First, I want to acknowledge that my post is 'off topic' for this forum since it relates to a baseboard hydronic system, not radiant.  I'm posting here since there seems to be a wealth of ModCon expertise and, frankly, this is what I need at this point.

Disclaimer out of the way, I have a restored small (1300 sq ft) 120+ year old house in Belfast, Maine (14F average low temp) in which I've installed a Laars Mascot HT 330 to provide both heat and DHW.   The system is baseboard (Slant Fin 30) as this was the most practical element to install without MAJOR rework to the infrastructure.  The HT 330 is set up for LPG since we don't have natural gas available in the neighborhood.

I've set up 4 zones, basically each room 'area' in the house, 2 upstairs, 2 down stairs.

Looking at the datasheets on the HT 330, it appeared to me that the integrated circulator would be sufficient to service the four small loops (no loop has more than 4 radiators in it or longer than 50 feet total loop length).  I've installed an outdoor reset sensor on the north east side of the house.

I've attached a photo of the 'working' portion of my installation.

Now, to my questions:

I've had the unit serviced because it was making loud, dramatic 'popping' sounds when firing and it seemed to fire multiple times within a few seconds.  This problem is bothersome, but the REAL reason for my question relates to the responses I got from the serviceman.  

The man seemed to have experience with this boiler and he did say that the other systems he worked on were radiant heat systems, but there were several comments he made that are inconsistent with my understanding of this unit.  By the way, my goal is NOT to knock the service man, but to 'get the facts' to understand what changes I should make to my system.

1. First comment was, "it's plumbed ALL wrong.  There needs to be a primary and secondary loop.  You only have one loop."
My understanding is that, with this small configuration, the integrated circulator would be sufficient and I didn't need a secondary loop with a separate circulator.  It seems to me that a second circulator would move TOO much water and I'd get water rushing sounds without any improvement in output.  However, I'm trying to learn here so please 'educate' me on this matter.

2. The service man disconnected the outdoor reset sensor.  "You only need that if you have a radiant system.  The boiler will never get hot enough with the outdoor sensor. Baseboards need 180 degrees."
My baseboard sizing calculations were based on running the loop input temperature at 140 degrees, 1GPM, using the tables published by SlantFin, so that the boiler would be able to modulate down to a low temperature and, to my understanding, operate at peak efficiency.

3. The service man cut the condensate drain hose so that it was a direct drain rather than having a single loop to act as a trap.
This seems inconsistent with the HT 330 installation guidelines.  I didn't notice this until he had left so I didn't get a chance to ask why...

4. I had put a 2:1 mix of water to RV Antifreeze in the system and the service man said this wouldn't provide protection and would increase corrosion.  He said I should use something like RhoGard.
I've done some more research on this and it does seem that having a specific heating system antifreeze with corrosion inhibitors is recommended, but, is it true that this mixture wouldn't provide freeze protection???

5. One final question is that my plumber 'consultant' said that I needed to have a vacuum breaker on the cold DW supply line to meet 'code requirements'.   I don't know what 'code' he was referring to, but, wanting to get approval, this was a quick last minute addition to the system (you can see the copper branch on the cold water supply line).  My question is, is this really necessary with this unit?  I thought it had a built-in backflow valve on the DW system.  Further, I think the Vacuum breaker is messing up the 'dynamics' of the system because, if I run the kitchen cold water tap and close it quickly, the boiler seems to think that there is hot water flow and will switch on the blower.  The duration is too short to actually fire the boiler, but it is disconcerting to get this unnecessary reaction.

That's basically it.   I might want to pursue the odd behavior that brought the service man out in the first place, but this post is really trying to understand a proper design implementation with this boiler.

Thanks in advance,
Tom

1. your boiler is likely at least 4 times too large for your whole house load. with part loads, and zoning, you are going to short cycle like crazy. you probably need to add a buffer tank to avoid killing the boiler prematurely.

2. Your service guy is right about primary/secondary piping. If you don't do this, you at least need a pressure bypass valve to ensure a minimum flow rate through the boiler at all times. This flow rate should be specified in the boiler's manual. This is causing your popping sounds, as you are probably flashing water to steam in your unit because it's just not moving fast enough to extract the heat being generated.

3. Reconnect your outdoor sensor... disconnecting that was ridiculous.

4. flush your system and get rid of that antifreeze. If you want freeze protection, put in inhibited propylene glycol. ONLY.

My opinions, nothing more, try at your own risk.
Primary secondary is what is factory recommended.
That said you will likley work as built but... I would merge the 4 zones to 2 combining to 2 thermostats. Logic is that there will be a greater demand for heat on boiler, and better flow across boiler heat exchanger. You are a bit over sized on the heat load but it is a needed to have the capacity of 125,00 btu to have the DHW function. not to worry there.
The popping is combustion, the HT330 can be tricky to settle down but you at this point should check with combustion analyzer the Co2, You will need the Seamans control to do the adjustment. Only a service agent with a seamans device will be able to help you.
Check around for someone familiar with BAXI 330. When Baxi (Marathon International in Canada) provided the boilers to LAARS for private label they removed the Seaman control in order to extract more profit, screwing up the ability for most service contractors to do any field work with out the control. That's the Baxi/Marithon way.

It is possible to remove the secondary loop trap (outside of boiler) on condensate drain, go straight out but not recommended by the factory at LAARS.
Baxi shows the instal with out the secondary loop trap. BAXI HT 330
 
Out door reset is an ether or, hook it back up, or manually lower the radiator loops in the spring. If you can keep the house warm and the delivered water temp to the radiators in the 120- 130 degree range your fuel efficiency will improve and you may also solve the short cycling and popping.

A final note, The New LAARS Mascott II is now a product manufactured/assembled completely by  LAARS in New Hampshire and has nothing to do with BAXI or there designs.

Again I suggest lowering the heat temp right off, it is easy, front panel control, see what happens.
Good luck,
Dan

Thanks to both for the very quick response. I greatly appreciate it!

To NRT.Rob, the system does have a differential pressure bypass valve, you can see it in the bottom most branch, right above the boiler drain spigots. Also, what size circulator would you recommend for the secondary circuit. The service man suggested a Taco 007 but this seems way overkill to me.

if you have set the bypass appropriately, then I would not go primary/secondary. the question is what is the minimum flow for this boiler and will you achieve that with the current bypass setting.

What Rob said especially about the trul-insane shortcycling you're going to incur.

Hell with the pumping capacity and primary/secondary niceities- even if 100% of that 50' LONGEST loop length was ALL FineLine 30, at 140F it would only be capable of emitting half the boiler's ~33KBTU/hr min-fire output. If only 20' of that 50' loop is baseboard the burn-times will be stunningly brief (and frequent) unless you crank the water temp WAY up.

How much baseboard do you have (total, and per zone)? If you make it into 2-zones (one per floor) how much baseboard would the zone with the least baseboard have?

If the radiation can't be better matched to the min-fire output you may have to add mass (Rob's buffer tank recommendation) to the system to keep it from short-cycling, and that would also allow you to run the outdoor reset at even lower temps without penalty. It may make sense to configure the buffer tank as the hydraulic separator on the primary/secondary (or not). But before going there, let's have the baseboard length numbers.

