By Julie Curnow

Frost proof solar hot water systems

If you live in an area that hits temperatures approaching zero degrees you need the right solar hot water system. To show you how frost can affect your system, let me first explain how it works. Standard solar hot water panels contain copper pipe (risers) filled with water. This water circulates around the panels where it attracts heat and is then stored in the tank as hot water. To maintain the heat, the water is recirculated from the tank to the panels.

Frost becomes a problem when no hot water is used for a while – which is often the case overnight. If the temperature outside approaches zero degrees centigrade, the water in the  risers or pipe may freeze. As the water freezes it expands and can cause the risers or pipework to break.This is an expensive problem because the risers cannot be repaired so the only solution is to replace the entire panel.

To avoid freezing pipework, your plumber should install the appropriate valve when the system was installed.

If you are considering buying a new system, there is also a range of different systems available that handle frost and overcome the risk of needing to replace costly panels. 

Solar Hot Water Systems that contain Glycol

How_Solar_Hot_Water_Works-01

Solar hot water systems that contain glycol (antifreeze) have a tank with an outer jacket. A mixture of glycol and water flows through the jacketed outer lining and the risers in the panels. This heated solution keeps the water in the tank hot through heat transfer. Since glycol freezes at much lower temperatures than water there is no risk of it freezing. These systems are rated to operate effectively in the cold parts of Australia.

Rinnai FTC Solar Hot Water Systems

Rinnai’s frost proof solar hot water systems (FTC range) still utilise water filled risers but the difference is, there is an extra half riser in the panel. This half riser contains a spring and seal, so that if the water freezes it can expand into the spare half riser riser by compressing the spring, thereby eliminating the risk of the risers breaking. These systems are rated to operate
effectively in temperatures down to -5˚C and are suitable for
nearly all of Australia.

How_Evacuated_Tube_Systems_Work

Evacuated Tube Solar Hot Water Systems

Evacuated tube solar hot water systems contain water filled glass risers. The water is in a vacuum so it cannot freeze. Rinnai’s evacuated tube solar hot water system is rated to operate at – 12˚C and so is suitable for the coldest parts of Australia.

Heat Pump

Instead of installing a solar hot water system, you can install a heat pump hot water system. Those living in cold areas should choose a model that is more efficient in frosty conditions. Heat pumps use air to heat the water. The water is sealed inside the tank and because of the volume of water (around 250 litres) it cannot freeze in Australian conditions. 

Which systems are the most cost effective?

The Rinnai FTC Solar Hot Water Systems and the Heat Pump are the most cost effective systems and are suitable for most Australian conditions. However, additional considerations come into play with the installation and insulation of the system in the coldest areas. In the coldest parts of Australia, such as areas outside of Canberra, you may need a glycol or evacuated tube hot water system.

Will a Frost Proof System Cost me More Money?

Yes, a frost proof system does cost more, but the extra cost varies from small (Rinnai FTC) to large (glycol panels) over the life of the system. The different types are compared below.

Glycol Solar Hot Water Systems

Compared to a standard solar hot water system:

  • The systems cost more to buy.
  • The tanks usually don’t last as long.
  • Are less efficient so need more boosting thereby increasing the running cost.
  • As the systems are less efficient, they do not attract as many STCs (small scale technology certificates) and so the government rebate you receive on the purchase of the solar hot water system is less.  

Evacuated Tube Solar Hot Water Systems

Compared to a standard solar hot water system:

  • The systems cost more to buy.
  • Are less efficient so they need more boosting, which increases the running cost.
  • As the systems are less efficient, they do not attract as many STCs and so the government rebate you receive on the purchase of the solar hot water system is less.  

Rinnai’s FTC panels

  • The price of the Rinnai FTC solar hot water system is more than the standard Rinnai solar hot water system.
  • There is no difference in the running cost, nor the panel life of the standard Rinnai solar hot water system compared to their FTC system.

Heat Pumps

Compared to a standard solar hot water system, heat pumps:

  • Are a similar purchase price
  • Attract less STCs than solar hot water systems, because they constantly use electricity to operate.
  • Have a shorter system life.

Speak to a solar hot water specialist to determine whether you need a frost proof system at your home and the one best suited to your needs. By getting a few quotes and doing your homework before you buy you should end up with the best value for money solution.

If you have any interesting stories to share about this from your own experience please share below!

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