Radiant heat -- replace mutiple circulating pumps with single variable speed pump

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Wrdaigle

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Here is my dilemma. I live in an off-grid house in Montana. Our power comes from solar, wind and a propane generator. On average, we use about 3500 watt-hours/day when the radiant floor heat isn't being used. We rarely use the radiant floor heat because it is such an energy hog. Luckily, we have a central wood stove that heats the place very efficiently...as long as we're home. So right now we only use the radiant heat when it gets bitterly cold or if we're away. The problem is, we currently have 3 Taco 007 pumps that each use about 85 watts. If they all run for 12 hours, that's 3060 watt-hours. This doubles our energy use when we're not even home. This means the generator will almost certainly need to run. If it's bitterly cold out, the generator may or may not start without some coaxing. If this happens, our batteries may get over discharged and fail. For a while I thought I would just have to live with this setup and cross my fingers, then I started researching variable speed pumps like the Grundfos Alpha:

http://www.grundfos.com/products/find-product/alpha2.html
http://grundfos.oreilly-depalma.com/2010/alpha-circulator.shtml

We have a small (1300sf) home with 2 floor heating zones. Since we mainly use the boiler for backup, I am hoping I can get away with combining the zones and replacing all 3 pumps (one for the boiler and one for each zone) with a single Alpha pump. At some point, I may consider installing zone valves, but I don't think it's necessary at this point.

Here are the specs of my current system:
boilerConfig.jpg
boilerPics.jpg

Here are a few other details that might be pertenent:
  • 2 zones
  • 7 loops total
  • ~200 ft of 1/2" pex per loop
  • glycol filled

My hopes are that I can just replace the boiler pump with a Grundfos Alpha and bypass the 2 circulating pumps. Would I also need to eliminate the boiler return loop or modify it in some way? Any thoughts, suggestions, things I'm not considering?

Thanks, Bill
 

Tom Sawyer

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The boiler return loop needs to stay. You may be OK with a VFD but you need a rough estimate of how long your radiant loops are so you can get an idea of total pump head and size the pump accordingly. You will loose your zoning but with radiant it makes little difference anyway. I prefer Wilo VFD's to grundfos also
 

Ballvalve

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I use just one pump, high efficiency and high head and it will drive several zones - I have one zone 22' overhead.

Usually I use a Grunfos 26-96f [guessing number] , but the Taco uses a bit less juice -

http://www.pexuniverse.com/store/product/taco-0011-f4-circulator-pump-ci

I control flow with valves to zones. But if you just want to keep the house from freezing, I'll bet you could run all the zones with one of the taco's you have now, and tie all the zones together.

Looked at the alpha. Interesting pump for energy use. Dont understand the "adaptive" part. How about one pump at the boiler inlet running, and just shut off the other two? Water will pass thru them as they sit un-powered. Easy to at least test it. Don't need a bypass.
 

Wrdaigle

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Well, I just did some number crunching and I think I'm well within range for either the Gundfos Alpha or the Wilo Statos ECO (thanks for the tip on that one Tom). However, I ran the numbers using water as opposed to glycol, so I'm not sure how far off I might be. Here is what went into my calculations:

BTU requirements:
I live in a cold area, but my house is extremely well insulated. Walls and ceiling are both > R40. My house is 1300sq ft and is designed for passive solar (If it's above 0F, we don't need supplemental heat until the sun goes down).
For my calculations, I used a heat requirement of 60,000BTU/hr, but I think this is definitely overkill.

Flow requirement:
The heating array is made up of (60) 30' lengths of 1/2" pex for a total length of 1800'. These are divided into 7 different loops of 257' each. If each loop is responsible for 8500BTU/hr and I am assuming a 20 degree temperature drop, then the flow through each loop should be 0.85 gal/min. Total flow for all 7 loops combined will be 5.95 gal/min.

Head Calculation:
Assuming 0.03 ft of head per foot and a loop length of 257ft, my total head is 7.71ft.

Again, all of this assumes there is water in the system. My system is 50/50 water/glycol. How should I adjust for this?

Here are the performance curves for the 2 pumps I am interested in and where my calculations fall.

pumpPerformanceCurves.jpg

Assuming glycol doesn't change the equation too much, does this seem reasonable?
 

