THLOAD: Thermal load analysis

Function

The block THLOAD (FB483) calculates the thermal load state, with the help of heating and cooling demand signals as well as room and outside temperature, which can estimate the thermal demand of a room or zone. The thermal load condition can be used to take advantage of available or less expensive energy sources for heating and/or cooling. For example, the calculated load condition can be used by blinds control to take passive advantage or solar heat or protect the room against solar heat. THLOAD_SiUn (FB483), THLOAD_UsUn (FB788)

Functioning

The following functions are integrated in the block:

On-going logging of heating demand [HDmd], cooling demand [CDmd] as well as room temperature [TR] and the room temperature comfort setpoints [SpHCmf] and [SpCCmf] over time period [TiPrd] (gliding timeframe). Logging is at a fixed interval of 15 minutes.
Determines recent heating demand [RctHDmd], recent cooling demand [RctCDmd] and the number of demand changes [DmdChg] within the time period [TiPrd]. [RctHDmd] and [RctCDmd] are set based on the minimum demand time [TiMinDmd].
Calculates over the time period [TiPrd] the minimum room temperature difference for heating [DTRH] between room temperature [TR] and heating setpoint Comfort [SpHCmf] as well as minimum room temperature difference for cooling [DTRC] between the cooling setpoint Comfort [SpCCmf] and room temperature [TR].
Calculates the thermal load condition [ThLdCnd]: Enables [EnDmdCal], [EnTRCal] and [EnTOaCal] can specific whether the thermal load condition is based on demand signals, room temperature and/or outside temperature.

Step	Process
1	Limit input signals to reasonable value ranges, in particular: The minimum demand time [TiMinDmd] is limited to ≤ [TiPrd]. The room temperature limit for forcing unloads [TRUnld] is limited to ≥ [TRLd]. The outside temperature limit for forcing unloads [TOaUnld] is limited to ≥ [TOaLd].
2	Calculate heating demand within the past time interval [TiPrd]: The time period for recent heating demand [TiHDmd] is calculated, i.e. the time within [TiPrd], during which [HDmd] = Yes. For [TiHDmd] ≥ [TiMinDmd], the recent heating demand is set to [RctHDmd] = Yes.
3	Calculate cooling demand within the past time interval [TiPrd]: The time period for recent cooling demand [TiCDmd] is calculated, i.e. the time within [TiPrd], during which [CDmd] = Yes. For [TiCDmd] ≥ [TiMinDmd], the recent cooling demand is set to [RctCDmd] = Yes.
4	Determine the minimum room temperature difference heating [DTRH] between the room temperature [TR] and heating setpoint comfort [SpHCmf] within the past time interval [TiPrd] for times during which [TRVld] = Yes: [DTRH] is positive if [TR] was always greater [SpHCmf] during [TiPrd] (for times where [TRVld] = Yes). [DTRH] is negative if [TR] was always less than [SpHCmf] during [TiPrd] (for times where [TRVld] = Yes). For [TRVld] = No during the entire period [TiPrd], [DTRH] is set to = 3.402822E+38.
5	Determine the minimum room temperature difference cooling [DTRHC] between the cooling setpoint comfort [SpCCmf] and room temperature [TR], during the past time period [TiPrd], for times where [TRVld] = Yes: [DTRC] is positive if [TR] was always less than [SpCCmf] during [TiPrd] (for times where [TRVld] = Yes). [DTRC] is negative if [TR] was always greater than [SpCCmf] during [TiPrd] (for times where [TRVld] = Yes). For [TRVld] = No during the entire period [TiPrd], [DTRC] is set to = 3.402822E+38.
6	Calculate thermal load conditions: The thermal load demand condition [LdDmdCnd] represents the load condition based exclusively on heating and cooling demand signals (for [EnDmdCal] = Yes), for calculation, see The thermal load condition room temperature [LdTRCnd] represents the load condition based exclusively on the room temperature (for [EnTRCal] = Yes); for calculation, see The thermal load condition outside temperature [LdTOaCnd] represents the load condition based exclusively on the outside temperature (for [EnTOaCal] = Yes); for calculation, see The thermal load condition [ThLdCnd] represents the total load condition based on heating and cooling demand signals (for [EnDmdCal] = Yes), room temperature (for [EnTRCal] = Yes) and the outside temperature (for [EnTOaCal] = Yes), for calculation see

Determine number of demand changes [DmdChg]

For the illustrated example, [DmdChg] = 3.

The number of changes between heating and cooling demand within the time period [TiPrd] is provided at [DmdChg]. It also counts changes when no heating or cooling demand exists between heating and cooling demand phases. If both heating and cooling demand exists simultaneously, it is counted as a demand change once every 15 minutes.

