Closed system Flow problem

Outdoor_Man

Looking for help on some questions I have regarding Flow.... I recently build a new garage and have a tankless heater, 5 - 300ft loops in the concrete and 1 circulator pump (Grundfos 59896155 Up15-42F Brute Pump) for all 5 (closed system).. My problem is: When I first turn the pump on I have .8 gpm flow, which seems to be enough to start the heater, but after approx 8-9 minutes, the flow slows to a point that the heater shuts down. I do have a sight glass on the outlet side of the pump and can see the flow slow, but doesn't completely stop, just not enough to start the heater. Do I need to add an additional inline pump? or do I separate the loops into 1-3loop and 1-2loop system with an additional pump?

EdTheHeaterMan

Piping design, manifold, and pictures will help us diagnose.
the boiler needs a minimum flow that the boiler circulator may be able to produce as long as the connected piping is not two restrictive. It sounds like this may be the case with your system. You may need to use a second pump called the system pump. you may also need a repipe of the near boiler piping. the instruction manual in the boiler will have the info needed to properly pipe the system.

Here is a diagram of the piping i mentioned from www.pmengineer.com/

Outdoor_Man

Outdoor_Man

EdTheHeaterMan

You have insufficient flow. the piping is too restrictive. 3/4" pipe into the manifold for the radiant tubing.

You have 2 options. A) get a stronger pump or Re-pipe with a second circulator.

Not sure what brand you have... but here is a diagram from one manufacturer on the near boiler piping




You can see two circulators. One pumps the heat from the boiler to the primary loop, the second is to circulate the heat thru the floor tubing.

Check your boiler install instructions. see if there is a similar diagram

If your instructions indicate installing it that way you did, then check the pipe size and pump flow info to determine the minimum pipe size needed for proper operation.



the info is in the manual!

Outdoor_Man

Ed... What do you recommend for a stronger pump? or How do you suggest I re-pipe? I do have a second pump because I thought I had a bad pump. Can I re-pipe by using both pumps either "inline" with each other? or 1 pump for 3 loops and 1 pump for 2?

EdTheHeaterMan

Model number of pump (looks like Grundfos UPS15 or UPS26) brand, and model number of boiler?

Outdoor_Man

I have a
Grundfos UP15-42F Circulator Pump (currently installed)
Taco 007-F5-7IFC Cast Iron Circulator Pump (on the bench)...
Takagi T-KJr2-IN-LP Tankless Heater

Jamie Hall

Two pumps in a series -- "in-line" -- with each other is very rarely a good idea, unless they are very much the same. Yours aren't, so don't do it.

Tankless heaters have rather high head loss, and I expect that the combination of the tankless heater and that piping, all in series, is more than either of your pumps can handle. Try the primary/secondary piping which the various kind folks above have posted.

Outdoor_Man

Can I add another Grundfos UP15-42F Circulator Pump where I circled in the picture? Would it help? or should I just replace the current one with a Grundfos UPS15-58FC, 3-Speed Circulator.... another note is the Tankless heater is 144,000 BTU and the connections on the heater are 3/4"

mattmia2

You should pipe it primary-secondary like the diagrams show. Is that an actual heating boiler, or is that a tankless water heater?

Oh, I see above. It is a tankeless water heater. You will have to add a boiler pump and pipe it primary-secondary with external pumps for both loops I think, unless it has a DHW recirculation pump built in that can be made the primary pump.

Outdoor_Man

Please be aware that I'm very green at this and everything you see on the wall is My DIY. I'm trying to understand the diagram but I don't understand the symbols.... and remember this is a closed system so there is No Supply.. I think that is what I'm trying to say. So, what I've been using for a pump.... Is that a boiler pump?

Jamie Hall

A second pump in that location really won't help much -- and worse, is on the other side of the loops, so may have too low an inlet pressure.

But I've just noticed another problem on your sketch above: you have a note "hot water to house" off it one corner. Is this your domestic hot water feed? No. That simply won't do. One of the real no-nos is open systems like that.

Outdoor_Man

Jamie.... No that got changed when I found out it was a no no... It's a closed system now... sorry I should have deleted that prior to posting

Outdoor_Man

So... Should I just split the loops by adding another pump? 1 pump for 3 loops and 1 pump for 2 loops? I'm unsure about the diagram as far as understanding it... I'm very green at this.. What's the simplest way to fix my problem? Thanks everyone for helping out

Jamie Hall

Take a good hard look at the AquaBalance diagram that @EdTheHeaterMan posted, and adapt that to your system. There's some repiping to do...

Outdoor_Man

I assumed adding an additional pump to the "boiler return side" is what I needed to do according to the diagram... I don't see what else is different than what I did? other than adding an additional pump on the return side and I don't understand #7 on the diagram, with these two connections here wouldn't the fluid just "take the shortest distance though the tees back to the boiler"?

mattmia2

That diagram si showing primary-secondary piping. There are effectively 2 seperated loops, one that only pumps water through the boiler to keep its flow adequate (and since it is a water heater it will fire based on water temp and flow which isn't ideal for domestic heating).

