Heating, Ventilating, and. Air Conditioning. Analysis and Design. Sixth Edition. Faye C. McQuiston. Oklahoma State University. Jerald D. Parker. Oklahoma. Heating Ventilating and Air Conditioning Analysis and Design pdf Contents 1. Introduction 2. Air-Conditioning Systems 3. Moist Air Properties. Heating Ventilating and Air-conditioning Analysis and Design (6th Ed.) - Ebook download as PDF File .pdf) or read book online.
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Request PDF on ResearchGate | On Feb 17, , Faye C McQuiston and others published Heating, ventilating, and air conditioning: analysis and design. Heating, Ventilating, and Air Conditioning Analysis and Design phichamhokouda.ga 6 /15 Heating, Ventilating, and Air Conditioning Analysis and. [PDF] Edition Heating, Ventilating and Air Conditioning: Analysis and Design PDF books; 2. Book Details Author: Faye C. McQuiston,Jerald D.
Cooling In most modern buildings cooling must be provided to make the occupants comfort- able, especially in warm seasons. Even in cold climates there may be need for year-around cooling in interior spaces and in special applica- tions.
Cooling is the transfer of energy from a space, or from air supplied to a space, to make up for the energy being gained by that space. Energy gain to a space is typi- cally from warmer surroundings and sunlight or from internal sources within the space, such as occupants, lights, and machinery. Energy is carried from the conditioned space to a refrigerating system and from there eventually dumped to the environment by con- denser units or cooling towers. In the usual process air to be cooled is circulated through a heat exchanger coil such as is shown in Fig.
As with heat- ing, the coil may be located in the space to be cooled in a terminal device , in the duct, or in an air handler in a mechanical room, with the air being ducted to and from the space. As with an air heating system, this is referred to as an all-air system because both energy and ventilation are supplied to the space by air. Both the cooling and the heating coils might be installed in a typical air handler.
Placed in series in the airstream as shown in Fig. Placed in parallel as shown in Fig. Notice in regard to fan-coil arrangement that Fig.
Cooling may involve only sensible heat transfer, with a decrease in the air tem- perature but no change in the moisture content of the airstream.
Equation is valid in this case, and a negative value for sensible heat rate will be obtained, since heat transfer is from the airstream. Usually condensation and removal of moisture occurs in the heat exchanger coil during the cooling process. The energy involved in the moisture removal only is called the latent cooling. The total cooling provided by a coil is the sum of the sensible cool- ing and the latent cooling.
The latent energy transferred in a humidifying or dehumidifying process is where: This will be covered more completely in Chapter 3.
Cooling system Energy rejected to surroundings Energy gains from surroundings Distribution gains Net flow of energy Internal gains Conditioned space Figure Air handler of the draw-through type with cooling and heating coils in series.
Heat transfer is associated with this mass transfer process and the term latent heat transfer is often used to describe the latent energy required. Courtesy of Spirax Sarco, Inc. Filters can be seen in the intake of the air handler shown in Fig. Controls and Instrumentation Because the loads in a building will vary with time, there must be controls to modulate the output of the HVAC system to satisfy the loads. An HVAC system is designed to meet the extremes in the demand, but most of the time it will be operating at part load conditions.
A properly designed control system will maintain good indoor air quality and comfort under all anticipated conditions with the lowest possible life-cycle cost. Controls may be energized in a variety of ways pneumatic, electric, electronic , or they may even be self-contained, so that no external power is required. Some HVAC systems have combination systems, for example, pneumatic and electronic.
The trend in recent times is more and more toward the use of digital control, sometimes called direct digital control or DDC 6, 8, 15, Developments in both analog and digital electronics and in computers have allowed control systems to become much more sophisticated and permit an almost limitless variety of control sequences within the physical capability of the HVAC equipment. By minimizing human intervention in the oper- ation of the system, the possibility of human error is reduced.
HVAC networks designed to permit the use of components from a wide variety of manufacturers are referred to as open networks. A gateway is a device needed between two systems operating on different protocols to allow them to communicate Some common control meth- ods and systems will be discussed in later sections of this text.
A brief review of control fundamentals may be helpful before proceeding further. All control systems, even the simplest ones, have three necessary elements: Consider the control of the air temperature downstream of a heating coil, as in Fig.
The position of the control valve deter- mines the rate at which hot water circulates through the heating coil. A temperature sensor is located at a position downstream of the coil so as to measure the temperature of the air leaving the coil.
The controller has been given a set point equal to the desired downstream air temperature and compares the signal from the sensor with the set point.
