How to dial in/settings: Navien ncb240e, hot water coil, buffer tank, outdoor reset

[Rkupon1]

Hey guys, new member here, so a little background history first. Im an hvac guy since 01', i ve only recently started to get into advanced hydronics and boiler systems. Pretty much been a forced hot air tin knocker my whole career. Im really startn to dig the controls aspect and high effeciency stuff nowadays. So this past year, my wife and i took the plunge and decided to build our own custom home in nj, on the jersey shore. Its a nice 2400sqft 3bdrm, 2.5bath 2story with a basement. I decided i wanted to over complicate my life and stray from my comfort zone alil bit. I have a spray foamed house(open cell), entire house is completely sealed and within the thermal envelope, natural gas Navien ncb240 combi mod con boiler, 2 zones(1st floor/basement and 2nd floor) air handlers with hot water coils atop each. My ductwork is sealed tight and insulated, and completely hard piped thruout the house. We used Honeywell ERVs for each system(vnt5070) and are using the honeywell prestige iaq system(equipment interface module). So far everything is going great and house is comfortable. We only just moved in couple weeks ago. But i pretty much spent all winter watching the heating system run n operate. I ve been taking notes. Wasnt making any adjustments bcuz house was still being worked on n built. So to many variables still existed. Now, id like to start dialing in my system n could use some help fine tuning. So for the long winded post, but i know the more details, the better. I originaly had a well respected tradesmen help me design my system and control strategy. Unfortunately, i believe his health has declined and is hard to get a hold of. I truly hope he s ok. I ve known him a few years now.
Id like to really fine tune my boiler and get it to run those infamous long n slow burn cycles. I have general knowledge of basic info, settings, and perameters. On colder days, it ll run 10min cycles on/off, back n forth between both zones calling. Im using an 80gallon buffer tank to help with the hydraulic seperation and micro zoning.

 

[Rkupon1]

Some pics of my work and current system set up

 

[Sponsor]

 

[Rkupon1]

Some basic info,
Heat calc loss
1st flr-12,000 btu s
2nd flr-14,000 btu s
Attached 2car garage(future zone for fan coil not in use right now)-14,000 btu s
Detached finished garage-30-40,000 btu s.
The detached shop isnt built yet, but will be next year. Planning on a 30x40 with radiant in floor concrete slab heat. Hence me going with the 240 sized navien. As of now, i have the navien high fire rate limited as much as i could down to 50%, aka 60,000 btu s. The low fire rate is apprx 18,000 btu s. This is why i was talked into installing a Caleffi 80gal buffer tank 2pipe system, to mitigate the over sized boiler. If i had a do over, i wouldnt even have used a npe240 linkd to my navien ncb240. I would have went with properly sized mod con boiler and an indirect for better low fire control and modulation. Trying to work with what i have installed now. Design is 0* with 24mph winds. I have the house heating well sofar with 140* water on 0* and 100* water on 62*. Warm weather shutoff set at 63*

 

[Dana]

So the only heat emitters so far is a pair of hydro-air handlers? Got some model numbers?

What output temperature are you running on the heating side of the NCB?

To hit 30-40KBTU/hr a 1200' garage has to be barely insulated, with the leaky uninsulated doors.

Who ran the load numbers (on the house, and the garage)?

To get much longer burn times with air handlers as the heat emitter requires that the air handlers be right sized for the load. Running outdoor reset with air handlers isn't usually very comfortable- you may be able to heat the place just fine with an entering water temp of 100F most of the year resulting in great burn times, but with exit air at the registers in the 80sF wind chill is an issue. Outdoor reset works a lot better with real radiation (not fin-tube baseboard), where the water temp can be varied smoothly. An 85F radiator that's keeping up with the load isn't a comfort issue the way 85F air out of tepid-air duct is.

If the air handler coils are big enough to emit air above 100F at all registers with 125F out of the NCB it'll still hit mid-90s efficiency. As long as the air handler can emit more than 17,000 BTU/hr at the water temps you're running it should run very long burn times, but if way oversized for the heat load the thermostats may still be satisfied in 10 minutes or less.

