Comments on Schematic?

Kestrel

Hello again.

Below is a schematic I'm beginning to settle on (many details left off, obviously).

Heat loss calc is done, I think: 9940 BTUH on second floor, 18500 BTHU on main floor, and 17500 in Basement, at design T of 20'F (Again big thanks to Brad White for all the help with HDD and gas use analysis!)

So, the schematic is similar to this - <a href="http://www.radiantandhydronics.com/RH/Home/Images/RH1210GF_fix_lg.jpg">http://www.radiantandhydronics.com/RH/Home/Images/RH1210GF_fix_lg.jpg</a> - though simpler, as I have fewer zones.



A few questions, to start with:

-When either the boiler pump or indirect pump is operating, it seems that flow will go to both the LLH and the indirect (in both my and Siggy's designs)- is that correct, and is it bad?

-Zone 1 is 1/2 PEX home runs to panel radiators, each with TRVs - 2 or 3 on the second floor and 4 in the basement.  Given the difference in the lengths of the homeruns and the difference in elevation, can they still be routed off the same manifold?

-In the interests of avoiding over-pumping - can P3 and P4 be consolidated?



Thanks in advance!

Kestrel

OOP - no schematic

I tried to attach a PP slide and it didn't attach - I'll try again.  Does it need to be .pdf?  Will JPEG work?

STEVEusaPA

few thoughts

Yes you left a 'few' things out. Was there another thread from you?

1. Unless you're doing something different with your controls, I don't see flow going thru your LLH, when you get a call for DHW.  Just seems like P2 handles DHW all  by itself. In the design you reference (Siggy's design), when the primary needs heat, no DHW,  the primary pump is running, and making a 'figure 8' if you will, thru the boiler, down, turn left (away from the indirect) thru the LLH, down and back thru the primary pump.  The secondary side takes what it need via one of its many pumps.

2.  Your drawing seems to conflict with what you say the zones are doing. Is  Zone 1 high temp & Zone 2  low temp? If so, they're doing two temperatures and are better off separated.  Also the radiant zones (zone 2) are going to need a pump that can handle a  much higher head.

Kestrel

thanks

I guess I was concerned that when either P1 or P2 are operating, hot water exit the boiler and could get to the first Tee, and go to both the LLH and the Indirect.

As to P3 and P4, yes, I still need to do the calculations for head and flow and choose a specific pump.  For P3, I was intending to use an ECM delta-P pump responding to the radiators with TRVs.

STEVEusaPA

re: ghost flow

With all the proper piping, flow checks, etc, think like water.  A zone calls for heat, P1 comes on, and a zone circ comes on.  As water exits the boiler it's heading for the LLH, the path of least resistance, and the greater pressure difference.  It's too lazy to try to work its way to, and through the indirect.

When the DHW calls, P2 comes on, and moves the water thru the indirect, and through the boiler.  When it passes that tee, it'll barely have time to wave in that direction.  The only time you'll see flow in both, is when both are calling for heat, unless you set your controls for DHW priority.

Just make sure you have all your shut-offs, and flow checks where you need them.

Kestrel

More refined schematic

Perhaps a little clearer, with fewer things left off...

Ironman

Schematic

Your last schematic looks fine. You'll need all 4 circs. since the rads and the floor will be on different temp zones and also have different head loss. They will need flow checks on each as your drawing shows.



Regarding your question on putting all the panel rads on the same manifold: It should be no problem since the manifold (a good one) comes with balancing valves and flow gauges. I would not get one from the Internet unless it's a name brand (Rehau, Roth, Upnor, etc.). Don't get a chinese one: they're junk. If the upstairs runs are substantially longer, then you may want to run 5/8" to them and 1/2" to the ones downstairs.



Elevation is not a factor in a closed loop. What comes down basically cancels what's going up. Head loss (resistance to flow) is what needs to be considered. Try to size for 4ft of loss per 100 ft of piping at your required gpm. Then add 50% for fittings, valves, rads, etc. Keep the velocity between 2 - 4 ft. per second and it will work fine. That's the nice thing about a Delta P circ: it senses the head (which will vary with TRV's) and adjust to maintain proper flow.



You'll need to address one other thing with your setup: The Delta P circ is powered constantly and will start flow in its loop when a TRV opens. But the boiler loop circ. will need something to signal it to run. You could put it on constant, but that can be wasteful. A simple way is to install a thermostat in the area of the panel rads and set it a little higher than any of the TRV's. That way it acts like a high limit to ensure you have water flowing between the boiler and the LLH when a TRV opens. You'll also need a pump control panel with multiple zones (Argo, Taco, Honeywell).

Kestrel

triggering the boiler from TRV

That last point is something I haven't considered - when a TRV opens a radiator, and the pressure drops and the ECM circ revs up - how do you make sure there is heat being generated?  Is there a way to detect that the ECM circ is running, and have that trigger the boiler and the boiler circ?

Ironman

Signaling Boiler

Using a pump control panel like I mentioned above is the simplest method. It not only starts the circ for any zone that calls, but it also signals the boiler to start which in turn brings on the boiler loop circ.



Another method is to place a jumper on the thermostat terminals of the boiler. Then the outdoor reset curve has to be finely tuned to match the load and the warm weather shutdown set to turn it off when no heat is needed. A call for DHW overrides this.

furthur

TT for boiler...

Could you also use a flow switch?

Ironman

Doubt It

I don't know of one that is sensitive enough to pick up  the flow if only one TRV is partially open.