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

PC7060

@mattmia2 - thanks for the information. I will keep the Boost option in reserve. Re the Anti-Cycling timing, I will leave at the default value. Not sure why it would need to be increased. Maybe if hooked up in a cascade of multiple boilers.

Thanks

mattmia2

Your system is an old converted gravity system so it has a lot of mass, there is a lot of water in the system and it is heating heavy cast iron radiation, so wouldn't need the anti short cycle timer unless you added a small zone of something like fin tube baseboard or a couple panel radiators. It could come in to play is one zone ends a call and another zone calls a minute or 2 later or even if that second zone calls while the first zone is calling but after the boiler has shut off because the mass of the system in the first zone is up to the water outlet temp setpoint.

Ironman

With a high mass system, parameter 14 should be set to 15*.

PC7060

@Ironman - parameter 14 is “reset burner operation time”. Is this the setting you are recommending to change?

mattmia2

you will have to tweak the swt and the thermostat anticipator setting so you don'tend up putting a ton of heat in to the system that overshoots for like an hour after the call ends.

PC7060

@mattmia2 - you lost me there with the anticipatory setting. Re the water temperature, I’m setting the top temperature to 140 deg F SWT @ 5 deg F outside temperature with top end of the slope at 68 deg F

edit: initially thought the outdoor temperature sensor was reading high but just confirmed it matches outside temp measured with the boss’s fancy digital thermometer.   

Ironman

PC7060 said:

@Ironman - parameter 14 is “reset burner operation time”. Is this the setting you are recommending to change?

In my manual it's "set differential temperate". The default setting is 27*, meaning if the high limit is set to 180*, the water temp has to drop to 153* before the burner starts.

The problem is that this applies to the ODR target temp as well. So if the ODR is targeting say 90*, the burner won't come back on until the water temp drops to 63* which means the house would have to be that cold or less before the boiler fires again. We've had no heat calls because of the factory defaul setting.

PC7060

@Ironman - wow! Very useful, thanks for giving me a heads up. Sitting in front of unit as we speak. 

PS: in the version of the manual I have, the code is 17 for differential temp setting. 

PC7060

Settings all updated, ready for system firing test in am.   Once I’ve got the final bugs worked out I’ll have my HVAC guy do a combustion analysis for the final sign off. 

Final installation pics....

PC7060

Only issue I’ve noted so far is the Webstone valve on the return side fails to fully close the drain side regardless of the position.  If I open the drain shutoff in the position as shown, I will get full flow out the drain side when should be fully closed.  I’ve taken the handle off and and rotated fully around and the drain line never closes. I’m doing a post install cleaning flush and will remove and inspect the valve once I drain the system down. Very strange, every other valve works just fine.  

mattmia2

@Ironman I'll have to see if i changed the differential. i ended up setting the swt to a fair bit higher than my heat loss calcs showed, but if i designed for 120 swt and it dipped to 90 before the burner kicked bak in, that wouldn't be much output.

PC7060

Thermostat wiring has me puzzled. I am using a Honeywell 9000 series tstat.

I measured the TT line outputs to ground and it measures 44V (approx.) I don't know if this is just unterminated noise or not because I measure it on both sides of TT terminal.

TT connections: RH will be TT (in) and W Heat Relay (TT (out).

Power for Honeywell Tstat: Seems like I will need to bring the 24VAC off the transformed terminal up to the tstat. Looks like the two connection should go to the C and Rc connections on the Honeywell.

Edit: Confirmed the above settings for TT power work. Also removed the Rh->Rc jumper on the TStat to isolate power from the TT controls.

PC7060

I've found the Outdoor sensor tends to read significantly higher than outside ambient when temps are in mid to low 20's (e.g Sensor =40F, ambient = 25F). I believe the error is due to heat from the house coming through the foundation. I'm trying slightly different locations / orientation to see if I can get more accurate reading. In the mean time, I've enable Boost mode with a 5F step after 40 minutes to address the situation.

