Help with triangle tube prestige excellence 110

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Climberken

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I am in the process of replacing a old Lennox boiler heating baseboard system with a new high effiecency radiant system. Back in the 80's I worked for a residential Lennox heating contractor as an installer. I'm pretty good at sweating pipe and making everything look pretty and understand the basics of my existing system. The new system looks like the space shuttle as far as complexity. I'm working with a local heating guy that has installed "a few" of the triangle tube boilers. He has not however installed the combination boiler and domestic water not that it is relevant to my question.

The basic system sort of makes sense to me, form the boiler supply side build a manifold for the six zone pumps. From each circulator run copper to radiant wisbro manifold connecting to the multiple loops. I'm running 1/2 inch pex under floor with joist track for the main floor and a new insulated concrete basement floor with 1/2-inch Pex.

So I have a few concerns, the boiler supply and return are 1 inch, my heating guy is suggesting building a 1 inch manifold with 1 tees to each pump........my concern is that if all zones are calling for heat at the same time the six taco 006 pumps are going to tear themselves apart by cavitation? I hate second guessing my guy but that's a lot of pump. Am I crazy?
 

Dana

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No, you're not crazy, and my gut tells me this guy doesn't do math.

First off, why such a large boiler?

The -110 is significantly oversized for 19 houses out of 20. The -060 is usually enough boiler for the other 19, especially in a highly efficient radiant system.

The problem with oversizing with the -110 is that the minimum modulated output of the thing can be at or above the design heat load of many houses, so it never or rarely modulates, only cycles. For instance, in my sub-code 1920s house the heat load doesn't reach the ~28,500BTU/hr min-fire output of the -110 until it's a bit lower than ~17-18F outside, and that's more than 5F below the hourly average temperature in January. In my house it would only modulate at night during the colder part of the winter, and during the day only on cold-snaps. Even if I moved my house to Fargo the -110 would be oversized, and the -060 would be enough.

And to make matters even worse, in your case you have six zones, probably none of which are capable of emitting the full 28K, which means it'll be cycling on/off like CRAZY on zone calls! You might be saved by thermal mass if the radiant is all concrete slab, but that's rarely the case in retrofits. You'd be better off having all zones sipping off a buffer tank, and slaving the boiler only to the tank.

In a micro-zoned system like yours it also makes more sense to use one large ECM drive pump and zone valves than a six pack of Taco-006s, even if you down-sized to a more reasonable boiler size.

First things first- get the boiler sizing right. If you have heating history on the place you can use fuel use against heating degree-days on some wintertime billing periods to come up with an upper bound on the whole house heat load using simple arithmetic. We'd need a ZIP code to come up with the outside design temp and the EXACT meter reading or fill-up dates & quantities to pull weather data from a nearby weather station on degreedays.net.
 

Climberken

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No, you're not crazy, and my gut tells me this guy doesn't do math.

First off, why such a large boiler?

The -110 is significantly oversized for 19 houses out of 20. The -060 is usually enough boiler for the other 19, especially in a highly efficient radiant system.

The problem with oversizing with the -110 is that the minimum modulated output of the thing can be at or above the design heat load of many houses, so it never or rarely modulates, only cycles. For instance, in my sub-code 1920s house the heat load doesn't reach the ~28,500BTU/hr min-fire output of the -110 until it's a bit lower than ~17-18F outside, and that's more than 5F below the hourly average temperature in January. In my house it would only modulate at night during the colder part of the winter, and during the day only on cold-snaps. Even if I moved my house to Fargo the -110 would be oversized, and the -060 would be enough.

And to make matters even worse, in your case you have six zones, probably none of which are capable of emitting the full 28K, which means it'll be cycling on/off like CRAZY on zone calls! You might be saved by thermal mass if the radiant is all concrete slab, but that's rarely the case in retrofits. You'd be better off having all zones sipping off a buffer tank, and slaving the boiler only to the tank.

In a micro-zoned system like yours it also makes more sense to use one large ECM drive pump and zone valves than a six pack of Taco-006s, even if you down-sized to a more reasonable boiler size.

First things first- get the boiler sizing right. If you have heating history on the place you can use fuel use against heating degree-days on some wintertime billing periods to come up with an upper bound on the whole house heat load using simple arithmetic. We'd need a ZIP code to come up with the outside design temp and the EXACT meter reading or fill-up dates & quantities to pull weather data from a nearby weather station on degreedays.net.


