Zone valves on indirects?

Solid_Fuel_Man

Why is it that the general consensus is to use a dedicated circulator for an indirect, ever on a zone valve job? Isnt the point of using valves that you can have one (really good ECM) circulator?

Most boilers I install have two relay outputs one for CH and one for DHW. I've just jumped them together and used it as a single output to run the boiler circulator and valves for the zones and the indirect, end switches connected to the appropriate TT and DHW inputs on the boiler.

No problems, but this it not covered in the wireing diagrams, nor ever it is mentioned to only use one circ and valves.

Curious as to why, and if this is considered poor practice?

JohnNY

My thought on this is somewhat irrational but I'm sticking to it: zoning with pumps is a *more sure* way of zoning and a lot of indirects have very high pressures drops through their heat exchangers. Sometimes that pressure drop is incompatible with the rest of the zones and a separate, isolated, single-speed circulator makes sense.

hot_rod

I did a few installations, 80K boilers where I use a high Cv 3 way zone valve right at the boiler, either DHW or heat depending on the position of the valve. A single circulator system.

Zman

JohnNY said:

My thought on this is somewhat irrational but I'm sticking to it: zoning with pumps is a *more sure* way of zoning and a lot of indirects have very high pressures drops through their heat exchangers. Sometimes that pressure drop is incompatible with the rest of the zones and a separate, isolated, single-speed circulator makes sense.

Which indirects have high pressure drops? I was honestly going the other way with this. We mostly see low temp systems with high head loss radiant loops. The indirect needs higher temps water and has a comparatively low-pressure drop. A dedicated circ, outdoor reset and DHW priority are a good fit.

In a high temp system, doing DHW priority with zone valves works well. I would think that a typical baseboard loop would have a higher resistance than most indirects.

I have always seen zoning with pumps as a "more sure" way to overpump and waste electricity. I do make an exception for 2 zone systems and systems where there is very different resistance or temps.

hot_rod

The 3 way ZV works with boilers running low temperature, a mod con for example, it goes into DHW priority call and up to 180F or so.

Even if the circ is oversized when in the DHW mode, it just speeds recovery for those 20 minutes or so. With ECM circulators that isn't much of an issue, power consumption-wise.

I wonder what a ∆P circ would do on a system like that? A low head DHW coil and high head distribution system? seems in constant pressure mode it may ramp down and not over pump? Or add a PIV if you want an exact indirect gpm.

Solid_Fuel_Man

@hot_rod that was along my same line of thinking. Combi's just have a 3 way valve to switch between heat and DHW through the FPHX. And those have likely 10x the capacity needed for heating.

Generally anything with 3 or more zones (indirect is a zone) gets valves and a 1 or 2 zone system gets circulators.

Unless there is one or more high head zones or gross imbalance, then zone circs make more sense, in my mind anyway.

Thanks for the thoughtful comments so far!

JohnNY

Zman said:

1. Which indirects have high pressure drops? I was honestly going the other way with this.
2. We mostly see low temp systems with high head loss radiant loops. The indirect needs higher temps water and has a comparatively low-pressure drop. A dedicated circ, outdoor reset and DHW priority are a good fit.

In a high temp system, doing DHW priority with zone valves works well.
3. I would think that a typical baseboard loop would have a higher resistance than most indirects.

4. I have always seen zoning with pumps as a "more sure" way to overpump and waste electricity. I do make an exception for 2 zone systems and systems where there is very different resistance or temps.

1. Superstor for one.
2. Then that's the same reason in reverse as I see it.
3. I do a lot of 2-pipe systems with cast-iron convectors in my neck of the woods.
4. I pump with ECM Motors and zone valves (and ODR) for any family and friends who ask me to work on their systems, but for most of my clients I opted out of that way of thinking long ago. People in 20 million dollar 4-bedroom homes don't give a crap what their gas or electric bill is. They also don't want to be taught what outdoor reset is. They want to push a button and get a very hot radiator, every time.

All that said, your post makes the right points and we're just doing things differently. Happy Thanksgiving to you.

Solid_Fuel_Man

@JohnNY

It's funny you say that! The one and only ODR (intalled by others) I bypasses was on a very high end and extremely fussy customer. I just let the boiler cold start and bounce off the run aquastat at 180 and he was completely blown away how well it worked.

He thought I was so much smarter than the guy who installed the boiler.

