Heat exchangers: double wall versus single wall

Your solar thermal system uses a heat exchanger to warm water using the energy collected by your solar heat panels. Solar thermal systems use either a single wall heat exchanger or a double wall heat exchanger. The single wall heat exchangers are commonly used, but sometimes there are requests to use a double wall heat exchanger. Often, customers are under the impression that a double wall heat exchanger is needed for their system, but that is not always the case. Here is a look at the difference between the two, and why it may be better to choose one over the other.

The difference between the two heat exchangers is something you may be able to guess- one wall, and two walls. A single wall heat exchanger has just one barrier. A double wall heat exchanger has an additional layer. The barrier is typically made of a metal, such as copper or steel, and works to separate the solar fluid from potable water. It prevents the solar fluid from contaminating your hot water reserves.

While some may think the extra protection is a plus, a double wall heat exchanger may be a detriment in other areas. They are more expensive, adding additional cost to your solar thermal system installation which may not be warranted. They may also reduce your system’s performance because of their design, giving you results which are less than you expect from an efficient solar thermal system. The gap between the two barrier layers acts as a layer of insulation so the heat cannot be transferred as efficiently.

Using a single wall heat exchanger provides excellent protection against contamination of your water source if you follow these recommendations:

•  Label the system so toxic fluids are not inserted where they shouldn’t be.
• Use a pressure relief valve that is properly rated for your system.

If you have any questions about which heat exchanger is appropriate for your solar thermal system, call Smith Sustainable Design. Our design and installation experts will give you the facts and information on the best equipment to keep you safe and help your solar thermal system work efficiently.