Handbook of air conditioning systems design

Electronic equipment often requires individual air conditioning. The manufacturers recommendation for temperature and humidity variation must be followed, and these requirements are often quite stringent. Ventilation Cfm per person, cfm per sq ft, scheduled ventilation agreement with purchaser , see Chapter 6. Excessive smoking or odors, code requirements.

Exhaust fanstype, size, speed, cfm delivery. Thermal storage Includes system operating schedule 12, 16 or 24 hours per day specifically during peak outdoor conditions, permissible temperature swing in space during a design day, rugs on floor, nature of surface materials enclosing the space see Chapter 3.

Continuous or intermittent operation Whether system be required to operate every business day during cooling season, or only occasionally, such as churches and ballrooms. If intermittent operation, determine duration of time available for precooling or pulldown.

The following is a guide to obtaining this information: 1. Available spaces Location of all stairwells, elevator shafts, abandoned smokestacks, pipe shafts, dumbwaiter shafts, etc. Possible obstructions Locations of all electrical conduits, piping lines, and other obstructions or interferences that may be in the way of the duct system. Location of all fire walls and partitions Requiring fire dampers also see Item Location of outdoor air intakes In reference to street, other buildings, wind direction, dirt, and short-circuiting of unwanted contaminants.

Power service Location, capacity, current limitations, voltage, phases and cycle, 3 or 4 wire; how additional power if required may be brought in and where. Water service Location, size of lines, capacity, pressure, maximum temperature. Steam service Location, size, capacity, temperature, pressure, type of return system. Refrigeration, brine or chilled water if furnished by customer Type of system, capacity, temperature, gpm, pressure.

Architectural characteristics of space For selection of outlets that will blend into the space design. Existing air conveying equipment and ducts For possible reuse. Building Survey And Load Estimate Drains Location and capacity, sewage disposal. Control facilities Compressed air source and pressure, electrical. Foundation and support Requirements and facilities, strength of building. Sound and vibration control requirements Relation of refrigeration and air handling apparatus location to critical areas.

Accessibility for moving equipment to the final location Elevators, stairways, doors, accessibility from street. Codes, local and national Governing wiring, drainage, water supply, venting of refrigeration, construction of refrigeration and air handling apparatus rooms, ductwork, fire dampers, and ventilation of buildings in general and apparatus rooms in particular.

The sun rays entering windows Table 15, pages , and Table 16, page 52, provide data from which the solar heat gain through glass is estimated. The solar heat gain is usually reduced by means of shading devices on the inside or outside of the windows; factors are contained in Table In addition to this reduction, all or part of the window may be shaded by reveals, overhangs, and by adjacent buildings.

Chart 1, page 57, and Table 18, page 58, provide an easy means of determining how much the window is shaded at a given time.

A large portion of the solar heat gain is radiant and will be partially stored as described in Chapter 3. Tables 7 thru 11, pages , provide the storage factors to be applied to solar heat gains in order to arrive at the actual cooling load imposed on the air conditioning equipment. These storage factors are applied to peak solar heat gains obtained from Table 6, page 29, with overall factors from Table 16, page The sun rays striking the walls and roofThese, in conjunction with the high outdoor air temperature, cause heat to flow into the space.

Tables 19 and 20, pages 62 and 63, provide equivalent temperature differences for sunlit and shaded walls and roofs. Tables 21, 22, 23, 24, 25, 27, and 28, pages , provide the transmission coefficients or rates of heat flow for a variety of roof and wall constructions. The air temperature outside the conditioned space A higher ambient temperature causes heat to flow thru the windows, partitions, and floors.

Tables 25 and 26, pages 69 and 70, and Tables 29 and 30, pages 73 and 74, provide the transmission coefficients. The temperature differences used to estimate the heat flow thru these structures are contained in the notes after each table.

The air vapor pressure A higher vapor pressure surrounding conditioned space causes water vapor to flow thru the building materials. This load is significant only in low dewpoint applications. The data required to estimate this load is contained in Table 40, page In comfort applications, this load is neglected. The air conditioning load is estimated to provide the basis for selecting the conditioning equipment.

