Thermo Siphon water heating systems

A thermo siphon water heating system is where the collector (evacuated tubes options or flat plate collector) is attached to the water tank. These types of systems are normally found on the roof tops/ground mounted in countries where there is no danger of the water freezing in the tanks or the absorber of the collector.

The down side to these systems is the huge water waste, waiting for the hot water to arrived at the shower head/taps etc (experience of this already gained from living in Cyprus). If an electrical heating element is included for winter hot water back up in winter months, again be prepared to have a higher electricity bill through night time heat loss.

There are a growing number of options being provided mainly by the Chinese SWH industry you need to be aware of, when considering placing an order with a manufacture you have not even been to China to discuss all the technical facts, as looking at a web site picture and being given a low cost, can cost you and the customer who put his/her faith in you.

  • The lowest cost system is a none pressure tank, where the water in the tank flows into the evacuated tubes, with a painted steel frame.
  • The latest tube design is a heat pipe, not to be confused with the copper one for heat pipe collectors. This new tube produces heat at the top of the tube where the glass heat pipe is bonded into the top of the standard tube. This reduces the potential freezing of water in the tubes, in areas of freezing where in China they are installed.
  • A number of pressure systems are offered by many Chinese manufactures. Be aware that unless you are convinced that the stainless steel is 316L or food grade, the tops and bottom is BUTT, TIG welded, acid washed and pressure tested to 10 bar, leave well alone.
  • If you are also offered a heat pipe thermo siphon system as shown above, make sure that the heat pipes fit into a closed pocket and again TIG welded. This allows the heat pipe/tube to be withdrawn without loss of any water.
  • One option of a safe system is a none pressure tank, still manufactured to the standard of BUTT TIG welded, but with a stainless steel helical coil heat exchanger inside that can easily take the mains pressure water, I have recommended to a Greek company, who after two years importing thermo siphon pressure systems with open heat pipes inside the tanks, is now seeing the problems the installations are causing. This company selected one of the Biggest names in the Chinese SWH industry, believing every thing they saw on the web site and sold to them.
  • Which manufacture you select, very few of them understand any technical issues covering, size of expansion vessel to volume of water, no knowledge of the affects of lime scale when cold water is heated to hot, or the correct quality valves needed for safety and plumbing pipe sizes

This picture shows a flat plate thermo siphon system installed in Sth Africa. Unlike the evacuated tube collector, if there is any sign of a frost at night below freezing, the copper pipes in the flat plate system will burst. Evacuated tube system have a greater choice in sizing, where the volume of water is selected first, then the number of tubes are matched to kWh needed of sunlight to heat the tank to the required temperature, unlike flat plate where the tank is sized for the number of panels, with heat losses through the panels when a certain temperature is reached.


In conclusion

If your company is considering these types of systems for what ever reason, feel free to contact us for further advice and direction, or use our services which cost on average 5% on the prices we have negotiated on your behalf with the manufacture.

More importantly, we do all we can for the first few orders to advise the manufacturing engineers and assemblers to switch to better quality component parts, change the design if I reconised a flaw in the system design.

Don’t be in a hurry to want an order made and shipped in 20 days, as this is where most of the problems lie.