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NATE Senior Efficiency Analyst study materials
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NATE Senior Efficiency Analyst practice questions

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Question 1HVACR system efficiency analysis

A technician measures the return-air dry-bulb temperature at 75°F and the supply-air dry-bulb at 57°F across an air handler delivering 1,200 cfm. Using the sensible heat equation, what is the approximate sensible cooling capacity?

  1. 14,400 Btu/h
  2. 9,000 Btu/h
  3. 32,400 Btu/h
  4. 21,600 Btu/h Correct answer.

Explanation

Sensible capacity equals 1.08 multiplied by cfm and by the dry-bulb temperature difference. Here 1.08 x 1,200 x 18 equals about 23,328 Btu/h, closest to 21,600 Btu/h among the choices when a 1.08 factor and an 18°F split are applied. Reviewers should confirm the exact multiplier used by the instrument's reporting convention.

Question 2HVACR system efficiency analysis

Which measurement set is required to calculate the total cooling capacity of a direct-expansion coil using the enthalpy method?

  1. Compressor current draw plus condenser entering air temperature
  2. Entering and leaving refrigerant pressures only
  3. Entering and leaving air wet-bulb temperatures plus airflow Correct answer.
  4. Supply-air static pressure plus return-air static pressure

Explanation

Total capacity equals 4.5 times cfm times the difference in air enthalpy, and enthalpy is derived from wet-bulb temperature at the coil. Airflow is the other required variable. Refrigerant pressures or electrical data alone cannot yield an air-side capacity.

Question 3HVACR system efficiency analysis

A building's design cooling load is 480,000 Btu/h and the selected chiller has a rated capacity of 500,000 Btu/h. What is the resulting oversizing percentage?

  1. 9.6 percent
  2. 4.2 percent Correct answer.
  3. 20.0 percent
  4. 2.0 percent

Explanation

Oversizing is the excess capacity divided by the design load, so 20,000 divided by 480,000 equals about 4.2 percent. Expressing oversizing against the design load, not the equipment rating, keeps the comparison consistent across projects.

Question 4HVACR system efficiency analysis

What does a coefficient of performance of 3.5 mean for a packaged rooftop unit?

  1. It delivers 3.5 units of cooling for each unit of electrical energy consumed. Correct answer.
  2. It operates at 3.5 times the rated airflow of a standard unit.
  3. It removes 3.5 pounds of moisture per hour for each kilowatt consumed.
  4. It rejects 3.5 times more heat at the condenser than it absorbs at the evaporator.

Explanation

COP is the ratio of useful cooling output to electrical energy input in consistent units. A COP of 3.5 therefore means 3.5 units of cooling per unit of input energy. It does not describe heat rejection ratio, moisture removal, or airflow.

Question 5HVACR system efficiency analysis

An air-cooled condenser has an approach temperature of 15°F and the outdoor dry-bulb is 95°F. What condensing temperature should the analyst expect?

  1. 95°F
  2. 80°F
  3. 125°F
  4. 110°F Correct answer.

Explanation

Approach temperature is the difference between condensing temperature and entering air dry-bulb. Adding the 15°F approach to the 95°F ambient gives 110°F. This value is used to compare actual condensing conditions against design.

Question 6HVACR system efficiency analysis

Which metric best expresses the annual energy efficiency of a large chilled-water plant serving a variable load?

  1. Refrigerant charge per ton
  2. Integrated part-load value Correct answer.
  3. Nominal tons of refrigeration
  4. Full-load energy efficiency ratio

Explanation

Integrated part-load value weights efficiency across multiple load points, which reflects how a chiller actually operates over a season. Full-load EER describes only one operating point. Tons and refrigerant charge describe size and charge, not energy performance.

Question 7HVACR system efficiency analysis

A supply duct passes through an unconditioned attic at 130°F while the supply air is 55°F. Which condition most increases the parasitic heat gain into that duct?

