Navien Tankless Combi Boiler

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  #41  
Old 04-01-13, 08:28 PM
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$50?
That might buy the 2 1-1/2" dielectric unions
What about all the ball valves, other unions, purge ports, relief valves and copper and fittings?

Where are there 1 1/2 unions?

How much is this manifold? I can price it out for you but most stuff on this manifold is not needed IMO...

Here is a Bosch I did... You tell me what it cost.....

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  #42  
Old 04-02-13, 09:14 AM
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Mike

Interesting ... what make/model boiler is that attached to? I also noticed the Navien model appears to have 12" spacing between the tees, it looks like you might have 6" tops... can you explain why that is?
 
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Old 04-02-13, 09:30 AM
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One of the things that I believe that the Navien attempts to accomplish is a thorough 'mixing' of the two flows, from the boiler and the system.

This looks like it is accomplished by increasing the size of the pipe in the vicinity of the CSTs to 2", and increasing the distance between the tees.

This increase in size also would tend to minimize pressure difference between the CSTs such that they can be further apart without excessive DP between them.
 
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Old 04-02-13, 10:01 AM
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This looks like it is accomplished by increasing the size of the pipe in the vicinity of the CSTs to 2", and increasing the distance between the tees.
Yes I see that...How does that relate to the port in and out of the heat exchanger I wonder? Surely smaller then 2"

Thats the oddest thing I have seen.
 
  #45  
Old 04-03-13, 07:18 AM
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Zl700:

I'm trying to locate a place on the web where I can buy that manifold, I'll add up all the parts and see if its cheaper for my to DIY the thing or not.

@lawrosa

Thanks for pointing me towards that heat loss calculator, MUCH more than I expected it to be in terms of completeness. I'm retaking measurements today, will let you know my btu requirement later.

@ZL700 again...

I've seen you post calculations on the varying heat flows working together to effectively provide the 180k BTU the 240 is capable of. Could you work that out with a 4GPM primary and secondary? Just glancing over your caluclations (which I don't fully understand) it seems like with even heat flows the system will still be limited to 50k BTU, and it indeed depends on the secondary (or with the CH-Manifold kit, primary) loop flowing much faster than the loop on the boiler. IDK, I think there is something I'm missing here, thats why I'm asking for your help.
 
  #46  
Old 04-03-13, 04:19 PM
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Thats the oddest thing I have seen.
Go here:

http://comfort-calc.net/primary-seco..._tutorial.html

and scroll down to "Here is something different"

This shows a 'flow reversal' at the CSTs, but it doesn't HAVE to.

It's the same idea as the manufactured Navien... the section of larger tubing allows a pressure drop in that section and the increased volume promotes blending of the flows.

I feel that with the decreased pressure in the larger section of pipe that the tees can be spaced a bit further apart without detriment. The idea of keeping the tees as close together as possible is to keep the pressure drop BETWEEN the tees to a minimum. By going up to say 2" pipe for that section, even if the tees are further apart, the pressure drop between them will still be acceptable and you will have the benefit of 'blended flows'.

This design is sort of a 'hybrid' between standard closely spaced tees and a hydraulic separator.

under $300 for this one

image courtesy taco-hvac.com
 
  #47  
Old 04-03-13, 08:46 PM
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OMG that has been THE most helpful link regarding p/s piping. Its finally starting to gel. So I think what I want to do is use the boiler on the secondary loop using CSTs, the independent zones will be setup on the primary loop using these manifolds: RHM02-50PK - Rifeng RHM02-50PK - 2 Loop Stainless Steel Manifold Package (1/2" PEX)

So they heating zones wont be 'secondary' in the sense that they don't use CSTs but the flow rates through each zone will be identical. I have more questions though:

Is 4GPM the max you can flow through 3/4" copper? I've read elsewhere that its the highest safe-operating speed for 3/4" copper, just confirming here?

I found the formula I was talking about, it was posted by HDE and reads:

Boiler flow 150 degree supply at 5GPM pipe primary secondary with secondary circuit, 15 GPM pump, 20 DT at room temp of 70 results in a mixed water temp return to boiler of 90 degrees

150 - 90 = a 60 degree boiler operating DT

60 x 500 x 5. = 150,000 BTU fire rate, thus you are not limited to 50-90MBTUH with proper install and piping
Posted by Ironman:
The Navien CH BOILERS work well. We've had no problems with them. As Chris pointed out, the models that the "horses mouth" gave you are water heaters, not boilers. The boilers also do not have a storage tank built in. But, the controls work very well in switching from space heating to domestic.

There is one caveat with these units: the on board pump can only deliver 5 gpm. for space heating. With high temp baseboard like you have, that translates to 50k btu'sat a 20* Delta T, 170* average water temp. It doesn't matter that the burner is 199k, the pump is only going to move enough water to deliver 50k btu's at the above numbers. The pump is sized for domestic heating and at 5 gpm, 77* Delta T, you get 192.5k btu's. The only way to get more btu's for space heating is to widen the Delta T which is only possible if your base board is over sized or you add more emitters which would allow for lower water temps. and a wider Delta T
So of course, I'm thinking "how convenient" I'm going to run the boiler at 150* with up to 5GPM on the secondary (boiler) loop. What comes next is how he got to the rest of those numbers:

20* DT @ room temp of 70 = 90* return temp... Can someone help me understand this? How did he get to a 90* design temp here? I thought DT is the difference between supply and return temps, so if supply temp = 150* and return temp = 90* then the DT is actually 60* not the 20 quoted in the equation. This is good because the higher my DT the more efficient the boiler is operating.

