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
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Chapter 3, Problem 3.52P
Under normal operating conditions a zone has a total cooling load of 120,000 Btu/hr (35 kW) with a SHF of 0.8. The space is to be maintained at 74 F (23 C) db and 50% relative humidity (RH). However, there are periods when the latent load is high and the SHF is estimated to be as low as 0.6. Assume that air enters the cooling coil at 8 F (29 C) db and 71 F (22 C) wb and the coil apparatus dew point is 48 F (9 C). (a) Devise a system and the associated psychrometric processes to cover the necessary range of operation. b) Define the various air states and show the processes on Chart ia. (c) Compute air-flow rate, coil load, minimum zone load, and any reheat that may be required. Assume constant air flow and standard sea-level pressure.
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An air-conditioning system operates at a total pressure of 1 atm and consists of a
heating section and a humidifier that supplies wet steam (saturated water vapor) at
100°C. Air enters the heating section at 10°C and 70 percent relative humidity at a rate
of 32 m /min, and it leaves the humidifying section at 20°C and 60 percent relative
humidity. Use data from the tables.
Sat. vapor
100°C
Heating
coils
Humidifier
10°C
Air
20°C
70%
60%
ymYmin
P=1 atm
Determine the temperature and relative humidity of air when leaves the heating section.
The temperature is
°C.
The relative humidity is
%.
In an uncomfortable summer day, the air is at 87OF and 80% relative humidity. A laboratory air conditioner is to deliver 1.00 x 103ft3/min of air at 55OF in order to maintain the interior air at an average temperature of 75OF and relative humidity of 40%.a. If the vent switch on the air conditioner is turned to the open position, outside air enters the unit as shown belown the air conditioner, the air is cooled to a temperature low enough to condense the necessary amount of water and reheated to 55OF, at which point it has the same absolute humidity as the room air. Determine the rate (lb/min) at which water is condensed, the temperature to which the air must be cooled to condense water at this rate, and the net tons of cooling required (Q), where 1 ton of cooling = -12,000 Btu/h.
Assume A = 87 οF, B = 80 %, C = 55 οF.
The design condition for a space is 77oF db and 50% relative humidity with 55oF db supply air at 90% relative humidity. A 50-ton, constant-volume space air- conditioning system uses face and bypass and water temperature control. Outdoor air is supplied at 95oF db, 60% relative humidity with a ratio of 1 lbm to 5 lbm re-circulated air. A part-load condition exists where the total space load is decreased by 50% and the SHF is increased to 90%. The outdoor air condition changes to 85oF db and 70% relative humidity. Assume sea-level conditions.
a) At full – load conditions:a. Show all the processes on a psychrometric chart.b. Determine the temperature must the air be supplied to the space at fullload conditions.c. Determine the apparatus dew point temperature at full load conditions.
b)At part – load conditions:a. Show all the processes on a psychrometric chart.b. Determine the temperature must the air be supplied to the space at partload conditions.c. Determine the apparatus dew point…
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...
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