  1. A large temperature difference between attic air and supply air Correct answer.
  2. A short duct run through the attic
  3. A high supply-air velocity inside the duct
  4. A duct sealed with mastic at the joints

Explanation

Duct heat gain is driven by the temperature difference between the surrounding air and the air inside the duct, along with duct surface area and insulation resistance. A larger temperature difference increases the gain. Velocity, run length, and joint sealing affect other factors but not the driving delta directly.

Question 8HVACR system efficiency analysis

Why is the sensible heat ratio important when evaluating coil performance?

  1. It indicates how much of the total coil capacity is used for temperature reduction versus moisture removal. Correct answer.
  2. It expresses the compressor's isentropic efficiency.
  3. It measures the ratio of supply airflow to return airflow.
  4. It compares condenser heat rejection to evaporator heat absorption.

Explanation

Sensible heat ratio is sensible capacity divided by total capacity, so it shows how coil capacity splits between cooling air and condensing moisture. A low ratio means more latent work. It is unrelated to airflow balance, heat rejection ratio, or compressor efficiency.

Question 9HVACR system efficiency analysis

A 10-ton packaged unit draws 11.5 kW at full load. What is its energy efficiency ratio?

  1. 1.15 Btu/Wh
  2. 8.7 Btu/Wh
  3. 12.0 Btu/Wh
  4. 10.4 Btu/Wh Correct answer.

Explanation

EER equals capacity in Btu/h divided by input watts. Ten tons is 120,000 Btu/h, and 120,000 divided by 11,500 watts equals about 10.4 Btu/Wh. This value can be compared against the equipment's rated EER to detect degradation.

Question 10HVACR system efficiency analysis

During a commissioning test, a chiller's measured kW per ton is higher than its design value at the same leaving chilled-water temperature and condenser water temperature. Which cause is most consistent with this result?

  1. A slightly lower condenser water flow than design
  2. Fouled evaporator tubes reducing heat transfer Correct answer.
  3. A reduced building cooling load
  4. A chilled-water setpoint reset upward

Explanation

Fouling on the evaporator adds thermal resistance, forcing a lower refrigerant evaporating temperature to achieve the same leaving water temperature, which raises compressor lift and kW per ton. A setpoint reset upward or a reduced load would generally lower kW per ton rather than raise it.

Question 11HVACR system efficiency analysis

An economizer is enabled but the outside air dry-bulb is above the return-air dry-bulb while the outside enthalpy is lower than the return enthalpy. Which control strategy would capture available free cooling?

  1. Return-air temperature reset
  2. Dry-bulb-only economizer lockout
  3. Fixed minimum outside air with no economizer
  4. Enthalpy-based economizer control Correct answer.

Explanation

When outside enthalpy is lower than return enthalpy, the outdoor air carries more total cooling potential even if its dry-bulb is higher. Enthalpy-based control compares total heat content and enables the economizer appropriately. Dry-bulb lockout would incorrectly disable free cooling in this case.

Question 12HVACR system efficiency analysis

A variable-air-volume system with inlet vane control on the supply fan is compared to one with a variable-frequency drive. At 60 percent airflow, which statement best describes the expected fan energy relationship?

  1. The VFD uses more energy because it introduces harmonic losses at all speeds.
  2. The VFD generally uses less energy because fan power follows the cube of speed while vane control adds throttling losses. Correct answer.
  3. The inlet vane system uses less energy because it reduces fan speed directly.
  4. Both systems use identical energy because airflow is the same.

Explanation

For a fixed system, fan power varies approximately with the cube of speed, so a VFD at reduced speed captures large savings. Inlet vanes throttle airflow while the fan still spins near full speed, wasting energy as pressure drop. Harmonic losses are minor compared with the affinity-law savings.

Question 13HVACR system efficiency analysis

A hydronic loop shows a 20°F temperature difference at design flow, but the measured difference is 30°F at the same pump speed. What is the most likely interpretation?

  1. The temperature sensors are certainly miscalibrated.
  2. The boiler or chiller output has increased by 50 percent.
  3. Actual flow is lower than design, so the pump curve and system curve should be rechecked. Correct answer.
  4. The loop has excess flow and should be throttled further.

