Been getting used to my new Modulating Condensing boiler for a week. Still not sure it is set up right. The system is as such...
Burnham Alpine 80 MBH 5:1 turndown w/ Taco 010 Boiler pump
Triangle Tube Smart 40 Tank-in-tank Indirect Hot Water (36gal DHW under 6gal boiler H2O)
Taco SR503 Zone controller w/ 3) Taco 007 zone circulators feeding IHW and downstairs/upstairs zones with baseboard convectors & Honeywell RTH 6000 T-stats
At first unit was short cycling (4 mins. on / 7 mins. off) before adjusting the ODR curve. Temps have been pretty mild here in PHL since New Years but I think I am pretty close. Currently set with “Outdoor low air temp” = 14*f , “High od temp” = 68*f, “Boiler low temp” = 100*f, “Boiler high temp” = 150*f. The ODR calculated setpoint is 134*f at 32*f outside. I am now getting about 7 min runs with 4 mins. off. Setpoint differences are at the factory default of 2*f above, 10*f below, although sometimes I will noticed on the status window that it will display 20*f below and then revert back to10. Can these be changed to help with the cycling? The system is modulating at about 40% when it is about 32*f outside, supply at 131*f, return at 120*f so I am condensing (Max. Eff. On” displayed). House is very comfortable, if not warm, at 68F.
I have put my t-stats on “Hold” and am not using a 3*f setback at night because the other day it took @ 4 hrs of constant running to recover, which I feel is a little long, and my daughter woke up to a cold house so some adjustment are still required. Even with these settings I notice the boiler is cycling but I think this is due to the thermostats as I can see the zone LED’s toggling. I have verified they are set up correctly with function code 1 = 2 “heating Only”, function code 5 = 3 “hot water system” . I have turned off the “Smart Responce” control thinking this was causing the cycling. There does not seem to be any “anticipator” or “swing” settings on these thermostats.
What are the best settings to start with for the IHW. I currently have DHW priority with a setpoint temp of 160*f. Is this too high? What should the tank T-stat be set at? I can always adjust the mixing valve to correct spigot temps. (We take mainly showers do not have large HW demands). A funny thing I did noticed was that when I have a Priority DHW call at the furnace that my zone pumps are still running. I know is not correct as they will be pushing 160* water in to the zones. The installers wired the DHW pump to the boiler contacts as opposed to the Taco zone controller. Is there a switch on the SR503 that needs to be set? Can I run a H2O T-stat wire in parallel to the zone controller so it knows when the DHW priority call is made?
Still not sure if the whole system is optimally piped, but that will be another post.