MOD/CON BUFFER TANK & DHW

hot_rod

Yes the Ergomax type of tanks need to be maintained at a fairly high temperature to get the DHW performance. You might check their output charts at lower than 180F tank temperatures to get an idea of DHW output.

It would be hard to use the boiler reset "ability" with the reverse indirect as the buffer.

hr

Bernie Riddle_2

MOD/CON BUFFER TANK & DHW

I'VE REPIPE AN AVEAGE 2500 SQ.FT. HOME SO THAT THERE ARE SEVERAL HIGH TEMP. BASEBOARD MICRO LOADS (5,000 BTU) AS WELL AS ONE SINGLE INDEPENDANT RADIANT LOAD (APPORX. 25,000 BTU.)

IN ADDITION THE IS A KITCHEN, TWO BATHS WITH 2.5 GALLON SHOWERS.

I HAVE PLANNED TO USE A DIRECT VENT PHASE III PRESTIGE 110 MOD/CON BOILER WITH A "ERGOMAX" TYPE BUFFER TANK WHICH WILL MAKE DOMESTIC HOT WATER.

I WAS PLANNING TO SET-UP THE BUFFER TANK USING A PRIMARY/SECONDARY PIPING ARRANGEMENT AND THE ESTABLISHING A SECOND PRIMARY/SECONDARY OFF THE BUFFER TANK THAT WOULD FIRST HAVE A STACK OF ZONE VALVES CONTROLLING THE HIGH TEMP BASEBOARD THEN FOLLOWED BY A VARIABLE SPEED INJECTION SYSTEM FOR THE RADIANT.

THE RADIANTS CONTROLS WOULD HANDLE MIXING ALONG WITH RESET.HOWEVER I WOULD LIKE TO USE THE RESET FEATURE OF THE BOILER. HOW CAN THIS BE DONE WITHOUT EFFECTING THE DOMESTIC HOT WATER. IF THE BOILER RESETS DUE TO OUTDOOR TEMP. CHANGES WOULDN'T THE BUFFER TANK WATER DROP TOO LOW TO CREATE SUFFICIENT DOMESTIC WATER.

IN ADDITION ISN'T IT TURE THAT THE LOWER THE RETURNING WATER TEMP. TO THE BOILER IS BETTER, HENCE THE WHOLE IDEA ABOUT USING A MOD / CON.

PLEASE ADVISE.

Mark Eatherton

Save your money, and find your CAPS LOCK key....

Throw a tempering valve (anti-scald) on the DHW side of the reverse indirect, and use IT as the buffer tank.

In answer to your return water temperature, yes, the lower the better, but even without the "perfect" return, these gems reduce the energy consumption by a minimum of 30%.

The reverse indirect also makes an excellent air removal unit, and dirt removal unit.

It has been my experience that the reverse indirects have to be maintained at a temperature about 10 degrees F hotter than what you want you DHW temp to be. I.E., 150 would kick plenty of 140 degree F water.

ME

Unknown

but mark, if you have a significant buffer... the modulation benefit is reduced.

If you are also reducing your condensation benefit by running high temp, where IS the benefit of using the mod/con.. besides silence?

Mark Eatherton

Still 30% Rob...

Nothing to sneeze at.

Little load, little burn. BIG load, BIG burn. The buffer simply keeps the boiler from short cycling too much.

Been there, done that, many times, works like a champ and saves a boat load of fuel.

ME

Buzz G.

Reverse indirect vs indirect

Still not sure what advantage reverse IDHW has over regular IDHW?

Mark Eatherton

BIG differences....

The typical American indirect has a teeney weeney (surface area wise) coil that requires HIGH operating temperature (typically around 180 degrees F) and in some cases has a SIGNIFICANT pressure drop through the coil, resulting in larger parasitic costs, greater standby losses during production and meager outputs.

The European reverse indirects (Thermomax, Ergomax) run the boiler water through the tank, where there is a BUTT load of highly conductive small diameter copper coil which maintains velocities adequate to avoid lime scale accumulation, AND have a turbulent water flow, effecting a greater heat exchange. The operating production temperature can be as little as 10 degrees F hotter than the final DHW temperature.

It is essentially a large area, large volume heat exchanger. It is obviously limited by the fire power connected to it.

In Colorado, it is recognized as a "heat exchanger", and is exempt from the ASME tank/vessel requirements.

It is more money, but properly set up, can be significantly more efficient than it's typical north american cousin.

ME

Unknown

but... if you are firing on a differential, and the buffer tank can absorb a base amount of BTUs, it's always a "big load". Just not for a long time...

More to the point, with the buffer controlling cycling, what's the downside of not modulating?

Tim Weaver

Other Considerations....

When you pipe your system as you have explained, boiler to the Ergo-max with all the heating loads coming off the Ergo-Max.. You need to realize a couple of things about how the Ergo-Max will operate (or actually call for the boiler to operate). The Ergo-Max has a aquastat which has approximately a 15+/- (2-3) degree temperature differential between open / close. When it closes, the boiler goes to full DHW output rate till the aquastat opens. There is going to be cycling because you may be operating this almost in a non modulating methodology and possibly in a minimal condensing mode also.. I am saying this "tongue in cheek" since I am not aware of the Prestige's alogorithm for DHW, but I think I am close for discussion purposes.. Now -- your piping draws the hot water for your radiant and mini loads off the Ergo-Max till a call comes back to the boiler to re-cycle the ergo-max again. This would be fine for a fixed rate firing boiler, but it almost seems like a waist for a modulating boiler with reset capability. By the way -- it will work, it is just not using the abilities of the boiler you are considering buying.

Another thought... or the start of one. Let the DHW Ergo-Max exist on its own secondary loop with no or minimal loads attached. This will allow you to both modulate and use the reset with your boiler for all the other heating loads. Now lets talk about your heating loads. Attach as much of your radiant and your mini-zones to the boiler primary loop directly as a secondary loop. I hope I have not confused you here. Combine as many of the mini zones into one common zone running at a lower temp for longer periods of time. I am not sure how many mini loads you have, and without knowing your design, I may be out of bounds here, but overall I believe you would enjoy increased home comfort as a result of combining some or most of these loads, while simplifying your system design..

Now you can benefit from the boiler reset AND the modulation capability of the boiler.. You really want it to run longer at reduced supply temps for your house heating needs and provide better overall comfort... Your original piping design would better serve a non-modulating boiler, which you do not have here. To optomize what you are considering for your system, may require a slight change in piping design, but would provide improved functionality.

Regards Alex

gerry_6

Wow, I'm sold!

Thanks Mark. I have a mod/con with a Smart 40 w/ a 194* dhw boiler supply stpt I'd love to try the Ergomax w/ a 140* dhw boiler supply temp delivering unlimited 130* dhw sounds very effeicent. I might have an idea for Brian put the high temp zones p/s piping with the Ergomax and then DONT use the injection pump and control but instead use SH mode with outdoor reset for low temp zones piped p/s and the money you might of spent on injection pump and control use a small 20 gal buffertank but pipe it to get hydralic seperation and put a auto air vent on top then I'd call it a hydro/dirt/air seperator buffertank.
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