Posted By Bisseti on 02 Apr 2010 04:20 PM
Thanks for your ongoing info Dana. Super helpful.
The water coming back to the boiler will be coming from the buffer tank in the reverse indirect set up (ergomax diagram you linked to) and straight back to the boiler with the indirect h20 set up? Do you think the reserve indirect set up would be best?
And the water temp/outdoor reset should be calibrated based on the length of baseboard. Meaning if I do get the +50 percent length, I could conceivably heat the apts with 120 degree heat on design day.
At build it solar.com, I calculated 20-25k/btu per hr heat loss for the 2 larger apt and about 10-12k for the smaller ones. That would add up to about 60 to 75k boiler. That seems pretty small, eh?
I did "bait" the "heat pro", but his bite was leary.
What were you using for an outdoor design temp? Those are credible numbers, if the place is decently insulated and very tight, but you'd hate to miss by 50%, and the B.I.S. program is about as crude as they come. HeatPro's IBR freebie is better, and there are others with more built-in sophistication, such as the
Warmly Yours calculator. Doing the room-by-room BTUs/room analysis is a necessary starting point for the radiation design, and may tell you whether you can get enough baseboard in there to run it at condensing temps.
But this is really left to a pro- somebody who is on the hook of designing it right and making it work once it's installed.
At 180F with a single cast-iron boiler the ErgoMax-centric buffer definitely works. If you're trying to squeak 95% efficiency out of a mod-con with 180F design-day temps it doesn't quite, but if the radiation is sufficient to deliver design-day heat at 130-135F you can beat 90% with an ErgoMax as the buffer. IIRC Peerless has a control board for the Pinnacle series mod-cons optimized for use with buffer tanks, which may be the right option if you go with a mod-con. I suspect the Munchkin Contender series load-sensing control (the dumbest version control that comes with all of them, not the zone control version that have outdoor temp sensing) can work well with a buffer tank too.
If you make the system a 4-zone off a mod-con with a separate "priority" zone for hot water you may be able to get a bit more efficiency out of a mod-con in heating mode if you can get the radiation temps down below 120F, which is lower than DHW temps. Using a single Ergomax as the indirect may still make more sense than 4 separate HW units if you go that route- the heat exchangers in the Ergomax can handle the flow, and you probably won't need to run it at more than 150F to serve 4 units if the boiler is over 100KBTU/hr out. If you're correct and you're in the 60-75KBTU design-day heat load range you may have to up-size the boiler a bit to serve enough hot water with 4 showers going. If it needs to be oversized for DHW, the modulating aspect of a mod-con and the keeps it from falling off an efficiency cliff, and going with the central buffer approach keeps the cycling losses down, even if you're only running 88% due to higher temps. There are many tradeoffs of cost/efficiency to be made- if hydronic design was simple, even
plumbers could do it.
Don't expect the definitive solution from a web-forum committee... But learn enough to keep 'em honest.
Start googling for NJ distributors for mod con boiler manufactures like Weil Mclain. Triangle Tube, Peerless, Burnham, Lochinvar, Slantfin, Munchkin, etc. then see if you can't get some recommendations for hydronic designers & installers in your area. (They may/may-not be the same people designing vs. installing.) You might be able to get some recommendations from ErgoMax too, but they're a pretty small outfit. The distributors know who is buying what in volume, and who complains about stuff all the time (an indication they probably doesn't know what they're doing.) "Plumbing & Heating" on the side of the truck or in the yellow pages isn't much of a credential, and you have to know quite a bit to detect all be the most eggregious of the duds. ANY heating contractor should provide their own room-by-room heat loss analysis (which rules out about half or two-thirds of them in my area right away), and they should be willing to provide a combustion-efficiency test as part of the punch-list when commisioning the boiler(s).