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Heating Ventilating And Air Conditioning Analysis And Design 6th Edition Faye C. McQuiston, Jerald D. Parker, Jeffrey D. Spitler - Solutions

=+v15-2 cycle. The condensing temperature is 48 C, and the evaporating temperature is -18 C. The power input to the cycle is 2.5 kW, and the mass flow rate of refrigerant is 0.05 kg/s. Deter-mine (a) the heat rejected from the condenser, (b) the coefficient of performance, (c) the enthalpy at the
=+15-3.tionless flow. Find the system hp/ton.Consider a reciprocating compressor operating with R-134a. Refrigerant enters the cylinder at
=+15-4.20 psia (138 kPa) and 20 F (-7 C), but leaves the evaporator saturated at 0.5 F (-18 C). The vapor is discharged from the cylinder at 180 psia (1.24 MPa). Compute the volumetric effi-ciency for (a) a clearance factor of 0.03, and (b) a clearance factor of 0.15. (c) Compare the mass flow
=+15-5.with R-134a. The proposed operating condition for the compressor is 100 F condensing tem-perature and 40 F evaporating temperature. It is estimated that the refrigerant will enter the expansion valve as a saturated liquid, that vapor will leave the evaporator at a temperature of
=+45 F. and that vapor will enter the compressor at a temperature of 55 F. Assume a compressor volumetric efficiency of 70 percent and frictionless flow. Calculate the refrigeration capacity in tons.
=+Consider the compressor of Fig. 15-7. (a) Construct the pressure-enthalpy diagram for a con-
=+15-6.densing temperature of 130 F (54 C) and an evaporating temperature of 45 F (7 C). (b) What is the heat transfer rate in the evaporator and the power input? (c) Suppose that the load on the evaporator decreases to 110.000 Bru/hr (32 kW), and find the evaporating temperature and power input.
=+15-7. Refer to Problem 15-6a, and sketch the capacity and power curves for 130 F (54 C) from Fiz.
=+15-7. (a) Sketch the capacity curve for the evaporator, assuming its capacity is proportional to the evaporating temperature in the ratio 4000 Bru/(hr-F) (2.1 kW/C), (b) The evaporator loud decreases to 130,000 Btu/hr (38 KW) while the condensing temperature decreases to 115 F
=+(46 C). Sketch the new evaporator capacity curve. (c) Suppose in part (a) that the evaporator operating conditions remain fixed but the condensing temperature increases to 145 F (63 C)What will the capacity and evaporating temperature be?
=+15-8.A refrigeration system using the compressor described in Fig. 15-7 is designed to operate with a condensing temperature of 115 F with an evaporating temperature of 50 F when the outdoor ambient is 95 F. After the system is put into operation, the evaporator pressure is measured to be 69
=+what might be done to obtain the design conditions.
=+15-9.Saturated R-22 at 45 F (7 C) enters the compressor of a single-stage system. Discharge pres-sure is 275 psia (1.90 MPa). Suction valve pressure drop is 2 psi (13.8 kPa). Discharge valve pressure drop is 4 psi (27.6 kPa). Assume the vapor is superheated 10 F (5.6 C) in the cylinder during the
=+(b) pumping capacity in Ibm/min (kg/s) for 20 ft3/min (9.44 L/s) piston displacement, and
=+(c) horsepower (KW) requirement if the mechanical efficiency is 80 percent.
=+15-10.Consider the single-stage vapor-compression cycle shown in Fig. 15-35. Design conditions using R-134a are:92=30,000 Btu/hr P, = 200 psia P1 = 60 psia saturated P3 - P4 = 2 psi P2 = 55 psia C=0.04 T = 60 F 77m= 0.90 PD= 9.4 cfm
=+(a) Determine W. q ., and m ... and sketch the cycle on a P-i diagram. If the load q, decreases to 24.000 Btu/hr and the system comes to equilibrium with P2 = 50 psia and 72 = 50 F.
=+(b) determine W. q ,,, and m, and locate the cycle on a P-i diagram.
