Water Heating Systems

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Water Heating Systems
Passive
Direct
Indirect
Active
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System Types

• Direct
• 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
• A heat exchanger is used to transfer heat from
  the circulating fluid to the potable water

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System Types

• Active
• Uses a pump, fan, or other powered device
• Passive
• Does not use a pump or fan - relies on natural
  forces Gravity density

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Direct System

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

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Direct System
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Direct Advantage

• Service water used directly from collector loop
• Circulation pump needs only to overcome friction
  losses - system pressurized
• Simple System No heat exchanger required

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Direct Disadvantages

• Quality of service water must be good to prevent
  corrosion, scale or deposits in components
• Freeze protection depends on mechanical valves
• Only recommended in climates with minimal freeze
  potential

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Indirect System

• Non-potable fluid (usually glycol) circulates
  through collector and heat exchanger
• Freeze protection
• Reduced Scale

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Major System Components

• Active System
• Collector(s)
• Storage tank
• Controller
• Pump or Circulator
• Passive System
• Collector(s)
• Storage tank
• Controller

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Indirect System Components

• Collector(s)
• Storage Tank
• Pumps / Circulators
• Controller
• Heat Exchanger

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Two Types of Indirect Systems Difference is
Collector Loop

• Circulating Glycol Pressurized Antifreeze
  Solution in collector
• Drainback Not Pressurized, normal Water in
  collector loop

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Active Systems
Active Indirect Pressurized Glycol Systems
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Active Indirect Glycol System

• Used where freezing or water quality is problem
• Anti-freeze is heat transfer solution
• Heat exchanger
• 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
• Requires relief valves/ air vents

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Active Indirect Glycol System
Antifreeze (glycol) circulates through collector
loop
Hot
Pressure Gauge
Cold
Heat Exchanger in or around the tank
Circulator
Check Valve
Expansion Tank
Drain Fill Valves
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Indirect Pressurized Glycol

• Pros
• Excellent freeze protection
• Can be PV driven
• Cons
• Must inspect/replace glycol periodically
• Can be problems when used for space heating

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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
Expansion tank
Hot Out
Pressure Relief Valve
Solar Storage Tank
Temperature Pressure Relief Valve
Two tanks required for Gas/LPG only Electric
element in 80-gallon storage tank for systems
with electric back-up
Gas/LPG Hot Water Heater
Check Valve
Ball Valve
Drain Valve
12 VDC Circulator
Tempering Valve
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Heliodyne External double pumped system
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Active Indirect Glycol System Single Tank with
Electric Back-up Element in Storage Tank
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Indirect Glycol Advantages

• Pressurized Glycol System
• Freeze protection provided by antifreeze fluid.
• Collector loop remains full and pressurized.
• Dont have to overcome head losses, etc.
• Careful sloping of pipe not important.
• PV can be used to power pump.

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Indirect Glycol 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

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Indirect Glycol Disadvantages

• Venting through pressure/temperature relief valve
  under stagnation conditions
• if excessive - will require refilling of system
  to proper operating pressure
• Potential for toxicity requires double wall heat
  exchanger or nontoxic freeze solution

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Active Systems
Active Indirect Drainback Systems
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Indirect Drainback

• Pros
• Excellent freeze and over temperature protection
• Low maintenance
• Best for space heating
• Cons
• Noisier than other types
• Requires larger pump
• Large solar fluid volume loses more heat
• Pipe slope is critical

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Active Indirect Drainback System

• Two pumps
• Solar Pump
• Water Pump

Water coil in the reservoir
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Active Indirect Drainback System
Normal water circulates through collector loop.
Electric Back-up
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Active Indirect Drainback System
GasBack-up
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Active Indirect Drainback System With External Hea
t Exchanger
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Drainback HEX around Storage Tank
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AET
Heat exchanger in the reservoir
Drainback Systems
Heat exchanger around the tank
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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.

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Drainback Advantages

• Positive Freeze Protection - Not dependent on
  electrical power or valve operation
• Uses water
• excellent thermal properties
• 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.

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Combined Hot Water and Space Heating Systems
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Solar Hot Water and Space Heating System
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Solar Hot Water and Space Heating System
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Active System Control Modes

1. Differential Control 2. Photovoltaic Control
3. Timer Control
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Differential Control Can be used for Active
Direct and Indirect Systems
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Active Indirect Drainback System
Differential Control
Hot
Drain back vessel large enough to hold all the
water in the loop.
Cold
Circulator
Drain Fill Valves
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Active Indirect Drainback System
Differential Control
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PV ControlledActive Systems
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Photovoltaic (PV) Controlled Active System

• PV (5-10 watt) regulates pump operation
• PV module generates electricity from solar
  radiation and provides electrical power for the
  dc pump
• No solar No operation
• PV module - dc pump compatibility
• Start stop characteristics
• Established for all FSEC certified systems
• Uses same valves/freeze protection as
  differential controlled system
• PV control also used in indirect systems

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Active Indirect Glycol System
PV Module
PV Controlled Indirect
Hot
Cold
DC Circulator
Heat Exchanger in or around the tank
Check Valve
Expansion Tank
Drain Fill Valves
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PV Controlled Direct System
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Passive systems
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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
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Passive System Types
1. Thermosyphon 2. Integral Storage System
(ICS) 3. Batch Heater Thermosyphon system can
be direct or indirect
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THERMOSIPHON System

• PASSIVE SYSTEM
• NO PUMP OR CONTROLLER
• THERMOSIPHON ACTION
• DIRECT AND INDIRECT SYSTEMS
• SIMPLE, RELIABLE SYSTEM
• SIMILAR VALVES USED

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Passive System
Thermosyphon Direct - Horizontal Tank
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Indirect Thermosyphon
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Passive Indirect System

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

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New Construction
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ICSIntegralCollectorStorage
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ICSIntegral Collector Storage

• Passive direct system
• Collector and tank combined
• Pre-heater
• Simple, no moving parts
• Lifestyle adjustment

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ICSIntegral Collector Storage
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ICSIntegral Collector Storage
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Batch Heater