It must take into account the heat coming into the space from outdoors on a design day, as well as the heat being generated within the space. A design day is defined as: 1. A day on which the dry-and wet-bulb temperatures are peaking simultaneously Chapter 2, Design Conditions. The time of peak load can usually be established by inspection, although, in some cases, estimates must be made for several different times of the day.

Actually, the situation of having all of the loads peaking at the same time will very rarely occur. To be realistic, various diversity factors must be applied to some of the load components; refer to Chapter 3, Heat Storage, Diversity, and Stratification. The infiltration and ventilation air quantities are estimated as described in Chapter 6. This form contains the references identified to the particular chapters of data and tables required to estimate the various load components.

Building Survey And Load Estimate The wind blowing against a side of the building- Wind causes the outdoor air that is higher in temperature and moisture content to infiltrate thru the cracks around the doors and windows, resulting in localized sensible and latent heat gains. All or part of this infiltration may be offset by air being introduced thru the apparatus for ventilation purposes.

Chapter 6 contains the estimating data. Outdoor air usually required for ventilation purposes Outdoor air is usually necessary to flush out the space and keep the odor level down.

Most air conditioning equipment permits some outdoor air to bypass the cooling surface see Chapter 8. This bypassed outdoor air becomes a load within the conditioned space, similar to infiltration; instead of coming thru a crack around the window, it enters the room thru the supply air duct. The amount of bypassed outdoor air depends on the type of equipment used as outlined in Chapter 8. Table 45, page 97, provides the data from which the ventilation requirements for most comfort applications can be estimated.

The foregoing is that portion of the load on the air conditioning equipment that originates outside the space and is common to all applications. The internal load, or heat generated within the space, depends on the character of the application. Proper diversity and usage factor should be applied to all internal loads.

As with the solar heat gain, some of the internal gains consist of radiant heat which is partially stored as described in Chapter 3 , thus reducing the load to be impressed on the air conditioning equipment. Generally, internal heat gains consist of some or all of the following items: 1. People The human body thru metabolism generates heat within itself and releases it by radiation, convection, and evaporation from the surface, and by convection and evaporation in the respiratory tract.

The amount of heat generated and released depends on surrounding temperature and on the activity level of the person, as listed in 5. Table 48, page Lights Illuminants convert electrical power into light and heat refer to Chapter 7.

Some of the heat is radiant and is partially stored see Chapter 3. Appliances Restaurants, hospitals, laboratories, and some specialty shops beauty shops have electrical, gas, or steam appliances which release heat into the space. Tables 50 thru 52, pages , list the recommended heat gain values for most appliances when not hooded.

If a positive exhaust hood is used with the appliances, the heat gain is reduced. Electric calculating machines Refer to manufacturers data to evaluate the heat gain from electric calculating machines.

Normally, not all of the machines would be in use simultaneously, and, therefore, a usage or diversity factor should be applied to the full load heat gain. The machines may also be hooded, or partially cooled internally, to reduce the load on the air conditioning system.

Electric motors Electric motors are a significant load in industrial applications and should be thoroughly analyzed with respect to operating time and capacity before estimating the load see Item 13 under Space Characteristics and Heat Load Sources. It is frequently possible to actually measure this load in existing applications, and should be so done where possible.

Table 53, page , provides data for estimating the heat gain from electric motors. Hot pipes and tanks Steam or hot water pipes running thru the air conditioned space, or hot water tanks in the space, add heat. In many industrial applications, tanks are open to the air, causing water to evaporate into the space. Tables 54 thru 58, pages provide data for estimating the hear gain from these sources. Miscellaneous sources There may be other sources of heat and moisture gain within a space, such as escaping steam industrial cleaning devices, pressing machines, etc.

In addition to the heat gains from the indoor and outdoor sources, the air conditioning equipment and duct system gain or lose heat. The fans and pumps required to distribute the air or water thru the system add heat; 2. Building Survey And Load Estimate heat is also added to supply and return air ducts running thru warner or hot spaces; cold air may leak out of the supply duct and hot air may leak into the return duct.