BTW is this the HT 330 ( http://www.laars.com/LinkClick.aspx?fileticket=N_0E5lZZN_c%3d&tabid=2559&mid=6431) or is it the combi-heater HT 1.330 ( http://www.laars.com/LinkClick.aspx?fileticket=TD8DGdhXoVo%3d&tabid=2559&mid=6431 )?

Here is more detail on each of the zones:
Zone 1: Guest bedroom, 2nd floor, 10 total feet of baseboard, calculated heat load: 2093 BTU/hr
Zone 2: Master bedroom, bathroom, Hallway, 2nd floor, 17 feet total baseboard, Myson Whispa50 Kickspace heater (low speed), calculated heat load: 4507 BTU/hr.
Zone 3: Living Room, Front Entry Hall, Half Bath, 1st Floor, 15 feet total baseboard, calculated heat load: 3128 BTU/hr.
Zone 4: Kitchen, Dining Room, back entrance, 1st floor, 9 feet total baseboard, Myson Whispa50 Kickspace heat (low speed), calculated heat load: 3505 BTU/hr.

The heat load calculations assumed the house was in finished condition, which it is not - still have old leaky windows and the front first floor (we discovered after tearing off the plaster) looks like a hodge podge of wood from an old stall - LOTS of thermal bridging going on.

The unit is the HT 330 combi.  The HT 1.33 is not a combi.

Right now the 4 zones are controlled by dumb thermostats hooked directly to the zone valve/switches (Taco EO75C2-3) but my intention is to add a smart controller & thermostats so that, if any thermostat calls for heat, the controller will check the temps at all the other thermostats and turn on any zones which are within the hysteresis band.   For example, if Kitchen is below the turn on threshold and Living Room is below the turn off threshold, both zones will turn on their respective zone valves until each one reaches its turn off threshold - this effectively makes the two zones into one with each one shutting off independently as necessary.   The intent is to try to 'encourage' overlapping heating rather than completely independent zones.

Tom

The way you have it set up now on Zone 1, with 10' of baseboard you're dumping 33,000 BTU/hr of heat into a zone that can only emit ~3200-3500 BTU/hr with 140F water, with less than 20lbs of water as thermal mass.  (I didn't look up the internal water volume of the boiler but ~50' of 3/4" plumbing is roughly 10lbs of water.)

That's about 30,000BTU/hr (500BTU/min) of excess heat going into the water, not the zone. The water in that zone is going to heat up, and FAST.  At 500 BTU/min of input 20 lbs of water heats up at a rate of 25F per minute. 

Even if the boiler has 10F of hysteresis around the nominal output temp (most will have less), the beast is going to be pinging away at a 10% duty cycle with short-burst burns measured in a few 10s of seconds of burn time each when just that zone is calling.  The wear & tear on the boiler going through that many ignition cycles is huge, and with every ignition cycle & flue purge it's throwing away a fixed amount of heat out the flue, RUINING the efficiency numbers.

Without looking up the 140F output of those kickspace heaters (I couldn't find them, only found specs for the E50 on the Myson site, a resistance-electric version) it's pretty clear you'll have similar short-cycling issues on zone 3, and probably with the others as well.   Their Whispa III 5000 hydronic kickspace heaters put out ~2500BTU/hr @140F water at the lower fan speeds.

Assuming 2500BTU output for the kickspace heaters, even with all  zones running you have 5000BTU/hr of kickspace heaters, and 51 feet of baseboard for another 16-17K of emitter @ 140F, call it 23KBTU/hr.  That would still leave 10,000 BTU/hr of excess going into the system, even running it all as a single zone, and as temp go lower with outdoor reset the BTU excess grows, inducing more short-cycling.

Short of scrapping it and starting over, add mass (and be sure that the full-mass is involved in every burn.)  A cheap 40 gallon electric HW heater has over 300 lbs of water in it and can be used as a buffer, and with 500 BTU/min of excess going into the system it heats up at about 1.7 degrees per minute. So even if the hysteresis on the boiler is only 5F, you'll get at about 3 minutes of burn out of it, with far fewer burns per hour no matter how many or how few zones are calling for heat. If it's just the smallest zone calling for heat you'd still only be looking at 2-3 burns/hr tops, instead of 30, at ANY water temp.

If you don't have the space you can use a 20 gallon water heater instead, but your burns/hr would double- still not necessarily tragic for the boiler, but going smaller than 20 gallons wouldn't be advisable.

Opinions will differ as to where this mass best lives relative to the boiler & pumps, but plumbing it in series with the return input on the boiler and the hydraulic separator works, as does using Tees at the input/output of the HW heater to make IT the hydraulic separator.  Buffering hydraulic separators like the Boiler Buddy work without the Tees and can handle much higher flow rates, since they come outfitted with 4 ports instead of just 2.  But with relatively low-flow systems like yours just Tee-ing into a HW heater should present no problem- the pumping-head presented by a HW tank is still pretty low- it's effectively the head of the dip-tube plus a little for the tees themselves.

When you start out with an over-sized boiler (for lack of a "real consultant") you go down a rough road. The problem is not fin-tube, it is small zones as stated. A buffer tank is the "easy" cure for this mess unless you can live without the micro-zones.

You didn't state where the condensing boiler came from, but seller should be answering these questions. If he can't, you simply bought from the wrong outfit. Fin-tube may be "practical" but wall-hung panel radiators are easier to install, with greater output at lower operating - more efficient - temperatures. Panel radiators also are available with individual thermostatic controls so they are a very good match for a properly sized condensing boiler. The combi-boiler, though appearing to be a simple solution to a common problem is alas for professionals only taking more time and knowledge to specify, install and maintain than most of the alternatives.

Hystererisis? You are worried about hysteresis? You are flying without a license to walk...

If your boiler expert read the installation manual, he would have done better.

The cast iron guys rail against the condensing boilers with claims that they will not work or will not save money if installed with fin-tube baseboard. After awhile ignorance becomes common sense...but not for everyone.

Sorry, I know it stings, but there are impressionable minds here.

Boy, you guys have time on your hands. I can't get to make a comment till after the work day is over and by that time you've said it all. LOL

I've put in too many of these boilers, which I buy direct from Marathon. Unfortunately, the Giannoni is a sometimes a hard HX to keep working properly and requires setup. It really likes a minimum flow so my advise is to get a full 1" primary loop on the boiler and put closely spaced tees that lead to a loops pump.

Get the outdoor sensor on it and add some more baseboard if possible. You can change the slope to match.

Wow! I knew this was the right place to come! Thank you all for your educational and frank discussion. I really appreciate it.

From what I've read here, it sounds like adding a buffer tank is my most effective 'fix'. I'll see what I can fit into the crawlspace directly below the boiler.

I am curious why the condensate loop trap is not longer considered necessary.

A condensing boilers condensate trap, like the typically specified p/s, may be built in to the cabinet or left to literate installer. Always read and understand the installation manual before risking life and limb.

Regarding using an electric HW heater as a buffer, would I leave the unused heating elements and anode in place or are there standard plugs that can be used to fill the openings?

