The Trithermogulator

Eastman

Here is Part 1 of The Trithermogulator.

Eastman

Context: The Trithermogulator is a hybrid solution to thermal buffering, DHW, and hydraulic separation.

Everyone always seem to think it's a bad idea, so I fleshed out an example that I hope is detailed enough to serve as reference for a useful discussion. This particular version relies on fixed synchronized flow rates and dual parallel ODR curves to control the storage and distribution of thermal energy to and from all parts of the system.

Eastman

Part 1: Boiler responding to a space heating call.

A common critique of this arrangement relates to a potential conflict in the supply temperatures required for the indirect tank and space heating system. An ODR curve that dips below the tank storage temperature would seem unwise, as surely this low temperature water would unproductively cool the DHW during a call for heat.

However, equal flow at the left and right of the trithermogulator results in 0 flow through the DHW storage tank heat exchanger, preventing space heating water temperatures from mingling with DHW storage. This can be readily accomplished if the boiler and system flows share a common range of acceptable fixed flows.

Thoughts???

hot_rod

Interesting. What causes flow thru the tank, and how much? Is it manually balanced? Are there multiple radiant zones?

Eastman

There is never flow through the tank while the boiler is responding to a space heating only call. The mix valve target ODR curve parallels above the boiler ODR target curve, the mix target line is intended to be coincident with boiler differential maximums. In other words, the boiler never produces water that exceeds the mix target temperature. (Edit: At least during a space heating only call.) Therefore, the 3 way mix valve is always fully open while the boiler is producing space heating temperatures. During this configuration, all flow must pass through the system at the desired synchronized flow rate of Xgpm, since this example assumes the distribution system has been configured as such.

Eastman

But to answer your other questions: The boiler and mix flows could be manually balanced --I indicated a pressure independent flow setter in the mixed loop. Multiple radiant zones could be handled together, but in this example the flow rate must be capable of adding up to Xgpm. This would be accomplished by that flow setter. Be aware that each zone should be able to pass the full system flow, again Xgpm.

wogpa67

I think a floating valve on the supply to tank with sensor mounted on heating side may be a better fit. You as well as I have way too much scrap paper to waste. But it keeps us sharp thinking outside of the box.

Eastman

How would that work as a thermal buffer? How would heat be drawn out of the tank and distributed to the system? That was one of the principle goals, since apparently, oversized equipment and over zoning seem endemic to hydronic heating.

wogpa67

the valve would modulate to the odr temp allowing residual flow through the tank, thus the boiler would modulate down and run off its onboard controls.

Ironman

@Eastman‌
If no flow goes through the tank during a space heating call, how then does it serve as a buffer during space heating? That is the object we're shooting for: to provide buffer during space heating to prevent short cycling.

Gordy

I'm not seeing a benefit, adds complexity,robbing Peter to pay paul.

Eastman

@Gordy I generally do not recommend the Trithermogulator as a starting point for system design --it's like advising one to add weight to an airplane, but sometimes a chunk of depleted uranium in the tall is the easiest way to keep the nose pointed up despite the best intentions of all involved after everything is riveted together.

I also typically wouldn't select this specific version of the Trithermogulator as being notably useful beyond the others, but I think this fixed flow version makes the analysis straight forward while being immediately relevant to JustinS.

Eastman

@wogpa67 There are quite a few ways utilize thermal storage. Can you post a schematic that illustrates precisely what you are describing?

Eastman

@‌Ironman regarding the question:

If no flow goes through the tank during a space heating call, how then does it serve as a buffer during space heating?

Your question leads into Part 2.

Eastman

Part 2 of The Trithermogulator:

Eastman

Part 2: Boiler target set point reached, but space heating call unsatisfied.

Earlier I described the synchronized flow rates present while the boiler is responding to a space heating call. Once the ODR target is reached, the onboard controls obviously shut the burner down. At this point the boiler pump should also stop while the system waits for the boiler differential limit to kick the burner back on again.

Let's look in detail at this boiler standby phase of the heating cycle. There is no flow through the primary. The system loops are still on though. This implies that fluid is now being diverted up through the indirect tank's heat exchanger. The boiler has effectively handed off the work to the indirect while it waits in standby. The mix valve modulates the flow of energy from the thermal storage, acting to maintain the parallel ODR target curve temperatures delivered to the emitters.

@Ironman To answer your question, there is indeed flow through the tank during a space heating call, but not while the boiler is responding to it.

RobG

Eastman said:

@Ironman To answer your question, there is indeed flow through the tank during a space heating call, but not while the boiler is responding to it.

Huh?