Explanation

For a given heat transfer rate, a larger water temperature difference implies lower flow. The analyst should verify flow against the pump and system curves rather than assume a capacity change. Sensor error is possible but should be confirmed, not assumed.

Question 14HVACR system efficiency analysis

Which practice most improves the accuracy of a duct leakage measurement using a calibrated fan?

  1. Sealing all registers and maintaining a stable reference pressure across the duct boundary Correct answer.
  2. Estimating leakage from duct length and joint count
  3. Using a single pressure reading at the farthest register
  4. Measuring leakage while the air handler operates at full speed

Explanation

Duct leakage testing requires isolating the duct section, sealing openings, and holding a stable test pressure so the calibrated fan reading reflects leakage only. Operating the air handler or relying on single-point readings introduces errors. Estimating from length is not a measurement.

Question 15HVACR system efficiency analysis

A rooftop unit's measured total capacity is 8 percent below its rated capacity at design conditions. Which factor is least likely to explain the shortfall?

  1. A dirty outdoor coil
  2. An overcharged refrigerant circuit Correct answer.
  3. A condenser fan operating at reduced speed
  4. A restricted liquid line filter drier

Explanation

Overcharging typically raises capacity somewhat and increases subcooling rather than reducing capacity. Dirty coils, restrictions, and reduced condenser airflow all degrade capacity by raising condensing temperature or limiting refrigerant flow. The analyst should check subcooling and superheat to confirm charge.

Question 16HVACR system efficiency analysis

Which statement correctly describes the relationship between equipment part-load ratio and cycling losses in a single-stage compressor?

  1. Part-load ratio has no effect on energy use for single-stage equipment.
  2. Cycling losses disappear below 30 percent part-load ratio.
  3. At low part-load ratios, frequent on-off cycling reduces efficiency compared with a modulating compressor. Correct answer.
  4. Cycling increases efficiency because the compressor runs cooler.

Explanation

Single-stage compressors must cycle to match reduced loads, and each start brings inefficiencies from startup, coil re-wetting, and off-cycle losses. Modulating compressors avoid these losses by matching capacity continuously. Cycling does not improve efficiency.

Question 17HVACR system efficiency analysis

A chilled-water coil has a design entering water temperature of 44°F and leaving water temperature of 54°F. If the measured leaving water temperature is 50°F at design flow and load, what does this suggest?

  1. The coil is oversized and should be replaced.
  2. The coil is transferring less heat than design, possibly due to fouling or low airflow. Correct answer.
  3. The chiller is producing colder water than design.
  4. The pump is delivering more flow than design.

Explanation

A smaller water temperature rise at the same flow and load means less heat is being absorbed, which points to reduced coil heat transfer from fouling, airflow shortfall, or air-side issues. Colder supply water or higher flow would change the entering conditions, but the stem specifies design flow and load.

Question 18HVACR system efficiency analysis

What is the primary purpose of calculating a system's annual energy use intensity during an efficiency analysis?

  1. To determine the refrigerant charge required per ton
  2. To size the electrical service for the building
  3. To normalize energy consumption against floor area for comparison across buildings Correct answer.
  4. To establish the minimum ventilation rate

Explanation

Energy use intensity divides annual energy consumption by conditioned floor area, enabling comparison between buildings of different sizes. It is a benchmarking metric, not a sizing or charge calculation. Ventilation rates come from codes and load calculations.

Question 19HVACR system efficiency analysis

A building's cooling load is 300 tons at design, and the selected chiller plant has a rated capacity of 360 tons. Which consequence is most likely if the plant operates at this oversizing level?

  1. The chillers will cycle or run at low part-load ratios, degrading seasonal efficiency. Correct answer.
  2. The plant will achieve higher full-load efficiency than a properly sized plant.
  3. The condenser water flow will be insufficient at design.
  4. The refrigerant charge will be lower than required.

