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.]

A compressed air system has a total volume of 247,500 liters. During a 30-minute break in production (air compressor system turned off and no production demand for compressed air), the system pressure drops from
7 bar, gauge (700 kPa, gauge) to 5 bar, gauge (500 kPa, gauge). Calculate the leakage rate in the compressed air system.

If the initial design process includes group relamping, how can this reduce the number of lamps required to illuminate a space?

In a typical compressed air system, energy can be saved by which of the following actions?

Which of the following best describes a dead band in controls?