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[Ridgekid]

Yeah. It's too early to tell. I'm just trying too hard to predict what's its going to do.

Btw my kill a watt check started the adaptive control over but it has set itself to 20 watts and 4 gpm.

We are still keeping our eye on it.

[woodywoodchucker]

I have a Grundfos 1/25 hp pump witch has 3 speeds that pumps the boiler water back to the boiler. On my instilation the water gravity feeds to the hx and is pumped back to the boiler. Is this ok or less efficient than mounting the pump on the boiler?  I also wander how to tell witch speed is best? Help me to understand.

[Ridgekid]

Woody. It depends on your application.  Since its a circulating pump it's just important that the pump and the pex lines are not located higher than the fill line on the sight glass of the OWF.

[Ridgekid]

12 hour Update
Pump appears to have settled on 18 watts and 3 gpm as the lowest set point for my system. No changes in last few hours as no heat has been used.

I ran a test of the pump to see how smart it really was.  I closed the discharge valve and it reported 0 gpm at 11 watts.  Guess i couldn't fool it!!!

We will see how it does overnight.   

[Ridgekid]

It's been 24 hours.........
So I went out this morning to see if I had any wood left in the Green Dragon. Yep, its there. Half of what I put in last night.
Next I checked to see how many times the Green Dragon came on. That was 2X. It was idle until 5:30 am. Thermostat kicks up at 6AM. So there was one burn cycle after that.
I check the Grundfos- 16 Watts at 3 GPM.

Interesting..... The last two days have been very similar in temperatures. The day before I had 2 more burns then I did last night.(For the same 8 hours)

Conclusion? The faster you move the water, the faster you loose heat? (When there is not heat load?)

[Ridgekid]

NEW INFO------PLEASE READ!!!
So after my post this morning I'm sitting all dumb and happy when I looked over at my Green Dragon temp display and see my Furnace is on, wife is using HW and the return temp to the boiler is 99*. WHAT? The furnace is pulling 30* out of the exchanger and the 20 plate is pulling almost 40*.

I run out to the pump and see it's auto adapted to 15 watts 2 gpm. If 99* water doesn't make it increase flow, it's time to set it on a desired pressure or speed control.

I know I had no issues at 4 GPM. So do I want speed or pressure control? I opted for pressure control. Why? Speed control will deliver the same amount at a given wattage set point. There would still be savings compared to the TACO.  Pressure control will deliver the same amount of flow, but as the water gets hotter it reflects a lower wattage.

I can live with 25-28 watts delivering 3-4 GPM.

We'll watch it again, but I don't expect any more problems.

[Scott7m]

Been thinking bout your sweet spot question and the whole idea in general.

I really don't think any of it matters.  You said your water was going back at 99, but heck only 2 gpm.  Your still extracting the same number of btu's regardless of how fast the water is moving.

Let's say you moved 1 gpm, and that water lost 50 degrees.  That's no different than 5gpm losing 10 degrees.  Just an example, same number of btu were used from the green dragon

[Ridgekid]

Thanks Scott. My concern was more of the cold water returning.  That can't be good to inject 99* water back into a hot boiler.  Then there's that magic number not to dip below. 140*. At that point your introducing oxygen. Correct? 

[Ridgekid]

Update-Day Two
Pumping more water does seem to be improving the performance. At 4 GPM,  I have 20* going across the heat exchanger when the furnace fan is on. So I would have to say 20* is the highest I would want to go.

I do want to also note I'm actually getting LESS # of burns at the slower GPM rate. (vs the Taco) After reviewing my records for the same daily average Temperatures and number of burns, I have reduced the number of burns by 1/3.

Today I'm going to operate at highest speed* to see if there are any changes, if not I will adjust back to highest Constant pressure.

We will continue monitoring the progress.

*=highest speed is 43 watts at 6 GPM.

[mcarter]

Thanks Scott. My concern was more of the cold water returning.  That can't be good to inject 99* water back into a hot boiler.  Then there's that magic number not to dip below. 140*. At that point your introducing oxygen. Correct?

 Ridgekid,

The lower the water temperature, the higher the oxygen solute.  Oxygen is not present in water at 180F degrees (82C).  For the purpose of comparison, which I think you may be interested in:

Oxygen solute (mg per liter of water):
    180F:  0mg
    140F:  14mg
    104F:  31mg
    68F:    43mg

This is the rationale for the setpoint of 180F degrees in an OWB.  Corrosion is prevented by the lack of oxygen.  Industrial applications take this a step further by pressurizing their boiler systems.

The 40F degree differential you reported would concern me a little (though, as you know, this isn't my profession) because of two things:
     1.  Cold stress/Hot stress of the steel (carbon steel in your case I believe)
     2.  It is not efficient

The different types of steel used in OWBs (mild, carbon, 304 and 409) probably have different characteristics that affect how each perform over the long term to cold/hot stress.  I don't even know the characteristics of my own (409), but I have to say, it was a significant investment that I want to last for a very long time and to that end, 180F is my preference along with <=20F differential.  No oxygen and reduce stress as much as possible.

There are so many factors that influence efficiency, it is hard to know where to even start.  I would think though, that as the temperature drops, a higher flow rate would be very beneficial to maintain the differential. 

Do you have a radiant setup?

Michael

[RSI]

The water is coming to the boiler at 180°, goes through the heat exchangers and drops to 100°. If there was no oxygen in the water when it came in it will have none on the way out.

2-4 GPM is a very small amount of water. and the temperature difference probably won't hurt anything. Is there is a pipe that goes a ways into the water jacket then it will be hot before it even mixes.

There is a lot bigger temperature difference in the firebox than 100°.

[Scott7m]

Hey rbi, have you experimented with the grundfos alpha pumps any?

[martyinmi]

Ridge,
   I'd run that puppy ba!!$ to the wall if its only drawing 43 watts That's still 107 less than the old pump. You have a lot invested in the dragon and it would be a shame if saving 6 or 8 bucks a month cost you even one year less longevity out of your pride and joy

   Marty

[Ridgekid]

This morning I set the Grundfos on max speed which showed 43 Watts at 6 GPM. When I got back from a meeting at the office it said 43 watts 4 gpm. I changed the setting back to pressure control 38 watts/4 gpm.

Across my furnace exchanger I get 20* heat load as long as I have 4 gpm. I'm good here!

For my 20 plate for my domestic hot water I'm dropping the return temp by 60-70* (Just witness this as wife filled up the tub). As soon as she was done filling it jumped right back up OWB return temp. (Return dropped to 104* during tub filling)

Based on all the replies, the distance I'm from the house to the Dragon and my test results I don't want to prematurely wear out the Dragon. Since I can't get the Grundfos to hold 6 Gpm, i think I'm going to be forced to put the TACO back on.

Anybody out there closer than 80' from their house to their OWF that wants to make arrangements for this Grundfos let me know. I need a TACO 009 F5 for a spare. (They are about the same price)

[Scott7m]

Wear it out?  If the water enters back into the stove and travels through a pipe inside the water jacket it's heated back up before the water is released into the water tank. 

I'm just not sure about all of this...    I like the principle and it seems were ruling out it's success based on some theories that I've never seen proven, at least in my perspective