Old house with oil/steam heat - help

gennady said:

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MY RESPONSE: something quite different is indicated in viessmann document. And this difference is that P/S does promote condensing in condensing boilers

and this is what i wrote in my post:
These are clear guidelines for LLH
also make a note that in viessmann opinion primary secondary arrangement does promote condensing in condensing boilers, quite different from your statement.

Again, the difference is that BadgerBoilerMN stated primary secondary is not progress where condensing boilers are concerned, and viessmann statement is that primary secondary does promote condensing in condensing boilers. you see, this is the difference

MY RESPONSE: P/S does promote condensing in condensing boilers according viessmann manual

Also if you read viessmann list of benefits, you see there are benefits in P/S, and this is quite different from the statement:
QUOTE: There is no logical argument for doubling electrical operated costs and the chance of a nuisance no-heat by adding a redundant circulator to any single zone hydronic system. END OF QUOTE

it is not just redundant pump and doubling electrical costs.
please read list of benefits.
Also Dan Hologan wrote a book, named " primary secondary pumping made easy", addressing all these benefits, you can see picture of its cover few posts earlier, read it, you might like it.

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I have a signed copy, thank you. Fortunately I have actually installed, distributed and manufactured condensing boilers for a living since the 80's. I agree that it is best for the average plumber to use P/S, one cannot argue this point. I am speaking mainly of single zone conversions in which the flow rate thought distribution is greatly enhanced in the case of a gravity system (any flow would be an improvement) and the flow through the low-mass condensing boiler (many will suffer a 45° delta-T) is easily satisfied with the smallest of common circulators. Adding a extra pump in such a case would be wasteful and ignorant neither of which I care to be associated with. Thus we do not use Buderus, Weil McLain Ultra, SlantFin condensing for small hydronic systems where P/S can't be rationally justified, as they share your the single-minded opinion, with one intellectual advantage; in benefits them in fewer service tech calls and they don't pay for the considerable installation and operating cost of the redundant pump.

Simply put, if the flow through the system and the boiler are adequate to both no advantage can be gained by applying P/S piping either for hydraulic separation or flow control. The design has it's applications, mostly commercial, multi-boiler and multi-temperature applications but a steam or gravity conversion most certainly is not one of them.

"Promoting" a practice is a very very distant cry from "mandating". When the math proves that it's not necessary, it's simply not necessary. Presuming that P/S is the only way to "do it right" is for folks who can't or won't do the math (which is apparently the vast majority of boiler installers.)

Since P/S piping can limit the damage from a host of design errors from the folks who can't/don't do math it's in the manufacturer's interest to promote the practice, but that doesn't mean it's always the right thing to do.

So, if you using TRVs, do you use p/s or you still using direct pumping ? Also buderus , Weil McLain and slant fin are great brand names and I feel good you some how place me in that group in regards of single minded average plumber I am.
So still do you use TRVs with direct pumped boiler ?

Two words " VFD pumps"

Here is why you should/must be using a LLH with a Vitodens 200. There is no TT on the boiler. The boiler logic utilizes a down stream/LLH sensor to maintain the proper supply side water temperature the system needs based on the set ODR curve. Second, Viessmann boiler pumps are sized for 40 degree rises meaning your boiler or primary side flow rate is much lower then the system side flow rate. As an example the max flow rate for a B2HA35, 19,000-125,000 is 6.2gpm. If the system side has a need for higher flow rate you must pri/sec or use a LLH. Now can you direct pipe it. Yes you can but you will now loose some of the control logic and features in the control.

For a direct piped system you would have to utilize the 143 plug, ie, external demand. Now you've just made a smart boiler dumb and have to tell it what to do. Generally the 143 plug is used when your either doing snowmelt or maybe a pool HX were you want a fixed set point.

The biggest issue with condensing boilers is the boiler pump selection. We select fixed speed pumps based off the traditional 20 degree rise that promotes high boiler side flow rates that the system side cannot take away and you end up with elevated boiler return water temps and short cycling condensing boilers. You can never oversize a condensing boiler on the high end output because the boiler will never get there unless it sees the design delta-t but it sure can be oversized in the low end and that fixed speed pump is always the culprit.

The additional benefits of air, dirt separation and protecting the HX from system debris and the utilization of the system side or LLH sensor is why Viessmann strongly recommends the LLH over pri/sec.

What happens to your fixed speed boiler pump when piped direct? Either one or two things. You over pump the zones or you beat the living day lights out of the pump because if your not splurging on a couple of tees you sure the heck aren't buying a pressure differential bypass.

BadgerBoilerMN said:

I have a signed copy, thank you..

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Maybe now is the time to read this book?

Dana said:

"Promoting" a practice is a very very distant cry from "mandating". When the math proves that it's not necessary, it's simply not necessary. Presuming that P/S is the only way to "do it right" is for folks who can't or won't do the math (which is apparently the vast majority of boiler installers.)

Since P/S piping can limit the damage from a host of design errors from the folks who can't/don't do math it's in the manufacturer's interest to promote the practice, but that doesn't mean it's always the right thing to do.

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Are you even reading my posts?

Tom Sawyer said:

Two words " VFD pumps"

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Sure VFD or at least bypass pressure differential. VFD will decrease flow trough system and boiler without separation when load will drop. Differential pressure by pass will keep same max flow trough the boiler even system flow might be very low, if there is no separation when load will drop. But there is certain flow and delta t requirements for the proper boiler operation. How can you meet those criteria in those conditions, if there is no separation?

gennady said:

Are you even reading my posts?

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Sure. Are you even reading BadgerBoilerMN's posts?

gennady said:

I had a chance to install steam boiler with modifications of steam heating system and condensing boiler on 2 identical brownstones within couple blocks from each other. The gas bills were within 20 dollars difference on winter month. Taking into account electrical charges to drive 2 pumps I would say it was very close call. Good steam system can compete with hot water system. And definitely not worth to convert steam system to hot water. On steam systems oil to gas conversions our average results are 70-75% fuel reduction, depending on how screwed up steam system was.

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Gennady,
would you please provide more information on changes made to the buildings (insulation, windows, etc.) when modification were made to steam heating system and when steam boiler was replaced by condensing boiler. I'm very interested in your observations. Hot water condensing boilers has an impressive energetic efficiency (based on 1 Law of Thermodynamics) but percentage of usable heat is low (2 Law of Thermodynamics, Carnot ratio) - http://homeenergypros.lbl.gov/profiles/blogs/scrutinizing-condensing-boilers-with-the-second-law-of
It works differently with steam boilers, looks like you have a live demo.