Solar Water Heating Systems
Direct
Indirect
Active
Passive
System Types
ActiveUses a pump, fan, or other powered device
PassiveDoes not use a pump or fan - relies on natural forces “Gravity & density”
Major System Components
•Active System•Collector(s) •Storage tank•Controller•Pump or Circulator
•Passive System•Collector(s)•Storage tank
System Types
DirectCity or potable water is circulated from the tank to the collector and back
IndirectFluid circulating through the collector never comes in contact with the city or potable water in the storage tankA heat exchanger is used to transfer heat from the circulating fluid to the potable water
Solar Hot Water System Types
Direct Indirect
System Components
Heat Collection and TransferHeat Storage - Vertical or HorizontalHeat Delivery - Pump or CirculatorFreeze Protection - If requiredControlsValves
System Components
Collectors
SOLAR COLLECTORS
Low- 70O F to 105O F21O C to 40.5O C
Medium- 105O F to 200O F40.5O C to 93O C
High- 180O F to 400O F80O C to 200O C
System Components
CollectorCollects the Solar EnergyHeart of the SystemDominant types of collectors:
Flat Plate Solar CollectorIntegral Collector Storage (ICS)BatchConcentrating
Low Temperature Collectors
Low Temperature
Unglazed or metal absorbers
PlasticPolypropyleneEPDMABSPolyethylene
Extruded Polyethylene Plastics
PVC schedule 40 PipeUV inhibitors
Mid-Temperature Collectors
Flat Plate Copper Collector
Collector Components
Absorber &Flow tubes
Enclosure
Glazing
Insulation
Inlet tube
Outlet tube
Flat Plate Collector
Side view at header
Glass
Insulation
FintubeHeader
Corner bracket
GlassAluminum Back-sheet
Rivets
Extruded Aluminum frame-wallSilicone grommets
Copper Header
Collector Components
Heat Pipe Evacuated Tube
Heat Pipe
Heat Pipe
CPCConcentrating Parabolic Collector
Receiver Tube with Non-Imaging Optical ReflectorConcentrating Parabolic Collector
CPC
Concentrating Parabolic Collector
Simple
Controls And Circulation Systems
10k Sensor
Differential Controllers Typically Have Ability To Set Differential:
ON: Between 8 and 30 degreesOFF: Between 3 to 5 degrees
Differential Controllers
RTD
New Controls May IncludeAbility To Meter Performance
Building Automation ControlsProtocols:
Turn On DifferentialTurn Off DifferentialTank Overheating (Glycol)
Turn Pump On ---Run Continuously Until Temperature In Tank Drops To Acceptable Level
Could Have Pressure Monitor And Alarm
Solar Water Heating SystemsDirectIndirect
GlycolDrain BackThermosyphon
Combi-Systems (Space Heating)Forced AirRadiant
Packaged Systems
Direct System
• Fluid in tank isheated in collector
• Most common systemtemperate climates
Typically not used in cold or freezing climates
Direct System
Circulates water from tank to collectorWater heated by collector and returned to tank
Stratification of warm water in tankDifferential controller regulates pump operationValvesFREEZE PROTECTION (may be required)
Freeze valve/manual DRAINDOWN
Direct System
Indirect System
•Non-potable fluid (usually glycol) circulates through collector and heat exchanger
•Freeze protection
•Reduced Scale
Two Types of Indirect Systems
Difference Is Collector Loop
• Circulating Glycol – Pressurized Heat Transfer Fluid is Antifreeze Solution
• Drainback – Not Pressurized, Heat Transfer Fluid is Water
Active Indirect Glycol System
Used where freezing or water quality is problem Anti-freeze is heat transfer solutionHeat exchanger
Internal or external to tankExpansion tank - for fluid thermal expansionFill and drain access valvesDifferential controller - ac pumpPhotovoltaic controller - dc pumpSimilar valves
Requires relief valves/ air vents
Indirect Pressurized Glycol
Pros:Excellent freeze protectionCan be PV driven
Cons:Must inspect/replace glycol periodicallyCan be problems when used for space heating
2KW 80-Gallon External Heat Exchanger with PV Pump and Control
Gas/LPG
Hot Water Heater
Solar Storage Tank
Cold In
Hot Out
Air vent
Expansion tank
Temperature & Pressure Gauge
Temperature Gauge
Pressure Relief Valve
Temperature & Pressure Relief
Valve
Check Valve
Ball Valve
Drain Valve
12 VDC Circulator
Tempering Valve
Coin Vent
Sensor
Differential Controller
Two tanks required for
Gas/LPG only
Electric element in 80-gallon
storage tank for systems with
electric back-up
Indirect Advantage
Pressurized Glycol System
Freeze protection provided by antifreeze fluid. Collector loop remains full and pressurized.
