Certified Energy Auditor HVAC Systems and Performance 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?

Accepted 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.

Answer

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?

Accepted Answer

The air-side economizer.

Answer

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)?

Accepted 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).

Answer

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?

Accepted Answer

Kilowatts per ton (kW/ton)

Answer

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 O₂ (oxygen) reading in the flue gas. What is the most likely cause of this condition?

Accepted Answer

Excessive scale buildup on the water side of the heat exchanger tubes.

Answer

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 O₂ 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 O₂ reading.

Certified Energy Auditor Certification Practice Test

Certified Energy Auditor Certification Practice Test

Certified Energy Auditor HVAC Systems and Performance Questions and Answers