The procedure for estimating the heat gains from these sources in percentage of room sensible load, room latent load, and grand total heat load is contained in Chart 3, page , and Tables 59 and 60, pages The heating load evaluation is the foundation for selecting the heating equipment.

Normally, the heating load is estimated for the winter design temperatures Chapter 2 usually occurring at night; therefore, no credit is taken for the heat given off by internal sources people, lights, etc. Chapter 5 contains the transmission coefficients and procedures for determining heat loss.

Chapter 6 contains the data for estimating the infiltration air quantities. Another factor that may be considered in the evaluation of the heating load is temperature swing. Capacity requirements may be reduced when the temperature within the space is allowed to drop a few degrees during periods of design load. This, of course, applies to continuous operation only. Table 4, page 20, provides recommended inside design conditions for various applications, and Table 13, page 37, contains the data for estimating the possible capacity reduction when operating in this manner.

The practice of drastically lowering the temperature to 50 F db or 55 F db when the building is unoccupied precludes the selection of equipment based on such capacity reduction. Although this type of operation may be effective in realizing fuel economy, additional equipment capacity is required for pickup. In fact, it may be desirable to provide the additional capacity, even if continuous operation is contemplated, because of pickup required after forced shutdown.

It is, therefore, evident that the use of storage in reducing the heating load for the purpose of equipment selection should be applied with care.

Since air conditioning load calculations are based on pounds of air necessary to handle a load, a decrease in density means an increase in cfm required to satisfy the given sensible load. The weight of air required to meet the latent load is decreased because of the higher latent load capacity of the air at higher altitudes greater gr per lb per degree difference in dewpoint temperature.

For the same dry-bulb and percent relative humidity, the wetbulb temperature decreases except at saturation as the elevation above sea level increases. The following adjustments are required for high altitude load calculations see Chapter 8, Table 66, page : 1. Design room air moisture content must be adjusted to the required elevation. Standard load estimating methods and forms are used for load calculations, except that the factors affecting the calculations of volume and sensible and latent heat of air must be multiplied by the relative density at the particular elevation.

Because of the increased moisture content of the air, the effective sensible heat factor must be corrected. After the load is evaluated, the equipment must be selected with capacity sufficient to offset this load.

The air supplied to the space must be of the proper conditions to satisfy both the sensible and latent loads estimated.

Chapter 8, Applied Psychrometrics, provides procedures and examples for determining the criteria from which the air conditioning equipment is selected air quantity, apparatus dewpoint, etc. This chapter presents the data from which the outdoor design conditions are established for various localities and inside design conditions for various applications.

The design conditions established determine the heat content of air, both outdoor and inside. They directly affect the load on the air conditioning equipment by influencing the transmission of heat across the exterior structure and the difference in heat content between the outdoor and inside air. For further details, refer to Chapters 5 and 6. This range varies with local climate conditions.

The maximum design dry-bulb and wet-bulb temperatures are simultaneous peaks not individual peaks. The moisture content is an individual peak, and is listed only for use in the selection of separate cooling and dehumidifying systems for closely controlled spaces. Each of these conditions can be expected to be exceeded no more than 3 hours in a normal summer.

The outdoor dry-bulb temperature can be expected to go below the listed temperatures a few times a year, normally during the early morning hours. The annual degree days listed are the sum of all the days in the year on which the daily mean temperature falls below 65 F db, times the number of degrees between 65 F db and the daily mean temperature.

The outdoor design conditions listed in Table 1 are the industry accepted design conditions as published in ARI Std. The conditions, as listed, permit a choice of outdoor drybulb and wet-bulb temperatures for different types of applications as outlined below. These outdoor design conditions are the simultaneously occurring dry-bulb and wet-bulb temperatures and moisture content, which can be expected to be exceeded a few times a year for short periods.

The dry-bulb is exceeded more frequently than the wet-bulb temperature. And usually when the wet-bulb is lower than design. When cooling and dehumidification dehydration are performed separately with these types of applications, use the normal design dry-bulb temperature for selecting the sensible cooling.

