DECLARATION
I hereby declare that the training work entitled Calculation study of HVAC systems is an authentic record of my own work carried out at Areva T & D, Noida as requirement of summer training for the sixth semester , under the guidance of, during June to July, J uly, 2011.
Date: ___________________ ___________________
Certified that the above statement made by the student is correct to the best of our knowledge and belief.
1
ACKNOWLEDGEMENT I wish to thank all those who helped me in the completion of my project, especially the employees in Areva T&D. -
Without whose help, support and understanding it wouldn’t have been possible for me to bring this project to the level and shape it currently stands in. I am especially indebted to my mentor and guide, for his invaluable guidance in the smallest of tasks to his keenness in explaining the more complex and tedious problems. I would like to give a special acknowledgement to Mr. Rajesh Batra for providing a good work environment, active supervision and for setting a firm direction and timeline. This helped us immensely in accomplishing our tasks in a timely manner and producing key deliverables.
2
ACKNOWLEDGEMENT I wish to thank all those who helped me in the completion of my project, especially the employees in Areva T&D. -
Without whose help, support and understanding it wouldn’t have been possible for me to bring this project to the level and shape it currently stands in. I am especially indebted to my mentor and guide, for his invaluable guidance in the smallest of tasks to his keenness in explaining the more complex and tedious problems. I would like to give a special acknowledgement to Mr. Rajesh Batra for providing a good work environment, active supervision and for setting a firm direction and timeline. This helped us immensely in accomplishing our tasks in a timely manner and producing key deliverables.
2
ABOUT THE COMPANY AREVA is a French public multinational industrial conglomerate that deals in energy, especially nuclear power. It was created on 3 September, 2001, by the merger of Framatome and Cogema (now AREVA NC). Its main shareholder is the French owned company CEA, but the German company Siemens also retains 34% of the shares of AREVA's subsidiary, AREVA NP, in charge of building the European Pressurized Reactor.
Energy Company AREVA is the world-leading company in nuclear energy. It is the only company with a presence in each industrial activity linked to nuclear energy: mining, chemistry, enrichment, combustibles, services, engineering, nuclear propulsion and reactors, treatment, recycling, stabilization, and dismantling. AREVA also claims to offer technological solutions for CO 2 free energy; and produces earth leakage ci rcuit breaker technologies. Three main subsidiaries form the core of AREVA:
•
AREVA NP (formerly Framatome ANP) - Nuclear Power: develops and builds nuclear reactors; Siemens has a 34% stake in AREVA NP
•
AREVA NC (formerly Cogema) - Nuclear Cycle: covers the whole nuclear fuel cycle, from mining to waste disposal. Owns Eurodif.
•
AREVA
T&D:
Transmission
and
Distribution:
power
transmission
and
distribution. It was bought from ALSTOM on 9 January, 2004. The major partners of AREVA include: Technicatome, Euriware, ST Microelectronics, Eramet, and SAFRAN. AREVA is part of the Global Nuclear Energy Partnership (GNEP) alliance, along with the Japan Atomic Energy Agency (JAEA), Washington Group International and BWX. GNEP is 3
a plan initiated in 2006 to form an international partnership to reprocess spent nuclear fuel in a way that renders the plutonium in it usable for nuclear fuel but not for nuclear weapons.
Administration The actions of the Chairman of the Executive Board, Anne Lauvergeon, are subject to considerable oversight by both the board of directors and the supervisory board. In 2006, Spencer Abraham, the former U.S. Secretary of Energy, was named non-executive chairman of AREVA Inc. , the U.S. subsidiary of AREVA. Jean-Pierre Raffarin's government announced the privatization of AREVA in 2003, but it was postponed several times, the French government opting finally for the privatization of GDF and EDF. At the end of October 2005, Prime Minister Dominique de Villepin announced that he had suspended the privatization process. Worldwide Presence Worldwide, the AREVA group has an industrial presence in 40 countries and its commercial network reaches more than 100 countries. It employs 58,000 people and has consolidated
sales revenue of €10.863 billion. In 2006, Fortune Magazine reported that AREVA was the “Most Admired Global Energy Company”. History AREVA has its roots iin n Framatome, which was founded in 1958 by several companies of the French industrial giant The Schneider Group along with Em-pain, Merlin Gérin, and the American Westinghouse, in order to license Westinghouse's PWR technology and develop a bid for Chooz 1 in Belgium. Called Franco - Américaine de Constructions Atomiques (Framatome), the original company consisted of four engineers, one each from eac h of the parent companies. The original mission of the company was to act as a nuclear engineering firm and to develop a nuclear power plant that was to be identical to Westinghouse's existing product specifications. The first European plant of Westinghouse design was by then already under construction in Italy
AREVA T&D One of the top three global players in the transmission and distribution of energy. It is a division of AREVA, world leader in the energy business. AREVA T&D offers solutions to bring electricity from the source onto the power network.
4
They build high and medium voltage substations and develop technologies to manage power grids worldwide. They are a full-fledged solution provider, offering safe, reliable and efficient power distribution.
Country Office:A-7, Sector – 65,Noida – 201301, Uttar Pradesh,Tel: +91 120 4790000Fax: +91 120 4791140
5
CONTENTS
Topics INTRODUCTION BRIEF HISTORY BENEFITS OF A HVAC SYSTEM DESIGN OF HVAC SYSTEM SELECTION PARAMETERS DESIGN OBJECTIVES HVAC COMPONENTS DETAILED COMPRESSOR STUDY COMPONENT SIZING PROCESS IN HVAC INDUSTRY AND STANDARDS REFERENCES
Page No.
