Lochinvar WB and WH boilers

[dwassner]

I am looking at the WB-051 or WH-055 knight boilers. The biggest differences I see are in the head loss, gallon capacity, and heat exchange surface area. The WB has a head loss of 11.0 at a delta T of 20 deg. while the WH has a loss of only .27. Why such a large difference? In what situation does one work better thank the other? The one with the lower loss has a 2.5 gallon capacity while the high head loss model has a .6 gallon capacity. Again, why such a difference? This seems huge to me. I was going to go with the WH-051 but found the other model on their web site and thought I would look into it.

[Mike Krall]

Probably too late with this...

The difference is in how water is heated. "051" has water in the tubes... "055" has water around the tubes (a "fire tube" boiler very similar to Triangle Tube condensing boilers).

The high head pressure comes from the wall restriction of the small tubes in the "051"... takes more pump (more watts) to move the water through and can be disposed to flashing, though that is avoidable through proper set up and run.

All around, the "055" is a more elegant solution, though both boilers are very good ones... especially for small-load, low temp. requirement, environments.

Mike

PS... All above is second-hand from "my" boiler and systems expert... Brad White, near Boston, Mass.

[dwassner]

your not too late actually, thanks for the reply. So what I am wondering is what circumstance you would want one or the other.

[Dana]

It's something of a subtle system design issue- the WB- use more pumping power for the same flow, but high flow may or may not be necessary. Water tube heat exchangers usually tolerate a higher delta-T too, and in some systems would produce a higher overall combustion efficiency. The low mass water tube boilers gives them somewhat lower standby losses than higher mass boilers, (lower-mass==less abandoned heat at the end of a burn) and running at a higher pressure isn't really a problem. But those differences are "in the noise" compared to good/better/best system designs around either.

In many systems it won't matter, but if higher flow really is needed the WH- may work out better. Until you dig into the real design on the real system & radiation you can't really say if one is more suitable than the other. Pump placement may also change- pumping away from the boiler is standard practice for fire-tube boilers, but pumping toward a water-tube boiler allows the system to run at lower pressure without sizzle on the heat exchanger.

I'm not sure how the WH can be considered inherently better suited to low-load low-temp systems than the WB series, but the converse might be argued- the WB can probably squeak more efficiency out of higher-temp radiation run at a higher delta-T. Both models mentioned modulate down to ~10KBTU/hr at low fire and have condensing heat exchangers- so it's not really the size of the load. The WB-51 had 23% more heating surface area on the HX than the WH-55, and may have inherently better heat transfer at any water flow or delta-T.

At home I'm currently using a high-head/low mass Takagi water heater (==water tube copper fin heat exchanger) as a boiler and running it at high delta-T/low flow on massive buffering hydraulic separator (with a potable HX for the DHW inside), and using other pumps to control the higher radiation flows. It probably would have taken a real monster of a pump to run the entire system off one pump, but if I had a low-head boiler a simpler system architecture might have been possible at least in theory. By the time it's multi/micro-zoned and an indirect HW heater is added maybe not- the centrally buffered single-temp approach made micro zoning without short cycles pretty easy. With a condensing boiler it would have sacrificed a couple percent in combustion efficiency, and may or may not have made up for it efficiency-wise with fewer but longer cycles.

Bottom line, the boiler (any boiler) is only as good as the system design that's around it, and the system parameters will adjust somewhat to get the most out of either.

[Dana]

[removed double-posting]

[Mike Krall]

your not too late actually, thanks for the reply. So what I am wondering is what circumstance you would want one or the other.

Only thing I can think of is the difference in net input... 45k for "051" and 50k for "055". In some circumstances (very low calculated heat loss) a person might want the lower turn down. (But I am thinking about high mass radiant... as opposed to low mass types... where condensing boilers get into ultra efficiency do to low temp water requirements. I mean, it's not like the 96% at higher temps is bad... just that the "051's" 98% and the "055's" 99% only exist in low water temp reality.)

We've got a 1750sq.ft. house that is 20% -25% passive gain and the calculated heat loss is 37.5k (without accounting for solar gain). This house is two person with very low hot water usage, so both these boilers are "too big"... Not that either wouldn't work very well.

There is a consideration in here for "normal" hot water use during min. temp days... person might find they need a bigger boiler to handle the DHW load AND heat the house... if all set to on demand. Where less hot water use and low calculated heat loss might get along with designating when the hot water was made (or when not made).

Here's a thing I got from Brad White a few weeks ago on the two...

"The old design was based on the Giannoni heat exchanger, a round bundle of flattened, rolled round tubes surrounding the combustion chamber. The oval cross section of the tube and small diameter made for good turbulence and "wiping action" against the walls of the exchanger. The downside was low water volume and high pressure drop, forcing all that water through small tubes. Low water volume says that if you do not have a fairly high head pump (1/6 HP or 245 Watts!), you could flash water into steam. Have to keep it moving.
We call the above a "water tube" design. Water in the tubes surrounded by flame, simply enough.

The Triangle Tube design which they now use, is a "fire tube" design, the combustion products are in tubes and the tubes pass through a small TANK of water. Lower pressure drops on the water side, higher volumes, less flashing likelihood. Smaller boiler pump! All good."

Mike

[Dana]

The fact that your design condition heat load is ~ 37.5K doesn't mean that ~50K boilers are "too big".

The passive solar gain during design conditions is pretty close to zero, since outdoor design temps tend to occur almost exclusively in the pre-dawn hours.

The fact that these boilers will modulated down to ~10K, means that in a well designed system they would track load very well during most of the heating season, and would not lose much in terms of efficiency.