Ironman

Eastman said:

Part 2:

@Ironman To answer your question, there is indeed flow through the tank during a space heating call, but not while the boiler is responding to it.

Then how would that prevent the boiler from short cycling?

Eastman

@Ironman The boiler hands of responsibility to the tank, it no longer needs to fire until either a) the tank calls for heat, or b) the the system ODR differential low limit has been reached triggering the next space heating burn cycle.

Eastman

@RobG Does this graphic help?

RobG

With a boiler that can modulate and handle multiple temps, why would you waste your time trying to design a discombobulator (sp)? As stated before, closely space tees, low loss header or a buffer tank would be my choices.

JMHO.
Rob

Eastman

@‌Rob Wasted time, space, and money is exactly what the Trithermogulator is designed to avoid. It's not the best solution all of the time. It's a solution some of the time.

Gordy

Most times if a buffer tank is needed it only needs be sized to cover the smallest load in and how it reflects on the lowest modulation of the boiler.

I would just as well stay away from the type of zoning / micro zoning of those small loads.

Really folks radiant can be very simple, effective, and elegant in its simplicity. It seems more, and more some try to apply new hardware to some systems that can be very simple. These are tools in a designers tool box. It's not necessary to use them all.

Bottom line it goes back to the beginning of initial design.
Heat loss
Boiler sizing
Emitter selection
Piping
Control strategy
If zoning is desired design your zones as to not be below min. Modulation of selected boiler.

I'm not so sure a tank in a tank indirect would fare well as a hydraulic separator I think the mixing, and flows would not be consistent as with a regular hydraulic separator, or a buffer tank.

Eastman

Hi Gordy,

I'm not so sure a tank in a tank indirect would fare well as a hydraulic separator I think the mixing, and flows would not be consistent as with a regular hydraulic separator, or a buffer tank.

Can you think of example that might cause an issue? A problem I see is ensuring the flows in the primary and secondary remain truly equal, but I'm not sure if it's a significant issue.

Gordy

Not so much an example it's the way the tappings are. What indirect tank in tank are you thinking of? Example if the TT smart indirect had tappings as for boiler supply/return on adjacent side also it may work. But then the inner tank may give undesirable mixes, and flows do to the inner tank.

Eastman

The TT Smarts. Like JustinS' Smart 80. Does anybody else make that style?

Eastman

To be clear, I had assumed the TT Smart did not have two sets of tappings. I didn't see anything like that in the docs. However, there is no function that requires mixing within the TT Smart heat exchanger --the flow is either up or down between the top and bottom boiler supply/return.

Gordy

I do not see how your drawing reflects the tappings of that indirect.

Eastman

Part 1, 2, or the one I made for Rob?

Gordy

Smart has boiler s/r at side. Hot, and cold domestic on top with auxiliary hot tapping on top.

Eastman

Right, your looking at the TT manuals I assume. The Trithermogulator schematic doesn't show the domestic and recirculation connections because they're not relevant. The red Tee in my schematic connects to the top boiler connection on the tank, the blue bottom Tee connects to the bottom boiler connection on the side of the tank.

Gordy

Hot supply goes into bottom of tank cold return is at the top

Gordy

You have an idea someone needs to make a tank with your desired tappings to do it.

Eastman

I want it the other way, why would you run the hot into the bottom?

Gordy

Come on now?better heating of the inner tank.

Gordy

Take look at the smart multi energy tank with a secondary heat exchanger, and go back to the board.

Gordy

Except Justin does not have that.

Eastman

I'm not sure what your getting at. TT literature shows it both ways. Parallel flow is thermodynamically less efficient. If you heat the tank this way you won't get the coldest return temps. I could see that it might create more internal mixing (less thermal stratification) that would help with the speed of recovery and give you higher performance.

Eastman

Regarding:

You have an idea someone needs to make a tank with your desired tappings to do it.

The Trithermogulator uses two connections on the tank. It uses the tank as is. The tank does not need new tappings. A tee is put on the top connection and another tee is put on the bottom connection.

Gordy

The coolest DHW will be at the bottom of the tank. So it makes sense to have the hottest boiler supply water come in at the bottom of the tank.they want the performance of the tank to deliver domestic hot water not worry about cool return temps to make a boiler condense. Not always used with a mod/con.

The smart multi energy has the hot going into the top.

Gordy

Eastman said:

Regarding:

You have an idea someone needs to make a tank with your desired tappings to do it.

The Trithermogulator uses two connections on the tank. It uses the tank as is. The tank does not need new tappings. A tee is put on the top connection and another tee is put on the bottom connection.

What bottom connection, or top? The only top is a spare 3/4" DHW connection not to the outter tank. The only bottom is boiler supply to the outter tank.