=+15-11.Consider an ordinary single-stage vapor-compression air-conditioning system. Because of clogged filters the air flow over the evaporator is gradually reduced to a very low level. Explain
=+how the evaporator and compressor will be affected if the system continues to operate,
=+15-12.
=+A vapor-compression cycle is subject to short periods of very light load; it is not practical to shut the system down. During these periods of light load, moisture condenses from the air flow-ing over the evaporator and freezes. Suggest a modification to the system to prevent this condition.
=+A vapor compression cycle is subject to occasional overload that leads to the tripping of cir-
=+15-1.3.cuit breakers. Explain how the system can be modified to prevent compressor overload with-out shutting the system off.
=+A saturated liquid aqua-ammonia solution at 220 F and 200 psia is throttled to a pressure of
=+18.14.10 psia. Find (a) the temperature after the throttling process, and (b) the relative portions of liquid and vapor in the mixture after throttling A solution of ammonia and water at 180 F. 100 psia, and with a concentration of 0.25 lbm
=+15-15 ammonia per Ibm of solution is heated at constant pressure to a temperature of 280 F. The vapor is then separated from the liquid and cooled to a saturated liquid at 100 psia. What are the tem-perature and concentration of the saturated liquid?
=+It is proposed to use hot water at 180 F (82 C) from a solar collector system to operate a sim-
=+15-16.ple absorption cycle. Compute the maximum possible coefficient of performance, assuming an environment temperature of 100 F (38 C) and an air-cooled evaporator with the air tempera-ture at 75 F (24 ℃).
=+Saturated water vapor at 50 F is mixed in a steady flow process with a saturated lithium
=+15-17.bromide-water solution having a concentration of 0.60 Ibml.iBr per Ibm of mixture. The mass of the liquid solution is five times the mass of the water vapor mixed. The mixing process occurs at constant pressure. Find (a) the concentration of the resulting mixture,
=+(b) the heat that must be removed, in Btu per Ibm of the total mixture, if a saturated liquid solution is produced.
Find the function v(t) that satisfies the following differential equation and initial condition:103 dvðtÞdtþ vðtÞ ¼ 0; vð0Þ ¼ 50V
Find the function i(t) that satisfies the following differential equation and the initial condition:500 diðtÞdtþ 25 k iðtÞ ¼ 0; ið0Þ ¼ 15mA
For nearly a century, visual displays of alternating signals on televisions, oscilloscopes, radar screens, and so on were seen using a cathode ray tube or CRT. In Europe, it was called the Braun tube named after its German inventor Ferdinand Braun in 1897. However, it was J. J. Thomson, an English
The current through a circuit element is 50 mA. Find the total charge and the number of electrons transferred during a period of 100 ns.
Figure 1–5 shows a circuit formed by interconnecting five devices, each of which has two terminals. A voltage and current variable has been assigned to each device using the passive sign convention. The working variables for each device are observed to be as follows: (a) Find the missing
The working variables of a set of two-terminal electrical devices are observed to be as followsUsing the passive sign convention, find the magnitude and sign of each unknown variable and state whether the device is absorbing or delivering power. D DEVICE 1 +10 V -3 A ?| DEVICE 5 DEVICE 2 DEVICE 3
1–1 Express the following quantities to the nearest standard prefix using no more than three digits.(a) 20;000;000 Hz(b) 1025W(c) 0:333 × 10−8 s(d) 33 × 10−12 F
1–2 Express the following quantities to the nearest standard prefix using no more than three digits.(a) 0:0022H(b) 50:7×105 J(c) 82:251 × 104 C(d) 5633 Ω
1–3 An ampere-hour (Ah) meter measures the time integral of the current in a conductor. During an 8-hour period,a certain meter records 4500 Ah. Find the number of coulombs that flowed through the meter during the recording period.