Don’t have to overcome head losses, etc.Careful sloping of pipe not important.PV can be used to power pump.
Indirect Disadvantages
Heat transfer properties of antifreeze fluids inferior to water - reduced performance –higher costsPeriodic maintenance required to ensure fluid properties have not deterioratedCollectors and antifreeze have to withstand stagnation when summer load is satisfied early in day
Indirect Disadvantages
Venting through pressure/temperature relief valve under stagnation conditions
if excessive - will require refilling of system to proper operating pressure
Code requirements may require using a double wall heat exchanger and nontoxic freeze solution
Indirect Pressurized Glycol
Demand Gas Heater
Active IndirectIndirect Pressurized Glycol
External Heat Exchanger
Pressurized GlycolBoiler with Indirect Water Heater
Packaged Systems
Packaged Systems
Inside views
Heat Exchanger Module
Front View
Heat Exchangers
•Internal•External•Thermosyphon•Single Wall•Double Wall
Leak Detection•Size - Heat transfer capability•Material- compatible to system & temperatures •Can it be disassembled to clean?
Counter Flow Through The Heat Exchanger
Tube-in-Tube Rod
Tube-in-Tube and Plate
Tube-in Shell
Double Wall Heat Exchanger and Air Separator
THERMOSYPHONHEAT EXCHANGER
Expansion Tank
Sized for the total expansion coefficient of the volume of fluid in the heat transfer loop at the highest operating temperature.
Larger vessels allow for more expansion at higher temperatures or stagnation of the system.
Water make-upPressure gauge
Back flow preventionWater meter
Active Indirect Drain Back System
Hot
Cold
Circulator
Drain & Fill Valves
Drain back vessel is large enough to hold all the water in the loop.
Active Indirect Drainback System
Water coil in the reservoir
Two pumps:
• Solar Pump
• Water Pump
Reservoir with Sight Glass
Reservoir With Dip Tube
Reservoir with Heat Exchanger
Indirect Drain Back System
Pump Options
1. High Head pump to provide lift and flow.
2. Two small circulatorsin Series to provide the required head.
After collectors fill, one shuts off to provide necessary circulation flow.
Drain
Back Systems
Two Types:• Heat Exchanger on Storage Tank
• Heat Exchanger in Reservoir
Heat exchanger in the reservoir
Heat exchanger around the tank
Drainback AdvantagesPositive Freeze Protection - Not dependent on electrical power or valve operationUses water
excellent thermal propertiesgood chemical stability, low cost
Thermal energy from collector is conserved in drainback tanks - not lost in exposed collectorsFluid stagnation not a problem in hot weather.Good for space heating.
Drainback Disadvantages
Collectors have to withstand dry stagnationRequired elevation differences between collectors and drainback tanksHigher collector loop pump head (pressure) required.Piping must be carefully installed to provide positive drain.
Combined
Hot Water and
Space Heating Systems
Indirect Pressurized Glycol System
Add a Heat Exchanger for the Heating Loop
Solar Assisted AHU Fan Coil Heater
2 Coil Storage with Boiler for Radiant Heating System
Density and Gravity
Cold water has more density than hot water.
