Solar Water Heaters - Should These Systems Be Banned as a Fire Hazard?

[FyrBldgGuy]

A solar water heater in an area where the temperature gets below freezing will usually have a closed loop cooling system with an antifreeze solution.

· Glycol/water mixtures

Glycol/water mixtures have a 50/50 or 60/40 glycol-to-water ratio. Ethylene and propylene glycol are "antifreezes." (from EERE Department of Energy)

If NFPA and the California State Fire Marshal believe that antifreeze solutions can result in deflagrations when the antifreeze comes in contact with flaming materials shouldn't these systems be banned as fire hazards.

 

[Frank]

The use antifreeze mixtures that the fire marshal is refering to sometimes resulting in deflagrations is when it is in fire sprinkler systems where it is sprayed under pressure onto a fire or hot patio heater. Testing of sprinklers with these solutions has shown that if the stronger solutions are sprayed through some sprinkler heads at some pressures on an intense ignition source in the wrong part of the spray pattern ignition of the spray cloud can and has occurred with some injuries and at least on fatality in real world incidents. This has led to an NFPA TIA banning the use of these solutions in new residential sprinkler systems.

The use of these same solutions in solar water heater collection loops is a different case in that the system is low pressure, these is no atomizing nozzle, and leaks would not be expected to be onto an existing fire.

These systems are a much lower hazard than an gas or oil fired water heater.

 

[Coug Dad]

What about contamination of the potable water supply from the antifreeze? Fire sprinkler systems that use food grade antifreeze have to provide reduced pressure backflow prevention. How is this justified?

 

[cda]

It is a closed system. No cross contamination should happen

Besides the home owner is dumping pesticides, gasoline, oil, so much it counter acts the other stuff

 

[Frank]

What about contamination of the potable water supply from the antifreeze? Fire sprinkler systems that use food grade antifreeze have to provide reduced pressure backflow prevention. How is this justified?

Through the use of a double wall heat exchanger with interstitial space drained that provides same level of cross contamination protection as RPZ.

 

[TimNY]

Same as any SuperStor connected to a hydronic system with antifreeze. Instead of the boiler, you are using the solar panels. I don't see it as any more dangerous than anything we already have in our homes.

 

[FyrBldgGuy]

Sprinkler systems are not at a high pressure and they do not have atomizing nozzles. The concentrations of antifreeze in solar systems are greater then the NFPA TIA for sprinkler systems.

We should also ban antifreeze in cars.

 

[Frank]

The sprinkler system typically operates at a significantly higher pressure than a solar collector loop.

While the sprinkler head is not an atomizing nozzle as such, they do, particularly residential type sprinklers, produce a significant number of fine droplets, particulalry in the area near the axis of the head that can produce zone of ignitable fuel air mixtures at temperatures considerably below the flash point of the liquid similar to the operation of an oil burner with an atomizing nozzle.

This NFPA report has an interesting discussion of this effect with sprinkler and antifreez solutions.

http://www.nfpa.org/assets/files//PDF/Research/RFAntifreezeSprinklers.pdf