Sense check on a two zone system with home run manifolds

MilkyDave

Hi,

I'm looking for a sense check on my proposed system. ~1500sf two story house in southern Ontario that I would like to zone by floor. Design load for the main floor is ~30kBTU and 25kBTU for upstairs. I'll be installing and piping to new panel radiators, 7 on the main floor and 5 upstairs sized at 160oF supply temp. I know this is on the high side for a condensing boiler but I expect to be able to run them cooler most of the heating season. The predominantly south facing glazing helps along with a planned gradual improvement in insulation and air sealing.

I'm planning 1/2" PEX home runs to each rad and should be able to keep it to 2 adapters per supply and return pipe. The shortest / longest 1-way run is 21' / 32' and 17' / 44' for the main floor and second floor, respectively.

See attached simple schematic. I've not decided on a boiler yet so the primary circulator will either be integral to the boiler, or sized based on minimum boiler flow rate requirements. Secondary circulator will be deltaP. Will a balancing valve per zone be sufficient? Or do I need to plan for finer tuning per rad?



Cheers,
Dave

hot_rod

Those H valves on the bottom of the radiator are available with balance/ shutoff valves built into them. So you could do some adjusting at the valve. The bypass is for when radiators are in series. You adjust how much each radiator receives.

TRVs are another nice option for temperature control at each radiator.

Rich_49

Use the bypass H valves at each rad for adjustment . Forget the balancing valves and use an ECM VS circ .

MilkyDave

Thanks both for the help. For a home run configuration it would be the isolation type H valve though right, not bypass? @hot_rod are you suggesting a single zone with TRVs is an alternative to consider or in combo with the zoning?

Rich_49

I prefer the bypass H valves and constant circulation . Hot fluid is always right there , using a T stat as a high limit is nice . TRVs , bypass H valves , 1 or 2 stats , constant circ and WWSD turns it on and off .

MilkyDave

Hey @Rich_49, the Beacon Morris bypass h-valve says "Not for use in dedicated/home-run piping configurations" but no explanation as to why. Any insight?

Leaning towards an NHB-80 but concerned with a mismatch primary and secondary flow. They don't seem to list the minimum boiler flow rate anywhere, but it seems like 2 GPM is a common figure for other water tube boilers (NTI TRX, HTP ELU). I've decided to scrap the two floor zoning and just rely on the TRVs, so a single deltaP pump with 12 loop manifold. I'm thinking 6 of 12 radiators will get TRVs while the rest just standard valves.

Assuming all the manual radiators are left wide open, the total secondary flow would range from 1.75-6 GPM. If i understand correctly, the bypass valve setup would solve this because you'd have more or less a constant secondary flow at all times. Isn't that a bit wasteful though and defeating the benefit of a VS deltaP pump?

In theory, would a deltaT primary pump also solve the P/S flow matching issue while also significantly reducing pumping power? Looks like the low speed settings of the Navien recommended 3-speeds is around 60W.

I've read a couple threads on the deltaT primary and it sounds like two concerns are heat exchanger protection, and boiler control (fire rate) fighting the pump control. Do you know any boilers that can/have been successfully pumped with a variable speed primary? Or any recommendations on boilers that I could forgo the primary completely and not worry about heat exchanger protection?

If not then I guess I'm back to the question on bypass h-valves and whether or not their suitable in a home run configuration.

hot_rod

There are two types of H valves. The ones with adjustable bypass are for one pipe systems that allow you to adjust the flow to radiators in series.

For two pipe or home run, you do not need to bypass, so a standard H, with iso valves included

The Lochinvar Knight boiler includes a variable speed boiler pump. The intend to to keep the boiler return low, promote condensing operation. Not to lock in a specific delta T

The most comfortable, arguably most efficient system would be constant circulation, constantly adjusting the SWT to the load, never stopping the flow. TRV systems on ODR can be, or be close to constant circulation

MilkyDave

Thanks hot rod. I thought that was the case with the H valves but was confused by Rich's suggestion.

Unfortunately the Knight is out of my price range. I got a hold of Navien and they suggested against a variable speed primary and confirmed the minimum boiler flow rate of 0.5 GPM at low fire (seems very low to me). I'll likely go with the NHB with one of the recommended 3 speed pumps. How would you typically go about operating a setup like this knowing that the primary and secondary flow rates will often be at a mismatch? Set the flow to a reasonable mid point and manually adjust if there's prolonged periods of RWT too high, or not where I'm not getting enough heat out of the emitters (SWT being mixed too low)?

Rich_49

Just to be crystal clear . (I have used the bypass H valves at each rad several times using constant circ , 2 pipe reverse return , ODR , WWSD , and t stats as high limits and Home Run manifolded systems also and everyone who lives with them , loves the systems . No idea why Beacon Morris says they should not be used .

MilkyDave

So is my understanding right that using the H-valves would solve the issue of a mismatched flow in primary and secondary? Secondary flow would be pretty much the same at all times, just the amount through the rads varies based on TRV activity?