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Retrofitted Gravity Hot Water designing further upgrades
I have a hot water radiator system, single loop (yep) gravity eureka tee based system with about a 4 in diameter main supply. The supply piping to the radiators actually get smaller the further along the loop run you get. All the iron pipe is in place and seems in pretty good shape. There is some small delay in heat at the last radiator but not all that much really. Originally it was a 1912 coal fired system (the original boiler is still in place). There was an expansion tank in the attic now removed and the system has been retrofit with a circulator, air eliminator, expansion tank, single zone with a bypass to the return side of the high mass cast iron Boiler (Dunkirk WPSB circa 2001 almost looks straight out of "Pumping Away"). The circulator is on the supply side. The Dunkirk has an aquastat set to 150 though originally the cast iron supply had an aquastat supplying at 180 (it is still there). The rads have an EDR around 90,000 BTU (at 150 F water) but the boiler is sized at 299kBTU (seems large to me there is also seems to be some short cycling). I still need need to do a heatloss calc for the house. I will also be doing some substantial upgrades to my enclosure.
It seems the folks who installed the systems and upgrades knew what they were doing. The last rad on the circuit is on the southeast and is in the kitchen. The thermostat is located on an interior wall on the north side of the house. The system actually works pretty well no real complaints, except I feel like my bill is a little high, there is a lot to be said for that.
So why post? I recognize that a 17 year old boiler may last a long time still but also may be on its last legs. I am also interested in possibly doing some upgrades for efficiency and even unconventional things. I think my system could run more efficiently and that my boiler could likely be downsized.
I think a reset on my system makes good sense.
I would consider installing TRVs as well. The house is historic (1912) so I do have some concerns about installing ugly TRVs and with threading on nice looking ones from Europe. Since it is a single loop eureka tee based system there is already bypass piping on the single loop. I also know that since it is a gravity retrofit some hot water will naturally head up the risers even when the TRV is shut. The circulator should minimize that some but not completely.
There are possibly two places that have had Rads removed that may benefit from being reinstalled. They were likely removed in the 30s.
Adding a loop to go directly to my domestic hot water (seems like at one time it did that but not currently set up that way).
Should I do a constant circulator system? What are the benefits/negatives for this on a gravity based retrofit with the type of tee I have?
I would consider installing a condensing/mod boiler. This seems like a no brainer, except I may want to go all electric for personal efficiency reasons.
I am particularly interested in possibly installing something like an air source heat pump or a residential reverse cycle chiller to deliver chilled water to my rads or pull a loop off (valved for the summer) something similar to commercial chilled beams.
So what do folks think? Anything I should just forget about outright? Anything I should do without question?