Determine room temperature differences heating and cooling [DTRH]/[DTRC]

(Temperature differences between past room temperature comfort setpoints and past room temperatures).

The room temperature setpoints are constant on Comfort in the graphic. They are considered if they change.

Calculation of thermal load condition demand [LdDmdCnd]

The thermal load demand condition [LdDmdCnd] represents the load condition based exclusively on heat and cooling demand signals (for [EnDmdCal] = Yes). For [EnDmdCal] = No, [LdDmdCnd] is set to neutral or to [SbstNeut].

[LdDmdCnd] is used to estimate the thermal load condition with the help of present and past heating and cooling demand signals. The last 24 hours are generally used ([TiPrd] = 24h):
This demand is supported and set to [LdDmdCnd] = Load, if within [TiPrd] only heating demand exists ([RctHDmd] = Yes, [RctCDmd] = No).
This demand is supported and set to [LdDmdCnd] = Unload, if within [TiPrd] only cooling demand exists ([RctHDmd] = No, [RctCDmd] = Yes).
Demand is unclear and [LdDmdCnd] = Neutral, if within [TiPrd] neither heating nor cooling demand exists ([RctHDmd] = No, [RctCDmd] = No).
It distinguishes various cases if within [TiPrd] both heating and cooling demand existed ([RctHDmd] = Yes, [RctCDmd] = Yes):

If present demand is only heating ([HDmd] = Yes, [CDmd] = No), the present demand is supported and [LdDmdCnd] = Load.
If present demand is only cooling ([HDmd] = No, [CDmd] = Yes), the present demand is supported and [LdDmdCnd] = Unload.
If [EnDmdChg] = No and no present demand exists for either heating or cooling demand, it is set to [LdDmdCnd] = Neutral.
If [EnDmdChg] = Yes and no present demand exists for heating or cooling, [LdDmdCnd] is set based on demand changes: [DmdChg] = 0 or [DmdChgExpt] = 1 or [TiRec] < [TiPrd] is set to [LdDmdCnd] = Neutral. Otherwise, it is assumed that the upcoming demand corresponds to the opposite of the last demand (demand changes alternatively between heating and cooling) and [LdDmdCnd] is set accordingly.

DmdChgExpt (Exception to demand change calculation): (i) Both heating as well as cooling demand within the same 15 minutes during [TiPrd]; (ii) Phases with no demand between heating demand phases during [TiPrd]; (iii) Phases with no demand between cooling demand phases during [TiPrd].

Calculation of thermal load condition room temperature [LdTRCnd].

The thermal load condition room temperature [LdTRCnd] represents the load condition based exclusively on room temperature [TR] (for [EnTRCal] = Yes). For [EnTRCal] = No, [LdTRCnd] is set to neutral or to [SbstNeut].

[LdTRCnd] is used to forecast thermal load condition with the help of past room temperatures. The last 24 hours are generally used ([TiPrd] = 24h):

[LdTRCnd] = Load if the room temperature [TR] is valid [TRVld] = Yes and less than [TRLd].
[LdTRCnd] = Unload if the room temperature [TR] is valid [TRVld] = Yes and greater than [TRUnld].
[LdTRCnd] = Unload if the room temperature (during valid phases) is in the upper comfort range ([DTRH] > [DTRC]).
[LdTRCnd] = Load if the room temperature (during valid phases) is in the lower comfort range ([DTRH] < [DTRC]).

Calculation of thermal load condition outside temperature [LdTOaCnd].

The thermal load state outside temperature [LdTOaCnd] represents the load condition based exclusively on outside temperature [TOa] (for [EnTOaCal] = Yes). For [EnTOaCal] = No, [LdTRCnd] is set to neutral or to [SbstNeut].

[LdTOaCnd] estimates the thermal load condition with the help of outside temperature [TOa]. The following rules (see graphic as well) apply for an outside temperature hysteresis [TOaHys] = 0:

For [TOaVld] = No, [LdTOaCnd] is set = [SbstNeut].
For [TOaVld] = Yes and [TOa] ≤ [TOaLd], [LdTOaCnd] is set to = Load.
For [TOaVld] = Yes and [TOa] ≥ [TOaUnld], [LdTOaCnd] is set to = Unload.
For [TOaVld] = Yes and [TOaLd] < [TOa] < [TOaUnld], where [LdTOaCnd] is set to = [SbstNeut].

The transition from forced state load to neutral state at [TOa] + [TOaHys] takes place if the outside temperature hysteresis [TOaHys] > 0; and the transition from forced state unload to neutral states takes place for [TOa] - [TOaHys].

A different selection of the outside temperature [TOa] can make sense depending on the application, for example:

The actual outside temperature used for the heating curve function.
The average of the outside temperature of a past time interval.
The present measured outside temperature.
A forecast value for outside temperature, e.g. from weather service.

