mod/con help

remodel

Had scorched air deiced to go to high eff. boiler (hired work out while I was GCing 2nd story pop top).  Have three good contacts to help me and have touched base with ME.  So I need to arm myself with some more good info, also my background is engineering so I do enjoy these discussions.

 1) mod/con lochinvar 155

2) Squire DHW 50 gal

3) no official heat loss calc that I know of, 1033 sq-ft first floor 1940 2x brick and plaster, 1033 sq-ft addition, R38, R21 etc.. and 700 sq-ft basement  

3a) 56 feet of WM baseboard-1st floor, 1-8200 FCU, 56 feet WM BB, 2-4200 FCU 2nd floor, 15-20 feet of BB in the basement.   

4) Three zones (all 3/4" pex piping) and DHW set as normal with a 26-99 pump set at low.  Noisy flow issue/air issue sometimes as well 

5) Main issue was boiler was installed about 2 months ago, kept locking out on outlet temp diff being the same (boiler water was real hot, still is but working), at the time the pumps were all set med to high.  The primary is the heating loop and the secondary the boiler (I think).  Boiler has 15-58 set at speed 1, system has 26-99 set at speed 1 and DHW has 26-99 at speed 1.  The boiler is working now after lochinvar rep helped me out.   

6) Also have a non working FCU on 2nd floor loop (in BR), only worked twice when system pressure was set to 50 psi and once before, otherwise airbound now.

7) system 26-99 pump is pumping towards PONPC  

The fix to date:

1) Set all pumps to low speed, ramp delay (20%, 30%,60%, 100% at 11mins), changed outdoor reset.  Here in Denver we had design temps and house was alright.  Checked last night on cycle times and I am at 9 minutes for boiler and 11 minutes for DHW. 

2) Still need to fix PONPC and fix FCU, isolator and purge ability?.

3) Still get a terrible Delta T at the boiler, 6-7 degrees.  I set anticycle down to 35 degrees diff. and set boiler temp to 160 with a max at 180.  This max is at 5 degrees and the 60degree high is set to 125.  ODR seems alright but I don't mind tweaking it.  The issue is my delta t and inherent short cycling.  The lochinvar says 15-58 at speed 3 which kills the boiler especially if basement zone calls.  

4) Attached some pic and one more bit or info, if my 1st floor zone calls, which is the typical zone calling (brick walls etc) the ramp is set at 20% for 7 minutes and the 56 feet of BB plus 8200 FCU supply 38440 btu/hr so I feel at that mod I am undersized and should get a good return even-though I only see 6-7 degree with the 15-58sp(1). If 2nd floor zone calls I get a bump and delta t at boiler goes to 13-15. 

Advice

1) Should I; put more heat load in the basement, I can't in the other rooms as they are finished unless I can take WM BB out and add runtal etc.. with more output.

2) Should I downsize pumps? Feel like boiler pump is still way oversized at low speed and don't know if I am getting anything accurate now that I am pumping towards PONPC.

3) Should I add a buffer?

4) Is this boiler going to live a short life?

Sorry for the long post, just been thinking about it.  Also can't say enough great things about the lochinvar rep and his helping me out getting this pig heating during (-10) degree temps.

Paul48

Seems

The boiler is way over-sized. How was it sized, if no heat loss was done? It doesn't even match the radiation, total. Not that, that is the right approach either.

hot_rod

it does sound

like it is oversized, even at low fire with the delays programmed in, it will cycle a lot.



A correctly sized boiler will cycle on load load conditions also, until we have products that can go from near zero to full output.



The question becomes what is an acceptable cycling period? I like to see a 10 minute on cycle. this was more critical with cast iron or copper tube style boilers to assure the HX and flue piping warmed above condensing conditions.



Withe your boiler the concern is component wear from excesive cycling, and the fact it drives you crazy just knowing it is happening



That boiler should have a cycle counter (odometer) to track this. I have heard cases where that counter is maxed out in 3 years or less! Not a best operating condition.



Downsize the equipment, or add a buffer tank. Dollar wise it may be the same fix. The buffer tank fix can offer other features and functions, hydro separation, ability to add solar or other input, DHW production with an external HX, etc.



