If a pressurized storage system is used, is a seperate dhw coil put into the storage tank? If the boiler is fired and the tank brought up to temp and then the boiler cools off would it not be inefficient to pump that hot water back to the boiler to heat the coil. In the case of a wood gun you would have to reheat the 80 gallon jacket and then that would disipated into the boiler room.
storage and dhw
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sgschwend
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Often a heat exchanger is used since storage is not potable water.
In concept or in practice a separate dhw heat exchanger coil is integrated into the storage system. It can be internal or external the choice can be made based on cost, material on hand, fabrication effort needed and certainly personal preference.
Since the storage system already must be setup for a hot water out port and cold water return port it is not that much more work to add moreconnections.
If your system is designed with a minimum of temperature drop you can also place the heat exchanger in series with the return line since you actually want a lower hot water temperature for the DHW anyway.
As to using boiler heat, I think it is a better approach to transfer the boiler heat to the storage. I do this by determining when the fuel is gone (automatically switching off the draft fan and the damper), then the boiler circulator is run until the boiler is at a lower temperature than the bottom of the storage, at which point the boiler circulator is automatically switched off.
In concept or in practice a separate dhw heat exchanger coil is integrated into the storage system. It can be internal or external the choice can be made based on cost, material on hand, fabrication effort needed and certainly personal preference.
Since the storage system already must be setup for a hot water out port and cold water return port it is not that much more work to add moreconnections.
If your system is designed with a minimum of temperature drop you can also place the heat exchanger in series with the return line since you actually want a lower hot water temperature for the DHW anyway.
As to using boiler heat, I think it is a better approach to transfer the boiler heat to the storage. I do this by determining when the fuel is gone (automatically switching off the draft fan and the damper), then the boiler circulator is run until the boiler is at a lower temperature than the bottom of the storage, at which point the boiler circulator is automatically switched off.
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