Energy Efficiency Flashcards

What does the term 'COP' stand for in HVAC system performance?

Answer: Coefficient of Performance

COP (Coefficient of Performance) is the ratio of useful heat or cooling energy output to the work energy input.

A heat pump has a heating COP of 3.5. What does this mean?

Answer: It delivers 3.5 units of heat for every 1 unit of electrical energy consumed

A COP of 3.5 means the heat pump delivers 3.5 units of thermal energy for every 1 unit of electrical energy input.

Which refrigerant property most directly impacts system energy efficiency?

Answer: Latent heat of vaporization

High latent heat of vaporization allows a refrigerant to absorb or release large amounts of heat during phase change, improving efficiency.

What is the purpose of an economizer cycle in a commercial HVAC system?

Answer: To use outdoor air for free cooling when conditions allow

An economizer uses cool outdoor air directly for space cooling, reducing or eliminating compressor operation when outdoor conditions are favorable.

What HVAC measure is most effective at reducing energy use in large commercial buildings during partial-load conditions?

Answer: Variable frequency drives (VFDs) on fans and pumps

VFDs reduce motor speed proportionally to load, cutting fan and pump energy consumption dramatically at partial loads.

Which of the following best describes 'sensible heat ratio' (SHR) in HVAC?

Answer: The fraction of total cooling load attributable to sensible (temperature) heat vs. total heat

SHR is the ratio of sensible cooling capacity to total cooling capacity (sensible + latent), indicating how much of the load is temperature-related vs. moisture-related.

How does subcooling refrigerant before the expansion valve improve system efficiency?

Answer: It increases the refrigerant's capacity to absorb heat in the evaporator

Subcooling ensures the refrigerant enters the expansion valve as a full liquid, increasing the enthalpy difference across the evaporator and improving system capacity.