Evacuated Tube Solar Hot Water Systems

This is the first article in a series on evacuated tube solar hot water system design and installation methods that not only make sense, but correct some of the design and installation mistakes that can cause a lot of problems down the road.  These systems should be designed to last for decades with a minimal amount of maintenance.

It is falsely believed that solar hot water systems aren’t feasible or cost effective in the Northeast compared to Southern and Western states because of lower insolation levels and the risk of freezing. 

However, evacuated tubes solve the freeze problem.  In the Northeast, evacuated tube solar hot water systems, when installed properly, not only eliminate the freeze risk, the insolation levels in the Northeast are more than adequate to make them an efficient and cost effective solution to reducing utility costs.

Be aware that a carefully designed system using robust components is the key to a successful, long term energy saving solution.  Many try to cut corners on installation design and equipment to cheapen the installed cost and lower the investment recovery timeline.  Big mistake… 

Unlike solar PV systems which are relatively passive and maintenance free, non gravity-feed solar hot water systems are active, require additional mechanical equipment and scheduled maintenance.

Without careful system design, failure of the system usually requires costly repairs or worse, collateral water damage to the building where it’s installed.  Here is one example of how to avoid a potentially costly design mistake.

Rule #1 – Every system has a weak link.  Never, ever make the weakest link in a solar hot water system in the supply and return lines.  That’s because the supply and return lines are more than likely run through an inaccessible area of the building.  Pipes, fittings and connectors make the difference for a reliable system or one that is set up with failure points.

Systems designed with the roof or mechanical room as weaker points are less likely to cause collateral water damage in ceilings and walls and more likely to incur lower labor costs for repairs if needed, simply because they are more accessible than say the supply lines. 

Supply and return lines should be run with minimum of thick wall copper type ”L“ which has a high temperature rating of 350 degrees.  Type ”K“ is even more robust but adds about $3 per linear foot.

Never use PEX tubing for solar hot water supply lines.  You’re just begging for trouble.  PEX tubing may very well work 95% of the time, even at high temperatures of up to 200 degrees.  However, if a temperature spike occurs on hot summer days, high temperatures of 280 – 350 degrees F are possible, far exceeding the maximum heat rating temperature of PEX tube. Supply and return lines are not an area of the system design where you want to save a few bucks at the cost of the overall integrity of the system

By:

Rick Contrata

Atlantech Solar

Ted Koester

Colorado Solar Design

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