Nevada C-21E Solar Air Conditioning Contractor Examination

Under NAC 624.380, what work does a Nevada C-21E Solar Air-Conditioning license authorize?

• AInstallation of collectors, piping, storage, and other equipment that convert solar energ…
• BInstallation of photovoltaic modules and inverters that power conventional vapor-compress…
• CInstallation of unglazed collectors used only to heat swimming pools
• DService of any refrigeration compressor regardless of whether solar collectors are present

Which tubing is the usual choice for a pressurized solar collector loop that can stagnate well above 250°F on a Nevada roof?

• APEX-A rated 180°F at 100 psi
• BType L copper tube
• CSchedule 40 PVC
• DFlexible elastomeric hose listed only to 140°F

Per UPC 2018 Table 313.3, what is the maximum horizontal hanger spacing for 1-inch soldered copper tube on a solar hydronic run?

• A4 feet
• B6 feet
• C10 feet
• D12 feet

Why is PEX generally prohibited on the collector side of a closed-loop solar air-conditioning system even though it is listed for some hydronic heating?

• APEX cannot be insulated
• BCollector stagnation and generator-loop temperatures routinely exceed PEX pressure-temper…
• CPEX is not allowed anywhere under the UPC
• DPEX cannot be joined with mechanical fittings

A copper solar collector supply is connected to a steel storage-tank fitting. What UPC joint practice prevents galvanic corrosion at that connection?

• AA dielectric union or other approved dielectric fitting
• BA PVC coupling
• CSoft solder only, with no dielectric
• DLeaving a 1-inch air gap in the pipe

On the chilled-water piping that leaves a solar-driven absorption chiller, where must the vapor retarder be placed?

• AAgainst the pipe wall, under the insulation
• BOn the outside of the insulation, sealed at every joint and penetration
• COnly on the chiller evaporator barrel
• DVapor retarders are not used on chilled-water pipe

How must collector-loop piping be pitched on a drainback solar air-conditioning system?

• ALevel, so the pump does not have to work against gravity
• BContinuously back to the drainback reservoir so the collectors and roof piping empty when…
• CUp toward the collectors so air is trapped at the array
• DOnly the return pipe is pitched; the supply may hog

Per UPC 2018 Table 313.3, what is the maximum horizontal hanger spacing for 3/4-inch solvent-cemented CPVC used on a lower-temperature hydronic run?

• A32 inches
• B3 feet
• C6 feet
• D10 feet

Per UPC 2018 Table 313.3, what is the maximum horizontal hanger spacing for 3/4-inch PEX?

• A32 inches
• B3 feet
• C4 feet
• D6 feet

Per UPC 2018 Table 313.3, what is the maximum horizontal hanger spacing for 1-inch threaded steel pipe carrying water?

• A6 feet
• B8 feet
• C10 feet
• D12 feet

What piping arrangement is used to give each parallel collector row nearly the same flow without individual balancing valves?

• ADirect-return headers, with the first collector taking both the first supply and first re…
• BReverse-return (Tichelmann) headers, so each row sees approximately the same developed le…
• CA single series string of every collector in the array
• DOpen discharge of each row into a common gutter

Compared with parallel collector piping, piping several collectors in series on a solar air-conditioning loop primarily does which of the following?

• ALowers the temperature rise and raises the flow through each absorber
• BRaises the temperature rise through the string and lowers the flow through each absorber
• CEliminates the need for a circulating pump
• DPrevents stagnation because series flow cannot overheat

When solar hydronic piping is buried between a roof mechanical well and a mechanical room, UPC practice requires the piping to be which of the following?

• ABare Type M copper laid in contact with slag backfill
• BApproved material, protected from corrosion and crushing, and bedded so rocks do not bear…
• CPEX with no sleeve because soil cools the glycol
• DOpen-joint drain tile so leaks can escape

A long copper generator-loop riser on a Las Vegas absorption plant will grow several inches between a 40°F night and a 200°F operating day. How is that movement accommodated?

• ABy rigidly clamping the riser at every floor so it cannot move
• BWith expansion loops, offsets, or expansion joints, plus guides that force movement into…
• CBy switching the riser to Schedule 40 PVC, which does not expand
• DBy omitting insulation so the pipe stays closer to room temperature

Which copper tube type has the thickest wall and is the preferred underground water-service tube for a solar hydronic feed?

• AType M
• BType L
• CType K
• DType DWV

What circulating velocity is the usual design band for copper solar hydronic piping serving an absorption or coil loop?