If the tem- perature described by the signal from the sensor is greater than the set point, the con- troller will send a signal to partially close the control valve. This is a closed-loop system because the change in the controlled device the control valve results in a change in the downstream air temperature the controlled variable , which in turn is detected by the sensor. The process by which the change in output is sensed is called feedback.
In an open-loop, or feedforward, system the sensor is not directly affected by the action of the controlled device. An example of an open-loop system is the sens- ing of outdoor temperature to set the water temperature in a heating loop.
In this case adjustment of the water temperature has no effect on the outdoor temperature sensor. The two-position or on—off action is the simplest and most common type. An example is an electric heater turned 14 Chapter 1 Introduction Figure Elementary air-temperature control system. To pre- vent rapid cycling when this type of action is used, there must be a difference between the setting at which the controller changes to one position and the setting at which it changes to the other.
In some instances time delay may be necessary to avoid rapid cycling.
Proceedings of the 8th International Symposium on Heating, Ventilation and Air Conditioning
Figure illustrates how the controlled variable might change with time with two-position action. Note that there is a time lag in the response of the controlled variable, resulting in the actual operating differential being greater than the set, or con- trol, differential.
For example, a thermostat in the heating mode may have a small internal heater activated during the on period, causing the off signal to occur sooner than it would otherwise. With this device installed, the ther- mostat is said to have an anticipator or heat anticipation. With this action the controlled device can stop at any point in its stroke and be reversed. The controlled variable must have a relatively rapid response to the controlling signal for this type of action to operate properly.
Modulating action is illustrated in Fig. The controlled device will seek a position corresponding to its own range and the output of the controller. The throttling range is the amount of change in the controlled variable required to run the actuator of the controlled device from one end of its stroke to the other. Figure shows the throttling range for a typical cooling system con- trolled by a thermostat; in this case it is the temperature at which the thermostat calls for maximum cooling minus the temperature at which the thermostat calls for mini- mum cooling.
The actual value of the controlled variable is called the control point.
The system is said to be in control if the control point is inside the throttling range, Fundamental Physical Concepts 15 Figure Two-position on—off control action. Control differential Controlledvariable Time Chapter The difference between the set point and the control point is said to be the offset or control point shift sometimes called drift, droop, or deviation.
The action represented by the solid line in Fig. The dashed line represents reverse action RA , where an increase in temperature causes a decrease in the controlled variable, for example, less heat input. The simplest modulating action is referred to as proportional control, the name sometimes used to describe the modulating control system. This is the control action used in most pneumatic and older electrical HVAC control systems.
The output of a proportional controller is equal to a constant plus the product of the error offset and the gain: High gain makes the system more responsive but may make it unstable. Lowering the gain decreases responsiveness but makes the system more stable. The gain of the control system shown in Fig. Controlledvariable Time Control point Throttling range Set point Offset Figure Typical equipment characteristic for thermostat control of room temperature.
S in the throttling range. In Fig. Figure illustrates an unstable system, where the control point continues to oscil- late about the set point, never settling down to a constant, low-offset value as with the stable system.
Some offset will always exist with proportional control systems. For a given HVAC system the magnitude of the offset increases with decreases in the control sys- tem gain and the load. System performance, comfort, and energy consumption may be affected by this offset.
The controller is designed to behave in the following manner: In this mode the output of the controller is additionally affected by the error inte- grated over time. This means that the error or offset will eventually be reduced for all practical purposes to zero.
In much of the HVAC industry, PI control has been referred to as propor- tional with reset, but the correct term proportional plus integral is becoming more widely used. Most electronic controllers and many pneumatic controllers use PI, and computers can be easily programmed for this mode. Controlledvariable Control point Set point Time Figure A stable system under proportional control. An additional correction involving the derivative of the error is used in the pro- portional plus integral derivative PID mode.
PID increases the rate of correction as the error increases, giving rapid response where needed. Although many electronic controllers are available with PID mode, the extra derivative feature is usually not helpful to good HVAC control.
System monitoring is closely related to system control, and it is important to pro- vide adequate instrumentation for this purpose. At the time of installation all equip- ment should be provided with adequate gages, thermometers, flow meters, and balancing devices so that system performance is properly established. In addition, capped thermometer wells, gage cocks, capped duct openings, and volume dampers should be provided at strategic points for system balancing.
A central system to monitor and control a large number of control points should be considered for any large and complex air-conditioning system. Fire detection and security systems as well as business operations are often integrated with HVAC monitoring and control system in BAS.
Testing, adjusting, and balancing TAB has become an important part of the process of providing satisfactory HVAC systems to the customer. In describing the future of the HVAC industry, a former ASHRAE president reminds us that we are in a people-oriented profession since our designs have a direct impact on the people who occupy our buildings Carlyle M.