If your radiation requires 150F+ water temps to deliver the 37.5KBTU of heat to the house the combustion efficiency at typical delta-Ts will be no better than 86%, and the 50K boiler would only be capable of delivering (0.86 x 50K=) 43K of heat in to the system at full fire for a ~38K load a bit more than 10% of margin, which is OK but definitely NOT overkill, and NOT too big.

Even if you're running slab radiant with 110F water on design day you're still in the low-90s for ~45K of output, call it 15% of margin, still not overkill.

Even if you assume your heat loss calc tool is padding it by 15% and the true design condition heat load is 32K you still won't lose anything to efficiency with a min-fire of 10K, less than 1/3 of peak load. At 45K of output at design condition it's only 1.5x "oversized" and would meet it's AFUE numbers even if controlled in a bang/bang on/off fashion at max fire.

For a mod-con boiler to be considered "too big" is if it's minimum output is over half the true design condition heat load, but even those systems can be designed to run efficiently, even if you have no use for it's higher output capability. The fact that the min-fire output is well under half your design condition load makes these boiler much closer to right-sized than "too-big". The max fire number is of lesser importance than the min-fire number. Even were a 40K boiler available, it might not be advisable to leave yourself that thin a margin, if it's buying you nothing in efficiency. AFUE numbers assume 1.6x oversizing, and are still pretty close to the steady-state 100% duty cycle efficiency of the boiler. A ~50K (45K output) boiler for a ~38K load is about as good a fit as you could possibly get!

Residential application that would require upsizing the boiler above the space heating load to be able to deliver the DHW load are pretty rare. Even at design condition most homes have enough thermal mass and insulation to not lose much temp during stored hot water recovery burns. Peak loads for DHW are often 2-5x the peak space heating load, but they're very short in duration, and easily handled by the stored thermal capacity in a tank.

At tiny space heating loads under 30K it's simpler and cheaper to forgo modulation & load tracking entirely, and take a bang-bang burner buffered approach, such as a condensing hot water heater. Even a ~75KBTU/hr Vertex will run with great thermal efficiency and would have burner to spare for a 25K heat load on top of typical DHW loads. Standard gas fired hot water heaters do just fine with an 80% combustion efficiency ~35K burner (~28K out), using the mass of the stored water to distribute the instantaneous very-high BTU/hr loads of tub fills or showers over a longer burn than the shower or fill time. No more than ~1% of the time is your heat load going to be the calculated design condition heat load- the rest of the time it's warmer outside and during daylight hours you'll have solar gain (even on dark and cloudy days the solar gain is greater than zero) picking up some (or all) of the load.

Even at 1gpm you don't have to raise the system pressure much to avoid flash steam on water-tube boilers if you're pumping toward the boiler. And it's pretty obvious when you're "there". At lower pressure & flows they sizzle audibly from the steam-boil, and at REALLY low pressure & flow they'll even pop & bang. Most hydronic systems for 1 & 2 story houses are run in the ~12psi range (measured static, not when pumping). I'm running mine at under 2gpm with a static pressure of ~18psi and hear nary a peep from it. The components for hydronic systems are almost universally good to at least 30psi, which is a typical pressure-relief valve setting. Pumping like crazy with a monster pump to treat the sizzle & bang flash steam issue since it's (usually) easily handled by modest pressure increase. I put a Taco 3-speed on mine but I run it at it's lowest speed (~70watts). I could have done fine with a -007 or similar, but I wanted to be able to monkey with it a bit in case I needed more DHW capacity.)

Water tube boilers aren't nearly as difficult to design around some people seem to think, but they may seem pretty exotic compared to high-mass low-head cast iron boilers, and from a drop-in replacement point of view it's probably easier to put in a lower-head mod-con. I have no direct knowledge of any peculiarities to the Lochinvar WB- series, but while they may have an order of magnitude higher head than some other boilers, they're within the range of other water-tube boilers at similar output.

[BadgerBoilerMN]

When choosing a boiler for a particular job I look to the heat load first, then to venting, controls and system design in general. When specifying condensing boilers, it is all about installation, local support and informed maintenance.

Having manufactured the first condensing boiler in the U.S. I could go on about fire-tube vs. water-tube, water content etc. but this is for those who have the time and experience to sort it out. For small residential work it simply doesn't matter as much as the proper system design and installation.

For instance, after installing more than 10 different condensing boilers in as many years, I don't even read the warranties any more, they are only as good as the guy that installed the boiler and the guy that sold it to him. The manufacturer has precious little control of his product once it leaves the factory.

Focus on the contractor. Has he installed his brand for long? How many does he have in the field.? Has he been to the factory training? Will he fill out the installation sheet after performing combustion analysis and testing the pH of the system water? In short, why does he by the boiler he is recommending for you?

[Mike Krall]

When choosing a boiler for a particular job I look to the heat load first, then to venting, controls and system design in general. When specifying condensing boilers, it is all about installation, local support and informed maintenance.

Having manufactured the first condensing boiler in the U.S. I could go on about fire-tube vs. water-tube, water content etc. but this is for those who have the time and experience to sort it out. For small residential work it simply doesn't matter as much as the proper system design and installation.

For instance, after installing more than 10 different condensing boilers in as many years, I don't even read the warranties any more, they are only as good as the guy that installed the boiler and the guy that sold it to him. The manufacturer has precious little control of his product once it leaves the factory.

Focus on the contractor. Has he installed his brand for long? How many does he have in the field.? Has he been to the factory training? Will he fill out the installation sheet after performing combustion analysis and testing the pH of the system water? In short, why does he by the boiler he is recommending for you?

That's a worth while post... thank you for making the time to do it... =]

Mike