6
INTRODUCTION HVAC (Heating, Ventilation, and Air Conditioning) refers to technology of indoor or automotive environmental comfort .HVAC system provisions shall be suitable to meet the requirements of 24 hour year round operational requirements of the building. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. HVAC is important in the design of medium to large industrial and office buildings such as skyscrapers and in marine environments such as aquariums, where safe and healthy building conditions are regulated with temperature and humidity, as well as "fresh air" from outdoors.
7
BRIEF HISTORY
Ventilation (architecture) on thedowndraught system, by impulsion, or the 'plenum' principle, applied to schoolrooms (1899)
Heating, ventilating, and air conditioning is based on inventions and discoveries made by Nikolay Lvov, Michael Faraday, Willis Carrier,Reuben Trane, James Joule, William Rankine, Sadi Carnot, and many others. The invention of the components of HVA C systems went hand-in-hand with the industrial revolution, and new methods of modernization, higher efficiency, and system control are constantly introduced by companies and inventors all over the world. The three central functions of heating, ventilating, and air-conditioning are interrelated, providing thermal comfort, acceptable indoor air quality, within reasonable installation, operation, and maintenance costs. HVAC systems can provide ventilation, reduce air infiltration, and maintain pressure relationships between spaces. How [1]
air is delivered to, and removed from spaces is known as room air distribution.
In modern buildings the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally "size" and select HVAC systems and equipment. For larger buildings, building services designers andengineers, such as mechanical, architectural, or building services engineers analyze, design, and specify the HVAC systems, and specialty mechanical contractors build and commission them. Building permits and code-compliance inspections of the installations are normally required for all sizes of buildings. The HVAC industry is a worldwide enterprise, with career opportunities including operation and maintenance, system design and construction, equipment manufacturing and sales, and i n education 8
and research. The HVAC industry had been historically regulated by the manufacturers of HVAC equipment, but Regulating and Standards organizations such as HARDI, ASHRAE, SMACNA, ACCA, Uniform Mechanical Code,International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement.
9
Benefits of an HVAC System
HVAC, or heating, ventilation and cooling, is a system that cleans your air and provides cool air o r warm air depending on your climate needs. HVAC systems are installed by certified technicians and are valued for their energy saving principles. More and more homes are incorporating an HVAC system into their home to control polluted air.
1.1 Indoor Air Quality The EPA states that indoor air quality is two to five times worse than outdoor air, mostly since the air flow is congested. This polluted air within your home can cause colds to linger longer and allergies to be more severe. An HVAC system can improve air quality by constantly exchanging the indoor air with fresh, outdoor air that is also filtered for the best quality possible.
1.2 Energy Conservation The initial investment for an HVAC system may be higher than the typical gas furnace, yet the longterm, energy saving benefits are noticeable each month. The HVAC system has both heating and cooling in one unit. This alone saves construction space, installation time and fees, and required power usage. The system is also run by renewable energy, sometimes in the form of solar panels. Energy conservation is even better since the coolant is nonchlorine-based, which happens to deplete the ozone layer.
1.3 Moisture Consistency Whether you live in a climate that changes drastically every three to four months, or you live in a climate that remains constant, your home is always subject to moisture retention. Since air inside the home does not circulate properly and is rarely exchanged with cooler, drier air outside when applicable, your home may easily grow mold or mildew inside walls and under floors. To reduce the chances of mold growth, which also causes health concerns and structural damage over time, the HVAC system consistently pulls warm, moist air out and sends dry, cool air inside in an exchange.
10
Design of the HVAC system The starting point in carrying out a heat estimate both for cooling and heating will depend on the ambient and inside conditions specified. However before taking up the heat load calculation, it is necessary to work out the fresh air requirement for each area in details, as pressurization is an important requirement.
11
Selection Parameters The following factors have been highlighted as being of primary importance in determination of a suitable HVAC system.
Comfort & Controls
System Flexibility
System Integration
Energy Efficiency and Green Star rating
Whole of life costs including capital costs, maintenance costs, energy costs and replacement cost
The above factors represent a minimum set of criteria against which HVAC system selection shall be assessed. Based on discussions with the user groups the consultant may need to include other design criteria for specific applications. In managing conflicting requirements in terms of optimising the HVAC system selection, the consultant shall prioritise parameters that affect the fit for purpose nature of the system (comfort, reliability). These parameters shall take priority over energy efficiency.
Comfort To achieve an internal environment that the occupants perceive as comfortable involves a range of subjective variables, including the perceived degree of control by the occupant. Certain systems may provide better comfort conditions as a result of system variables such as air distribution, radiant cooling effect, controllability of supply air temperature, etc. System options will be assessed on their ability to meet the agreed temperature design criteria. Alternative design criteria such as comfort (Predicted Mean Vote) may be utilise by the Consultant based upon an agreed set of design parameters established in association with (users, sponsor, EEP). Modelling will be required to be undertaken to indicate compliance with comfort criteria. The likely percentage of time that it is estimated that the design criteria are likely to be exceeded due to extreme ambient conditions shall also be examined by the consultant.
12
System Control and Robustness Given the regular turnover of staff the system shall provide robust automatic controls which require little or no interaction between the user and HVAC system. Consideration shall be given to the appropriate level of reliability of the HVAC plant, suitable redundancies, the consequences of failure of an item of plant, and alarm notifications particularly for facilities with high Occupational Health and Safety (OH&S) and technological risks/requirements (e.g. calibration centers).
System Flexibility It is likely that from time to time the users may need or wish to change the layout of rooms or the intended use of the internal environment. They may prefer systems that facilitate this to minimise consequent disruption and cost. Some systems lend themselves to adaptation o f cellular layouts or from open plan to cellular. The HVAC System Selection Report shall clearly indicate any limitations on system suitability of the preferred system.
