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THE BASIC RADIANTEC SOLAR DOMESTIC WATER HEATER“What is the use of a house if you haven’t a tolerable planet to put it on?” – ThoreauIntroduction - The “Radiantec Basic Solar Domestic Water Heater” is a pre-engineered “packaged”residential solar water heater that will provide abundant quantities of domestic hot water for a typicalresidential family.The Radiantec Basic Solar Domestic Water Heater can serve as a point of departure for more versatilesolar energy systems. Useful supplements such as radiant underfloor heating, solar-assisted gardening, snowmelting, pool heating and passive cooling applications can be added to the basic system either initially or inthe future. For clarity, this manual refers only to the basic water heating system. We encourage you toconsult with Radiantec Company for appendices and other information about supplemental uses.The Radiantec Basic Solar Domestic Water Heater is intended in part tomeet the basic requirements of solar certification agencies and taxauthorities. The solar energy system described by this manual, whenproperly installed and maintained, meets the minimum standardsestablished by the Solar Rating and Certification Corporation (SRCC). Thiscertification does not imply endorsement or warranty of this product bySRCC.Please pay particularattention to any itemsshown in red as theywill relate to safetyconsiderations.Description and Operation The Radiantec Basic Solar Domestic Water Heater consists of a solar collectorarray, a solar hot water storage tank with "wrap around type" heat exchanger, a pump, an electrical controland other mechanicals. A simple control will turn on a pump whenever the temperature inside the solarcollectors is warmer than the temperature at the location where the heat will be used. When the sun comesup in the morning, the solar collectors become warm and the heat is passed to a "heat transfer fluid",generally water or a non-toxic glycol antifreeze solution.1

A thermal sensor near the solarcollectors sends temperatureinformation to the solar controller. Thecontroller compares this informationwith the temperature on the pipereturning from the storage tank. If thecollector temperature is warmer, thepump comes on and circulates the heattransfer fluid so that the heat energy istransferred to the solar storage tank.The Radiantec Basic Solar DomesticWater Heater can be technicallydescribed as a “closed loop, hydronic,antifreeze-based, indirect solarwater heater – In layman’s language,this means that a solar collector warmsup a solution of antifreeze and water.Then the antifreeze solution iscirculated by a pump from the solarcollector to a copper heat exchangerthat wraps around the bottom of thehot water storage tank, and then backto the solar collector to be reheated.COMPONENTSSolar collector arrayThree solar panels from Alternative Energy Technologies will make up the solar collector array. The modelnumber is AE-32 and the dimensions are approximately4’X 8’. The net solar aperture is approximately 90 squareft and is relatively large in comparison to many othersolar collectors. The net solar aperture is the actualamount of black solar absorption area that is exposed tothe sun and is a very important factor in performance.The solar panel is a shallow aluminum box with glasscover. It is essentially a heat trap, like an automobile on asunny day. Solar radiation passes through the glass cover into the collector where itturns into heat. The collected heat cannot escape easily by radiating back out. The heatis then carried away by a black copper absorber plate with attached fluid passages. Inother words, the solar collector turns solar energy into a hot antifreeze solution.2

The solar collectorThe solar storage tank holds 120 gallons of potable water. It isheated by a “wrap around type” heat exchanger made ofcopper tubing. Heated solar fluid from the solar collectorscirculates through the “wrap around” heat exchanger and theheat is passed to the water in the tank by conduction. The“wrap around” heat exchanger design gives the higheststandard of protection for the potable water: Double-wallventing prevents any contamination of water in the tank.SolarStorage TankElectricElementBack-up heating element - An electric element is locatedwithin the top 1/3 of the tank as a backup, and it is energizedwhenever there is insufficient solar energy available. Thewater heater maintains its own temperature independentlyfrom the solar control. For example, if you set the tankthermostat to 1000 F., the electric element will be activated bythe water heater control to maintain the set-point. Its positionThe solar storage tank with integralin the top third of the tank fosters thermal stratification such that“wrap around” heat exchangeronly the top third of the tank is heated electrically while thewater towards the bottom of the tank remains at a cooler temperature so that solar energy may contribute tothe domestic hot water need. The electric element should be set to the minimal acceptable watertemperature. Some users will shut the electric element off manually at the electrical box during favorablesolar conditions. In some cases, very high temperatures within the tank could trip the breaker in the tank andneed to be reset by pressing the red button.3

