Sizing circulators

[tmudd]

I have been asked for assistance on getting a radiant floor project off the ground. My experience consist of getting my wood fired boiler running and from the good advice form people on this site it works flawlessly.
Here is what I have to contend with. It was installed 10 years ago but never hooked up. It was set up for an outside wood boiler but the owners have now decided to use a 110000 BTU Elite brand condensing boiler.
It has a 1" supply and return ports. I was going to do the near piping as a supply return system.

-Heat loss calculations on the building were figured by the local utility company at 103000 btu
- Slab floor heat with 15 zones 320' plus or minus 1/2" pex under slab pipe. The slab is insulated at
the perimeter of the foundation and 2' around the perimeter of the slab.
- The system has 77' of 1" supply and 77' 1" return pipe supplying 4 of the the fifteen zones with a 4
block manifold. Each zone has approximately 320' of 1/2" pex under slab.
- The rest of the system will have 68' of 1" supply and 68" of 1"return pipe supplying 11 of the
remaining 320' 1/2" pex under slab zones with an 11-12 ? block block manifold.

-The boiler came with a small circulator for the boiler loop to be hydraulically separated from the
supply return piping to the system . I have chosen to control the system with circulators. .

My question is what size pumps do I need for the 11- 12 block manifold and the 4 block maniflold. this calculation is over my head.

T-boy

 

[maple1]

No insulation under the slab? Except for the 2'?

 

[BoilerMan]

No insulation under the slab? Except for the 2'?

Exactly what jumped off the page at me too!

Hopefully the slab is well drained, there is going to be a lot of heat loss to the earth.

TS

 

[tmudd]

No insulation under the slab? Except for the 2'?

 

[tmudd]

Maple,
That is correct about the insulation.This is the deck that I have been dealt. The work was engineered when the building was built by someone else 10 years ago, You have to understand the Midwest is foreign to water heat generally. There are a lot of old copper in the slab jobs run on gas boilers with no insulation at all on pre 50's homes and brick building in more urban areas, but when air conditioning went mainstream people switched to forced air because of the unbearable summer humidity and heat. Lately in the last 5- 7 years outside wood boilers were all the rage.

Boilerman,
The slab is well drained situated on the site about 12" higher than any thing else with ground sloping away on all 4 sides.
Any thoughts on how to approach sizing this?

 

[heaterman]

Here's a rough stab at it....

The 11 loop manifold :
Using a Grundfos 15-58 on Speed 2 will give you .6 gpm per loop @ about 8 ft of head.
With an entering water temp of 120* that zone will crank out about 88,000 btu's.

The 4 loop manifold
Using the same pump on speed 1 will give you about .75gpm per loop @ about 9 ft of head
The same entering water temp will deliver about 37,000 btu's

The boiler will run at max output until the slab temp starts to stabilize and that's not a bad thing. I think that the boiler you are working with has the capability to modulate the firing rate.

Two questions.....What are you going to use to mix the water temp down?
What size is the boiler pump? Make and model?

It is absolutely critical to have enough flow through the small heat exchangers in these condensing boilers. Offhand I would say you need a 26-99 Grundfos (speed 2) or equivalent to keep that boiler happy. Something that will do an honest 10-12 GPM into pretty significant head is needed to carry away the heat that little bugger will put out.

You want to make the boiler piping its own loop. Put the pump on the return so it is pumping into the boiler. Install your air scoop, feed water valve and expansion tank just "upstream" of that pump. Do NOT pipe the boiler in a typical header fashion. Make it a loop. Just out and circle back to the return of the boiler.
Use a pair of closely spaced Tees in that loop to build your manifold out to the zone pumps. Those can be just a simple supply/ and return header arrangement.

Lot's of unknowns such as the number of fittings and valves in the mains going to the manifolds but these numbers will be close.

 

[tmudd]

Here's a rough stab at it....

The 11 loop manifold :
Using a Grundfos 15-58 on Speed 2 will give you .6 gpm per loop @ about 8 ft of head.
With an entering water temp of 120* that zone will crank out about 88,000 btu's.