Calculation of thermal load condition [ThLdCnd].

The thermal load condition [ThLdCnd] represents the load condition based on heating and cooling demand signals (for [EnDmdCal] = Yes), of room temperature (for [EnTRCal] = Yes) and the outside temperature (for [EnTOaCal] = Yes). This load condition [ThLdCnd] essentially unites the states [LdDmdCnd], [LdTRCnd] and [LdTOaCnd] under one common state.

The threshold values for room temperature [TRLd] and [TRUnld] have the highest priority, followed by forcing by threshold values for the outside temperature [TOaLd] and [TOaUnld]. The priority for [ThLdCnd] is determined by heating and cooling demand if the room temperature and outside temperature are within the threshold values. If there was no heating or cooling demand during [TiPrd]: [ThLdCnd] is determined based on room temperature [TR] and its comfort setpoints.

Note: [TR] and the associated [TRVld], [SpHCmf], and [SpCCmf] are polled and logged at 15-minute intervals. Thermal load calculations together with [TR] values are based on the logged data. Room temperature threshold values to force the thermal state is based on the last calculated values for [TR].

Inputs

Pin	Description
EnFnct	Enable function Yes: The function is enabled. No: The function is disabled.
TiPrd	Time period The function considers data (demand signals and room temperature signals) within a sliding, past timeframe for this period. The default value is 24 hours and the maximum value is 72 hours.
SbstNeut	Substitution value for load condition neutral The state can be substituted if the subsequently queried functions are unable to process the state neutral (through load or unload).
EnDmdCal	Enable demand calculation No: The calculation for the thermal load condition does not consider heating and cooling demand signals. Yes: The calculation for the thermal load condition considers heating and cooling demand signals.
EnDmdChg	Enable demand changing logic No: In the event of demand changes within [TiPrd], an arriving demand is not expected, i.e. [LdDmdCnd] is set = Neutral or [SbstNeut]. Yes: In the event of a demand changes within [TiPrd], an arriving demand is anticipated, i.e. [LdDmdCnd] is set opposite the past demand.
CDmd	Cooling demand Present cooling demand of the room or zone
HDmd	Heating demand Present heating demand of the room or zone
TiMinDmd	Minimum time duration for demand account The time is used to calculate demand: The heating demand is ignored if the sum of all heating demand times within [TiPrd] is less than [TiMinDmd]. The cooling demand is ignored if the sum of all cooling demand times within [TiPrd] is less than [TiMinDmd].
EnTRCal	Enable room temperature calculation No: The calculation of thermal load condition does not consider the room temperature. Yes: The calculation of thermal load condition considers the room temperature.
TR	Room temperature
TRVld	Valid room temperature Yes: The room temperature is valid, i.e. it can be used to calculate the thermal load condition. No: The room temperature is invalid, i.e. it cannot be used to calculate the thermal load condition.
SpCCmf	Cooling setpoint for comfort Room temperature setpoint for operating mode Comfort.
SpHCmf	Heating setpoint for comfort Room temperature heating setpoint for operating mode Comfort.
TRLd	Room temperature to force load The thermal load condition is forced to load state if the room temperature is valid and less than [TRLd]. It takes priority over the force using outside temperature limits [TOaLd] and [TOaUnld].
TRUnld	Room temperature to force unload The thermal load condition is forced to unload state if the room temperature is valid and greater than [TRUnld]. It takes priority over the force over outside temperature limits [TOaLd] and [TOaUnld].
EnTOaCal	Enable outside air temperature calculation No: The calculation of thermal load condition does not consider outside temperature Yes: The calculation of thermal load condition considers the outside temperature.
TOa	Outside temperature A different selection of the outside temperature can make sense depending on the application, for example: The actual outside temperature used for the heating curve function. The average of the outside temperature of a past time interval. The present measured outside temperature. A forecast value for outside temperature, e.g. from a meteorological service.
TOaVld	Outside air temperature valid Yes: The outside temperature is valid, i.e. it can be used to calculate the thermal load condition. No: The outside temperature is invalid, i.e. it cannot be used to calculate the thermal load condition.
TOaHys	Outside temperature for switching hysteresis Hysteresis for the threshold values [TOaLd] and [TOaUld] to prevent frequent switching of the thermal load condition based on deviating outside temperature.
TOaLd	Outside air temperature to force load The thermal load condition is forced to load state if the outside temperature is valid and less than [TOaLd]. It has a lower priority than the force over the room temperature limits [TRLd] and [TRUnld].
TOaUnld	Outside air temperature to force unload The thermal load condition is forced to unload state if the outside temperature is valid and greater than [TOaUnld]. It has a lower priority than the force using room temperature limits [TRLd] and [TRUnld].
Reset	Reset No: Normal mode. Yes: Data logging is restarted, all data logged by the function is deleted. The function automatically resets the input to No.