The second loop will be for your heat emitters. It will have a separate pump only to produce flow for the

The "closely spaced Tees" in the diagram effectively isolate the effects of the 2 pumps to their respective loops. The water intermixes, but each pump can be thought of as only moving water through its respective loop. Loop 1 is the primary loop and its pump only moves water through the boiler. Loop 2 is the secondary loop and its pump moves water through the heating zones.

The hydraulic separation section of this explains it:
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_15_na.pdf

Outdoor_Man

That makes sense am I able to use two of the same model pumps that I have listed?

Jamie Hall

Consider the primary/secondary diagram. There are two circulating loops. Consider one of them to start at pump 8. The flow in that one goes from the pump to the boiler, through the boiler, out to one of the closely spaced Ts at 7, to the other closely spaced T -- or to the radiant loops, or both, depending on the relative flow rates -- and then to the other closely spaced T and back to pump 8. Now consider the other loop, starting with pump 5. Pump 5 takes water (at, it's rather important to note, the pressure in the expansion tank -- the expansion tank being the lowest pressure in the whole system) and pushes it out to the heating loops. The flow returns from the heating loops and goes to one of the closely space Ts at 7, then either to the boiler or to the other closely spaced T -- or both -- depending on the flow rate in the two loops -- and then back to the expansion tank and pump 5.

Now let's look at some other aspects of the operation. Pump 5 will be running any time the floor is asking for heat -- which, if the system is set up properly, should be all the time. A sensor on the floor circuit will sense whether the water temperature is correct (in more advanced systems, the set temperature varies with the outdoor temperature -- hotter water when it's cold outside). If the water temperature becomes too low, that sensor will turn on the boiler and pump 8, which will take some -- perhaps most -- of the water from the radiant loops and run it through the boiler and return it, nice and warm (the boiler's controls will determine how warm is warm), at the other T. Then, when the loop temperature is warm enough, the boiler and pump 8 turn off.

That's the basic approach. With more advanced controls and pumps, and modulating boilers, things can get considerably more complex -- and, potentially, more efficient. But that's basically the way it works, and not to worry about the fancy stuff.

hot_rod

Happens all the time, folks trying to use a tankless water heater as a boiler, not a good match.
Here is the pressure drop for that unit.

Do you know the GPM you need? 5 loops, call it .65 gpm per loop, call it 3.5 gpm.

So just the heater pressure drop would be around 6-7 ft of head, plus the piping valves, etc.
Now pull up the pump curve for then 15-42, looks a bit small for your application.
Add an additional 15-42 in series would be them least expensive fix.

Outdoor_Man

So... 2....15-42 would work together? or one something and one something else? So.... letting you know I have a thermostat on the current pump because it is a "on demand" boiler.....when the temp lowers the pump kicks in and the boiler turns on.... this matter in this situation?

Outdoor_Man

what about 2 of the UPS15-58FC, 3-Speed Circulator pumps might be better???

hot_rod

Is the 15-42 a single speed? If not try speed 3.

Yes the 15-58 has more output and adjustability as it is a 3 speed.

Ideally the circulator is sized by, flow rate and head required. Without knowing that it will be a bit of a guess. Multi speed circulators give you some additional range.

Based on your 5 loops, I'd guess 3-3.5 gpm, the left axis shows head, I think this circ may cover that.

EdTheHeaterMan

sorry, I needed to leave the conversation. It appears that @Jamie Hall and others have given you a better understanding of the preferred piping layout for your system. The boiler is of course not intended for your use, however, it does not mean it won't work.

Here are 3 illustrations to help you visualize what Jamie
described. This is the recommended piping


The Yellow circuit is the secondary loop with the "Boiler Circulator"


The Green circuit is the Primary Loop that has the "System Circulator"


Now think of them as separate systems with a very short common pipe that transfers the cold system water to the boiler and the hot boiler water to the system. Think about making this common pipe 1" copper with 1" copper tees. This will help with the traffic jam (of water) at the common pipe created by the 2 pumps using the same pipe. Try using the Taco 007F for pump #5 in the diagram. Use the Grundfos on the highest speed for the boiler circulator #8

If you still have a problem, then get the more powerful pump for the boiler pump #8 but I think the pump you have should work The flow rate of the #8 pump will determine the BTU rate of the burner, so you may find the pump you have is not powerful enough during the coldest days but will be adequate most of the time. That is a whole other discussion.

EdTheHeaterMan

one further comment you made about having no "Supply Water" because it is a closed system... We use the term Supply to mean the hot water leaving the boiler and the term Return to mean the cooler water (still pretty hot though) coming back to be heated. So on your boiler Supply is labeled HOT and return is labeled COLD

Outdoor_Man

Hoping this is my last post... Everyone has been so helpful and I thank you... This is what I came up with, thoughts? *note the bottom left comment

hot_rod

A hydrosep is another option, it gives you 4 critical functions, air, dirt, magnetic, and hydraulic separation.
Also a cleaner way to pipe P/S, really no reason to pipe a high point if you use a good microbubble type air separator.