Tom

The boiler has a built in condensate trap. Do not remove it.
The LAARS manual for the HT330 adds an additional external loop condensate trap, I think it is shown in the photo on your instal, lower right corner.
The Popping is common in these boilers. You need to confirm the settings of the CO2. With or with out a bufferin tank you will pop, You will need a technician that has the Seamns control or go to your supplier and see if you can locate a control there.
Last as I have said lower delivered water temp, merge two zones to one, you might also open the bypass valve as much as possible you will still have flow to the small radiator loops even with that wide open, then lower the water temp out to 120.
The boiler will modulate way down.If this does not help, then you might try adding a Buffer tank,
These are "fixes" that will not cost you hard earned $ aside from the combustion check that should have been done when commissioned you will need a professional familiar with Baxi or LAARS HT330.
 You will need the control.
Co2 settings p. 4 http://media.blueridgecompany.com/documents/Baxi_LunaHT330.pdf       BAXI manual
LAARS Manual     http://media.blueridgecompany.com/documents/LaarsHT330.pdf

Dan

Thanks Dan. The service man who was here is familiar with the unit and had the proper tools to adjust. For the most part he was able to significantly reduce the popping but wanted to check with Laars to see if there was anything else he could do. Now it seems to 'pop' only if the unit is warm. When starting up cold it seems to come on smoothly with barely a 'whoosh'.

Thanks for the tips, I'll make the changes. If it seems that the boiler cycles more than warranted I'll add the buffer.

Thanks again to all for your help and advice. I really appreciate it.

"When you start out with an over-sized boiler (for lack of a "real consultant") you go down a rough road. The problem is not fin-tube, it is small zones as stated. A buffer tank is the "easy" cure for this mess unless you can live without the micro-zones. "

Even running it at a SINGLE zone he's still 10KBTU/hr shy of balancing radiation & boiler output at min-mod even with 140F water-  an output temp only needed at the outdoor design temperature, presuming the heat load calc was at all close. 

There's probably less than 50lbs of water in the whole system, and it would still short-cycle under ODR control when the boiler output drops the output temp to 120F or lower, which would be most of the time.   Even the minimum modulated output of the boiler is close to 50% oversized for the calculated load, so this beast is literally never modulating on a space heating load.  With flow tweaked right (to keep it at minimum-fire), it'll still always be a bang/bang on/off burn except when serving the domestic hot water load on the combi-end of it.

I don't think there is any choice BUT to add thermal mass to the system, short of scrapping it and starting over.  But when plumbed primary/secondary with the thermal mass within the boiler loop it doesn't matter whether it it's micro-zoned or not- the buffer band-aid fixes the short cycles no matter what, so you can just leave the micro-zones in, if that's you're preference.

What this re-invents is the high mass well insulated boiler, but with an external condensing burner twist.  A cleaner looking (and usually cheaper) solution for design loads that low would have been a condensing tank HW heater (which is self-buffering), with heat-exchanger on the heating-system end.  But since the buffer tank's temp will average lower than hot water tank the average standby loss is lower, and if properly engineered (that's a big "IF") it'll be ever so slightly more efficient than a condensing tank heater solution.

FWIW: Since we're just hackin' here, without doing the actual math on the whole system as-is (which I ain't gonna do, even if I had specs on every pump zone-valve & pipe, but I encourage YOU to do better than a lipstick-on-mirror or back-of-napkin calculation) it's probably less risky to put the buffer in series with the boiler's radiation-return & hydraulic separator rather than plumbing the tank itself as the hydraulic separator.

There is also a short cycle delay function in the control of the boiler. you can extend the relight time there.
I am not oppose to the Bufferin tank, just seems preferred to use the controls, merge the zones first.
I suspect the tank is not needed.

Dan;

There you go, reading the installation guide again...did you sell him this thing? hhehehehee

Controls are great, but I'm with Dana on this one. I think buffer tanks are generally best used to fix mistakes (short of engineered solar, ground source etc.) but if you are going to DIY it to the end, A buffer tank can hide a load of sins. 40ga. elec. with some help on the near piping.

Even if you consolidated it to two zones I'm not sure you'd get enough condensing efficiency out of it if you simply let it keep on burning for 3 minutes to be nice to the boiler given that the water temp would be rising at something like 15F/minute. (We'd need the real water volumes to know the real rate, but it's still going to be pretty damned fast.)

At the recent propane pricing, spending a few hundred on a tank with some DIY plumbing would pay off in short years by keeping it condensing nearly 100% of the time rather than 25% of the time.

100% of the time as long as the radiation is designed at <130°F AWT. As you pointed out, that's a lot of baseboard.

Sell it on ebay and have a professional size the boiler.

Why do we want a boiler that "pops"?

I could name 8 or 10 condensing boilers that will not "pop" if properly installed and tuned.
In most cases, where a combi-boiler is chosen and condensing water heater would perform better and where large amounts of DHW are needed a dedicated condensing boiler sized to the heat load and indirect water heater are more appropriate, particularly if a large tub is to be filled.

If he designed it with 140F AWT in mind at 99% design temp, that's "close 'nuff" to 100% at the level of "design" we're doing here, for comparison to something guaranteed to overshoot the condensing threshold every burn by setting a min-burn time with the internal controls.

But point taken- I was being less than precise. (But probably not less precise than the heat load calculations on which the system radiation was specified. ;-) )

The zone-by-zone heat loads specified add up to only ~13K, which would be hard to hit in a 1300' antique house in Belfast ME without a serious insulation & air sealing retrofit. (Design temp there is in low to mid negative single digit's F). With some down-east Maine fudge factorin' and a big WAG I figure reality is probably more like 20K, maybe even 25K. His existing radiation delivers 23KBTU/hr @ 140F AWT, so if reality is between his calc and my WAG it might actually get to 100% condensing with fine-tweaking on the reset curve, but 90% of the time seems more likely. If the real heat load is the calculated 13K even the smallest mod-cons would be running in bang-bang mode, but if it's really 20-25K there would be some modulating room for a smallest in class unit from any number of vendors.

I've yet to see a 1300' home with a 13K heat load at -5F. I'm sure they're out there, but they're not 1890 vintage timber-frames with retrofitted cavity-insulation. With 4-5" of exterior foam and U0.20 windows & doors with a similar upgrade in attic-R to match etc. it might be that low though.

The short cycle delay function delays the re lite, It does not extend the burn.
The manual on these boilers must be read like a trashy novel, some parts twice or more!
And yes the propane Laars/Baxi pops some times,
but it may be possible to tune it out,
oh well,
I need a bufferin
Dan

Condensing water heater for sure.

All propane condensing boilers must be set up by an experienced technician, using a flue gas combustion analyser.

My point early on, that's why it pops!!! This boiler requires a seamans control as well to fine to the unit
wheres that bufferin

Posted By Blueridgecompany.com on 30 Aug 2012 04:25 PM
The short cycle delay function delays the re lite, It does not extend the burn.
The manual on these boilers must be read like a trashy novel, some parts twice or more!
And yes the propane Laars/Baxi pops some times,
but it may be possible to tune it out,
oh well,
I need a bufferin
Dan

If it only delays the re-light, not the flame-out  it's worthless for regaining efficiency or saving the boiler when serving low-radiation output zones.  With bursty burns and a long re-light delay it may even interfere with output capacity to the point that the load can't be met!

Is it more entertaining to re-read in French? (The English isn't compelling enough- a real snooze! )

I'm with Morgan- a condensing tank water heater would be a better starting point, but a buffer tank solution can still work.  Unless something close to the full value paid of the combi-heater can be recouped on resale, the buffer tank will be cheaper than starting over.  Paraphrasing Rob, when you start out with a boiler 4x the size of what's called for your options tend to be limited.

