Panel Radiator/Mod Con piping advice

sibellc

Hi,

I'm attempting to retrofit a 2700 square foot ranch with panel radiators, 50 Gallon Lochinvar Square indirect heater, and a mod/con boiler. The radiators are Myson T6, fitted with TRVs, and the boiler is a Lochinvar Knight KHN-085. My heat loss calculation is 45,000 BTU/H at 17 degrees outside temp. Each radiator is home-run using PEX. The boiler will be piped primary/secondary using a hydraulic separator and a delta p system circulator. The plumbing company is completely unfamiliar with this setup, so we are working with a Lochinvar rep. As this seems to be uncharted territory for most involved, I have some questions:

1) The first 8 radiators are temporarily piped using a copper manifold with isolation ball-valves on the supply and return sides. The manifolds are sweated to several feet 1/2 copper, which continue up the wall, and along several feet of the ceiling before transitioning to the PEX. There will be 16 circuits, of vastly different lengths. There are no balancing valves or flow-meters on the copper manifold. The radiators have built in flow-valves. The Buderus manual says to defeat the built-in flow valves when using a TRV. The Myson manual, though the design and the valve seems to be the same, does not indicate this. Should I just stick with the copper manifold as is (expanding it for the additional circuits), add flow-meters and balancing valves to it, or swap it out for pre-assembled brass or steel manifolds with built in valves and meters?

2) Is there much of a functional/reliability difference between a B&G ecocirc auto and a Grundfos Alpha for the system circuit?

3) The boiler has a capability to control a 0-10v variable speed pump "maintain a minimum delta T across the heat exchanger, as well as prevent high limit lockouts when the flow in the primary loop is extremely low." This sounds like a good thing, as well as more electrically efficient, and I am thinking of using a Grundfos UP15-42F/VS, but the rep suggested that it's unnecessary on such a small system, and needlessly complicated, and suggested sticking with the included Grundfos UPS 15-58FC or a B&G ecocirc vario. Based on the I&O manual, the boiler will only need 8 GPM and 1 foot of head. Is the boiler-controlled pump overkill, should I use a manual ECM pump for electrical savings (Looks like 5 watts vs 60), a delta T ECM pump, or stick with the included 3-speed?

4) The myson rep recommends against using a TRV on the towel warmer. Its output neatly matches the calculated heat-loss of the room. If I run this without a TRV, will the outdoor reset/boiler modulation keep the room at a roughly appropriate temperature, or will it likely overheat? The Lochinvar rep recommends using a TRV.

Thanks!

Ironman

Why are you using the KHN 085 when the 055 would better match up? Over-sizing a mod/con is not a good thing.

What's the smallest rad that you're gonna connect to the boiler?

P/s piping may not be necessary because of the low head loss of the fire tube HX. I'd recommend that you go ahead and use quality manifolds with flow meters (Caleffi, Rehau, Viegga), no Chinese junk.

Use a Grunfos Alpha or equivalent delta P circ. Open the flow setters on the rads 100%, adjust the flow setters at the manifold to the necessary flow for the size of the rad with the TRVs uninstalled, then put them on. Set the ODR curve based upon the required SWT at design.

If your smallest connected load won't match the minimum firing rate of the boiler, then you may need a buffer tank. Use that to provide hydraulic separation instead of p/s piping.

Zman

Ironman said:

Why are you using the KHN 085 when the 055 would better match up? Over-sizing a mod/con is not a good thing.

What's the smallest rad that you're gonna connect to the boiler?

P/s piping may not be necessary because of the low head loss of the fire tube HX. I'd recommend that you go ahead and use quality manifolds with flow meters (Caleffi, Rehau, Viegga), no Chinese junk.

Use a Grunfos Alpha or equivalent delta P circ. Open the flow setters on the rads 100%, adjust the flow setters at the manifold to the necessary flow for the size of the rad with the TRVs uninstalled, then put them on. Set the ODR curve based upon the required SWT at design.

If your smallest connected load won't match the minimum firing rate of the boiler, then you may need a buffer tank. Use that to provide hydraulic separation instead of p/s piping.

Like he said...

sibellc

Thanks! I chose the 085 because it has a higher turndown ratio than the 055, so the minimum output is only 300btu/hr higher 7790 vs 8075. The smallest radiator is about 800 btu/hr in a small bathroom. It's hard to imagine a scenario in which that is the only call for heat. Do I really need a buffer tank? Any thoughts on the primary circulator?

Leon82

Im using an 1816 on my whn primary dialed as low as it can. When the ecm 0-10 volt come out I'll switch to that

Ironman

sibellc said:

Thanks! I chose the 085 because it has a higher turndown ratio than the 055, so the minimum output is only 300btu/hr higher 7790 vs 8075. The smallest radiator is about 800 btu/hr in a small bathroom. It's hard to imagine a scenario in which that is the only call for heat. Do I really need a buffer tank? Any thoughts on the primary circulator?

