MOD-CON after one year... with gas consumption/HDD stats

NY_Rob

I replaced my 1960's era cast iron boiler and 10yo stand alone gas fired hot water heater a year ago this month.

Before deciding to go with the MOD-CON and Indirect I read many posts claiming 20-30% energy savings over older atmospheric boilers. Now I have a year's worth of data on my system....

The 12 month usage period for 2016-2017 had about 8% more HDD's vs. the same 12 month period in 2015-2016 but I used about 16% less gas for that colder 12 month period with the MOD-CON.

ChrisJ

How was the 1960s boiler sized to the building and how was it running? Why was it replaced?

Were any other changes made to the system or home?

NY_Rob

The Old boiler was a Hydrotherm HC-100 (100K BTU input, 80K BTU Output) all the 1960's homes in our development got that boiler installed. The 2-story home is 1,800 sqft.

The old boiler had a small CO leak between sections, but it otherwise ran OK. Luckily, the CO leak was at the rear of the boiler, so almost any CO that leaked out was drawn up the draft hood.

I added 6' fin tube to one room, and an 8' section to two other rooms to make up for the low temp CH water coming from the MOD-CON.

I re-sealed the upstairs (four bedrooms and a bath) windows over the summer.

The new MOD-CON is the HTP UFT-80W with a 30gal SS Ultra Indirect.
I have the max fire rate of the UFT set at 75% so it's limited to 60K BTU's output for spaceheating.

Robert O'Brien

Nice to see documented real world results, I would have expected a little better but correcting for DD, 22% savings isn't bad

Solid_Fuel_Man

What return temps can you get with fintube and tweaking?

NY_Rob

^ you're probably right about expecting a higher number Robert...
From June till mid Jan I was running with a control board with old FW that was activating the boilers "Boost" function even though I had it disabled in the installer menu.
Once I realized what was happening and installed the new control board with the new FW that nonsense stopped. I figure I lost some efficiency there because I was pumping 15+ degree hotter CH water then my ODR curve called for after 30min of continuous boiler operation.

Gordy

What were your system return temps at design day, if you hit that.

NY_Rob

Our DD Temp here on LI is 15F... we hit a few times last winter.

Here's the ODR curve I settled on after replacing the controller board in Jan with the newer one that didn't automatically engage Boost after running for 30min.


I never really saw a SWT/RWT delta of 20deg on my system... more like 12-15F after stabilizing.

Next winter will be slightly different..
I'm currently replacing 18' fin tube with 20' of cast iron (Burnam Baseray) baseboard to add thermal mass in one zone, and I'm going to replace another 30' or so of standard fine line 30 fin tube with Heating Edge 2 or similar (Synergy) low temp baseboard this summer.
The goal is to get my SWT/RWT DT higher and max SWT temps lower- while still keeping warm

NY_Rob

Solid_Fuel_Man said:

What return temps can you get with fintube and tweaking?

Sorry I didn't see your question when you posted...

IIRC I never got returns below 108-110F.

I cap my low end SWT at 120F because I risk short cycling on my shortest zone if I go lower than that.

Once the outdoor temps go above 40F I have a thermostatically controlled relay that kicks in combines my two ground floor zones to keep burn times long. Luckily, the two zones have similar heatloss characteristics at warmer (above 40F) temps so it works out very well.

Ironman

Was there any significant change in your domestic useage? If so, that could skew the numbers.

Solid_Fuel_Man

Nice! I like the ingenuity of combining zones with warmer temps.

BTW 22% is significant!

NY_Rob

Ironman said:

Was there any significant change in your domestic usage? If so, that could skew the numbers.

No, same four people living here as before.
Both kids still with the same college schedule and my wife and my own work schedules haven't changed.

One thing to note... with the old CI boiler I used night-time setback of 6deg, with the MOD-CON I only use 2deg night-time setback.

NY_Rob

Solid_Fuel_Man said:

Nice! I like the ingenuity of combining zones with warmer temps.



BTW 22% is significant!

Believe it or not... the "digital thermostat" I use to combine the power feed to the two zone valves is a $7 item on Amazon and even less on ebay...
https://www.amazon.com/2013newestseller-Thermostat-Temperature-Thermometer-50-110-c/dp/B00GWFK7FA/ref=pd_sim_60_2?_encoding=UTF8&psc=1&refRID=RKKCE1H9NNK7F030QH7R

I have the thermistor probe running to the outside under the 2" PVC intake pipe for the boiler.

Gordy

What is your system circ choice? Seem to remember delta p ecm circ.

With out forcing a delta of 20 you'll never see that 20 only if it is a cold start up on the system, and emitters, flow rates, etc were designed to that. Otherwise I wouldn't complain about 12-15.

By forcing I'm saying a delta t pump.


I like the ingenuity,and implementation of the controller to pull zones together on warmer days. Nice job. That's something that I see being in the tool box for designers/installers in a micro zoning system.

hot_rod

NY_Rob said:

Our DD Temp here on LI is 15F... we hit a few times last winter.

Here's the ODR curve I settled on after replacing the controller board in Jan with the newer one that didn't automatically engage Boost after running for 30min.


I never really saw a SWT/RWT delta of 20deg on my system... more like 12-15F after stabilizing.