Harry H. Shirley J. Fantasy or Nightmare? Michael G. Alex J. Guy W. Operation and Maintenance, 2nd ed. Roger W. Andrew P. Richard B. Convert the following quantities from English to SI units: Convert the following quantities from SI to English units: A pump develops a total head of 50 ft of water under a given operating condition. What pres- sure is the pump developing in SI units and terminology?
A fan is observed to operate with a pressure difference of 4 in. What is the pressure difference in SI units and terminology? The electric utility rate for a facility during the months of May through October is 4. During the August billing period the facility used 96, kw-hrs and set a peak demand of kw during the time between 4: Cal- culate the August electric bill.
For the business whose monthly electrical energy use is described in Problem , estimate the average rate of energy use in kw, assuming it uses energy only from 7: Assume that the month starts on a Monday to give Problems 19 Chapter Calculate the ratio of the peak demand set during that month to the average rate of energy use.
What reasons would likely cause the ratio to be high? Determine the interest rate at which the project in Example would become feasible. Do higher interest rates make this project more feasible or less feasible? Would a longer life for the equipment make this project more feasible or less feasible? What would a price escalation in energy do to the project feasibility? The company uses an annual interest rate of 12 percent in making investment projections. The decrease in temperature of the water is 5 C, and the mean bulk temperature is 60 C.
Use SI units. Air enters a heat exchanger at a rate of cubic feet per minute at a temperature of 50 F and pressure of At what temperature does the air leave the heat exchanger?
The water enters at a temperature of 90 C, and the air is at 0. At what temperature does the water leave the exchanger?
Use Eq. A chiller is providing 5 tons of cooling to an air handler by cooling water transfer between the two devices. The chiller is drawing 3. Notice that the cooling tower is rejecting not only the energy removed from the cooled space but also the energy input to the chiller. Air is delivered to a room at 58 F and the same amount of air is removed from the room at 76 F in order to provide sensible cooling.
The room requires 0.
Assume an air density of A chiller is to provide 12 tons of cooling to a chilled water stream. Air is being furnished to a ft by ft by ft room at the rate of cfm and mixes thor- oughly with the existing air in the room before it is continuously removed at the same rate. How many times does the air change completely each hour air changes per hour? If cold outside air at 20 F is leaking into a ft by ft by ft room where the heating sys- tem is trying to maintain a comfortable temperature of 72 F, then the same amount of air might be assumed to be leaking out of the room.
If one were to estimate that this rate of leakage amounted to about 0. Natural ventilation is variable and depends on outside climatic conditions relative to the indoor environment.
The two driving forces that generate the airflow rate i. Natural ventilation may be difficult to control, with airflow being uncomfortably high in some locations and stagnant in others.
There is a possibility of having a low air-change rate during certain unfavourable climate conditions. There can be difficulty in controlling the airflow direction due to the absence of a well-sustained negative pressure; contamination of corridors and adjacent rooms is therefore a risk. Natural ventilation precludes the use of particulate filters. Climate, security and cultural criteria may dictate that windows and vents remain closed; in these circumstances, ventilation rates may be much lower.
Natural ventilation only works when natural forces are available; when a high ventilation rate is required, the requirement for the availability of natural forces is also correspondingly high.
Design manual for heating, ventilation, plumbing and air conditioning systems
Natural ventilation systems often do not work as expected, and normal operation may be interrupted for numerous reasons, including windows or doors not open, equipment failure if it is a high-tech system , utility service interruption if it is a high-tech system , poor design, poor maintenance or incorrect management.
Although the maintenance cost of simple natural ventilation systems can be very low, if a natural ventilation system cannot be installed properly or maintained due to a shortage of funds, its performance can be compromised, causing an increase in the risk of the transmission of airborne pathogens. These difficulties can be overcome, for example, by using a better design or hybrid mixed-mode ventilation.
Other possible drawbacks, such as noise, air pollution, insect vectors and security, also need to be considered.
Because of these problems, natural ventilation systems may result in the spread of infectious diseases through health-care facilities, instead of being an important tool for infection control. Table 2. Summary of advantages and disadvantages of different types of ventilation systems for hospitals. Mechanical versus natural ventilation for infection control The decision whether to use mechanical or natural ventilation for infection control should be based on needs, the availability of the resources and the cost of the system to provide the best control to counteract the risks.
For example, in the United Kingdom, the National Health Service policy tends to limit the adoption of mechanical ventilation to the principal medical treatment areas such as airborne infection isolation rooms, operating theatres and associated rooms.