System Integration The system shall be in sympathy with the building design so that it is practical to install, operate and maintain and so that the aesthetics are complementary with those of the architecture. Early consideration needs to be given to co-ordination with the project architect to the proportion of the building that would be occupied by central plant and distribution systems, as this will have an impact on the size and cost of the building. Issues such as integration of the proposed system with the Building Management System, existing plant types etc must be taken into consideration as well.
Energy Efficiency and Green Star rating Consideration shall be given as to how each system may be enhanced to reduce energy consumption and improve the building Green Star rating. Energy optimisation measures shall be considered and justified as part of the Cycle Costing process. Prior to finalisation of the design energy modelling will be required to be included in the HVAC System Selection Reports to indicate the system design will meet requirements and green star rating.
13
Whole of Life Capital, running costs, maintenance costs, and plant replacement costs need to be taken into account so that the selected system demonstrates value for money to Defence and is economical to install and operate. An important consideration is how much energy is used by a system and energy optimisation measures need to be assessed during the Life Cycle Costing process. Ideally the selected system will have low requirements for maintenance and components will be easy to replace. Preliminary Whole of Life considerations shall be undertaken by the consultant at the schematic design stage as part of the consultant’s decision as to their proposed HVAC system
design.
OH & S Issues As part of OH & S legislation safety is a responsibility of the design consultant. Where possible mechanical plant shall be located in ground floor plant rooms. Where this is not possible, and plant room access cannot be provided via standard circulation routes, a dedicated stairway will be provided to access mechanical plant to minimise the use of temporary lifting devices and scaffolding. Roof mounted plant shall be avoided. Furthermore, the HVAC system shall provide safe and sound environment for the staff, contractors and visiting public.
User Interface Requirements HVAC system design, particularly control design shall not be over-reliant on user interaction to operate the system. Once HVAC plant has been initiated no user interaction shall be required to maintain stable energy efficient operation of the plant. HVAC plant operation shall require a minimum of user education.
14
DESIGN OBJECTIVES The design objective of HVAC systems shall include but not limited to the following:
Maintain specified temperature,humidity and indoor air quality within occ upied areas and for proper operation of equipments within plant and equipment room.
Maintaining building design criteria in the event of equipment failures by providing adequate standby equipments .
Maintain positive indoor pressure to minimise outside air filtration .
Minimize energy requirements for air-conditioning equipment to the extent feasible and practicable.
To facilitate evacuation paths during fire.
15
HVAC SYSTEM COMPONENTS
Chilled beam
Heater
Circulator pump
Heat exchanger, including 'coils'
Cooling tower
Heat Pump
Damper (flow)
Heat recovery ventilator
Dedicated outdoor air system
Humidifier / Dehumidifier
Diffuser
HVAC control system
Displacement Ventilation
Piping
Duct
Valve
Economizer
Variable air volume
Evaporative cooler
Variable-frequency drive
Fan coil unit
Underfloor air distribution
Fan (mechanical)
16
COMPRESSORS –HVAC MAJOR COMPONENT
Types of HVAC Compressors Many types of HVAC compressors are used for different products on the market today. The compressor is the key part to any type of cooling system. From automobiles to large buildings, if it has a cooling system, it has compressors. If you need cold air you will find a compressor whether it is a refrigerator, freezer, air conditioner, car or building. You can use several different types of compressors depending on the size and needs of the area you're cooling. Any HVAC system has many more components than just the compressor, and they all have a job to do; but without the compressor, none of the other components can o perate.
Rotary Compressor This type of compressor is used for smaller jobs. It may be small, but a rotary compressor is one of the most reliable types of compressors available. Along with reliability, another desirable feature is that a rotary compressor is quiet. Although the rotary compressor is not the most efficient compressor, its other attributes make it desirable for many small uses. This is the type of compressor you see in most window air conditioning units.
Reciprocating Compressor
Another type of compressor is the reciprocating compressor. It is the most commonly used compressor today. It is used for many applications, from residential to light commercial use. This type of compressor is versatile to say the least. Along with the applications already mentioned, you'll find it i n refrigerators, freezers and ice machines. Reciprocating compressors are also very economical to operate.
17
Scroll Compressor
The scroll compressor is becoming more common for use in HVAC equipment; it may even surpass the reciprocating compressor as the most commonly used compressor. Since first used in the 80s, it has proven itself reliable and efficient, which is the reason it is used in more equipment than ever before. The main reason for its reliability is the fact that it has less moving parts than the reciprocating compressor.
Screw and Centrifugal Compressors Other types of compressors on the market are generally used for chilled water applications in large buildings. The most common of these is the screw compressor. You may also find a centrifugal compressor handling these types of applications. Both of these are large compressors, but they are becoming smaller as technology advances, which means you can use them for smaller applications, and they may become more prevalent as time passes. These are categorised by,
the seal type (e.g. completely sealed, semi-sealed and open type), and the operation type (e.g. piston, scroll, rotary and centrifugal)
the basic characteristics that ALL compressors share. That set of basic characteristics is broken into,
the pressure rating p (in bar or pounds per square inch - psi) 3 -1 the flow rating ṁ (in m s or cubic feet per minute - cfpm), and the speed rating N (in rpm)
These characteristics will be plotted to form a compressor map for a specific compressor.
