw/ton at air conditioning levels. 57
- 58. D. Absorption Type This is a type of equipment that uses steam or high temperature water as motive power and it is, therefore, used mostly where these media are available. It is applicable for chilled water systems only. It comes in single sizes from 90 to 1500 tons capacity. Per ton of nominal cooling capacity its steam consumption is about 10 pounds per hour at 115 psi pressure for double stage models and about 18 pounds per hour at 20 psi pressure for single stage models. 58
- 59. 6.0 Air Distribution Air distribution in the air-conditioned space is accomplished through constant volume air supply or through variable air volume (VAV) boxes. 59
- 60. 6.1 Constant Air Volume Method In the constant air volume method, which is still much employed today, the rate of air flow into the space is kept the same no matter what the cooling demand is in a particular room or zone. The result is that sometimes rooms are too warm or too cold depending on the occupancy or where the sun exposure is at any particular time. 60
- 61. 6.2 Variable Air Volume Distribution System To improve on the above system, the variable air volume (VAV) distribution system was introduced, and this is now in use in high-end office buildings. In this method, an automated volume damper is provided upstream of a supply outlet to a room or supply duct branch to a zone. The damper actuator is controlled by a room temperature sensor. The damper is modulated to open or to throttle down to supply more air or less air into a room or zone to keep the temperature almost constant no matter what the occupancy or sun exposure the room or zone has. 61
- 62. Figure 14a 62
- 63. Figure 14b 63
- 64. 6.3 Air Duct Design There are two (2) generally used methods in air duct design: 6.3.1 Equal – friction: The principle of this method is to make pressure loss per unit of duct length the same for the entire system. 64
- 65. 6.3.2 Static – regain method: This is a design procedure in which the reduction in air velocity after each branch take-off that results in a gain in static pressure is made used of. This regain in static pressure is taken advantage of to offset the pressure loss in the succeeding duct section. This method is employed mostly in large systems where high duct velocities are adopted. It results in lower fan horsepower. 65
- 66. 6.3.3 Because it is simpler and easier to apply, the equal friction method is more widely used. Enclosed herewith is an equal-friction chart used for sizing air ducts. Also enclosed is a table for recommended and maximum velocities for air ducts and other components of conventional systems. 66
- 68. Recommended and Maximum Duct Velocities For Conventional System Designation Recommended Velocities, Fpm Residences Schools, Theaters, Public Buildings Industrial Buildings Outdoor Air Intakes Filters Cooling Coils 500 250 450 500 300 500 500 350 600 Air Washers Fan Outlets 500 100 - 1600 500 1300 - 2000 500 1600 - 2400 Main Ducts Branch Ducts Branch Risers 700 – 900 600 500 1000 – 1300 600 – 900 600 - 700 1200 – 1800 800 – 1000 800 68
- 69. Designation Maximum Velocities, Fpm Residences Schools, Theaters, Public Buildings Industrial Buildings Outdoor Air Intakes Filters Cooling Coils 800 300 450 900 350 500 1200 350 600 Air Washers Fan Outlets 500 1700 500 1500 - 2200 500 1700 – 2800 Main Ducts Branch Ducts Branch Risers 800 – 1200 700 – 1000 650 - 800 1100 – 1600 800 – 1300 800 - 1200 1300 – 2200 1000 – 1800 1000 - 1600 69
- 70. 7.0 Chilled Water Distribution Sometime in the near past it has been discovered that economy in chilled water pumping energy can be realized by varying the speed or RPM of the pump with the use of a variable frequency drive motor controller based on cooling demand. This method neatly makes use of one of the affinity laws for pumps, namely: BHP1 = GPM1 3 BHP2 GPM2 70
- 71. Very seldom is a chilled water plant 100% loaded. Most of the time, the load is only about 70% (or even less) of design capacity and therefore, only 70% of the design chilled water flow rate need to be supplied to the system. Following the above equation, if the flow is reduced down to 70%, the pump power will be reduced down to the cube of 70% or down to 34.3% of the original power, which is very significant. 71
- 72. Figure 15 72
- 73. 8.0 Indoor Air Quality 8.1 Definition by ASHRAE ASHRAE defines acceptable Indoor Air Quality as “air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a majority (80% or more) of the people exposed do not express dissatisfaction.” The absence of it may result into the so-called sick building syndrome or SBS. 73
- 74. 8.2 Sources of Contaminants •Those generated within the space •Those that come with the fresh air supply such as dusts, vehicular exhaust fumes, pollens, etc. •Miscellaneous organisms that breed within the space due to high humidity – molds, mildew, and fungi. They are the most harmful contaminants. They can even be pathogenic or can cause disease. 74
- 75. 8.3 Amount of Outside Air (OA) to be introduced to the space •Before, it was only 10 CFM per person •Now, this was increased to 20 CFM per person •Recommended rates are meant to limit CO2 concentration in the space to 700 ppm above the outside air CO2 level. Generally, outdoor air CO2 level ranges from 300 to 500 ppm, which means that the CO2 level in the space must be between 1000 to 1200 ppm. 75
- 76. •But the outside air is very expensive to refrigerate down to the room dew point temperature. For comfort conditioning at 75oF and 50% RH, it takes about 100 Btu per hour to refrigerate 1 CFM of OA. Example, in a space of 75 square meters, with 10 people needing 200 CFM of OA, 20,000 Btu per hour or 1.67 tons of refrigeration is needed. •If investment would permit, an energy-saving device such as an air-to-air Heat Exchanger may be used. With an effectiveness of 60%, this load could be reduced down to 12,000 Btu per hour. 76