PC7060

I've move the Outdoor sensor to a temporary location where it appears to be reading ambient more accurately.  I'll need to come up with a permanent solution that can be tucked in a discrete location since the sensor is on the front of the house near front door.  I'm planning to mount the sensor on small piece of aluminum angle  and use thermal paste to improve sensor accuracy.

I disabled Boost Mode (more on that later) last night and let the system operate per design. The temperature last light was in the mid 20's and the boiler held temperature very well running for very long periods circulating 109F water at at 5-7GPM. 

I currently have max water temperature set to 130F with lowest outside temperature of 5F (default). This gives me approximately 120F water temperature for a design day temperature of 15F with a bit of insurance if temps drop further.

Two notes:

Note 1: The house is designed with 19 radiators over 3200 SFT, however 8 units are are offline due to ongoing renovations.  I set the TRV to full open for the 11 operating rads  and the systems is maintaining temperature and running smoothly.  Certainly the room with rads disconnected are bit cooler but not dramatically.  Lesson: Air  sealing and spray foam insulation really pay off. So do really big rads!

Note 2: Boost mode drives the water temp up too quickly causing the unit to short cycle. Based on my analysis and tests, there appears to be a bug in the firmware that controls boost mode temperature steps.  I've found that the boiler always uses the default values for 10:bd Boost Degree (10F ) and 11:bl Boost Interval (20 MIN ) regardless of  what is programed in (5F / 40min).  

mattmia2

The outdoor temp sensor just needs to track outdoor temp, it doesn't necessarily need to accurately read the exact temp. It just needs to read colder when it is colder and warmer when it is warmer. You can tweak the min and max outdoor temps to compensate.

There is someone from htp that is on here sometimes or you can e-mail their support and ask about the boost. there might be something you're missing that needs to be set or used for it to not use the default.

PC7060

Boss seems to like new system. Asked me about the hooting from the air intake. That’s the sound of heat be produced!

PC7060

Posting as built system systems drawing per @MAF request.

PC7060

I've ran the system for 1 weeks after install and will flush/refill after replacing the bad Webstone shutoff valve at the return line.

I'm adding one gallon Sentinel X100 Corrosion Inhibitor since my new system is approx. 100 Gallons. I'll verify amount when I refill.

Question: I assume the 1% ratio of conditioner is a target and a variance of +/- 5% to volume is acceptable.

PC7060

30 degrees outside tonight and boiler has been running continuously and quietly for past few hours holding temperature at 70F.  

Measured the gas burn rate at 1/4 cubic foot per minute or 15 cubic feet / hour equating to 15,555 btu hour.  Pretty good for a 92 year old house!

I’ll be very interested to see the BTU usage at deign temperature of 15F but expect it will be much lower than the design phase 65KBTU/Hr Heat loss projections.  

Want to thank everybody on the site for their help on my project with a extra shout out to @mattmia2, @hot_rod and @Ironman

Great site, great people!

mattmia2

somewhere in the menu it will show you the percentage firing rate.

PC7060

@mattmia2 - Thanks for tip; found it under Cascade information section M:Self. Have to push control button 2x to display. 

Displays “30” which I guess is 30% of max. This matches up to the current gas consumption of 25K BTU/hr. Temperature has drop a several degrees so system is running 110F water temperature versus 104F from earlier. 

I must have caught it during a lull in heating cycle earlier.  Makes sense because the that BTU/Sft seems really low now that I think about it. 

mattmia2

Yeah, that's it. I thought that it was weird that it is shown as a cascade parameter but it read in standalone mode. It was really helpful to show that it was transferring all the heat it could to the indirect when the temp was dropping and that it is only transferring about 35% to my garage when I thought i designed it for around 70%.

PC7060

Drained down my system to flush out post install gunk and replace my problematic Webstone valve. Fortunately I included unions at key points so draining system took more time than replacing valve. 