The 4 loop manifold
Using the same pump on speed 1 will give you about .75gpm per loop @ about 9 ft of head
The same entering water temp will deliver about 37,000 btu's

The boiler will run at max output until the slab temp starts to stabilize and that's not a bad thing. I think that the boiler you are working with has the capability to modulate the firing rate.

Two questions.....What are you going to use to mix the water temp down?
What size is the boiler pump? Make and model?

It is absolutely critical to have enough flow through the small heat exchangers in these condensing boilers. Offhand I would say you need a 26-99 Grundfos (speed 2) or equivalent to keep that boiler happy. Something that will do an honest 10-12 GPM into pretty significant head is needed to carry away the heat that little bugger will put out.

You want to make the boiler piping its own loop. Put the pump on the return so it is pumping into the boiler. Install your air scoop, feed water valve and expansion tank just "upstream" of that pump. Do NOT pipe the boiler in a typical header fashion. Make it a loop. Just out and circle back to the return of the boiler.
Use a pair of closely spaced Tees in that loop to build your manifold out to the zone pumps. Those can be just a simple supply/ and return header arrangement.

Lot's of unknowns such as the number of fittings and valves in the mains going to the manifolds but these numbers will be close.

 

[tmudd]

Heaterman,
Thanks for the response. I have always respected your opinion on this forum. When I figured my loops I came up with this. Tell me if I am figuring this correctly

- 110,000 BTU for 15 outlets = 80663BTU for 11outlets
- 80606/10000= 8.06GPM
- 8.06/11outlets = .7327 GPM/circuit
- 330' 1/2"pex x .03 = 9.9 ft of head
Do I then add my 68' of 1" supply, 68' 1" return piping , valves, t's etc into the equation?I will have 4 -1" copper T's
7- 1" 90's, a swing check and 4 fullport ball valves in the system,I Do I average out the different ft of head and GPM from the supply return piping with the manifold outlets that we just figured?

I have not received the boiler yet for the pump size they included. But studying the installation manual off the web you are correct. I will have a primary secondary arrangement with hydraulic separation feeding the supply return manifold in on continuous loop. I agree with the location of the air scoop, expansion tank, feed water will be upstream from the location of the pump which will be pushing water through the return side.

Will I have to mix the water? I thought that the condensing boilers could just deliver the correct temp i.e 120 degree's continuously. My wood boiler mixes my own floor heat down to 135 degree for pex under floor. Isn't there a rule of thumb for concrete slabs not to be hotter than 120 degree water?

Thanks for all your help
Regards,
T-Boy

 

[heaterman]

Sounds like you're on the right track with the pumps/flow rates/btu's.

The calculation I did included the 1" tube you mentioned going to each manifold. I assumed that each zone pump would be located somewhere in that 1" main.

You should be able to dial that condensing boiler in at whatever you want. I'd probably start with 105-110* and work up from there if you have to. Keeping the water temp as low as possible will boost the efficiency of that boiler a bunch.

 

[tmudd]

Sounds like you're on the right track with the pumps/flow rates/btu's.

The calculation I did included the 1" tube you mentioned going to each manifold. I assumed that each zone pump would be located somewhere in that 1" main.

You should be able to dial that condensing boiler in at whatever you want. I'd probably start with 105-110* and work up from there if you have to. Keeping the water temp as low as possible will boost the efficiency of that boiler a bunch.

Sounds like you're on the right track with the pumps/flow rates/btu's.

The calculation I did included the 1" tube you mentioned going to each manifold. I assumed that each zone pump would be located somewhere in that 1" main.

You should be able to dial that condensing boiler in at whatever you want. I'd probably start with 105-110* and work up from there if you have to. Keeping the water temp as low as possible will boost the efficiency of that boiler a bunch.

Heaterman:
Thanks for the support. I'll try to keep everyone up to date once I get started. I intend to have flowmeters and gauges at the floor manifold to help dial it in. The boiler has a touch screen display temp/functions etc so the set up will be fast.
Here's for BetterBoileren
T-Boy