1–4 Electric power companies measure energy consumption in kilowatt-hours, denoted kWh. One kilowatt-hour is the amount of energy transferred by 1 kW of power in a period of 1 hour. A power company billing statement reports a user’s total energy usage to be 1500 kWh. Find the amount of energy
1–5 Fill in the blanks in the following statements.(a) To convert capacitance from nanofarads to microfarads, multiply by .(b) To convert resistance from megohms to kilohms, multiply by .(c) To convert voltage from millivolts to volts, multiply by .(d) To convert frequency from megahertz to
1–6 Which of the two entries is larger?(a) 1000 microfarads or 0:0003333 F(b) 0:005 × 106 Hz or 66 kHz(c) 0:333 pC or 810 fC(d) 220 millihenries or 0:150H
1–7 Awire carries a constant current of 30 μA. How many coulombs flow past a given point in the wire in 500 ms?
1–8 The net positive charge flowing through a device is q t ð Þ=20+4t mC. Find the current through the device.
1–9 Figure P1–9 shows a plot of the net positive charge flowing in a wire versus time. Sketch the corresponding current during the same period of time. Charge (C) 30 20 10 1 2 3 4 5 6 Time 0 (s) -10 -20L FIGURE P1-9
1–10 The net negative charge flowing through a device varies as q t ð Þ=2:2 t2 C. Find the current through the device at t =0, 0:5, and 1 s.
1–11 A cell phone charger outputs 9:6 V and is protected by a 50-mA fuse. A 2-W cell phone is connected to it to be charged. Will the fuse blow?
1–12 For 0 ≤ t ≤ 5 s, the current through a device is iðtÞ = 3t A.For 5 < t ≤ 10 s, the current is iðtÞ = 30−3t A, and iðtÞ = 0A for t > 10 s. Sketch iðtÞ versus time and find the total charge flowing through the device between t = 0 s and t = 10s.
1–13 The charge flowing through a device isq t ð Þ=1−e −1000t μC.What will the current be after 1:6094 ms?
1–14 The 12-V automobile battery in Figure P1–14 has an output capacity of 100 Ah when connected to a head lamp that absorbs 200 W of power. The car engine is not running and therefore not charging the battery. Assume the battery voltage remains constant.(a) Find the current supplied by the
1–15 The current through a device is zero for t < 0 and is iðtÞ = 5e−3 t Afor t ≥ 0. Find the charge qðtÞ flowing through the device for t ≥ 0.
1–16 A string of holiday lights is protected by a ½-A fuse and has 100 LED lights, each of which is rated at 30 mW. How many strings can be connected end-to-end across a 120-V circuit without blowing a fuse?
1–17 When illuminated the i – v relationship for a photocell is i = ev − 12 A. For v = −2, 2, and 3 V, find the device power and state whether it is absorbing or delivering power.
1–18 A new 6-V alkaline lantern battery delivers 237:5 kJ of energy during its lifetime. How long will the battery last in an application that draws 20mA continuously. Assume that the battery voltage is constant.
1–19 The maximum current allowed by a device’s power rating is limited by a 25-mA fuse. When the device is connected to a 9-V source, what is the maximum power the device can dissipate?
1–20 Traffic lights are being converted from incandescent bulbs to LED arrays to save operating and maintenance costs. Typically, each incandescent light uses three 100-W bulbs, one for each color R, Y, G. A competing LED array consists of 61 LEDs with each LED requiring 9 V and drawing 20mA of
1–21 Two electrical devices are connected as shown in Figure P1–21. Using the reference marks shown in the figure, find the power transferred and state whether the power is transferred from A to B or B to A when(a) v = +12 V and i = −1:2A(b) v = + 80 V and i = + 10mA(c) v = −240 V and i =
1–22 Figure P1–22 shows an electric circuit with a voltage and a current variable assigned to each of the six devices. The device voltages and currents are observed to be as follows:Find the power associated with each device and state whether the device is absorbing or delivering power. Use the
1–23 Figure P1–22 shows an electric circuit with a voltage and a current variable assigned to each of the six devices. Use power balance to find v4 when v1 = 20V, i1 = −2A, p2 = 20W, p3 = 10W, i4 = 1 A, and p5 = p6 = 2:5W. Is device 4 absorbing or delivering power?
1–24 In Figure P1–24 the voltage v2 is 10 V and v4 is 5 V. Find the voltage associated with each element. + 1/2 + V4 + V3 + VI + V5 FIGURE P1-24
1–25 For t ≥ 0, the voltage across and powerabsorbed by a twoterminal device are vðtÞ = 2e −t V and pðtÞ = 40e −2t mW.Find the total charge delivered to the device for t ≥ 0.
