Need some advice (opinion?) on a ModCon installation
Last Post 06 May 2013 10:17 AM by TomWS. 77 Replies.
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TomWSUser is Offline
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29 Aug 2012 10:44 AM
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



NRT.RobUser is Offline
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29 Aug 2012 10:57 AM
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.
Rockport Mechanical
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Blueridgecompany.comUser is Offline
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29 Aug 2012 11:20 AM
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

Dan
BlueRidgeCompany.com
TomWSUser is Offline
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29 Aug 2012 11:31 AM
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.
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29 Aug 2012 11:33 AM
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.
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Dana1User is Offline
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29 Aug 2012 11:56 AM
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 )?
TomWSUser is Offline
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29 Aug 2012 04:22 PM
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
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29 Aug 2012 06:05 PM
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.

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29 Aug 2012 06:37 PM
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.
MA
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29 Aug 2012 07:48 PM
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.
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30 Aug 2012 07:21 AM
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.
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30 Aug 2012 07:33 AM
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.
MA
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TomWSUser is Offline
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30 Aug 2012 07:46 AM
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
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30 Aug 2012 11:31 AM
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


Dan
BlueRidgeCompany.com
TomWSUser is Offline
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30 Aug 2012 11:49 AM
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.

Dana1User is Offline
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30 Aug 2012 12:10 PM
"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.
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30 Aug 2012 12:39 PM
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
BlueRidgeCompany.com
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30 Aug 2012 02:07 PM
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.
MA
www.badgerboilerservice.com
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30 Aug 2012 02:49 PM
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.
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30 Aug 2012 03:26 PM
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.

MA
www.badgerboilerservice.com
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