Pool Boiler Temperature Controller: Difference between revisions

Pool Boiler Temperature Controller (view source)

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Matt Parnell

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-== Background ==
+== Overview ==
-=== Pre-2022 Design ===
+The boiler temperature controller was created to enhance control and monitoring over the unit used prior to 2022 (a Johnson Controls C450CCN-3).
-In the prior design (pre-2022), a xxx provided two-stage burner control and over-temperature shutdown.
+During the 2021 season, there were multiple observed instances of the boiler operating at a sub-optimal temperature.  To prevent condensation, the boiler should operate at about 120 degrees or higher.  This is achieved by mixing inlet water (ideally at 80 degrees or warmer) with water recirculated from the boiler outlet.  This circulation pump is shown in the <b>Boiler Loop</b> section on page 2 of the [[Process Flow Diagram]].
-The new controller adds important features:
+The occurrence of low temperature was likely due to air trapped in the pump; a condition that is possible after air is introduced into the system when the [[strainer basket is cleaned|Cleaning the Strainer Basket]] or the [[filters are backwashed|Backwashing]].  The controller cannot prevent this condition, but it can detect it and alert the operator to minimize the impact of condensation.
-* Shutdown of both stages if the boiler temperature does not reach a minimum temperature threshold after a warm-up period.  This may occur if the recirculation pump fails, or is providing insufficient return water into the loop (due to air in the pump, improper valve position).  Operating the boiler at low temperature for an extended period may result in condensation, which may reduce the life of the boiler.
+The key features of the new controller are as follows:
+* Provides feedback of the boiler temperature via LCD display and via Modbus (RS-485) to the automation system.
+Like in the [[Pool Temperature Controller]], the following principles are used in its design:
+* The core function (temperature control) shall be performed by a proven, durable controller.  In this case, a Euroterm 3504 was chosen due to its enhanced logic control capabilities.
+* The automation system shall not be required for operation.  Failure of other components should have minimal impact upon its operation.
 == Theory of Operation ==
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 === Main Valve Active ===
-The main valve active input is energized via boiler terminal #30.  This is the same signal that provides "Boiler ON" feedback to the [[Pool Temperature Controller]].  When the main valve is active, the first stage is presumed to be operating.  If the main valve is not active some period of time after the low operator is activated, a boiler fault may be assumed.
+The main valve (MV) active input is energized via boiler terminal #30.  This is the same signal that provides "Boiler ON" feedback to the [[Pool Temperature Controller]].  When the main valve is active, the first stage is presumed to be operating.  If the main valve is not active some period of time after the low operator is activated, a boiler fault may be assumed.
 === High Operator ===
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 * All conditions for the low operator are met.
+* The main valve (MV) is active.
 * The boiler temperature is below the second stage threshold (timing rules apply).
+== Security ==
+TBD.
 == Eurotherm 3508 ==