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

A common extract air temperature can be used to control to the average value of the room temperatures if the supply air is used for multiple rooms and there is no reference room suitable for room/supply air temperature cascade control.

The extract air temperature is used instead of the room temperature sensor to create extract/supply air temperature cascade control from plant example Ahu21.

① Basic setpoints temperature control
② Seasonal temperature compensation
③ Temperature cascade control
④ Supply air temperature control

The present room temperature setpoints [PrSpHiT] and [PrSpLoT] are calculated the same as for plant example Ahu21. The extract air temperature actual value is used instead of the room temperature actual value to calculate the present supply air setpoints [PrSpHiTSu] and [PrSpLoTSu] in the cascade controller Cas_Ctrl. Plant components Erc, Hcl, and Ccl are controlled as per the deviation between the supply air temperature setpoint and the supply air temperature actual value.

Direct room temperature control may be desirable where there is no supply air temperature sensor or the plant only operates a single room. Unintended high or low supply air temperatures may result, however, from a lack of ability to check the supply air temperatures.

The following modifications are required to use plant example Ahu21 for room temperature control:

① Basic setpoint temperature control
② Seasonal temperature compensation
④ Supply air temperature control

The high and low temperature setpoints [PrSpHiT] and [PrSpLoT], corrected by the seasonal temperature compensation, are used as the present room temperature setpoints.

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

Plant components Erc, Hcl, and Ccl are controlled as per the deviation between the room temperature setpoint and the room temperature actual value.

Direct supply air control may be desirable if heating and cooling demand in the rooms is not supplied via ventilation, but rather in another form. Ventilation can support local heating / cooling at low / high outside temperatures.

The following modifications are required to use plant example Ahu21 for supply air control:

① Basic setpoint temperature control
② Seasonal temperature compensation
④ Supply air temperature control

[PrSpLoTSu] and [PrSpHiTSu], corrected by the seasonal temperature compensated heating and cooling setpoint [SpH] and [SpC], are used directly as the supply air setpoints. Plant components Erc, Hcl, and Ccl are controlled as per the deviation between the supply air temperature setpoint and the supply air temperature actual value.

The basic setpoints of temperature control [SpH] and [SpC] are narrowly defined, e.g. at 1 [K] difference for creating a neutral zone between heating and cooling.

The settings for seasonal temperature compensation must be modified accordingly if additional support is desired for heating and/or cooling at a low or high outside temperature. This occurs on function block CHAR_LIN within the nested chart SsnCmpT (season temperature compensation).

Example

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

Modify supply air temperature, based on outside temperature, as follows:

• Between -10 [°C] and -15 [°C], the supply air temperature is increased continuously up to a maximum increase of 2 [K]. This provides support to heating at low outside temperatures.
• Between 30 [°C] and 34 [°C], the supply air temperature is lowered continuously down to a maximum setback of 2 [K]. This provides support to cooling at high outside temperatures.

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