Instead of paying big money for an expensive 3-way valve, couldn't I put an aquastat before the return to the boiler and hook it to a small circulator in the bypass loop?
Danfoss 3-way or Aquastat/circulator combination
- Thread starter markpee
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markpee said:
I think that's what Econoburn does. I use a zone valve in the bypass loop controlled based on inlet temp.
Can you go into some more detail? I would like to avoid ordering the Danfoss - how is it controled? Do you use an aquastat?
markpee said:
I can go into a great amount of detail, but I'm not sure that's what you want. If you like that sort of thing, check out my web site - link in my signature.
Basically, I have a bypass from the hot outlet through a zone valve back to a point just before the circulator, which is connected to my boiler cold inlet. I have a temp sensor measuring the temp between the circulator and the boiler inlet. If it's too cold, I open the zone valve. This provides some bypass flow, but there's also still flow through the zones.
You could use an aquastat instead of the temperature sensor / computer / relay scheme that I'm using.
So can it be that simple? I will attach the aquastat to the zone valve on the bypass loop and set the stat for 140? That's it? Do I need a balancing valve before the zone valve? If this is the solution, why do the manufacturers only mention the Danfoss?
markpee said:
Using a circulator or zone valve for bypass is a more crude way of controlling inlet temperature. The Danfoss does a much more elegant job of controlling inlet temp, and it's simpler and probably more reliable.
In the graph below, you can see that the inlet temperature cycles repeatedly as the valve opens and closes. Since all we're doing is trying to avoid condensation building up on the inside of the boiler, I think that's fine. In fact, I suspect that you really need input protection only if you're heating something large and cold that would keep the inlet below 140 for a long time, like a depleted storage tank.
Graph explanation:
The black and magenta lines are the wood boiler outlet and inlet. The colored horizontal lines near the bottom show what's happening with the controls. 'Demand' (the light brown line) means baseboard heat demand. The orange line is the controller forcing heat to the indirect hot water tank. Black is heating the hot tub, and blue is heating storage.
Green is the bypass zone valve. You can see that it's open while the boiler is coming up to temp, and open again for a good while as storage starts getting up to temp.
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The Danfoss valve is extremely simple and elegant. It really is nothing more than a housing for a car-type thermostat. It is much simpler than having a separate circulator/mixer trying to control the inlet water temp. I am not sure what the price is, since my dealer (AHONA in upstate NY), included one with the price of the EKO boiler. I didn't understand it at first, but after plumbing in the boiler, and thinking about it a while, the Danfoss valve is probably the simplest, and I would guess cheapest, solution available to control the boiler inlet water temp.
markpee said:
That's kinda where I came down, except that I could do a valve and a thermistor for about $70 - already had the controller. Still, the Danfoss is a more elegant solution.
Another inexpensive way ($91.98 http://www.accentshopping.com/product.asp/P_ID/151589) for boiler protection is to use an AM-102R-US mixing valve in the same place as the Danfoss.
The cheapest way (no modulation) would be to connect a line with a ball valve between supply and return and experimetn with how far to open to maintain a minimum return temperature - will affect efficiency after boiler is hot.
The cheapest way (no modulation) would be to connect a line with a ball valve between supply and return and experimetn with how far to open to maintain a minimum return temperature - will affect efficiency after boiler is hot.
If you are running 24/7 and your return water stays at or above 130-140, then no 3-way or other setup is needed to maintain bypass for boiler return water temperature protection. In this situation a manual valve on the bypass loop is needed only for startup until return water from system is where it should be.
If your return water regularly is falling below 130, then you need some other system on the bypass loop to protect the boiler. I have the Termovar, and it maintains return water at a minimum of 130 (surface temp on return pipe).
The elegance of a Termovar or Danfoss or other mixing valve to modulate boiler return water is a desirable way to go. Fewer parts, less complicated plumbing, and maybe in the end less cost too.
If your return water regularly is falling below 130, then you need some other system on the bypass loop to protect the boiler. I have the Termovar, and it maintains return water at a minimum of 130 (surface temp on return pipe).
The elegance of a Termovar or Danfoss or other mixing valve to modulate boiler return water is a desirable way to go. Fewer parts, less complicated plumbing, and maybe in the end less cost too.
The Termovar has no manual adjustment. It is factory pre-set. That said, Termovars are available with different temp settings and pipe sizes to fit your requirements.
I had a gate valve which I installed, rather than a ball valve. Essentially, once you think you have it set for the right flow (more closed than open), you never touch it again.
Trial and error. I closed the valve down all the way, and then opened it a number of turns. Fired the boiler. During operation I just opened the valve more or closed the valve more, seeking the point where it "felt" that bypass flow was about at the minimum to achieve and maintain return water temp. This ended up being open 4 full turns from fully closed. Less than that and it seemed not enough water was being returned through the valve to the boiler. Open more than that and it seemed no beneficial impact. The goal was maximum flow through the system while yet sufficient return temp protection. All I can say now is that it seems to work well without any noticeable issues.
Science at its best!
Science at its best!
jebatty said:
In my situation at least, there's no 'right' bypass flow. When storage is cold I need lots of bypass flow. If I'm not heating storage and the boiler is going well, I need no bypass flow at all.
Where is everyone buying the Termovar? Danfoss is hard enough to find, and pricey - I'd like to get a quote.
Do you really need a valve ahead of the termovar ?
Contact Dave at Cozy Heat to get a price on the termovar.
Contact Dave at Cozy Heat to get a price on the termovar.
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