18
Performance of manufactured compressors will be tested, to obtain results of the pressure ratio, efficiency, mass flow rate, and surge/maximum pressure ratio limit, against the compressors’ rotational speed. Results will be plotted in a compressor map. A compressor map will consist of a set of speed curves, and a surge/maximum pressure ratio. The y-axis will be the pressure ratio range of the compressor, and the x-axis will be the mass flow rate of the compressed medium. A contour of compressor efficiency ranges will be plotted within the speed lines. The maximum efficiency of a compressor will be in the centre contour area. The centre contour will be,
away from the surge/maximum pressure ratio line, and away from the maximum achievable flow rate of the compressor, at a given speed
Surge/maximum pressure, maximum flow rate and efficiency: Any compressor rotating at a specific speed N1 will only be capable of,
sustaining a maximum flow rate of ṁ1, and a maximum pressure ratio of p1/ p0, where p0 is the pressure of the gas at inlet
Maximum flow rate The maximum flow rate could not be exceeded simply because the speed is already fixed.
The surge/maximum pressure ratio Now, imagine if the air conditioning compressor keeps compressing the refrigerant, but the overload protector is malfunctioning and the condensate line is blocked. Pressure in the system will rise. There will come a point, when the compressor could no longer support the rising pressure and backflow of compressed refrigerant will start to happen.
19
This is known as the surging/maximum pressure point. Backflow will occur quite violently from this point onwards, and damage to compressors will be significant, due to high vibration. This happens as the force from compression, is lower than force from the downstream high pressure gas. The only way to get pass this point is by,
lowering the downstream gas pressure, or increasing the compression force by increasing the compression speed
However, the latter choice will utilise more shaft power from driver, per compression work. In other words, the efficiency will drop. Lowering the downstream pressure would be more practical to avoid surge/maximum pressure ratio. The efficiency will increase, as an effect to that. However, lowering the downstream pressure too low will make the compressor inefficient, as the shaft power conversion into c ompressing the gas will be very low. Surge occurs only for centrifugal compressors, axial compressors and fans, as backflow may occur between the tip of the blade, and the casing. Surge can be easily detected by the “low hammering” or pulsating sound. One word. Compressor surging is bad. Ok, that’s four words.
Other tightly sealed compressors will only face the maximum pressure ratio, as the back pressure from the compressed gas, will overcome the driver’s (e.g. an electr ical motor) force.
Compressors’ efficiency Defined as the actual work done to compress gas, per energy input from the driver’s shaft. The driver is usually an electric motor. Compressors’ efficiency (and that includes air conditioner compressors as well), is proportional to the product of mass flow rate, and pressure ratio.
We have to bear in mind that, the pressure ratio is low when the mass flow rate is high. The compressor will act to transport the gas, rather than compressing it. On the other hand, the mass flow rate is low when the pressure ratio is high. This makes sense, as the back pressure from the gas will slow down the gas transfer. Yes, absolutely. The maximum compressor efficiency will be attained at moderate mass flow rates and pressure ratio.
20
The maximum compressor efficiency is normally around 80%. The compression power of air conditioner compressors are normally rated in horsepower hp, or kilowatt kW . One horsepower is equivalent to 0.7457 Kw.
21
Sealing of compressors: There are three types of air conditioner compressors construction. The completely sealed, semisealed, and the open type. Completely sealed compressors are also known as the hermetic type, and the semi-sealed are known as the semi-hermetic type.
hermetic compressors will have direct connection to the motor, and sealed in a welded casing. This type of construction allows no maintenance except in factories with proper repair tools and skill semi-hermetic compressors will have direct connection to the motor. However, the sealing is not a complete one. There will be a provision to dismantle the casing for parts replacement, and maintenance open type, has the compressor and driver separated from each other. The compressor and the driver will be separate entities, connected by a coupling. Sealing of refrigerant gas from atmosphere is achieved by means of labyrinth and mechanical seals. Yes, this compressor construction is suitable for high capacity cooling
Air conditioner compressors for residential, and for average-large sized office buildings, will normally be of hermetic, and semi-hermetic construction. Moving on, to the advantages and disadvantages of these two sealing types.
Hermetic
Semi-hermetic
Advantages
Higher efficiency, as the possibility of Possible to do maintenance and compression leakage is very small parts replacement, without having to change the complete unit
Disadvantages
Consider buying a new air Lower compression efficiency. conditioning compressor, if you note Leakage from compressor body is signs of trouble highly possible
22
Operation types of air conditioner compressors: The list is almost non-exhaustive. We have centrifugal, rotary, screw type, roots blower type, sliding vane type, plunger ty pe, ejector type, liquid-ring type, axial type, swash plate type and gear lobe type.
The piston or reciprocating compressor It’s the oldest type of compressor, going back as far as 1600’s . Very robust and simple in construction, able to deliver very high compression pressures. Just to illustrate, a reciprocating compressor with 40 mm cylinder length, is able to deliver about 12 barG (gauge) of pressure (or 150 psiG or 120 metres of water height).
This type of compressor is constructed using,
piston head – functions as the gas compressing “agent” by continuously reducing the cylinder volume piston rings – functions as the sealant between the piston head, and the cylinder, to prevent gas leakage from the compression chamber crank shaft – a shaft that enables the reciprocating motion of the piston piston rod – the connecting piece between the piston head, a nd the crankshaft spring loaded suction and discharge valves – separates low pressure side and high pressure side from the compression chamber. Enables positive displacement of ga ses, by correct opening and closing of the valves. Suction valve will open as the piston moves away from the valves, and discharge valve will o pen as the piston moves towards the valves. The valves will otherwise, be in closed position and, compressor’s cylinder block – functions as the housing for the compressor parts
23
Those are the basics. However, modifications are carried out in air conditioner compressors of this type, to have two pistons, and oriented horizontally, to improve the compression efficiency.
24
Identifying a reciprocating compressor is quite easy, even without opening its casing. The casing is almost square in shape, with similar height of its width. Most approved refrigerants are compatible with this type of compressor. Those are, R-22, R-134a, R-404A, R407C and R-507.
