Why cant I wrap my head around this?

morgo

So I had a plumber freind help me install a Bosch greenstar 151p recently exactly how its shown in the manual except I only have one zone so one circulator.We haven't commissioned it yet but I just dont get how this primary secondary loop works as shown. Wouldn't the hot water want to go to the right back into return if the circulator pump isn't going and then get pushed to the left out through the radiators when it calls for heat? Sorry if this is a dumb question but it bugs me that I cant understand him or this picture.

neilc

how are you controlling the zone circs? thru the boiler?
the boiler should be shut down if the circs aren't calling,
or if the primary sensor #7, is satisfied,

Jamie Hall

Two things. First, water is very lazy. yes, the boiler pump would push water through the heating loops --and will, but not much, as much the easiest thing for the water to do is to right back around through the boiler. That said, phantom or ghost flow can be a concern -- hence flo-checks.

Now as to when the circulators and the boiler pump are both operating, The primary ---boiler -- flow will be much as before, but the trick is in that short pipe between the two boiler connections. Depending on how much flow the circulator pump or pumps is calling for, the water will be pulled out into the system, and the direction of flow in the short pipe may actually be either way.

ratio

There's a pump inside the boiler, all it does is circulate water thru the boiler. You're right, when no zones are calling for heat, it just goes right back into the boiler. The boiler is watching it's internal temperature & will turn down or off as the temperature climbs. Once a zone pump comes on, however, things change. The zone pump starts sucking some of the water that's leaving the boiler & return water from the zone will enter the boiler. If you had more then one zone, they would be operating independently without effecting the operation of each other.

morgo

Thanks for the responses. Im so glad I found this page. When I look at this it seems like  the boiler pump would be pushing water counter clockwise through the primary and when the circulator in the secondary turned on it would pull it clockwise causing some sort of turbulence. 🤷‍♂️ I'm glad to be able to help with this install but my ignorance is stressing me out. 

ratio

You're right. With the boiler pumping and the zone off, all of the water will be going backwards between the two tees. When the zone pump turns on, it will move it's volume thru the system. How much—and what direction—the water flows between the two tees will depend on how much the two pumps are moving. If they're moving an identical volume, the the flow between the two tees will be zero. If the zone is moving less than the boiler, water will still be flowing backwards between the two tees. If the zone is pumping more than the boiler, the water between the two tees will be moving faster than the rest of the system. This is normal. The mixing that occurs is not an issue. (If you look at your piping diagram, you'll see note 7, "supply temp sensor", is located on the outlet side of the tees, so the boiler can account for any mixing that occurs.)

I suggest you read a book called "Primary-Secondary Pumping Made Easy!", available here. It gives a good explanation of what's going on & why it's that way.

hot_rod

At Lochinvar U they have a handy simulator. Plug in your numbers
In this case the boiler is flowing 15 gpm. The system is flowing only 10. So 5 is reversing flow through the pipe between the tees back into the boiler

A tip for the supply sensor#7, put it a foot or so downstream of the tees, so the flows have a chance to blend.

morgo

@ratio and @hot_rod I'm pretty mechanically inclined and have been  fabricating,  machining and maintenance for about  17 years so it gets to me when I can get these things. I appreciate ya  taking the time, great page

EdTheHeaterMan

neilc said:

how are you controlling the zone circs? thru the boiler?
the boiler should be shut down if the circs aren't calling,
or if the primary sensor #7, is satisfied,

OP original statement is:

So I had a plumber freind help me install a Bosch greenstar 151p recently exactly how its shown in the manual except I only have one zone so one circulator.

So your query should be How are you controlling your System Circ?

Just sayin'

EdTheHeaterMan

@morgo
You want to look at this video to understand the piping on your GreenStar
https://www.youtube.com/watch?v=0sA-b2vLU78

Remember that your boiler has a pump inside it and since the system has the expansion tank on it, the system is the primary loop and the boiler is the secondary.

morgo

@EdTheHeaterMan I actually watched that but didn't think of my boiler as the secondary 👍 as far as control. For now we hooked up my existing thermostat and a  taco zone switching relay to a  taco 007e pump.

neilc

EdTheHeaterMan said:

neilc said:

how are you controlling the zone circs? thru the boiler?
the boiler should be shut down if the circs aren't calling,
or if the primary sensor #7, is satisfied,

OP original statement is:

So I had a plumber freind help me install a Bosch greenstar 151p recently exactly how its shown in the manual except I only have one zone so one circulator.

So your query should be How are you controlling your System Circ?

Just sayin'

I'm still learning how to read, comprehension is my weakness