HPAC 2021: Our Monthly Quiz

The heating, piping, and air conditioning industry has been a fixture of ‘civilized’ life on Planet Earth for well over a century, and the focus of this venerable publication since 1929. The inventive and problem-solving work of engineers, manufacturers, and building owners have continuously helped to expand the impact of the HVACR industry beyond creature comforts and food and data storage to life and death issues like greenhouse gas reductions and, especially today, virus mitigation.

 

With all that in mind, HPAC Engineering here welcomes you to join us on a fun monthly ride through the milestones, innovations, people, places, problems and products that have come to define this industry and your work. Hopefully, there may even be a chuckle or two along the way. So, here goes, and see below for your chances to win a $50 Amazon gift card.

Photo Credit: Thinkstock

With an assist from Honolulu-based test prep service Engineering Pro Guides, here are five more problems to test your skills this fall.

 

A counter-flow heat exchanger has 5,000 cfm of air entering the coil at 40°F. Water is provided to the heat exchanger with entering conditions of 75°F and leaving conditions of 65°F. What is the logarithmic mean temperature difference (LMTD) if the air leaving the coil is at 55°F?

17°F

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30°F

36°F

A pipe has an outer diameter of 1.315 in. and an inner diameter of 1.049 in. The thermal conductivity of the pipe material is 20 Btu/h-ft-°F. The inner convective heat transfer coefficient between the fluid within the pipe and the inner pipe walls is 150 Btu/h-ft2-°F. The outer convective heat transfer coefficient between the outer pipe and the ambient air is 50 Btu/h-ft2-°F. What is the overall heat transfer coefficient per length of pipe?
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42 Btu/h-ft-°F

85 Btu/h-ft-°F

107 Btu/h-ft-°F

There are 15 workers in a large, air-conditioned warehouse, which houses fruits and vegetables. The workers drive (2) 10 HP electric golf carts throughout the warehouse. The motor has an efficiency of 80% and the golf carts only used 10% of the time (assume a 0.1 usage factor). In addition, the full capacity of the motor is not used. Assume an 80% load factor. Measured in Btu/hr, what is the heat load from the golf carts alone?

1,800

2,500

3,260

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An office is maintained at space conditions of 75 F and 50% RH. There are 15 office workers located in a 2,000-sf office building. Each worker has their own computer with flat screen. What is the total heat load from the people to the space? (Btu/hr)

1,750

3,000

3,750

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An existing clear class window with an inefficient film and a shading coefficient of 0.9 is being replaced by a new low-e glass with a shading coefficient of 0.6 and a transmissivity of 0.75. What will be the percent reduction in solar heat gain by switching to the newer glass? (Assume an area of 18 square feet and an SCL of 40 F.)

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54%

66%

72%