I have a contractor who knows his stuff; one last decision to be made. With the Buderus GC 144/3 CI boiler net output of 54Kbtu, Turbomax 23 first hour rating is let's say 95 gallons, (since it's 88gal @50kbtu
I figure 8% more @54kbtu
.) continuous 80gal? That's with boiler water temp feed 160, return 140. 80deg rise from 40 to 120º output. What I'm trying to do is keep max boiler water temp 160, mix down to 120 for house. Not sure if that's what is figured for first hour 95gallons.
Issues overall are 1)enough dhw? 2)DHW recovery interferes with heating cycle? 3) Do I need the buffering of the Turbomax to stop short cycling or is standard indirect the simpler way to go here?
1-Ordinarily the most water the most water my wife and I use would use is back to back showers, say 15 minutes x 2 = 30 x 2.2 = 66gallons. We use cold water for laundry, so if we had a dishwashing load just before our shower supposedly that's another 4-6 gallons per cycle?, so it seems Turbomax would easily handle hw load--currently supplied by stand alone 50 gallon 30-40K btu hwh mixed down from 140 to 120 that's never run out of water. Conversely, after a long heat cycle in cold weather, maybe first hour rating is no longer 95gallons?
2- contractor states that on a cold day and after a DHW load, the heat cycle might be delayed a as long as an hour. Our house is decently insulated so an hour delay sounds like a lot, but is it? (I know the Buderus Logamatic 2107 allows 30 minute max dhw priority cycle...--we won't have the 2107 here.)
3-Heat Loss 38K @10º
design temp. 2 cast iron zones, basement baseboard. Note that at 40º outside temp, my overall house loss is 20K, Zone 1 8500Kloss/9200gain, Zone 2 4700Kloss/6600gain and Basement: 6900Kloss/4800gain. So Buderus net is 54Kbtu with smallest zone 2 calling for 4700kbtu loss. So when 54K net output his 3000-4000 btu small zone will short cycling be severe? Or on a more normal winter 20 degree day when smallest zone loss is 8100 when it alone calls for heat? And how much would the Turbomax 23 curtail any short cycling? Are we defining short cycling at more than three cycles per hour per zone?
(Note that this will be set up with ECM circ and three zone valves; piping is in series for each zone; also, contractor prefers hydrolevel control to Beckett Aquasmart? that the Buderus may ship with due to some reported issues with that.) Also my guess is that the 38K heat loss is really more like 30.