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NABCEP SHSI practice questions

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Question 1Solar Heating System Design and Sizing

In a solar water heating system, which component transfers heat from the collector loop to the domestic potable water while keeping the two fluids physically separate?

  1. The vacuum breaker
  2. The expansion tank
  3. The heat exchanger Correct answer.
  4. The tempering valve

Explanation

A heat exchanger isolates the collector loop fluid from potable water and transfers thermal energy across its walls. This separation is essential when glycol antifreeze or other treated fluids circulate in the collector loop. The other listed devices perform pressure, temperature, or safety functions rather than heat transfer.

Question 2Solar Heating System Design and Sizing

A solar thermal collector array is described as having a gross area of 6.0 m² and an aperture area of 5.1 m². Which area should be used when comparing the array's rated thermal output to manufacturer performance data?

  1. The absorber area, because it is always smaller than both other areas
  2. The aperture area, because performance ratings are referenced to the area that admits solar radiation Correct answer.
  3. The total roof area, because shading losses must be included
  4. The gross area, because it includes the frame and mounting hardware

Explanation

Collector efficiency and output ratings are conventionally referenced to aperture area, the glazed opening that admits solar radiation to the absorber. Gross area includes frames and flanges and therefore understates output per unit of active area. Comparing values requires matching the reference area used in the rating.

Question 3Solar Heating System Design and Sizing

A designer is sizing a drainback solar water heating system in a climate with hard freezes. Which design feature is most important to protect the collectors?

  1. Installing a larger expansion tank on the collector loop
  2. Adding a tempering valve at each fixture
  3. Sloping all collector piping and the collectors so they drain by gravity to a reservoir when the pump stops Correct answer.
  4. Increasing the collector tilt to 60 degrees from horizontal

Explanation

Drainback systems protect against freezing by allowing the collector loop to empty into a reservoir whenever circulation stops. This requires continuous slope back to the reservoir with no traps or low points where water could remain. The other measures address pressure control, scald protection, or winter yield rather than freeze protection.

Question 4Solar Heating System Design and Sizing

Which quantity is needed to convert a site's daily solar irradiation on the collector plane, expressed in kWh/m²/day, into an estimate of daily collector energy gain before losses?

  1. The controller set-point differential
  2. The collector aperture area Correct answer.
  3. The pipe insulation thickness
  4. The storage tank volume

Explanation

Irradiation per unit area multiplied by the collecting area yields incident energy in kWh per day. Losses and efficiency are applied afterward to estimate useful gain. Tank volume, insulation thickness, and controller settings affect performance but do not convert irradiance into incident energy.

Question 5Solar Heating System Design and Sizing

A solar collector loop uses a propylene glycol solution instead of water. What is the primary reason designers account for this in sizing calculations?

  1. The glycol solution has a higher boiling point that eliminates the need for a pressure relief valve
  2. The glycol solution has lower specific heat and higher viscosity, reducing heat transfer and increasing pump energy Correct answer.
  3. The glycol solution removes the need for a heat exchanger in a closed loop
  4. The glycol solution increases the collector aperture area available for absorption

Explanation

Glycol mixtures carry less heat per unit volume and resist flow more than water, so both collector efficiency and pumping power change. Designers adjust flow rates and select pumps accordingly. Glycol does not remove safety devices, alter collector geometry, or eliminate the need to separate loop fluid from potable water.

Question 6Solar Heating System Design and Sizing

A domestic hot water load is estimated at 200 liters per day raised from 10 °C to 55 °C. Using a water density of 1 kg/L and a specific heat of 4.19 kJ/kg·K, what is the approximate daily energy requirement?

  1. About 9.4 MJ
  2. About 18.9 MJ
  3. About 75.4 MJ
  4. About 37.7 MJ Correct answer.

Explanation

Energy equals mass times specific heat times temperature rise: 200 kg × 4.19 kJ/kg·K × 45 K ≈ 37,700 kJ, or about 37.7 MJ. This equals roughly 10.5 kWh per day. Doubling or halving the temperature rise or the volume produces the other listed values.

Question 7Solar Heating System Design and Sizing

In a solar domestic hot water system, what is the function of the differential thermostat controller?