SOLAR MECHANICAL PACKAGEThe Solar Mechanical Package contains all of the parts needed to operate aclosed-loop system, including filling, draining, etc. A fuller explanation of thefunction of the components in the mechanical package is in the following“Installation Manual”. In a closed-loop system the solar fluid is circulatedfrom the solar collector to the tank heat exchanger by means of a pumpwhenever solar energy is available. The system is said to be closed because theworking fluid remains within the system and is never removed except formaintenance. All components of the Solar Mechanical Package, includingthe pump, can become very hot during operation.SOLAR HEAT TRANSFER FLUIDAn antifreeze solution is the medium that transfers heat from the solar collectors to the solar storage tank.The solution will be a 50-50% solution of propylene glycol and water, which is non toxic (see attachedtechnical data sheet).Freeze Protection - The solution will prevent damage from freezing down to -50 degrees F.High Temperature Protection - The antifreeze solution has a higher boiling temperature than water.Corrosion Protection - The antifreeze solution has corrosion inhibitors for long service life.Lubrication - The antifreeze solution serves to lubricate the pump for long service life.The solar fluid can be dangerously hot under certain conditions. Do not open the fill and drain valvesin the “Solar Mechanical Package” if hot.THE SOLAR CONTROLLERThe Radiantec Solar Controller serves several useful functions: Displays the temperature at important points in the system.Operates the pump either fast or slow according to solaravailability.Activates a heat dump.Signals system malfunction.4

Solar Controller Operation – There are two electrical temperature sensors (S1 and S2). S1 is placed whereit will read the temperature of the fluid coming out of the solar collectors and S2 is placed on the pipingreturning from the storage tank where it will read the temperature going back to the solar panels. Thecontroller compares the two temperatures, and if S1 is greater than S2 by a selectable amount, the pumpcomes on and fluid circulation begins between the solar collectors and the tank heat exchanger. When thetemperature difference is small, the variable speed pump runs slowly and when the temperature difference isgreater, the pump runs faster. The variable control feature has many benefits including improved low sunperformance, less control cycling and conservation of electrical energy at the pump.The placement and insulation of thetemperature sensors is a very important.Performance can suffer by 20% or moreif the sensors are not installed properly.See the installation manual for moredetails.The heat dump - The Radiantec Solar Heat Dump is a supplemental method for controlling undesirableoverheating of the solar energy system by automatically consuming some domestic hot water and sending itdown the drain. The occupant can select a lower setting for the activation of the heat dump if it desirable tohave lower overall temperatures in the solar system. Whenever the temperature at S1 (coming out of thesolar collectors) is greater than a selectable temperature (default is 250 degrees F), the heat dump isactivated.The solar heat dump is a small solenoid type valve that sends a small 1/4” stream of water down the drain.The effect is to slowly and gently cool down the entire solar energy system without consuming very muchwater. The volume of a typical heat dump is only about ten gallons and it tends to occur twice per day ifthe structure is not occupied and once per day or not at all if the building is occupied. Operation of the heatdump will not compromise a septic system because of its low volume and high temperature, whichfacilitates bacterial action.Stagnation – A solar heating system is said to be in stagnation when the solar collectors are exposed tosunlight but the heat is not being taken away and put to use. This condition can occur for any of thefollowing reasons: Pump failure Controller failure Electric power failure An air bound system Under stagnation conditions, the temperature in the solar collectors may go as high as 275 degrees Fand the system pressure could go to 50 psi. As a condition of certification, solar collectors must be able towithstand prolonged periods of stagnation. Nevertheless, these very high temperatures could eventuallycause appearance problems with the solar panels due to out-gassing of materials within the panel andsubsequent condensation in the inside of the glass cover sheet. Also, temperatures above 250 degrees F willeventually degrade the glycol and cause it to require early replacement. Stagnation is an abnormal condition5