Jadnashua

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ANtifreeze in the water decreases the heat transfer ability about 20% if I remember correctly. Need to double-check that. FWIW, your boiler is setup as a primary/secondary loop system, and the pump on the primary loop must remain. Often, it must run some minimum gpm through the boiler, or you'll have problems so a variable speed may not solve your problems if a single pump tried to push less than the minimum through the boiler on the primary loop.
 

Wrdaigle

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I think I'm definitely up for giving it a try. My only question is, how would I know if I'm not getting the minimum gpm through the boiler? I'm not necessarily opposed to getting 2 variable speeds. At some point I would like to add additional inputs (solar hot water) and outputs (dhw). I assumeI will need at least 2 pumps at that point anyway.
 

hj

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quote; How about one pump at the boiler inlet running, and just shut off the other two? Water will pass thru them as they sit un-powered.

Water will NOT flow through them since they are NOT on the "circuit" for the operating pump. You have to know WHY they used three pumps in the first place, since it could have been operated with a single pump, (millions of systems are done that way), and proper piping. If it was for zoning, then you either have to eliminate that function or change to zone valves.
 

Ballvalve

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from his diagram they appear to be in the circuit with the water flowing thru a heat exchanger in the boiler. And a tempering valve on the outlet.

My only question is, how would I know if I'm not getting the minimum gpm through the boiler?
Add some thermometers to your pipes and watch your thermometer in the house.
 

Wrdaigle

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HJ is right. The 2 circulating pumps are on the secondary heating loop. The following diagram depicts what I'm proposing...

boilerConfig2.jpg

I have talked with the plumber who did the original work. The reason for the 2nd and 3rd pump were simply for zoning. The previous owner wanted multiple zones. I don't particularly care. The plumber didn't seem comfortable with the idea of zone valves and I don't think he really understood the ramifications of the added electricity on the power system. If do the modifications in the diagram, what is to stop all of the water from simply flowing through the primary (2" copper) loop. It seems like this would be the path of least resistance. Sorry for my ignorance. Just trying to make sure I have a good grasp on the consequences.
 

Jadnashua

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If you maintain the primary/secondary loops, and the boiler manufacturer may dictate that, you'd need at least one other pump to the zones, I think, or you'll get just what you thought...water mostly circulating in the primary loop. Now, the 007 may be big for the primary loop, and you might be able to save a little wattage there. My Buderus came with the primary loop components which included a variable speed pump. For my system, it is always supposed to be set at medium to provide the proper flow through the boiler heat exchanger. You could use whatever you needed for the secondary loop(s).
 

hj

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Eliminate the "primary loop". If you have single pump you eliminate the zoning, and thus the need to operate the boiler independent of the heating demands. Wire the boiler for the pump AND burner to come on simultaneously so there is ALWAYS maximum flow, and then there is no concern about a "minimum flow". And, install the pump the "proper way" by putting it on the line from the boiler TO the radiant lines, NOT the line from them to the boiler. You boiler is a "rat's nest" of piping, but if your drawing is correct the "pressure tank", (really an expansion tank), is in the wrong location. It should be at the point of "zero pressure change", namely on the boiler, or at the most at the "air scoop" which should have a tapping on the bottom for it. You will probably also have to install "balancing cocks" in the returns so you can equalize the heat output of the two systems.
 
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Wrdaigle

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Ah...when in doubt, check the manual. The Burnham ES2 has no minimum flow requirements. I think the plumbing diagram provided by Burnham has all of the detail I need.

burhnamSingleZoneConfig.jpg

I looks like I don't necessarily need a primary/secondary loop. It does say that a bypass is required for a high volume system. I'm not sure I qualify or not, but it seems like just repositioning my primary circuit pump to the current secondary loop, upstream from the current zone split, would accomplish this.
 

Ballvalve

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As I said much earlier, ONE pump just about anywhere will run your system. The ONE could be an existing, likely, and save the what I guess is a huge tab for that new pump. You can push or pull water, I last heard.

You do not have a high volume sys.
 

Wrdaigle

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As I said much earlier, ONE pump just about anywhere will run your system.

Thanks ballvalve. I wasn't purposefully ignoring your previous message. To start, I will likely make it work with my existing pump. That alone will half(at a minimum) my energy consumption. If I can half it again through use of a more efficient pump, than that well worth a few hundred dollar investment. Watts are hard to come by in the middle of the winter.
 

hj

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quote; You can push or pull water, I last heard.

True, but if you were versed in hot water heating, you would KNOW that the pump "pushing" away from the boiler creates fewer problems than "pulling it" back to the boiler.
 
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