Drain-Down System

Draindown solar hot water systems act as a sort of “solar add-on” into a grid-tied hot water installation. They are made up of a collector array, a tank as well as pipes which attaches to the regular household plumbing, plus optional controllers, gauges and valves. The draindown solar thermal set up is probably the most efficient installation offered when it’s functioning. It is a direct system which heats the household supply straight into the collector array however it only works if the sun is out. Given that it utilizes a collector (normally a flat-plate model ), it’s generally much more efficient compared to an ICS and since it only works whenever the sun shines, it could utilize a PV-powered pump. Normally, the system is empty and nonproductive till the sun comes out. Then a controller takes over and operates a Sunspool – a unique valve – which open up and allows the home water supply flood the system. The pump switches on and flows the water on the regular method for direct systems.

Once the sun disappears, the pump is turned off, the valve closes and then the water on the drainback solar thermal system is able to run off via a waste tube. This little bit of water is disposed of unused.

In case you install a drainback system using a PV-powered pump, you could eliminate the controller as well as its reliance upon an external power source, because it will just function whenever the sun’s radiation is adequate to warm up the water on the collector array.

Drainback Water Heaters Pros and Cons

Drainback system is among the common solar water heating systems in whose primary advantages over other kinds are simplicity, reliability and low maintenance. The drainback solar water heater isn’t the easiest, and it needs a little knowledge, money and time to design and install it correctly. It’s less expensive compared to the closed-loop system having the antifreeze (propylene-glycol based active sort) however more costly compared to the ICS system.

The possibility of boiling water, high pressure, freezing as well as bursting pipes is literally low, so long as the down-flow pipe is big enough, and also the fluid loop on solar collectors and pipes is sloped properly for draining.

Drainback technology makes use of water that doesn’t corrode the pipes as well as other metal components or deteriorates since the heating fluid has added additives (just like antifreeze). Moreover, water cost less, its qualities are better, and maintenance is lesser.


Among the primary disadvantages of the drainback solar water heater is a substantial source of heat loss whenever the pump isn’t working, just like during the night time exposure. This system needs the biggest pumps of all the systems.

The drainback concept is easy, however the special attention must be directed at its solar loop design. Probably the most complex thing would be to design the system, so that all the water coming from collectors runs down to the little reservoir once the pump stops. Water drains because of the gravity as the air flows upwards to the solar panels as well as outdoor pipes. It’s the trickiest part.

Given that the presence of air should be taken into consideration in these systems, you must also consider the probability of metal corrosion.


The drainback solar water heater is suitable for all weather, perhaps even the coldest as it drains the fluid out from the collector and exposed pipes. This is why the system should be developed in a method to drain the fluid quick and thoroughly. The tank should be installed as high as possible however low enough to enable full draining. Keeping that in mind, refrain from horizontal pipes, be sure all of them have no less than 15-degree slope; also utilize 45-degree fittings rather than 90-degree one.