domestic hot water too hot in cold weather - options

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Old 01-13-13, 07:04 AM
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domestic hot water too hot in cold weather - options

Hi all,

Hoping that some of you may have ideas on this. I think I know what the problem is, but not sure of the best way to fix it.

I have a Buderus boiler with a Logomatic controller on it, which provides hot water to an indirect water heater, and also provides hot water heat to 2 zones, upstairs and downstairs. Here is a simplified diagram that shows the set-up (leaving out some details like expansion tank, etc.):

http://i123.photobucket.com/albums/o...ps20818d0a.png

[ATTACH=CONFIG]7834[/ATTACH]

During the summer, the DHW temperature in the indirect stays almost exactly at 120 F, which is the temperature I have it set to on the Logomatic controller. In the fall, when it gets colder outside and the boiler starts to heat the house, the DHW creeps up into the 130s and 140s. In winter, when it gets into the teens and twenties outside and the heating zones are calling for even more heat, the DHW can get up into the 160s or 170s.

I think the issue is that the main circulator pump which is circulating hot water to the 1st and 2nd floor of the house, is also pushing water through the second circulator to the indirect hot water heater. The flo-chek valve does nothing to prevent this because it's only preventing backflow.

I've talked with my plumber about this - smart, capable, nice guy (he didn't do all of this set-up originally, by the way) - and we're thinking that replacing the flo-chek valve with a Taco zone valve, and wiring it back to the Logamatic, might be the way to go. The idea would be to set it up so that the new Taco zone valve only opens up when the indirect is calling for hot water and the circulator next to the indirect is running. He and the electrician (another smart guy) would figure out a way to wire all this into the Logamatic and make it work.

It seems reasonable, but am curious about this set-up and just wanted to also run this question by all the experienced folks in this forum as a sanity check: Have you run into this sort of situation before? Are there other options you'd suggest - alternative ways of fixing the situation? What would be the ideal way of plumbing this kind of set-up if you were doing it from scratch?

Thanks in advance!
 
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Old 01-13-13, 08:52 AM
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The heat side circ should be on the other side of the tee that goes to the indirect as far as I see... That will probably fix your issue.

Others will chime in
 
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Old 01-13-13, 10:12 AM
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Yeah adding a zone valve would probably 'fix' the issue... is it the right way? No. Is it acceptable? I wouldn't want it on my system.

This is more like what it should have been:

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They do, by the way, make circs with flow check built in. Taco designates this with -IFC (Internal Flow Check) in the model number... I forget what Grundfos uses... but something in the number tells that it has one.
 
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Old 01-13-13, 10:21 AM
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By the way, if that's not rain water on your chimney, it is likely condensate from the flue gases from your boiler and will eventually eat the mortar and brick because the stuff is acidic.

Newer boilers run cooler flue gas temps and increase the likelihood of the flue gases condensing and destroying the chimney.
 
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Old 01-17-13, 01:02 PM
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Thank you, lawrosa and NJ Trooper. That diagram that you did was extremely helpful, NJ Trooper, appreciate it. Makes it very clear.

One question since you both seem very knowledgeable on this - what is the "downside" of doing it the incorrect way that I had described earlier?

I do believe that what NJ Trooper showed in the diagram looks much cleaner and neater - am only trying to educate myself about the potential problems of doing it the other way.

Thank you!!
 
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Old 01-17-13, 01:08 PM
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The way you have it two circs are pumping towards the indirect. The heat circ is actually working as a indirect circ....
 
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Old 01-17-13, 01:17 PM
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Thanks for the quick response! I see what you mean. It seems redundant to have two circulators both pumping toward the indirect. Would it cause any actual harm, or have any disadvantages, like wearing down one of the circulators prematurely? Or is it just that it's pointless and a waste to have two circulators when one would do the job?
 
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Old 01-17-13, 02:25 PM
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Or is it just that it's pointless and a waste to have two circulators when one would do the job?
Yes, that... I don't think anything would actually be damaged by it ...

The real problem is that you are overheating the domestic hot water... and wasting energy...

If the reason you ask is because you are thinking of 'living with it' until warmer weather in order to get it fixed when you don't need the heat on, sure... if you can live with it.
 
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Old 01-17-13, 03:03 PM
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Thank you NJ Trooper. You guys are very knowledgeable - I'm really grateful for the information and the quick responses!!
 
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Old 01-17-13, 03:16 PM
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You're quite welcome CC, let us know if you have any more Q's!
 
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