Hydronic Piping Design

solpanc

I am studying Modern Hydronics Heating book. Can someone please explain why circulater C5 is only needed for the floor heating assembly and NOT the baseboard zones. I attached an image from the book.

Jamie Hall

Perhaps needless to say -- there are other ways of doing it. However, in that diagram, circulators one through 5 maintain flow in the various loops. Circulator 6 takes water from the main heating loops and injects it into the floor piping system at a rate controlled by the injection mixing controller. And circulator 7 keeps the water circulating in the floor loops -- at a very different temperature from the main heating loops.

Hilly

C5 is what will bring the warm boiler water over to the closely spaced tees at the injection loop. Other wise water will not get from the boiler to the injection loop. If you did not have the C5 and only ran C6 there would be no difference in water temperatures preventing any modulation for the radiant floor distribution.

solpanc

Hilly,
Are you saying c1,c2,c3&c4 dont need c5 because they arent taken off from closely spaced t's? Thank you

Mark Eatherton

C5 is needed for the boiler. It's location in relation to secondary output pumps is irrelevant. It is just moving water through the boiler on a space heating cal. Period. It is in the "primary" loop. The only thing that is critical is that it, and all other pumps must pump away from the point of no pressure change (PONPC).

If the take off for the DHW tank were immediately after the PONPC, then the next component in the primary loop could be the C 5 circulator.

If you put it downstream of the PONPC, but before the DHW circuit branch, it would cause a bypass of flow that would cause the DHW tank to over heat. Any time you have pumps in parallel (C5 and C1) both pumps must have check valves on their outlets to avoid mechanically induced unwanted flows, and should pump away from each other.

ME

hot_rod

C5 turns a basic S&R header piping into a primary secondary loop.

Notice the large pipe size headers on the boiler S&R headers. These provide adequate flow capacity for the baseboard loops which are parallel piped.

solpanc

The book says c5 is only turned on for the radiant subassembly and not for c1-c4. I still don't have a clear answer what is the difference between the baseboard that does not need c5 and the radiant system that does need c5.

Gordy

The radiant sub assembly is primary secondary. With out c5 running the boiler would see no flow. Where the baseboard portion is piped so the zone circs flow through the boiler because supply is before c5, and returns are after c5. So c5 is not needed when there is not a call for radiant zone.

hot_rod

flow for the baseboard zones is enabled directly from S&R headers off the boiler.

To get a continuous supply of hot water to the radiant C5 caused flow across those closely spaced tees. The addition of the closely spaced tees creates a primary secondary piping arrangement.

So the radiant gets a mixed down temperature via a variable speed pump C6.

While looking unorthodox that piping works quite well for supplying multiple temperatures.

Gordy

a primary secondary duet. The radiant zone can run what ever flow it wants with out disruption of the variable speed injection loop. The variable speed injection loop runs what ever flow it needs to accomidate the SWT requirement for the ODR with out conflicting with the flow in the primary c5 loop.

solpanc

Thanks for all the comments!!

Mark Eatherton

solpanc said:

The book says c5 is only turned on for the radiant subassembly and not for c1-c4. I still don't have a clear answer what is the difference between the baseboard that does not need c5 and the radiant system that does need c5.

Please note that the C2,3,and 4 are piped parallel to C5 and each has its own check valve. C5 has to wash heat by the radiant circuits.

My previous statement was incorrect. I didn't look close enough due to poor picture quality (my bad).

Please note also that this is a high mass boiler that isn't flow critical. If it were a low mass or mod con boiler, my previous statement would be more true

The statement about all pumps having to pump away from the PONPC is absolutely TRUE...

I tried to click on DISAGREE on my own post, but the software won't allow it...

ME

Ironman

Without reading the context, I believe the drawing is primarily intended to show a simple method of adding a radiant floor to an existing CI boiler with baseboards. Though, it could obviously be a new install also.

If you'll notice, the piping for C5 is just another direct return loop like C1 - C4. The pumps on C1 - C4 create flow through their individual zones as well as the boiler. C5 is doing the same thing, the only difference is it's pumping through closely spaced Tess for a tertiary loop (the injection bridge with C6), instead of pumping through a BB rad. C5 is parallel to C1 - C4.

Just turn the C5 piping 90* counterclockwise and it becomes more clear.

Zman

The drawing shows a fairly (overly) complex system likely to show how complex systems can be controlled. Smart mixing valves were not as prevalent at the time.
If the boiler is cast iron with no minimum flow requirements, it would be simpler to eliminate C5 and use a smart valve in place of the injection assembly.

Eastman

@Zman
What do you mean by a smart mixing valve?

Zman

Taco I series valves are a good example

Solid_Fuel_Man

Motorized 3 way or 4 way valve. It eliminates a circulator and the need for variable speed injection. Both injection loops, and mixing valves have their place IMHO.

Injection mixing becomes more cost effective in large scale radiant systems, where a properly sized mixing valves are quite expensive. Not always true though.

Also it is kind of a "zone by circulator" vs "zone with valves" kind of thing. Both have their pros and cons. There is no always correct answer.

Taylor

hot_rod

I think that chapter was to introduce the readers to many of the options available. Injection mixing was the most common strategy used in the early 90's radiant heyday.

It still is a great option for mini tube injection, moving big loads with small diameter tube leveraging 80° ∆Ts