Boiler Delta T/Cycle Counts/Run Time Efficiency?

ckeefer79

I have to be honest in saying this boiler is the first system I have ever owned and operated. I have always been around and involved with forced air systems but I ended up with a residence that had a system that came close to dating back to the original installation.  I thought I had tweaked the system to the point I was getting the boiler within it’s best efficiency range while providing the house with proper comfort but based on the colder December we are experiencing this year, I am not so sure it’s completely functioning at it’s highest.



I know context is always a good point to start with so here is a brief description of my house and setup.  I have a 2000 sq. ft. two story twin, 1925 construction with mass walls but no insulation (3 layers of brick, 1.5” air space and ½ plaster on ¾” lath boards) located in Philadelphia.  The house has an unfinished, technically unheated basement – however the boiler and piping run uninsulated through the basement space so it actually becomes heated.  All of the windows were replaced with U-0.27 windows with the exception of the large steel picture window at the front of the house.  The heating elements are in-wall convection boxes (slat-fin recessed into the wall cavity with grills at the bottom and top of the steel box).



The boiler is a Burnham Alpine ALP150 – which after the installation was completed and I really started working to fix the short cycling, I realized was grossly oversized for the heating load of the residence.  The system does have a 35 gal. indirect HW tank which is piped as a separate heating zone (with it’s own circulator).  I have pushed the limits with tweaking the ODR on the boiler and feel it’s dialed in fairly good but note that I cannot push down my return water temps below a 7 to 8 degree delta T.  I have included the numbers from the past couple of days, which gives a good indication of my run time and cycles as well as my natural gas usage (however, I do have a gas cooking stove which is also used off the same meter I am reading the boiler usage).  Over the course of this observation days, I am seeing my supply water temp around 123 to 126 F and my return water temp around 116 to 119 F.  I have never had the boost setting overrun the standard boiler cycles, so I feel the temperatures hitting the convection boxes are sufficient to supply the t-stat with it’s requirements before it hits the 30 minute limit.  My question is simple, should I be seeing a delta T around the boiler design point of 20 to 25 degrees?  If so, I don’t know what else to do to the system to get the returning temp down to around 100 F – the house doesn’t need more radiation (as it’s super comfortable even on the coldest of nights).  I have read a ton of information and there appears to be a lot of different opinions on how things should run and work.  I have the boiler running long cycles with supply (and thus return) temps in the condensing range while running the boiler at around 66% of it’s max fire capacity but I am not hitting anything near a 20 F delta T.  Should it be?



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12-15:

Outdoor Temp 34 F High/27 F Low

39 cycles – 13 hrs. run time = 20 minutes per cycle

7 ccf used



12-16:

Outdoor Temp 39 F High/30 F Low

38 cycles – 13 hrs. run time = 20.5 minutes per cycle

7 ccf used



12-17:

Outdoor Temp 34 F High/19 F Low

38 cycles – 15 hrs. run time = 23.6 minutes per cycle

9 ccf used



12-18:

Outdoor Temp 32 F High/21 F Low

42 cycles – 16 hrs. run time = 22.8 minutes per cycle

8 ccf used



System setting:

C.Heating set point 140 F with 2 F below and 10 F above allowance (boiler appears to always over shot by at least 3F



ODR:

-4 F low outdoor temp

67 F high outdoor temp

110 F min water temp

Boost set to 30 minutes



Modulation set to 3650 RPM max – Minimum 1100 RPM (factory min.)



T-Stat set to 70 F indoor temp with 2 cycles per hour setting for the target cycle count.

Rich_49

What

pump is currently doing the heavy lifting of your system water ?  How is the short cycling doing during the cold ?  Pretty well I suspect but it will start short cycling again on warmer days . There are solutions to both problems .

ckeefer79

Pumps

The boiler pump, on the return side of the boiler is a Grundfos UPS 26-99 FC while the two heating zone pumps are Taco 007-FS-7IFC (the main heating loop and one on the indirect domestic HW tank).  The entire house is on one zone with the t-stat located in the large, high ceiling living room on the first floor. 



The system during moderate weather (50 to 60 range) will only run about 7 to 10 minutes max with about 2 cycles per hour (sometimes it runs a little longer but rarely).  That's a great improvement over where I started last winter and my gas bill reflects that, but I still fill like it's not giving me everything it could be as far as efficiency.  My gas bill usage (at least for the past couple of months) is down by about 20 to 25% over last year and I have an added body living in the house this winter using hot water over where I was last - my water bill is about double where I was last year, if that give an indication of the change in water usage).  Last year the boiler only ran in about 3 to 4 minute cycles during moderate weather and might have given me 7 to 8 minutes during cold weather.  The system was installed Aug. 2012 and as of this morning my cycle count equaled 14,072 with a run time of 1385 hrs, given me an average of almost 6 minutes per cycle, which to be honest is greatly increasing because I have been able to get the boiler this winter to run much longer during it's cycles.



The system over all is giving me great returns over the dinosaur it replaced which probably wasn't really hard to do, a 85% cast iron standard boiler would have had no problems doing the same but given the fact this unit is a high efficiency, I would like to continue to tweak the system to get the most out of it, while also reducing the wear and tear on it (as I understand it, it's not good for the system parts to cycle on and off constantly like a force air system does).



After reviewing the plumbing diagram for my boiler, it certainly looks like my near boiler piping is very short compared to what the book shows.  I attached some pictures, but basically my supply comes to the top of the boiler and the tees in with the return piping - it does appear the required 12" distance between tees exist, but by no means do I have anything close to 75' of the "design limit" Burnham talks about with pump selection.  If I did my math correctly, I have 2-90 elbows, 2 tees and two standard port ball valves with about 7' of straight pipe (not including anything inside the boiler) so somewhere equal to 30' of piping in 1" copper piping making up my near boiler loop.  I am guessing my near boiler piping is the problem with not gaining the proper delta T on the return.  I have noticed that no matter what speed I have the Grundfos on (1,2 or 3) it also doesn't affect the return temperature (or at least noticeably)

Rich_49

Bumble Bee

This is what I would recommend for your heating zone . Delta T operation in your case .  I would also look at the indirect zone to pinpoint how that is performing .  Can't clearly tell difference between S & R , the black kinda runs together in spots , probably just my old eyes though .  This pump will tell you how many GPM are being pumped and the wattage being used in real time . Makes it pretty easy to know exactly what's going on .  A buffer tank would greatly improve everything in this system also . Do you know the btus for your heating zone ? 

ckeefer79

Heating zone

I don't have an exact number of btus/hrs that the rooms need if that is what you are asking.  If you are looking for the btu output of each emitter and number of total emitters, I would have to measure the lengths and depths (some rooms have deeper fin units than others.



Are you saying to replace the Taco 007 pump on the convection heating zone with a Bumble Bee pump and have it set to a delta t setting or replace the Grundfos pump on the return side of the boiler with the bumble bee?

Rich_49

Leave

the Grundfos alone . The Bumble Bee moving your heating water to the emitters is what you want . It will keep the designed for Delta T near target .  BJ Terroni in Bensalem is distributor in your area , you should be able to locate and obtain easily .