First off, thanks Dana!

I'm stuck with the 110, I'm going from a 140,000 btu boiler and a 80,000 btu water heater. I'm surprised the 110 is going to be too big considering it only has a 14 gallon internal domestic tank to heat water plus heat the house too, I'm running a recirculating pump for the domestic also. But , then again My ignorance gets me shocked a lot these days and I'm certainly not saying you are wrong to have a smaller boiler but this is what I got! I'm feeling like the customers I had replaced the old conversion burners with a Lennox pulse........25% the physical size, they just couldn't get around the much smaller size and btu.
I've got a pre 70's 3000 sq. ft house with 900 of it in the basement. Over half the house is over crawl space, single story with cathedral ceilings, 18 ft in the middle.......lots of windows (410 sq. ft.) just to give you an idea. I had originally done an online heat calc and came up with close to 30,000 btu/hr. If my math is right I'll be running close to 3000 ft of pex. A couple of the zones are only 280 sq. ft but they both also have 110 sq. ft of double pane windows. Don't think it's a grandiose home, I've got lots of work to do!

The original plan was to go with a grundfos alpha 15-55f pump with high flow Honeywell zone valves going to the radiant manifolds. Would that be my closest save? I've dug a pretty good hole to bury myself in.
 

Dana

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First off, thanks Dana!

I'm stuck with the 110, I'm going from a 140,000 btu boiler and a 80,000 btu water heater. I'm surprised the 110 is going to be too big considering it only has a 14 gallon internal domestic tank to heat water plus heat the house too, I'm running a recirculating pump for the domestic also. But , then again My ignorance gets me shocked a lot these days and I'm certainly not saying you are wrong to have a smaller boiler but this is what I got! I'm feeling like the customers I had replaced the old conversion burners with a Lennox pulse........25% the physical size, they just couldn't get around the much smaller size and btu.
I've got a pre 70's 3000 sq. ft house with 900 of it in the basement. Over half the house is over crawl space, single story with cathedral ceilings, 18 ft in the middle.......lots of windows (410 sq. ft.) just to give you an idea. I had originally done an online heat calc and came up with close to 30,000 btu/hr. If my math is right I'll be running close to 3000 ft of pex. A couple of the zones are only 280 sq. ft but they both also have 110 sq. ft of double pane windows. Don't think it's a grandiose home, I've got lots of work to do!

The original plan was to go with a grundfos alpha 15-55f pump with high flow Honeywell zone valves going to the radiant manifolds. Would that be my closest save? I've dug a pretty good hole to bury myself in.

Your old boiler had different radiation (maybe enough to balance with the boiler output, maybe not) and more thermal mass, and you probably had only one or two zones(?).

A boiler with a MINIMUM modulated output of 28,500 BTU/hr for a house with a 99% design temp heat load of 30,000 BTU/hr is a LOUSY match, even if it were operated as a single zone. It's guaranteed to never modulate! When you compound that by chopping it up into 6 zones, it's going to short-cycle itself into low efficiency on zone calls, and into early grave. With any of the TT -110s with low-mass radiation you're guaranteed to only have reasonable burn times 5% of the time at your design heat load & zoning, and that's only if you dial in the outdoor reset curves to perfection.

If you're "...stuck with the 11o..." you won't be stuck with it for too many years- you'll short-cycle it to death, unless you either reconfigure the heating system topology to include a significant amount of buffering thermal mass, or run it as a single zone. As a single zone with the reset curve dialed it'll run reasonable burn times and far fewer cycles during calls for heat, but it's probably not what you were looking for.

There are no combi-heaters out there other than tank-types that will work with your zoning as-is unless you add a buffer tank, at which point it makes more sense to go with a tank-type combi heater.

There are several boilers out there that modulate down to under 10K, some go as low as ~7,600 BTU/hr out (eg, the HTP UFT-80W, there are a few others ) which would do just fine with your zone setup, and would have plenty of burner to serve up domestic hot water with an indirect HW heater as the priority zone. Even though it's oversized for any single zone, it's reasonably sized for the whole house load, and which you get the outdoor reset curve dialed right you'll be guaranteed to have overlapping zone calls, and it'll burn almost continuously throughout the winter.

