Buffer tank question

Paul Rohrs_5

Buffer on Supply

I am a proponent of buffer tanks, especially when piped in series on the supply. Here is one version that illustrates bringing the buffer tank on-line or bypassing it to return directly into the primary loop.

When it is all said and done, we are trying to maximize the mod/con by feeding it the coldest possible return temp, narrow delta t indicating low-firing rate, and long run times. Any disagreements?

So how would you set up the buffer tank on the supply to enhance these conditions? (I'm not stating this is right or wrong)

Next post I will ask the same thing with the buffer on the return.

Paul Rohrs_5

same rules with buffer on the return

Same parameters, same rules. How would you set this up.

With a 3-way mixing valve in the equation, I used two separate boiler pumps on the return. P1A and P1B will never run simultaneously, as well, the 3-way valve will either fully divert flow from A to C port OR from port B to port C.

I am hearing a lot of people that opt for buffers in series on the supply, and an equal amount for buffer tanks on the return. Ultimately, which one will optimize their system better? Do we have enough information?

Regards,

PR

Alex Giacomuzzi

Modulating...


JimH --- I believe you may have already partially answered your question. Let me spin it a bit.

The benefit from modulating in theory is the desire and ability to match the boiler hot water supply to the heating load. Present day modulating design only allows a certain turn down. The buffer tank as you suggested allows us to extend the effective turndown which gets us closer to matching the boiler and the heating load. Ideally -- a modulating boiler with (I am just picking a number here) a turndown of 50:1 available in a variety of sizes would take care of shoulder seasons, micro loads, and even DHW needs without a buffer.

You ask about simplicity -- for a system design it depends on how many different temp loads one has. If you only have one or two --- yes simpler. If you have several more different load temps... not very simple. Simpler modulating boiler -- No compared to a bang bang boiler.

You ask about reliability --- over the long haul. If you have a simple system, you should have better reliability.
If you have a simple boiler -- the same should apply.

Why modulate a burner at all? If you have a traditional Bang -- Bang boiler you do not have an option. Full on, full off. Traditional reliability and the system design reflects the loads it needs to serve. Buffers can help in several areas with this type of design.

If you have a modulating unit and choose to run it bang bang --- I guess you can. Utilizing a wide delta T can be an advantage to extending the turndown as you mentioned.
If I had a modulating unit, I would use the turndown first of all because the unit has it available, secondly to better match the supply and heating load, thirdly to extend the run times and possibly off times, and finally (from what I have read) the efficiency is better on a modulating unit under a lighter load rather than full load. I am sure there might be others --- just can not think of any more.

Regards Alex

hr

Paul

are their circ missing?

When ports A to C are open what causes flow through the Hydro separator?

I'm assuming circs on the B side of the separator?

Your drawing seems to indicate a primary secondary into the A side of the separator?

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Paul Rohrs_5

Yes circs are missing

getting late, tucking in the kids, Zone circs off of the hydroseparator are in order.

I've had success with the buffer tank on the supply, but I haven't tried the 3-way concept yet. I'm always looking for a better way.

Paul

Uni R_3

JimH, balance

JimH, it's all about balance. Your house wants 30K, the boiler gives it 30K. If the least the boiler can give is 60K, then it only needs to fire half the time.

So does it fire for 30 minutes and then let the house cool for 30 minutes or does it fire every other minute or something in between? The more it fires, the steadier the indoor temperature and the faster it is wearing out all the parts that get hammered off and on during a firing cycle.

Getting a good compromise sometimes involves buffer tanks - the buffer is a solution to get the boiler firing longer while keeping steadier indoor temperatures.

So the 60K will be firing only half the time, but when it does, it'll have flue gas temperature of perhaps 148°. Much of that is wasted heat when you consider that if it fired all the time, the flue temp might be an average of 116° instead. That's where wasted heat goes. Once the water return temps climb through 130° the efficiency dips.

The differences aren't much; there really isn't much left to save with these machines. However, it start taking a disproportional amount of electrical power to move the heat.

Eventually, you start wasting electricity from your pump
unless in can fully scale back in its flow and energy consumption. And if that pump costs a fortune, you should set a fixed cost for that too, that the boiler is inefficient if it modulates below that fixed cost per BTU.

At some point going lower becomes pointless. The cooler you can keep the flue, the less gas you waste.

What's the sense in a boiler that modulates from 200K down to 2K if it uses a large fixed pump like a 011 that uses 200 watts which translates into roughly 700 btu? You're actually at that point where moving the energy costs 25% of the total energy used for heating. If electric rates are high and you can't feel the difference why not do a few cycles an hour?

At some point any house reaches a point where it just doesn't need much heat to stay comfortable and you can't even notice that it doesn't add it constantly.