1–26 Repeat Problem 1–22 using MATLAB to perform the calculations. Create a vector for the voltage values, v =[15 5 10 −10 20 20], and a vector for the current values, i = [−1 1 2 −1 −3 2]. Compute the corresponding vector for the power values, p, using element-by-element
1–27 Using the passive sign convention, the voltage across a device is vðtÞ = 240 cosð314tÞ V and the current through the device is iðtÞ = 4 sinð314tÞA. Using MATLAB, create a short script (m-file) to assign a value to the time variable, t, and then calculate the voltage, current, and
1–29 AC to DC Converter A manufacturer’s data sheet for the converter in Figure P1–29 states that the output voltage is vdc = 12 V when the input voltage vac = 120 V. When the load draws a current idc = 15A, the input power is pac = 300 W. Find the efficiency of the converter. iac ide + + AC
1–30 Charge-Storage Device A capacitor is a two-terminal device that can store electric charge. In a linear capacitor, the amount of charge stored is proportional to the voltage across the device. For a particular device the proportionality is qðtÞ = 10 −7vðtÞ. If vðtÞ = 0 for t < 0 and
1–31 Computer Data Sheet A manufacturer’s data sheet for a notebook computer lists the power supply requirements as 7:5A@5V, 2A@ 15 V, 2:5A@ −15 V, 2:25A@−5 V, and 0:5A@ 12 V. The data sheet also states that the overall power consumption is 115 W. Are these data consistent? Explain.
1–32 Light Source Comparison Today people have three competing light sources for home use.This problem asks you to determine the trade-offs between the costs of the three types of lights. In this example, all three emit the same amount of light (lumens). The following table shows the salient
=+11-1. A free isothermal jet is discharged horizontally from a circular opening. There is no nearby sur-face. The initial velocity and volume flow rate are 850 ft/min (4.3 m/s) and 300 cfm (142 L/s).respectively. Estimate (a) the throw for terminal velocities of 50, 100, and 150 ft/min (0.25,
=+11-2.A free jet is discharged horizontally below a ceiling. The initial velocity and volume flow rate are 1100 ft/min (5.6 m/s) and 300 cfm (165 L/s). The initial jet temperature is 100 F (38 C).whereas the room is to be maintained at 72 F (22 C). Compute the throw and the difference in
=+11-3.To ventilate a space, it is desired to discharge free isothermal jets vertically downward from a ceiling 24 ft (7.3 m) above the floor. The terminal velocity of the jets should be no more than 50 ft/min (0.25 m/s), 6 ft (1.83 m) above the floor. Determine a reasonable diameter and initial
=+11-4.A free isothermal jet of 125 cfm (60 L/s), 6 in. (15 cm) diameter, is discharged vertically from the floor toward a ventilation hood 12 ft (3.7 m) above the floor. Approximately what capacity must the hood exhaust fan have to capture all of the airstream at the entrance to the hood?
=+11-5.A given space requires a very large quantity of circulated air for cooling purposes. What type of diffuser system would be best? Why?
=+11-6.Consider a single-story structure with many windows. What would be the best all-around air-distribution system for (a) the northern part of the United States and (b) the southern states?Explain.
=+11-7. A space has a low but essentially constant occupancy with a moderate cooling load. What type of air-diffuser system would be best for heating and cooling? Explain, Assume that the space is on the ground floor.
=+11-8.Consider a relatively large open space with a small cooling load and low occupancy located in the southern part of the United States. What type of air-distribution system would be bes?Explain.
=+11-9.A 10 in. (25 cm) round ceiling diffuser from Table 11-4 is to be used with 650 cfm (307 LA)Compute the total pressure, throw, and noise criteria for this application.
=+11-10.A 4 in. (10 cm) linear diffuser from Table 11-3 is to be used with 150 cfm/ft (0.23 m3/(s-mi ina 6 ft (1.8 m) total length. Compute the total pressure, noise criteria, and throw for this application.
