I've had several conversations here and elsewhere about open vs. pressurized storage. My conclusion is that the big limitation of open storage is that you have a heat exchanger in between the boiler and storage, and that heat exchanger transfers less heat per minute as storage heats up. Eventually, you can't transfer the full output of the boiler and you start to idle.
Here's a screen shot from this evening. I reloaded at about 7:30, and the combustion temp climbed quickly to my setpoint of 1200 (divided by 10 here to fit on the screen). The combustion fan does a nice job of holding it right there - the spikes are purge cycles.
After a while both the top and bottom of storage have risen to the point that the boiler outlet reaches 190 - my 'overheat' point. I drop the target combustion temp to 700 and dump heat to the main floor for a few minutes until the outlet drops to 185. This will repeat for the rest of the burn.
With pressurized storage and decent stratification, I'd see nice low return temps until storage was almost completely full.
![Open Storage Limitations Open Storage Limitations](https://www.hearth.com/talk/data/attachments/128/128149-3e6a1c47d28042bb6ecc430ae1a497d3.jpg)
Here's a screen shot from this evening. I reloaded at about 7:30, and the combustion temp climbed quickly to my setpoint of 1200 (divided by 10 here to fit on the screen). The combustion fan does a nice job of holding it right there - the spikes are purge cycles.
After a while both the top and bottom of storage have risen to the point that the boiler outlet reaches 190 - my 'overheat' point. I drop the target combustion temp to 700 and dump heat to the main floor for a few minutes until the outlet drops to 185. This will repeat for the rest of the burn.
With pressurized storage and decent stratification, I'd see nice low return temps until storage was almost completely full.
![Open Storage Limitations Open Storage Limitations](https://www.hearth.com/talk/data/attachments/128/128149-3e6a1c47d28042bb6ecc430ae1a497d3.jpg)