Frequently, the design conditions at other times of the day and other months of the year must be known. Table 2 lists the approximate corrections on the drybulb and wet-bulb temperatures from 8 a. The dry-bulb corrections are based on analysis of weather data, and the wet-bulb corrections assume a relatively constant dewpoint throughout the hr period. Table 3 lists the approximate corrections of the drybulb and wet-bulb temperatures from March to November, based on the yearly range in dry-bulb temperature summer normal design dry-bulb minus winter normal design dry-bulb temperature.

These corrections are based on analysis of weather data and are applicable only to the cooling load estimate. Find: The approximate dry-bulb and wet-bulb temperatures at noon in October. Solution: Normal design conditions for New York in July at p. Daily range in New York City is 14 F db. These conditions are based on experience gathered from many applications, substantiated by ASHAE tests.

The optimum or deluxe conditions are chosen where costs are not of prime importance and for comfort applications in localities having summer outdoor design dry-bulb temperatures of 90 F or less. Since all of the loads sun, lights, people, outdoor air, etc. The commercial inside design conditions are recommended for general comfort air conditioning applications.

If the temperature in the conditioned space is forced to rise, heat will be stored in the building mass. Refer to Chapter 3, Heat Storage, Diversity and Stratification, for a more complete discussion of heat storage. With summer cooling, the temperature swing used in the calculation of storage is the difference between the design temperature and the normal thermostat setting. The range of summer inside design conditions is provided to allow for the most economical selection of.

Applications of inherently high sen-sible heat factor relatively small latent load usually result in the most economical equipment selection if the higher dry-bulb temperatures and lower relative humidities are used. Applications with low sensible heat factors high latent load usually result in more economical equipment selection if the lower dry-bulb temperatures and higher relative humidities are used.

For winter season operation, the inside design conditions listed in Table 4 are recommended for general heating applications.

With heating, the temperature swing variation is below the comfort condition at the time of peak heating load no people, lights, or solar gain, and with the minimum outdoor temperature.

Heat stored in the building structure during partial load day operation reduces the required equipment capacity for peak load operation in the same manner as it does with cooling.

Table 5 lists typical temperatures and relative humidities used in preparing, processing, and manufacturing various products, and for storing both raw and finished goods. These conditions are only typical of what has been used, and my vary with applications. They may also vary as changes occur in processes, products, and knowledge of the effect of temperature and humidity.

In all cases, the temperature and humidity conditions and the permissible limits of variations on these conditions should be established by common agreement with the customer. Some of the conditions listed have no effect on the product or process other than to increase the efficiency of the employee by maintaining comfort conditions. This normally improves workmanship and uniformity, thus reducing rejects and production cost.

In some cases, it may be advisable to compromise between the. Generally, specific inside design conditions are required in industrial applications for one or more of the following reasons: 1. A constant temperature level is required for close tolerance measuring, gaging, machining, or grinding operations, to prevent expansion and contraction of the machine parts, machined products and measuring devices.

Normally, a constant temperature is more important than the temperature level. Non-hygroscopic materials such as metals, glass, plastics, etc.

The density of this film increases when relative. Load Estimating Chapter 2. Design Conditions humidity increases.

Hence, this film must, in many instances, be held below a critical point at which metals may etch, or the electric resistance of insulating materials is significantly decreased. Where highly polished surfaces are manufactured or stored, a constant relative humidity and temperature is maintained, to minimize increase is maintained, to minimize increase in surface moisture film.

The temperature and humidity should be at, or a little below, the comfort conditions to minimize perspiration of the operator. Constant temperature and humidity may also be required in machine rooms to prevent etching or corrosion of the parts of the machines.

With applications of this type, if the conditions are not maintained 24 hours a day, the starting of air conditioning after any prolonged shutdown should be done carefully: 1 During the summer, the moisture accumulation in the space should be reduced before the temperature is reduced; 2 During the winter, the moisture should not be introduced before the materials have a chance to warm up if they are cooled during shutdown periods. Control of relative humidity is required to maintain the strength, pliability, and regain of hydroscopic materials, such as textiles and paper.

