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:
The following diagram illustrates the Economy function within a control loop:
The Economy control icon is composed of six internal modules:
The following diagram illustrates the relationships between the modules.
Fig. 156. Economy statement components
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
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
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
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
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.
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
|
|
|
|
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
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
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 |
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 |
- |