I also understand fin tube baseboard is effective down to 100*, if I've got a 90* return temp then whatever length of pipe is running off 90* water is just a drag on my system and wasted money and is only effective in adding length to the heat runs to increase my DT.... gotta be a better way, maybe run the boiler at 160* and get 100* return temp?

I also noticed that for these p/s setups, they usually have the flow through the heating element pretty high, some of them are suggesting flow rates up to 15GPM... sure, I could get a 007 pump that can handle that no problem but I'm afraid that speed is way too high for copper and probably exceeding what the pex can handle.
 

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  #48  
Old 04-04-13, 10:01 AM
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I Think I'm More or Less on the Right Track

Hello again everybody, I'm sharing a diagram of what I think the piping layout should look like. Please provide your feedback and ideas, let me know how I'm doing.
  • I'm planning on having the boiler on a secondary loop using CSTs.
  • I would like to have 3 separate heating zones for the sake of comfort. Those zones won't be on a separate loop so-to-speak because they won't be using CSTs so I don't know whether to consider them primary or secondary piping?
  • I figure if each zone is calling for heat at the same time and set for 4GPM flow rate, my primary loop has to provide at least 12 GPM. So I figure my primary loop needs a circulator of its own that will provide that flow rate, and return 5 GPM to the circuit to keep sufficient flow through the boiler secondary loop which will be at about 4 GPM. So I've calculated the circulator on the primary loop to need to provide 17 GPM. (what goes into a tee must come out of a tee)
  • Each heating zone is flowing at 4GPM
  • I've calculated a DT of 16.05 at 17 GPM on the primary, and 22 at 12 GPM on the primary. This leaves me with not a very high DT, so not making full use of the condensing efficiency of the boiler ... I don't know what to do about this.
  • Let me know what you think PLEASE

Math:

Boiler does 150k BTU @ 91% so netting 136,500 BTU capacity...

136,500 / n(500) = 17 >>>> 17n = 273 >>> n = 16.05DT
or
136,500 / n(500) = 12 >>>> 12n = 273 >>> n = 22DT

Math Source:
Page 10 of Weil-McLain Manual
http://www.weil-mclain.com/en/assets...ler_manual.pdf
 
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  #49  
Old 04-04-13, 03:52 PM
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Is 4GPM the max you can flow through 3/4" copper? I've read elsewhere that its the highest safe-operating speed for 3/4" copper, just confirming here?
It's more or less a 'standard' design value that is used. Makes the math easy and puts one in more or less the 'middle' of the flow range.

It's not the GPM you are concerned with really, but the VELOCITY, THE FEET PER SECOND, the SPEED of the water.

For ANY size pipe, you want to keep the VELOCITY between 2 and 4 FT/SEC.

No less than 2 in order to keep the air bubbles in the stream moving, and no more than 4 to prevent velocity noise and eventual erosion and pinholes in the copper.

I think, going from memory here, that 4 FPS in 3/4" tube is a bit more than FIVE GPM. So the theoretical maximum is a bit more than 4 GPM. If I recall, 2 FPS is a bit under 2 GPM. (charts are available on the internet to verify, I'm just too lazy to look right now.)

We just use 4 GPM (in 3/4") to ensure quiet operation and elimination of air.

Keep in mind that a little under or a little over won't make any noticeable difference in performance.
 
  #50  
Old 04-04-13, 04:00 PM
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How did he get to a 90* design temp here?
results in a mixed water temp return to boiler of 90 degrees
Not sure what you mean 'design temp'... that's not what he's talking about.

This is referring to the "MIXED WATER TEMP". In other words, when the hot boiler water mixes with the cooler return water in the volumes mentioned, the result will be 90 water.

I think... I'm being lazy again and just glossing over it, but that's my impression.

In other words, X gallons of Y temperature water mixed with A gallons of B temperature water yields C temperature water.
 
  #51  
Old 04-04-13, 04:03 PM
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they usually have the flow through the heating element pretty high, some of them are suggesting flow rates up to 15GPM
I suspect a misconception here.

15 GPM in what size pipe? Certainly not 3/4 or 1. Probably not 1-1/4 either... maybe 1-1/2 ?
 
  #52  
Old 04-04-13, 04:07 PM
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I have 'issues' with your proposed design, but before we get to that, I don't understand what you are doing with this:

I've calculated the circulator on the primary loop to need to provide 17 GPM.
You don't need to add the flow in the boiler loop to the primary loop.

Those two flows are HYDRAULICALLY SEPARATED. They have no effect on each other.

If you have 3 zones running 4 GPM each, then the loop they connect to will run 12 GPM max when all three zones are open.
 
