Need advice on reverse-indirect buffered modcon system design

LexMA02421

I'm a homeowner in MA (Bedford weather station) looking to convert from oil to gas. HW is indirect. I have 62mbh of baseboard radiation (at 180*), micro-zoned as 26/23/12, but boiler-based measurements indicate an actual design-day heat-loss of under 30mbh. I don't trust that last number enough to risk a boiler which cannot generate the full 62mbh. The current boiler is a System2000 firing 105mbh input, which has somehow withstood 28 years of short-cycling and is still flue-testing at 86%. I'm hoping for a gas system with even higher efficiency, in the manner BNL measures it (<a href="http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf">http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf</a>).



Also, I'm tired of seeing heating season reflected in my electric bill. I think that means ECM pumps, and my bank account says only as many as necessary.



Searching these forums has been a real education, though probably not the easiest way to get it. I think I can probe most of the right issues and understand most of the answers. Thanks a lot. I think I'll need it: The bids I've been getting for a gas system were all at or above my current firing rate, and never addressed trying to avoid short-cycling. I'm looking to do a collaborative installation where I roughly spec the system I want and find professionals who can execute using all the good practices that I'll never know. All I need to do is figure out what that optimal system is.



I'm hoping that the system can run most of the time in the range where baseboard temps, HW temps, and condensing come together. If my heat-loss data is right, I should be able to hold a comfortable design-day temperature with 140* water. And I think we would be comfortable down to 110* HW. It would be really neat if you bear out my thinking, because I would get a much better system at negligible increase in price over the usual bids (boiler, indirect, many 007 pumps). On the other hand, I do tend to overreach ….



I'm currently thinking modcon and buffer to get the efficiency I want. I like the Solo110 and the KNB081 for their self-cleaning and low-head HX. My gas company on the other hand is discounting the Alpine. I would lean toward the Knight because it can handle my maximum radiation but has a 16mbh turndown. The Solo would give me faster HW, but with only one full bath I don't think I need that.



I'm hoping to combine the buffer and HW by using a reverse-indirect. That would save me space, money, and standby-loss. I'm hardly being innovative here - this configuration has been in earlier forums (<a href="http://www.greenbuildingtalk.com/Default.aspx?tabid=53&aff=14&aft=74997&afv=topic">http://www.greenbuildingtalk.com/Default.aspx?tabid=53&aff=14&aft=74997&afv=topic</a> among other). I like the 4-port Ergomax (<a href="http://www.ergomax.com/New-Tanks.htm">http://www.ergomax.com/New-Tanks.htm</a>), but some have questioned its insulation and build quality. I'm not sure how to pipe a Turbomax . I think the 24-33 gallon sizes would give me enough buffering, but I could afford larger if you say that it is worth it. I've lost several electric HW tanks to galvanic corrosion at the copper-steel junction. Do these units avoid that problem? What is the current thinking about whether the SH secondary should pull from the top or bottom of the tank?



I know I need an ECM pump to reduce power use, and probably a smart pump to adjust for the varying active zones. But I have no idea how that translates into a choice of product. The Solo manual seems to indicate it can run with a single pump if a delP valve is used. Is that accurate and is it a good way to go? Does that also apply to the Knight, where the manual does not suggest it?



Finally, I'm a little insecure about the controls. I would like to go with digital setting and reading of HW temp. If I go with the Knight, can their HW sensor attach to a "foreign" tank? It seems to me that I can ignore the HW pump output since the boiler pump will come on and make HW for all calls, and that the Knight needs no additional controls.



I've learned a lot, but I'm still a newbie to hydronics and modcoms. Are my understanding and assumptions correct? Would it work? Are there better options? Are there some critical factors that I haven't mentioned which should really be specified? This is a niche case of all-baseboard and modest HW seeking efficiency. Please help.