  1. It measures the flow rate through the collector array
  2. It limits the temperature of water delivered to fixtures
  3. It starts the circulator when the collector is hotter than storage by a set margin and stops it when the advantage disappears Correct answer.
  4. It regulates the pressure in the collector loop by venting excess fluid

Explanation

A differential controller compares collector and storage temperatures and operates the pump only when useful heat can be collected. The on and off set points prevent short cycling. Pressure regulation, scald limiting, and flow measurement are handled by other devices.

Question 8Solar Heating System Design and Sizing

Which condition most directly reduces the useful solar fraction of a solar water heating system without changing the collector area or the load?

  1. Increased thermal losses from poorly insulated storage and piping Correct answer.
  2. A slight increase in the collector tilt angle
  3. A change from a differential controller to a set-point controller
  4. Use of a larger expansion tank

Explanation

Solar fraction is the share of load met by solar energy, so heat lost from storage and piping reduces the delivered solar contribution. Better insulation raises the fraction. Tilt adjustments and control or expansion-tank changes do not by themselves represent a direct loss mechanism.

Question 9Solar Heating System Design and Sizing

A designer must estimate the daily hot water load for a building with unknown occupancy. Which approach is most defensible for initial sizing?

  1. Assume the storage tank will be filled once per day regardless of occupancy
  2. Size the collectors for the maximum summer irradiance and ignore the load
  3. Use published per-person or per-fixture demand figures and document the assumption for later verification Correct answer.
  4. Use the collector area from a similar building without checking its load

Explanation

When actual demand data are unavailable, standard per-person or per-fixture demand values provide a transparent, adjustable basis for sizing. Documenting the assumption allows the design to be revised when real data arrive. Assuming full tank use or copying another building's collector area lacks a defensible load basis.

Question 10Solar Heating System Design and Sizing

A flat-plate collector array faces due south at a latitude of 40° N. For a year-round domestic hot water load, which tilt is generally recommended as a starting point?

  1. Approximately latitude plus 10 to 15 degrees Correct answer.
  2. Vertical, at 90 degrees
  3. Horizontal, at 0 degrees
  4. Approximately latitude minus 15 degrees

Explanation

Tilting collectors steeper than latitude biases collection toward the lower winter sun, which is often desirable for year-round hot water in heating-dominated loads. A common starting range is latitude plus 10 to 15 degrees. Shallow or horizontal mounting favors summer and can increase overheating and soiling losses.

Question 11Solar Heating System Design and Sizing

A pressurized glycol system must accommodate the expansion of loop fluid as it heats from cold fill to stagnation temperature. Which combination of devices is appropriate?

  1. A tempering valve plus a flow meter
  2. A properly sized expansion tank plus a pressure relief valve Correct answer.
  3. A differential controller plus a bypass valve only
  4. A vacuum breaker plus a check valve only

Explanation

Heated loop fluid expands, and a correctly sized expansion tank absorbs that volume change while maintaining pressure. A pressure relief valve provides a safety limit if pressure exceeds design. Tempering valves, flow meters, and controllers serve unrelated functions.

Question 12Solar Heating System Design and Sizing

How does the angle of incidence of sunlight on a collector surface affect the energy absorbed by the absorber?

  1. The absorbed energy increases with angle because light passes through more glazing
  2. The absorbed energy is independent of the angle of incidence for a glazed collector
  3. The absorbed energy decreases as the angle from perpendicular increases because the same beam spreads over a larger surface Correct answer.
  4. The absorbed energy depends only on ambient temperature, not on incidence angle

Explanation

Beam radiation striking at an angle spreads over a larger area, so the energy per unit of absorber surface falls. Glazing also reflects and absorbs more at oblique angles. This is why incidence angle modifiers are applied in performance modeling.

Question 13Solar Heating System Design and Sizing

A drainback system's pump must lift fluid from a reservoir to collectors mounted 8 m above. Which pump characteristic is most critical for reliable operation?

