Solar Heat Storage

[Robby]

I am installing 1100 gal storage tank for my wood boiler. I has many 3/4" inlets and I wish to add soft copper coils between them to supplement with evacuated tube system. How many BTU per ft. does copper lose to water? The copper comes in 25 and 50 ft coils, I was thinking of one 50 ft. Is this enough? I have no Idea!


Thanks

Robby

 

[steam man]

I wish I could give you a definate answer. The factors to consider are # and realistic output of the collectors. Since the tank is a "dual fuel" use that will affect the collector performance. 1100 gallons seems to be on the high side for collectors unless you have a lot of them or extremely low heating temp requirements. I will tell you this, 50' probably won't get you anywhere. I would suggest using STSS tank site to use their recommendations for copper coil length based on the number of panels to be used. They have done studies with copper coils. You have to also take into consideration how much water is to be heated and can you realistically reach that temperature at the end of the average heating day to be useable. I would say in the case of solar a larger heat surface area is better. Pump loss will be a consideration as well as the fact that the wood boiler will reduce the efficiency of the solar collection while in use.

I am looking for a tank around that size for a similar setup. Where did you get yours and is it pressurized or not?

Mike

 

[Robby]

Hi Steam Man

I have 120 evacuated tubes. They are on the roof and behind my boiler shed. The 1100 gallon tank right beside. I had intended to run boiler to tank and return. Then tank to house and rerurn. That way the tank is a seperate entity and I don't lose heat via boiler when is not lit.

The solar system will run from boiler shed into my utility room in basement, through bottom coil in dual coil 75 gallon tank. Mixing valve on main DHW tank set at 130 degrees. When main tank up to temp (about 150, maybe more) an aguastat will switch 3 way valve and send solar hot water to second hot water storage tank.

The DHW is piped from cold through second tank (dip tube) then from hot output to cold on main tank, then out main hot water outlet.

If second tank is also up to setpoint temp. then a second 3 way valve, in boiler shed, would direct solar hot water through the copper coil(s) in the 1100 gallon storage tank. That way it would act as a heat dump to maintain temperatures under 190 degrees and no heat is wasted. If enough heat is generated to heat the 1100 gallon tank, which I doubt, the automatic system would ensure that at some point the excess heat would be dumped through it's overheat zone.

The tank was advertized as a water pressure tank. it turned out to from a small towns pressure system and they had changed to something else. I think I got lucky. It is rated at 250PSI and 650 degrees F, and built in 1988. It has a 15" x 11" manhole, I definatly won't fit, (4) 4" threaded outlets and (5) 3/4 threaded outlets. I know that I should install vertical, but that seems a little unstable.

Any and all thoughts are more than welcome. I hate learning after I'm done, there was a better way.


Robby

 

[steam man]

Ironically, I also have a 120 tube system that I use to heat a 120 preheat tank and use a circulator to heat an additional 40 gallon tank. Ultimately it will use a three way valve to switch to a larger tank for space heating and a pool for summer use as soon as I make the connections. I do heat my domestic water pretty easy but I think I am going to get to 180 tubes to provide some radiant heating.

I have my eye on some large pressurized water tanks that may get scrapped. Not quite 1100 gallons though. For you in Alberta (had to look that one up) but I am thinking that you could put a copper coil in it to use it as a preheat coil before your 75 gallon domestic tank. That way if your dhw tank is up to temp you can still keep collecting BTU's more efficiently at a lower temperature.

I'll be out of internet range for awhile so I will check in in a few days.

later,

Mike