Card 9 - THERMST Analyzer Thermostat Definition

This optional card specifies the parameters and options for defining a thermostat, heater controller, or fan controller.

Note:

Use improved CONTROLLER Card to model the thermostat, or heater controller, or fan controller.

Parameters: KODE, N1, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10

KODE

KODE is the code THERMST (or 10)

N1

N1 is the element number or group name of the thermostat's temperature sensor. If N1 is a group name, then the sensor temperature is considered to be the average of the N1 elements.

T1

T1 is the element number or group name where the thermostat's heater(s) are located. If T1 is a group name, a heater is placed on all the elements of the group.

T2

T2 is the thermostat's cut-in temperature. If T6 is PID, i.e., the thermostat acts as a PID controller, then T2 is the set point of the controller defined as a constant value or time-dependent table.

T3

T3 is the thermostat's cut-off temperature. T3 > T2 for heater control and T3 < T2 for cooler control.

T4

T4 may be:

  • T4 = 0 or blank: The thermostat controls the total heat input into the element T1, including additional heat loads not specified in T4.
  • T4 = value: It is a heat input, and the thermostat controls only this heat input to the element. If this value takes on the form Tn (e.g., T576), then n is a table number of a QNODE vs TIME table, specifying the time-dependent heat load value to the heaters.
  • T5 = FAN, then T4 is not a heat input, but rather a user-assigned thermostat ID.
  • T5 = ID, then T4 is not a heat input, but rather a user-assigned thermostat ID that can be referenced in a table operation.

T5

T5 is a mnemonic that characterizes the heat input T4 into element T1 if T4 > 0.

  • T5 = ABSOLUTE: The heat input value T4 is specified for each element T1.
  • T5 = AREA: The heat input value T4 * area(T1) is specified for each planar, beam, or lump mass element T1, and a heat input value of T4 * volume(T1) is specified for each solid element T1.
  • T5 = TOTAL: The elements of group T1 receive the total heat input T4.
  • T5 = FAN: The thermostat controls no heaters, and T4 is a user-assigned element ID.

T6

T6 may be the code PROPORTIONAL, in which case the heat input Q to the heaters follows the relationship:

or it may be blank, in which case a thermostat with a dead zone is modeled, and:

or it may be the code PID, in which case a proportional PID controller is modeled. The heat inputs Q to the heaters are calculated as follows:

T7

T7 is the gain if a PID controller is specified in T6, otherwise it is ignored.

T8

T8 is the integral constant if a PID controller is specified in T6, otherwise it is ignored.

T9

T9 is the derivative constant if a PID controller is specified in T6, otherwise it is ignored.

T10

T10 is the bias if a PID controller is specified in T6, otherwise it is ignored.

Code example

QNODE HEATERS 5
THERMST SENSOR1 HEATERS 70 72
$ A thermostat operating between temperatures 70 and 72 degrees turns ON and OFF
$ the heat load of 5 units to the elementS HEATERS. The temperature is sensed at
$ the element SENSOR1.
$
THERMST SENSOR1 HEATERS 70 72 100 TOTAL
$ A thermostat operating between temperatures 70 and 72 degrees turns ON and OFF a
$ total  heat load of 100 to the elementS HEATERS. The temperature is sensed at
$ the element SENSOR1. the individual elements will  receive heat inputs in
$ proportion to their areas.

Notes

If T6 is blank, the thermostat models a dead zone between the cut-in and cut-out temperatures, in which the ON/OFF state of the heater does not change. The heater is switched ON if the sensor temperature is below the cut-in temperature, and is switched OFF if the sensor temperature is above the cut-out temperature.

If T6 is PROPORTIONAL, then the thermostat acts like a proportional controller between the temperatures T2 and T3.

For cooler control, the negative heat load T4 must be of the form Tn, that references a table of QNODE versus TIME.

A number of options exist for handling thermostats in steady state, all defined on a Card 9 PARAM THERMOSTAT. If a PARAM THERMOSTAT is not present, one is automatically created with the AVGTEMP option. With this option, the heaters are defined to be SINK elements, with the average temperature of the cut-in and cut-out temperatures. This is an approximation, but it allows the calculation of heat flows into the heaters for the defined conditions.

Use the improved CONTROLLER Card to model the thermostat, heater controller, or fan controller.