He had little care that his hearing bill went up a few percent.

mattmia2

So is there a way to do this with the built in relay and built in DHW temp sensor (i can see how it would work with an aquastat but not the thermistor). I ended up with a 120 v coil relay to detect a DHW call and open the DHW zone vale and a 24 v coil relay connected to the end switches to run the pump once any of the valves are open. The pumps are run off the system pump relay through the end switch relay.

I'm thinking the 3 way valve could do it with the deenergized position DHW and a flow check on the DHW.

hot_rod

mattmia2 said:

So is there a way to do this with the built in relay and built in DHW temp sensor (i can see how it would work with an aquastat but not the thermistor). I ended up with a 120 v coil relay to detect a DHW call and open the DHW zone vale and a 24 v coil relay connected to the end switches to run the pump once any of the valves are open. The pumps are run off the system pump relay through the end switch relay.

I'm thinking the 3 way valve could do it with the deenergized position DHW and a flow check on the DHW.

A 120V 3 way zone valve should be all you need, connect it to the DHW priority connection in the boiler as you would a DHW circ.

Robert O'Brien

https://mechanical-hub.com/indirects-zone-valves/

It's all about flow rate, doesn't matter how you get it

Solid_Fuel_Man

Great read @Robert O'Brien

That pretty much sums it all up, math doesn't lie.

Solid_Fuel_Man

Be careful with 3 way valves and feeding the common port. I've done this once (at my own house actually..its the ongoing proving grounds) and it slammed when changing positions with the circulator running.

I solved this problem with a 1.5 second delay timer triggered by the end switch on the 3 way actuator. Turns off the pump (0015 speed 2 as boiler pump) for 1.5 seconds as the valve us moving via the spring return back to heat position.

This valve feeds the top coil of a dual coil indirect, water than goes to the heating loop where it goes through a dedicated valve for the bottom coil then returns to the mod/con. Its piped this way because my wood boiler just heats the bottom coil. This gives me the lowest return temps to the mod/con in DHW mode.

Solid_Fuel_Man

Picture of valve. You can see the 3/4 supply and return to the mod/con. The supply goes to the common port on the 3-way. This was cut into the 1" pipe run which was from an old oil boiler. Remember my own house is the grand proving grounds!

Solid_Fuel_Man

Piping conceptual drawing.

"Heavy weighted check" is a standard 1-1/4" iron check that I removed the small brass weight and made a 3x as heavy brass weight to give me a 2 psi drop at 12 gpm. This was so I can over pump the gasification boiler with a 0010 for return protection. The 2,200 square feet of radiant slab is before all the cast iron radiation to lower temps when burning wood.

mattmia2

So to hijack this thread a little with the comment about "it is all about flow", with an HTP UFT boile, if i keep the flow above the minimum of 1.5 gpm in the smallest zone, i am ok, right?

Side note, i like the Taco valves a lot because of the ball valve design. I'm a little less happy about the 30 second or so opening time, especially in something like this where the boiler may be starting its ignition sequence at the same time the valve is given the call to open. Taco makes a 120v 3 way valve in the zone sentry series.

Solid_Fuel_Man

Lengthen your pre-purge time to 10 seconds longer than it takes for the valve to open.

Zman

mattmia2 said:

So to hijack this thread a little with the comment about "it is all about flow", with an HTP UFT boile, if i keep the flow above the minimum of 1.5 gpm in the smallest zone, i am ok, right?

Side note, i like the Taco valves a lot because of the ball valve design. I'm a little less happy about the 30 second or so opening time, especially in something like this where the boiler may be starting its ignition sequence at the same time the valve is given the call to open. Taco makes a 120v 3 way valve in the zone sentry series.

If you use a zone controller, the boiler and circ will not turn on until the end switch proves. This seems like an easier solution.

EdTheHeaterMan

@Solid_Fuel_Man asks: Why is it that the general consensus is to use a dedicated circulator for an indirect, even on a zone valve job? Isn't the point of using valves that you can have one (really good ECM) circulator?
Don't you know that boiler manufacturers have a instruction manual for designing control systems for their boilers? HERE IS QUESTION # 36
Does your boiler require a specified GPM thru the heat exchanger. Would the zone valve add additional restriction the DHW circuit? Does the installer (other than @Solid_Fuel_Man) take that into consideration when sizing the circulator? Is the indirect DHW tank is the same room as the boiler on every job? Are there other variables on some jobs that will also contribute to poor performance? If you can answer YES to any of these questions then instruct your installing contractors to use 2 circulators