Solar Storage Tanks 5.21.2010
SUNMAXX SOLAR HOT WATER SOLUTIONS
SOLAR THERMAL STORAGE TANKS
Date : 05/21/2010
Solar Thermal Storage Tanks:
OK! Well, good afternoon. Id like to welcome everybody to the first of our SunMaxx solar webinar series! This is GeoMaxx tanks. What I’d like to do today over the next half hour is go through the features of some of our GeoMaxx tanks, and different design configurations: pressure related things, heat exchangers
You each have a chat button . You can ask some questions as we go . I’ll try to answer them as I can, and of course you do have constant contact with one of your dealer reps
If you have any questions following this webinar please don’t hesitate to get in touch with us .
OK ! Well, our new line of tanks is really an obvious evolution from just a simple dual coil stainless steel tank . You know the dual coil serves a lot of purposes . It allows you to pull your solar loop off of the bottom , which increases the efficiency of the collectors . It also allows you, using your solar tank not only as solar storage but also as an indirect water heater off of your boiler , to replace your existing water heater altogether , and just tie a separate zone off of the boiler with the top coil .
Now this is just a simple closed loop indirect system where we can also – if we look at this slide – we can also use the top coil to tie into a heating zone , depending on the capacity of your tank . The top coil can transfer up to one hundred ninety thousand BTUs per hour , which is pretty significant heat exchange for a coil . One of the reasons for such a large rate of heat exchange is the large surface area , but there is also some degree of turbulence inside the coil , which increases the heat exchange through the walls of the coil .
Now with a system like this we can go from something very simple to complex , easily, with some control valves, 3 way valves , or additional circulators . Our control modules – the intellisol domestic hot water combi plus – has 11 configurations .Our simplest controller has 11 configurations !
So to go from a simple domestic hot water system to something a little bit more complex , like a combi system, is quite simple .
OK ! With regard to the tanks , these are obviously very versatile and have a much longer life span than most tanks that you see in the united states . But what I like about them the most is their heat exchange capacity . Over the last couple of years we’ve designed several versions of tanks , and one of the limiting factors was their ability to transfer heat through the top coil . As I have already mentioned, the 130 gallon tank has a top coil has the ability to transfer 190k BNTU of heat per hour , and that would satisfy most houses . Additionally they are very well insulated . There are two inches of polyurethane foam surrounding the tank proper, around which is another jacket of insulation that zips around the tank.
As you can see there are 6 ports in the front . We have the cold and hot supply and return , and also the two ports for the coils, the bottom and the top . Around the back side of this tank is a 6 inch clean out port, on the bottom . It opens up and allows you to service the tank. We expect at least 20 years out of these tanks. They are warrantied for 10 years . One of the features that make these tanks relatively unique is this enamel coating. So, not only do we have a high grade steel (which is 1.4571 High-grade steel) , but additionally an enamel coating . Now that coating offers a corrosion prevention measure, but it also insulates the inside of the tank slightly . It reduces the heat transfer through the metal of the steel of the tank. A third level of corrosion resistance is an anode rod . The anodes are designed to take out the ions from the solution , or ‘promote oxidation .’ The anode rod is really one of the most important things you can do for a tank, and we took it a step up by utilizing a commercial grade anode rod, which has a lot of magnesium ready to become oxidized and sacrifice itself for the good of the tank .
Additionally that anode rod can be replaced. As is generally the case with most anode rods, it is advisable to replace, or at least inspect the anode rod after five years. Now obviously the quality of the water will dictate the life expectancy of the anode , but part of this solar installer service contract , or maintenance contract, should include inspection of the anode , as well as obvious: the PH, and concentration issues with the glycol . Inspection should happen in a timely fashion, even 2 years wouldn’t hurt, although it will require you to drain the glycol below that level . On the top of the tank you’ll see a port for hot water . The hot water supply is where you will tee off to pressure relief valve. This tank does not come with a pressure relief valve ; different municipalities have laws that are different than others . I know New York state for example has a unique temperature and pressure rating for solar vessels at 180 degrees , and I believe 75 PSI . So the valves are not standard on this system but are easily added .
Another thing I want to point out now is that as you out your tee off to this hot water supply you’re going to run your pipe down into bucket – so you tee this into a bucket . It shouldn’t ever pop, really. The systems are designed in the solar side of things to have enough expansion . We have learned a lot about the importance of expansion vessels , especially when it comes to stagnation and steamback . With evacuated tubes expansion vessels are important but they are not the end all. We obviously also need to dissipate heat rather than just allow for expansion. But with the flat plates, though, if we size the system properly, we shouldn’t have this TP valve ever open up .
I did have some questions regarding the UL certification . I want to point out that the UL certification is not required for tanks that do not come with an electric element. So what you’ll have with this tank is an inch and a half port that will accept an element up to forty five hundred watts . Up to a 4500 watt element is suitable for a tank this size. It can be plugged, which most often is the case . Just to point out, even though you can get stratification from top to the bottom, ideally what we will find is forty degree stratification from the top to the bottom of the tank. Now that allows the efficiency of our collectors, to be greater , because the colder the return back to the collectors, the greater their efficiency. But at the same time, it keeps our wives happy, because they are taking hot showers!
Ideally, we might have two separate tanks: one as a preheat tank, and the other as your hot water tank, that maintains that minimum temperature. But with this design we are able to maintain about a forty degree to fifty-five degree, stratification. This is extremely important, lets say on a cloudy day .
In particular, in upstate New York we see probably two hundred fifty cloudy days a year. On a cloudy day, whether we are using flat plates or evacuated tubes we might only get our collectors up to ninety five, one hundred degrees . If that temperature does not meet the minimum temperature of our set point , then our pump will never kick on. If we have significant stratification, even though we might have a hundred and twenty up here at the top of the tank, we might have seventy five or eighty down here,
which gives us a much greater amount of utilization . It is essentially like having two separate tanks: one as a preheater, and one as your heat source .
Looking at different TSOL reports, or RETscreen reports, or SRCC OG-300 systems, these systems that use a preheat tank have a higher solar fraction. What we’ve been able to do is essentially have a separate strata here that represents a preheat tank – it operates at a different temperature than the top of the tank. Now this isn’t anything new, obviously. In Europe they’re further advanced than we are, and this is something very common in Germany and Austria, for example, where they really exploit the stratification of the tanks to get higher efficiencies in the collectors.