.Buildings.DHC.Plants.Combined.Controls.BaseClasses.ModeCondenserLoop

Information

Tank charge fraction and rate of change

The tank charge fraction fraChaTan (-) is computed as the 5-minute moving average of the following expression: (∑_i (TTan_i - min(TTanSet)) / (max(TTanSet) - min(TTanSet)) / nTTan - fraUslTan) / (1 - fraUslTan), where TTan_i is the measurement from the i-th temperature sensor along the vertical axis of the tank, TTanSet are the tank temperature setpoints (two values for each tank cycle), nTTan is the number of temperature sensors along the vertical axis of the tank, fraUslTan is the useless fraction of the tank which is computed as follows: fraUslTan = ((max(TTanSet[2]) - min(TTanSet)) / (max(TTanSet) - min(TTanSet)) * hThe + hHee) / hTan, where hThe is the height of the thermocline (1 m by default) which is considered useless only during the second tank cycle, hHee is the upper and lower heel heights above and below the diffusers (1 m by default), hTan is the tank height (used as an approximation for the normal operating level of the tank at minimum temperature).

The rate of change of the tank charge fraction ratFraChaTan (h-1) is computed over several time periods (10, 30, 120, 240 and 360 min) as: ratFraChaTan(Δt) = (fraChaTan(t) - fraChaTan(t - Δt)) / Δt * 3600, where Δt is the time period in seconds.

Operating modes

Three operating modes are defined within Buildings.DHC.Plants.Combined.Controls.ModeCondenserLoop.

Charge Assist

The mode is enabled whenever any of the following conditions is true for 5 min. Any of the rates of change exceeds the values specified with the parameter ratFraChaTanLim. The tank charge fraction is lower than 97 % and 1 - fraChaTan > 0.08 * abs(nHouToWarUp - 2), where fraChaTan is the tank charge fraction and nHouToWarUp is the number of hours between the present time and the start time of morning warmup (4 AM by default). The 2-hour offset forces Charge Assist mode two hours before morning warmup if the tank is not fully charged.

The mode is disabled whenever none of the Enable conditions is true for 15 min, or the flow rate out of the lower port of the tank is positive for 5 min and the temperature at the bottom of the tank is higher than the maximum tank temperature setpoint minus 2 K for 5 min.

Heat Rejection

The mode is enabled whenever all of the following conditions are true. The Charge Assist mode is disabled for 5 min. The flow rate out of the lower port of the tank is positive for 5 min. The tank charge fraction is higher than 97 % for 5 min or the temperature at the bottom of the tank is higher than the maximum tank temperature setpoint minus 2 K for 5 min.

The mode is disabled whenever there is reverse flow through the cooling heat exchanger for 1 min.

Tank Charge/Discharge

The mode is enabled whenever neither Charge Assist nor Heat Rejection mode is enabled.

Revisions

• August 29, 2023, by Hongxiang Fu:
  Because of the removal of Logical.And3 based on ASHRAE 231P, replaced it with a stack of two Logical.And blocks. This is for #2465.
• February 24, 2023, by Antoine Gautier:
  First implementation.