Like the Ergomax E23 I mentioned several posts back:
They run about a grand at full retail, and won't give you anything like the full water heating performance you'd get out of a standard indirect. The aquastat on it has about 7F of hysteresis, and if you set it to ~130F and use it as the priority zone on the zone controller it'll do OK as a water heater with the -110 behind it, but would be pretty marginal with the -60.
When the other zones are calling for heat you can let the boiler output track an outdoor reset curve (at temps above 130F anyway), and the ~215 lbs of water in the E23 gives it a minimum burn time no matter how many zones are (or aren't) calling for heat. I suspect with the curves dialed in, most of the time you'd be looking at 130-135F water out, 115-120F water back from radiation, which would still be into the 90s for AFUE. When only the ErgoMax is calling for heat it'll be condensing whenever there's actual water being drawn, but at the end of the burn you'd be running 85-88% thermal efficiency.
You'll need to watch the max delta-T on the boiler when you set up the system design and flows with one of these. If you set the output of the boiler to 180F for the "priority" call from the E23, and it's average temp is about 125F, the bottom of the tank could be under 120F. I'm not sure what the max delta is on the TT Solo is, but I suspect it's not rated for 60F+. Whatever that is, respect it, assume that under heavy DHW draws the water entering the boiler will be 10-15F below the aquastat setpoint, so if the spec is 40F max, and the E23 is set to 130F, program the boiler to deliver no more than 155F water, and design the flow rate on the loop to ~3-4gpm. At 3 gpm on the loop with a 40F delta it can deliver the full ~60,000BTU/hr, and you can take reasonably long 2 gpm showers despite the fact that it's only a 26 gallon tank, but you might bust over the max delta-T on high-rate tub fills. It's not ideal by any means.
Like I said, there's a lot of crayon-on-napkin math to designing the system, and it may be easier to just use a bargain-basement $200 40 gallon electric hot water heater (not wired up) as a buffering hydraulic separator, and set up the boiler flows to run at pretty much a minimum-modulation, unless it's not keeping up with the heating loads. You can then just run it under outdoor reset control with the floor at about 120F (below which the heat output of fin-tube is pretty non-linear), with little risk of stressing the boiler with excessive delta-T the way it's technically possible with "reverse indirects" like the E23.
There's lots of tweaking and dialing-in to be done to max out the efficiency once it's installed, no matter how it's configured.
And you're still better off running all of the numbers a couple of times before doing any more plumbing on the system or buying any more hardware. This includes developing realistic whole-house heat load calculations, and measuring the radiation per-zone. That will all be necessary for figuring out a reasonable starting point on the reset curves, and will tell us whether even the smaller boiler would need to be buffered.
They run about a grand at full retail, and won't give you anything like the full water heating performance you'd get out of a standard indirect. The aquastat on it has about 7F of hysteresis, and if you set it to ~130F and use it as the priority zone on the zone controller it'll do OK as a water heater with the -110 behind it, but would be pretty marginal with the -60.
When the other zones are calling for heat you can let the boiler output track an outdoor reset curve (at temps above 130F anyway), and the ~215 lbs of water in the E23 gives it a minimum burn time no matter how many zones are (or aren't) calling for heat. I suspect with the curves dialed in, most of the time you'd be looking at 130-135F water out, 115-120F water back from radiation, which would still be into the 90s for AFUE. When only the ErgoMax is calling for heat it'll be condensing whenever there's actual water being drawn, but at the end of the burn you'd be running 85-88% thermal efficiency.
You'll need to watch the max delta-T on the boiler when you set up the system design and flows with one of these. If you set the output of the boiler to 180F for the "priority" call from the E23, and it's average temp is about 125F, the bottom of the tank could be under 120F. I'm not sure what the max delta is on the TT Solo is, but I suspect it's not rated for 60F+. Whatever that is, respect it, assume that under heavy DHW draws the water entering the boiler will be 10-15F below the aquastat setpoint, so if the spec is 40F max, and the E23 is set to 130F, program the boiler to deliver no more than 155F water, and design the flow rate on the loop to ~3-4gpm. At 3 gpm on the loop with a 40F delta it can deliver the full ~60,000BTU/hr, and you can take reasonably long 2 gpm showers despite the fact that it's only a 26 gallon tank, but you might bust over the max delta-T on high-rate tub fills. It's not ideal by any means.
Like I said, there's a lot of crayon-on-napkin math to designing the system, and it may be easier to just use a bargain-basement $200 40 gallon electric hot water heater (not wired up) as a buffering hydraulic separator, and set up the boiler flows to run at pretty much a minimum-modulation, unless it's not keeping up with the heating loads. You can then just run it under outdoor reset control with the floor at about 120F (below which the heat output of fin-tube is pretty non-linear), with little risk of stressing the boiler with excessive delta-T the way it's technically possible with "reverse indirects" like the E23.
There's lots of tweaking and dialing-in to be done to max out the efficiency once it's installed, no matter how it's configured.
And you're still better off running all of the numbers a couple of times before doing any more plumbing on the system or buying any more hardware. This includes developing realistic whole-house heat load calculations, and measuring the radiation per-zone. That will all be necessary for figuring out a reasonable starting point on the reset curves, and will tell us whether even the smaller boiler would need to be buffered.
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