Often this boiler pops and has lighting issues because there is liquid backing up in the combustion chamber. Make sure this is not the case and an additional trap does NOT help. It is also the smallest of the condensing boilers that Baxi makes and IIRC the only smaller one is the smallest Viessmann Vitodens 100 (my favorite) regardless. If your heat loss really that low, look for the smallest you can get or put in a Polaris or equiv.

Now I get your accent Dana!

Poor Dan. I have been on more than one boiler that was too "big" to heat the house...well done Dana.

The delayed ignition can be useful, but again for professionals only. In most applications it is just another trip wire for the layman and professional alike.

I have to say, it isn't that hard if you have an experienced professional produce a computer generated heat load before you buy a new boiler. Buying an over-sized boiler is just shooting a hole in your own boat.

Actually, HTP, Lochinvar and Triangle all make lower output boilers and their minimum fire (most important when designing micro-zone hydronic heating systems) is in the low teens. The Viessmann Vitodens is one of my favorites as well but has one of the highest low-fire outputs in the business at 31mbtuh.

Thus the need for experienced hydronic designers.

I'm not sure what the hydronic heating talent pool in sleepy Belfast ME is like- it's a pretty low key real-folks kind of town compared to the more moneyed & touristy spots on Penobscot  Bay.  (It's been awhile, but I have friends living in Belfast.)

I'd hate to think he would have to go as far as Gardiner to find competent help for a system re-design or a heat load calculation.  There must be someone closer.  SOMEBODY is designing fully functional hydronic systems for those empty-but-winterized & heated summer palaces on Penobscot Bay.

I know that you know, the location of the designer is irrelevant as long as he knows what he is doing. I even design systems in Quebec and hardly know my de jour from my Alouette!

Posted By Dana1 on 30 Aug 2012 12:10 PM
<...snip> it's probably less risky to put the buffer in series with the boiler's radiation-return & hydraulic separator rather than plumbing the tank itself as the hydraulic separator.

Dana,
if I understand this suggestion correctly, this configuration would have the two conventional loops, one primary, one secondary.  The P/S loops are connected through a 'hydraulic separator', AKA Closely Spaced Tees.  The return from the hydraulic separator to the boiler would have the buffer tank installed in series (would the Boiler side of the buffer use the 'cold' or 'hot' side of the tank?  I expect 'hot', but want to make certain).  An external expansion tank would have to be installed somewhere in the loop due to the increase in water volume (again, on the 'hot' side of the tank?). The secondary loop would be plumbed from the secondary side of the separator with its own circulator pump connected to and drawing from the 'supply' side of the separator and the 'micro zones' (as they've been referenced) would tap off the existing manifold/zone valve configuration.

Is this a correct interpretation?

If I understand this correctly, the buffer tank would buffer the primary side and the secondary loop would only draw from the buffer tank when the boiler circulator is operating. Is this correct?

Tom

When using a HW tank as a buffer you want the direction of flow to be into the cold, out of the hot. If you do it the other way the turbulence will cause mechanical fatigue the dip-tube (which is attached to the cold side). It's not a disaster to hook it up backwards, but the dip tube may fail sooner, and all of the flow would be across the top of the tank, bypassing the thermal mass of the rest of the water.

Depending on your flow you probably want to build the hydraulic separator out of something fatter than closely spaced tees on a foot long section of 3/4" pipe, but the concept is right. Using a a short section of 1-1/4" copper pipe with the full sized tee on each end, with 4 reducers to match the diameter of the plumbing to the boiler/buffer and the radiation side would be more similar to the well-engineered commercial versions. eg:

http://ecomfort.com/images/Watts_Radiant/watts_radiant_hydraulic_separator_sweat_union_medium.jpg

Posted By Dana1 on 31 Aug 2012 12:29 PM
<...snip> Using a a short section of 1-1/4" copper pipe with the full sized tee on each end, with 4 reducers to match the diameter of the plumbing to the boiler/buffer and the radiation side would be more similar to the well-engineered commercial versions. eg:

http://ecomfort.com/images/Watts_Radiant/watts_radiant_hydraulic_separator_sweat_union_medium.jpg

COOL!  I just so happen to have some left over chunks of the 1 1/4" manifold I used for the zones...   "Well Engineered"?  Probably not, but serendipitous, absolutely!

Thanks again,
Tom

Just curious,
Before you do put in the bufferin tank solution $$$,,,
try my suggestion and report back on the popping if you wouldn't mind.
We assume that the system has had the CO2 checked adjusted with seamans control and meets CO2 design parameters for a propane system.

Lower delivered heating temp to 135. Check
Pump speed in 1
Now, open manually 1 of the zones, call for heat on the other.
See what happens?
Popping on re lite,
There is also I think a setting to spread the delta T between the supply and return temperature, perhaps a setting of delivered water out at 140 with a 20 degree delta T would also solve the issue with out reconfiguring the boiler room. The boiler would not be compelled to re lite until the lower temp was The appliance has some fairly sophisticated built in functions. It would be a waste not to try them.
Dan

even if you stop the popping, you will not stop short cycling with a boiler this large on a heating system this small. settings can't fix physics. a 20 degree dt on a small amount of water is still a small number of BTUs to extract before you hit limit and cycle off... period.

heat has to go somewhere. or it won't. solving a popping sound doesn't fix a short cycling issue. It just removes the most noticeable symptom.

could add a buffer tank for a few hundred. doesn't have to be big bucks. cheaper than a premature service call or boiler replacement by a fairly wide margin.

Granted a combustion is necessary, and a tank the "easy" fix, but I would lean to one zone for all and/or added radiation (the real thing, not fin-tube).

Dan,
I'll try your suggestion (probably won't be able to for a day or two) to see the effects.  I'll report back when I've run the tests.  The popping is significantly lower since the service man tuned the CO2 and gas pressure settings.  Now it only pops occasionally and it seems that the pops occur mostly when the boiler has run recently and is somewhat warm (not hot since there is no immediate burn, but warm).  Obviously the boiler is only being used for DHW at this time of year so I have no idea what it will do on heat demand.  Also, the outdoor reset is still disconnected and this needs to be reinstalled to run the test.

I do understand the principle that NRT.rob and Dana have been discussing and it makes sense to look into adding the buffer.

One thing, in all this 'redesign' discussion taking place no one asked me WHY I chose this particular boiler.  I knew it was oversized for the heat load, but, as someone observed, I need the high heat output for the on-demand HW.  And while there may be other combinations that are more optimum from an HVAC/efficiency perspective, this one combi boiler had the smallest footprint of all the solutions I saw available to me.   

When I bought this old house, the services (Oil fired forced Air furnace, electric service panel, and electric HW heater) were in the crawlspace.  A dirt floor maze of old tree trunk piers that made it a nightmare to change a simple fuse.   I've since removed EVERYTHING from the crawlspace and have all the services easily accessible in the kitchen.  I couldn't have done this without this boiler. 

Now, it seems I may have to go back into the crawlspace with the buffer tank, but, at least, this is a passive device and I should be able to fit it in without too much trouble.

