[MON_ERC] Energy recovery monitoring

Thermal stable operation

Efficiency is monitored if the energy recovery unit is in thermal stable operation [StblOp]. Thermal stable operation is determined based on static evaluations of temperature measured values.

The following conditions must be fulfilled:

• A temperature difference greater than 5.0 [K] (9 [°F]) between the extract air temperature [TEx] and the outside temperature [TOa].
• Nearly constant air temperature values for [TOa], [TEx], and [TAfErc].

The output [StblOp] is set to 1 as long as thermal stable operation is achieved.

Sensor placement

Three measured values are necessary to calculate energy efficiency: [TEx], [TOa] and [TAfErc]. [TAfErc] can be placed in either the supply air duct or extract air duct.

If [TAfErc] is located in the extract air duct, set the value for [SnlcTErc] to 2 (extract air). The following formula calculates efficiency:

If [TAfErc] is located in the supply air duct, set [SnlcTErc] to value 1 (supply air). The following formula calculates efficiency:

Consider the distance to the heating coil if [TAfErc] is positioned on the supply air duct. Position the sensor at least 150 mm from the heating coil to avoid the influence of heat radiation.

[TlcrFan] can be configured to consider the influence of the extract air fan on measuring the extract air temperature [TEx]. The value at [TlcrFan] is added internally to the value from [TEx].

The measured values of the temperature sensor are acquired every 60 seconds and then filtered to prevent short-term interference to temperatures.

The reheat value does not match the efficiency as indicated by the manufacturer since it (efficiency) is calculated from temperature measurements and sensor position. No definitive statement can be made on the absolute quality of energy recovery.

The calculated reheat value is influenced by the flow ratio of extract air to outside air. If the shares of extract air and the outside air are not equal, calculating the reheating can indicate higher or lower values.

Causes for a poor efficiency

Energy recovery operates at lower efficiency. This may mean:

• The energy recovery unit is iced, defective, dirty, or incorrectly connected.
• Poor air volume through the energy recovery unit.
• Imprecisely measured temperature downstream of the energy recovery unit.
• Bypass dampers reduce volume flow through the energy recovery unit. The MON_ERC function must be switched off with [EnFnct] = 0 when using bypass dampers.

The limit to efficient operation

The permissible limit value of efficiency [LmRd] is set with value 1, if all conditions are fulfilled for the time [DlyLmVio]:

• Efficiency [Efcy] is less than or equal to the preset efficiency limit value [EfcyLm].
• Thermal stable operation is achieved ([StblOp] = 1).
• The energy recovery unit is operating at full capacity ([CtlVal] = 100 %).

Enable and reset the energy recovery unit

If the input enable function [EnFnct] is set to 0:

• The output efficiency [Efcy] = 0.0
• The output stable operation [StblOp] = 0.0
• The timer for signal delay after a limit value violation [DlyLmVio] is reset
• The output efficiency limit value [LmRd] is not set to 0

If input [Reset] is set to 1, MON_ERC performs the same steps as if the enable function [EnFnct] is set to 0, with the following difference:

• The output limit reached [LmRd] is set to 0.
• The input [Reset] is automatically set to 0.
• Only the positive edge on the input [Reset] always sets back the output limit reached [LmRd] to 0.