=+11-11. A model 28, H-48 T-bar diffuser from Table 11-6 is to be used with 270 cfm (127 L/1), Find the total pressure, throw, and noise criteria for this application.
=+11-12.A linear floor diffuser is required for a space with an air supply rate of 600 cfm (283 L/s), The room has a 12 ft ceiling and a cooling load of 40 Btu/(hr-ft-) (126 W/m-). (a) Select a diffuser from Table 11-3 for this application. (b) Determine the total pressure and NC for your selection
=+11-13.Suppose a round ceiling diffuser is to be used in the situation described in Problem 11-12. The room has plan dimensions of 26 × 28 ft (8× 8.5 m). (a) Select a diffuser from Table 11-4 for.this application. (b) Determine the total pressure and NC for the diffuser,
=+11-14.Assume that two high sidewall diffusers are to be used for the room described in Problems
=+11-12 and 11-13, and they are to be installed in the wall with the longest dimension. (a) Select suitable diffusers from Table 11-5. (b) Determine the total pressure and NC for the diffusers.
=+11-15.Select a suitable return grille from Table 11-7 for the room described in Problem 11-12. Total pressure for the grille should be less than 0.10 in. wg (25 Pa), and one dimension should be 12 in. (30 cm).
=+11-16.Select a perimeter-type diffuser system for the building shown in Fig. 11-13. It is general office space.
=+11-17.Select a round ceiling diffuser system for the building in Problem 11-16.
=+11-18.Select a high sidewall diffuser system for the building in Problem 11-16.
=+11-19.Select return air grilles for the building in Problem 11-16. Assume that the return system must be placed in the attic and each room must have a return.
=+11-20.Consider a room with a 20 ft exposed wall that has two windows. The other dimension is 42 ft(12.8 m). The room is part of a variable air-volume system. (a) Lay out and select T-bar diffuser from Table 11-6 if the room requires a total air quantity of 800 cfm (380 L/s) and the maximum total
=+11-21. Consider a 18 x 30 ft (5.5 x 9 m) room in the southwest corner of a zone. There are windows on both exterior walls, and the peak air quantity for the room is 1000 cfm (470 L/s). (a) Lay out and select T-bar diffusers from Table 11-6 using a maximum total pressure of 0.15 in. wg(38 Pa). (b)
=+11-22. Select perimeter-type diffusers for the room shown in Fig. 11-14. The perimeter distribution is for the heating system that is secondary to the VAV cooling system. The perimeter system requires 1800 cfm (850 L/s) evenly distributed along the exterior walls. Locate the diffusers on the
=+11-23.Select round ceiling diffusers for the room shown in Fig. 11-14. The room has a cooling load of 112.000 Btu/hr (32.8 kW) and a design air supply rate of 2600 cfm (1225 L/s). Locate the diffusers on the floor plan. A maximum total pressure of 0.12 in. wg (30 Pa) is allowed.
=+11-24.Select T-bar (slot) diffusers for the room shown in Fig. 11-14, and locate them on the floor plan.The cooling load is 100,000 Btu/hr (29.3 kW), and the design air supply rate is 3200 cfm(1500 L/s). The maximum allowable total pressure is 0.10 in. wg (25 Pa).
=+11-25.Select and locate a return grille(s) for the room of Problem 11-23. A quiet system is desirable.
=+11-26. Select and locate return grilles for the room of Problem 11-24. Limit the NC to less than 30.
=+12-1. A centrifugal fan is delivering 2000 cfm (0.94 m/s) of air at a total pressure differential of
=+1.9 in. wg (473 Pa). The fan has an outlet area of 0.84 ft- (0.08 m2) and requires 1.1 hp (0.8 kW) shaft input. Compute (a) the total power, (b) the total efficiency, (c) the fan static pres-sure, and (d) the static efficiency.
=+12-2.The fan of Problem 12-1 is operating at 1000 rpm. The fan speed is increased to 1200 rpm.Compute the capacity, the static and total pressure, and the shaft power at the higher speed,
=+12-3 The fan represented by the curves in Fig. 12-8 is operating at a speed of 800 rpm. (a) Construct

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