Solar Hot Water Specialists Auckland
Alternative methods to connect solar hot water systems in New Zealand;
Differential controller operated solar water heater pumped system;
The direct pumped system, has one or more solar energy collectors installed on the roof, plus a solar storage tank below, either in the ceiling or a cupboard. A very quiet, low power consumption solar pump circulates the water from the tank up to the collector and back again. This is called a direct pumped solar plumbing system design (or open loop type commonly used in New Zealand) where the suns heat is transferred directly to the potable water circulating through the solar collector tubing and storage tank; no anti-freeze solution or heat exchanger is used.
Solar heating design incorporates a microcomputer differential controller which senses temperature differences between the water leaving the solar collector and the coldest water in the storage tank. When the water in the collector is about 8°c warmer than the water in the tank, the pump is turned on by the controller. When the temperature difference in the collector drops about 4°c below that of the lower part of the tank, the pump is turned off, this ensures the solar panel receives the coolest water plus any solar panel heat gained when the solar pump switch is activated.
Frost protection is provided by a frost valve installed at the highest point of the solar collector providing freeze protection.
When ever temperatures approach freezing, the valve opens to let warm water flow through the collector.
Automatic recirculation is another means of freeze protection. When the water in the collector reaches a predetermined temperature near freezing, the micro computer controller turns the pump on for a few minutes to circulate warm water from the tank through the collector.
Indirect Pumped Solar Water Heating System Layout
This indirect plumbing system design is common in colder climates where freezing occurs more frequently. An antifreeze solution circulates through the solar collector, the heat exchanger transfers the heat from the antifreeze solution to the solar tank water. The system illustrated below is an example of how this system should be setup & where the heat transfer solution is pumped through the collector in a closed loop. The loop includes the collector, connecting pipes, solar pump, expansion tank and a heat exchanger. The heat exchanger coil should be in the lower half of the storage tank for effective heat transfer from the exchanger to the potable water in the solar storage tank, this method separates the potable water from the glycol mixture.
A micro computer differential controller, controls the system in conjunction with sensors located in the solar collector and solar hot water tank, which in turn controls the pump thus circulating the glycol mixture.
The fluid used in this system should be a food grade glycol mix, not the type used in cars.
Indirect types of solar water heating setups dramatically reduce the chances of failure due to severe cold, however indirect systems are less efficient plus require more maintenance.
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