Again, Thanks to all.  I enjoy this forum and appreciate the 'education' (and tolerance for my ignorance) 
Tom

Excess BTU, This is the beauty and curse of a combination boiler.
I was the one early on that mentioned the DHW side and the BTU load.
These have a 3 way valve and flat plate heat exchanger, diverts H20 from heat loop to flat plate with heat demand.
You have the benefit of on demand tank-less DHW, and if I now understand it pops on the demand for DHW as well as heat,
Buffer tank will do nothing for the pop on DHW. It is the gas build up and ignition sequence, Might check the quality of the ignitors, check condition and gap
Perhaps pre gas calibration if you ran this for a year or so and the fuel was out of set if has carbon in the ignighter. also cleaning the combustion chamber helps, They call for service every year in the manual If I recall.
I am skeptical if bufferin will help on the heat side though I understand the idea of fuel savings.  ... . ..  maybe... ;)
The Baxi/LAARS Mascot on propane from what I have seen on some units is just plane hard to iron out the pop. Not sure why, we have a similar situation with a unit installed locally by one of our regular contractors could never settle out the occasional pop.
I wholly agree with Morgan, merge to one zone, a 1,300 sq ft place is not that big to need micro zones. But it is not my choice.
I am curious how your test will go. Doesn't have to be heating season to try, just a cool night.
Dan

Dan,
I think the "pop" issue is independent of the Heating efficiency question, although it may have been the short cycling/poor CO2 calibration that exacerbated the "pop" problem.  The "pop" occurs less often, maybe 30-40% of the start up firing,  and occurs regardless of if the cycle is a heating cycle or DHW cycle.

The upstairs zones are separated so that we could actually turn off one room (Guest Bedroom) which will be rarely used.

The downstairs zones exist, uh, because I could..

These would be simple to join into one.   I think I'd still like to have the upstairs and downstairs as separate zones, however and I'd be willing to add a buffer tank to the system in order to have the multiple zones work effectively.

Tom
PS: Does this forum have a private message mechanism?  I'd like to ask you another question about the HT 330 that perplexes me...

There is a private function,
Click on the member link, I think that's how it works,
Or you e mail direct [email protected] I'll be there Tuesday, barring me winning the lotto...
Dan

If using a standard water heater for a buffer, cap the cold in and change the drain to a tee and put the cold in there. The element ports can be made into ports for the loops (or the boiler, if desired)

Posted By MikeSolar on 02 Sep 2012 10:20 PM
If using a standard water heater for a buffer, cap the cold in and change the drain to a tee and put the cold in there. The element ports can be made into ports for the loops (or the boiler, if desired)

Thanks for the tip, Mike.  By 'put the cold..." you mean the return side of the Hydraulic Separator?  With the 'hot' of the water tank/buffer connected to the boiler return?

Tom

He means the cold water inlet port to the hot water tank (which, yes, is what you would plumb to the return side of the hydraulic separator.) But I think he's also talking about making the TANK the hydraulic separator with a Tee at the top ( the hot-output) and a Tee at the bottom (the drain port.)

The cold feed to most water tanks is (for the plumber's convenience) located at the top of the tank not far from the hot-out port. To keep it the cold/hot from mixing or short-circuiting at the top of the tank, the cold water is directed to the bottom by an internal dip tube, which given enough time will corrode & fall off (much more quickly when used as a hot water heater than as a buffer tank, since fresh water is 100x more corrosive than "dead" heating system water.) By capping off the normal cold port to the tank and using drain port at the bottom instead, it takes the dip-tube out of the equation.

Whether plumbed in series with the boiler-return or Teed as a hydraulic separator, if it's easy enough to plumb it in that way it's a good approach.

Thanks Dana!

Yea, Dana speaks for me when I am mute....LOL

But the elements can be removed to gain two more ports as well.

A couple of last questions re using a water heater as a buffer.  

The Temperature/Pressure relief valve, that is typically mounted on the HWH, is not needed in this case (since there is one on the boiler), is it?

Also, is there a plug that will fit the heater element fittings so I can remove these and not worry about them corroding or leaking?

Tom

The T/P valve can stay where it is IF there is another properly sized one on the boiler, which there has to be or it won't get passed. The one on the tank is typically set at 150psi so it should never trip.

I wouldn't worry about the elements corroding and leaking. One reason they do corrode is that new oxygenated water is constantly being introduced and the tanks normal operation promotes galvanic corrosion. This is almost nil or at least far less when it is used as an un powered buffer tank.

I also don't think you need anything bigger than 60 gal, perhaps even 40gal but it depends on how you remove the heat from the tank, which zones are open or closed.

Personally, I try to stay away from a large number of zones unless the zoned areas are vastly different in their heating needs......such as a basement vs a sunroom.

Lastly, you will now have much more boiler water in the system so the exp tank will have to be upsized. I don't know the volume of the system but at minimum a #60 tank should be used, maybe a #90. Rule of thumb is that you can seldom oversize an expansion tank but it is easy to undersize one.

Sizing buffer and expansion tanks is a matter of established science and thus eliminates the need for any "rule of thumb". There are a few rules, such as volume, fill temperature, operating temperature and heat transfer fluid.

A 60 gallon buffer would be overkill, even with his current radiation & zoning (the very rough napkin-math on 40 gallons on his 10' baseboard zone appears in a prior post).

I was looking at 40 gallons as the probable lowest-cost/least work solution: Smaller electric water heaters are as expensive as 40 gallon versions (and sometimes more), so there's no need to fine tune it unless it simply won't fit in the allotted space. Without substantially more radiation or making it a single zone it'll need at least 20 gallons, but at 40 gallons it's already in no-brainer land no matter how it's zoned.

From these very useful discussions, I've concluded that a 40 Gallon tank would be the right choice IF I can get it into the crawlspace.

With the removal of all services in the crawlspace I was able to convert the full door and stairs down into a half bath and a small access closet. Since Hot Water Heaters generally don't bend, I'm going to have to revisit my model to make sure a 40 gallon will fit into the opening.

Surprisingly, I think a 48 inch tall HWH may fit better than a low boy because of the smaller diameter. If I find that a 40 doesn't fit, I'll have to try progressively smaller tanks until I can get one to fit. IF, as a possible consideration, only a 20 will fit, would TWO 20's in series (or parallel for that matter since it's all about thermal mass) work?

Tom

Posted By BadgerBoilerMN on 06 Sep 2012 07:18 AM
Sizing buffer and expansion tanks is a matter of established science and thus eliminates the need for any "rule of thumb". There are a few rules, such as volume, fill temperature, operating temperature and heat transfer fluid.

Badger, we are discussing the possible remedies for the Ops boiler issues. It is Ok to use a rule of thumb to give a general idea of what he should expect and that is all I have done. If he wants to pay an engineer to run through the numbers, it is up to him, but he may not.  If you want to do it for him, feel free. If he wants, I would be happy to provide the proper formulas, no skin off my nose.

I would never do a rule of thumb heat loss, nor do I size boilers or radiation this way but it is not unreasonable to give an opinion on the general direction he should take or the issues he will encounter. Stating that it is more dangerous to undersize a exp tank than to oversize it, and to give an example, should not be a problem. 

Posted By TomWS on 06 Sep 2012 01:16 PM
From these very useful discussions, I've concluded that a 40 Gallon tank would be the right choice IF I can get it into the crawlspace.

With the removal of all services in the crawlspace I was able to convert the full door and stairs down into a half bath and a small access closet. Since Hot Water Heaters generally don't bend, I'm going to have to revisit my model to make sure a 40 gallon will fit into the opening.

Surprisingly, I think a 48 inch tall HWH may fit better than a low boy because of the smaller diameter. If I find that a 40 doesn't fit, I'll have to try progressively smaller tanks until I can get one to fit. IF, as a possible consideration, only a 20 will fit, would TWO 20's in series (or parallel for that matter since it's all about thermal mass) work?

