Heating Ventilating and Air Conditioning: Analysis and Design
6th Edition
ISBN: 9780471470151
Author: Faye C. McQuiston, Jeffrey D. Spitler, Jerald D. Parker
Publisher: Wiley, John & Sons, Incorporated
expand_more
expand_more
format_list_bulleted
Videos
Textbook Question
Chapter 3, Problem 3.54P
Outdoor air is mixed with room return air to reduce the refrigeration load on a cooling coil. (a) For a space condition of 77 F (25 C) db and 68 F (20 C) wb, describe the maximum wet bulb and dry bulb temperatures that will reduce the coil load. (b) Suppose a system is designed to supply 10,300 cfm (5 m3/s) at 64 F (18 C) db and 63 F (17 C) wb to a space maintained at the conditions given in part (a) above. What amount of outdoor air at 68 F (20 C) db and 90 percent relative humidity can be mixed with the return air if the coil SHF is 0.6? (c) What is the apparatus dew point in part (b) above? (d) Compare the coil refrigeration load in part (b) above with the outdoor air to that without outdoor air. Assume sea-level pressure.
Expert Solution & Answer
Want to see the full answer?
Check out a sample textbook solution
Students have asked these similar questions
1. Moist air enters a refrigeration coil at 89 F dry-bulb temperature and 65 F thermodynamic wet bulb temperature at a rate of 14oo cu ft per min. The surface temperature of the coil is 55 F . If 3.5 tons of refrigeration are available, find the dry bulb and wet bulb temperatures of the air leaving the coil. Assume sea level pressure.
1) Given 753.06 kW electrical power supplied to a boiler when the temperature of the entering water is 20 C and the exiting temperature is 89 C. The flow of the pressured water is 2 Kg/s. There is a negligible pressure drop through this boiler and it operates at a constant pressure of 3 bars. The specific heat is c = 4,370 J/(Kg K). There is a 1.5(10^5) W rate of heat loss from the boiler during this process to a surrounding at 293.2 k.
Answer the following:
a) Calculate the exergy destroyed in the process below. The exergy of the fuel entering this process is 51.82 MJ/Kg. The dead state temperature is 293.2 K and pressure is 1 bar. The products of combustion leave this process at the dead state.
Process: 0.015 kg is the mass flowrate of fuel (natural gas, CH4) required to heat the water flow to the conditions of the problem above. if the electrical heating device is replaced with a gas fired boiler. The high heating value (HHV) of the fuel is 50.02 MJ/kg.
b) The utility providing the…
The following data refer to summer air conditioning of a building:
Outside design conditions
43 °C DBT, 27 °C WBT
Inside design condition
25 °C DBT, 50% RH
Room sensible heat gain
84000 kJ/h
Room latent heat gain
21000 kJ/h
BPF of cooling coil
0.2
The return air from the room is mixed with the outside air before entry to
cooling coil in the ratio of 4:1 by mass. Determine: (a) Apparatus dew
point of the cooling coil (b) Entry and exit conditions of air for cooling
coil (c) Fresh air mass flow rate and (d) Refrigeration load on the cooling
coil.
Chapter 3 Solutions
Heating Ventilating and Air Conditioning: Analysis and Design
Ch. 3 - A space is at a temperature of 75 F (24 C), and...Ch. 3 - Determine the humidity ratio, enthalpy, and...Ch. 3 - Suppose the air of Problem 3-2 is at a pressure...Ch. 3 - What is the enthalpy of moist air at 70 F (20 C)...Ch. 3 - The inside surface temperature of a window in a...Ch. 3 - What is the mass flow rate of dry air flowing at a...Ch. 3 - Determine the dew point of moist air at 80 F (27...Ch. 3 - A room is to be maintained at 72 F (22 C) db. It...Ch. 3 - Air is cooled from 80 F db and 67 F wb until it is...Ch. 3 - Conditions in a room are measured to be 80 F db...
