CEM Certified Energy Manager: Steam, Industrial and Thermal Storage 3

Question 1

A facility uses a steam-to-process heat exchanger with an effectiveness of 0.82. If the maximum possible heat transfer is 500,000 BTU/hr, what is the actual heat transferred?

Accepted Answer

410,000 BTU/hr

Answer

Actual heat transfer = effectiveness × maximum possible = 0.82 × 500,000 = 410,000 BTU/hr.

Question 2

Which factor most significantly degrades heat transfer in a steam-heated process vessel over time?

Accepted Answer

Air and non-condensable gas accumulation

Answer

Non-condensable gases (air, CO₂) form an insulating layer on heat transfer surfaces, drastically reducing the overall heat transfer coefficient.

Question 3

For a chilled water ice-on-coil thermal storage system, what is the typical storage capacity per ton of ice produced?

Accepted Answer

12,000 BTU per ton of ice

Answer

One ton of ice stores 12,000 BTU (1 ton-hour = 12,000 BTU/hr × 1 hr), which is the latent heat of fusion for one ton of ice.

Question 4

A boiler's stack gas temperature is reduced from 450°F to 350°F by installing an economizer. Assuming 1°F stack temperature reduction saves approximately 0.5% fuel, the estimated fuel savings is:

Accepted Answer

50%

Answer

A 100°F reduction in stack gas temperature × 0.5% per °F = 50% savings; however, practical economizer savings are typically 1–5%; the rule states approximately 1% per 40°F, so 100°F ÷ 40°F × 1% = 2.5% fuel savings, making 5% the closest realistic answer.

Question 5

In industrial process heating, 'recuperation' refers to:

Accepted Answer

Recovering heat from exhaust gases to preheat combustion air

Answer

Recuperation is the process of using a heat exchanger to capture waste heat from exhaust gases and transfer it to incoming combustion air, improving furnace efficiency.

CEM - Certified Energy Manager Practice Test

CEM - Certified Energy Manager Practice Test

CEM Certified Energy Manager: Steam, Industrial and Thermal Storage 3