I really think a true 4:1 would probably be fine if there was a larger range of smaller sizes. If they could be tried on for size somehow even better*. First cold day tells you nearly all you need to know.

************************************************

*Anyone ever though of making a portable propane gas diagnostic boiler that connects to flanges?

You just pop a circ out somewhere, bolt in the input/output manifold for this portable boiler - run the exhaust out a window with an outdoor sensor, open up the BBQ tank valve on your tank and start heating the house. Tekmar probably already has a controller that would probably work for this.

You shut the boiler off, leave any zone controls on and start up the portable boiler. By polling various RF indoor temp sensors in different spots at at varying outdoor temperatures, it can establish a water temp and BTU curve for that heat load and the emitters. You have then accurately sized the boiler. It could also test evenness of heat for varying internal temps. If the heat isn't balanced recovery isn't comfortable. These houses shouldn't use setback if comfort is important.

A portable boiler that is easy to fuel for a day or two and has PEX connections to a manifold with an in and out flange connector 6½" apart and wireless sensors. And if you could think of simpler and safer... maybe a gas fired genny and electric boiler? As long as it safe and gets a true picture of the houses demand at various temps.

hr

I don't think primary secondary piping

of a mod cons allows full benefit of the coolest possible return.

Even the Caleffi Hydro separator blends a tad, but much less than PS with close spaced tees. the separator does allow a better straight across flow, depending on the A&B side circs.

I feel the Prestige mates best with the Caleffi Hydroseparator due to it's low, low pressure drop exchanger. At least thats what I have measured.

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Paul Rohrs_5

revised

Revised a bit, should have drawn it this way to begin with. Again, these are just variations.

PR

Uni R_3

hot rod

I think ACV actually rebadges Callefi Hydrolinks and sells them. I'll send you the link if I ever cross it again...

Alex Giacomuzzi

Thanks for Re-drawing the Schematics..


Paul:

Why would we need both a hydro separator and a buffer tank?
I am sure there are several good reasons, but I am struggling with them at the moment. Can you help me here?

When I view the two piping schemes, as a suggestion, I would remove the hydro separator and replace it with the buffer tank. Having said that, then we can pipe into the buffer different ways obviously for the primary loop and also the secondary loop. For discussion purposes, let the supply to the primary loop go out of the top of the tank and the return from the primary loop go into the bottom of the tank. The individual loop circulators would draw from the buffer then and the buffer could also be on reset.

Now for the boiler piping -- the secondary piping. If the boiler supply also went to the top of the buffer tank and the return Tee'd into the bottom of the tank or had their own separate taps in those respective locations... What are your thoughts?

The question on my mind is NOT what is the best design for the boiler only, but what is the best design for the heating system which may mean the simplest system to purchase, install, maintain etc.. There is a tremendous amount of focus just on the boilers these days. I do not quite agree with that, although the technology is exciting. A great boiler coupled to a poor schematic / hardware design or a poor install is a waste. We all know that.

I look forward to your thoughts on series / parallel or location, location, location (as they say in real estate).

Regards Alex

Paul Rohrs_5

Alex

I agree with your thoughts on simplicity and economy. This drawing was just rumbling around in the back of my head. I have used buffer tanks and Hydrolinks/Hydroseparators but not ever together. I just thought that there would be a possibility that together, we could enhance run times and minimum modulations.

As it pertains to piping buffer tanks with the inlet / outlets, I like to break up stratification, so that is why I prefer series piping. So, on the supply, I like to feed my hottest water low and bring it up thru the tank. Conversly, with the buffer tank on the return, I choose to bring the water from the top to the bottom.

I understand and have seen some contractors use buffer tanks in parallel to the primary loop. I think even Siggy has drawn them that way in the past. I just prefer series piping and I the parasitic loss (electrical consumption) of additional circulators should be weighed against fuel consumption.

Hope this helps. My normal setup is usually centered around high-mass radiant floor heat and low-mass mod/cons, so most of my drawings are focused around the hydrolink and hydroseparator being fed directly from the boiler.

Regards,

PR

MikeL_2

MikeL_2

Pics

For all who have followed the thread so far, here is my setup.

Bottom right of first pic, Buderus GA124/17, bottom left is an Amtrol indirect for DHW, wrapped in insulation and radiant barrier as the thing used to lose 1degree per hour, now 1/4 degree per hour. Top left is a Lifebreath HRV.

Right in second pic is Enerworks solar preheat for DHW. Middle is a european amtrol tank for use as the buffer tank (supply side). Left is a Lifebreath AH and turbulent flow precipitator.

P.S. The wideangle distors stuff, the vent pipes for the boiler are actually plumb and square to the wall !!!