On the contrary, I can very easily see bathroom rads set up higher than the rest of the house and therefore being the only thing calling.

You don't want a delta T circ pumping the boiler. It's logic and response won't match the boiler's and it will play havoc with it.

sibellc

Fair point. For a 10 minute run time and a 7K BTU difference between minimum output and smallest radiator, at 20 degrees delta T, I would need 7 gallons of buffer. The boiler, primary piping, hydraulic separator, circuit and radiator should contain 5 gallons of water. Is this volume counted? It would appear to provide a 7 minute run-time.

If I use a Caleffi (668S1) manifold, I will need more than one, as I'll have 16-18 circuits, and 14 appears to be the largest size. How do I pipe two manifolds into the system?

Ironman

What you're not considering is that those numbers are at design temps which occur 1 - 2% of the season. Ther rest of the time, they will be far more disproportionate. This is a common error in designing: assuming the best case scenario will apply under all conditions when you should assume the worst case scenario. I'd recommend that you consider adding some buffer.

Caleffi addresses this very thoroughly in one their iDronics issues and shows various ways to pipe in buffer tanks to yield the best efficiency and benefits.

Just pipe the manifolds in parallel, but do the math to make sure that one circ will handle both.

delta T

I would definitely use a buffer. What is your SWT at design?

Boon

The thought of building my own manifold(s) drains me, and if I built it then it would look like I built it. I opted for two, 9-port caleffi 668 manifolds in parallel. I still have six circuits to connect when our addition is finished. If you use the 668s and if you reverse the drains & air separators then make sure the drain cock lever is to the side or front of the manifold. If it isn't, as you can glean from the photo, it may interfere with mounting. I love that every single connection I made to these manifolds worked the first time without any massaging or manipulation.


I mounted one manifold lower, one mounted higher and out in front of the lower one. All the pipes to the lower manifold enter from behind and from the left side of the house. All the pipes to the upper manifold enter from the front and from the right side of the house. I'm shocked at how well it came together.

output neatly matches the calculated heat-loss of the room ... if I run this without a TRV, will the outdoor reset/boiler modulation keep the room at a roughly appropriate temperature, or will it likely overheat?

If the ODR curve is set to your liking, I don't see how the room can overheat unless the room can get more heat from somewhere else, like a second panel or the sun coming through the window.

sibellc

Thank you all very much for your help. I'm going to use an 18 gallon boiler buddy - in the grand scheme, it's not terribly much more than a hydraulic separator. SWT at design is currently 160, in the spring, the house is going to get new windows, insulation, and 2 inches of exterior foam, which will reduce SWT to 140. Boon, that picture was very helpful.

sibellc

Follow-up question: how necessary is it to use radiant manifolds with flowmeters and balancing valves over a plain copper manifold? I'd prefer not to throw what was over a full day of labor possible, though considering half the radiators are yet to be plumbed, the labor savings might be a wash. I've attached a picture of the current install.

SWEI

You almost certainly need balancing valves, which I don't believe I see there.

Flow meters are handy, but generally not critical.

Ironman

I can see how you wouldn't want to re-do that.

Good radiant manifolds accomplish these things:
1. Provide prefabded multi port connection point
2. Provide a means of isolating individual loop(s)
3. Provide a means of purging each loop
4. Provide a mean of measuring flow on each loop
5. Provide a means of regulating flow on each loop (balancing)
6. Provide a means of zoning each loop.

You've accomplished the first two things, doubtless, at a greater cost. But what about the others?

You may not need to regulate flow since the rads have flow setters. And you probably won't need to be able to add actuators for zoning, but what about #3 & #4?

Boon

If you want balancing valves on the supply you can leverage the manifolds you made by repurposing all 16 ports as returns. Cut them out - as whole as possible - so that you can easily re-use & re-mount them. Then, buy or build your supply manifolds with balancing valves. You might consider mounting the return manifolds on the ceiling where the pex transitions to copper so that you don't have to rework from the transition to the wall.

I don't think I explained this well. The takeaway here is (1) I think there is possibility that you can repurpose the work you did; and (2) think outside the box for where to mount your return or supply manifolds as there is no rule they need to adjacent.

sibellc

I went over all this with the plumber and rep yesterday - they proposed to save all the beautiful copper by adding balancing and drain valves on the existing manifold (which they are considering more of a header), and for the 10 circuits to be added, adding another set of Ts and piping a radiant manifold into the end of the existing one. It seems like this should work. Any issues to watch out for? Anyone have a favorite balancing valve? Adding 8 Caleffi Quicksetters would probably cost more than just replacing the copper. The B&G circuitsetter is much cheaper, but I wonder how accurate it is. Something like a Caleffi 130 or a Danfoss STV look fine, but I don't think the plumber has the proper meter.