Ventilation control by extract air, supply air, or room temperature for nested plants

The Ahu21x air handling unit contains an extract/supply air temperature cascade control.

This base solution can be adapted to the following applications with just a few modifications:

• Room air / supply air temperature cascade control
• Pure supply air temperature control
• Pure room temperature control

The following description is also valid for Ahu22x and Ahu23x.

Room air/supply air temperature cascade control

The room air temperature is used instead of the extract air temperature sensor to create a room/supply air temperature cascade control.

The following changes are required:

Manual adaptation of the program

In the program block (chart) "TSenSpCtl" of type "AhuTCtl21", move the connection to the input pin "T" of the program block (chart) "TClt" from the present value "PrVal" of the function block R_A "TEx" to the present value "PrVal" of the function block R_A "TR".

Room temperature control

Direct room temperature control may be desirable where there is no supply air temperature sensor or the plant only operates a single room. However, unintended high or low supply air temperatures can occur because there is no way to verify the supply air temperature.

The following changes are required:

Configuration

Use the Function configurator on "TSenSpCtl" or within "TSenSpCtl" on "TCtl" and change the alternative from "TCasCtr21" to "TSuCtr21".

Manual adaptation of the program

In the optional program blocks "Erc", "DmpMx", "Hcl", and "Ccl", connect the analog input for room temperature "TR" to the "TSu" of the function blocks R_A ("TSu" is replaced by "TR") and delete the analog input for the supply temperature (if it does not exist).

In the program block (chart) "TSenSpCtl" of type "AhuTCtl21", move the connection to the input pin "TSu" of the program block (chart) "TClt" from the prent value "PrVal" of the function block R_A "TSu" to the present value "PrVal" of the function block R_A "TR" and change the name of the calculated value object from "Present setpoint supply temperature" to "Present setpoint room temperature".

If there is a supply temperature sensor, the logic for its limitation can be implemented in "TSenSpCtl" (reading the supply air temperature and shifting the room setpoints).

Supply air temperature control

Direct supply air control may be desirable when the heating and cooling demand in the rooms is not supplied by ventilation, but in some other form, or when there is a requirement to provide a supply temperature with given parameters. In some cases, ventilation can support local heating/cooling at low and high outside temperatures.

The following changes are required:

Configuration

Use the Function configurator on "TSenSpCtl" or within of "TSenSpCtl" on "TCtl" and change the alternative from "TCasCtr21" to "TSuCtr21".

Manual adaptation of the program

Define the basic setpoints of temperature control [SpH] and [SpC] narrowly, e.g., at 20 °C and 21 °C.

Change the supply air temperature, based on the outside temperature (in the optional chart "SsnCmp", part of the option "Seasonal temperature compensation"), as follows:

• Between -10 °C and -15 °C, the supply air temperature increases continuously up to a maximum increase of 2 K. This supports the heating when the outside temperature is low.
• Between 30 °C and 34 °C, the supply air temperature decreases continuously to a maximum setback of 2 K. This supports the cooling when the outside temperature is low.

SpTR = Room temperature setpoint
SpTSu = Supply air temperature setpoint
PrSpShftHi = Output of the function seasonal temperature compensation
PrSpShftLo = Output of the function seasonal temperature compensation
TOa = Outside temperature