Next winter will be slightly different..
I'm currently replacing 18' fin tube with 20' of cast iron (Burnam Baseray) baseboard to add thermal mass in one zone, and I'm going to replace another 30' or so of standard fine line 30 fin tube with Heating Edge 2 or similar (Synergy) low temp baseboard this summer.
The goal is to get my SWT/RWT DT higher and max SWT temps lower- while still keeping warm

Increased efficiency will come from lower return temperatures, I would not worry so much about ∆T, especially if comfort is sacrificed.

If you could find that elusive sweet spot where the boiler and distribution (pumps and emitters) always matches the load, never cycling on and off, with the lowest RWT to keep the condenser, condensing that would be an ideal efficient system.

I like the combining also, clever thinking.

NY_Rob

Gordy said:

What is your system circ choice?
Seem to remember delta p ecm circ.

Good memory Gordy!

I use the Grundfos Alpha in Delta P mode for my CH pump.
On the DP "2" setting I see 2gpm flow with one zone open, 4gpm with two zones open and 6gpm with all three zones open. Took some time to settle on speed "2" but it seems to keep the HX happy.

For the 30gal SS Ultra indirect tank I use a Grundfos 15-58 3-speed pump on speed "II".

Gordy said:

I like the ingenuity,and implementation of the controller to pull zones together on warmer days. Nice job. That's something that I see being in the tool box for designers/installers in a micro zoning system.

Was there a high-end MOD-CON with that feature already built in or was it on a zone controller board maybe?

The 43' zone that's boarderline short on warmer days is the one where I'm in the process of replacing the 18' of fin tube with 20' of cast iron baseboard. I'm hoping that will solve any short cycling issues on that zone naturally with all the added mass (170lbs of cast iron per 10' section x 2 sections w/o water).

NY_Rob

hot rod said:

Increased efficiency will come from lower return temperatures, I would not worry so much about ∆T, especially if comfort is sacrificed.

If I can successfully replace about 30' of std fin tube with Heating Edge 2 and/or Synergy baseboard this summer... I think I could possibly get my returns down another 5+ deg. Both have pretty much 2x the output of standard fine line 30.

hot rod said:

If you could find that elusive sweet spot where the boiler and distribution (pumps and emitters) always matches the load, never cycling on and off, with the lowest RWT to keep the condenser, condensing that would be an ideal efficient system.

I've tried... to the point of having digital thermometers on the supply and all three returns, a clipboard with notes and a stopwatch hanging from the boiler (and a padded folding chair vs. the bucket)
But I've come to accept the fact that it's not going to happen in my house with the two additions made since 1964 , etc.. When the homes in my area were built in the early 60's they had a single t-stat running an upstairs and a downstairs loop with two globe valves for balancing. Now with additions made to the original structure over time we have three loops with three t-stats. Of course the upstairs and downstairs zones have different heating requirement as does the one addition.

I really wish I had cast iron all around as it would really smooth things out. All that mass would be excellent for the MOC-CON.

Paul48

I don't think that replacing 18' of fin-tube with 20' of CI baseboard will solve short cycling issues. There isn't that much of a difference in output between the two. The advantage of the cast happens after the boiler shuts off, in that it holds the heat much longer. You have to be able to shed the heat applied, regardless of the emitter used. Over-radiating provides the advantage of allowing lower SWT, but there again, if you don't reduce the SWT, you will short-cycle.

NY_Rob

Thanks Paul...
I think I probably used the wrong phrase regarding short cycling as you mentioned- I can't shed any more BTU with the CI than I did with the fin tube.

I looking to reduce the number of daily cycles in the zone where I'm replacing the fin tube with cast iron baseboard.

Gordy

Hmm a trade off. While cast BB holds heat longer. It also takes longer to warm up. I think it gives a slight advantage over fintube.

Fintube absorbs btus faster than ci. Which means it reaches equilibrium faster than ci.

This could mean longer cycles.

Another test for you Rob to come back to us with. However it won't be apples to apples since the new ci is longer.

NY_Rob

I'll add some more fun math to the equation Gordy....

After pulling out the out fin tube yesterday afternoon... I found that due to using the recommended Burnham 4-5/8" compression connector at the corner end and needing a male adapter to the riser elbow on the other end... I can only use a 9' CI section on one side and a 10' on the other side. So my 18' of fin tube baseboard will now be replaced with 19' of CI baseboard instead of 20' of CI.

With that in mind...
At 130 AWT Fine Line 30 puts out 260 BTU/ft.
At 130 AWT Cast Iron BB puts out 231 BTU/ft.

So..
Fin tube gave me 18' x 260 BTU = 4,680 BTU
Cast Iron gives me 19' x 231 BTU = 4,389 BTU
I'm actually losing 291 BTU's radiation in that 160sq/ft room.

I'm still looking at 27.4 BTU/Sq/Ft in that room, so that should still be sufficient... and upon removing the fin tube this weekend- some if it was pretty blocked w/dust bunnies... so it wasn't putting out at full rated output either.
I'm betting.. er hoping... overall, the heat output will be a wash between the new and the old radiators and they'll now take longer to heat up and retain their heat longer giving me the longer cycles I'm looking for and better comfort in that room.

If I had been able to use the full 20' cast iron BB as originally planned It would have matched the old fin tube output almost perfectly, but I can't move the risers so I'm kind of stuck there.

I'm sure my buddy at Blackman is going to be super-happy with me tomorrow when I ask him to exchange the 4' right hand section for a 3' right hand section