Closed loop Solar Hot Water Heating Systems

Closed loop systems use heat-exchangers that circulate heat-transfer fluids through the panels and feed pipes. This type of system is called a closed-loop system, because the solar exchange fluid is closed-off from the external atmosphere or isolated from the potable water through utilization of a heat exchanger.

A closed-loop system works essentially by heating solar fluid that is pumped through the solar collectors. The heated solar fluid flows through a copper or stainless steel heat exchanger located near the solar storage tank. The heat from the solar fluid transfers to the potable water within the solar storage tank. Another small circulator pump may be used to circulate the water through the potable side of the heat exchanger.

Drainback systems work slightly differently to closed-loop systems described above.

strengths

The anti-freeze heat exchange fluids can withstand freezing temperatures, allowing the system to operate during periods when there is the greatest temperature difference between cold incoming water, and temperatures reached in the solar collectors. The system can have the greatest performance benefits at this time. Also, if maintained properly, these systems will not corrode or scale the passage ways in the solar collectors and pipes. Closed-loop systems tend to have the lowest overall operating costs --other than passive systems-- and are especially adapted to work in regions with extended periods of freezing temperatures, and commercial environments that are used daily (including weekends).

A closed-loop system is a good alternative to consider if installation conditions inhibit installing a drainback system, for example because the feed and return pipes to the solar panels cannot be plumbed at an adequate slope (usually 0.25inch per 1 horizontal foot or steeper).

weaknesses

Closed-loop systems tend to have the highest installation cost associated with them. They heat water slightly less efficiently than direct open-loop systems, (but can work more and longer when it is risky to operate open-loop systems). These systems are designed to operate daily, and may overheat (releasing heat transfer fluid) if the fluid in the closed-loop does not circulate during a hot summer day --for example, when a unit is shutoff because residents leave for vacation. At these times, instructions sometimes call for panels to be covered to prevent discharges due to overheating.

system configurations

Closedloop systems are configured according to energy demands, solar energy availability and other factors at the point of installation. Closed-loop systems generally consist of at least these parts:

• 1: goldline-sb SB sensor, 10K
• 2: maidomist-71 MaidOMist Air Vent No.71
• 3: sensor wire
• 4: taco-005f2 Taco 005F2 Cartridge Circulator
• 5: watts-100xl4 T/P Pressure Relief Valve 212F,150psi
• 6: goldline-sb SB sensor, 10K
• 7: watts-100xl4 T/P Pressure Relief Valve, part of existing tank No.18
• 8: letro-sl2dw3 Letro SL-2DW3 Thermometer
• 9: watts-70a Watts 70A Tempering Valve
• 10: hot water output
• 11: cold water feed line
• 12: knob adjusts water temperature output
• 13: tomlinson-c-75 Thomlinson Quadflow bypass "H" valve
• 14: other-s480-075 NIBCO S-480 In-line Check Valve
• 15: solar panel inlet
• 16: watts-100xl4 T/P Pressure Relief Valve 212F,150psi
• 17: ksp-ks-40 KS-40 Clear Coat Flat-Plate Solar Panel
• 18: existing hot water tank, 40 to 60 gallon, electric or gas (optional)
• 19: rheem-rhm80hx Rheem Storage Tank, 80gal with internal heat exchanger*
• 20: goldline-gl30 Goldline GL-30 differential controller
• 21: other-p570k-100lm pressure gauge
• 22: amtrol-4un87 Amtrol Expansion Tank
• 23: letro-flow2s Letro LDF357B flowmeter

not shown:

• copper piping
• pipe insulation
• heat transfer fluid
• transfer fluid "fill tree" consisting of 2 spigots
• two tank systems should have a bypass valve or 3 shut-off valve "H" configuration

* - a regular hot water tank with an external heat exchanger and a second stainless steel circulator can take the place of a tank with internal heat exchanger. This configuration is common with retrofitting systems, such as when converting draindown systems to closedloop systems.

sizing systems

For best results, systems should be matched according to energy use patterns.

King Solar offers these closed-loop system kits to get you started saving energy:

• ECL-4 Solar Water Heating System for 3 or 4 people, powered by 110VAC

King Solar offers closed loop systems that work completely off of the electric grid. These systems are great for hot water heating in remote locations and where electrical power is intermittent.

Choosing a domestic or commercial solar system that best fits your circumstances can be a challenging exercise. If you are uncertain, the best thing to do is send us your requirements.

Tell us:

• how the solar hot water heating system will be used. For example, will it be used in a home or as part of a boiler system in a commercial environment
• how many gallons of hot water are used per day. We can approximate by knowing how many people live in the residence, or how much heat is created per day by a boiler etc.
• where are you geographically located

Contact us for a price quote. We will reply within 48 hours with a suggested set of equipment specifications to meet your alternative energy needs.