- 77. 9.0 Refrigerants, Ozone depletion, Global Warming 9.1 In 1974, scientists theorized that CFC’s (chlorofluorocarbons) posed a threat to the ozone layer. This was verified by measurements. 9.2 In 1986, it was concluded that CFC’s and global warming and climate change are connected. 77
- 78. 9.3 In 1987, the Montreal protocol was convened by the industrialized countries, and the participants decided to restrict the use of CFC’s, such as CFC – 11, 12, 113, 114 and 115. 9.4 In the year 2000, the production of CFC’s was halted. Two (2) new refrigerants were invented and these are: 78
- 79. 9.4.1 HFC – 134a (tetrafluroethane). This is a replacement for CFC – 12 9.4.2 HCFC – 123 (dichlorotrifluroethane). This is a replacement for CFC – 11, 113, and 114. These refrigerants are used in centrifugal chillers. 9.4.3 An existing refrigerant, R – 22, or HCFC – 22 (chlorodifluromethane) is still widely used today. 79
- 80. However, because of their ozone depleting potential, both HCFC – 22 and 123 will no longer be used on new equipment manufactured after January 1, 2010 in industrial countries. It is safe to assume that Third World Countries would be forced to follow suit not very long after that date. 80
- 81. 10.0 Thermal Energy Storage System (TESS) 10.1 Reasons for adapting TESS 10.1.1 Where there is an incentive like lower electric energy cost to shift high electrical demand form on-peak hours to off-peak hours to reduce strain on the electric power plants. 81
- 82. 10.1.2 There is a need to handle short duration but high- cooling load requirements, such as churches, auditoriums, etc. 10.1.3 Need to provide cooling for small after-office hours loads such as restaurants, individual offices and computer rooms. 82
- 83. 10.2 Generally, there are two (2) types of TESS: 10.2.1 Liquid storage, primarily chilled water in stratified type storage tanks. 10.2.2 Phase change, primarily ice. Ice is frozen during off-peak hours and then melted for use during the air-conditioning hours. 83
- 84. 10.3 Because of smaller chiller plant size as compared to the conventional system, TESS has the following advantages: 10.3.1 On the part of the user: • The lower electric power demand would result in his paying less transmission charge and distribution charge. • Lower investment cost on electrical power feeders, transformer and switch gear. • Smaller emergency Genset if 100% standby power is desired. 84
- 85. 10.3.2 On the part of the electric power providers, there will be less strain on their power plants. Their load factor would be high and they would have better operating efficiency. Because of this, they could even postpone adding new plant capacities. 10.3.3 On the part of the country as a whole, the improved operating efficiency will result in reduced oil importation. 85
- 86. 10.4 On the other hand, the disadvantages that have to be shouldered by the user are the following: - Higher investment cost - May need additional operating personnel due to longer operating hours of the TESS. 86
- 87. Figure 16 87
- 88. 11.0 Cogeneration 11.1 Cogeneration is defined as the sequential production of electricity and useful thermal energy from a single fuel source. 11.2 The thermal energy that is otherwise dissipated into the atmosphere through the engine exhaust and jacket cooling water is trapped to generate steam and/or high temperature water. 88
- 89. Figure 17 89
- 90. In air-conditioning applications, the generated steam or hot water is used to power an absorption-type water chiller. Figure 18 90
- 92. 11.3 Normally, on straight electricity production, a diesel-generating set has a thermal efficiency of about 33%. In cogeneration for air-conditioning purposes, the efficiency is increased to about 42%. 11.4 On the other hand, based on straight electric energy production, a gas turbine driven generating set has a thermal efficiency of only about 20%. With cogeneration for air- conditioning, the efficiency is increased to about 34%. 92
- 93. 12.0 Some Energy-Saving Devices in Air-Conditioning Systems 12.1 The air-to-air heat exchanger is constructed of thin aluminum sheets coated with solid desicant material corrugated to form a multitude of narrow flutes through which streams of exhaust air and outside air pass from opposite direction. In the process, the cool exhaust air from the air- conditioned spaces pre-cool the warm and humid outside air. 93
- 94. Figure 19 94
- 95. This device, depending upon the ratio of outside air intake to that of the exhaust air could save about 50% of the energy required to cool the required outside air required to the room dew point condition. This saving is very significant. For high density occupancies such as in casinos, theaters, auditoriums, restaurants or even offices where outside air intake and exhaust can be centralized, it is advisable that this device be adapted. 95
- 96. 12.2 Heat reclaim from a refrigerant hot gas desuperheater. The discharge gas from a compressor is very hot. The available heat energy from it, which would otherwise be dissipated into the atmosphere, can be trapped through a desuperheater to produce hot water of around 130oF In many instances, the available heat can fill the entire hot water requirements of hotels, motels, and hospitals. In most instances, it is also sufficient to supply the reheat requirements of the air-conditioning systems of some manufacturing processes. 96
- 97. Figure 20 97
- 99. Figure 21 99
- 100. Figure 22 100
- 101. - end - 101