Interesting Mod-Con Boiler Comparison

Perry_2

Tube heat transfer 101:

The actual conductance of the metal lhas little to do with the heat transfer of a heat exchanger. Not that it is insignificant; but....

From memory (I literally had to pull the book and explain this to 2 different engineers in two different plants yesturday - So I have a reasonably good memory of the chart).

What provides resistance to heat flow through a tube.

Here is a summary of my memory of the diagram for a Steam Condenser Tube:

Steam side water film 12%

Steam side tube fouling 23%

Tube Wall 2%

Tube side fouling 35%

Tube side water film 18%

Note that the water films are the "thin" stationaly layers of water on the tube wall. Gas heat exchangers has an equivalent gas flim (that is a lot more dominant than water films).

Change the tube material to about whatever you want - and you only effect its contibution by a single percentage point or so. This is obviously true for cast heat exchangers as well.

The commercial HX industry uses mainly Steel based alloys for heat exchanger tubes or plates. Copper, and copper alloys, are rarely used in larger HX's anymore unless it is needed for a specific corrosion reason.

Many large HX's have been retubed; changing the tube material from copper, or copper alloys, to stainless steels - without much, if any, noticable loss of HX capacity. I will admit that you do see a small effect on a multi-million square feet of surface area power plant steam condenser; but, it takes getting that large to really see the difference.

I will admit that HX design (and boiler design) is a compromise. You cannot have everything - there are tradeoffs.

The correct Stainless Steel alloy (there are many) tends to be more durable than many other things out there.

Perry

Perry_2

Interesting Mod-Con Boiler Comparison

Which Mod-Con boiler is right...

A question that many ask.

They all have similar firing rates... They are all efficient; and (I'll get to the "and" later).

Price is one comparison: I can buy one small mod-con for about $2200 delivered. Another cost $5000

So what are you really getting?

Here is an interesting way to look at them: By weight.

Vitodens 200 6-24 (22-81 KBtu/hr) 143 Lb (Actual)

Munchkin T80M (19 - 80 Kbtu/hr) 58 Lb (shipping weight)

W-M Ultra 80 (15 - 75 Kbtu/hr) 149 (shipping weight)

Triangle Solo 110 (28-103 Kbtu/hr) 106 Lb (actual)

Now I'm a beliver that in general mass buys longevity in boiler components. I am also aware that the Vitodens has a highly advanced control system built in. However, electronics only weighs a few pounds....

I also note that the Ultra is in the same weight range.

So my real question is... What did some of the other's cut out as weight - "AND" how will that affect long term durability and reliability?

Or am I really off base with my simplistic look at one factor of the various Mod-Cons?

Please add other models that you may have information on.


Perry

ALH_4

LB/HP

I'm pretty sure that method of comparison will tell you very little. A BMW might weigh the same as a Pontiac. I guess I'd probably rather have the BMW.

All I can say is that when you work with a Vitodens you can tell that everything is engineered without much compromise. Having lifted a few 15-60's and hung them on the wall, I can say that I would prefer a lighter boiler at those moments. The big Vitodens is a pretty heavy unit to be hanging on the wall off of a couple of lag screws.

The Prestige is simple and therefore lighter. There is no heavy coil of stainless steel. I like it for its simplicity.

The Ultra has a fairly heavy aluminum heat exchanger inside. There is nothing wrong with an Ultra.

The Munchkin has what, in my opinion, is a very substandard molded plastic jacket. It's the cheapest beause it's the cheapest.

The Vitodens has a pretty hefty stainless steel heat exchanger, an integral variable speed pump(24&32), as well as the controls built in. The intake air compartment is of gasketed steel construction.

-Andrew

hr

Weird way to compare

The Weil is a cast aluminum block in a partial metal frame with a fairly heavy plastic (sound deadening) cover.

The others are stainless coil HXers. Two are in metal enclosures. The Munchkin in an all plastic case.

Are you including the step up transformer power module in the Viessaman weight?

I'd say remove the HXers from all the units and weigh them if you are trying to equate HX mass and weight to quality or longevity. Although comparing a cast block to a tubular design doesn't add up in my mind.

Knowing what I know about mod cons, I'd concern myself more with ease of service, especially HX cleanings. Access to parts, both consumables and 15 year warranty components

Factory, rep, and dealer knowledge and support. And number of units in operation. Failure or complaints would be another number of importance but skewed by improper installation, comissioning and routine service and adjustments, no doubt.

I'd guess the units sold via www to DIYers would have a high % of problems from improper piping and installation, start up checks and adjustments.

Water qualit is a sleeping giant in my mind, especially with ph sensitive metals, like aluminum. That's a failure waiting to happen that you can't see from the outside. stainless, too, has some limitations regarding fluid quality.