My Lochinvar 120K is twice my load, but with a 50 gallon buffer tank I get nice long 10 minute cycles under small load conditions. I used the 120K to get the onboard DHW module.

remodel

Yep

Not to rehash too much about the job, I hired a licensed contractor with 30 yrs of experience....  Supposedly the supply house did a heat loss and set radiators using my approved city plans with dimensions etc...  I got what I got, can't return it.  Now I am checking it b/c of other issues and trying my hardest to optimize this boiler.  So to justify what I got and try to optimize it here is what I think.  Don't disagree the pig is oversized.  Do I still need a pretty good size boiler to heat my DHW with a family of 5 (3 girls/2guys, 50 gal indirect I=B=R=133K)?  Kids all little now but once high school hits, oh no! 

Here in the mile high lets say I actually have a 90% eff boiler (chances are I will rarely condense) plus derating at 3%/1000ft.  So really I have 150,000btu/hr *.9*.85=114750.  Using a man J I get around 90k-100k house load.  All radiators and FCU I get about 85K-90K.  So I have about 25% oversized boiler.  Should I try and add more radiators, buffer tank etc., slower pump (boiler & system)?  Any advice from hear on or I am just screwed.  Or have I done what I can after I fix PONPC and FCU.   Thanks Paul.                 

Paul48

One Choice

        Since you're stuck with it, your only choice is to increase the load. For this heating season, lose the zones and let the boiler handle the whole structure. Your 25% oversized was based on combined load. Now figure it chopped up into zones.

       

remodel

Not a

bad point.  I could pull all other stats and run one huge zone.  What about setting max fire to 80%.  Beside the basement zone, at 20%-30% fire with one zone calling I am in pretty good shape (.2*115=23).  Is that a bad way to look at this?  That is why I am thinking about adding some radiators or something to basement or put basement on first floor zone as well.  2nd floor zone calls very little and typically calls when 1st floor is calling too.  I am just under that 10 minute cycle time, I calced 9 minutes.  Seems like these things are iterative to begin with and now I have the oversize problem.  One last question my 1st floor stat is in the coldest room in the house, should I move it to a more insulated room?           

Jean-David Beyer

increase the load

I have a small baseboard zone that is not enough load for my boiler that is oversized when driving only that zone. The boiler is a mod-con and I did several things to get the cycle rate down. One was that I raised the minimum supply for that zone from about 85F to 110F so the baseboard would dump more of the heat. When the supply is 135F, the cycle rate is acceptable. I also raised the range from 10F to 15F. That helped a lot. Now it cycles 4 to 6 times an hour instead of every few minutes.

Paul48

Winter

      Take the season to do your own room-by-room heat loss.Over-radiating would allow you to run lower temps, and get that beast condensing.Getting the system in order would go a long way to alleviating the problems with the oversized boiler. Some of the pros here can speak of constant circulation, and running the system ODR only, and no T-Stat.

       I think of zoning with a mod/con along the same lines as night set-backs.The boiler  is going to produce a temperature, based on the outddoor temperature. Now...let's let half the structure get colder, because we're not using it.This has an affect on any adjacent spaces that might be in use, and when the colder zone does call for heat, the boiler is not getting correct information.

     I know a lot of people like to keep their bedrooms cooler at night, and I could see using TRV's with bypass for the bedrooms. Just my opinion...

remodel

yep TRV

Just didn't have the $$ to do a TRV system.  House is in real nice shape after 6-7 months of demo etc.  Don't even think it is feasible now to get panel rad on the 1st and second floor without major demo to try and get monoflows in etc..  The thing is this system, zones, BB and mod/con was 30% cheaper than euro rad and TRV and I still spent a hefty price to get this system in.  I will not give up on her but it is tough to hear these systems don't respond well to BB and if they are installed with BB they need to be over-radiated or 30%-50% undersized.  I will mess with it get things as fine tuned as possible.  Someone should invent a retrofit BB that has TRV and more heat output.      

remodel

As...

hotrod said.. nothing like knowing your boiler is short cycling.  At 155k should I just eat this install and sell this way oversized boiler and get the correct sized boiler.  She is still running on a 10 minute average cycle.  I have her tweaked so she runs at 20% for ten minutes then ramps to 30% for 2 minutes ect to a max fire of 80% after 20 minutes using ramp delay.  I also put her on a long anti-cycle and set point diff.  Comfort is now an issue but I can have the family suck it up.  Its like buying a deuce-and-a-half to commute to my job 30 miles away.  Doesn't make sense.  Is there a market for a used boiler that has 530 hour on it?