Patient wards are usually not required to be mechanically ventilated and natural ventilation through opening windows is usually the most common solution Mills, Mechanical ventilation is expensive to install and maintain in isolation rooms. It often does not deliver the recommended ventilation rate and may fail to maintain negative pressure and may even be under positive pressure.
For example, Pavelchak et al. In addition, a number of problems related to the use of mechanical ventilation can arise from the lack of active collaboration between medical and technical personnel, which can also occur with natural ventilation.
For example ISIAQ, : building repair, without adequate control, may adversely affect nearby areas with high cleanliness requirements; sophisticated and expensive ventilation systems are often not properly integrated into the building design, and then maintained, or even used; and medical staff often have poor knowledge of the intended operational performance of ventilation systems, even with regard to their protective functions; systems that were originally properly designed can be misused to the extent that the intended functionality is reduced, leading to increased risks.
Other problems with mechanical ventilation include the loss of negative pressure differential in isolation rooms due to the opening of the doors; clogged filters; and adjacent, negatively pressurized spaces Fraser et al. The negative pressure, airflow path, air-change rate and local ventilation effectiveness were measured in selected isolation rooms in nine major hospitals Li et al.
Most of these problems can also occur with natural ventilation. A comparative analysis of mechanical and natural ventilation systems looked at eight hospitals in Lima, Peru Escombe et al. Seventy naturally ventilated clinical rooms for infectious patients were studied. These rooms were compared with 12 mechanically ventilated, negative-pressure respiratory isolation rooms built after The analysis found that: opening windows and doors provided a median ventilation of 28 ACH — more than double the recommended 12 ACH in mechanically ventilated, negative-pressure rooms, but relies on correct door and window operation; none of the rooms were normally operated with windows and doors open; and facilities built more than 50 years ago, characterized by large windows and high ceilings larger values of the volume to patient ratio , with windows and doors open, had greater ventilation than modern, naturally ventilated rooms 40 ACH versus 17 ACH.
However, these results should be used with caution. The ventilation rates in the analysis were reported without detailed information on climatic conditions, such as wind velocity and direction. The ventilation rate measurements were also affected by the carbon dioxide measurement device, and the fact that measurements were taken in buildings with multiple, inter-connected spaces, which would have affected the mixing conditions within the measured interior space.
Summary The use of outdoor air for natural ventilation, combined with natural cooling techniques and the use of daylight, have been essential elements of architecture since ancient times and up to the first part of the 20th century ASHRAE, b.
Classical architecture with H, L, T or U-shaped floor plans was used, together with open courts, limited plan depth and maximum windows sizes, to exploit natural ventilation and daylight. In recent times, natural ventilation has been largely replaced by mechanical ventilation systems in high- and middle-income countries.
Specific product lines include OmegaFlex flexible gas piping and SpacePak high velocity central air conditioning systems. Nuheat Industries Ltd. Radiantec Company - This Vermont radiant heating company has a very informative Web site that promotes the use of underfloor heat systems.
They produce water heaters, central warm air furnaces, air conditioners, heat pumps, swimming pool heaters and commercial boilers. Spruce Environmental Technologies Inc. Originally designed for use in sub-slab radon mitigation systems, Spruce inline fans are now used in bathroom and kitchen exhaust systems, dryer vent duct boosting, moisture removal, fresh air injection, make-up air supply, general ventilation and other indoor air quality applications.
Sanyo Heating and Air Conditioning - Manufacturers of ductless air conditioners, wall mounted air conditioners and heat pumps, recessed and suspended ceiling air conditioners and heat pumps, concealed duct heat pumps, through the wall units, and portable air conditioners. Stadler-Viega - Hydronic heating systems manufacturer whose products include floorheating systems, snowmelt systems, manifold plumbing systems, and radiator connection systems.
Manufacturers of commercial, industrial, and residential heating, air conditioning, and ventilation systems and controls. The company was acquired by American Standard in Unico, Inc. Conditioned air is sent at high velocity through flexible "mini-ducts" consisting of a main plenum that is either 7 or 9 inches in diameter and 2 inch supply tubing that runs to each supply outlet.Directory of Certified Product Performance - this database, from the Air-Conditioning and Refrigeration Institute ARI , offers applied and unitary certified performance ratings for air conditioners, air-to-air heat pumps, water-source heat pumps, and other residential and small commercial HVAC equipment.
Watts Radiant, Inc. The two-position or on—off action is the simplest and most common type. The room requires 0. Lakes and rivers are sometimes used for an energy sink.
Other problems with mechanical ventilation include the loss of negative pressure differential in isolation rooms due to the opening of the doors; clogged filters; and adjacent, negatively pressurized spaces Fraser et al.
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