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Storage

Note: This section is in progress. Content is not completed.

For any heating system utilizing wood or solar heat, heat storage provides improved convenience, comfort, and efficiency. Storage allows excess heat to be stored for later use. There are many types of heat storage, and many ways to add heat storage to a system. For this exercise, pressurized storage will be added as a heat source in parallel with the existing wood and oil boilers, and as a heat load in parallel with the existing zones.


Operation

When the wood boiler is generating more heat than the heating zones can absorb, the wood boiler temperature will rise. Without storage, the temperature will eventually reach the boiler's limit and the wood boiler controller will shut off the air supply. This causes 'idling' in which the fire is suppressed through lack of oxygen. This results in poor efficiency and creosote buildup in the chimney. With storage in the system, the storage zone valve can be opened allowing hot water to flow into the top of the storage tank. Cold water is removed from the bottom of the tank through the storage zone valve and back to the boiler.

If there is heat demand, the wood boiler is not hot enough, and the storage is hot enough to provide heat, then the storage circulator can be activated. Just like the wood and oil circulators, it will draw cool water from the return manifold. This will force hot water out the top of storage and through any zones that are calling for heat.

Controls

The control wiring is not shown in this diagram – it will be discussed in the next section. Both the storage circulator and the storage zone valve will be controlled by the NFCS. Storage adds some complexity to the control logic. There are now three possible heat sources, each with a different priority.

Desired System Behavior

Most of the rules that were developed earlier still apply. However, there are some changes and some new rules:

  1. If the wood boiler is hot, use the wood boiler to satisfy any demands.

  2. If the wood boiler is near its high temperature limit, open the storage zone valve.

  3. If there is demand and the wood boiler is not hot and the storage is hot enough, turn on the storage circulator.

  4. If storage is hot enough, disable the oil boiler.

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