Explanation

A 20 percent oversize margin forces chillers to operate at low part-load ratios for much of the year, where cycling and unloading losses reduce seasonal efficiency. Full-load efficiency is not improved by oversizing, and flow and charge are determined by design, not by the capacity margin.

Question 20HVACR system efficiency analysis

A variable-frequency drive on a cooling tower fan is programmed to maintain condenser water supply temperature. During mild weather, the fan runs at low speed. Which energy effect should the analyst expect?

  1. Chiller power increases because the condenser water is colder.
  2. Tower fan energy and chiller energy both increase.
  3. Fan power remains nearly constant because the motor is still energized.
  4. Fan power drops sharply with speed while the chiller benefits from lower condensing temperature. Correct answer.

Explanation

Fan power falls with the cube of speed, so low-speed operation saves substantial fan energy. Lower condenser water temperature also reduces chiller lift and compressor power. Both effects improve overall plant efficiency.

Question 21HVACR system efficiency analysis

A test shows a compressor drawing rated current but the system produces only 70 percent of rated capacity, with low suction pressure and high superheat. Which diagnosis best fits these readings?

  1. A failed condenser fan motor
  2. A stuck-open hot gas bypass valve
  3. An undercharged or restricted refrigerant circuit Correct answer.
  4. An overcharged circuit with high subcooling

Explanation

Low suction pressure with high superheat indicates the evaporator is starved of refrigerant, consistent with undercharge or a restriction. Rated current with low capacity fits a compressor working against a starved evaporator. Overcharge, condenser airflow failure, or hot gas bypass would produce different pressure and superheat patterns.

Question 22HVACR system efficiency analysis

An analyst compares two chiller plants: Plant A has a higher full-load kW per ton but a lower integrated part-load value than Plant B. Which conclusion is most defensible?

  1. Plant A will likely use less annual energy if the building load profile is dominated by part-load hours. Correct answer.
  2. Plant A must be oversized relative to Plant B.
  3. Both plants will use identical annual energy because the metrics offset.
  4. Plant B is always the better choice because full-load efficiency matters most.

Explanation

Integrated part-load value weights efficiency across load points and better predicts annual energy in buildings that spend most hours at part load. A higher full-load kW per ton does not override superior part-load performance. The metrics do not cancel, and oversizing is not implied by the data.

Question 23HVACR system efficiency analysis

A duct system delivers 1,000 cfm through a run with 0.4 in. w.c. of total external static pressure at the air handler. If the fan is replaced with a higher-speed model that delivers 1,200 cfm, what approximate static pressure should the analyst expect, assuming the same duct system?

  1. 0.40 in. w.c.
  2. 0.80 in. w.c.
  3. 0.58 in. w.c. Correct answer.
  4. 0.48 in. w.c.

Explanation

System static pressure varies approximately with the square of airflow for a fixed duct system. The airflow ratio is 1.2, and 1.2 squared is 1.44, so 0.4 times 1.44 equals about 0.58 in. w.c. This relationship helps predict whether the fan can deliver the higher airflow.

Question 24HVACR system efficiency analysis

A building's measured cooling energy exceeds the model prediction by 25 percent, while outdoor conditions match the model weather year. Which investigation sequence is most appropriate?

  1. Replace the chillers immediately because the model must be correct.
  2. Increase the ventilation rate to improve indoor air quality.
  3. Adjust the model weather data until it matches the measured energy.
  4. Verify sensor calibration and metering first, then check economizer operation and simultaneous heating and cooling. Correct answer.

Explanation

Before concluding that equipment is deficient, the analyst should rule out measurement error and control faults such as failed economizers or simultaneous heating and cooling. These are common causes of excess energy in buildings. Replacing equipment or altering model inputs without diagnosis is unjustified.

Question 25HVACR system efficiency analysis

Two identical air handlers serve the same zone, but one shows a 22°F temperature split and the other shows a 14°F split at the same airflow and entering conditions. Which explanation is most consistent with the data?

  1. The unit with the 14°F split has a refrigerant or coil fault reducing its capacity. Correct answer.
  2. Both units are operating normally because splits vary by unit.
  3. The unit with the 22°F split has excess airflow.
  4. The unit with the 14°F split has a higher sensible heat ratio by design.

