Design updates for ModCon Boiler in 100 year old high mass gravity system

PC7060

I have a 1928 house with original expansion tank and piping in a series-parallel configuration (2" primary and 1" and 3/4" radiator feeds). The system was last updated 30-40 years ago when a 145K BTU New Yorker gas boiler replaced an oil fuel boiler and a circulatory pump was added on the return side of the boiler. The boiler is plumbed with a direct In/Out configuration without a by-pass loop causing the boiler to routinely crash during calls for heat.

I mitigated the crashing by adding a Micro Controller (MC) in line with the thermostat low voltage heating call wiring; the MC cycles the pump off and / on based incoming water temperature to ensure the boiler temperature never goes below 140 degrees F.

The heating requirement for the house is 75K BTU based on a heat loss / load analysis of the house performed as part of the to the current renovations. The house has large radiators and heats very well at radiators temperatures of 100-120 degrees on coldest days. All radiators have been updated with Honeywell Brauman TRV.

Requirement: Remove and replace boiler, circulator pump and expansion tank.
ModCon Boiler with outdoor reset and target baseline water temperature of 120F (currently 160F).
Low flow circulator pump configured in a pumping away configuration with expansion tank. Prefer to use a Taco’s ECM high-efficiency 0015e3 or similar.

Optional: Secondary loop for DHW.

Question: looking for recommendation on boilers and equipment configuration.

Concerns: Given the age of the system the new boiler must be able to handle/mitigate "dirty" water.


Thanks in advance.

EdTheHeaterMan

Primary secondary piping is the best design. It is usually included in the boiler installation manual. Some have accessory mixing manifolds with provisions for piping the DHW indirect tank. Also, use a dirt separator with a magnet just before the boiler inlet
Use the outdoor sensor and set the operating temp at 140° for the design temperature. let the outdoor reset feature built into the boiler (or the ODR Accessory) control to select the water temperature for heating and DHW. It's in there, It's all in there.

As far as the TRVs... you may want to add a bypass with a Differential Pressure Regulator valve around the "System Circulator" so the circulator can operate if all the TRCs are closed but the boiler is signaling the System Circulator to operate. https://bellgossett.com/hydronic-plumbing-accessories/flow-control-valves/db-34-differential-bypass-valve/

it is all explained on page 20 of this Text:
http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf

We are not supposed to make recommendations of brand names however I can say that I have had good experiences with Bosch and Buderus. Also Crown boiler, now Velocity Boiler Works of Philadelphia

Good Luck with your project.

hot_rod

A hydraulic separator like a Sep 4 would be a good option. In addition to the critical hydraulic separation for the boiler and distribution, you get excellent air and particle removal in addition to magnetic separation to protect ECM circulators.

The separator allows you to accurately size the circulators for the boiler and distribution. With TRVs a delta P circ would be nice for distribution.

Additional info and piping options here.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_15_na.pdf

PC7060

@EdTheHeaterMan - Thanks for the information on zoning and the primary secondary; I've been going over the information and its a good read.

Regarding the bypass for the circulator, the the TRV on the two rads closest to the TStat have the control heads removed and are in full open to keep rads synced to thermostat and provide a minimum system flow for the ridiculously over sized circulator pump.

As I said previous post, I am going to use a much lower flow rate in the new system using one of the smart ECM.

@hot_rod - the Caleffi link you provided is very good, thanks! The Caleffi folks have very good technical data and the training video very well made. I will be designing the SEP 4 into the new system with either 1" or 1-1/4" configuration.


Question: The boiler manufacturers recommend doing a systems cleaning using Sentinel X400 System Restorer or similar. Is this process hard on the piping?

The existing systems has been drained three times over the past couple years as part of the renovations to the house which included sandblasting and powder coating the radiators.

I piped a 1 quart pot mixer into the loop but the only additive I've included is a quart of Hercules Boiler Liquid to mitigate a issue with a very small section leak in one of the large radiators.

I'll be using the pot mixer to add Corrosion Inhibitor to the system once the updates are complete.

That's enough for now; thanks again for the great information.

hot_rod

Most of the hydronic system cleaners are a strong soap or detergent. They should be safe for all the components in your system.

