Certified Energy Auditor HVAC Systems and Performance Questions and Answers — Questions and Answers
Question 1: What is the primary difference between the SEER (Seasonal Energy Efficiency Ratio) and EER (Energy Efficiency Ratio) ratings for air conditioning systems?
- SEER is used for heating performance, while EER is for cooling.
- SEER ratings are only applicable to commercial rooftop units, whereas EER is for residential split systems.
- EER is calculated at a single set of outdoor and indoor conditions, while SEER represents performance over a typical cooling season with varying temperatures. (Correct answer)
- EER includes the energy consumed by the indoor air handler fan, while SEER does not.
Correct answer: EER is calculated at a single set of outdoor and indoor conditions, while SEER represents performance over a typical cooling season with varying temperatures.
EER measures efficiency at a single, fixed outdoor temperature (95°F), indoor temperature (80°F), and humidity (50%). SEER is a more comprehensive metric that averages the EER over a range of outdoor temperatures (from 65°F to 104°F) to simulate a typical cooling season, making it a better indicator of real-world performance.
Question 2: An energy auditor is inspecting a rooftop unit (RTU) on a commercial building in a temperate climate. They notice that on a cool, low-humidity day (55°F outside), the RTU's compressor is running to cool the interior space, which is at 74°F. What HVAC component is most likely malfunctioning or improperly controlled?
- The condenser fan motor.
- The air-side economizer. (Correct answer)
- The reversing valve.
- The thermostatic expansion valve (TXV).
Correct answer: The air-side economizer.
An air-side economizer is designed to use cool, low-humidity outside air for 'free cooling' when conditions are favorable, rather than running the mechanical cooling (compressor). In this scenario, the 55°F outside air is suitable for cooling the 74°F space, indicating the economizer is not functioning correctly and forcing the compressor to run unnecessarily. Common economizer failures include stuck dampers, failed actuators, or faulty sensors.
Question 3: Which of the following best describes the relationship between fan speed and power consumption in a Variable Air Volume (VAV) system equipped with a Variable Frequency Drive (VFD)?
- Power consumption is directly proportional to the change in fan speed (e.g., a 20% speed reduction yields a 20% power reduction).
- Power consumption is proportional to the square of the change in fan speed (e.g., a 20% speed reduction yields a 36% power reduction).
- Power consumption remains constant regardless of fan speed; only airflow changes.
- Power consumption is proportional to the cube of the change in fan speed (e.g., a 20% speed reduction yields a ~49% power reduction). (Correct answer)
Correct answer: Power consumption is proportional to the cube of the change in fan speed (e.g., a 20% speed reduction yields a ~49% power reduction).
According to the fan affinity laws, the power required by a fan is proportional to the cube of its rotational speed. Therefore, a small reduction in fan speed results in a much larger reduction in energy consumption. For example, reducing fan speed to 80% (a 20% reduction) reduces power consumption to approximately 0.8³, or 51.2% of the original, which is a 48.8% reduction.
Question 4: An energy auditor is evaluating the performance of a large water-cooled centrifugal chiller. Which of the following metrics is the most common and direct measure of its energy efficiency at full-load conditions?
- Kilowatts per ton (kW/ton) (Correct answer)
- Coefficient of Performance (COP)
- Energy Efficiency Ratio (EER)
- Integrated Part Load Value (IPLV)
Correct answer: Kilowatts per ton (kW/ton)
While COP and EER are also valid measures of efficiency, kilowatts per ton (kW/ton) is the standard industry metric for expressing the full-load efficiency of large chillers. It directly relates the electrical input power (kW) to the cooling output (tons of refrigeration). A lower kW/ton value indicates a more efficient chiller. IPLV is a measure of part-load efficiency, not full-load.
Question 5: During a combustion analysis of a natural gas boiler, an energy auditor measures a high stack temperature and a low Oâ‚‚ (oxygen) reading in the flue gas. What is the most likely cause of this condition?
- The boiler is cycling on and off too frequently.
- There is too much excess air in the combustion process.
- Excessive scale buildup on the water side of the heat exchanger tubes. (Correct answer)
- The fuel-to-air ratio is too rich (insufficient combustion air).
Correct answer: Excessive scale buildup on the water side of the heat exchanger tubes.
Scale buildup on the water side of the heat exchanger acts as an insulator, impeding heat transfer from the hot combustion gases to the water. This forces the heat to go up the stack, resulting in a high stack temperature. The low Oâ‚‚ reading indicates that the combustion air is being consumed, but the heat generated isn't being effectively transferred. A rich mixture would typically result in high CO, and excessive excess air would result in a high Oâ‚‚ reading.
Question 6: Which of the following is a primary energy-saving advantage of a Variable Refrigerant Flow (VRF) system compared to a traditional chilled water system?
- They eliminate the need for any outdoor equipment, reducing heat loss to the environment.
- They can provide simultaneous heating and cooling to different zones and recover heat from one zone to use in another. (Correct answer)
- They use natural gas as the primary energy source, which is typically cheaper than electricity.
- They operate at a much lower refrigerant pressure, significantly reducing the risk of leaks.
Correct answer: They can provide simultaneous heating and cooling to different zones and recover heat from one zone to use in another.
A key advantage of heat recovery VRF systems is their ability to serve different zones with opposite needs simultaneously. They can extract heat from a zone that requires cooling and transfer that heat via the refrigerant to a zone that requires heating. This heat recovery dramatically improves overall system efficiency compared to a system where one central plant provides either heating or cooling, and rejected heat is simply lost to the atmosphere.
Certified Energy Auditor HVAC Systems and Performance Questions and Answers
What is the primary difference between the SEER (Seasonal Energy Efficiency Ratio) and EER (Energy Efficiency Ratio) ratings for air conditioning systems?