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Solar Water Heating Systems Passive




System Types †

Active ¾


Uses a pump, fan, or other powered device

Passive ¾

Does 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 †

Direct ¾


City or potable water is circulated from the tank to the collector and back

Indirect Fluid circulating through the collector never comes in contact with the city or potable water in the storage tank ¾ A heat exchanger is used to transfer heat from the circulating fluid to the potable water ¾

Solar Hot Water System Types †




System Components † † † † † †

Heat Collection and Transfer Heat Storage - Vertical or Horizontal Heat Delivery - Pump or Circulator Freeze Protection - If required Controls Valves

System Components Collectors

SOLAR COLLECTORS Low- 70O F to 105O F 21O C to 40.5O C Medium- 105O F to 200O F 40.5O C to 93O C High- 180O F to 400O F 80O C to 200O C

System Components

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Collector Collects the Solar Energy Heart of the System Dominant types of collectors: Flat Plate Solar Collector ¾ Integral Collector Storage (ICS) ¾ Batch ¾ Concentrating ¾

Low Temperature Collectors

Low Temperature

Unglazed or metal absorbers Plastic Polypropylene EPDM ABS Polyethylene

Extruded Polyethylene Plastics

PVC schedule 40 Pipe UV inhibitors

Mid-Temperature Collectors

Flat Plate Copper Collector

Collector Components Enclosure

Absorber & Flow tubes

Outlet tube Glazing Inlet tube Insulation Flat Plate Collector

Side view at header





Collector Components

Copper Header

Extruded Aluminum frame-wall

Silicone grommets Corner bracket

Rivets Aluminum Back-sheet


Heat Pipe Evacuated Tube

Heat Pipe

Heat Pipe

CPC Concentrating Parabolic Collector

Receiver Tube with Non-Imaging Optical Reflector Concentrating Parabolic Collector

Concentrating Parabolic Collector


Simple Controls And Circulation Systems

Differential Controllers

Differential Controllers Typically Have Ability To Set Differential: ON: Between 8 and 30 degrees OFF: Between 3 to 5 degrees

10k Sensor

New Controls May Include Ability To Meter Performance


Building Automation Controls †

Protocols: Turn On Differential ¾ Turn Off Differential ¾ Tank Overheating (Glycol) ¾



Turn Pump On ---Run Continuously Until Temperature In Tank Drops To Acceptable Level

Could Have Pressure Monitor And Alarm

Solar Water Heating Systems † †

Direct Indirect Glycol ¾ Drain Back ¾ Thermosyphon ¾


Combi-Systems (Space Heating) Forced Air ¾ Radiant ¾


Packaged Systems

Direct System

• Fluid in tank is heated in collector • Most common system temperate climates

Typically not used in cold or freezing climates

Direct System † †


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Circulates water from tank to collector Water heated by collector and returned to tank ¾ Stratification of warm water in tank Differential controller regulates pump operation Valves FREEZE PROTECTION (may be required) ¾ 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 † † †

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Used where freezing or water quality is problem Anti-freeze is heat transfer solution Heat exchanger ¾ Internal or external to tank Expansion tank - for fluid thermal expansion Fill and drain access valves Differential controller - ac pump Photovoltaic controller - dc pump Similar valves ¾ Requires relief valves/ air vents

Indirect Pressurized Glycol


Pros: ¾ ¾


Excellent freeze protection Can be PV driven

Cons: ¾ ¾

Must inspect/replace glycol periodically Can be problems when used for space heating

2KW 80-Gallon External Heat Exchanger with PV Pump and Control

Temperature Gauge Temperature & Pressure Gauge Air vent Sensor

Cold In

Differential Controller Coin Vent

Hot Out Expansion tank

Pressure Relief Valve Temperature & Pressure Relief Valve

Solar Storage Tank


Check Valve

Ball Valve Drain Valve 12 VDC Circulator Tempering Valve

Hot Water Heater

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 †


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Freeze protection provided by antifreeze fluid. Collector loop remains full and pressurized. ¾ 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 costs Periodic maintenance required to ensure fluid properties have not deteriorated Collectors 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 ¾ 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

Indirect Pressurized Glycol Active Indirect External Heat Exchanger

Pressurized Glycol Boiler with Indirect Water Heater

Packaged Systems

Packaged Systems

Heat Exchanger Module

Inside views

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


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-up Pressure gauge Back flow prevention Water meter

Active Indirect Drain Back System

Drain back vessel is large enough to hold all the water in the loop.