Robust and powerful as it may be, volumetric efficiency became a co ncern, as the valve opening do not happen as soon as the piston is on suction stroke. In addition to that, failure rate of reciprocating compressors is quite high due to mechanical stresses from the alternating motion.
25
Scroll compressor It was invented in the beginning of 1900’s. As usual, initial inventions need improvements, but all credits to Léon Creux who created it, so we can work on improvements. It was optimised and improved around late 60’s. Scroll type compressors, able to achieve the flow rate, and outlet pressure, similar to reciprocating compressors, at a smaller size, and better efficiency. However, cooling for scrolls are quite difficult compared to piston air conditioner compressors. This is the reason for its performance drop against piston type, at higher compression ratios. Nevertheless, most air conditioning applications require scroll compressors to be used against piston type, due to the advantages .
This type of compressor is constructed using,
a stationary scroll and an orbiting scroll – the orbiting spiral scroll will orbit around the stationary scroll, thus continuously and progressively trapping gas and directing towards the centre of the scrolls, to be discharged pass the discharge check valve, and towards discharge line crank shaft – used for creating the orbiting motion. This shaft is equipped with counter weights to equalise the centripetal force due to eccentric shaft rotation casing – to ensure that the discharge part is separated from the suction part, and motor winding is separated from the refrigerant
26
Sealing between high pressure and low pressure side of the scrolls are helped by the downward force to the stationary scroll, by the discharge gas pressure. This type of air conditioner compressor, could handle similar refrigerants to piston compressors. Courtesy: Sanyo
Identifying this type of compressor is not that easy though. Yes it is normally a vertical cylinder, but rotary compressors share the same shape. But if you look closely, scroll compressors have a "cap" like top cover, and the discharge line is on top of the casing. Whereas discharge line for rotary compressors is on the side, slightly lower than the top part.
27
COMPARISONS POINTS
RECIPROCATING CENTIFUGAL ROTARY HERMETIC
EFFICIENCY
MEDIUM
HIGH
HIGH
LOW
NOISE LEVEL
HIGH
LOW
HIGH
LOW
SIZE
LARGE
LARGE
MEDIUM
SMALL
MAINTENANCE
LESS
HIGH
HIGH
HIGH
CAPACITY
LARGE
LARGE
MEDIUM
LOW
Supporting parts for air conditioner compressors: Air conditioner compressors are supported by important parts such as,
bearings spiral grooved shaft for lubrication oil distribution, and strainers to prevent solid ingress into the compression chamber
What manufacturers normally practice? Designing air conditioner compressors is a tedious process, as there is the need to balance with the heat extraction requirement at the evaporator. Manufacturers will normally have a standard list of common compressor sizes and ratings, to be matched with a suitable evaporator and condenser. The compressor type and size selection, will be made based upon the refrigerant used, and the desired heat removal at the evaporator.
28
COMPONENT SIZING Contractor calculates heat loss from the building through walls and ceilings, leaky ductwork, and infiltration through windows, doors, and other penetrations as well as heat gain into the building from sunlight, people, lights and appliances, doors, walls, and windows, and infiltration though wall penetrations. Design conditions for the area are also used as inputs into load calculations. Air infiltration measurements must be estimated unless a blower door test is performed. The use of blower door test results will provide more accurate sizing calculations at a slightly higher design expense. Again, increases in design costs can be offset by decreased equipment size which lowers initial cost
Attributes Proper HVAC sizing can reduce short-cycling of equipment, resulting in longer equipment life and better control over indoor environmental conditions. The benefits of properly sizing HVAC systems include satisfied and comfortable customers, lower initial and operating costs, reduced callbacks, longer equipment run times and less cycling, and proper dehumidification during the coo ling season.
Calculate a Gas Furnace Size
Finding the appropriate size furnace is important. A furnace that is too small won't be able to heat the area effectively, and a furnace that is too large will short-cycle, causing it to turn off and on more often, which will use unnecessary energy and cost you money. There is a fairly simple way to size a gas furnace. Though it is not 100 percent accurate, it will provide a helpful guide for purchasing one.
29
Instructions Determine the amount of output BTU (British Thermal Units) you need to heat the area; output BTU is a measure of the amount of heat the furnace produces. As a general rule, start with about 30 to 35 output BTUs per square foot; however, this c an vary depending on climate and how well insulated the area is. Now you need to know how to find the output BTU of a furnace. Generally, furnaces will have a list of product specifications. The trick is that many will list input BTU instead of output BTU to make it seem like they are better than they really are. Luckily, they are also required to list efficiency. So, if a furnace doesn't list its output BTU, locate its efficiency rating and its input BTU. Multiply the furnace's input BTU by its efficiency. For example, if you were looking at a furnace specification list, and its listed efficiency is 85 percent, and its input BTU is 100,000. You would multiply 100,000 by .85 to get 85,000. This is the amount of output BTU the furnace has. Compare the furnace's output BTU to the amount of BTU you need for the area. It is fine to have a difference of 10 to 15 percent, but any more than that and you will either be getting too large a furnace or too small a furnace.
30
Find the HVAC Duct Size of Each Room
The size of an HVAC duct is based on the square footage of the place it's going in. Therefore, it is entirely possible to need a certain size of duct in one room and a larger or smaller duct in a nother room, based on the room's size. You can find the HVAC duct size of each room by performing a few basic calculations and taking the information you learn and matching it with the appropriate sizing charts.