Also took a hint from @mattmia2 and reworked domestic hot water connection to tank to add back flush pipe and valve. Install went well but ended up with a leak at a street 90 into a Viega 3/4 mpt press. This is the 3rd time I’ve have leaks at street connections to Viega MPT brass press. Crimps to standard pipe works fine. What a PITA. 

The copper JW versions seems to work well with street connection so won’t waste my money on the Viega. 

Reworked to take out street, not as pretty but works fine. There a shutoff on feed line behind Amtrol.  Open top valve, close lower to feed supply water into top connection to flush out through bottom connector. Nice that the Caleffi Angle shuts off when the pressure in shut off to the cold side. 

mattmia2

The street fitting might not be long enough to fit in to the press fitting properly.

I really like using these valves for drains where I want to flush or purge something. They are full port and they have a cap attached as a secondary protection against leaks or accidental opening. i even used one when i replaced the cold water to my mom's washing machine.
https://www.supplyhouse.com/Apollo-Valves-70104HC-3-4-Full-Port-Cap-Chain-Ball-Valve-w-Reverse-Handle

PC7060

I put a couple spring mounted thermometer from Supply house one my system to get return water temps for CH and DH returns.   Both units read 25F low relative to boiler display panel and a digital thermometer. Even used thermal paste but no change. 

Edit: torqued the nut on back of case to calibrate gauge to my range of interest. Seem to work ok over +/- 25F which is fine for me. 

PC7060

The ongoing problem with ODR sensor sensor not getting true outdoor temperature reading was causing boiler to not keep up on cold night. 

While I did figure out how to set up boost mode, I didn’t like the impact to run times. 

Adjusting slope also didn’t address problem since error was not linear (got worse as temp dropped). 

Determined I needed to move ODR sensor away from house 2’ and location of the outside AC compressor made it a good option.  Mounted the sensor to underside of wire connection box and connected back to boiler using spare wires from low voltage control lines for compressor. Now reads accurate temp and my 120F max at design temp slope appears to be a good match for building heat loss. 

Since repositioning the sensor, Boiler runs over very long periods while maintaining temperature.  Boiler also seems more than adequately sized running at 25-35% capacity during recent 25F nights.

 

PC7060

Only remaining issue I’ve noted is tendency for thermostat to short cycle boiler (15-20 minute runs then start again in 5 minutes) in evening as temperature of day starts to taper off.  No way to adjust the cycle per hours on tbe Honeywell 9000 series thermostat so I set the Boiler anticycle time (setting 16) up to 20 minutes (CPH=3).   
However, UFT80 doesn’t seem to follow the time out and will fire up up immediately when TT is triggered.  Not sure if the anticycle delay is from start of last cycle or from the end of last cycle / TT disconnect time.    
Have a email into HTP tech support but no response. Not a huge issue but I’m watching it.

The 9000 series seems to use a tight band, maybe +/-0.5F.  Doesn’t appear to be anyway to adjust that either. 

mattmia2

I think the anti short cycle timer only stops the burner from firing, it doesn't keep the pump from turning on. Have you checked that the burner is indeed firing? It also doesn't apply to a dhw call.

PC7060

mattmia2 said:

I think the anti short cycle timer only stops the burner from firing, it doesn't keep the pump from turning on. Have you checked that the burner is indeed firing? It also doesn't apply to a dhw call.

Yes, burner is firing (flame symbol, CH water produced).  I do see the situation you describe occur when diff temp of supply water / return water less than setting 17 delta T (set to 15F) by some amount (5F approx. )   This seem normal.   

Thanks

PC7060

Just got my bill for first full month of boilers operation with DHW. Gas utilization is 32% less that same period two years ago with a 800SFT larger envelope. Nice!

Reduction is due to combination of much higher efficiency boiler running low water temps (120F SWT @ 11F outside) and the benefits of the well sealed and insulated addition.

And of course with the long boiler runtime, the house has much more even heating and the cat always has a warm radiators to snooze on. Indirect DHW is a big hit with the family (not so much for the cat).