 

[Rkupon1]

Yes, i shall do my best to relay answers to your questions as info.
We are using 2-Goodman avptc29 air handler(s), both are only running between 550-650cfms. Duct design is tite and sized accordingly, we have all 4"+5" stackhead supplies thruout. Lotsa returns. The idea was the less is more theory, but could still "lose" the air if more cfms needed.

The hot water coils are Aquecoil hhu-gs1. I ve attached a pic of thier performance charts

Output temp? If your refering to the combi, i have it turned down as far as it ll go at 50%=60,000btu s. Still to big for the house with future garage hot water fan coil. Next winter, thats coming. Almost out of money,lol. Thus far, i have the taco 1618 pumps turned way down on fixed speed and am achieving 20*+ deltas on supply n return water lines closest to the hot water coil.

I submitted my house plans to a close friend, Rich Mcgrath for the heatloss calcs. The future 30x40 shop will be a finished polebarn, r19 batt insulation, sheetrock, and 12'6" cielings.

Yes, what your saying makes sense. We were glad the hot water coils were still oversized even in smallest avail. option for this reason. For me, i thought keeping the air moving as long as possible with heat barely keepn up would make for great IAQ in this tite house. I ve yet to mess with the erv settings, but as of now, they are just set to POT(20%). Despite thier effeciency, id hoped they add some load to the house so to speak

 

[Rkupon1]

Fyi, i also incorporated a taco pc700-2 with a sensor well in the buffer tank half way up. Its tied in with a sr504EXP switching relay

 

[Rkupon1]

Heatloss

 

[Rkupon1]

Aquecoil

 

[Rkupon1]

Heres a quick snapshot 4pm,
38* outside, there was a call for heat, 6min burn cycle with 108*-110* water.
I believe my reset ratio design was 140* water on 0* day, than it was 100* water on a 62* day. WWSD is set for 63*. I believe thats my outdoor reset curve. Bare with me as this science/approach is very new to me. But im hooked, its fascinating!

 

[Dana]

Yes, i shall do my best to relay answers to your questions as info.
We are using 2-Goodman avptc29 air handler(s), both are only running between 550-650cfms. Duct design is tite and sized accordingly, we have all 4"+5" stackhead supplies thruout. Lotsa returns. The idea was the less is more theory, but could still "lose" the air if more cfms needed.

The hot water coils are Aquecoil hhu-gs1. I ve attached a pic of thier performance charts

Output temp? If your refering to the combi, i have it turned down as far as it ll go at 50%=60,000btu s. Still to big for the house with future garage hot water fan coil. Next winter, thats coming. Almost out of money,lol. Thus far, i have the taco 1618 pumps turned way down on fixed speed and am achieving 20*+ deltas on supply n return water lines closest to the hot water coil.

I submitted my house plans to a close friend, Rich Mcgrath for the heatloss calcs. The future 30x40 shop will be a finished polebarn, r19 batt insulation, sheetrock, and 12'6" cielings.

Yes, what your saying makes sense. We were glad the hot water coils were still oversized even in smallest avail. option for this reason. For me, i thought keeping the air moving as long as possible with heat barely keepn up would make for great IAQ in this tite house. I ve yet to mess with the erv settings, but as of now, they are just set to POT(20%). Despite thier effeciency, id hoped they add some load to the house so to speak

This combi boiler can be programmed to a fixed output temperature ( in degrees, not BTUs). Take a deep dive on chapter 10 beginning on page 54 of the manual, until you understand all of the settings and parameters and how to change them.

The HHU-GS1 has specified output at 140F & 180F across a range of air handler speeds and water gpm.

At an entering water temp (EWT) of 140F at 600 cfm and 4 gpm the return water temp is 126F, right on the very edge of condensing, and delivering 28,250 BTU/hr, which is twice your biggest zone's heat load. The exit air temp at the air handler under those conditions is 112F.

