Old Boiler As Backuo

Mike T., Swampeast MO

Don't forget that this particular client already has TRVs on the radiators so (as long as continuous circulation is in use) they're already used to rads that are only as hot (or warm) as they need to be to heat the space.

My personal system was similar (had TRVs and constant circulation before) and the new condensing/modulating boiler was absolute "icing on the cake". Fuel consumption took a nose dive with the boiler being the ONLY system change.

The radiators do seem to run a few degrees cooler than before, but I'm at a loss to explain how this is possible.

Dick_3

Old Boiler as Backup

Talk me out of this:

We have a job where the owner is concerned with high fuel bills on his hot water system with cast iron rad's and TRV's. The existing gas fired cast iron boiler is 40 years old, but in good shape w/ no problems, other than, poor efficiency.

The owner is willing to approve us installing (1) hi-eff boiler, but will not approve a modular system w/ 2 or 3 boilers due to the added cost.

We don't like the idea of only one new hi-eff boiler (no backup).

What's wrong with installing one hi-eff boiler sized to the connected load of 240M, using the existing pump as the system pump, piping the new boiler and the old boiler primary/secondary. This would allow for a backup boiler if/when the new boiler fails.

A new Tekmar staging control would be installed, along w/ small secondary pumps for each boiler.

P/S piping the old boiler would eliminate Hod Rod's "cooling tower effect" when the old boiler is typically off-line.

If in the future the owner wants to spend a couple more bucks or the old boiler fails, we'll demo the old boiler and install the second hi-eff boiler.

Just doesn't sound right, please, talk me out of this idea,

Steamhead

What I'd do

is install a new condensing boiler about 1/2 the house's heat loss, and use the staging control to call in the old boiler when it gets real cold.

Otherwise, your idea is fine- go for it!

bob_34

2 boilers yes

this is exactly what i am doing at my own house. very simple. the end switch from the existing 6 zone control can activate either boiler and flow is diverted by running the return of the old into the return of the new boiler and the feed from the new boiler back out to the feed and air scoop of the old boiler. all the existing zone controls stay the same and the computer on the new boiler does all the good work it is designed to do sipping away as needed. bob.

Mike T., Swampeast MO

As long as there are TRVs on ALL of the radiators, you don't necessarily need primary/secondary. With a decent reset curve, the TRVs will keep the system flow within a reasonably tight range in all but the warmest weather when your required differential pressure bypass valve will begin to open and thus keep flow through the boiler from dropping too low.

Is that 240M load from a heat loss calculation, based on the size of the current boiler or worst, based on the amount of radiation? Your load should be from a thorough heat loss calculation.

A condensing and modulating boiler will prove both exceptionally efficient and comfortable on such a system and in some cases with some boilers you need use no more than one circulating pump for the entire system. A variable speed pump is great, but not always practical or available.

If you valve the old and new boilers such that each can be isolated from the system, you can keep the old for backup while using the new at other times. That's what I did in my house and to switch between boilers I only have to close two valves, open two others, turn one switch on and another switch off.

With cast iron radiators, TRVs, constant circulation, reset and a condensing/modulating boiler GREATLY resist the temptation to oversize the boiler. The ENTIRE system achieves nearly perfect balance between BTUs delivered and BTUs lost. Heat loss calculations assume the worst. The I=B=R rating of my new boiler is 85% of the loss calculated by HVAC-Calc yet the boiler still had significant reserve with outdoor temps about 8° below design and strong, gusty winds. I did NOT assume any transmission loss in the heat loss calculation nor did I assume any loss in the basement (other than 55° air below the ground floor) that averages a bit more than half above grade with lots of windows and doors.

Ron Schroeder_3

talk me out of using the old boiler as back up

Hello ****. I am concerned with your customer's perception that exchanging a well serviced, high temperature gas fired boiler, that drives a high temperature heating system, for a new high temperature gas fired boiler that is going to continue to drive a high temperature heating system, will save him any significant amount of operating expense. I was called out to a client that had an old atmospheric Fireman gas fired boiler exchanged for a new atmospheric CI gas fired boiler. The old boiler had old thin fiberglass insulation no motorized vent damper and a standing pilot. The new boiler has new slightly thicker fiberglass insulation, a motorized vent damper and spark ignition. The emitters are columnar cast iron radiators. No other changes were made to the heating system. I received the call because I sit at the Technical Support desk and, while the client had been sold the boiler changeout in response to their stated concern over the rising cost of heating their home, in fact after spending over 4 kilo after tax dollars the fuel consumption did not decrease.

The morals of this story are as follows:

-Merely changing iron in the basement does not equate to fuel consumption reduction.

-Promoting one brand over another without considering the heating system as a whole does not equate to fuel consumption reduction.

-Without reducing the heat losses of the building envelope fuel consumption reduction cannot be assured.

-For the new high efficiency equipment to run at high efficiency, return water temperatures that induce condensation of the flue gasses must be achieved. The greater the condensation, the higher the efficiency. Otherwise the new equipment runs as efficiently as the old high temperature equipment.

- The return water temperatures can only be lowered by enlarging the delta T of the emitter (technicians' method of preference) or by reducing the supply temperature to the emitter. (I know, you will see significant gains just because the heat demand naturally drops due to seasonal climatic influences. But if you do significantly lower the operating temperatures of the heating water all year, your client will see real benefit.)

Offer your client a modulating high efficiency boiler (read condensing)to create a win win partnership. He gets the one boiler he wants to see, you get the variable firing rate that you know should be installed. (If you cannot induce the boiler to condense then you are wasting the client's money and corrupting your good name.)

