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Solar Water Heating Systems Passive

Direct

Indirect

Active


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 †

Direct

†

Indirect


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

† † †

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

Glass

Header

Fintube

Insulation


Collector Components

Copper Header

Extruded Aluminum frame-wall

Silicone grommets Corner bracket

Rivets Aluminum Back-sheet

Glass


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

CPC


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

RTD


Building Automation Controls †

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

z

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 † †

†

† †

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 † † †

† † † † †

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

Gas/LPG

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 †

†

† †

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


THERMOSYPHON HEAT 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-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

Circulator

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

† † † †

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


Storage

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 † † †

† † †

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


AIR VENT †

† † †

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 †

† †

†

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 †

† †

† †

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 †

†

† †

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  

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

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