VitoSol Conundrum

Paul Pollets

2 panels of the Vaccuum tubes has been providing 70% of the the yearly DHW in this residence in Seattle. B-92 Viessmann tank with 2 coils(with boiler backup)Siemens PV panels do 90% of the electrical load.

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Constantin

What has been your experience with the VitoSol 300?

I am seriously considering adding $$$ to the house construction costs by going with solar water heating. Since I and my heating installer have been infected by the Orange Plague, it has to be a VitoSol system with all the fixings.

From what I can tell, the VitoSol system is highly regarded and may give our Vitola the summer off, if sized correctly. However, there is a little wrinkle in the story that has me a bit concerned.

It is my understanding that solar hot water systems should be sized to cover IDWH needs 100% in the summertime only. Our contractor is proposing a H30 system, which would probably produce enough hot water for about 6 people in the Boston latitudes. That sounds great, except that the planning and production department in our household have yet to produce multiple offspring.

• So, how well would a VitoSol H30 system handle only the IDWH needs of two people initially? We currently plan to use the 300l SS tank.
• Is this a scenario where I'd disengage some of the tubes until our hot water needs increase to meet the total capacity of the H30 array? Or do I put white socks over some tubes in the summertime, pulling them off in the winter?
• What happens in solar hot water systems when the occupants go on vacation in the summer? Where does all that waste heat get dumped?

I have ordered "Lessons Learned", it hasn't gotten here yet. Oh wisdom of the wall, don't fail me now...

kevin coppinger_4

you could ...

invite friends and neihbors over for showers....How 'bout a car wash style custom shower...say 23 gal/min...:) kpc

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Paul Pollets

2 panels

does 75% of the yearly DHW load using 2 3m panels and a Viessmann B-92 tank with 2 coils (boiler backup) Thermomax SMT400 controller. The Siemens PV panels do 90% of the electrical load. We'll be taking a look at this project in detail at my ISH seminar in Boston next month.

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Brad_9

Overheat?

So Paul, that's a large enough collector to seriously overheat 92 gal of water in the summer, how did it do, what did it do?

With flat plate collectors the temperature eventually gets high enough that the losses equal the collection. I've seen some pretty hot tanks of water though. My own 4x10 flat plate collector heating the lower half of a dual coil 80 gal tank never got over 155* F this summer, but it's a poorly insulated tank so my utility room got very hot (to be remedied). Still, my water heater didn't turn on more than twice between May and Sept.

With a drain back system you can set the controller to turn off and let the collector drain when it gets too hot. This lets the collector stagnate, not a problen for a high quality flat plate collector. I don't know if you can do this with an evacuated tube collector. I'm not sure that the header would drain properly.

For evacuated tube collectors, I belive all of your suggestions would work, also you could just turn the tubes so that the edge of the absorber plates were facing up, instead of flat. I also seem to remember that evacuated tube heat pipe collectors stop pumping internally at some temperature, but I'm not sure.

I think for vacation, if you didn't do any of the other suggestions, you could plumb a loop of copper somewhere in the solar loop so that you could parallel some of the fluid through a radiator, possibly just un-insulated pipe would do it. Is there a low head temperature diversion valve made to make it automatic?

Paul Pollets

No overheating

The system design does not overheat the water. When solar gain is at its peak, the tank recovers faster. There's a tempering valve at the DHW outlet for protection, and the relief valve has never blown off. The control can change all parameters of the system, from differential setpoints to multiple pumping and storage tank scenarios. BTW,This is not a drainback system. The owner has been datalogging both the PV and DHW panels. In the summer, (June, Jul, Aug) the panels provide close to 95% of all electric and potable hot water load. In Dec-Feb, he gets 55%. Not bad for a 4000SF home. There's also waste recovery on all plumbing DWV.

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Weezbo

i like the lash up.

how do you deall with snow loads icing and wind? i know thats three really small ?'s with probably volumes of to do items...however i have time...and i think this would work here also. our temps in the shade on the concrete walls were like 104¡ãF ... i think the 23+hrs of daylight is a wonderfuld deal in some respects...the 23 hrs od night and cold ..well That! Is , highly overated:))

Ron Huber

overheating

This evacuated tube system (Thermomax, Viessmanns supplier of tubes)has 120 tubes, installed in 95/96 , heated indoor pool and 120 gallon Viessmann DHW, when the pool was closed down for insurance reasons, all the tubes eventually lost their charge due to stagnation, they are now useless, If they have addressed this issue since then that would be great. Have a Vitosol DHW system runnig for about 4 years on the 92 gallon tank,tubes were ok last time I checked.

Constantin

So, in other words...

... over-heating can be a problem, even with a system as sophisticated as the VitoSol 300. However, I think your example is a bit extreme... no tank/pool to dump waste heat into... I'd like to think that a H30 system with the 79 Gallon tank would tolerate periods of non-occupancy without serious stagnation issues.

Reading more of their literature, it could be as simple as rotating some cylinders 180° out of sun alignment to minimize their solar uptake, no?

Ted_5

Look at the Vitosol 100 system

That is new this year. It uses flat plate collectors. If you are only going for DHW it is a good choice and is less money the the 300. The system is all the same, just the collector is different. The 100 collectors can go unused with out damage. Use 2 collectors now and you can always slide more on the rack at a later date.

Ted
Viessmann rep.

jerry scharf_2

a few thoughts

I was in a similar situation, and came up with a couple things to help the overheat problem out.

First, I put the collectors on an A frame, and tilted it for max winter collection. This reduced the summer output and flattened the overal output. You could do this to intentionally derate the solar until you have greater demand. This requires a trip or two to the roof, and the neighborhood architectural police might not approve.

Second, put in a hot tub and dump the extra heat there.

jerry