For a limescale problem an acid based cleaner is sometimes used, like Hercules Sizzle and others.
Limescale is more common in boilers that have had a continuous leak and constant fill water added.

PC7060

@hot_rod - Figure 8-1 in the Caleffi idronics_15_na document looks like a good layout for the new boiler piping. Two questions:

1. The bladder tank is on the return side of the SEP4 secondary loop with the secondary circulator on the supply side.

a. Does this meet Mr. Holohan's recommendation that the circulator should "pump away" from the expansion tank since the SEP flow will enable flow through the secondary return to the secundary supply?
b. Or could the expansion simply be moved to a position between the SEP 4 and the circulator?

2. Figure 8-2 illustrated the use of a buffer tank to prevent boiler short cycling "because of the extensive zoning" created by the TRV. Is this typically an issue with radiator configured with TRV?

PC7060

oh and thanks for the information on the cleaning agent.

hot_rod

Yes the expansion tank could connect at any of the 4 ports and the sep becomes the PONPC. Either bottom port would be lower temperature and maybe easier to pipe the tank.

PC7060

I attached a design using the SEP4 with either a Rinnai I090SN or M090SN.

I'm leaning toward the I090SN because of the 6:1 turn down ration for the 90K BTU unit.

Question: The M090SN includes a Internal modulating Pump, would this have to added for the I090SN?

As you can see from the image the design includes a system circular along with a Priority circulator for the DHW.

Question: Both the I090SN and M090SN include Outdoor reset controller;does this would require a mixing valve in the secondary loop?

@hot_rod - Just watched the your Caleffi session on buffer tanks, good subject and the huge LP conversion buffer tank is really cool.

Thanks in advance.

hot_rod

As long as the indirect circulator is sized for the boiler requirement also. The boiler will either include the circ, or guide you to the choices for the correct, user supplied on.

The ODR function is on most boilers, no need to add another mixer if that is the case. Place the supply sensor downstream of the sep a bit.

Boiler would kick up to high temperature when the indirect calls, again, on most boiler controls, check to see if the models you are considering have ODR and DHW priority.

PC7060

Is it feasible to use DHW type tank to completely isolate the heating loop from the boiler? I'm concerned additives such as Hercules boiler fluid will adversely affect the performance and life of the MODCON boiler. However, replacing the SEP 4 with a isolation tank increases the system cost and complexity with extra tank, fill line and expansion tank plus a ODR mixer in the heating loop.

I've seem employed in industrial applications and I'm curious if this approach is is feasible for home systems .

mattmia2

A fire tube boiler might handle the debris from the old system a bit better than a water tube boiler.

The HTP phoenix is like a boiler and buffer tank all on one, might be a good option if you are breaking the system up in to a lot of very small zones such that their demand on average days is less than the lowest fire of the boiler. Many boilers have a 10:1 turndown ratio, that is an option for matching load.

The indirect will work as a HX and buffer tank although you will likely have to run the boiler a little hotter than you otherwise would and lose a little efficiency on the boiler to make heat move across the heat exchanger, although the tradeoff is you might be able to run a lot less cycles of the boiler and satisfy a lot of demands from just the heat stored in the tank and gain efficiency there.

You might look for an inexpensive boiler that has a 0-10v control and use your own separate controls or even a programmable controller since you sound like you want to micromanage this thing. You pay a lot for the built in software in the boiler the more sophisticated it gets. You might want to just do it with separate controls. Viessman products have a lot of options for tailoring the behavior built in.

Also take in to account that your biggest load by far might be DHW.

hot_rod

Your high mass, high volume radiators should buffer well with out needing a tank. I think a wide modulating fire tube boiler with a good 4 in 1 sep would offer the best protection for air, dirt, etc, and cover the zoned rads just fine.

A buffer would help some to collect debris, ideally you want to collect it in a sep and flush occasionally.

On your first drawing, maybe add an additional DirtMag on the indirect as it doesn't flow thru the sep.

mattmia2

That also means you want to get the supply water temp and reset curve dialed in so you don't end up filling all that mass with hot water that continues to overshoot for a significant time period after the t-stat is satisfied/the trv has closed.