  1. A low wattage rating regardless of head
  2. Sufficient head at the design flow rate to overcome static lift plus piping friction Correct answer.
  3. The ability to run dry indefinitely without damage
  4. A high maximum temperature rating only

Explanation

The pump must overcome both the static elevation difference and the friction losses in the loop at the required flow. Selecting on wattage or temperature rating alone can leave the system unable to circulate. Running dry is a condition to avoid, not a design goal.

Question 14Solar Heating System Design and Sizing

A solar storage tank is sized much larger than the daily hot water draw. What is the most likely consequence?

  1. Higher collector efficiency because the tank stays cooler
  2. Increased standby losses and slower temperature recovery, reducing effective solar fraction Correct answer.
  3. Guaranteed freeze protection for the collectors
  4. Elimination of the need for a tempering valve

Explanation

Oversized storage increases the surface area and time over which heat is lost to the surroundings, and it can leave the tank stratified poorly. The result is lower delivered solar energy relative to the load. Oversizing does not provide freeze protection or remove scald protection requirements.

Question 15Solar Heating System Design and Sizing

When estimating the solar fraction for a proposed system, a designer finds the monthly load is high in winter and low in summer while solar availability peaks in summer. What does this imply for the annual design?

  1. The system may need to be sized on winter performance, with summer stagnation and overheating addressed separately Correct answer.
  2. The load profile has no effect on collector sizing
  3. The collector area should be increased until summer output equals winter load
  4. The system should be sized on summer output because that is when collectors perform best

Explanation

A mismatch between seasonal load and solar availability means summer surplus cannot offset winter deficit. Sizing should consider the limiting season, and the design must manage summer stagnation through controls, drainback, or heat rejection. Sizing on summer output alone would overstate useful contribution.

Question 16Solar Heating System Design and Sizing

What role does the collector loop flow rate play in the thermal performance of a liquid flat-plate system?

  1. Higher flow increases heat transfer from absorber to fluid but raises pump energy and piping losses Correct answer.
  2. Flow rate has no effect on collector efficiency as long as the pump runs
  3. Lower flow always improves efficiency by allowing the fluid to heat more
  4. Flow rate only affects freeze protection, not thermal performance

Explanation

Flow rate governs the temperature rise across the collector and the heat transfer coefficient between absorber and fluid. Higher flow reduces absorber temperature and losses but requires more pumping power. Designers balance these effects rather than assuming one extreme is always better.

Question 17Solar Heating System Design and Sizing

A building's hot water is supplied at 60 °C from storage, but fixtures require delivery no hotter than 49 °C. Which device should be installed and where?

  1. A vacuum breaker at the top of the collector loop
  2. A tempering valve at the outlet of the storage tank feeding the distribution system Correct answer.
  3. A check valve on the cold water inlet to the tank
  4. An expansion tank on the domestic cold water line

Explanation

A tempering or mixing valve blends hot storage water with cold water to limit delivery temperature and protect against scalding. It is installed downstream of storage and ahead of fixtures. Check valves, vacuum breakers, and expansion tanks perform different hydraulic safety functions.

Question 18Solar Heating System Design and Sizing

A designer is comparing a flat-plate collector and an evacuated-tube collector for a cold-climate application with moderate irradiance. Which characteristic most favors the evacuated-tube option?

  1. Simpler mounting on sloped roofs without rails
  2. Elimination of the need for a heat transfer fluid
  3. Lower initial cost per unit of aperture area
  4. Lower heat loss to the environment because of the vacuum between absorber and cover Correct answer.

Explanation

Evacuated tubes suppress conductive and convective losses between the absorber and the environment, which improves efficiency when the temperature difference to ambient is large. They are not generally cheaper or simpler to mount. They still require a heat transfer fluid and a complete loop.

Question 19Solar Heating System Design and Sizing

A solar hot water system uses a load-side heat exchanger in the storage tank. Which statement best describes the effect of a fouled or scaled heat exchanger on system performance?

  1. The collector loop temperature drops and efficiency rises
  2. The storage tank pressure increases, so no relief valve is needed
  3. Heat transfer improves because scale conducts heat efficiently
  4. Heat transfer is reduced, so the collector loop runs hotter and useful solar gain falls Correct answer.

