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A variable-air-volume VAV cooling system is a type where the quantity of air supplied and the supply air temperature are controlled. The space is to be maintained at 75 F (24 C) db and 63 F (17 C) wb. Under design conditions, the total cooling load is 15.0 tons (53.0 kW) with a sensible heat factor of 0.6, and the supply air temperature is 60 F (16 C) db. At minimum load, about 1.8 tons (6.3 kW) with SHF of 0.8, the air quantity may be reduced no more than 80 percent by volume of the full load design value. Determine the supply air conditions for minimum load. Show all the conditions on a psychrometric chart for (a) English units and (b) SI units. Assume sea-level pressure.
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Chapter 3 Solutions
Heating Ventilating and Air Conditioning: Analysis and Design
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- 1. A variable-air-volume cooling system delivers air to a controlled space maintained at 24 C db and 17 C wb. Under design conditions, the total cooling load is 60 kW with a sensible heat factor of 0.60, and the supply air temperature is 16 C db. At minimum load, about 7.5 kW with SHF of 0.80, the air quantity may be reduced no more than 75% by volume of the full load design value. Calculate the minimum volume of air to be supplied to the space at minimum load, cu.m/min.arrow_forwardAir refrigeration systemarrow_forwardA boot strap cooling system of 20 tonnes is used in an airplane. The temperature and pressure conditions of atmosphere are 15°C and 0.9 bar. The pressure of air is increased from 0.9 bar to 1.2 bar due to ramming. The pressures of air leaving the main and auxiliary compressor are 3 bar and 4 bar respectively. The 50% of the total heat of air leaving the main compressor is removed in the first heat exchanger and 30% of their total heat of air leaving the auxiliary compressor is removed in the second heat exchanger. The cabin pressure is 1.02 bar and temperature of air leaving the cabin should be greater than 25°C. Assume ramming action, compression and expansion are isentropic. Take CP=1 kJ/kg.K and γ=1.4. Find: (A) Power required to take cabin load. (B) COP of the system.arrow_forward
- The by-pass factor of single cooling coil in an air-conditioner is 0.7. The by-pass factor, if thres such cooling colls with the same apparatus dew point are kept one behind the other, will bearrow_forwardAir Conditioningarrow_forwardA laboratory space to be maintained at 24oC DB and 50% RH experiences a sensible-cooling load of 42 kW and a latent load of 18 kW. Because the latent load is heavy, the air-conditioning system is equipped for reheating the air leaving the cooling coil. The cooling coil has been selected to provide outlet air at 9 oC and 95% RH. What is (a) the air rate and (b) the temperature of supply air? Air pressure is 101.325 kPaarrow_forward
- Determine the cooling capacity and the coefficient of performance of the air conditioning system?arrow_forwardThe by-pass factor of single cooling coil in an air-conditioner is 0.7. The by-pass lactor, if three such cooling coils with the same apparatus dew point are kept one behind the other, will bearrow_forwardThe mass flow rate of the refrigerant in a Single Stage Vapor Compression (SSVC) refrigeration system is 0.015 kg/s and the evaporating and condensing temperatures shall be -20°C and 50°C, respectively. Determine the refrigerating efficiency.arrow_forward
- The mass flow rate of the refrigerant in a Single Stage Vapor Compression (SSVC) refrigeration system is 0.015 kg/s and the evaporating and condensing temperatures shall be -20°C and 50°C, respectively. Determine the following: (1) cooling capacity in tons, (2) work of compressor in kW, (3) COP of the system, (4) EER of the system, and (5) refrigerating efficiency. refrigerant= R-32 h=200kJ/kg s=1.00kJ/(kg*K)arrow_forwardThe mass flow rate of the refrigerant in a Single Stage Vapor Compression (SSVC) refrigeration system is 0.015 kg/s and the evaporating and condensing temperatures shall be -20°C and 50°C, respectively. Determine the following: (1) cooling capacity in tons, (2) work of compressor in kW, (3) COP of the system, (4) EER of the system, and (5) refrigerating efficiency.arrow_forwardQuestion 4 A VRF cooling unit, having a cooling capacity of 25 kW, have the following COPS: COP100% = 369, COP75% = 5.72, COP50% = 6.65, COP25% = 8.16. Assume that the cooling unit has 13 hours of usage daily, having standby power of 200 W and energy tariffs of 41 cents per kWh. Using NEA's recommended AEC estimation, determine the annual energy cost up to 2 decimal points. Do not include "S" in your answer. Selected Answer: O 5,643.75 Correct Answer 5,584.12 0.01%arrow_forward
- Refrigeration and Air Conditioning Technology (Mi...Mechanical EngineeringISBN:9781305578296Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill JohnsonPublisher:Cengage Learning
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