1.4 Instructions 1.4.1.1
Things You'll Need Ductulator
Gather all the necessary information about each room in your home. Measure the length, width and height of each room. Find any information you can about the windows installed in each room, as window thickness and insulation plays a part in the size of the HVAC duct. Also find any information you can about the insulation in the rooms of your home, particularly the thickness. Use a Ductulator. A Ductulator is a handheld piece of equipment that you can take with you as you go room-by-room in your home. Input the dimensions of each room as well as specific information about the home's heating and air conditioning unit, and the Ductulator will display the exact size of the duct needed in each room. Use the HVAC Books Duct Calculator. The Duct Calculator is an online calculator that functions like a Ductulator using your Web browser. Input all the requested information about your heating or air conditioning unit, including its size and its cubic feet per minute output. Also input all the requested information about the rooms in your home to learn the size of ducts needed in each location.
31
How to Calculate the Square Foot for HVAC Tonnage
This is an example of an HVAC unit. The terms Heating, Ventilation and Air Conditioning, or HVAC all refer to technology used to control indoor temperature. Typically, modern HVAC systems are designed with one central unit that manages the heating and cooling load for a building or section of a building. It is critical to calculate the proper HVAC size for a space to ensure ideal heating and cooling and to keep energy costs down. An HVAC unit that is too small for a building will run constantly and may never fully cool the interior. An HVAC unit that is too large can short-cycle and use excessive energy
1.5 Instructions 1.5.1.1
Things You'll Need Tape measure Calculator
Measure the total square footage of the space you plan to regulate with an HVAC unit. You can calculate square footage by multiplying the length times the width of a room. If you plan to regulate multiple rooms, you must measure the dimensions for eac h room and add the totals together. Building blueprints or leases often stipulate the total square footage of the space, but you may wish to measure to double-check those numbers. Determine the Cubic Feet per Meter, or CFM, figure for your environment. Airflow i s measured in CFM and a general rule of thumb for most of the United States dictates one CFM per one square foot. There are exceptions to this rule, for example areas with many windows may require two CFM per square foot. Divide the CFM figure by 400 to convert it into tons. For example, if the total square footage you intend to regulate is 1,200, and you determined you need 1,200 CFM, divide 1,200 by 400 and you will find that you need a three-ton air-conditioning unit in your HVAC system.
32
How to Size a Filter in an HVAC System Properly sizing an air filter for a HVAC (heating, ventilating and air conditioning) system will not only make the unit efficient but keep the air inside the home cleaner and healthier. Air filters are usually placed just inside the HVAC air intake grill. This allows for easy access to the filter and keeps the entire duct system clean.
1.6 Instructions 1.6.1.1
Things You'll Need Cubic feet per minute of HVAC unit
Understand that the size of the air filter is based solely on the air movement of the blower fan contained inside the HVAC unit. This air movement is measured in cubic feet per minute (CFM). The CFM of HVAC units can be found on the side of the blower fan housing. Typically it will be placed on a metal tag. For example, it may read 2,000 CFM. Find the required size for the air filter. A safe recommendation for air filters is to use a base formula of 2 CFM of airflow for every square inch of disposable air filter. This number ensures that the air filter will not clog too fast or collapse in the air stream. For example, divide 2,000 CFM by 2. The result is equal to 1,000 square inches of air filter material. Find a commercially equivalent filter to match this surface area. In described example, two air filters that are 20 inches by 25 inches (500 square inc hes each) should be used.
Industry Practise It is always better to oversize the filter intake area than under size the opening .
33
PROCESSES IN HVAC HEATING
Central heating unit There are many different types of standard heating systems. Central heating is often used in cold climates to heat private houses and public buildings. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air, all in a central location such as a furnace room in a home or a mechanical room in a large building. The use of water as the heat transfer medium is known as hydronics. The system also contains either ductwork, for forced air systems, or piping to distribute a heated fluid and radiators to transfer this heat to the air. The term radiator in this context is misleading since most heat transfer from the heat exchanger is by convection, not radiation. The radiators may be mounted on walls or buried in the floor to give under-floor heat. In boiler fed or radiant heating systems, all but the simplest systems have a pump to circulate the water and ensure an equal supply of heat to all the radiators. The heated water can also be fed through another (secondary) heat exchanger inside a storage cylinder to provide hot running water. Forced air systems send heated air through ductwork. During warm weather the same ductwork can be used for air conditioning. The forced air can also be filtered or put through air cleaners.
34
Heating can also be provided from electric, or resistance heating using a filament that becomes hot when electric current is caused to pass through it. This type of heat can be found in electric baseboard heaters, portable electric heaters, and as backup or supplemental heating for heat pump (or reverse heating) system. The heating elements (radiators or vents) should be located in the coldest part of the room, typically next to the windows to minimize condensation and offset the convective air current formed in the room due to the air next to the window becoming negatively buoyant due to the cold glass. Devices that direct vents away from windows to prevent "wasted" heat defeat this design intent. Cold air drafts can contribute significantly to subjectively feeling colder than the average room temperature. Therefore, it is important to control the air leaks from outside in addition to proper design of the heating system. The invention of central heating is often credited to the ancient Romans, who installed a system of air ducts called a hypocaust in the walls and floors of public baths and private villas.
35
VENTILATION
An air handling unit is used for the heating and cooling of air in a central location (click on image for legend). Ventilating is the process of "changing" or replacing air in any space to control temperature or remove moisture, odors, smoke, heat, dust, airborne bacteria, car bon dioxide, and to replenish oxygen. Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided [3]
into mechanical/forced and natural types.
Ventilation is used to remove unpleasant smells and
excessive moisture, introduce outside air, to keep interior building air circulating, and to prevent stagnation of the interior air.