Explanation

Scale and fouling add thermal resistance between the loop fluid and potable water, reducing the heat transfer coefficient. The collector loop must run hotter to deliver the same energy, which increases losses and lowers efficiency. Fouling does not improve conduction or remove safety requirements.

Question 20Solar Heating System Design and Sizing

A solar water heating system is being designed for a site with significant afternoon shading from a neighboring building. Which approach best addresses this constraint during sizing?

  1. Add a larger storage tank to compensate for the shading
  2. Increase collector tilt to vertical so the shading is avoided
  3. Model the hourly shading and reduce the assumed solar resource accordingly Correct answer.
  4. Ignore shading because annual averages smooth it out

Explanation

Shading losses depend on timing and geometry, so hourly modeling captures how much of the daily solar window is blocked. Annual averages can mask large seasonal or afternoon losses. Tilt changes and larger storage do not reliably compensate for blocked irradiance.

Question 21Solar Heating System Design and Sizing

A designer calculates that a proposed collector array would deliver more energy in summer than the load can use, leading to stagnation. Which design response is most appropriate?

  1. Remove the pressure relief valve to allow boiling
  2. Increase collector area to capture even more summer energy
  3. Reduce collector area or add a heat-dump or control strategy to manage excess energy Correct answer.
  4. Disable the differential controller in summer

Explanation

When summer output exceeds demand, the system risks stagnation and excessive temperatures. Reducing area or providing a controlled heat-dump or circulation strategy manages the surplus safely. Increasing area worsens the problem, and removing safety devices is never acceptable.

Question 22Solar Heating System Design and Sizing

A closed-loop glycol system has a design flow of 1.5 m³/h and a total loop pressure drop of 45 kPa. What pump head is required at that flow, ignoring safety margin?

  1. About 450 m of water column
  2. About 0.45 m of water column
  3. About 4.6 m of water column Correct answer.
  4. About 45 m of water column

Explanation

Head in meters of water equals pressure in pascals divided by the product of density and gravitational acceleration: 45,000 Pa ÷ (1,000 kg/m³ × 9.81 m/s²) ≈ 4.6 m. This conversion lets the designer match the pump curve at the required flow. The other values misplace the decimal or omit the conversion.

Question 23Solar Heating System Design and Sizing

A solar combisystem provides both domestic hot water and space heating. Which factor most complicates sizing compared with a DHW-only system?

  1. Collectors cannot be used for space heating
  2. Domestic hot water demand is always larger than space heating demand
  3. The space heating load varies strongly with weather and can be large and seasonal, changing the solar fraction month to month Correct answer.
  4. Space heating requires no storage in any combisystem

Explanation

Space heating loads are weather-driven and can dominate in winter, while DHW loads are comparatively steady. This seasonal and magnitude mismatch means solar fraction varies widely and storage and control must serve both loads. DHW-only sizing does not capture these interactions.

Question 24Solar Heating System Design and Sizing

A designer uses the f-chart method to estimate annual solar fraction. Which input most directly accounts for the thermal capacitance and loss characteristics of the storage tank in that method?

  1. The storage volume-to-collector-area ratio Correct answer.
  2. The controller set-point differential
  3. The collector tilt angle
  4. The pipe insulation thickness

Explanation

The f-chart method uses dimensionless parameters that include a storage capacity term, commonly expressed as storage volume per unit collector area. This ratio captures how storage size and losses affect the fraction of load met by solar. Tilt, insulation, and control settings are not the storage parameter in the method.

Question 25Solar Heating System Design and Sizing

A solar thermal system is designed with a collector loop that can reach stagnation temperatures above the rated limits of some components. Which design practice best protects the system?

  1. Specify the lowest-cost components available for the loop
  2. Rely on the controller to prevent stagnation under all conditions
  3. Reduce the pressure relief valve setting below normal operating pressure
  4. Select components rated for stagnation conditions and provide a means to shed or tolerate excess heat Correct answer.

Explanation

Stagnation can occur during power outages, pump failures, or full storage, so components in contact with the loop must be rated for the resulting temperatures and pressures. Providing heat-dump capability or drainback tolerance adds protection. Controllers cannot guarantee prevention, and lowering relief settings below operating pressure causes nuisance discharge.

