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