Ch. 3 - The environmental conditions in a room are to be...Ch. 3 - Air enters a cooling coil at the rate of 5000 cfm...Ch. 3 - Air flowing in a duct has dry and wet bulb...Ch. 3 - Air is humidified with the dry bulb temperature...Ch. 3 - Air at 38 C db and 20 C wb is humidified...Ch. 3 - Two thousand cfm (1.0 m3/s) of air at an initial...Ch. 3 - Air at 40 F (5 C) db and 35 F (2 C) wb is mixed...Ch. 3 - Rework Problem 3-25, using Chart 1a, with the...Ch. 3 - The design cooling load for a zone in a building...Ch. 3 - Assume that the air in Problem 3-22 is supplied to...Ch. 3 - The sensible heat loss from a space is 500,000...Ch. 3 - Air enters a refrigeration coil at 90 Fdb and 75...Ch. 3 - A building has a total heating load of 200,000...Ch. 3 - Reconsider Problem 3-36 for an elevation of 5000...Ch. 3 - The system of Problem 3-34 has a supply air fan...Ch. 3 - An evaporative cooling system is to be used to...Ch. 3 - A cooling system is being designed for use at high...Ch. 3 - Consider a space heating system designed as shown...Ch. 3 - A variable-air-volume VAV cooling system is a type...Ch. 3 - Rework Problem 3-43 for an elevation of 5000 feet...Ch. 3 - The design condition for a space is 77 F (25 C) db...Ch. 3 - Rework Problem 3-45 for an elevation of 5000 feet...Ch. 3 - It is necessary to cool and dehumidify air from 80...Ch. 3 - Conditions in one zone of a dual-duct conditioning...Ch. 3 - Rework Problem 3-48 for an elevation of 5000 ft...Ch. 3 - A water coil in Problem 3-48 cools return air to...Ch. 3 - A multizone air handler provides air to several...Ch. 3 - Under normal operating conditions a zone has a...Ch. 3 - An interior zone of a large building is designed...Ch. 3 - Outdoor air is mixed with room return air to...Ch. 3 - Consider an enclosed swimming pool. The pool area...Ch. 3 - One particular zone served by a multizone air...Ch. 3 - A research building requires 100 percent outdoor...Ch. 3 - A space requires cooling in the amount of 120,000...
Knowledge Booster
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.Similar questions
- An ammonia refrigeration plant operates between a condensing temperature of 40°C and an evaporating temperature of –10°C. The vapour is dry at the end of compression. Only the following property values are given: 8. °C kJ/kg kJ/kg kJ/kg.K 40°C 371.5 1473 1.36 |-10°C 135.4 1433 0.544 The specific heat of NH3 vapour is 2.1897 kJ/kg.K. Calculate the theoretical coefficient of performance of the cycle.arrow_forwardAn engineer has been given the following data on a conditioned room: Sensible heat gain 30 kW Latent heat gain 15 kW Supply air 18°C Outdoor air 35°C DB and 24°C WB Desired room condition 27°C DB and 50% RH For ventilation, 15% is outdoor air, the balance of air requirement being recirculated from room conditioned with some portion being by-passed around the cooling coil. There is no reheater, the desired room state is attained by the by-passing of air. It is found that the apparatus DP temperature of coil is 10°C. Find the: a. tons of refrigeration; and b. mass flow rate of the time by-passed air.arrow_forward20 kg/s of steam enters a condenser at a pressure of 0.08 bar and quality of 0.68 and exits as saturated liquid at the same pressure. What is the mas flow rate of cooling water if the temperature rise of cooling water is 10 oC and its specific heat equals 4.2 kJ/kg.k?arrow_forward
- Problem 5.7 For air-conditioning system operation in cold weather, it is possible to introduce enough outdoor air to eliminate cooling by the air conditioner. This is called an economizer, and the control strategy is to vary the amount of outdoor air entering a plenum so that the outlet state is at the set point. For zone conditions of 75 F and 50 % and a constant circulating air flow rate of 25,000 cfm, determine the outdoor and return air flow rates necessary to maintain a 55 F supply air leaving the plenum. The outdoor air temperature varies between 10 F and 50 F and the relative humidity is always 30 %. Draw some conclusions from your results.arrow_forwardA 72 tons refrigeration system is used to produce chilled water from 20 ° C to 4 ° c. determine the volume flow of waterarrow_forwardThe sensible and latent heat gains to a room are 10 kW and 1 kW, respectively. The occupancy of the room is 12 people and the minimum fresh air allowance is 12 Li/s for each person. The outside summer design state is: 28ᵒC dry-bulb, 19.5 ᵒC wet bulb, 10.65 g/kg dry air. The room state is: 22 ᵒC dry-bulb, 50 percent saturation, 8.366 g/kg dry air, 43.39 kJ/kg dry air. Select a suitable air state, specify the states on and off the cooler coil and calculate the design cooling load. Analyse and check the cooling load. The temperature rise through the extract system is estimated as 0.5 ᵒC. A low velocity supply system is to be adopted and the temperature rise for supply fan power and duct heat gain is estimated 2ᵒ. Minimum fresh air requirement Plot the process on the psychrometric chart Determine the SHR. Contact Factor & Bypass Factor Total Cooling load.arrow_forward