Dropping the flow to 2gpm will lower the return water temp a little, and would knock about 5% off the BTU output but it would still be 2x oversized.

Dropping the EWT to 130F would drop the air handler output to about 22-23,000 BTU/hr, and would still have exit air in the 100F range, still above human body temp, not too tepid for comfort and would deliver exiting water temperatures in the 118-120F range, which would be a boost to boiler efficiency if that's the EWT at the boiler.

With air handler coils that big there is no point to the buffer tank, since the NCB is capable of modulating down to about 17,000 BTU/hr out. If you dropped the fixed-output temperature on the boiler to 120F the NCB would be delivering about 18,000 BTU/hr, and efficiency & burn times would be great 95% or so, but the exit air temperature at the furthest registers might be too tepid for comfort. You can play around with it a bit, but somewhere between 120F and 130F there's a sweet spot balancing comfort/wind-chill against efficiency.

I'm surprised you didn't run the system design by Richard McGrath first (or did you?). A wet-heat like him probably would have steered you away from using hydro-air for heating, or may have spared you the cost of the superfluous buffer tank on the heating side of the combi boiler. (Next time you see him give him my regards! He knows who I am, though we've never met outside of cyber space.)

R19 batts are in the category "genuine imitation insulation" that leaks air like a tennis racquet and even when installed perfectly only performs at R18 in a 2x6 cavity. (It's only R19 when it's at 6.25" of loft, with air barriers on all six sides.) At the very least go for mid-density R20 fiberglass (which performs at R21), or better yet, R23 rock wool, which is completely fireproof. It won't move the needle on the load calculations very much but it's at least something worth owning.

Under a heated slab you'll want at least 3", preferably 4" of EPS. Reclaimed roofing EPS is available at at 1/3 or less the cost of virgin stock goods, and when applied over a drainage bed of 3/4' washed gravel with a 4" reinforce slab above it performs just fine. Don't sweat the compression ratings of the somewhat lower density foam- you can park your Caterpillar D9 on a 4" reinforced slab without compressing the foam or cracking the slab. There is a lot of reclaimed polyiso out there too, but that isn't suitable for sub-slab use since can slowly wick & retain moisture. It's great for walls though. A 2x4/R15 rock wool wall with 2" of continuous reclaimed roofing polyiso on the exterior outperforms any 2x6 wall by quite a bit (even one with 5.5" of closed cell foam in the cavities.)

 

[Dana]

Heres a quick snapshot 4pm,
38* outside, there was a call for heat, 6min burn cycle with 108*-110* water.
I believe my reset ratio design was 140* water on 0* day, than it was 100* water on a 62* day. WWSD is set for 63*. I believe thats my outdoor reset curve. Bare with me as this science/approach is very new to me. But im hooked, its fascinating!

What is the exit air temperature at the furthest register when running 100F water? Heating the house to a particular temperature isn't exactly the same as comfort. The additional efficiency benefits of 100F output water vs. 120F output are pretty small, but the difference in human skin wind-chill factors at the registers is large when the temps drop below 90F, and are even noticeable when temps drop below 100F.

The other efficiency aspect of very low temperature operation of the air handler is that the air handler power is the same whether it's getting 100F water or 180F water. Going for that last 1-2% of combustion efficiency may save you a few percent on gas, but the much longer duty cycle of the air handler starts to add up on electricity use, possibly more than erasing the operating costs gains of the slightly higher combustion efficiency. Electricity is a much bigger fraction of the operating costs with air-delivery heat vs. pumped hot water. With ECM drive smart pumps most of my radiator zones can run for a couple of months on the electricity my hydro-air zone uses on just one cold day, and that's at an EWT of 125F, not 100F.