• A0.5 to 1.0 feet per second
• B2 to 5 feet per second
• C10 to 12 feet per second
• D15 to 20 feet per second

Per UPC 2018 Section 312.9, copper or plastic hydronic tube that passes within 1 inch of the face of a stud must be protected by which of the following?

• ADuct tape wrapped around the tube
• BA steel nail plate not less than 18 gauge, extending at least 1-1/2 inches beyond the tube
• CAn extra layer of fiberglass insulation only
• DNo protection if the tube is Type L

Why are galvanized steel fittings and zinc-coated components avoided on a closed propylene-glycol collector loop?

• AZinc is too expensive for solar work
• BHot glycol attacks zinc, producing sludge that fouls collectors, pumps, and heat exchange…
• CGalvanized fittings cannot be threaded
• DThe UPC requires galvanized pipe on every glycol loop

A 240 ft² glazed collector array for a solar absorption plant is designed at the common FSEC/solar-thermal rate of 0.02 gpm per square foot. What collector-loop flow is required?

• A1.2 gpm
• B2.4 gpm
• C4.8 gpm
• D12.0 gpm

A solar hydronic loop serving an air-handler heating coil circulates 7.5 gpm of water with a 16°F temperature drop. What heat is being delivered? Use Q = 500 × gpm × ΔT.

• A12,000 Btu/h
• B48,000 Btu/h
• C60,000 Btu/h
• D96,000 Btu/h

A closed collector loop circulates 6.0 gpm of 50 percent propylene glycol (specific gravity 1.04, specific heat 0.85 Btu/lb·°F) with an 18°F rise. What heat is the array delivering?

• A27,000 Btu/h
• B47,700 Btu/h
• C54,000 Btu/h
• D64,800 Btu/h

A drainback collector array sits 22 feet above the reservoir water line. Friction and fittings add 9 feet of head at design flow. What total head must the collector pump overcome while the array is filling and circulating?

• A9 feet
• B13 feet
• C22 feet
• D31 feet

What energy conversion is the defining purpose of a C-21E solar air-conditioning system?

• ASunlight to electricity that then drives a packaged rooftop unit
• BSunlight to heat in a fluid, then that heat to space heating or thermally driven cooling…
• CSunlight to heat used only to warm a swimming pool
• DSunlight to domestic hot water with no air-side equipment

A project wants to run a conventional rooftop air conditioner from a roof full of photovoltaic modules. Does that work fall under C-21E?

• AYes, because any solar equipment that affects cooling is C-21E
• BNo. C-21E is solar-thermal collectors, piping, and storage for air-temperature control, n…
• CYes, if the modules are glazed
• DOnly if the rooftop unit uses R-410A

What generator inlet temperature band is typical for a single-effect lithium bromide–water absorption chiller driven by solar collectors?

• A90°F to 110°F
• B160°F to 200°F
• C280°F to 350°F
• DBelow 50°F, the same as a vapor-compression evaporator

For a solar-fired absorption chiller, thermal COP is defined as which ratio?

• AElectrical input at the solution pump divided by generator heat
• BUseful cooling at the evaporator divided by heat supplied to the generator
• CCooling-tower fan power divided by collector area
• DStorage tank volume divided by collector area

In the northern hemisphere, what collector azimuth gives the highest annual solar yield for a fixed hydronic array?

• ATrue north
• BTrue south
• CDue east only
• DMagnetic west regardless of declination

Las Vegas is about 36°N. For a solar air-conditioning array that must peak in summer, which fixed tilt is the most appropriate starting point?

• AAbout 21° (latitude minus 15°)
• BAbout 36° (latitude) even though summer sun is higher
• CAbout 51° (latitude plus 15°)
• D90° (vertical wall) to reject summer sun

Why are evacuated-tube collectors often chosen over unglazed or ordinary flat-plate collectors to drive a single-effect absorption chiller in Nevada?

• AThey produce electricity as well as heat
• BThey keep useful efficiency at the 160°F to 200°F generator temperatures that flat plates…
• CThey cannot stagnate
• DThey require no freeze protection anywhere in the state

Which three methods are the accepted ways to protect a solar collector loop from freezing?

• ADrainback, inhibited glycol closed loop, and (where listed) automatic recirculation or fr…
• BPainting the collectors black, adding extra insulation on the roof, and opening a window
• CUsing PVC pipe, burying the collectors, and shutting the isolation valves
• DRelying on Las Vegas sunshine so freeze protection can be omitted statewide

What is the principal difference between a drainback collector loop and a closed glycol collector loop on a solar air-conditioning plant?

