Solar preheat unused

Bobcat_2

The solar preheat tank sits at a temp higher than the boiler fired indirect. A recirc pump eventually (quite often) lowers the indirect tanks' temp so the boiler fires to maintain the set temp. My customer complains that the solar preheater could deliver the higher temps (when available) instead of the boiler always firing obnoxiously. When hot water is drawn from any tap all is good and the solar is serving it's purpose. But when the system sits idle and the recirc system drops the temps, I'm back in trouble. I suggested installing a timer on the recirc but my customer stays home frequently and wants it running continuously. Any suggestions would be helpful.

hr

Is the

complete recirc line and hot water piping well insulated?

This would be a good place to invest some time and money. If all the piping is inside and well insulated (1" wall thickness insulation) you shouldn't be loosing that much energy.

Consider adding a snap stat at the recirc return to shut down the pump when the loop is up to temperature. Often used in conjunction with a timer.

If they want instant DHW 24/7 they will have to pay a price, small or large depending on how much energy leaves the piping

I've often thought of installing a 3 way zone valve with a differental control somehow. If the solar tank is warmed up, DHW pulls from it only. As it drops below useable temperature the valve switches to the indirect. Haven't thought it through completly yet, but I understand what you are trying to accomplish, and have the same goal, although low on my project list

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Mark Eatherton1

Howsabout...

A differential controller, sensing the solar tank as the collector, and the auxilliary tank as the storage. Delta T is greater than 20, a 3 way diverter on the circ return diverts return water into solar Pre Heat tank. When delta T drops to 5 degrees F, circ return is diverted back to the aux tank, bypassing the solar tank. It would work, but seem like an awfully big waste of precious btu's. But, if you consider the fact that they're free, I guess it just don't matter...

ME

Rich W

recirc

I like all of the above. I use an inductive relay and a snap stat. Turn on the bathroom light and the circ starts. If you take too long on the morning paper work the stat will turn off the circ. Either way, you've got to have good insulation.Good luck.

Bobcat_2

snap switch

sounds reasonable and economical. Of course the masterbath is at least 60 ft away with a tough crawl. The new construction afforded for good insulation detail although my attention was on the solar lines and radiant lines only, (pass the buck here). ((By the way I hate the inefficiency of recirc systems)). M.E. mentioned the use of a differential controller but perhaps a set-point controller might be more appropriate in conjuction with your three-way idea. The DHW boiler control is set at 128, I think. Once the solar storage approaches this setpoint, or exceeds it (adj), a three-way diverts the recirc pump into the solar storage, ie. flow through both tanks. I'm beginning to see some light here. OK??

Carl PE

A recirc pump eventually (quite often) lowers the indirect tanks' temp

So the pre-heat tank isn't part of the recirc loop?

Ok, if I understand what's going on here (and that's a big IF)... why don't you re-pipe the recirc loop to include the pre-heat tank? Then you can use your 3-way valve and aquastat (in the tank) to bypass the pre-heat when it's not up to temp?

hr

And the smallest

circ pump money can buy! You need very little flow to keep a recirc line warmed. More flow, from an oversized pump, increases the heat loss from that piping.

Consider all the indirect manufactures rate the tanks at less than 1/2° per hour loss through the jacket. In 8 hours that is 4°! That alone is not enough to cycle that tank on, even once, with a typical 15° differential on the tanks aquastat. As such, virtually all of that cycling is caused by piping loss, if they haven't used any DHW.

Even if it is a crummy job, insulate those DHW and recirc lines, both under the home and in the boiler room.

Make sure the indirect is piped and protected with checks on both supply and return, or they can, and do, thermosiphon back to a cold boiler. Which is then boiler standby loss and flue loss. Hot goes to cold regardless of the direction of travel.

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Kevin_in_Denver_2

D'mand systems > recirc

By now everyone at this site should know about the Taco or Metlund D'mand type of instant hot water:
http://www.gothotwater.com/News/saws.asp
No pipe insulation needed, no third return line, no timer, no continuous heat loss.
The only disadvantage is you must push a button a few seconds before you want hot water.