- The sensible and latent heat gains to a room are 10 kW and 1 kW, respectively. The occupancy of the room is 12 people and the minimum fresh air allowance is 12 Li/s for each person. The outside summer design state is: 28ᵒC dry-bulb, 19.5 ᵒC wet bulb, 10.65 g/kg dry air. The room state is: 22 ᵒC dry-bulb, 50 percent saturation, 8.366 g/kg dry air, 43.39 kJ/kg dry air. Select a suitable air state, specify the states on and off the cooler coil and calculate the design cooling load. Analyse and check the cooling load. The temperature rise through the extract system is estimated as 0.5 ᵒC. A low velocity supply system is to be adopted and the temperature rise for supply fan power and duct heat gain is estimated 2ᵒ. Solve for the following: 1. Minimum fresh air requirement2. Plot the process on the psychrometric chart3. Determine the SHR.4. Contact Factor & Bypass Factor5. Total Cooling load.arrow_forwardQ2// A parallel - feed double - effect evaporator with equal vaporized for both, are fed with 5 Kg/s liquor with 10 percent for each effect. The overall heat transfer coefficients are 1.25 and 1.7 KW / m². K respectively. Steam is feed at 1.8630 bar and the second effect operates at 0.2856 bar. If the mass fraction from the 1st effect was 40 percent, What will be the total concentrated liquid from both? And compute the Temperature distribution for the system. Cp=4.18kJ/kg.karrow_forwardFind the mass of water, in kg, that can be cooled from 24 0C to -80C from a 10 tons refrigeration system for 15 hrs. ANSWER: 4197.930 kg A refrigeration system is used to cool water in the evaporator at 3 kg/s of water from 22 oC to ice. Find the tons of refrigeration required. ANSWER: 364.48805 TR A two stage cascade refrigeration system uses R-11 as the working substance. The evaporator is at -30 0C and the high pressure condenser is at 300C. The cascade condenser is a direct contact type. The refrigeration load is 24 tons. Given that, h2 = 393 kJ/kg; h6 = 408 kJ/kg. Find the mass flow rate in the low pressure loop. ANSWER: 0.4771 kg/sarrow_forward
- Q1: An engineer claimed that his device produces two streams of 1 am air (outlet 1) and 1.5 atm (outlet 2) at temperatures of 460 °R and 635 °R, respectively, if he enters 530 °R of the air at 5.1 atm. If the ratio of outlet 2 to outlet 1 is 0.6, justify the engineer's claim. Assume ideal gas process with a constant heat capacity of 0.24 Btu/lb.°R.arrow_forwardT, = 38°C rit = 2 kg/s T,= 10°C P= 140 kPa Saturated liquid P= 140 kPi mz = 0.42 kg/s T = 120°C P:= 140 kPa Above figure provides steady-state operating data for a mixing chamber in which entering liquid and vapor streams of water mix to form an exiting saturated liquid stream. Heat transfer from the mixing chamber to its surroundings occurs at an average surface temperature of 38°C. The effects of motion and gravity are negligible. Let To = 20°C, po = 1 bar. For the mixing chamber, determine, each in kl/s, (a) enthalpy of the stream 1, 2, and 3, (b) entropy of the stream 1, 2, and 3, (c) the rate of heat transfer between the chamber and environment, (d) the accompanying rate of exergy transfer due to the rate of heat transfer in (a). (e) the rate of exergy destruction.arrow_forwardAn ideal gas at 15 lbf/in2, 77°F flows horizontally at 516 ft/s into an adiabatic diffuser. It exits at 28 ft/s. Assume the heat capacity of the gas is constant.a. Determine the change in specific enthalpy (in Btu/lbm) and the outlet temperature if the gas is He.b. Repeat for R-125.c. Repeat for ozone (O3), which has a Molecular Mass of 47.9982 and a Cv0 of 0.1538 Btu/(lbm∙°R).arrow_forward
arrow_back_ios
SEE MORE QUESTIONS
arrow_forward_ios
Recommended textbooks for you
Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University Press
Mechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSON
Thermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEY
Mechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage Learning
Engineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY
Elements Of Electromagnetics
Mechanical Engineering
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Oxford University Press
Mechanics of Materials (10th Edition)
Mechanical Engineering
ISBN:9780134319650
Author:Russell C. Hibbeler
Publisher:PEARSON
Thermodynamics: An Engineering Approach
Mechanical Engineering
ISBN:9781259822674
Author:Yunus A. Cengel Dr., Michael A. Boles
Publisher:McGraw-Hill Education
Control Systems Engineering
Mechanical Engineering
ISBN:9781118170519
Author:Norman S. Nise
Publisher:WILEY
Mechanics of Materials (MindTap Course List)
Mechanical Engineering
ISBN:9781337093347
Author:Barry J. Goodno, James M. Gere
Publisher:Cengage Learning
Engineering Mechanics: Statics
Mechanical Engineering
ISBN:9781118807330
Author:James L. Meriam, L. G. Kraige, J. N. Bolton
Publisher:WILEY
Heat Transfer – Conduction, Convection and Radiation; Author: NG Science;https://www.youtube.com/watch?v=Me60Ti0E_rY;License: Standard youtube license