Hot Cold


Drain & Fill Valves

Active Indirect Drainback System

Two pumps: • Solar Pump • Water Pump

Water coil in the reservoir

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 circulators in Series to provide the required head. After collectors fill, one shuts off to provide necessary circulation flow.

Heat exchanger in the reservoir

Drain Back Systems Two Types: • Heat Exchanger on Storage Tank • Heat Exchanger in Reservoir

Heat exchanger around the tank

Drainback Advantages †





Positive Freeze Protection - Not dependent on electrical power or valve operation Uses water ¾ excellent thermal properties ¾ good chemical stability, low cost Thermal energy from collector is conserved in drainback tanks - not lost in exposed collectors Fluid stagnation not a problem in hot weather. Good for space heating.

Drainback Disadvantages †




Collectors have to withstand dry stagnation Required elevation differences between collectors and drainback tanks Higher 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 Thermosyphon Direct - Vertical tank

Thermosiphon System †

Passive System ¾

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No Pump Or Controller

Thermosiphon Action Direct And Indirect Systems Simple, Reliable System Similar Valves Used

Passive Indirect System †

Thermosiphon system Include an antifreeze solution and a heat exchanger in the roof mounted tank ¾ Roof mounted tanks can also incorporate a heating element ¾

Indirect Thermosyphon


Simplified graphic of a solar storage tank.

Collector return

Cold Inlet

Collector feed

Hot out

Element & Thermostat

Anode rod

Indirect Stone/Cement Lined Tank

Wrap Around Or Internal Heat 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 † † †

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Necessity In Solar Water Heating Systems Expel Air Limit Excessive Temperatures And Pressures Prevent Vacuum Locks Isolate System Sections Prevent Thermosiphon Losses


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Allows Air That Has Entered System To Escape ¾ Air In System Would Restrict Fluid Flow Located At The Highest Point Of The System Mounted In Vertical Position Dust 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

Removes Air From System And Shut Off

Air Vent with Ball Valve

Pressure & Temperature Relief Valve †

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Protects System And Components From Excessive Pressures And Temperatures Storage Tank Collector Loop (Isolation) ¾ Usually At Collector Outlet Area P&T Valves Installed In Building Must Be Drained To Safe Location

Pressure Relief Valve † †


Protect From Excessive Pressures Pressure Rating Less Than Pressure Ratings Of Other System Components Preferred Over Pressure-temperature Valves At The Collector

Pressure Relief Valves †

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Protect components from excessive temperatures and/or pressures Lowest pressure rating in system Are installed inside or outside the building and must drain to a safe location (the vent water is hot!) Pressure-only relief valve at collector Pressure & temperature relief needed at storage tank

Pressure Relief Valve

No temperature probe

Isolation Valves †



Isolates Sections Of Solar System ¾ Collector Loop From Tank ¾ Cold Service Ball Valve ¾ Most Efficient/Flow Barrier ¾ Also Comes In Three-way Isolation/Drain Gate Valve ¾ Less Effective Than Ball ¾ Separates Components Of The System For Maintenance Or Replacement

Ball valves are preferred

Gate valves will fail

Drain Valves †

Used To Drain Collector Loop, ¾ ¾

Storage Tank Fill the System

Check Valves †



Critical In Solar System ¾ Prevents Loss Of Hot Tank Water At Night Thermosiphoning ¾ Cold Water Is Heavier Than Warm ¾ Cold Pushes Hot Water ¾ Cold From Collector At Night Would Force Hot Water In Storage Tank Back Up To Collector Freeze Prevention Valve

Check Valves †


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Vertical Check Valves ¾ Most Common ¾ Spring Check ¾ Modified In Relation To Type Of System Horizontal Check Valve ¾ Mount In Horizontal Position Motorized Check Valve Plumbed Near Storage Tank In Collector Loop Piping

Spring & Swing Check Valves

Anti-Scalding Valves †




Safety 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 C More accurate than mixing valve

Tempering Valve Mixes cold and hot water Delivery temperature set by the user.

Used between the solar storage tank and the gas heater to prevent overheating burner control element

Commercial Mixing 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.

Ultrasonic Flow Meter

BTU Meter Calculator

Pipe and Fittings Copper / Brass

End of Systems and Components

System Types  
System Types  

Active Indirect Direct Passive Passive Active Does not use a pump or fan -relies on natural forces “Gravity & density” Uses a pump,...