Caleffi 280 Thermostatic Mixing Valve

I suppose it depends a bit on how the radiators are piped. If you end up with a wide delta the radiators at the end of a loop may not output enough heat?

That was the one design criteria with gravity systems the length of the run outs that would allow enough gravity flow. This is one reason B&G developed the "booster pump" to allow conversions, or performance improvements on gravity piping systems.

I would try the lower cartridge first. My concern is the mixing valve has added just enough flow resistance to push you to the limit, maybe beyond of what that pump can do.

But if the system ran those low SWT/ RWT without the valve, you really need a protection valve. you do not want to run that boiler constantly at 130- 140 supply temperatures. Did you note the return at the boiler at those temoerature conditions?

Without being able to calculate the piping circuit, it will take a few trial and error steps. If the pump is not up to the task you could upsize or add another 33 in series to double the head.

If we assume you in fact need to move 23 gpm to get the job done (230,000 @ 20∆)

Looking at the pump curve the 33 will only get you about 5'. Two in series would get you closer to 10' head.

Attached is a 23 gpm flow in a 17 Cv valve, 4.23' head.

Another check would be to pull the top off the air sep, we have seen a number of cases where the mesh or media inside gets plugged with teflon tape , rust, sludge etc. That will add a bit more flow resistance.

But you want to get to a design condition or near it to get the info you need for the next step. It is always easier to get heating systems to perform adequately on mild days :)

More flow always = more btu output from the heat distribution. And yes even in cast iron radiators that were on a gravity system.

I've tested 4 different cast radiators from 1/2 gpm - 8 gpm. Increased flow always sped up the heat output and raised the average temperature across the radiator.

That being said once over 2-3 gpm the output increase is not very significant. See how the below curve flattens at @ 2 gpm. So depending on the pump size and power consumption the last few % may not be worth chasing. head loss increases with the cube of the flow rate. If flow is doubled head increases 3 to the 3rd power.

Graph 2-13 is pretty accurate for any type of heat emitter.

Fig 2-14 is a 250' loop of 1/2 pex in concrete, SWT costant 110°

With radiators it is mostly a surface area game, the greater the surface area the steeper the slope.

So to answer your question the PL 36, considered a high head circ, would move more gpm. I doubt with large diameter piping and wide open radiators that you will get velocity noise. This red valve looks to be a gate valve? If it is a globe valve it would be a perfect balance valve. Even the gate valve would allow you to do some balance.

The PL 45 is a bit flatter curve, but a bigger body pump 8-1/2" flange to flange.

If money were no object I'd consider a small Grundfos Magna that you could vary speed and save 50% or more on power $$ It would involve flange changes however.

This small Magna in the 20- 25 gpm range is operating at 83% efficiency.

At the B&G site you can enter system spec and it shows pump options. I put 23 gpm at 10'. The PL 36 has a wire to water of 31% Where the black and green lines cross is the operating point OP with the numbers 23 gpm, 10' I entered.

The PL 45 is on a better spot on its curve so 37% wire to water efficiency.

Any Y strainers in the system?

I just entered your spec at the sizer program and it gives the selection. I'm not sure why no NRFs show up?

Performance is similar. The PLs are open frame motors, a bit more efficient compared to a wet rotor where the motor is sloshing in the fluid.

This pump curve chart below shows more of the NRF 3- speed selection, at various speeds.

If you want 23 gpm at 10', Speed 2 on the NRF 36 or NRF 45 is on the money. Since you want to work with the flange to flange spacing you have the 36 is the choice.

check at www.dsireusa.org for ECM pump incentives in your area.

Here is an example from Mass Saves

Figure around 2200 hours of operation, using your kWh, see how the ECM matches the PSC for operating costs. With the rebates, if applicable, the numbers lean towards high efficiency

2028 is when all circs will be ECM, that is why you see the manufacturers stepping up their ECM product offerings. The U.S. may be one of the only places where PSC are still being used.

1/3 of all electrical energy consumed in the world spins a pump, of some sort. So reducing that consumption by at least 50% with ECM technology could be a big deal.

Although AI server farms, giving us instant answers like this, will gobble up that savings I imagine😏

it’s a fair question @jesmed1. I have visited practically every radiator with my air bleed key many times. There are a couple where the bleed valve is damaged or inaccessible but by and large I’m not encountering any air. Importantly, many of the cold radiators have functioning and accessible bleed valves and all I get out of them when bleeding is cold water. So I don’t think it’s air, at least in most cases. Even on the cold radiators where the valve is inaccessible or damaged, it’s not like the bottom of the radiator is hot and the top is cold. It’s cold from the supply pipe up.

I don’t know if it’s easily visible in the pictures I posed above, but my bypass cannot be isolated. It’s something I wish I had thought to ask for…

I will give long bleeds a try at some of these colder radiators. Physically what do you think would be going on there? The air is stuck at the top of some sections, but not all? I can’t visualize a situation in my head where the supply pipe is cold and the problem is air, but I’m still a novice here.

if you look at piping examples of gravity systems the piping always slopes up to the radiators. This also helps the purging as the air rises into the top of the pipe and up into radiator , any droops or low points in the piping, or changes that created high points will make it much harder to purge.

With large diameter pipe you would need a substantial gpm. GEO loop field pump carts are generally 35 gpm and up.

I met a GEO looper in Iowa at a training and he bought a used fire truck to carry water and provide plenty of pump capacity for even a field of 2” loops

Boosting fill pressure is another trick to help expel air, you always want 5 psi at the highest point in the system. Boosting fill for a few hours to maybe 20- 25 psi basically squeezes the bubbles smaller and can assist the bubbles to move with the flow.

You need 2 fps velocity for air to move along with the water. In 2” pipe you need about 20 gpm. Here is an online calculator for gpm/ fps calculation