Economy

Function

The Economy statement decides on the most economical system operation for full and partial air conditioning systems.


For a full air conditioning plant, it calculates the control signal “Out” for energy recovery on the basis of actual outdoor air enthalpy, return air enthalpy, and demand.

In partial air conditioning systems, you can use this control icon for heat recovery with temperature comparison.

Economy makes decisions based on the following information:


Economy Operation

The following diagram illustrates the Economy function within a control loop:


The Economy control icon is composed of six internal modules:

  1. Heating or cooling need
  2. Humidify or dehumidify need
  3. Characteristic curve positioning
  4. Temperature recovery need
  5. Moisture recovery need
  6. Energy selection logic


The following diagram illustrates the relationships between the modules.


Fig. 156.  Economy statement components


Module 1 Heating/ Cooling


Based on the positioning signal from the basic temperature controller “In Temp Control”, this module decides whether there is a need for heating or cooling. To ensure stability for smaller deviations as well, the module establishes a hysteresis symmetrically around the zero point of the basic controller (50 percent). It calculates the amount of hysteresis as follows:

Hysteresis = P1 * 0,15

In other words, hysteresis is 15 percent of the working range.


Fig. 157.  Economy switching between heating/ cooling


Module 2 Humidify/ Dehumidify


Based on the positioning signal from the basic humidity controller “In Hum Control”, this module decides whether there is a need to humidify or dehumidify. To ensure stability for smaller deviations as well, the module establishes a hysteresis symmetrically around the zero point of the basic controller (50 percent). It calculates the amount of hysteresis in the same way as for Module 1 (15 percent of the working range).


Fig. 158.  Economy switching between humidifying/ de-humidifying


Module 3 Characteristic Curve


This module calculates the position of the characteristic curve of the Economy icon on the basis of outdoor air enthalpy and return air enthalpy in full air conditioning systems or on the basis of outdoor air temperature and return air temperature in partial air conditioning systems. The following conditions apply:


Gradient of the characteristic curve is positive if:


Gradient of the characteristic curve is negative if:


Where:


Fig. 159.  Economy characteristic curve


Module 4 Temperature Recovery

This module calculates a continuous positioning signal OutT from the basic temperature controller “In Temp Control”. If there are no limitations (that is, P4 is zero), the module outputs a positioning signal OutT from 0 to 100 percent.


Fig. 160.  Economy temperature recovery


If there is a limitation, the module converts it into a maximum limitation with mixed air damper operation and into a minimum limitation with regenerative transfer operation. Depending on the position of the characteristic curve from Module 3, the positioning signal is direct-acting or reverse-acting. Economy uses the maximum limit for the direct control of mixing, return, and fresh air dampers that operate with one motor.


Maximum limitation with mixed air damper operation:


Fig. 161.  Economy mixed air temperature operation with maximum limitation


Direct acting signal has a solid line. Reverse-acting signal has a dashed line.

Minimum limitation with regenerative transfer operation:


Fig. 162.  Economy mixed air temperature operation with minimum limitation

Module 5 Moisture Recovery

This module functions the same as Module 4 except that it calculates a signal from the humidity controller “In Hum Control”. The module outputs continuous positioning signal OutF.


Module 6 Selection Logic

This module evaluates the results from Modules 1 through 5 and decides whether to transmit positioning signal OutT or OutF to output “Out” of the Economy control statement. The following table summarizes module logic.


Table 111.   Economy logic decision table


Need for Heating


Need for Cooling


Reduce Humidity


Increase Humidity

HOA   >  hRA

hOA  <  hRA

Cooling more expensive

Heating more expensive

Cooling more expensive

Heating more expensive

0

1

0

1

MAX

MAX

MIN

MIN

0

1

1

0

MAX

MAX

MIN

MIN

1

0

0

1

MIN

MIN

MAX

MAX

1

0

1

0

MAX

MIN

MIN

MAX


A zero in the table indicates no need. A one indicates a need.

MAX indicates selection of the maximum of either the OutT or OutF signal for the “Out” signal.

MIN indicates selection of the minimum of either the OutT or OutF signal for the “Out” signal.

In a partial air conditioning system (only temperature control), this module just sends the OutT signal from Module 4 to output “Out”.

The following diagrams illustrate table output (MIN and MAX for temperature and humidity).


       MAX Temperature Controller

       (hOA > hRA)

       and

       MAX Humidity Controller

       (hOA > hRA)


>

Fig. 163.   Economy sequences cooling


       MIN Temperature Controller

       (hOA < hRA)

       and

       MIN Humidity Controller

       (hOA < hRA)


>

Fig. 164.   Economy sequences heating


Economy Example

The following diagram illustrates the use of the Economy control icon in a complete control loop.


Fig. 165.   Economy wire-sheet programming example


Note that the control loop must reverse the outputs from the temperature and humidity controllers before they connect to the Economy statement. The PID controllers reverse the outputs with the reversed connection of the measured values and setpoints (connect the measured values to the “In W” inputs and the setpoints to the “In X” inputs to reverse the signals)


Fig. 166.   Wire-sheet Icon

Fig. 167.   Property Sheet

Fig. 168.   Slot Sheet

Inputs and Outputs

Table 112.   Inputs

Inputs

Type

Functional description

In Temp Control

numeric

temperature controller

[-50 % through +50 %], for example, the output of a PID that controls basic temperature. Expect this inputs from direct-acting controllers, that is, controllers that react to a deviation with a change of the positioning signal in the same direction

In Hum Control

numeric

humidity controller

(-50 through +50 percent rh), for example, the output of a PID that controls humidity. This input is optional. Expect this inputs from direct-acting controllers, that is, controllers that react to a deviation with a change of the positioning signal in the same direction

In Outdoor Temp/ Enth

numeric

Outside air temperature/ enthalpy

Must be the same type of input, either temperature or enthalpy. You can use Enthalpy control statements to calculate outdoor air and return air enthalpies

In Return Temp/ Enth

numeric

Return air temperature/ enthalpy

Must be the same type of input, either temperature or enthalpy. You can use Enthalpy control statements to calculate outdoor air and return air enthalpies

In Temp Control

numeric

Enables and disables integral control action. When “In Integral En.” is zero, integral action in the master and cascade controllers is disabled and the integral sum is reset

In Enabled

boolean

If the input “In Enabled” is set to false disabled in the slot sheet, the output “Out” will be disabled and is set to the value “0”.


Table 113.   Outputs

Outputs

Type

Functional description

Out

numeric

Out” 0 through 100 percent


Parameter List

Table 114.   Parameter List

Description

Value Range

Default Value

Unit

Economy Range

The operation range of the ECO icon is located symmetrically around the zero point of the basic controller (50 percent)

0...100%

30%

%

System Type

0 = partial system (temperature only)

1 = full system (enthalpy control)

0/ 1

0

-

Control Device

0 = heat recovery wheel

1 = mixing air dampers

0/ 1

0

-

Minimum fresh air rate/ wheel speed

0…100 %

20 %

%

Energy Cost

0 = heating costs less than cooling costs

1 = cooling costs less than heating costs

0/ 1

0

-