Filling solar collectors.........

[WoodMann]

I'm cobbling together a closed loop DHW system consisting of 2 panels, a 40 gallon water heater/ tank and heat exhanger. I know anti- freeze is required in the collector loop side, question is- can I use any automotive anti- freeze or is there a specific kind for solar applications...........

 

[velvetfoot]

I think the thing is that auto antifreeze is poisonous and that you'd have to use the glycol stuff.

 

[peakbagger]

Most of the antifreeze out there is glycol. The toxic stuff is ethylene glycol and the non toxic is polypropylene glycol. If you want to go really green there is polypropylene glycol that is made with a corn based feedstock. Depending on your heat exchanger, you do not need to use non toxic glycol on a SHW system.

If you have a heat exchanger that is hydraulically disconnected from the domestic water source, so that a leak in the heat exchanger could not leak into the potable side, no need for non toxic. An example of this would be a copper coil filled with glycol wrapped around a water tank. If the tube leaks, it leaks on the floor, not into your potable water. Obviously if the copper coil was inside the water tank, you need non toxic. You can buy indirect shell and tube type exchangers as well as flat pllate exchangers that look like they are direct heat exchangers, but they are designed with a internal double wall that will drain out of the side of the exchanger if a tube or plate fails. They look very similiar to direct units used in heating applications so make sure that whomever you buy them from, can assure you that they are indirect rated for potable water use.

From a practical basis, used etyhlene glycol is low grade hazardous waste and must legally be disposed of as such, while polypropylene glycol can be poured down a drain as its used as a food additive. Why set your self up for future hassle?

 

[WoodMann]

Cool, thamks for the explanation. Yes- the 2 liquids will not mix, I just thought that there might be a special anti- freeze; for whatever reason in DHW systems. But yeah- taking into consideration to avoid hassel, going with the edible stuff is a good idea from the get go..............