The humidity must also be controlled in some applications to reduce the effect of static electricity. The temperature and relative humidity control are required to regulate the rate of chemical or biochemical reactions, such as drying of Varnishes or sugar coatings, preparation of synthetic fibers or chemical compounds, fermentation of yeast, etc.

Generally, high temperatures with low humidities increase drying rates; high temperatures increase the rate of chemical reaction, and high temperatures and relative humidities increase such processes as yeast fermentations. Laboratories require precise control of both temperature and relative humidity or either. With some industrial applications where the load is excessive and the machines or materials do not benefit from controlled conditions, it may be advisable to apply spot cooling for the relief of the workers.

Generally, the conditions to be maintained by this means will be above normal comfort. Generally, it was found that the equipment selected on this basis was oversized and therefore capable of maintaining much lower room conditions than the original design. Extensive analysis, research and testing have shown that the reasons for this are: 1. Storage of heat in the building structure. Non-simultaneous occurrence of the peak of the individual loads diversity. Stratification of heat, in some cases.

This chapter contains the data and procedures for determining the load the equipment is actually picking into account the above factors. Application of these data to the appropriate individual heat gains results in the actual cooling load. The actual cooling load is generally considerable below the peak total instantaneous heat gain, thus requiring smaller equipment to perform a specific job.

The smaller system operating for longer periods at times of peak load will produce a lower first cost to the customer with commensurate lower demand charges and lower operating costs.

It is a well-known fact that equipment sized to more nearly meet the requirements results in a more efficient, better operating system. Also, if a smaller system is selected, and is based on extended periods of operation at the peak load, it results in a more economical and efficient system at a partially loaded condition.

Since, in most cases, the equipment installed to perform a specific function is smaller, there is less margin for error. This requires more exacting engineering including air distribution design and system balancing.

With multi-story, multi-room application, it is usually desirable to provide some flexibility in the air side or room load to allow for individual room control, load pickup, etc. Generally, it is recommended that the full reduction from storage and diversity be taken on the overall refrigeration or building load, with some degree of conservatism on the air side or room loads.

This degree should be determined by the engineer from project requirements and customer desires. A system so designed, full reduction on refrigeration load and less than full reduction on air side or room load, meets all of the flexibility requirements, except at time of peak load. In addition, such a system has a low owning and operating cost. The instantaneous heat gain in a typical comfort application consists of sun, lights, people, transmission thru walls, roof and glass, infiltration and ventilation air and, in some cases, machinery, appliances, electric calculating machines, etc.

A large portion of this instantaneous heat gain is radiant heat which does not become an instantaneous load on the equipment, because it must strike a solid surface and be absorbed by this surface before becoming a load on the equipment. This load is normally a relatively small part of the total load, and for simplicity is considered to be the instantaneous load on the equipment.

The load from machinery or appliances varies, depending upon the temperature of the surface. The higher the surface temperature, the greater the radiant heat load. This temperature. Load Estimating Chapter 3. Heat Storage, Diversity And Stratification difference causes heat flow into the material by conduction and into the air by convection. The heat conducted away from the surface is stored, and theheat convected from the surface becomes an instantaneous cooling load.

The portion of radiant heat being stored depends on the ratio of the resistance to heat flow into the material and the resistance to heat flow into the air film. With most construction materials, the resistance to heat flow into the material is much lower than the air resistance; therefore, most of the radiant heat will be stored. However, as this process of absorbing radiant heat continues, the material becomes warmer and less capable of storing more heat.

The highly varying and relatively sharp peak of the instantaneous solar heat gain results in a large part of it being stored at the time of peak solar heat gain, as illustrated in Fig.

The upper curve in Fig. The cross-hatched areas Fig. Since all of the heat coming into a space must be removed, these two areas are equal. The relatively constant light load results in a large portion being stored just after the lights are turned on, with a decreasing amount being stored the longer the lights are on, as illustrated in Fig.

The upper and lower curves represent the instantaneous heat gain and actual cooling load from fluorescent lights with a constant space temperature. The dotted line indicates the actual cooling load for the first day if the lights are on longer than the period shown. With light construction, less heat is stored at the peak less storage capacity available , and with heavy construction, more heat is stored at the peak more storage capacity available , as shown in Fig.

