Using 1000 gallon water storage tank with solar

[nrcrash]

Has anyone tied in there thermal storage tanks from their boilers in conjunction with solar tubes to provide hot water in the summer? I was not sure if this would be a good idea, or even possible....

 

[Armaton]

They do. Bob Rohr has an 80 gallon tank ( I believe), he uses for solar. Not sure how large you could go and still maintain usable heat though. Awful hard to keep 1000 gallons hot unless you have alot of solar panels.

 

[Bob Rohr]

They do. Bob Rohr has an 80 gallon tank ( I believe), he uses for solar. Not sure how large you could go and still maintain usable heat though. Awful hard to keep 1000 gallons hot unless you have alot of solar panels.

Typically 1.5 - 2 gallons of storage per square foot of collector. So unless you could just heat the very upper portion of a large tank like that and add the HX at that very top layer, you would need a large array for 1000 gallons. might be better to find a smaller solar tank.

I have 5 collectors, 4X8 connected to a 160 gallon tank, which shuttles over to an 80 gallon tank.

The 80 gallon tank has a 40 plate HX on the outside that supplies DHW. I'll get at least 3 months of DHW without any LP consumption.

For a typical family of 3 or 4 a 60- 80 gallon solar tank with a 4X8 or 4X10 collector, should provide a good portion of DHW, depending on your location 30- 45%.

 

[tom in maine]

If a 1000 gallon tank is insulated reasonably well and you start off at, say 120F, it would replace daily DHW usage this time of year without back up.
We have customers who have done this with solar thermal and/or heat pump water heaters.
The key is to have a decent insulation value (about R-30) not too much surface area (maybe up to 200 sq. ft.) and enough solar thermal collectors for an average household. One I can think of is a customer in Canada, with an 820g tank who uses about 64 sq. ft. of collector in the summer.
His DHW is coming from the solar system. Of course, if the insulation value is less or the surface area is more, you bump up the system with
an occasional fire or a heat pump. Most folks seem to not need back up.

This does fly in the face of what we always considered an appropriate ratio of collector to storage, but it does work in the summer.

 

[Bob Rohr]

If a 1000 gallon tank is insulated reasonably well and you start off at, say 120F, it would replace daily DHW usage this time of year without back up.
We have customers who have done this with solar thermal and/or heat pump water heaters.
The key is to have a decent insulation value (about R-30) not too much surface area (maybe up to 200 sq. ft.) and enough solar thermal collectors for an average household. One I can think of is a customer in Canada, with an 820g tank who uses about 64 sq. ft. of collector in the summer.
His DHW is coming from the solar system. Of course, if the insulation value is less or the surface area is more, you bump up the system with
an occasional fire or a heat pump. Most folks seem to not need back up.
This does fly in the face of what we always considered an appropriate ratio of collector to storage, but it does work in the summer.

Great points Tom, once the tank temperature is high enough, keeping the energy stored is the key. Maybe never letting the tank slip below 120 after the wood boiler goes off for the season is the way to start. then the array just needs to offset the daily use, and loss through the insulation. thanks for the input and experience.

 

[flyingcow]

Great points Tom, once the tank temperature is high enough, keeping the energy stored is the key. Maybe never letting the tank slip below 120 after the wood boiler goes off for the season is the way to start. then the array just needs to offset the daily use, and loss through the insulation. thanks for the input and experience.

No thermal collector, just a tarm wood boiler for heat. But I know if i let my tank 820 gal tank get below 110/120f in the summer I get a little grumbling about the shower not hot enough.

 

[maple1]

Seems to me the actual type of DHW exchanger, and tanks, might play a part here also. If you have a flat plate that pulls off the top of the tank, and you can maintain good stratification, you would only have to keep a small part of your tanks (the top) at temp. Which would have a secondary effect that there would be even less stand by losses since most of your tank isn't hot. Therefore not as much overall heat input needed - I think?

 

[tom in maine]

We have done this with and without coil heat exchangers. Similar results. When using DHW, the tank naturally stratifies. The big volume aids in this.
A plate hx might be worse depending on pick up points for the hx and the flow. The passive flow of a coil seems to work well.