Tom

I'd add radiation  & combine zones before putting two 20 gallon tanks in series, but in practice 20 gallons may be enough even if you keep the same radiation & zoning- it kinda depends on the hysteresis around the output temp setpoint in the boiler's internal controls. 

With 20 gallons even on the zone with  10' stick o' fin-tube you're now looking at about 180lbs of water, and with ~30KBTU/hr (500BTU per minute) of excess output it's only ramping up at (500/180=) ~2.8F per minute.  I'd be shocked if you couldn't get at least something on the order of  1.5 minutes of burn time minimum out of it, even when serving just the single zone, with flows/delta-Ts properly tweaked so that it's running at min-modulation for most of the burn.

Do take the time least learn the napkin-math, eh?

Water at standard temperature & pressure has 8.34lbs/gallon (
It takes 1btu to raise 1lb of water 1F

3/4" plumbing has about 0.8lbs of water per foot 1/2" plumbing has about 0.4lbs of water per foot (< crudest possible generic numbers for easy math)

The volume of water in the boiler is usually specified (I didn't look it up, but YOU should.)

From there it's 6th grade math to convert BTUs/hour in to BTUs per minute, gallons per minute into pounds per hour, etc to calculate how fast the temp rises, and get a first-order estimate how long a minimum burn time at the boiler's minimum output might be at a given temperature hysteresis on that thermal mass.  I can't imagine any boiler would have as little hysteresis as 3F, but it might- most of the time it's not in the spec.  Figure on ~5F, give or take, but set it up and make some observations.

On a cold zone just calling for heat the initial burn will be a bit longer since there's a bigger delta-T on the water-mass, but after that it'll just cycle until the call for heat is satisfied.  Turn all of the T-stats for other zones off, crank the T-stat for the smallest zone up, then time the boiler's burns, and the time intervals between burns to get sense of what the minimum burn time will be.  None of your zones have enough radiation or mass to make a huge impact on burn time at low output temp, but there will be some.  Even if you crank them all on at the same time (or run it as a single zone), even at 140F you still have ~10KBTU/hr of excess boiler output than the radiation will deliver, so if your min-burn on the tiny zone was 1.5 minutes with 20 gallons of buffer, as a single zone the min-burn will still be under 5 minutes- it never balances for continuous burn.  And you'd need a LOT more radiation to get it to balance at 120F AWT.

The goal is to get the number of burns down to under 5 per hour under any conditions to minimize the wear & tear on the boiler.  Efficiency will increase if you can get the minimum burn time up, since every ignition cycle & flue purge throws away a fixed amount of heat. That wasted heat will be a significant fraction of the total burn on a 20 second burn, whereas on a 3-minute burn that loss-fraction is a bit more than 1/10th of that.  If with the lower mass you're looking at 6,8, even 10 burns/hour, it isn't the same disaster in terms of boiler wear that 30+ burns/hour would be.  But burn times of under a minute are an efficiency-disaster worth mitigating at current propane prices.

EXCELLENT reply, Dana!  Thank you very much!  This has helped me immensely!  Too bad this forum doesn't support 'likes'!

I've tried to 'install' a medium height 40 gallon tank in my 3D model and it is not clear it will fit.  A 40 gallon low boy or 30 gallon medium will.  I'll look at the information you've provided and decide if 30 Gallon is enough.

Thanks again,
Tom

it's pretty unlikely you'd need a 40 gallon buffer on even a midsize modcon. you only need to store about 5,000 BTUs per burn to get a 10 minute runtime out of a 30kBTU/hr min output, and that's with zero load factor. that's 600 gallon-degrees (5k/8.4 lbs per gallon). Divide by hysteresis and you have a buffer size. Hysteresis should be AT LEAST 20 degrees if you are trying to minimize cycling and I'd push to 30 if possible, but it depends on the max water temp you need and the max operating temp of the boiler. with wider settings you need to be careful you don't overlap room temp at the bottom end of your reset curve though or you'll have to wait for the house to get cold to fire the boiler again. ask me how I know this.... this is fixed by raising the start temperature of your reset curve.

and that is a 10 minute runtime, which is arbitrary and considered "ideal" by siggy. boiler MFGs who are paying attention to water content on mod/cons are still using much less and as Dana shows above it's probably overkill by a fairly wide margin.

When manufacturing the first condensing boiler, without the benefit of modulation, we considered burn over 5 minutes more than adequate. Buffer tanks were a common after-no-heat-load band-aid. Really no excuse then and even less now, but people will not change.

Posted By NRT.Rob on 08 Sep 2012 10:16 AM
it's pretty unlikely you'd need a 40 gallon buffer on even a midsize modcon. you only need to store about 5,000 BTUs per burn to get a 10 minute runtime out of a 30kBTU/hr min output, and that's with zero load factor. that's 600 gallon-degrees (5k/8.4 lbs per gallon). Divide by hysteresis and you have a buffer size. Hysteresis should be AT LEAST 20 degrees if you are trying to minimize cycling and I'd push to 30 if possible, but it depends on the max water temp you need and the max operating temp of the boiler. with wider settings you need to be careful you don't overlap room temp at the bottom end of your reset curve though or you'll have to wait for the house to get cold to fire the boiler again. ask me how I know this.... this is fixed by raising the start temperature of your reset curve.

and that is a 10 minute runtime, which is arbitrary and considered "ideal" by siggy. boiler MFGs who are paying attention to water content on mod/cons are still using much less and as Dana shows above it's probably overkill by a fairly wide margin.

Here is what I've measured/calculated:

The smallest zone is the Guest bedroom zone with 12 ft of baseboard and approximately 60 feet of 3/4" PEX (7.8 Gallon, including boiler's 0.95 Gal).

The boiler has minimum output spec'd at 32804BTU/hr.  Gallon Degrees = 655.5.

Running the system on this smallest zone, with outdoor temp at 66 degrees, the burn time was only 36-37 seconds with a temperature hysteresis of 16 degrees F (on at 33C, off at 42 C), setting the set point higher only shifted the on/off temps, the hysteresis was about the same.  Off time shifted, however, but that is sort of meaningless with these warm outside temps.

Dan, I didn't see any parameter that would change the hysteresis directly.  There was a parameter to shift the curve and the control on the front of the unit also does this.

Gallons required for a 10 minute burn: 41
Less Gallons in smallest loop: 33.2

Seems like a 30 gallon buffer would be 'ideal'.
A 20 Gallon buffer would be about a 6.8 minute burn.

Whatcha think?

Tom

Posted By Dana1 on 07 Sep 2012 12:08 PM <...snip>

3/4" plumbing has about 0.8lbs of water per foot 1/2" plumbing has about 0.4lbs of water per foot (< crudest possible generic numbers for easy math)

I'm struggling with 0.8 lbs/ft for 3/4" plumbing.  According to what I've seen, 3/4" plumbing would have about 2.8 Gallons per 100 ft.  This means 0.028 gallon per foot and, at 8.34 lbs/gal, that puts a 3/4" pipe at about 0.233 lbs per foot, not 0.8...

What am I missing?

