Plumbing the Boiler...

[goneflyin2002]

I'm setting up the plumbing for my new boiler- it's a Viessmann 100W-26 mod/con unit, connecting to my radiant floor.

Some specs:
floor- 2000 sq', 1/2" pex tubing 2100', spaced 12" in the grid
manifolds- simple copper 1" , with 9 branches
circulator pump- Grundfos UPS 26 3 speed

I've done heat loss calcs, and the results range from 37K to 50Kbtu's.

The question that I'm having a hard time finding an answer to is, can I just plumb this circuit directly or does it have to have a 'low loss header'/closely spaced tees?

Flow rate calcs show 2.7gph, head loss 4.7 and water temp 108*.

Many thanks!

Don

 

[Ron Lombardo]

If you go to the Manufacturer of the tubing with a floor plan of the Garage ...they will lay it all out and make you the material list and do the calculations for you.

My quick look at what you have ...usually 250 sf ft per loop is the max which in your case is 8 loops ... and I dont have the pump curve in front of me ...but makes sure the grunfos pump your using equals the taco 0013 ... because your going to need a high head pump to pump thru 9 loops of 1/2 tube. 2000 sqft in a average winter here in NY would net aprox 75 -100 btu input ... with out seeing your garage and being your in Canada I would suspect you dont want to go too small of a unit ... otherwise it will run constantly ..

My 2 cents

 

[goneflyin2002]

Thanks Ron,

that all sounds about right-

The Grundfos pump's specs are: •Flow Range: 0-33 GPM; •Head Range: 0-29 ft;

It's a powerful 3 speed pump, and I hope to use the 3 speeds to tweak the system once it's running.

My 9 loops are pretty consistent in length, ranging from 225' to 250'.

Just need to know if the boiler piping system can be made a single loop or if it has to be a 'primary/secondary' system (with another circulator also).

My thinking here is I wouldn't need the primary secondary system because my circuit is a big single zone, with no interruptions in flow, like zone valves etc.

Looking for opinions!

thanks,

Don

 

[Jackfre]

I'm setting up the plumbing for my new boiler- it's a Viessmann 100W-26 mod/con unit, connecting to my radiant floor.

Some specs:
floor- 2000 sq', 1/2" pex tubing 2100', spaced 12" in the grid
manifolds- simple copper 1" , with 9 branches
circulator pump- Grundfos UPS 26 3 speed

I've done heat loss calcs, and the results range from 37K to 50Kbtu's.

The question that I'm having a hard time finding an answer to is, can I just plumb this circuit directly or does it have to have a 'low loss header'/closely spaced tees?

Flow rate calcs show 2.7gph, head loss 4.7 and water temp 108*.

Many thanks!

Don

The boiler I'm working with (Rinnai) supplies the low loss header with every unit. It just simplifies the piping lay-out so much. Closely spaced tees are fine IF you have your fastball. I'd suggest you fabricate a llh. I think in the long run it makes the system easier all the way around. One reason I say that is that if there are problems with the system it is typically easier to see if it is a "boiler problem" or a "system problem"

 

[goneflyin2002]

Thanks Jack,
One question- does the Rinnai unit have an internal pump- so in total 2 circulator pumps in your circuit?

Don

 

[Ron Lombardo]

Primary and secondary loop system will require two pumps ... the size of the pumps are key to the efficiency and operation of the system. I have been playing around with 24v pumps to try to save on electric ..

 

[Jackfre]

Thanks Jack,
One question- does the Rinnai unit have an internal pump- so in total 2 circulator pumps in your circuit?

Don

Yes, the pump is installed in the boiler to supply the LLH/boiler loop. You have to select/buy your system pump. It also has the full outdoor reset package with the sensor included. It is a nice package. So is your V, but the included LLH makes piping a lot simpler.

 

[goneflyin2002]

Thanks for the messages guys,

I'm just trying to wrap my head around why this is necessary on a Mod/Condensing boiler...

I can understand the need to have the low loss header on a conventional boiler where you might need a bit of mix to keep the return temps high enough to avoid condensation in the stack.

But on this type of boiler, isn't it better to have a fairly cool return for best efficiency?

The shop where I got this boiler didn't mention me having to install the header (only supplied the main circulator)- I just saw some installations here on GJ and am trying to grasp the concept.

Thanks
Don

 

[Jackfre]

You can do this without the LLH. It may work. It may work well, if you are lucky with your selection of pumps, piping etc. The purpose of the llh is to separate the boiler loop from the heating loop. You separate the pressure drop of the boiler from your distribution system. For instance the boiler I'm most familiar with will do nothing but modulate the pump first and then the firing rate to maintain a 36F temp rise across the boiler. You then pick the correct system pump for your slab. Your system is going to have a small delta T just by the nature of the distribution system. Based on your reset curve you are going to have a low temp system. Does your model 100 come with the outdoor reset curve and sensor? You do need it. Viessmann makes a good boiler. Set it up right and you are good.

 

[goneflyin2002]

Great post Jack,
Thank you for that.

So the options are:

Set up the system with no header- but with these characteristics:
1.) maintain a 30-40*F delta across the boiler
2.) might have warm/cool spots in the floor
3.) probably a very low flow rate

Or set it up as a primary/secondary with the LLH, add a primary circ pump (a small one I think), and have these characteristics:
1.) more easily maintain the 30-40*F delta across the boiler to have best condensation
2.) have a low delta (10-20*F) in the secondary loop (floor)
3.) really move the water in the floor, higher flow rate with the main circulator
4.) less chances of warm/cool spots

So I assume I would just wire the two pumps to come on simultaneously with the control relay.

Also, yes the Viessmann boiler comes with the outdoor reset. There is a separate temp sensor that I will install.

Looks like a beautifully made unit.

I will check into the Viessmann LLH which might be available, or maybe will just make one with T's.

Don