Most moral of all: Not exceeding the customers' expectations is bad for business.

I doesn't matter what you like. What matters here is the client. Period.

What is wrong with your approach is your understanding of the label "high efficiency". Advertisers' claims notwithstanding no manufacturer's boilers operate at high efficiency unless they condense (not mine either). To condense you have to think "low temperature emitter". The old high temperature boiler will be much too large when you have reworked the emitters/TRV to operate at the new lower supply temperature. This will lead to cycling and we all know that the only thing that is good for is our waist lines ;-)

Allow the boiler's onboard microprocessor to do its job. You do not need another redundant operating system.

Redundant boilers are only to be installed if this is the building owners request/demand. In commercial installations we have paired one condensing and one non condensing boilers. The redundancy was to appease the specifier and the building owner who did not believe our heat loss calculation. When the condensing boiler is a t high fire and cannot any longer keep up and the high temperature boiler is called upon, both operate at standard efficiency. It is rarely defensible to install such complexity in a single family dwelling.

Offering your customer an indirect fired DHW tank can really save them fuel over and against a direct fired one, particularly in comparison with a condensing boiler. Aas the incoming water is always 50F or less the resultant flue gasses almost alway condense. Condensation = high efficiency.

On the other hand, if your client doesn't really want high efficiency (when they take a short sighted view of the cost of the conversion), then fall back to mid efficiency and a moderate reset strategy. Sorry to have to plug my own product here, but the Vitola 200 boiler can withstand an advertised 94F return temperature with impunity. This boiler series can be modulated within a fairly broad range without condensing and so realize most but not all of the advantages of a fully condensing boiler. Alas they are not available with a modulating burner. The Vitola is available with burners that can be used with Natural Gas, LPG, or Fuel Oil.

Mike T., Swampeast MO

Fred: While we're both making some assumptions here, it's hard to consider an American standing-iron system as "high temperature". "Mid-temperature" maybe and a good chance of low temperature (e.g. SUPPLY temp that never exceeds 140--let alone return). By "high efficiency" I am assuming (perhaps incorrectly) a condensing if not condensing/modulating boiler.

Even with fin-tube baseboard systems people are finding that a condensing/modulating boiler has return temps below 140 the vast majority of the time.

Ron Schroeder_3

we are in essential agreement

though we might speak different languages. For the purpose of education here on the wall I defined High efficiency as fully condensing. Fully modulating ices the proverbial cake.

Yes, there is some efficiency to be gained even in baseboard systems that were traditionally designed by their manufacturers to run between 160F and 190F.

I think that I should explain that here, on the West Coast, baseboards have been sized extremely conservatively during the 1980s and 1990s, with the fin tube barely being as wide as the windows under which they are installed. Additionally as our climate is usually quite temperate, cast iron radiators were not oversized either. Over the years homeowners have generally become accustomed to running their heating systems at very high supply temperatures in order to feel warm enough. I have seen many boilers with their operating aquastats set to 200F or higher.

Early on in the rush to high efficiency little attention was paid to the operating conditions of the buildings and low temperature condensing boilers were installed without thinking about what the HO had come to expect. When the systems were run where the boiler condensed, occupants complained that the baseboards felt too cold. Mind, I did not say the complaints were that the rooms were too cold; that was a separate issue, just that the baseboards felt too cold. When the supply water temp was raised to the point where the cold baseboard complaints disappeared, the boilers no longer condensed. When the boilers stopped condensing the payback period became greatly extended.

Standing columnar radiators are even more within reach than fin tube baseboards are. If your client is used to leaning against a toasty warm radiator, he may complain about its new cool temperature, regardless that we assure him that all is well and that he is now saving a wheelbarrow full of money.

What I intended to remind us all of is that we carefully listen to what our clients expect. Ask very many questions before offering any solutions. What we think is good for them, even if we are correct in our assumptions, may not infact exceed or even meet the HO expectaions.

This is all about the home owner and his/her perceptions and expectations. The end results do not have to meet our expectations as long as the HO is thrilled (provided we are not building lobster traps).

IMHO

Ron Schroeder_3

as long as the customer's expectations are being met

all is golden.

BTW did you keep your old boiler on line?

Mike T., Swampeast MO

Yes. Old boiler still in place and functional for backup. Can isolate either the new or old boiler to use one but they cannot be used at the same time.

Deliciously simple system using a Vitodens 6-24. When it's in use ONLY circulator used is the one built in. No low-loss header needed because of the TRVs.

Will experiment with outdoor temperature diversity this winter in an attempt to realize 50% seasonal fuel savings. Already achieved a touch over 43% but honestly believe I can better this via compensation for daytime solar gains.

Mike T., Swampeast MO

Great Post and an Interesting Statement, Fred

When the systems were run where the boiler condensed, occupants complained that the baseboards felt too cold. Mind, I did not say the complaints were that the rooms were too cold; that was a separate issue, just that the baseboards felt too cold.

While comfort is always subjective, those occupants may well have been experiencing something similar to my own perceptions.

For a number of days of moderately cold weather (20s night, 40s day) I set the reset curve for the bare minimum required to maintain space temperature. Datalogging thermometers throughout the house verify that neither the average nor fluctuation in space temperature changed.

With the same indoor air temperature (64°-68° approximately) I felt a completely unfamiliar chill in the house. I resumed my normal reset curve (141° @ 8° with 0.8 slope) and the strange chill disappeared.