James Robins
New Member
Decided to post my problem here as I have benefitted greatly from Dana D's clear advice on various mod-con challenges posted, not to mention how others have chimed in, as well.
In late March 2021 I installed a Bosch Greenstar freestanding 151 with Laars 50 gal. double wall indirect (rebadged Bradford White - 43 gal actual capacity) heating a Victorian style 2,500 sq.ft - cast iron radiators. Turn down on the Bosch is 34kBTU/hr minimum, and eventually I learned of the poor thermal transfer on the DW tank - 23.5kBTU/hr. max at very high temps. Single wall is not allowed in my jurisdiction.
Many installer return visits involved the following limited remedies: 1) check valve on radiator send (solved the radiator runaway heat problem in shoulder heat season), 2) check valve on boiler return from DHW tank - did nothing for high temp - 142F at faucet - and slightly helped correct quick loss of hot water with moderate use; 3) move sensor from normal mid-tank to above tank with wrap - very little improvement; 4) add mix valve - turn up indirect heat to 142F, then 147F - with mix down to 125F at faucet. This is good in terms of finally getting adequate hot water storage and proper temp at faucet. HOWEVER, the DHW process still took at least 1:3o hours for daily recovery with excessive DHW short cycling to bring the reported temp up to satisfy the boiler. For the first hour, the DHW temp actually drops several degrees before slowly recovering. Inspector correctly predicted that in full heating season, too much heat will be lost due to the long draw, and full solution will need to be found.
The system is set up as a single zone and heating parameters of heat and DHW are not separated. It became apparent (at least to me) if there is no hot water demand going on, the sensor does not really know that the tank has fully heated... so the wasteful lengthy process of overheating is taking place. The hot water has two branches... and a total of about 70 feet of mostly 3/4" pipe in the basement alone. My proposed solution is the Taco SPE-1 set to pulse (5 min. on, 10 min. off) with the 006e3 variable circulator set on the low end. PEX return to the bottom of the tank. PEX at basement level only - evenly divided between the two branches so no balancing valve needed. So "storing" some heat in the pipes, flow giving the sensor an accurate temp reading, and bringing back warm water to the bottom of the tank might mitigate the recovery problem. I get the benefit of quicker hot water at the tap too. The installer plans to get more expert advice, but with current cold spell he's dealing only with emergency situations.
In the meantime, I decided to drizzle drip the laundry faucet on the 2nd floor so that overnight I don't get 5F extra temp drop (which was showing up on 15F nights)... just because the tank recharge was cycling so long. It worked. Even last night, at -12F (design temp) it all worked out fine. So, for several days now, I haven't seen the long tank recharge problem. I was fairly confident that this make-shift solution would work because I had been able to turn on the basement hot faucet and consistently halt the lengthy short cycling-recharge problem several times in a row before the truly cold weather arrived.
I'm not fond of the solution I've proposed (circulator pulse water draw endlessly) because such a complicated solution shouldn't be necessary for what seems like a fairly simple problem. Of course, dripping hot water out the laundry faucet isn't a practical long-term solution either.
Any expert advice will be greatly appreciated!
In late March 2021 I installed a Bosch Greenstar freestanding 151 with Laars 50 gal. double wall indirect (rebadged Bradford White - 43 gal actual capacity) heating a Victorian style 2,500 sq.ft - cast iron radiators. Turn down on the Bosch is 34kBTU/hr minimum, and eventually I learned of the poor thermal transfer on the DW tank - 23.5kBTU/hr. max at very high temps. Single wall is not allowed in my jurisdiction.
Many installer return visits involved the following limited remedies: 1) check valve on radiator send (solved the radiator runaway heat problem in shoulder heat season), 2) check valve on boiler return from DHW tank - did nothing for high temp - 142F at faucet - and slightly helped correct quick loss of hot water with moderate use; 3) move sensor from normal mid-tank to above tank with wrap - very little improvement; 4) add mix valve - turn up indirect heat to 142F, then 147F - with mix down to 125F at faucet. This is good in terms of finally getting adequate hot water storage and proper temp at faucet. HOWEVER, the DHW process still took at least 1:3o hours for daily recovery with excessive DHW short cycling to bring the reported temp up to satisfy the boiler. For the first hour, the DHW temp actually drops several degrees before slowly recovering. Inspector correctly predicted that in full heating season, too much heat will be lost due to the long draw, and full solution will need to be found.
The system is set up as a single zone and heating parameters of heat and DHW are not separated. It became apparent (at least to me) if there is no hot water demand going on, the sensor does not really know that the tank has fully heated... so the wasteful lengthy process of overheating is taking place. The hot water has two branches... and a total of about 70 feet of mostly 3/4" pipe in the basement alone. My proposed solution is the Taco SPE-1 set to pulse (5 min. on, 10 min. off) with the 006e3 variable circulator set on the low end. PEX return to the bottom of the tank. PEX at basement level only - evenly divided between the two branches so no balancing valve needed. So "storing" some heat in the pipes, flow giving the sensor an accurate temp reading, and bringing back warm water to the bottom of the tank might mitigate the recovery problem. I get the benefit of quicker hot water at the tap too. The installer plans to get more expert advice, but with current cold spell he's dealing only with emergency situations.
In the meantime, I decided to drizzle drip the laundry faucet on the 2nd floor so that overnight I don't get 5F extra temp drop (which was showing up on 15F nights)... just because the tank recharge was cycling so long. It worked. Even last night, at -12F (design temp) it all worked out fine. So, for several days now, I haven't seen the long tank recharge problem. I was fairly confident that this make-shift solution would work because I had been able to turn on the basement hot faucet and consistently halt the lengthy short cycling-recharge problem several times in a row before the truly cold weather arrived.
I'm not fond of the solution I've proposed (circulator pulse water draw endlessly) because such a complicated solution shouldn't be necessary for what seems like a fairly simple problem. Of course, dripping hot water out the laundry faucet isn't a practical long-term solution either.
Any expert advice will be greatly appreciated!