Plumbing Guidelines For Solar Heaters
Systems can be configured in several different ways depending on the type of standard hot water cylinder you have;
Low pressure conversion diagram
Mains pressure conversion diagram
How to attach a solar hot water system to an existing
Explanation of how to deal with overheating
Mains Pressure Water Cylinder
Hotwater cylinders if not manufactured specifically for solar will have a manufacturers maximum temperature limit, in most cases this will be 70°c - 80°c.
1. Check the cylinder specifications for parameters suiting your temperature application.
2. Install a temperature limiting device to bring the operating temperature to within specifications 1m² of solar collector panel should have at least 1.5 kilowatt heat dissipation.
Low Pressure Cylinder
Low pressure hot water cylinders are usually manufactured from copper, insulated, having specifications stamped on the cladding, providing details of the pressure rating etc.
Low pressure hot water cylinders are excellent candidates for conversion to storage tanks.
Cylinders Used For Conversion
Cylinders best suited for solar conversion are either stainless or copper both of these tank liners have the ability to sustain high temperatures.
Stainless cylinders can operate to 90 degrees c, however this is the maximum your tank should reach bearing in mind someone should be using hot water every day to prevent overheating.
Copper hot water cylinders usually have a 70 degrees c maximum operating temperature this means you will probably have to de-tune your panel to prevent excess heat.
Vitreous enamel tanks have a maximum operating temperature of 70 degrees celcius, measures should be taken not to exceed recommended maximum temperature.
Solar Ready Tank Replacement
Converting your existing standard hot water cylinder will halve your investment giving outstanding performance and savings.
We recommend getting maximum value using your existing cylinder until the tank fails then upgrading to a solar ready tank, should you get 3 or more years use from the cylinder you would be well on your way to paying for the new cylinder, once your solar ready tank is fitted you will enjoy even more efficiency.
Performance modelling recommends Peter Cocks solar ready cylinder complying with current nz standards.
SR868C8 controller can be programmed to heat to 60ºc plus through three different time frames throughout 24 hours, controller will automatically trigger the electric element when 6 degrees below the pre-set electric booster setting.
Sixty degrees celcius should be achieved every day either by the sun or electrical element this will reduce legionella growth.
Once a frost valve has been installed the exit point should be facing downwards (permits total drainage) during frosty conditions the frost valve opens releasing a slow water flow through the collectors until water temperature is low enough for closing the frost valve.
Frost valves should be fitted at the water exit end of the collector on an extended 300mm of un-insulated pipe.
Frost valves are used as a backup to the solar controller frost protection.
Frost valves are not a fully reliable method of frost protection but the chances of total failure when used with a solar controller reduces dramatically.
Frost valves can also be used in a thermosyphon systems where no solar controller is fitted.
Heat Rejection Thermal Pressure Relief Valves
Hot water systems either standard or solar ready must have some way of releasing pressure in the event of failure. Solar collectors need an independent relief system of the cylinder itself, to prevent the cylinder from exploding, this is achieved by either a relief valve (TPR) or open vent. Relief valves must not have isolation valves installed between the heat source and the relief discharge point (drain all roof valves to the gutter).
It is important not to oversize the solar water heating system.
Temperature Pressure Relief Valve
The TPR pressure relief path is to be sized for the total output of the solar heating system @ 99 degrees celcius and 1500 w/m2 and 45 degrees ambient temperature plus any additional heating source.
Discharge On Roofing Material
Caution must be taken where valves discharge on to building (rooftops) roofs or other material, discharge will damage surfaces if adequate care is not taken. When freezing occurs these discharge locations need to be of such a length freezing will not occur. An air break or TUNDISH is required to be piped away safely, if in doubt check the manufacturers specifications or someone qualified to assess the problem.
Roof Penetration Methods
It will be necessary for both solar pipes and electrical cables to penetrate the roof.
Roof penetrations should be done as per standard practice using either lead flashings or rubber DECTITE seal as required.
Methods for roof penetration could include using a low cost CARBORUNDUM hole saw, fitting threaded brass plumbing tube through the hole, fit brass basin back nuts either side of the roof material, stainless washer to the sun side of the roof being careful not to over tighten particularly on concrete tile, apply silicone under the washer so as to shield the silicon from the sun,care should be taken the integrity of the roof is not compromised.
Hot Water Circulating Pump Used In Secondary hot water systems
Wilo solar pumps are designed to pump hot water from minus 10 to 100 degrees c, consuming a minimal 100 watts
of electricity (230v) at maximum speed.
All rotating parts of the solar pump are surrounded by flowing water, including the motor rotor.
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