Stagnant water in a solar DHW setup

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.

btuser

Minister of Fire
Jan 15, 2009
2,069
Principality of Pontinha
I'm trying to put together a list of parts. My goal is to preheat my dhw, not replace it. I've made up my mind to use factory-made collectors, and other than that the only big part is the tank. I currently have a stainless indirect producing off my boiler. 2 years old, good condition and produces a TON of hw. I'd like to preheat the incomming cold water to reduce the dino btus.

In a perfect world I'd replace the indirect with a 100 gallon dual coil, but unless I can find one of those for cheap I'm going with 2 tanks, one to preheat and one to boost to temp. Most 2 tanks setups are of two options: The first is a tank full of preheated water with coil used to exchange water from the collectors. The second is the storage part of the tank holding the fluid from the collectors, and then running the cold water through the coil to preheat. This is the design I'd favor because it would allow the most btus stored per the size of the tank, but because of where my collectors will end up (below the storage tank) I'm going to have to use a glycol solution for freeze protection, and because of the volume of heat diffusion liquid I would need a huge exansion tank.

Do the packaged solar setups take stagnant water into consideration?
 
Stagnation in the collectors is an issue with glycol breaking down and turning into acidic sludge. This is dealt with by avoiding stagnation and testing the ph of the glycol. Is there another issue you're thinking about?

I don't work with indirect tanks. I'm just an ameteur tinkerer. From what I read, indirect seem to be much more common in the Northeast. I've never seen a system with the solar fluid stored in an indirect tank and the cold water run through the coil. Is this a common set up? I've seen pictures of unpressurised tanks that typically have a larger volume and larger coil for this same purpose.
 
The limiting size of storage is of course as we all know your tank volume. Because I'm only thinking of water tempering (I don't think I'm going to be able to get to 140 degrees with my usage/exposure) I want to preheat the incomming water to the indirect. If I use the coil of the preheating tank I'd be left with about 30-50 gallons of luke warm water on cold cloudy days and pretty hot water on warm sunny days.

My plan is to use a reverse indirect, and I'm trying to keep away from glycol because of the expansion properties of an antifreeze mix. With a reverse indirect I'd end up with close to 100 gallons, and need a 30 gallon expansion tank as well! If I ditch the reverse indirect and just heat a second tank to whatever temp I can get that would lower my mix to about 10 gallons which is much more managable, but leave me open to a large quanity of luke warm water that may or may not be re-heated to 140 degrees in the primary tank upon draw down.

How much for a quality 100g indirect tank with two coils? 2 grand! Ouch. This is why I'm leaning towards just a 2nd tank, becaue then I could just pick up a used Superstor on craigslist for 200-300 bucks and be off to the races.
 
I'm not so much worried about what kind of tank, just whether or not 40-100 gallons of water between the temperatures of 50 and 120 degrees is a health hazzard. I still plan to push through the oil-fired indirect and boost the temp to 140 degrees, but that may not kill every beastie.
 
Status
Not open for further replies.