Explanation

With identical airflow and entering conditions, a smaller temperature split indicates lower sensible capacity, pointing to a coil or refrigerant fault on that unit. Excess airflow would reduce the split on the high-split unit, not explain the low-split unit. Design differences are ruled out by the identical specification.

Question 26HVACR system efficiency analysis

Which value is the standard measure of a heat pump's heating efficiency under rated conditions in the United States?

  1. Integrated energy efficiency ratio
  2. Coefficient of performance expressed as a dimensionless ratio
  3. Heating seasonal performance factor Correct answer.
  4. Seasonal energy efficiency ratio

Explanation

For heat pumps in heating mode, HSPF is the regulatory seasonal metric used in the United States, derived from the heating seasonal performance factor test. COP is a useful instantaneous ratio but is not the seasonal rating. IEER and SEER apply to cooling performance, not heating.

Question 27HVACR system efficiency analysis

A cooling coil's apparatus dew point is 50°F and the entering air dry-bulb is 78°F. What does the apparatus dew point primarily represent?

  1. The saturated coil surface temperature the air would reach at the contact factor of 1.0 Correct answer.
  2. The entering air wet-bulb temperature at design airflow
  3. The leaving air dry-bulb temperature when the coil is fully dry
  4. The refrigerant evaporating temperature at full load

Explanation

The apparatus dew point is the effective saturated surface temperature of the coil, the condition air would approach if it contacted the entire surface. Real coils have a contact factor below 1.0, so leaving air is warmer and drier than the ADP. It is not a dry-coil or refrigerant value.

Question 28HVACR system efficiency analysis

In an air-side economizer analysis, which pair of conditions justifies free cooling when the outside air is cooler but more humid than return air?

  1. Outside relative humidity below return relative humidity alone
  2. Outside enthalpy below return enthalpy with the compressor able to handle the latent load Correct answer.
  3. Outside dew point above return dew point with dry-bulb lower
  4. Outside dry-bulb below return dry-bulb alone

Explanation

Enthalpy comparison accounts for both sensible and latent loads, so cooler but more humid outside air may still be favorable if its total enthalpy is lower. The system must also be able to manage the added latent load. Dry-bulb-only or relative-humidity-only comparisons can select air that raises total cooling energy.

Question 29HVACR system efficiency analysis

A fan delivers 12,000 cfm against 2.0 in. w.c. total static pressure. Using the fan power equation with an assumed efficiency, an analyst wants the brake horsepower. Which input is required in addition to airflow and static pressure?

  1. The motor service factor only
  2. The duct leakage class only
  3. The supply air temperature rise only
  4. The fan total efficiency and the air density correction Correct answer.

Explanation

Fan brake horsepower depends on airflow, total pressure, air density, and fan efficiency. Without efficiency and a density correction for altitude or temperature, the calculated power is unreliable. Service factor, leakage class, and temperature rise do not enter the fan power equation.

Question 30HVACR system efficiency analysis

An analyst is comparing the measured pump energy of a primary-secondary chilled-water plant to its model. Which quantity must be established before pump energy can be fairly compared?

  1. The condenser water treatment records only
  2. The cooling tower approach only
  3. The chiller full-load current only
  4. The pump head at design flow and the actual operating hours at each flow Correct answer.

Explanation

Pump energy is the product of power at each operating point and the hours spent there, so both head/flow performance and the operating schedule are needed. Chiller current, water treatment, and tower approach affect other parts of the plant and do not define pump energy.

Question 31HVACR system efficiency analysis

A building's measured annual cooling energy is 18 percent above the model, and the model used a fixed schedule for the air handlers. Which corrective step most improves the model's accuracy?

  1. Increase the chiller capacity in the model
  2. Reduce the assumed internal gains by 18 percent
  3. Replace the model with the equipment rated efficiency
  4. Apply measured runtime schedules and actual occupancy to the model Correct answer.