I had you pegged as having a clear winner already selected But then again you haven't even mentioned the other 10 or so mod cons in your group. You've got a lot more homework to do.

hot rod

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Brad White_116

Buying boilers at the Delicatessen

"I'll take a pound of boiler, sliced thin, please."

Personally, I like the imported kind, but then again at some level, they all are.

Boilerpro_5

Actually, the Prestige is not a coil...

but a downfired vertical firetube boiler within a tank of water. I suspect it resembles an old GE boiler...from what I heard about them. That construction would certainly add mass over the Munchkin coil design, whose heat exchanger is common with several other condensors.

Boilerpro

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Perry_2

I agree in part...

Actaully, I do know which boiler I would like. I'm overcomming sticker shock.

You are right that different features can add or subtract weight without affecting quality. I agree to a point; and it depends what they did.

However, the question has produced some interesting information about several of the boilers I did not know.

Have a nice day.

Perry

Perry_2

Ketchup or mustard...

Would you prefer Ketchup or mustard with that; and perhaps some ginsing on the side for energy....

Perry

Perry_2

Hot Rod Says: Water qualtiy is the sleeping giant.. Aluminum

"Water qualit is a sleeping giant in my mind, especially with ph sensitive metals, like aluminum. That's a failure waiting to happen that you can't see from the outside. stainless, too, has some limitations regarding fluid quality."

I totally agree. When I started my search and looked at the first "aluminum" heat exchanger I wrote down 3 issues:

1) Galvanic corrosion with the pipes connected to it.

2) Resistance to long term and steady hot acid environment

3) Proper boiler water chemistry.

Item 1 and 2 are longer term issues; but boy when they develope... Galvanic isolation flanges tend to get bypassed or just dirty enough so that the process starts. This is an area I know about because I just started a multi $millon HX replacement project becasue of galvanic issues this year (all becasue people didn't understand the galvanic issues a while back).

Items 3. I can't see homeowners periodically testing and treating their boiler loop water. Worse yet, the cheapest chemicals to control the normal issues create sludge. What makes you think that the homeowners wont use it (I can just see how to treat your boiler loop cheaply on an Internet "how to" page). Who wants to fill their radiators and boiler with sludge over a few years. I know what sluge lined boiler tubes look like.... (I actually have a really cool fouled boiler tube sample that I saved from a repair job a long time ago: I ask people in the industry "Fire tube - or Water tube" - no one has ever gotten it right). It will plate out on the cast AL boiler first further restricting heat transfer and efficiency.

This is one area where I'm going to adopt the Missourie attitide: Show me. In 15 years show me that Al Mod-con boilers have lasted without problems.

Stainless Steel or bust ! is my attitude on a Mod con.

Perry

big bill_3

mod-cons

looking at a cross section of vitodens ht ex the wall thickness is well thick and it modulates in 1% increments-purrs like a **** cat on mild days

[Deleted User]

There is a saying in this business...

And I believe it was coined by my good friend and associate Jeff Young, a.k.a. HeatBoy.

It goes "It's not so much a matter of 'you get what you paid for', as it is 'you didn't get what you didn't pay for and you didn't get what you thought you were going to get in the way of efficiency, longevity and bottom line comfort' " By then, its too late, and it IS going to cost a lot more to do it right, the second time.

Okay, I may have paraphrased it somewhat, but you get the gist.

As an educated consumer, you are looking into this much deeper than most, and are to be congratulated on your efforts. Just don't get too wrapped up in the numbers game. It leads to Confusion due to dillution to the solution...

JMHO

ME

Boston

Agreed

Building a boiler is always a compromise from an engineering point of view.

Stainless steel heat exchangers are great for long lasting resilience to the boiler condensate but they have to have narrow water galleries to get the heat transferred into the CH. This is due to two things, the boiler has to be a certain physical size, due to customers need to fit boiler in small spaces, and the poor thermal conductivity of stainless steel.

Consequently the stainless steel HE will need replacing sometime in its life because of blocked water galleries. This may be resolved by cleaning but again the HE will need to come out.

Aluminum on the other hand will rot through during its lifetime. Pure Aluminum will last longer than an alloy but it will need to be replaced. But because of the much better thermal conductivity the HE can have large waterways, which will not block from the CH debris.

So you take your choice.

[Deleted User]

The heat transfer of stainless steel...

is not as bad as you'd think it would be. Trust me, I have MANY hours logged watching my stainless steel mod con ramping up and down to handle load variations, and I would have to say that it's reaction time is better than cast iron by a LONG shot, and is even better than most coper finned tube boilers due to its modulating capabilities.

Obviously, copper is much more conductive than S.S., but I have yet to see one that can handle the pH of condensation...

Here are a few graphs of the thermal reactions of my mod con...

ME

Boilerpro_5

Take a look at the Prestige

They ain't narrow. The tubes sit in a tank of water...One of the things that I think will really make it shine as the years roll by.

Boilerpro

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