Question 26Solar Heating System Design and Sizing

A designer is selecting a collector for a solar domestic hot water system that must deliver useful heat during winter in a cold, partly cloudy climate. Which collector characteristic most strongly favors an evacuated-tube collector over a flat-plate collector in this service?

  1. Higher optical efficiency at normal incidence than any flat-plate design
  2. Ability to operate without any freeze protection in the loop
  3. Low thermal loss from the absorber to ambient because the vacuum suppresses convection and conduction Correct answer.
  4. Lower installed cost per unit of absorber area

Explanation

The defining advantage of an evacuated-tube collector is that the vacuum between absorber and glass nearly eliminates convective and conductive losses, so the absorber stays hot even when ambient is cold. That raises efficiency in cold, low-irradiance, or high-delta-T conditions. Cost, normal-incidence optical efficiency, and freeze protection do not follow from the vacuum design.

Question 27Solar Heating System Design and Sizing

In a solar combisystem, why is sizing the collector array and storage more difficult than for a domestic hot water only system?

  1. Combisystems cannot use heat exchangers between the collector loop and storage
  2. Domestic hot water loads disappear entirely during the heating season
  3. Collector efficiency falls to zero whenever the space heating loop is active
  4. Space heating demand is seasonal and weather-driven, so the load profile varies far more across the year Correct answer.

Explanation

A combisystem must serve a domestic hot water load that is fairly constant plus a space heating load that is large, weather-dependent, and concentrated in winter. Matching collector output to that combined, highly seasonal profile is what makes sizing harder and drives oversizing risk in summer. The other statements misstate how combisystems are built and operated.

Question 28Solar Heating System Design and Sizing

A solar water heating system uses a load-side heat exchanger immersed in the storage tank. Which effect does this configuration have on the system?

  1. It separates potable water from collector fluid but introduces a temperature difference that lowers useful delivery temperature Correct answer.
  2. It allows the storage tank to be unpressurized while still supplying mains-pressure hot water directly
  3. It removes the need for an expansion tank on the collector loop
  4. It eliminates the need for a circulation pump in the collector loop

Explanation

An immersed load-side exchanger keeps collector fluid out of the potable water, which is essential for glycol loops. The penalty is a temperature approach: the tank must run hotter than the delivery setpoint, and the delivered water is cooler than the tank. Pumping, pressure, and expansion requirements are unaffected by the exchanger's presence.

Question 29Solar Heating System Design and Sizing

A designer is sizing a solar storage tank for a system serving a daily hot water draw of 300 liters. Which storage volume is most consistent with common design guidance for a liquid flat-plate domestic hot water system?

  1. About 3,000 to 6,000 liters
  2. About 7,500 liters
  3. About 300 to 600 liters Correct answer.
  4. About 30 to 60 liters

Explanation

Common guidance sizes solar storage at roughly one to two times the daily draw for a domestic hot water system, so 300 liters of draw points to roughly 300 to 600 liters. Undersized tanks swing in temperature and waste collector output; grossly oversized tanks lose heat and rarely reach useful temperature. The other ranges are an order of magnitude off in either direction.

Question 30Solar Heating System Design and Sizing

A designer is estimating the daily hot water load for a small office with a known count of fixtures but no measured consumption data. Which input is most appropriate to anchor the estimate?

  1. The stagnation temperature rating of the selected collector
  2. The peak instantaneous flow rate of the building's main water service
  3. A published per-person or per-fixture daily hot water allowance for office occupancy Correct answer.
  4. The collector aperture area divided by the storage volume

Explanation

When metered data are unavailable, loads are estimated from standard allowances tied to occupancy or fixture count, adjusted for the building type. Those allowances give a defensible daily energy figure that can be multiplied by the temperature rise and specific heat. The other quantities describe equipment or hydraulics, not daily draw.

Question 31Solar Heating System Design and Sizing

A collector array on a building is shaded by a neighboring structure every afternoon between 14:00 and 17:00. Which design response best preserves the system's useful solar fraction?