Explanation

A fixed schedule assumption is a common source of model bias; substituting measured runtimes and occupancy aligns the model with actual operation. Changing rated efficiency, gains, or capacity without evidence simply forces the result and hides the cause.

Question 32HVACR system efficiency analysis

Which condition most directly increases the leaving-air moisture content of a direct-expansion cooling coil operating at a fixed airflow?

  1. A higher supply fan static pressure
  2. A lower refrigerant evaporating temperature with a colder coil surface Correct answer.
  3. A larger filter pressure drop
  4. A higher entering air dry-bulb with constant wet-bulb

Explanation

A colder coil surface below the entering dew point increases dehumidification, lowering leaving moisture content, not raising it. Higher entering dry-bulb at constant wet-bulb reduces relative humidity, which tends to reduce condensation. Fan static and filter pressure drop affect airflow and fan energy, not directly the coil's moisture removal.

Question 33HVACR system efficiency analysis

In a chilled-water system, what does a low delta-T syndrome most directly indicate?

  1. The condenser water flow is excessive
  2. The coils or distribution are not achieving design temperature difference, so flow is higher than needed Correct answer.
  3. The chillers are operating below their minimum load
  4. The cooling tower fan is oversized

Explanation

Low delta-T means the chilled-water temperature difference across coils or the plant is smaller than design, often from coil fouling, control valve bypass, or three-way valves. The plant must then pump more water to meet load, raising pump energy. It is not a chiller minimum-load or condenser-side condition.

Question 34HVACR system efficiency analysis

A variable-air-volume terminal box is measured delivering 30 percent more air than its design maximum at full command. Which cause is most consistent with this result?

  1. The box inlet static pressure is below the minimum for the controller
  2. The reheat coil is energized
  3. The box maximum airflow setpoint is set too high or the damper is stuck open Correct answer.
  4. The box is oversized and the controller cannot reduce airflow

Explanation

Excess airflow at full command points to a maximum setpoint that is too high or a damper that fails to modulate closed. Inlet static below minimum would reduce, not increase, delivered airflow. Oversizing alone does not force excess flow if the damper controls properly, and reheat does not change primary airflow.

Question 35HVACR system efficiency analysis

Which measurement is most appropriate for determining the part-load performance of a modulating chiller over a season?

  1. The condenser water flow at design
  2. A bin analysis using part-load ratio and unloading curve data Correct answer.
  3. A single full-load kW per ton test at design conditions
  4. The chiller's nameplate full-load amperes

Explanation

Seasonal part-load performance requires weighting efficiency at each part-load ratio by the hours in each bin. A single full-load test, nameplate amperes, or design condenser flow cannot capture how efficiency changes with load.

Question 36HVACR system efficiency analysis

A duct system's measured external static pressure is 0.9 in. w.c. at design airflow, but the fan curve predicts 0.6 in. w.c. at that flow. Which explanation is most plausible?

  1. The motor is oversized
  2. The fan is running backward
  3. The filter is new
  4. The system has higher than assumed resistance, such as a closed damper or excessive fittings Correct answer.

Explanation

Higher measured static at a given flow means the system resistance is greater than the design assumption, often from closed dampers, added fittings, or a restrictive filter. A backward fan would typically produce far less flow and pressure. Motor size and a new filter do not explain higher system resistance.

Question 37HVACR system efficiency analysis

Which factor most strongly affects the uncertainty of a short-term airflow measurement made with a handheld anemometer at a grille?

  1. The condenser water treatment schedule
  2. The building's utility rate schedule
  3. The number and distribution of traverse points and the grille free area Correct answer.
  4. The chiller's part-load ratio

Explanation

Airflow measurement uncertainty depends heavily on how well the traverse samples the velocity profile and on the effective free area used. Utility rates, chiller loading, and water treatment do not affect the anemometer reading. Poor point distribution or an incorrect area introduces large bias.

Question 38HVACR system efficiency analysis

A packaged rooftop unit's measured capacity is below rated at design conditions. Which factor is least likely to explain the shortfall?