 

[Rkupon1]

Ok, great. I have alot to digest here. Rich n I have known each other for years thru business. Unfortunately, by the time i reached out to him on this job, my custom built house, i was already very convinced what i was doing would be great. We are now trying to salvage comfort n effeciency at best with my current set up. I did not have the time or money to install radiant during my build. Honestly, theres days i wish i had shelfed all this and just went with Goodmans gmec96% 30k btu furnaces and the comfortnet system. Had it in my last house, worked great. This is what i get for thinkn on my own. Lol. Im alil late to the game getting into hydronic heat. But, hey, i took a shot n here we are. Thank you for all your help sofar, i will try n do alil more test n tune for now.

P.s. the buffer tank and pc700-2 was Riches idea. That came after i had my combi hangn on the wall n plumbed in with my hot water coil, etc

 

[Dana]

I hear you on the raw economics and reasonable comfort of a 30K condensing Goodman! Simple and cheap to install, very efficient use of gas.

Another ducted option that would make it in New Jersey on a house/load your size is a 2.5 ton modulating cold climate heat pump. Unlike a 2-stager these things modulate in baby steps with load, and can deliver better-than-advertised efficiency when right-sized to the load like this. The output air temperature increases with load, much like your hydro-air setup does. With a "set and forget" approach to the thermostats it modulates up/down with load delivering very stable air temperatures and very high efficiency.

If zoned floor by floor a pair of 3/4 ton mini-ducted Fujitsus would handle it, probably cheaper to install than a single 2 ton Mitsubishi with a big modulating air handler zoned with zone dampers, with a wider modulation range and even higher efficiency to boot. Old-school hot air guys get nervous about designing the lower static pressure mini-duct cassettes, but the Fujitsus are way better than the competition, and even though not advertized as a cold-climate heat pump, they use the same vapor-injection scroll compressor technology used in cold climate units. The 3/4 tonner is good for 14,000 BTU/hr @ -5F outdoors, 70F indoors (despite being nominally tested for efficiency at 12,000 BTU/hr output at +17F & +47F under the AHRI protocol). They make a 1 ton an 1.5 ton versions too- the 1 tonner is good for a bit more than 15K @ -5F, the 1.5 tonner a bit more than 18K @ -5F, per the capacity tables in the Design & Technical Manual. Since they can all modulate down to 3100 BTU/hr @ +47F there isn't a huge efficiency or comfort hit from oversizing them a bit to get more Polar Vortex disturbance event margin. Even at -20F they're delivering real (if unspecified) heat.

 

[Rich McGrath]

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

 

[Dana]

And?

When operating the zones within the modulation limits of the boiler there isn't a lot to be gained with buffer tanks. When individual zones can't emit the minimum fire output the buffer can cure a lot of ills.

 

[Rkupon1]

The buffer tank will work as the lowest down fire rate(18,000 btu s) defly is further away from whats typical btu s needed here in 20s and 30s. Not design btu s. My problem is finding that happy medium between boiler run/condensing and boiler off/stored thermal mass. I agree this system wasnt as well designed as id hoped. I brought Rich into the game alil late. Thats my fault, but as of now, it is comfy, it is effecient, and it is working. Maybe not as good as some, but defly better than others. Theres alot to be dialed in and balanced between ecm motors, blowers, and the Navien mod con. Theres another element here to consider, IAQ and my systems ability to run and use the ERV. I believe these benefits could out wiegh the savings of couple bucks on electric. If i could do it all over again, yes, itd be different. But for now, we ll maximize what we have and learn along the way.
Next custom house i build would most defly have a mod con boiler, ODR, priority indirect dhw, and a heluva turn down ratio for micro zoning. Im a good hvac guy, but i ve learned more about hydronic heat and mod cons in last 6mo ths than i have in 18yrs. Im really into it n would like to learn more and execute better installs for comfort and effeciency. The controls and integration is really cool these days. Im all about it

 

[Dana]

"Theres another element here to consider, IAQ and my systems ability to run and use the ERV."

Combining the ventilation function with the heating/cooling function is usually far less the optimal. You need about the same amount of ventilation air all the time, whether the heating or cooling load is high or low, or whether there is no load at all. The duct sizes needed for ventilation are a fraction of what's needed for heating or cooling, in all but PassiveHouse type houses.