Water velocity in the thin manifold and cavitation issues are the least of it. I can't/won't spec a pump for you even if I had the full system description to calculate the pumping head and flow requirements from, but somebody with the right design software tools could (for a price.) This is not a design-by web-forum level of fix. There are folks posting on this forum who could do the necessary re-design for you and specify the "save" well enough for your heating guy (or a dedicated DIYer) to manage it. But it starts with the real room-by-room heat loads and the room-by-room radiant component details that are already installed.

If I had to guess, a tightened up 3000 foot pre-1970s 2x4 house in Boulder would have a heat load closer to 45-50K @ 0F (Boulder's 99% outside design temp) than 30,000 BTU/hr but that's not going to be enough to save you here. If you have a fuel use history on the place, let's run fuel-use against heating degree days to at least nail down a reasonable upper bound on it.
 

Climberken

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Thanks again Dana. I'm going to talk to my boiler guy, see if I can possibly change out the boiler to a smaller unit like the 60. I had 3 estimates for installing the boiler for radiant all of them came back with around a 100,000 boiler for a combi. Then again most of them just wanted to know how much fin tube I had in the house. Radiant is a bit more complicated then that apparently! I'll give you a heads up on how this goes.
 

Dana

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With the smaller zones even a TT -060's min-mod output is going to be a problem unless you can combine them, but it would probably work fine against the whole-house load.

Did you really have six zones of baseboard?

Yes, radiant with modulating condensing boilers is more complicated than high temp baseboard systems with bang-bang on/off controls. The heat rate that the radiation emits varies with temperature. With baseboards as long as each zone can emit a major fraction of the boiler's output with 200F average water temp you can size the boiler to where it won't short-cycle. As long as that heat rate equals or exceeds the heat load at the 99th percentile outside temperature bin it'll heat the place just fine. At 1.7x oversizing for the load or less it will even meet it's AFUE tested efficiency as long as it's not short cycling. But at 2-3-4x oversizing for the 99% load it's efficiency drops off with oversizing factor, since the jacket & distribution losses become an ever higher fraction of the total.

With radiant under outdoor reset control the idea is to adjust the water temperature so that the radiant emits only what is needed for the instantaneous load, letting the boiler modulate it's firing rate for highest efficiency. The lower the return water temp entering the boiler, the higher the efficiency. Condensing efficiency only begins when the entering water temp at the boiler is in the mid-120s, but is soars from there on down to about 100F EWT. But to keep continous efficent burns at low water temp means the radiation has to be able to emit the amount of heat the boiler is putting into the system. When heat-in is greater than heat-out, the boiler has to cycle on/off, and the greater the ratio of BTU-in/BTU-out the shorter those cycles become. With every ignition cycle there is heat thrown away in flue purges and lower efficiency combustion during the initial 10-15 seconds. That's not a big deal on a 10 minute burn, but if the average burn cycle is 60-100 seconds, it's a measurable hit in efficiency. Every ignition cycle also takes a toll on the equipment too. So, when a zone can't emit even half the min-fire output of the boiler at condensing temps (or even at the maximum output temp) of the mod-con you're screwed, on both efficiency and longevity. Fewer zones and lower min-fire output are simply better.

A common work-around is to add sufficient thermal mass (say, a buffer tank) that even though the boiler is cycling when serving small zones, the minimum burn times are at least 100 seconds (200 seconds is better), with the water temp swing around the programmed outdoor reset temp. But at ~30K minimum burn that's a pretty big buffer tank to guarantee a minimum burn time that long. The 14 gallons of potable water inside the combi-boiler is only a small fraction of what's needed.

Some tank type combi systems may have similar min-fire output, but 4-5x or more thermal mass. The smallest of the HTP Versa series can modulate heating outpu down to about 12K-out (from a max of over 100K), with a burner that modulates down to ~25K, but it has 4x the thermal mass to work with and some smart controls to manage the thermal mass & burner optimally. It would probably be pretty simple to drop one of those in your system, once you get your flow & temperature issues straightened out. (A task I'm not convinced your boiler guy is up to doing compentently.)

I'll PM you some hydronic design/radiant contractor contacts who have experience with both Triangle Tube & HTP (and others), who are capable of good design reviews remotely via internet.
 
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