Cold water is heavier than hot water - gravity pulls the cold to the bottom of the storage tank - pushing hot water up to the top
Passive System
ThermosyphonDirect - Vertical tank
Thermosiphon
System
Passive SystemNo Pump Or Controller
Thermosiphon ActionDirect And Indirect SystemsSimple, Reliable SystemSimilar Valves Used
Passive Indirect System
Thermosiphon systemInclude an antifreeze solution and a heat exchanger in the roof mounted tankRoof mounted tanks can also incorporate a heating element
Indirect Thermosyphon
Storage
Simplified graphic of a solar storage tank.
Collector feed
Collector return
Element&Thermostat
Hot out
ColdInlet
Anode rod
Indirect Stone/Cement Lined Tank
Wrap AroundOr
InternalHeat Exchanger
Stainless Steel Tank
Internal Coil Heat Exchanger
Duel Coil Solar Hot Water Storage Tank
Heat Exchanger and
Solar Pump
Water pump is considerably smaller than the solar pump.
Air separator in the solar loop
VALVES
Necessity In Solar Water Heating SystemsExpel AirLimit Excessive Temperatures And PressuresPrevent Vacuum LocksIsolate System SectionsPrevent Thermosiphon Losses
AIR VENT
Allows Air That Has Entered System To EscapeAir In System Would Restrict Fluid Flow
Located At The Highest Point Of The SystemMounted In Vertical PositionDust Cap On Valve Must Be Left Open Approx. 1/4 - 1/2 Turn
Air Vent / Float Vent
Brass housing-high temp float
•Allows air out of system
•Prevents air lock
•Installed in highest point in plumbing system
Air Vent with Ball Valve
Removes Air From System And Shut Off
Pressure & Temperature Relief Valve
Protects System And Components From Excessive Pressures And TemperaturesStorage TankCollector Loop (Isolation)
Usually At Collector Outlet AreaP&T Valves Installed In Building Must Be Drained To Safe Location
Pressure Relief Valve
Protect From Excessive PressuresPressure Rating Less Than Pressure Ratings Of Other System Components Preferred Over Pressure-temperature Valves At The Collector
Pressure Relief Valves
Protect components from excessive temperatures and/or pressuresLowest pressure rating in systemAre installed inside or outside the building and must drain to a safe location (the vent water is hot!)Pressure-only relief valve at collectorPressure & temperature relief needed at storage tank
Pressure Relief Valve
No temperature probe
Isolation Valves
Isolates Sections Of Solar SystemCollector Loop From TankCold Service
Ball ValveMost Efficient/Flow BarrierAlso Comes In Three-way Isolation/Drain
Gate ValveLess Effective Than Ball Separates Components Of The System For Maintenance Or Replacement
Gate valves will fail
Ball valves are preferred
Drain Valves
Used To Drain Collector Loop, Storage TankFill the System
Check Valves
Critical In Solar System Prevents Loss Of Hot Tank Water At Night
ThermosiphoningCold Water Is Heavier Than WarmCold Pushes Hot WaterCold From Collector At Night Would Force Hot Water In Storage Tank Back Up To Collector
Freeze Prevention Valve
Check Valves
Vertical Check ValvesMost CommonSpring CheckModified In Relation To Type Of System
Horizontal Check ValveMount In Horizontal Position
Motorized Check ValvePlumbed Near Storage Tank In Collector Loop Piping
Spring & Swing Check Valves
Anti-Scalding ValvesSafety Feature To Prevent Scalding Water From Reaching Fixtures
Solar water heating systems can create temperatures high enough to scald users.Adjustable between 105-140 degrees CMore accurate than mixing valve
Tempering Valve
Mixes cold and hot waterDelivery temperature set by the user.
Used between the solar storage tank and the gas heater to prevent overheating burner control element
CommercialMixing Valve
Flow Balancing Valve
Set flow rate of each bank of collectors in a
commercial solar system
Pulse Flow Meter
Determines Flow Rate For Calculating The Energy Production.
UltrasonicFlow Meter
BTU MeterCalculator
Copper / Brass
Pipe and Fittings
End of Systems and Components