PC7060

My HTP UFT80 continues to perform very well and I’m coming up on my annual cleaning / maintenance period.  

@Ironman - The IO&M manual pg. 66 provides detailed instructions on flushing the water sections; is this required if the system is treated with Sentinel 100? We also have low mineral content in our water and very little if any makeup water has been added since installation. 

I see a reference to cleaning the combustion chamber on page 67 but no instructions. Am I missing something?

mattmia2

I have been meaning to ask the second half of that question for let's say about 2 and a half years now.

It really looks like a cut and paste from a tankless water heater manual.

PC7060

With the current polar vortex chilling a large portion of the US, I finally had the chance to measure the hydronics heating system performance for my house at design day temp of 11 F (Virginia). Manual J analysis for the house predicts 54KBTU for design day. 

UFT80 Modcon Boiler (80KBTU) with ODR
Running at 46% capacity (36.8KBTU) with outside temperature of: 11F
Emitters: CI Radiators. 
SWT: 110F
RWT: 98F
Exhaust Gas: 104F
ODR Slope:
86F SWT @ 68F outside
116F SWT @ 0F outside

hot_rod

One thing to keep an eye on as it warms up and TRVs start closing down and off. You may want the circ in one of the delta P modes instead of constant speed?

And be sure the boiler gets the minimum flow they indicate when TRVs are off or closed way down.

Sounds like a big win, overall!

PC7060

hot_rod said:

One thing to keep an eye on as it warms up and TRVs start closing down and off. You may want the circ in one of the delta P modes instead of constant speed? And be sure the boiler gets the minimum flow they indicate when TRVs are off or closed way down. Sounds like a big win, overall!

Thanks @hot_rod, I’m very happy
with the performance. Re the TRV shutting down, several of the radiators run without controls heads including the two in the shop.  The majority of the remaining units are at 5-6 range (max heat)  with a couple dialed down as required for comfort or economy for used rooms.  

I read an article about use of TRV in low temp hydronic systems (maybe Caleffi Idronics July 2019?) and the author recommend running the TRV hotter and adjusting temp curve down to maintain a more consistent flow rate through the boiler. After adjusting the TRV per the article, I adjusted the curve down from 120F at design day to current setting of 116F at 0F temp. The boiler run times are typically >4 hours on days warmer than 40F.  On cold days (low 30s and below), the boiler runs all day.  

The numbers from the Alpha2 are consistently in the 7-8 GPM range (at 8 watts, amazing) so that approach seems to work. 

tim smith

pc7060, one thing I noticed on your radiator valve supporting the kitty, we usually use side mount angle valves instead of standard angle valves in that configuration. This way the actuator does not get the direct radiant heat off the side of radiator it then sticks out to side of valve. Just makes control more accurate.

PC7060

tim smith said:

pc7060, one thing I noticed on your radiator valve supporting the kitty, we usually use side mount angle valves instead of standard angle valves in that configuration. This way the actuator does not get the direct radiant heat off the side of radiator it then sticks out to side of valve. Just makes control more accurate.

@tim smith - thanks for the information. I’ve read the tech data on the preferred orientation being horizontal to avoid the heat from the pipe coming vertically from below prematurely shutting off the TRV. I originally selected the vertical configuration of the TRV to protect the head from adjacent foot traffic.  This was before I understood the advantage of the horizontal configuration but I’ve gotten good performance with vertical orientation by reducing the flow rate (on original boiler) and SWT with new modcon boiler. 

PC7060

The original boiler had a stupidly oversized 1/6 hp circulator on the 2” return. The boiler had a 40 gallon internal tank at 180F so it was quite noisy at startup due to the rapidly expanding pipes.  I put a microprocessor inline with the thermostat to control the pump runtime based on return water temperature and stack temp. Ran something like 15 seconds on / 180 seconds off at cold startup.  Really helped to even out the boiler run and eliminated the pipe clanging at start. Spent many hours tweaking the numbers, drywall buckets make good temporary work desks.