Exam CEM Topic 2 Question 92 Discussion
Actual exam question for AEE's CEM exam
Question #: 92
Topic #: 2
Question #: 92
Topic #: 2
Natural gas costs $4.80/GJ. How much does it cost to heat 500 liters of water from 18°C to 50°C using a natural gas water heater with an efficiency of 85%? [The efficiency and fuel price are both based on HHV.
The specific heat of water (C) is 4.2 kJ/kg-°C.]
The specific heat of water (C) is 4.2 kJ/kg-°C.]
Suggested Answer: C Vote an answer
To calculate the cost of heating water using natural gas:
Step 1: Compute Energy Required to Heat the Water
Given:
* Mass of water = 500 L = 500 kg
* Temperature rise (#T) = 50°C - 18°C = 32°C
* Specific heat of water (Cp) = 4.2 kJ/kg-°C
Energy Required (Q)=m×Cp×#T
=500×4.2×32
=67,200 kJ=67.2 MJ
Step 1: Compute Energy Required to Heat the Water
Given:
* Mass of water = 500 L = 500 kg
* Temperature rise (#T) = 50°C - 18°C = 32°C
* Specific heat of water (Cp) = 4.2 kJ/kg-°C
Energy Required (Q)=m×Cp×#T
=500×4.2×32
=67,200 kJ=67.2 MJ
by semerewolde12 at Jul 09, 2026, 12:19 PM
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