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

in Gas Heating
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.
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.
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Comments
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.
Retired HVAC Contractor from So. Jersey Shore.
Cleaned & services first oil heating system at age 16
Specialized in Oil Heat and Hydronics where the competition did Gas Warm Air
If you make an expensive repair and the same problem happens, What will you check next?
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
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
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.
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
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?
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
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.
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
I've seem employed in industrial applications and I'm curious if this approach is is feasible for home systems .
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.
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
@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.
Looks like some 11-1 turndowns out there now.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
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.
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
Interesting, similar to the compressors for Heat pumps and AC units. Who manufacturers the HX?
Does the Knight use a 3rd party HX?
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
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
So these HX have larger tubes, what’s the relative pressure drop? How do they compare to a Fire tube variant?
I thought this was the case for all ModCon type boilers.
Are you referring to Fire tube periodic maintenance versus Water tube?
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
Thanks!
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?
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
I watched a video from the UK which demonstrated routine maintenance and cleaning of the Viessmann Vitodens 200. It was remarkably easy to disassemble.
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.
Product
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
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?
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
Does the boiler control the primary pump speed based on the ODR.
Download the UFT installation manual and take a look through it.
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.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me