• ADrainback is always potable; glycol is always steam
• BDrainback empties the roof piping when the pump stops; a closed glycol loop stays full an…
• CDrainback cannot serve an absorption generator
• DA closed glycol loop cannot use a heat exchanger

When FSEC or SRCC collector ratings are used to size a solar air-conditioning array, which collector area is the rating based on?

• ANet absorber area only, ignoring the frame
• BGross collector area, including the frame and unglazed border
• CThe roof area of the entire building
• DThe aperture area of a neighboring skylight

What storage-volume rule of thumb does FSEC-style solar-thermal practice use per square foot of collector to limit overheating when the load is small?

• A0.25 gallon per square foot
• B1.5 to 2.0 gallons per square foot (use the higher end in a hot, sunny climate)
• C10 gallons per square foot
• DOne gallon per ton of cooling, regardless of collector area

A differential controller on a solar collector loop typically starts the pump when the collector is how much hotter than the storage sensor, and stops it when the difference falls to about what?

• AOn at 2°F, off at 1°F
• BOn at about 8°F to 20°F, off at about 3°F to 8°F
• COn at 80°F, off at 70°F regardless of tank temperature
• DOn only at solar noon, off at sunset on a time clock

Where are the two primary sensors placed on a differentially controlled solar collector loop that heats a storage tank for an absorption generator?

• ACollector inlet (coldest header) and the top of the tank
• BCollector outlet (hottest absorber leaving fluid) and the tank region that feeds the coll…
• COutdoors on the north wall and on the cooling-tower basin
• DOnly on the chilled-water supply, with no collector sensor

Why is a check valve required on a closed solar collector loop that serves a hot storage tank?

• ATo stop reverse thermosiphon that would dump tank heat out through the collectors at night
• BTo raise the collector stagnation temperature
• CTo replace the pressure relief valve
• DTo keep glycol from wetting the absorber fins

A closed collector loop uses inhibited propylene glycol to heat potable or process water that later serves an occupied building. Under UPC cross-connection rules, what heat-exchanger construction is required if the glycol is not listed as potable?

• AA double-wall heat exchanger with a visible leak path between the walls
• BA single-wall coil with no leak path to sight
• CDirect mixing of glycol into the storage tank
• DAn open barrel used as a heat exchanger

A solar absorption air-conditioning plant commonly uses two thermal stores. What does each store do?

• AThe hot store buffers collector heat to the generator; the cold store buffers chilled wat…
• BBoth stores hold refrigerant only
• CThe hot store holds ice; the cold store holds steam
• DOnly one store is ever used, and it must be the expansion tank

Where does a water-cooled LiBr absorption chiller reject the heat from the absorber and condenser?

• ATo a cooling tower or other heat-rejection loop
• BOnly back into the solar collectors
• CInto the building supply air, which provides free reheat
• DIt does not reject heat; absorption machines have no condenser

What operating mistake is most likely to crystallize lithium bromide in a solar-fired absorption chiller?

• AAllowing the solution to become too concentrated and too cool, often from a cooling-tower…
• BRunning the generator a few degrees hotter than design on a clear day
• CUsing Type L copper on the chilled-water piping
• DFacing the collectors 10° west of south

Compared with a lithium bromide–water absorption chiller, an ammonia–water absorption machine is chosen when the plant must do which of the following?

• AProduce temperatures at or below 32°F, because water is not the refrigerant
• BProduce chilled water only above 50°F
• CRun entirely without a generator
• DUse unglazed pool collectors as the only heat source

A Nevada solar air-conditioning plant will overheat on a holiday weekend when the building is empty. Which overheat strategy is appropriate?

• AA listed heat dump (fan coil, night radiator, or auxiliary load), collector drainback, or…
• BCap the relief valve so it cannot open
• CPainting the collectors white after installation
• DClosing the collector isolation valves at Friday quitting time and leaving the array wate…

A building needs 3 tons of solar-driven cooling. The single-effect chiller COP is 0.70 and the collectors can deliver 210 Btu/h·ft² at generator temperature. What collector area is required at that instant?

• A100 ft²
• B171 ft²
• C245 ft²
• D360 ft²

What does solar fraction mean on a solar air-conditioning plant?

• AThe fraction of the building's heating or cooling energy that the solar plant actually su…
• BThe fraction of roof area covered by collectors
• CThe fraction of glycol in the collector loop
• DThe COP of the absorption machine

Which Nevada climate fact most affects C-21E collector and storage design?

• AHigh beam irradiance and dusty air, with freeze risk in the north and extreme stagnation…
• BContinuous cloud cover that makes drainback unnecessary
• CCoastal salt spray on every job
• DNo temperature swing between day and night