Tom

Posted By TomWS on 09 Sep 2012 09:17 PM

Posted By Dana1 on 07 Sep 2012 12:08 PM <...snip>

3/4" plumbing has about 0.8lbs of water per foot 1/2" plumbing has about 0.4lbs of water per foot (< crudest possible generic numbers for easy math)

I'm struggling with 0.8 lbs/ft for 3/4" plumbing.  According to what I've seen, 3/4" plumbing would have about 2.8 Gallons per 100 ft.  This means 0.028 gallon per foot and, at 8.34 lbs/gal, that puts a 3/4" pipe at about 0.233 lbs per foot, not 0.8...

What am I missing?

Tom

Its effect may be minimal depending on how many feet of pipe there is. The tank and boiler piping may grossly over shadow the lack of volume in  the piping but you need to measure it first and know if it is type L or M copper (although the difference is minimal, 0.0251 vs 0.0268 gal/ft).

...and PEX has it's volume/ft that varies with temperature, etc, and they all have at least SOME thermal mass.

I did the fuzzy "in your head" math using "a bit shy of one water-gallon equivalent mass for every 50' " for generic 3/4 plumbing half that for half-inch and STILL got it wrong (by not doing the math correctly in my head- SHOOT ME! or buy me a cup o' coffee... :-) )

It's a rare system where even that gross error in the pipe-borne thermal mass makes a difference- in your system that error would be in the statistical noise of exactly how much water there ACTUALLY is in a nominal 40 gallon tank.

I didn't read the manual closely enough to see if the internal hysteresis around the outdoor reset setpoint is programmable in that boiler, but if it is you can get a lot out of even small buffers, as Rob described. A 16F hysteresis is on the high side compared to a few other non-adjustable boilers I've seen. My napkin-analysis was based on a hysteresis of 5F, which is lower than any boiler I've seen (but not a huge amount lower- I've seen 7F), a number chosen to demonstrated that it's a no-brainer bet. If you're measuring 16F of hysteresis, 20 gallons also enters no-brainer land- it's enough.

There's no magic in 10 minute minimum burns vs. 5, but if you're looking at a dozen burns/hour & counting it's boiler-abuse.

Burns under 1 minute in duration are just plain KILLING efficiency- as much as 10% of the source-fuel BTUs could be wasted on flue purges & ignition cycles on those 35-40 second burns, which gets reduced to a 1% source-fuel waste for a 350-400 second burn. A 10 minute minimum burn isn't dramatically more efficient than a 5 minute minimum burn.

Put another way, assuming the average return water temps would deliver 95% combustion efficiency steady-state, with the short-cycling boiler you're looking at about 85% as-used efficiency on the bursty 35 second burns, but with 20 gallons of buffer lengthening the burns by an order of magnitude you're getting ~94% as-used efficiency. Bumping it up to 40 gallons would buy you another 0.5%- there are diminishing returns.

Thanks Dana! No problem on the 'misstatement', I just needed to confirm so I can tweak my numbers accordingly. And, if you are in my neck of the woods, I would be most happy to buy you a coffee or your favorite beverage ;-)

We had a cool morning this morning so I tried the system with all zones open and got a 3 minute 17 second burn once it was cycling. In my earlier calculations I had come up with something in the order of 11 gallons for the total system which is why I had to re-look at the volume I had calculated for the smallest zone - 7+ gallons just for that zone didn't make any sense. I'm glad we got that resolved. Unfortunately I left my original calculations in my workshop office back home, I'll check them once I return. Sigh.

Looks like I've got a 'project' to work on in the spring!

Thanks to all!

Tom

Welcome to hydronics 101- you now know more than the consultant who told you to run the baseboard at 180F (at least he had the primary-secondary part going in the right direction, if little else) and probably more than you ever wanted to know about heating systems. :-)

Keep the napkin-math handy- put it in a spreadsheet, even print it out, tuck it in to a dust-protected envelope on your zone-manifold board along with the boiler documentation, etc, in case you (or the next guy) decides to hack away at it in the future.

And don't forget to tweak the reset curve once you get a real heat load. You really DON'T want to run it at 150F+ all winter unless buck-a-gallon propane has made a comeback.

I've finally gotten around to adding the buffer tank to this system.  We've had the system shut down and winterized since Sept and were only able to return to Maine to install the Buffer Tank the last week of April.  Results are 'mixed'...

I've attached photos of the installation, but, basically, I've disconnected the boiler supply and return from the radiator loop manifolds, created a primary loop with the boiler feeding a 28 gallon hot water heater (used as a storage tank) and returning directly to the boiler.  I've installed a closely spaced tee manifold to connect the radiators as a secondary loop into the primary loop supply line feeding the bottom drain port on the tank.  The top 'Hot' port of the tank was then connected back to the boiler return, included in that line is a tee to an additional 2.1 gal expansion tank (the boiler has a 2.2Gal built-in, but calculations showed that I needed a bit more with this additional water in the system).

The secondary loop has its own circulator (Taco Bumblebee HEC-2 running in deltaT mode).  This circulator pumps into the secondary supply manifold that feeds the heating zones through zone valves.  The returns from the heating zones are gathered into a return manifold that feeds into the lower side of the hydronic separator.

The circulator deltaT sensors are placed on the shut off valve on the input side of the circulator and on the return manifold near the hydronic separator return port.

As I said, the results are mixed.  When first starting up, the boiler runs for a good long time to bring the tank up to temperature.  The time depends on outside temperature conditions due to the outdoor reset and the boiler modulation, but it's run between 16 to 25 minutes to get to a quiescent state.  Once in this state, however, the boiler still seems to burn for a very short amount of time. Again, exact time depends on outdoor conditions,  but it's almost always less than a minute. 

I measured the return from the tank into the boiler and it seems to stabilize at an almost constant temperature that is just above the boiler's low trip point.  The boiler has about 7-8 degrees C hysteresis, and seems independent of the outdoor temp (the trip points move with outdoor temp, but the difference between high and low remains the same).

The boiler, when it's burning, is definitely pumping hotter water into the supply side,  you can see it rise on the boiler's output temp gauge, I've measured it at the zone supply manifold, and the circulator adapts its speed as the temperature rises.  However, the boiler's output temperature seems to reach the high point very fast AND does not seem to be solely driven by the return temperature (which is always about 6-7 degrees C lower).

One thing I did discover, after tearing my hair out and replumbing the tank though practically every permutation (the tank has four ports which I tried to use for both primary and secondary ports), was that the boiler has an internal "automatic" bypass between the supply and return, just above the respective shutoff valves.   Thinking that too much heat was circulating in the bypass loop and that this might be adjustable, I looked for an adjustment control.  There is none.  The only thing that appears 'automatic' about the bypass is that it is ALWAYs bypassing, the only 'control' is that the diameter of the bypass tubing appears about 3/8" vs the 3/4" piping I'm using for the hydronic loops.  

Other than providing a safety in case the supply and return shut off valves are closed, does anyone know the purpose of this bypass loop?  And, is there any way I can limit it so that more of the return heat is used?

The main reason I'm getting any reasonable use from this setup is that I've modified the boiler burner 'off' time limit from 3 minutes to 6 minutes thereby limiting the number of cycles it goes through in an hour.  It sure would be nice, though, if the buffer tank actually served as a thermal mass for the boiler.  Now it's nothing more than a storage tank, proving heat to the secondary loop when the boiler is not able to burn...

