Combi Boiler System Installation Help

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John Gayewski

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It looks like from the info provided by the boiler a circulator capable of moving 4.4 gpm with 12 ft of head would get you less than 20 degrees of temp drop. For the primary loop.

Maybe go with something a little less powerful. A combi boiler wants cooler water returning to it. The longer it runs the better the effeciancy. Looks like you could go up to the 40 degree range of you wanted to.
 

Reicherb

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I feel really good about everything now except that I have the correct flow rate and head loss numbers. I can't seem to find a website that explains it in a way I can understand... Can you help me verify it?

Main zone:
30'x40' with 6-200' loops of 1/2" PEX
BTU load of 33,000

Flow rate is GPM = BTU / Delta T x 500
Flow rate is GPM = 33,000 / (20 x 500)
Flow rate is 3.3GPM
Is it correct to use Delta T of 20 in a radiant slab system?

Head Loss:
3.3GPM/6 circuits = .15
This is where the wheels come off for me. What is the typical head loss of 1ft of 1/2" pex at .15gpm? I can't find a table that goes that low...Looking at the charts I can find helps me estimate it to be .001/ft. At 200' loops that would be a head loss of 2. I assume that is wrong...

Additional 2 zones:
10'x20' with 1-200' loop of 1/2" PEX
BTU load of 5,500

Flow rate is GPM = BTU / Delta T x 500
Flow rate is GPM = 5,500 / (20 x 500)
Flow rate is 0.55GPM
Is it correct to use Delta T of 20 in a radiant slab system?

Head Loss:
A flow rate of .5 has a head loss of .01/ft. At 200' that's a head loss of 20. I'm assume this is wrong...
 

Reicherb

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It looks like from the info provided by the boiler a circulator capable of moving 4.4 gpm with 12 ft of head would get you less than 20 degrees of temp drop. For the primary loop.

Maybe go with something a little less powerful. A combi boiler wants cooler water returning to it. The longer it runs the better the effeciancy. Looks like you could go up to the 40 degree range of you wanted to.

I was doing my math and didn't see you post again... You're talking about the secondary loop. Correct? The primary isn't as important because the heat loss isn't there. Correct? The Taco 007e can't overcome 12' of head. The Taco 0015e3 seems like it might be too big. What about the Grundfos UPS15-58FC?
 

John Gayewski

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Head loss. I use a short cut that works and is simplified. Longest loop (highest pressure drop) in feet x 0.06= head loss for the zone.

This is a common way to do it. The more complicated way that site shows doesn't get more accurate in enough of a way to hassel with it, mainly becuse you have manifolds valves and fittings to worry about. Some people will do the same equation using 0.03 as the multiplier for pex systems and they say it works. I don't have experience with this. If I were to use that multiplier I would also multiply my longest run by 1.5 to account for fittings and manifolds.

The primary loop head loss I grabbed from the chart in the manual.

Your primary loop will be mixing with the secondary loop's return water. The faster the primary loop the less it mixes. If you slow the pump down the return water in the primary loop will get cooler.
 

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Head loss. I use a short cut that works and is simplified. Longest loop (highest pressure drop) in feet x 0.06= head loss for the zone.

This is a common way to do it. The more complicated way that site shows doesn't get more accurate in enough of a way to hassel with it, mainly becuse you have manifolds valves and fittings to worry about. Some people will do the same equation using 0.03 as the multiplier for pex systems and they say it works. I don't have experience with this. If I were to use that multiplier I would also multiply my longest run by 1.5 to account for fittings and manifolds.

The primary loop head loss I grabbed from the chart in the manual.

Your primary loop will be mixing with the secondary loop's return water. The faster the primary loop the less it mixes. If you slow the pump down the return water in the primary loop will get cooler.

Thanks. Taco 0015e3 the right choice then? Taco 007e is too small. Correct?


Combi boiler has two heat exchangers, one burner. Its either- or but not both at the same time. Radiate runs at 80*- 85* dhw 120*

Does that mean no need for a mixing valive?
 

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Fitter30

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Ball and gate valves are not balance devises only globe valve ( piped in the bottom out the top) ,circuit setter or flow control valve. Need to reread this article
https://www.pexuniverse.com/how-size-circulator-pump
Dhw 2 gpm @ 70* rise being in a pole barn for a sink can set reasonable water temp mixing valve shouldn't be needed. Expansion tank ,air eliminator, fill suction side secondary loop pump. Antifreeze can't be automotive made for heating / cooling systems they have the proper additives. Propylene gylcol minimum 30% for the additives. Whatever is the coldest ambient temp need glycol not for freezinag but slushing. Two reasons mix will be easier to pump and won't burst the piping. Percentage of glycol has to be in the calculation of picking the pumps.
https://www.amazon.com/Nu-Calgon-Propylene-Glycol-Blue/dp/B008HQ79A8/ref=asc_df_B008HQ79A8/?tag=hyprod-20&linkCode=df0&hvadid=366299818038&hvpos=&hvnetw=g&hvrand=14102940878060927578&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023803&hvtargid=pla-806676113715&psc=1&tag=&ref=&adgrpid=79955528327&hvpone=&hvptwo=&hvadid=366299818038&hvpos=&hvnetw=g&hvrand=14102940878060927578&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023803&hvtargid=pla-80667611371
1/2" pex . 92 gallon per 100'
 