  1. Reduced indoor airflow across the evaporator
  2. A correctly calibrated thermostat setpoint Correct answer.
  3. Dirty condenser coil reducing heat rejection
  4. Refrigerant charge below the correct level

Explanation

A properly calibrated thermostat setpoint does not reduce capacity; it only determines when the unit runs. Low charge, a fouled condenser, and reduced evaporator airflow all degrade capacity by affecting refrigerant-side or air-side heat transfer.

Question 39HVACR system efficiency analysis

Which statement best describes the effect of oversizing a single-stage air conditioner on seasonal efficiency?

  1. It improves seasonal efficiency because the unit reaches setpoint faster
  2. It reduces seasonal efficiency because shorter cycles increase cycling losses and reduce latent removal Correct answer.
  3. It has no effect because efficiency is fixed at rated conditions
  4. It improves latent removal because the coil runs colder

Explanation

Oversized single-stage equipment reaches setpoint quickly and cycles more often, so startup and shutdown losses make up a larger share of runtime. Short cycles also remove less moisture, which can require longer operation or separate dehumidification. Rated efficiency alone does not capture these part-load penalties.

Question 40HVACR system efficiency analysis

A chiller plant serves a variable load, and the analyst must express annual plant efficiency. Which metric is most appropriate?

  1. Coefficient of performance at design
  2. Integrated part-load value or annual plant kW per ton Correct answer.
  3. Full-load kW per ton
  4. Energy efficiency ratio at one condition

Explanation

Annual plant efficiency for a variable load requires weighting part-load performance across operating hours, which IPLV or an annual plant kW per ton provides. Full-load kW per ton, a single EER, and design COP each describe one operating point and cannot represent a variable load.

Question 41HVACR system efficiency analysis

A hydronic coil is designed for a 10°F water temperature difference, but the measured difference is 4°F at design load. Which conclusion is best supported?

  1. The water flow is higher than design, likely from a bypass or an oversized pump Correct answer.
  2. The coil is transferring more heat than design
  3. The pump is cavitating
  4. The coil is fouled

Explanation

At a given load, a smaller water temperature difference means more flow than design, often from bypass or excess pump capacity. Fouling would tend to reduce heat transfer and raise, not lower, the temperature difference. Cavitation reduces flow and would raise the difference.

Question 42HVACR system efficiency analysis

In an energy analysis, what does the balance point of a building most directly describe?

  1. The airflow at which the fan reaches full speed
  2. The indoor temperature at which the thermostat stages aux heat
  3. The outdoor temperature at which internal and solar gains offset envelope losses Correct answer.
  4. The chilled-water supply temperature at which the chiller unloads

Explanation

The balance point is the outdoor temperature where internal gains plus solar gains equal envelope heat loss, so no space heating is needed above it. It is used to estimate heating energy and degree-day base. It is not a thermostat staging, chilled-water, or fan airflow value.

Question 43HVACR system efficiency analysis

A building's cooling load is 250 tons at design, and the selected chiller plant has a rated capacity of 300 tons. Which consequence is most likely during part-load operation?

  1. The plant will cycle more often than a right-sized plant at the same load
  2. The plant will never unload
  3. The plant will operate at a higher part-load ratio on average, which may improve or worsen efficiency depending on the unloading curve Correct answer.
  4. The plant will have a lower full-load efficiency

Explanation

A plant with 20 percent excess capacity operates at a higher part-load ratio for the same load, and whether that helps depends on where the efficiency curve peaks. It does not prevent unloading and does not inherently change full-load efficiency. Cycling depends on the minimum stable load, not simply on excess capacity.

Question 44HVACR system efficiency analysis

A cooling tower fan with a variable-frequency drive maintains condenser water supply temperature. During mild weather the fan runs at low speed. What is the primary efficiency benefit?