  1. Relocate or reorient the array so the afternoon sun is unobstructed, if the site allows Correct answer.
  2. Increase the storage volume to absorb the lost afternoon output
  3. Add a second circulation pump to increase flow during shaded hours
  4. Raise the collector tilt to vertical to reduce the shading angle

Explanation

Shading during high-irradiance afternoon hours removes energy that no downstream component can recover, so the primary fix is siting or orientation that avoids the obstruction. Storage and pumping changes redistribute or move heat but cannot replace irradiance that never reaches the absorber. Tilt changes shift the seasonal profile and do not reliably solve a fixed afternoon obstruction.

Question 32Solar Heating System Design and Sizing

A designer calculates that a proposed collector array would deliver more energy in summer than the load can use, causing stagnation. Which change best addresses this while keeping winter output?

  1. Increase the collector loop flow rate above design
  2. Reduce the array area or increase the storage volume to absorb surplus summer heat Correct answer.
  3. Reduce the collector tilt angle to lower summer incidence
  4. Remove the differential controller and run the pump continuously

Explanation

Surplus summer output relative to load is a sizing mismatch, and the standard remedies are trimming array area or enlarging storage so the excess is stored rather than stagnating the loop. Lowering tilt generally raises summer yield, which worsens the problem. Flow and control changes affect heat transfer and operation but not the seasonal energy balance.

Question 33Solar Heating System Design and Sizing

A closed-loop glycol system has a design flow of 1.5 m³/h and a total loop pressure drop of 45 kPa. What pump head must the circulator provide at that flow?

  1. 67.5 kPa
  2. 45 kPa Correct answer.
  3. 30 kPa
  4. 3 kPa

Explanation

The pump must overcome the total pressure drop of the loop at the design flow, so the required head equals 45 kPa. Flow rate is used to locate the operating point on the pump curve, not to divide the head. Multiplying or dividing by flow gives a number with no physical meaning here.

Question 34Solar Heating System Design and Sizing

In the f-chart method, which input most directly accounts for the thermal losses of the storage tank and the collector loop piping?

  1. The number of collectors in series
  2. The collector heat removal factor and the system loss coefficient embedded in the dimensionless parameters Correct answer.
  3. The potable water hardness
  4. The site latitude

Explanation

The f-chart correlations use dimensionless groups built from collector efficiency parameters and a system loss term that reflects how much of the collected heat actually reaches the load. Latitude, series count, and water chemistry are not direct inputs to those groups. This is why f-chart results are only as good as the loss assumptions behind them.

Question 35Solar Heating System Design and Sizing

A designer is comparing a drainback system with a pressurized glycol system for a site that experiences hard freezes. Which statement best describes the drainback system's advantage?

  1. The system requires a glycol mixture to prevent freezing in the collectors
  2. The system cannot use a heat exchanger between the loop and storage
  3. The drainback reservoir must be pressurized to mains pressure
  4. The collector loop drains by gravity when the pump stops, so no antifreeze is needed in the loop Correct answer.

Explanation

In a drainback system the collectors and exposed piping slope so that water drains to a reservoir whenever the pump stops, leaving nothing in the collectors to freeze. That removes the need for glycol and its maintenance. The reservoir is unpressurized and the loop normally uses a heat exchanger to protect potable water.

Question 36Solar Heating System Design and Sizing

A solar hot water system is being designed for a household whose daily draw is expected to be 250 liters at 55 °C. Which combination of collector area and storage is most consistent with typical residential practice?

  1. Roughly 0.5 m² of aperture with 1,000 liters of storage
  2. Roughly 10 m² of aperture with 5,000 liters of storage
  3. Roughly 20 m² of aperture with 100 liters of storage
  4. Roughly 4 to 6 m² of flat-plate aperture with 250 to 500 liters of storage Correct answer.

Explanation

Residential solar hot water systems typically use about 1 to 2 m² of collector per 50 to 100 liters of daily draw, paired with storage of one to two times the daily draw. For 250 liters that points to roughly 4 to 6 m² and 250 to 500 liters. The other combinations pair far too little collector with too much storage or the reverse.

Question 37Solar Heating System Design and Sizing

Which condition most directly reduces the useful solar fraction of a solar water heating system without changing the collector area?