Reicherb

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Ball and gate valves are not balance devises only globe valve ( piped in the bottom out the top) ,circuit setter or flow control valve. Need to reread this article
https://www.pexuniverse.com/how-size-circulator-pump
Dhw 2 gpm @ 70* rise being in a pole barn for a sink can set reasonable water temp mixing valve shouldn't be needed. Expansion tank ,air eliminator, fill suction side secondary loop pump. Antifreeze can't be automotive made for heating / cooling systems they have the proper additives. Propylene gylcol minimum 30% for the additives. Whatever is the coldest ambient temp need glycol not for freezinag but slushing. Two reasons mix will be easier to pump and won't burst the piping. Percentage of glycol has to be in the calculation of picking the pumps.
https://www.amazon.com/Nu-Calgon-Propylene-Glycol-Blue/dp/B008HQ79A8/ref=asc_df_B008HQ79A8/?tag=hyprod-20&linkCode=df0&hvadid=366299818038&hvpos=&hvnetw=g&hvrand=14102940878060927578&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023803&hvtargid=pla-806676113715&psc=1&tag=&ref=&adgrpid=79955528327&hvpone=&hvptwo=&hvadid=366299818038&hvpos=&hvnetw=g&hvrand=14102940878060927578&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023803&hvtargid=pla-80667611371
1/2" pex . 92 gallon per 100'

I've read that article over and over and over and have some sort of block that is stopping me from fully understanding it... What are you suggesting I'm missing?

I was thinking I'd use this anti-freeze:
https://www.supplyhouse.com/Hercules-35284-Cryo-Tek-100-Anti-Freeze-Glycol-5-Gallon

I guess 60% glycol would be required as on rare days, the temp could approach -20. Maybe that doesn't matter because in theory it would take a while for the building to get that cold.
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/35284-Product Overview.pdf

I could for 50% for the stuff you sent but it's more expensive:
https://www.nucalgon.com/media/6687/3-72_freez-kontrl.pdf
 

Dana

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If there is one circulator that can do the tiny zones and the big zone then use one, but I'm gonna doubt that.

If you buy a variable speed circulator be aware that it WILL shorten the life of the circular.

'splain me that one, please!

An ECM drive smart pump set up for pressure feedback with zone valves is a pretty standard power-sipping and long-lived solution, even when the zones sizes differ.
 

Dana

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Can you find an example drawing of what that would look like?

While purpose-made hydraulic separator components will do the job, it can also be done with fittings (for a lot less money) with closely spaced tees if you follow some prescriptive parameters carefully:

rzhxpftnz3h4.png
:

Making the hydraulic separator out of somewhat fatter piping than either the primary or secondary manifold plumbing improves overall performance as a separator.

A thermally massive higher volume buffering hydraulic separator also mitigates against short cycling on your smaller zones:

PME_0907_Feat2Fig10Lg.jpg


In low flow applications such as yours an electric water heater (unpowered) can be utilized as a buffering hydraulic separators (think of the tank as a ridiculously fat section of pipe), using the hot feed & drain ports as one of the loop connection pairs, the upper and lower heater element ports as the other loop connection pairs.

Note that direction is important- both the primary and secondary loop flows need to be in the same direction (whether closely spaced tees or any other hydraulic separator component or scheme.)
 

John Gayewski

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'splain me that one, please!

An ECM drive smart pump set up for pressure feedback with zone valves is a pretty standard power-sipping and long-lived solution, even when the zones sizes differ.
Vfd' s are not good for pumps. Splained.

There is a long more technical explanation. But to simplify. Your adding tons of complexity and expense. Vfds break A lot and they are expensive. Balancing the zone will lower the amp draw. No need to add a device.

If one wants to go with one pump a thermostatically controlled balancing valve will do better than a pump with a vfd.
 
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Reicherb

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'splain me that one, please!

An ECM drive smart pump set up for pressure feedback with zone valves is a pretty standard power-sipping and long-lived solution, even when the zones sizes differ.

So... Will the Taco 0015e3 with 50% gycol be a good solution based on the loops and load listed above.

And thanks for the education on the primary and secondary loops.

Thanks!
 

Reicherb

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Dana, if I use closely placed Tees, can the primary and secondary both be 1" with the secondary then going to manifold with smaller lines?
 

Reicherb

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Dana, based on the information that I've posted, dos the Taco 0015e3 seem like the appropriate circulator for the secondary loop?

Thanks.
 
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