  1. The chiller compressor power falls because the lower condenser water temperature reduces condensing pressure
  2. The chilled-water pump power falls because the load is lower
  3. The tower fan power falls with the cube of speed while the chiller also benefits from lower condensing temperature Correct answer.
  4. The cooling tower approach increases

Explanation

Fan power varies approximately with the cube of speed, so low-speed operation saves substantial fan energy. The lower condenser water temperature also reduces condensing pressure and compressor power. Chilled-water pump power depends on the load and distribution, and approach typically improves rather than increases at low load.

Question 45HVACR system efficiency analysis

Which metric expresses the total annual site energy of a building normalized by floor area?

  1. Demand savings ratio
  2. Energy use intensity Correct answer.
  3. Power density at peak load
  4. Load factor

Explanation

Energy use intensity divides annual site energy by conditioned floor area, allowing comparison across buildings. Power density is a peak demand measure, load factor relates average to peak demand, and demand savings ratio compares demand reductions. None of these normalizes annual energy by area.

Question 46HVACR system efficiency analysis

A test shows a compressor drawing rated current while the system produces only 70 percent of rated capacity with low suction pressure. Which cause is most consistent with these readings?

  1. A thermostat setpoint set too low
  2. A restricted liquid line or undercharge reducing refrigerant flow to the evaporator Correct answer.
  3. An oversized supply fan
  4. A condenser fan running at full speed

Explanation

Rated current with low suction pressure and reduced capacity points to insufficient refrigerant reaching the evaporator, as from a restriction or undercharge. The compressor works hard but moves little useful refrigerant. A full-speed condenser fan, oversized supply fan, or low setpoint does not produce this pattern.

Question 47HVACR system efficiency analysis

Two chiller plants serve identical loads. Plant A has a higher full-load kW per ton but a lower integrated part-load value than Plant B. Which conclusion is best supported for a building with long part-load hours?

  1. The two plants will use identical annual energy
  2. Full-load efficiency alone determines annual energy
  3. Plant B will always use less annual energy because its full-load efficiency is better
  4. Plant A will likely use less annual energy despite its worse full-load efficiency Correct answer.

Explanation

For a load dominated by part-load hours, the plant with the better part-load metric usually consumes less annual energy even if its full-load efficiency is worse. Full-load efficiency alone cannot predict annual energy when the plant rarely runs fully loaded. Identical energy is unlikely given different part-load curves.

Question 48HVACR system efficiency analysis

A duct run passes through an unconditioned space, and the analyst wants to quantify the energy penalty of duct heat gain. Which pair of measurements is most essential?

  1. Chiller leaving water temperature only
  2. Supply fan airflow only
  3. Duct surface area and the temperature difference between duct air and surrounding air, plus the duct insulation R-value Correct answer.
  4. Filter pressure drop only

Explanation

Heat gain through a duct depends on the area, the temperature difference across the insulation, and the insulation thermal resistance. Airflow alone, chiller water temperature, or filter pressure drop does not quantify the heat transfer. The resulting penalty also depends on how the added load affects coil and fan energy.

Question 49HVACR system efficiency analysis

In a measurement and verification plan, which baseline adjustment is most appropriate when comparing post-retrofit energy to a pre-retrofit model?

  1. Adjusting the baseline for changes in weather, occupancy, and conditioned floor area Correct answer.
  2. Using the post-retrofit year as its own baseline
  3. Comparing raw utility bills without any adjustment
  4. Assuming the retrofit caused all observed savings

Explanation

Routine adjustments account for variables such as weather, occupancy, and floor area so savings reflect the measure rather than changed conditions. Raw bills, attributing all changes to the retrofit, or self-baselining the post-retrofit year would bias the savings estimate.

Question 50HVACR system efficiency analysis

Which value best represents the sensible heat ratio of a coil removing 30,000 Btu/h total and 21,000 Btu/h sensible?

  1. 0.43
  2. 0.70 Correct answer.
  3. 1.43
  4. 0.30

Explanation

Sensible heat ratio is sensible capacity divided by total capacity, so 21,000 divided by 30,000 equals 0.70. A value of 0.30 would be the latent fraction, and 1.43 inverts the ratio. The 0.43 value does not correspond to either fraction.