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Maximizing efficiency of a mod con question
I have been reading posts about maximizing condensation in all the new mod cons. I have only installed a few of them and both were on hi mass rad systems single zones so set was easy and we saw a great delta t with those and with the ord curve condensed most of the time. Both work great and were lochinvars piped p/s with the supplied 15-85 primary.
Last week I installed a new knight whn85 in my house. Combined heat loss calcs came in at: addition 16k, main 1st flr 16k, in law 12k, garage 10k, 2 basement futures have done a Heat calc yet. 55k btu not including basement, and a possible future hx for a hot tub...a bit of a dream...may not happen. So I chose a 85 based on the above....the 55 seemed too tight for any of the possible futures.
I figured on radiant from go but after getting pricing...there is no way I can swing the costs right now.
Due to costs I chose slant fin 30 oversized for lower temps. this was figured with sf chart using 260 for a multiplier.
47 ft in addition (running)...really sized for 140 due to limited wall space....but it is it's own zone and the house is an open floor plan so I plan to do 130f still for the rest. The addition would want 58 ft at 130f so I will be pushing a bit at design. With the open floor plan the fact we rarely if ever even come close to design I think it will be fine.
53ft 1st floor, 46 ft 2nd floor in law, 20k modine in garage with sep reset curve and target of 160 or so...will tweak for lowest. This will be on second heating zone with a sep reset curve and target. Unfortunately if this calls when the lower temp bb calls....it will get the higher temp water. Not a big deal as the garage heater will not be used to maintain high temps, but just to keep it above 50 when I am in the shop.
All bb zones are 130f target for 0 degree day. Today it is 34f and the addition zone is the only zone running ( nothing else has been piped for the rest of the system) and the target is 116f.
My issue is this: how hung up should I be on maximizing condensing with this set up?
I am becoming obsessed with it. I know that this hx can handle not being piped is ps if you can maintain the minimum flows in table 6-2 in the manual. I do not know how figure this out if someone could help me with that. Of course with such a little load (16k) and non design loads probably have that....the boiler is short cycling a bit even at 20percent. So I am sure I am not getting accurate first impressions but so far I have a concern on the delta tees I am getting. Piped per lochinvar specs just like diagram on page 40 sans the indirect. We heat hw via tankless.
Running at the above specs I am only seeing a 3-5 degree delta tee, again just on the addition loop 47ft sf30 116 target based on ord. When I piped this I piped a web stone purge bv between my close tees as a drain (low point). With the system pump at speed 1 (all pumps are grundfos 15-85s) and the primary at 1 (lochinvar states to use spd2) I get the 3-5 delta t. With speeds. Higher on either it narrows to 2-3.
Running with the ps ball valve shut....I get a solid 10 degree delta t.
So...at this point I am seriously regretting using pumps for all zones...I woulda shoulda coulda done a vs secondary aka system pump and zone valves. Too late now....I really don't want to change at this point all the near boiler piping is done incl. futures...wired etc.
Am I just obsessing here...? It is overshooting target a bit sometimes so with the ps piping that means 125 out, 122 back. Not what I had in mind designing a 130f 0degree system in the mid 30s. This is my own house and any tweaks, gains I learn can the be passed on to my customers. Partly why I am obsessed...I am the guy that likes....nah....needs to do the best job that I can do. I cannot even decipher whether delta t is of great importance or not. Excellent points have been made in both directions...ie uneven heating with large delta tees etc. I mean if my return temps are below 130 shouldn't I be condensing regardless of the delta? I did an experiment with the same run time with the ps open, verses shut thereby making it a push pull...with the boiler pump still running though...and with the latter and aforementioned delta of 10 I got an extra 1/3rd condensate produced for the same run time, same target.
I am unsure at this point wether the existing boiler pump will be oversized when all the zones get going or not. Right now it is very clear it is oversized resulting in hot supply water to go right back into the hx and lowering delta t to just 3-5 and causing less condensation.
Wow this is a lot...sorry for a long post. But this is we're I am at with all of this mod con stuff. There is much information out there and depending on who you talk to different answers.
I would like to know what recommendations you mod con experts have to tweak this system. If you think I should wait until all other zones are piped I think that may make the most sense and see how it is when there is enough demand to get above 20perc. Fire.
Lochinvar states the boiler pump can be variable. That would be awesome and I don't know why this isn't the standard. I have looked for pumps and can't find a suitable pump or info on how to set it up
Run as push...pull and shut bv between close tees...run with boiler pump off, or remove boiler pump.
Install smaller fixed spd boiler pump
Clock bv between tees for better delta t. A globe valve would be better.
Say the heck with it and run it....not in my nature...lol. Wish it were....would make my life a lot easier! Lol.
Lastly, how much does delta t really have on condensate with such low temps. The charts that I have seen seem to indicate anything under 130 return will be in condensate mode.