Question

In: Mechanical Engineering

1. True or false: heating air de-humidifies it.

 

1.      True or false: heating air de-humidifies it.

2.      What capacity (power) electric heater would be needed to raise the temperature of 300 cubic feet of concrete from 65° F to 150° F in 120 minutes? As this is electrical power, state response in watts or kilowatts.

3.      What would be the total cost of #2 fuel oil to operate a boiler expected to perform the task in question 2 if the boiler were operating at full fire with an efficiency of 80% and the cost of #2 fuel oil is $2.50/gallon?

4.      How does a chilled beam save energy in the operation of an HVAC system?

5.      What are the four major components of a vapor-compression refrigeration machine?

6.      What is the purpose of a VFD in an HVAC system?

 

Solutions

Expert Solution

1. False , on heating moisture content remains same.

2.Initial temp. = 65°F =18.3333°C , Final temp. =150°F = 65.556°C , Q = 300 ft^3 =8.495m^3 , density = 2400kg/m^3

Specific heat = 1000j/kg , time = 120min. = 7200sec.

Power of heater = m*cp* (T2-T1)/ (time ) = 8.495*2400*1000*(65.556-18.333)/ (120*60) = 133.72 kW

3. No of gallons required = Total required energy/ Heating value/ efficiency = 133.72*1000*120*60/133000/ 1055/0.8 = 8.6 gallons

Hence , cost = no of gallons* cost of 1 gallons = 2. 5* 8.6 = $21.5

4.Excessive fan energy is minimized in chilled beam which saves energy.

5. Four major components are - compressor, condensor, throttling valve, and Evaporator.

6. Based on demand , VFD adjusts the speex of fan or pump motor ,hence saves energy and prolonges equipment life.


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