Mechanical or forced ventilation "Mechanical" or "forced" ventilation is provided by an air handler and used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates much energy is required to remove excess moisture from ventilation air. Kitchens and bathrooms typically have mechanical exhaust to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. If ducting for the fans traverse unheated space (e.g., an attic), the ducting should be insulated as well to prevent condensation on the ducting. Direct drive fans are available for many applications, a nd can reduce maintenance needs. Ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature because of evaporation of perspiration on the skin o f the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor. Ceiling fans do not provide ventilation as defined as the introduction of outside air.
36
Natural ventilation Natural ventilation is the ventilation of a building with outside air without the use of a fan or other mechanical system. It can be achieved with openable windows or trickle vents when the spaces to ventilate are small and the architecture permits. In more complex systems warm air in the building can be allowed to rise and flow out upper openings to the outside (stack effect) thus forcing cool outside air to be drawn into the building naturally through openings in the lower areas. These systems use very little energy but care m ust be taken to ensure the occupants' comfort. In warm or humid months, in many climates, maintaining thermal comfort solely via natural ventilation may not be possible so conventional air conditioning systems are used as backups. Airside economizers perform the same function as natural ventilation, but use mechanical systems' fans, ducts, dampers, and control systems to i ntroduce and distribute cool outdoor a ir when appropriate.
37
Air conditioning Air conditioning and refrigeration are provided through the removal of heat. The definition of cold is the absence of heat and all air conditioning systems work on this basic principle. Heat can be removed through radiation, convection, and by heat pump systems through a process called the refrigeration cycle. Refrigeration conduction mediums such as water, air, ice, and chemicals are referred to as refrigerants. An air conditioning system, or a standalone air conditioner, provides cooling, ventilation, and humidity control for all or part of a house or building. The refrigeration cycle consists of four essential elements to create a cooling effect. The system refrigerant starts its cycle in a gaseous state. The compressor pumps the refrigerant gas up to a high pressure and temperature. From there it enters a heat exchanger (sometimes called a "condensing coil" or condenser) where it loses energy (heat) to the outside. In the process the refrigerant condenses into a liquid. The liquid refrigerant is returned indoors to another heat exchanger ("evaporating coil" or evaporator). A metering device allows the liquid to flow in at a low pressure at the proper rate. As the liquid refrigerant evaporates it aborbs energy (heat) from the inside air, returns to the compressor, and the cycle repeats. In the process, heat is absorbed from indoors, and transferred outdoors, resulting in cooling o f the building. In variable climates, the system may include a reversing valve that automatically switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a residence or facility to be heated and cooled by a single piece of equipment, by the same means, and with the same hardware. Central, 'all-air' air conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in modern residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required to carry the needed air to heat or cool an area. The duct system must be carefully maintained to prevent the growth of pathogenic bacteria such as legionella in the ducts. An alternative to central systems is the use of separate indoor and outdoor coils in split systems. These systems, although most often seen in residential applications, are gaining popularity in small commercial buildings. The evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspend from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity, so that short lengths of duct handle air from the indoor unit to vents or diffusers around the room or rooms. Dehumidification in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below dew point, moisture in the air condenses on the evaporator coil 38
tubes. This moisture is collected at the bottom of the evaporator in a condensate pan and is removed by piping it to a central drain or onto the ground outside. Air dehumidifier is an airconditioner-like device that controls the humidity of a room or building. It is often employed in basements which have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal ai r. Conversely, air humidifier increases the humidity of a building. Air-conditioned buildings often have sealed windows, because open windows would disrupt the attempts of the HVAC system to maintain constant indoor air conditions, resulting in the compressor being over-worked. All modern air conditioning systems, down to small "window" package units, ar e equipped with internal air filters. These are generally o f a light weight gauze-type element, and must be replaced as conditions warrant (some models may be washable). For example, a building in a high-dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads. Failure to replace these filters as needed will contribute to a lower heat-exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; also low air flow can result in "iced-up" or "iced-over" evaporator coils, and then there is no air flow at all. Additionally, very dirty or plugged filters can cause overheating during a heating cycle, and can possibly result in damage to the system or even fire. It is important to keep in mind that because an air conditioner moves heat between the indoor coil and the outdoor coil, both must be kept just as clean. This means that, in addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor, because the condenser coil is responsible for discharging both the indoor heat (as picked up by the evaporator) plus the heat generated by the electric motor driving the compressor. Outside, "fresh" air is generally drawn i nto the system by a vent into the indoor heat exchanger section, creating a positive air pressure. The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent.
39
Energy efficiency For the last 20 to 30 years, manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient. This was originally driven by rising energy costs, and has more recently been driven by i ncreased awareness of environmental issues. In the USA, the EPA has also imposed tighter restrictions. There are several methods for making HVAC systems more efficient.
Heating energy Water heating is more efficient for heating buildings and was the standard many years ago. Today forced air systems can double for air conditioning and are more popular. A couple of benefits of forced air systems, which are now widely applied in churches, schools and high-end residences,are 1) better air conditioned effect 2) up to 15-20% energy saving, and 3) evenly conditioned effect. A drawback is the installation cost, which might be slightly higher than traditional HVAC system. Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintain a proper temperature.
Ventilation energy recovery Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air. This is done by transfer of energy to the incoming o utside fresh air.
Air conditioning energy The performance of vapor compression refrigeration cycles is limited by thermodynamics. These air conditioning and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe the performance of these devices. The Coefficient-of-Performance (COP) measures performance, but this dimensionless measure has not been adopted, but rather the Energy Efficiency Ratio (EER). EER is the Energy Efficiency Ratio 40
based on a 35 °C (95 °F) outdoor temperature. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER is used, and is the Seasonal Energy Efficiency Ratio (SEER). SEER ratings are based on seasonal temperature averages instead of a constant 35 °C outdoor temperature. The current industry minimum SEER rating is 13 SEER. The SEER article describes it further, and presents some economic comparisons using this useful performance measure.