 

[Rkupon1]

The ERV runs independant of heat/ac call. If the air handler is running during a heat or ac call, than great. But the erv and fan motor are both doing a great job sofar for IAQ. I ve lived in 3 houses sofar, im 36. One was built in 55' with high effeciency equipment and r8 insulated/energy star sealed hvac ductwork. Other house was built in the 90s with much more modern techniques. Altho the hvac was lackluster in design n performance imho. And thsn my new house, which i personally GC'd and had an end goal in mind. My new home is certainly larger than both previous houses by a couple hundred sqft with alot of windows/doors/sliders etc. Its head n shoulders above the other 2 in comfort and utility costs sofar. Now i know for a fact, theres homes that are better sealed and built over my new one, and prolly use less energy. But at some point, build cost will always outwiegh energy savings. I have a pretty detailed diary on what this house cost to build. All in all, i believe im at a pretty good happy medium in terms of build costs vs. Comfort/IAQ. Theres defly things i would have done alil differently, but thats life. Maybe on the next one. Dialing this system in has been the real challenge. I ve learned more past year than i have in last 17yrs in this business. Its changing, and quickly. Its very hard to unlearn all the bad habits we picked up as hourly rough guys. Truth be told, im alil late to the game, but im on board for all of it. I truly wish i had contacted rich mcgrath from jump when my plans were finalized. But i didnt. Yet he still jumpd in and helpd me maximize what i did on my own here...and its not all bad. We talk all the time, and in the end, its still hard to convince people less is more. Within the past couple years, i havnt used many 6" or bigger supplies or even furnaces larger than 40k btus. Im on the right track in design n install practices. Cant remember the last time i installed a condensing 100k+ btu furnace. When i was hourly, it seemd like everything was that big. I hope this new generation in this trade learns more and applies it. Lotsa theory and controls out there now that werent around in my apprenticeship. And if they were, not many were employing them. Everything was "HURRY UP AND GET THE CHECK ATTITUDE". Im doing my best to adapt n apply what im learning, id luv to spend more time installing mod con boilers with all the fancy controls and webstone valves, etc. But in the end, i cant get average people to change filters or program honeywell pro 4000 thermostats. Good luck selling them 30k+ boiler installs that recquire dialing in and customer feedback. They usually go with the 15k oversized forced hot air qoute with set it n forget it controls. Heck, even the gas companies around here emcourage contradicting tips on energy savings

 

[Rkupon1]

Cliff notes^^^

Theres a big difference between what is PRACTICAL and TECHNICAL. Cost will always factor in. Especially upfront. Im doing my best to find that happy medium myself. Rich and i have been doung some fine tuning, and sofar so good honestly.

 

[Dana]

Good luck selling them 30k+ boiler installs that recquire dialing in and customer feedback. They usually go with the 15k oversized forced hot air qoute with set it n forget it controls. Heck, even the gas companies around here emcourage contradicting tips on energy savings

And then at the other end of the scale there are people installing a 15K TOTAL (at max fire) Dettson gas furnace using mini-ducts small enough to run in partition wall studs, married to a 1-2 ton modulating Alize heat pump for cooling (and heat, when it's more economical or comfortable due to the lower minimum output level compared to the furnace) where the furnace and heat pump can fit in a closet, using a set & forget strategy (and it works!). There's no need to put these things in the attic when you can bore 2" holes in the framing to run the ducts.

At NJ type 0utside design temps just one of those setups can usually handle a 1500-2000' house built to IRC 2018 code minimum.

People (including most HVAC contractors, and 99.9% of homeowners) have no clue as to what the actual heating and cooling loads are, or how to serve those loads most comfortably & efficiently.

On forums such as this there is ample opportunity to push back on people on system sizing, pointing it out when they have enough burner to keep the place warm at an outdoor temperature south of -100F, or more boiler capacity than radiation capacity, etc. Bigger is definitely not better.