Energy Efficiency & Conservation Techniques Flashcards
7 cards from real EMP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Energy Efficiency & Conservation Techniques flashcards as text
An industrial facility has a motor operating at 90% of its rated load. The facility engineer recommends keeping this motor rather than replacing it with a premium efficiency model. From an energy management standpoint, when is this reasoning MOST valid?
Answer: When the motor's current efficiency is already near the premium efficiency level and replacement ROI is poor
If the existing motor already operates near premium efficiency ratings, the incremental savings from replacement may not justify the capital cost.
In steam systems, what is 'steam trap' failure in the open position, and why is it an energy problem?
Answer: Live steam continuously passes through to the condensate return, wasting thermal energy
A failed-open steam trap allows live steam to escape into the condensate return line, wasting significant thermal energy and fuel.
A hospital energy manager considers installing a combined heat and power (CHP) system. What is the PRIMARY energy efficiency advantage of CHP over grid electricity plus a separate boiler?
Answer: CHP simultaneously produces electricity and useful heat from one fuel source, achieving overall efficiencies of 70–90%
CHP captures waste heat that conventional power plants reject, achieving combined thermal and electrical efficiencies far above separate generation systems.
What is the 'payback cliff' risk when evaluating energy conservation measures (ECMs) using only simple payback?
Answer: Simple payback ignores the time value of money and long-term savings beyond the payback period
Simple payback ignores the time value of money and may reject measures with excellent long-term returns if their payback period exceeds an arbitrary threshold.
Which HVAC economizer control strategy is MOST energy-efficient for humid climates in the southeastern US?
Answer: Enthalpy-based control that limits economizer use to periods of low outdoor humidity
Enthalpy-based control prevents introducing humid outdoor air that would increase latent cooling loads, which is critical in humid southeastern climates.
An energy manager identifies that a refrigeration system's condenser coils are fouled with scale and debris. How does this condition affect energy consumption?
Answer: It increases compressor energy use because condensing pressure and temperature rise
Fouled condenser coils impede heat rejection, raising condensing pressure and forcing the compressor to work harder, increasing energy consumption.
An energy audit reveals that a facility's compressed air system operates at 120 psi, but end-use equipment only requires 90 psi. What is the approximate energy savings from reducing system pressure to 95 psi?
Answer: 12–15%
A rule of thumb is that every 2 psi reduction in compressed air pressure saves approximately 1% in compressor energy, so a 25 psi reduction saves roughly 12–15%.