  1. A shorter pipe run between collectors and storage
  2. A higher collector tilt in summer
  3. A larger daily hot water draw at the same delivery temperature Correct answer.
  4. A lower ambient temperature at night

Explanation

Solar fraction is the share of the load met by solar, so increasing the load while holding collector output fixed lowers the fraction. Nighttime ambient temperature and tilt shift output modestly but do not change the load. Shorter piping reduces losses and would tend to raise, not lower, the fraction.

Question 38Solar Heating System Design and Sizing

A designer is using the f-chart method to estimate annual solar fraction. Which input most directly accounts for the thermal losses of the storage tank and the collector loop piping?

  1. The potable water hardness
  2. The number of collectors in series
  3. The site latitude
  4. The dimensionless storage-loss and pipe-loss terms in the correlation Correct answer.

Explanation

The f-chart correlations include dimensionless groups that represent how much of the collected heat is lost from storage and piping before it reaches the load. Latitude, series count, and water chemistry are not direct inputs to those groups. This is why f-chart results depend on the loss assumptions behind them.

Question 39Solar Heating System Design and Sizing

A solar thermal system is designed with a collector loop that can reach stagnation temperatures above the rated limits of the loop components. Which design measure best protects the system?

  1. Reduce the collector tilt to lower stagnation temperature
  2. Specify components rated for stagnation temperature and provide a heat-dump or controller strategy Correct answer.
  3. Increase the storage volume beyond twice the daily draw
  4. Remove the expansion tank to reduce loop pressure

Explanation

Stagnation occurs when the pump stops and the absorber sits in full sun with no heat removal, so components must be rated for the resulting temperature and a dump or control strategy must shed excess heat. Tilt changes shift the seasonal peak but do not eliminate stagnation. Removing the expansion tank would create a dangerous pressure rise.

Question 40Solar Heating System Design and Sizing

A designer is calculating the daily energy needed to heat 200 liters of water from 10 °C to 55 °C. Which value is closest to the required energy, using a specific heat of 4.18 kJ/(kg·K) and a density of 1 kg/L?

  1. About 9.4 MJ
  2. About 75.2 MJ
  3. About 18.8 MJ
  4. About 37.6 MJ Correct answer.

Explanation

The energy is mass times specific heat times temperature rise: 200 kg × 4.18 kJ/(kg·K) × 45 K, which equals about 37,600 kJ or 37.6 MJ. That is roughly 10.4 kWh per day. The other values come from using half, double, or an incorrect temperature rise.

Question 41Solar Heating System Installation

In a closed-loop drainback solar water heating system, what is the primary function of the drainback tank?

  1. To provide a backup heat source during cloudy periods
  2. To receive the collector-loop fluid when the pump stops and allow air into the collectors Correct answer.
  3. To filter sediment from the heat-transfer fluid
  4. To store potable water for domestic use

Explanation

A drainback system uses gravity to empty the collectors whenever the circulator stops, so the fluid must have somewhere to go. The drainback tank holds that fluid volume and lets air enter and leave the collector loop, which also protects the loop from freezing.

Question 42Solar Heating System Installation

Which collector mounting practice best preserves the structural integrity of an asphalt-shingle roof during a solar heating installation?

  1. Attaching standoffs to the rafters and flashing each penetration above the shingle course Correct answer.
  2. Suspending the collector frame from the fascia board without roof penetrations
  3. Driving lag bolts through the shingles directly into the roof sheathing
  4. Sealing mounting feet to the shingle surface with construction adhesive only

Explanation

Roof-mounted collectors must transfer wind and snow loads into the structure, so fasteners should reach rafters or blocking. Proper flashing layered over the shingle course keeps each penetration watertight, which adhesive or unflashed bolts cannot do.

Question 43Solar Heating System Installation

For a flat-plate collector array in the northern hemisphere, what tilt is commonly recommended to maximize annual solar gain for a year-round domestic hot water load?

  1. Horizontal, 0 degrees from level
  2. Tilted 45 degrees steeper than the site latitude
  3. Tilted at an angle roughly equal to the site latitude Correct answer.
  4. Vertical, 90 degrees from level

Explanation

A tilt near the local latitude balances the higher summer sun against the lower winter sun and yields good annual collection. Steeper tilts favor winter production, while flatter tilts favor summer, so neither is optimal for a year-round load.