PC7060

Thanks for the response!

@mattmia2 @hot_rod - can you point me to a couple of the fire tube type boilers in the 80-110K range?

I looked at the Navien NFB but at 177K is way bigger than I need even with the 10:1 turndown.

mattmia2

HTP. Lochinvar. Weil Mcclain. Noritz might have one, i know they have a combi that is similar to an HTP UFT but their web site was hard to find heat only boilers on.

hot_rod

So many, almost too many, choices. My experience is mainly Lochinvar, HTP, Triangle Tube & Viessmann. NTI and IBC are a few others that are getting a lot of attention and have a good support team behind them.
Looks like some 11-1 turndowns out there now.

PC7060

Thanks for the information.

Looking at HTP UFT and the Lochinvar Knight. The Knight seems to a step up in price from the HTP; would love to know what are the discriminators between the two systems.

Not looking for recommendation, just technical details.

hot_rod

Usually the control functions is the price difference. I think the Knight also has a larger fire tube compared to the HTP. The HTP and the Lochinvar Nobel may share the same HX, but the Nobel is combi only.

Here is an example of the nice control features on the Knight. The ramp delay, gradiant, & boost, are all really nice features once you know how to use them. You can also adjust the boiler output on an indirect call, if the indirect cannot handle the full output.
I think the Knight comes with a variable speed ECM circulator also.

PC7060

@hot_rod - "The HTP and the Lochinvar Nobel may share the same HX"

Interesting, similar to the compressors for Heat pumps and AC units. Who manufacturers the HX?

Does the Knight use a 3rd party HX?

hot_rod

Kiturami is a Korean made fire tube boiler HX that appears in a lot of boilers these days. They may have different versions? The Knight looks like a taller fire tube design?

I like the water tube style personally.
NTI, Utica, Viessmann and others have a larger diameter water tube style. That eliminates the high pressure drop concern with the Sermeta style that has been predominate for the last 20 years in dozens of brands of boilers.
I think burner removal is a bit easier on water tube style, everything loads from the front.
Read the warranty closely, they really need to be opened and serviced regularly. Some manufacturers want that documented to assure warranty coverage, now.

The water tube has less welds to fail, better flame spread. Fire tubes tend to have a lot of heat concentration up top and may have issues with tube sheet failures, gasket leaks. I think TT was one of the first fire tube and they have gone through a few revisions and HX suppliers.
I visit a lot of wholesalers and make a point to spy in the returns section and boneyard. I ask the counter staff what models get returned most often. Gives you a good idea of which tanks and boilers do or don't

psb75

There is in fact a version of Lochinvar Noble that is not a combi.

hot_rod

psb75 said:

There is in fact a version of Lochinvar Noble that is not a combi.

I thought there was too? It doesn’t show up at the Lochinvar website?

PC7060

Interesting, so looking at the NTI based on your comment @hot_rod. Love their marketing guys; “HTI TRX is a high-efficiency, wall-hung boiler equipped with an Innovative XTRATECH® stainless steel heat exchanger.”  Xtratech?  Seem like they ran out of ideas naming that one!

So these HX have larger tubes, what’s the relative pressure drop?  How do they compare to a Fire tube variant? 

PC7060

@hot_rod - “Read the warranty closely, they really need to be opened and serviced regularly”

I thought this was the case for all ModCon type boilers.

Are you referring to Fire tube periodic maintenance versus Water tube?

Or new larger water tube variant such as NTI, Utica mentioned above versus the Sermeta style?

hot_rod

PC7060 said:

@hot_rod - “Read the warranty closely, they really need to be opened and serviced regularly”

I thought this was the case for all ModCon type boilers.

Are you referring to Fire tube periodic maintenance versus Water tube?

Or new larger water tube variant such as NTI, Utica mentioned above versus the Sermeta style?

Im think NTI is building their own large diameter coils in this model. I suspect Viessmann does also?

PC7060

Nice!  Significantly larger tubing; continuous run is good too. 

PC7060

@hot_rod - Sourcing NTI locally is presenting a challenge. Which of the Viessmann boiler were you thinking has the large water tube HX made in house?

