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Wood Boiler Management

Introduction

While the EKO boiler has its own embedded control system that manages the circulator and combustion fan, there are several operating parameters that the embedded controller cannot manage:

  • To avoid condensation and boiler corrosion, the boiler inlet should always be above 140°F
  • Baseboards work best with temperatures as close to 180°F as possible.
  • The embedded controller will lower the fan speed as the boiler temperature appraoches 180°F, which reduces boiler output.
  • The embedded controller will turn off the circulator if the boiler outlet drops below 140°F.

Based on these considerations, boiler management has several goals:

  1. Keep boiler inlet and outlet above 140°F.
  2. If any baseboard zone needs heat, keep the boiler outlet just far enough under 180°F to keep the controller from reducing fan speed.

In order to accomplish these goals, the TS-7260 has several options:

  1. Open or close the boiler recirculation valve. This valve allows a portion of the water to recirculate through the boiler, raising the inlet and outlet temperatures.
  2. Open or close the hot tub zone valve. If the hot tub needs heat, this allows heat to be dumped as needed.
  3. Open or close the hot water heater zone valve. The hot water heater can be heated to 160°F. As with the hot tub, this allows heat to be dumped.
  4. Open or close the external storage tank zone valve. As with the hot tub and water heater, this allows heat to be dumped.

In this example, the lines on the graph are as follows:

  • Heavy black line - boiler output
  • Heavy magenta line - boiler inlet
  • Heavy dark green line - hot water heater
  • Heavy light green line - top of external storage tank
  • Top two fine black lines - top floor and main floor 'warm' (thermostats)
  • Bottom three fine black lines - Hot water tank zone valve, recirculate zone valve, and storage tank zone valve

    A fire is started a little after 4:00, and temperatures start to climb. At point A, the recirculation valve opens. Very shortly afterward, the EKO controller turns on the circulator pump (not shown on chart). This causes an immediate rapid drop in outlet temperature (heavy black line), and the EKO controller shuts off the circulator

    The outlet temperature starts to climb again, and the EHO turns on the circulator again. This causes a second drop, but this time the temperature stays high enought that the pump stays on.

    At point B, the inlet and outlet temperatures are high enough, and the TS7260 controller shuts off the recirc valve. This causes a brief drop in inlet temperature, but the temp stays above 140°F, so the recirc valve stays shut.

    Neither the top floor nor the main floor is warm, so heat is being circulated through the baseboards (not shown on graph). By point C, the boiler outlet has risen to the point where the EKO controller might drop the fan speed. To prevent this, the TS7260 opens the hot water zone valve, dumping heat into the hot water tank. A little while later, the boiler outlet is climbing again. At about 5:25, the TS7260 starts cycling the storage tank zone valve, dumping heat into the external tank as well.

    At point D, the main floor is warm. Heat is still being sent to the top floor, so the boiler temp has to be kept as hot as possible without causing the fan speed to be reduced. The TS7260 continues to cycle the hot water and storage tank zone valves.

    Just before point E, the hot water tank reaches the target temperature of about 158°F. The hot water zone valve is closed.

    At point E, the top floor is warm as well. The boiler does not have to be kept hot to maximize baseboard output, so the TS7260 dumps heat into the external tank with the exception of a top floor thermostat hiccup at about 7:15.