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... in with the new.
Burnham V34 SN 7551110 with a Frankenburner that might have started life out as a Carlin, but only the original frame has not been replaced. It has 1.0GPH nozzle and was last measured at 70% efficient. That may be an overstatement. Has a tankless coil. Converted to cold start two years ago, no leaks. This beast has had a long life.
3200 sq ft "cottage" built in 1919 in Metrowest of Boston. Design temperature 0F.
Three heating zones with roughly equivalent loads, two with 1/6 HP circulators, one with 1/25 hp. All circulators on the return. Total radiation is ~140Mbtu/hr.
Potable water circulator through tankless coil and 50G electric water heater (no electrical hookup to elements) as a "booster" tank. Relay system to call for heat with top thermostat, end call when bottom thermostat is satisfied. This keeps a single guy in hot water by firing for less than 1/2 hour every two days. Under 75 gallons of oil from late May to early October.
Honeywell AQ-2000 control with Honeywell communicating thermostats and ODR controlling all four circulators and boiler via aquastat on boiler. Aquastat is really just functioning as a combination burner relay and high limit safety.
Yesterday nature gave me a chance to compute the building's heat loss. There was a heavy overcast with snow and near constant 13F outside temperature. I set all of the t-stats to 66 and waited for the building temp to stabilize. Over the course of 190 minutes the burner was on 94 minutes and off 96. The average boiler temperature when the burner turned off was 146. The ODR was setting the high limit to 155-157, but it never got there, 151 was the highest I saw. By the end of the test the AQ had synchronized the heating zones so that all three circulators would start at the same time.
Oil burned at 1GPH with 70% efficiency means the output of the boiler is ~98Mbtu/hr as I figure it. The On/Off ratio of 94:96 means the burner was on 49.5% of the time for an average loss of 48.5Mbtu/hr. That was a 53 degree rise. Normalizing that to a 65 degree rise I get a building loss of 59Mbtu/hr. Please correct me if I got the arithmetic (or concepts) wrong.
I want to split each zone in two to get to six zones. The house lies east/west with a large number of windows to the south and north. Each floor of the original house is one zone (one feed on the north, one feed on the south, with each floor having a common return. A large addition has two distinct areas, an open kitchen/family room and a small laundry/mudroom. In addition, I would like to have radiant heat in the two bathrooms (6'x8' stacked, one on each floor).
Here is what I think I want. A high efficiency boiler (condensing?) with an output ~75Mbtu/hr using either a buffer tank and flat plate HE for the booster or a reverse indirect (which seem to be disappearing) for DWH. I would use a mixing valve controlled by the AQ2000 to supply the building zones with the low limit set to 90F and high at 180. The buffer/reverse indirect would be the load on the boiler. Both the boiler circulator and the system circulator will be DT controlled.
If I go the reverse indirect route, I would probably use the smallest available. I don't know how I would size a buffer tank.
Any advice, comments, corrections, jokes etc will be most welcome.
OK, I have this written, now to prove that I might be a human.