 Thanks!

PC7060

Link to Noble standard non-combo boiler.

https://www.lochinvar.com/products/residential-boilers/noble-boiler

having a hard time figuring out the difference between the non-combo Noble and the Knight, any ideas?

hot_rod

The Knight has a larger fire tube HX, probably more control features.
I think the Nobel has a Kiturami HX. Some consider that to be the price point HX design.

Just looking at the physical size difference you see how them HX compare.

PC7060

I see what you mean about ease of maintenance of the water tube front accessible versus the top on these units. Is that a common characteristic of Fire tube type HX?

I watched a video from the UK which demonstrated routine maintenance and cleaning of the Viessmann Vitodens 200.  It was remarkably easy to disassemble. 

PC7060

@hot_rod - Regarding your recommendation to add a dirtmag before the indirect tank, I see those units also act as a small pot mixer for adding chemicals. I couldn’t locate any drawings which indicated the internal fluid volume. Would you know if the Caleffi library has that information? I’ve already got a home built 1 quart pot mixer in my system so just curious.

hot_rod

once you once the system is flushed and cleaned, filled with good water just squirt some inhibitor into the valve
chrch the conditioner with the test kit, boost every few years if needed

I’d use a combination dirt and magnetic sep, ball valve with hose connection for flushing and injecting

The cleaner and conditioners come in aerosol cans with the hose and connection, super simple to maintain hydronic systems. 

Caleffi dirtmag does a great job with debris and magnetite



Product

PC7060

Reading a thread “the Holohan Project”. 

@Paul Pollets did a beautiful job; love the Viessmann Vitodens 200 and the expansion tank brackets. 

What’s the pressure drop through the Viessmann Vitodens 200 HX? Does this unit have the larger cross section tubing? Impressed with the maintenance access to the system. 

PC7060

I've selected the HTP UFT08W for the boiler and updated the piping to use a single zone per Figure 8 of page 20 of the I&O manual.

The original Taco 0015e3 pump I specified is a constant pressure pump with L/M/H settings. Give the low head to the 2" pipe and many radiators, I'd like to use a ECM that can limits flow based on ODR with the minimum flow defined by the lower limit of the HX with max flow around 5GPM.

Any recommendation on pump? Would the 0-10v control out be the proper way to control pump speed?

hot_rod

It might be better to use a hydraulic separator if you plan on zoning all the radiators. The boiler need a minimum flow rate, you need to assure that.
A Sep 4 would handle all the necessary functions, hydraulic, air, dirt, and magnetic separation in one component.

A delta P circulator would adjust to the TRVs opening and closing, no additional controls needed.

mattmia2

The 0-10v on a UFT is an input, it can control supply water temp setpoint from an external control. There is a min flow for max output from the UFT, that is probably mainly a consideration for the DHW.

PC7060

Two large radiators close to tstat are locked wide open to ensure minimum flow rate. 

Looking at the flow rate for the Taco 0015e, the pump ranges to 12GPM at low setting while maintaining 5 Ft. head.  I’d like to keep the max flow rate at around 8GPM to minimize noise. Are there ECM pumps that have configurable max flow rate? 

Does the boiler control the primary pump speed based on the ODR. 

Based on the heat transfer eq., the system will require 5GPM max flow rate to deliver required BTU at design temperature with a delta T of 30 and 7.5gpm with delta T of 20.  I’m assuming the delta will be somewhere in that range. 

mattmia2

The UFT80 has no internal pump nor control for external pump beyond an on/off relay. The pump would have to have a controller built in or external controller that would modulate it on pressure, flow, or temperature if you wanted to modulate the pump speed.

Download the UFT installation manual and take a look through it.

PC7060

@mattmia2 - “Download the UFT installation manual and take a look through it.” 

  

hot_rod

You mentioned a 120 SWT are you sure running a 30∆ will give you enough output at the end of the road? You might need a homerun system to assure each radiator sees 120 SWT?

For the distribution side a delta P circulator adjusts it output based on valves opening and closing. The control logic is built into the circulator, no additional control required. Plug it into a 120-V circuit, select the appropriate setting and walk away.