Question 44Solar Heating System Installation

What is the main reason glycol-water mixtures are used in closed-loop solar heating systems in cold climates?

  1. To increase the thermal conductivity above that of water
  2. To raise the boiling point so stagnation is eliminated
  3. To lower the freeze point of the heat-transfer fluid Correct answer.
  4. To prevent corrosion of copper absorbers

Explanation

An antifreeze solution depresses the freezing point so the loop fluid does not freeze and rupture piping in cold weather. Glycol also raises the boiling point somewhat, but it does not eliminate stagnation and it slightly reduces heat transfer performance.

Question 45Solar Heating System Installation

A solar storage tank is being connected to a collector loop and a backup electric element. Where should the collector loop return enter the tank to promote thermal stratification?

  1. At the same port as the domestic cold-water inlet
  2. Near the bottom of the tank Correct answer.
  3. At the mid-height of the tank
  4. Near the top of the tank

Explanation

Stratification keeps the hottest water at the top for draw-off and the coolest at the bottom for collection. Returning cool fluid from the collectors low in the tank preserves the temperature layers instead of mixing them.

Question 46Solar Heating System Installation

Which sensor placement is correct for the differential controller of a solar domestic hot water system?

  1. Both sensors clamped to the same pipe near the pump
  2. Collector sensor on the absorber plate near the outlet and storage sensor low in the tank Correct answer.
  3. Collector sensor in the drainback tank and storage sensor at the tank outlet
  4. Collector sensor on the glazing and storage sensor at the tank top

Explanation

The controller compares collector temperature with the coolest part of storage to decide when the pump should run. Placing the collector sensor on the absorber near the outlet and the storage sensor low in the tank gives the most representative differential.

Question 47Solar Heating System Installation

During commissioning of a pressurized closed-loop solar heating system, what is the purpose of pressure testing the collector loop before filling with glycol?

  1. To confirm the circulator can overcome pipe friction
  2. To verify the loop and fittings hold pressure without leaks Correct answer.
  3. To set the differential controller setpoints
  4. To measure the thermal expansion of the glycol

Explanation

A pressure test proves the assembled loop is leak-free before expensive heat-transfer fluid is added. Finding a joint failure with air or water is far cheaper and cleaner than discovering it after the system is charged with glycol.

Question 48Solar Heating System Installation

Which condition indicates that a solar thermal system should be protected against stagnation?

  1. The collector loop reaches high temperature when the pump is off and no hot water is being drawn Correct answer.
  2. The storage tank reaches its setpoint during a sunny afternoon
  3. The differential controller cycles the pump several times per hour
  4. The expansion tank bladder is at its precharge pressure

Explanation

Stagnation occurs when collectors sit in strong sun with no flow and no load, driving the absorber toward very high temperatures. Components such as glycol, seals, and piping must be rated for these conditions or protected by drainback, heat dump, or pump strategies.

Question 49Solar Heating System Installation

A pump in a closed-loop solar heating system is cavitating shortly after startup. Which cause is most likely?

  1. The collector sensor is reading too low
  2. The expansion tank precharge is too high
  3. The glycol concentration is too high
  4. Air is trapped in the loop or the pump inlet is starved Correct answer.

Explanation

Cavitation occurs when pressure at the pump inlet drops below the fluid's vapor pressure, often because air remains in the loop or the pump is not properly primed. Purging air and confirming adequate static pressure at the inlet resolve the problem.

Question 50Solar Heating System Installation

What is the primary role of an expansion tank in a pressurized glycol solar loop?

  1. To store hot water for evening use
  2. To separate air from the glycol before it reaches the collectors
  3. To increase flow rate through the collectors
  4. To absorb the volume change of the heat-transfer fluid as it heats and cools Correct answer.

Explanation

As the loop fluid heats, it expands and would otherwise raise pressure until the relief valve opens. The expansion tank provides a gas-charged cushion that accepts this volume change and keeps loop pressure within safe limits.