41
HVAC industry and standards International ISO16813:2006 is one of the ISO building environment standards. It establishes the general principles of building environment design taking into account healthy indoor environment for t he occupants, and protecting the environment for future generatio ns, and promoting collaboration among the various parties involved in building environmental design to provide a sustainable building environment. ISO16813 is applicable for new construction and the retrofit of existing buildings. The building environmental design standard aims to :
provide the constraints concerning sustainability issues from the initial stage of the design process, including building and plant life cycle together with owning and operating costs to be considered at all stages in the design process;
assess the proposed design with rational criteria for indoor air quality, thermal comfort, acoustical comfort, visual comfort, energy efficiency and HVAC system controls at every stage of the design process;
make iterations between decisions and evaluations of the design throughout the design process.
North America USA In the United States, HVAC engineers generally are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). ASHRAE is an international technical society for all individuals and organizations interested in HVAC. The Society, organized into Regions, Chapters, and Student Branches, allows exchange of HVAC knowledge and experiences for the benefit of the field's practitioners and the public. ASHRAE provides many opportunities to participate in the development of new knowledge via, for example, research and its many Technical Committees. These committees meet typically twice per year at the ASHRAE Annual and Winter Meetings. A popular product show, the AHR Expo, is held in conjunction with each Winter Meeting. The Society has approximately 50,000 members and has headquarters at Atlanta, Georgia, USA. The most recognized standards for HVAC design is based on ASHRAE data. ASHRAE is the American Society of Heating, Refrigerating and Air-Conditioning Engineers. The ASHRAE Handbook's most general volume, of four, is Fundamentals; it includes heating and cooling calculations. Each volume of the ASHRAE Handbook is updated every four years. The design professional must co nsult ASHRAE data for the standards of design and care as the typical building codes provides little to no
42
information on HVAC design practices; such codes, such as the UMC and IMC, do include much details on installation requirements, however. Other useful reference materials include items from SMACNA, ACCA, and technical trade journals. American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated a nd published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local Building Permit Departments are charged with enforcement of these standards on private and certain public properties. In the United States, as well as throughout the world, HVAC contractors and companies are members of NADCA, the National Air Duct Cleaners Association. NADCA was formed in 1989 as a non-profit association of companies engaged in the cleaning of HVAC systems. Its mission was to promote source removal as the only acceptable method of cleaning and to establish industry standards for the association. NADCA has expanded its mission to include the representation of qualified companies engaged in the assessment, cleaning, and restoration of HVAC systems, and to assist its members in providing high quality service to their customers. The goal of the association is to be the number one source for the HVAC cleaning and restoration services: first time, every time. NADCA has experienced phenomenal membership growth and has been extremely successful with the training and certification of air systems cleaning specialists, mold remediators, and HVAC inspectors. The association has also published important standards and guidelines, educational materials, and other useful information for the consumer and members of NADCA. Their headquarters are located in Washington, D.C.
Europe United Kingdom The Chartered Institute of Building Services Engineers is a body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electrotechnical,heating, ventilating, air conditioning, refrigeration and plumbing industries. To train as a building services engineer, the academic requirement are GCSEs (A-C) / Standard Grades (1-3) in Maths and Science, which are important in measurements, planning and theory. Employers will often want a degree in a branch of engineering, such as building environment engineering, electrical engineering or mechanical engineering. To become a full member of CIBSE, and so also to be registered by the Engineering Council UK as a chartered engineer, one must also attain an Honours Degree and a Masters Degree in a relevant engineering subject.
43
CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include for various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:
Guide A: Environmental Design
Guide B: Heating, Ventilating, Air Conditioning and Refrigeration
Guide C: Reference Data
Guide D: Transportation systems in Buildings
Guide E: Fire Safety Engineering
Guide F: Energy Efficiency in Buildings
Guide G: Public Health Engineering
Guide H: Building Control Systems
Guide J: Weather, Solar and Illuminance Data
Guide K: Electricity in Buildings
Guide L: Sustainability
Guide M: Maintenance ENgineering and Management
Within the construction sector, it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas, electricity, water, heating and lighting, as well as many others. These all help to make buildings comfortable and healthy places to live and work in. Building Services is part of a sector that has over 51,000 businesses and employs represents 2%-3% of the GDP.
Australia Air Conditioning and Mechanical Contractors Association of Australia (AMCA) Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), CIBSE
Asia India The Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE) was established to promote the HVAC industry in India. ISHRAE is an associate of ASHRAE. ISHRAE was started at Delhi in 1981 and a chapter was started in Bangalore in 1989. Between 1989 & 1993, ISHRAE chapters were formed in all major cities in India and also in the Middle East.
44
Pakistan Air-conditioning technology has been in use in Pakistan since 1947, the time of its independence. At that point local expertise was dependent on the supply and installation of imported equipment in accordance with the system designs from abroad. Once Pakistani engineers recognized the importance of the field they became act ive in developing expertise in design, manufacture, installation, operation, and maintenance. In 1995 the Pakistan HVACR Society was formed, and has organized the various disciplines of the field under its umbrella, and has regularly holds an Annual Expo & Conference, which rotates yearly between the ci ties of Karachi, Lahore & Islamabad, and is the premium industry event in Pakistan, and a lso attended by many international manufacturers and visitors. In 2003 the ASHRAE Pakistan Chapter was formed, followed by ASHRAE Northern Pakistan Chapter in 2005, and also subsequently ASHRAE Central Pakistan Chapter in 2011.
45
