I have posted here before about how my builder, HVAC installer and the manufactured home company have left me out in the cold. I have spent over a year researching my situation, and educating myself about home heating so that I can make the most informed decision and ultimately, the best resolution from the three above-mentioned parties that agree that somebody dropped the ball.
First, some basic specs:
Home size & insulation
Clg-R38, Wall-R19 (except basement stair walls-R11), Floor-R19
Ent Doors-U.35, Doors-U.45, Wind-U.35
Home location & zone
Bosch 151 Combi on LPG
Baseboard fin tube - 34-feet
Single zone loop. No pri/sec
Taco single zone controller and 3-speed pump in addition to Bosch integral 3-speed pump
One BM K42 Kickspace in parallel (not a restriction concern for entire system)
F/L 30 output per foot, in btu/h:
580 @ 180F
320 @ 140F
260 @ 130F
K42 output, in btu/h:
4,278 @ 180F
2,590 @ 140F
2,175 @ 130F
Description of problem:
From October to April, the home cannot recover from even a 3-degree F set-back (69 to 66) in under 5-hours. Boiler short-cycles, running for under 1 minute at a time. A set supply temp of 180F never results in more than minimum fire, and only for a minute or two, even during tests with water temp less than 90F. Fuel usage is high, at ~150 gallons LPG in 30 days. My HVAC installer chose not to install the comfort room sensor/thermostat, or the outdoor reset, so my system is being run in a "dumber" mode.
When showering with a DHW set temp (higher than desired) of 120F results in hot-cold-hot cycling 5min into showering. Removal of water saving features of faucets and shower heads is what got us to 5m. Before, we were cycling within under 2m. My research and the HVAC installer agree that this is because our hot water need is less than the minimum flow rate of the combi on the DHW side.
Heat loss calc info:
The modular home manufacturer supplied me with their heat loss calculation figures ("GcrackerHeatLoss.PDF" attached) , and I am hoping for some input here, as I am only barely familiar with this info. I see that they used a DTD of 80F, though I feel that a Maine home in Zone 6 ought to be calculated at 90F at least. Maybe my opinion is wrong there. It also looks like they didn't calculate for any windows or doors in most rooms. Their HLC lists total heat loss at 21,521btu/h. At 180F and 1Gpm, all combined baseboard is capable of a theoretical max output of 19,720btu/h, and the K42 adds 4,278btu/h. I have to have the K42 on at all times to even maintain temperature - without it, temps drop. Even with the K42, heat is hard to maintain, leading me to believe that the manufacturer's heat loss figures are off by a wide margin.
My own amateur heat loss calculation ("Heatloss Calc.PNG" attached, resulting in 31,489btu/h total heat loss) using the Slant Fin app left me with a few questions regarding the manufacturer's calculations. First, the manufacturer's "infiltration" value includes an apparent area calculation multiplied by 0.96 in all rooms except the "Kit/DR/Bath 2" which multiplies by 1.44. How does this equate to the app and the use of much smaller figures? I don't think I will follow a formulaic explanation, but am wondering if my figures likely effectively mirror theirs. As mentioned above, they don't seem to have bothered to calculate any windows except in the "Kit/DR/Bath 2" despite having three bedrooms with single 36x52 double-glazed windows, and the LR having two 36x52.
I would be interested to know if there is a heat loss calculator for home-owners that allows changing the design water temp for compatibility with condensing boilers.
Running 180F negates the condensing feature of the boiler, shedding up to 20% efficiency in the process. If I continue to run 180F water temps - which I hope not to do - my home requires closer to 60-feet of baseboard. If I want to run 140F to allow condensing of flue gasses, I think I need closer to 100-feet (effective). If I were to run 140F with the same amount of baseboard, even with the K42 on all the time, my calculations (320 x 34 = 10,880 + 2,590 = 13,470) put my max theoretical output at 13,470btu/h. That is roughly one-third of my total heat loss according to my own heat loss calculation.
Without the ODR and the intelligent room comfort sensor, I effectively have a brand new 1950's boiler in on/off mode, with some modulation, but unrelated to room and outdoor temps.
I know that some might advise me against addressing my concerns with the responsible parties, but I have to make an earnest effort to go that route at least once, with all the knowledge I have now. Ultimately, I think there are three people pointing fingers away from themselves, and they are all equally responsible. The manufacturer put too little baseboard in and used figures from Pennsylvania in their HLC. The builder chose an HVAC company inexperienced with condensing boilers. The HVAC company didn't bother doing their own HLC, and used the old school of thought when choosing/sizing a boiler: go huge (151k/btu when system is designed for 24k). He also tied the system in with inferior controls unnecessarily, probably because they are used to them. Finally, HVAC installer omitted ODR and intelligent sensors as he is unfamiliar with them and claims they are unnecessary "for small systems" like mine.
To effectively utilize a condensing boiler in Maine, what emitters should I be using? Obviously, I can't install 100 to 125 feet of baseboard, so should this system have been paired with high-efficiency radiator panels? Should radiant heat have been used instead?
If conventional wisdom (that I've gathered from my amateur research) says that a condensing boiler running low water temps should be roughly 100% oversized to recover from setback of 8F, then with my total heat loss of 31,489btu/h, shouldn't my boiler be roughly 60,000btu/h to 70,000btu/h? Wouldn't that make it so that when the boiler modulates down to (the apparently common minimum modulation of) 30%, or 18,000btu/h, it has actually modulated below the total heat loss? If there are combi boilers in that output range, wouldn't that also likely have a lower minimum DHW flow rate, and eliminate the hot-cold-hot showers?
I have to be able to describe exactly what remedy I want to correct my situation, and I think the following would be ideal, but highly unlikely that all parties would agree:
Engineer the system to run low water temps (more baseboard, efficient emitters, possibly some radiant)
Replace Bosch 151 combi with a 65k/btu combi
Add more baseboard OR add efficient emitters OR both
Your wisdom and guidance is greatly appreciated. Thank you all for the help you have provided thus far.