Tom

If Tom was to plumb the tank set up differently.
Boiler teed into the pressure relief valve. Boiler return from the lower heat element boss.
Secondary supply from the "hot" outlet. Secondary return to the "cold" inlet.
Fire the boiler using the tanks internal aqua stat. This totally isolates the boiler from the system. Just heats the buffering tank. Should allow boiler to condense at all times. Should give about 29 - 30 gallons of water for the boiler even if there is no heat demand.
Would it work? Would it work better or worse than his present setup??

Your suggestion has merit IF I was willing to store heat when there is no call from the zone thermostats and ignore the outside reset modulation control (since the tank temp would be controlled by the tank's mechanical thermostat). That seems counter to the supposed efficiency that this boiler should produce with existing controls.

As I said in my last post, I've tried plumbing the tank in various ways using virtually all ports except the TPRV port. You'll notice that the upper side port is at the same level as the TPRV port - in various trials I've plumbed either the supply or the return to this side port with virtually no difference in behavior.

The problem isn't with the tank or the ports used, the problem is that the boiler, for some reason, is bleeding too much of its heat output through its internal bypass tube and shutting off the burner prior to the tank temperature rising above the low set point.

If ALL of the heat output from the boiler did, in fact, circulate through the tank, the system would have the expected thermal mass and 'should' operate efficiently.

Tom

I haven't read all you wrote, but you are sure that the boiler is getting enough flow to move the heat it is producing?

I'm not sure I understand your question. The boiler, Laars Mascot HT330, has an internal circulator pump (Grundfos UPS 15-62), which is capable of moving up to 12GPM. There is very little head in the primary loop so it should not be restricted in any way. I've also measured the temp coming from the supply side and it does increase significantly when the burner is on. Also, when the burner is off, with the primary circulator running, the tank's heated water does flow through the boiler and the boiler temperature reading matches the tank's temperature. So there is flow. It appears as if there is too much bypass flow causing too much heat to return to the boiler without circulating through the tank.

Tom

A wild guess - the bypass is there to allow the output of higher temperatures. But the valve that controls it is defective.

I may be missing something but why are you drawing the return to boiler off the top "hot"? Would it not make sense to draw the colder water from the bottom to be reheated?
Also it would seem that if there is a lot of bypass the must be some restriction in the 3/4 primary. The difference between 3/4 and 3/8 is pretty significant.
Also check to make sure that the tank does not have any internal baffles that might be messing with the flow. The element hole and the TPRV port will not have any.

This boiler is a Baxi in disguise. It should also be properly set up with a combustion analyzer as I have see some pretty weird operating Baxis when it hasn't been set up. There is an optimum flow rate through the HX and it may be that the pump can be slowed down a bit if need be. That boiler should be able to run on minimum fire on the outdoor sensor just to maintain the temp in the tank which, given the amount of baseboard you have, is needed. Without the tank, you will have a LOT of cycles /hour. Insulate the tank really well and the primary loop piping to reduce the losses.

I think there is a theoretical point to changing the in/out on the tank top to bottom but I don't think there is any going in going from the top port to the PRV port.

Mike,
thanks for the reply.  One thing I remembered last night is, when I installed the boiler, the distributor mistakenly sent me the pipe fitting set for the HT 1330, rather than the fitting set for the HT 330.  I had already plumbed the supply side when I realized the error and was able to use the valve by capping off the "cold water mains inlet". 

I wouldn't think that this would be a problem, but, at this point, I suspect anything and everything...  What do you think?

Here are the photos of the different fitting sets for reference:
HT330:  The supply valve is labeled 'K'.


HT 1330: The Supply valve is labeled 'L'.



Tom

Posted By FBBP on 04 May 2013 12:28 AM
...
Also check to make sure that the tank does not have any internal baffles that might be messing with the flow. The element hole and the TPRV port will not have any.

The tank is a pretty inexpensive electric hot water heater.  I doubt that there would be any internal baffles.  I have plumbed and re-plumbed the supply/return on both the primary and secondary loops in multiple ways, including swapping top to bottom, without any significant difference in behavior.  The current setup is the one recommended by the consensus of the guys commenting back in Sept.

The only thing that 'helped' get some benefit from the tank at all was increasing the delay between burns. 

There is no adjustment (that I can see) for the bypass.  But, maybe, as you suggest, there is some restriction in the supply valve (all the other plumbing has been double checked or actually replaced).  See my previous post on this question.

Tom

There isn't much difference between the two except for the DHW option. I guess you will need to go back and get the extras. The threads are BSP parallel thread so our fittings don't work on them except for the gas. You may get something to screw on but it is not a good fit. IIRC, the internal pump is a 3 speed and the manual MAY tell you that you can turn it down IF the gas valve has been reduced on max heating output to the approximate heat load of the house. You will have to check on this though, as i have stopped using Baxi boilers a few years ago and there may be a few changes.

A pair of vise grips would reduce that 3/8 bypass flow down to about zero.

Posted By jonr on 04 May 2013 09:26 PM
A pair of vise grips would reduce that 3/8 bypass flow down to about zero.

Yes, you can believe that I HAVE considered exactly this 'solution'.  A small C clamp would give me 'one time' adjustability...

Seriously, since I have control over the use and service of the boiler I don't see any risk of doing that as a last resort (other than possibly splitting the tubing - that wouldn't be good - it would be difficult to replace/repair). 

I think I will remove the supply  side valve and thoroughly check the flow through the valve and port.  If I don't find an obstruction and there aren't any other recommendations, I'll probably squeeze down the bypass tube.

Tom

Posted By MikeSolar on 04 May 2013 07:59 PM
There isn't much difference between the two except for the DHW option. I guess you will need to go back and get the extras. The threads are BSP parallel thread so our fittings don't work on them except for the gas. You may get something to screw on but it is not a good fit. IIRC, the internal pump is a 3 speed and the manual MAY tell you that you can turn it down IF the gas valve has been reduced on max heating output to the approximate heat load of the house. You will have to check on this though, as i have stopped using Baxi boilers a few years ago and there may be a few changes.

When I installed the boiler, the distributor did finally send the correct fitting set for the HT330 so no problem on the fittings other than I kept the 1330 Supply Valve since it was already plumbed in.  I do have the HT330 valve 'somewhere' but I think I may need to re-fit the copper to use that instead of the HT1330 valve.

Regarding changing the circulator speed, I think you may be right, I think I can change that parameter.  Are you thinking that the current speed may be too high and the bypass is bleeding because of that?  This implies that there is a pressure differential valve in the bypass loop.  Do you think there is one?  I thought it was just a passive tube.

Tom

Odd that I don't recall ever having the problem of a bypass that I cannot adjust, unless there is a part missing. There is an optimal flowrate that the boiler likes with just enough turbulence without too much pump head loss. I have to find my old manuals to be sure about the values but I really think finding someone with a combustion analyser is useful as they were not designed to run without the set up.

Posted By MikeSolar on 06 May 2013 07:05 AM
Odd that I don't recall ever having the problem of a bypass that I cannot adjust, unless there is a part missing. There is an optimal flowrate that the boiler likes with just enough turbulence without too much pump head loss. I have to find my old manuals to be sure about the values but I really think finding someone with a combustion analyser is useful as they were not designed to run without the set up.

Mike,
thanks for looking into this, I appreciate it.

I did have a heating contractor analyze the combustion back in Sept (he's the one who recommended removing the outdoor reset
I'll have it rechecked now that I can get the boiler to burn longer.

Tom