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Old 04-04-13, 04:11 PM
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I don't understand your diagram.

by what method are the zones connected? What do those pinkey purpley boxes represent?

Why is the end of the loop closed?

Why do you even need the pump on the so-called 'primary loop' ?

Why not do this and be done?

 
  #54  
Old 04-04-13, 04:15 PM
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With all that said, I still can't say that I understand how with a boiler pump that maxes out at 5 GPM, one can get 150K BTUH out of this boiler without running a 60F delta T across the boiler.
 
  #55  
Old 04-04-13, 04:50 PM
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...

Thanks NJ Trooper for you input. Insofar as the 15GPM, if you click through some of the links I provided the contributors I mentioned clearly say 15GPM in some of those discussions. I'm not sure what size pipe they're suggesting that go through, but it just seems unsustainable, if not even physically possible. I imagine to get 15GPM I'd need mayb 2 or 3 inch pipe, which would reduce the FPS, correct? It seems such a large pipe would throw off the balance a hydronic system requires.

As far as the primary loop goes, I see how 12GPM is sufficient, I wasn't sure about that which is why I calculated it twice in my previous post. At a 12GPM flow, I'd be getting a 22* DT.

The purpley boxes are these manifolds: RHM02-50PK - Rifeng RHM02-50PK - 2 Loop Stainless Steel Manifold Package (1/2" PEX)

One thing that irks me about the available manifolds out there is that ALL of them have only 1/2" loop connection sizes, so I'll have to use an adapter right there to open it up to 3/4" inch which is what the size of the baseboards are.

I don't know if you saw the picture before I updated it or not but the primary loop is not closed, it goes around (purple line going over the purpley boxes) from the red line to the blue line. So I'm not sure what you mean by the loop being closed.

I wasn't sure or not if I needed the pump on the primary loop. I guess I thought that since the heating loops are not hydraulicly separated, if one turns on (4GPM), all that's available to the loops downstream is 4GPM which is sufficient for their flows but maybe not the heat flow? Also, from what I've read, I think I understand that a p/s system for mod/cons depends on the 'other' loop from the boiler being much faster than the boiler's internal capacity. So, for example, if the boiler is secondary and only flowing at 4GPM, it depends on the primary loop to be moving much faster to get the heat out and achieve 136k BTU instead of the 50k on the secondary loop.

In effect, the drawing I made is just a "complete" picture of what you've shown. It has the boiler on a secondary loop, It has 3 zones coming off the primary loop. My drawing just "completes" the one you provided by showing where the cool water returns to the system. I also added the pump on the primary loop.
 
  #56  
Old 11-28-13, 09:45 AM
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i have the navien combo unit and have a 'general use' operating question. it's already installed by a professional and working fine. i remember the plumber telling me when setting the thermostat program not to have too large a delta between the temperature when we're away at work, to the temperature for the hours we want to be home and have heat. i think he said no more then 3-5 degrees. is that right? also, we keep the house at 60F when we're away and manually turn it up to 65 when we want heat. I'm wondering it wouldn't cost much more $ (in heating bills) to just have it set at 67 or so when we're away and 71 when we're home. does the Navien use less energy to maintain a temperature then to quickly jump to a new higher temperature?
 
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Old 11-28-13, 11:44 AM
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i think he said no more then 3-5 degrees. is that right?
Usually in the range of what I recommend. I usually tell people THREE for a period of 8 hours or less.

I'm wondering it wouldn't cost much more $ (in heating bills) to just have it set at 67 or so when we're away and 71 when we're home
Of course it will cost more to keep a higher temperature. It depends on the price you put on your comfort whether it is worth it to you. I don't think it will cost THAT much more... a couple percent I guess?

does the Navien use less energy to maintain a temperature then to quickly jump to a new higher temperature?
The following applies to ANY HEATING SYSTEM, not just the Navien.

There's no question that setting a thermostat back CAN save fuel. It doesn't ALWAYS save fuel. There's a 'balancing point of diminishing returns' in the amount of setback that will save money, in spite of what the DOE or anyone else says.

Think about it... if you set the thermostat back 5 while you are away or sleeping, when you want to raise the temperature back to where you are comfortable, it will take TIME, and during this time the boiler will need to input EXTRA heat into the home to reheat the entire building, it's contents, and the air inside the building.

Setting back a thermostat WILL save energy during the setback period because the DIFFERENCE between indoor and outdoor temperature is what determines the HEAT LOSS of the building during this time. Less difference between indoor and outdoor means a SLOWER (less) heat loss.

The 'balancing point' comes when you reheat the building. Will it take the SAME energy to reheat as you have saved during the setback? Maybe LESS? Maybe MORE? Who knows? It would take some heavy duty experimentation and lots of data collection to figure out.

Bottom line? Stick with the 3-5 and you'll be fine. If you find that the system has to run extra hard to get the house comfortable after a setback, reduce the setback a degree or two.
 
  #58  
Old 12-03-13, 01:45 PM
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thank you NJ Trooper! i'll work with this info.
 
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Old 12-03-13, 03:34 PM
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You're welcome! Good Luck! ..................
 
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