This aspect affects the extent of zoning required in the design of a system for a given building; the lighter the building construction, the more attention should be given to zoning. The upper curve of Fig. One more item that significantly affects the storage of heat is the operating period of the air conditioning equipment. All of the curves shown inFigs. If the equipment is shut down after 16 hours of operation, some of the stored heat remains in the building construction. This heat must be removed heat in must equal heat out and will appear as a pulldown load when the equipment is turned on the next day, as illustrated in Fig.

Heat Storage, Diversity And Stratification Adding the pulldown load to the cooling load for that day results in the actual cooling load for hour operation, as illustrated in Fig.

The upper curve represents the instantaneous heat gain and the lower curve the actual cooling load for that day with a constant temperature maintained within the space during the operating period of the equipment. The dotted line represents the additional cooling load from the heat left in the building construction. The temperature in the space rises during the shutdown period from the nighttime transmission load and the stored heat, and is brought back to the control point during the pulldown perios.

Shorter periods of operation increase the pulldown load because more stored heat is left in the building construction when the equipment is shut off. Adding this pulldown load to the cooling load for that day results in the actual cooling load for hour operation, as illustrated in Fig.

The upper and lower solid curves are the instantaneous heat gain and the actual cooling load in average construction space with a constant temperature maintained during the operating period. The cross-hatched areas again represent the Heat Stored and the Stored Heat Removed from the construction. The light load fluorescent is shown in Fig. Mains: 4 x KV2 ES 1. Front fills: 2 x KV2 EX JBL monitors.

System designed and integrated by, um…me! Lights by Muvmental Lighting and Susannah Scott. Photo by me, 6 seconds at f A complete, fully revised HVAC design reference Thoroughly updated with the latest codes, technologies, and practices, this all-in-one resource provides details, calculations, and specifications for designing efficient and effective residential, commercial, and industrial HVAC systems.

Detailed illustrations, tables, and essential HVAC equations are also included. This comprehensive guide contains everything you need to design, operate, and maintain peak-performing HVAC systems. Coverage includes: Load calculations Air- and fluid-handling systems Central plants Automatic controls Equipment for cooling, heating, and air handling Electrical features of HVAC systems Design documentation--drawings and specifications Construction through operation Technical report writing Engineering fundamentals-fluid mechanics, thermodynamics, heat transfer, psychrometrics, sound and vibration Indoor air quality IAQ Sustainable HVAC systems Smoke management.

This textbook provides a concise, systematic treatment of essential theories and practical aspects of refrigeration and air-conditioning systems. It is designed for students pursuing courses in mechanical engineering both at diploma and degree level with a view to equipping them with a fundamental background necessary to understand the latest methodologies used for the design of refrigeration and air-conditioning systems.

After reviewing the physical principles, the text focuses on the refrigeration cycles commonly used in air-conditioning applications in tropical climates. The subject of psychrometry for analysing the various thermodynamic processes in air conditioning is particularly dealt with in considerable detail. This text incorporates such tables and charts so that the students are exposed to solving real-life design problems with the help of ASHRAE Tables.

Finally, the book highlights the features, characteristics and selection criteria of hardware including the control equipment. It also provides the readers with the big picture in respect of the latest developments such as thermal storage air conditioning, desiccant cooling, chilled ceiling cooling, Indoor Air Quality IAQ and thermal comfort. Besides the students, the book would be immensely useful to practising engineers as a ready reference.

Air Conditioning System Design summarizes essential theory and then explains how the latest air conditioning technology operates. Load calculations, energy efficiency, and selection of technology are all explained in the context of air conditioning as a system, helping the reader fully consider the implications of design decisions.

Internal and System Heat Gain8. Applied Psychrometrics. Part 3. Piping Design - General2. Water Piping3. Refrigerant Piping4. Steam Piping. Part 5. Water Conditioning - General2. Scale and Deposit Control3.

Corrosion Control4. Slime and Algae Control5. Water Conditioning Systems6. Part 6. Air Conditioning Apparatus3. Unitary Equipment4. Accessory Equipment. Part 7.