Outputs

Pin	Description
ThLdCnd	Thermal load condition The thermal load condition represents the thermal load of a room or zone while considering past heating and cooling demand (if [EnDmdCal] = Yes), past room temperatures (if [EnTRCal] = Yes), and the outside temperature (if [EnTOaCal] = Yes).
LdDmdCnd	Thermal load demand condition The thermal load demand condition represents the thermal load of a room or zone under sole consideration of past heating and cooling demand.
LdTRCnd	Thermal load room temperature condition The thermal load room temperature demand condition represents the thermal load of a room or zone under sole consideration of past room temperatures. Note: The calculation is based on the logged data.
LdTOaCnd	Thermal load outside air temperature condition The thermal load outside temperature condition represents the thermal load of a room or zone under sole consideration of outside temperatures.
RctCDmd	Recent cooling demand No: The sum total of heating demand times within [TiPrd] is less than [TiMinDmd]. Yes: The sum total of cooling demand times within [TiPrd] is greater than [TiMinDmd].
RctHDmd	Recent heating demand No: The sum total of heating demand times within [TiPrd] is less than [TiMinDmd]. Yes: The sum total of heating demand times within [TiPrd] is greater than [TiMinDmd].
TiCDmd	Time of recent cooling demand Sum total of cooling demand time within [TiPrd].
TiHDmd	Time of recent heating demand Sum total of heating demand time within [TiPrd].
DmdChg	Number of recent demand changes Counts all demand changes within [TiPrd] between heating demand and cooling demand. Changes are counted based on 15-minute intervals: It counts as a demand change if heating and cooling demand exists at the same time within a 15-minute interval.
DTRC	Room temperature difference coefficient Minimum difference {[SpCCmf] – [TR]} within [TiPrd], only for times where [TRVld] = Yes. [DTRC] ≥ 0: All valid room temperatures within [TiPrd] were less than or equal to [SpCCmf]. [DTRC] < 0: At least one valid room temperature within [TiPrd] were greater than [SpCCmf]. [DTRC] = 3.403E38: No valid room temperatures within [TiPrd].
DTRH	Room temperature difference heating Minimum difference {[TR] – [SpHCmf]} within [TiPrd], only for times where [TRVld] = Yes. [DTRH] ≥ 0: All valid room temperatures within [TiPrd] was greater than or equal to [SpHCmf]. [DTRH] < 0: At least one valid room temperature within [TiPrd] was less than [SpCCmf]. [DTRH] = 3.403E38: No valid room temperatures within [TiPrd].
TiDTRC	Time of minimum room temperature difference cooling Data and time where the (minimum) room temperature difference cooling [DTRC] occurred. Note: Functionality is disabled.
TiDTRH	Time of minimum room temperature difference heating Data and time where the (minimum) room temperature difference heating [DTRH] occurred.
TiRec	Time of recorded data [TiRec] < [TiPrd]: Parameterized record length [TiPrd] not yet fully reached. [TiRec] = [TiPrd]: Parameterized record length [TiPrd] fully reached.

Input values

Pin	Description	Data type	Standard value	Engineering unit or text group	Min.	Max.
EnFnct	Enable function	BOOL	1	No, Yes
TiPrd	Time period	TIME	T#1D_0H_0M_0S_0MS
SbstNeut	Substitution value for load condition neutral	INT	3	Load, Unload	1	3
EnDmdCal	Enable demand calculation	BOOL	1	No, Yes
EnDmdChg	Enable demand changing logic	BOOL	1	No, Yes
CDmd	Cooling demand	BOOL	0	No, Yes
HDmd	Heating demand	BOOL	0	No, Yes
TiMinDmd	Minimum time duration for demand account	TIME	T#0D_0H_15M_0S_0MS
EnTRCal	Enable room temperature calculation	BOOL	1	No, Yes
TR	Room temperature	REAL	20.0	°C	0.0	50.0
TR	Room temperature	REAL	68.0	°F	32.0	120.0
TRVld	Valid room temperature	BOOL	1	No, Yes
SpCCmf	Cooling setpoint for comfort	REAL	24.0	°C	0.0	50.0
SpCCmf	Cooling setpoint for comfort	REAL	75.0	°F	32.0	120.0
SpHCmf	Heating setpoint for comfort	REAL	21.0	°C	0.0	50.0
SpHCmf	Heating setpoint for comfort	REAL	70.0	°F	32.0	120.0
TRLd	Room temperature to force load	REAL	15.0	°C	0.0	50.0
TRLd	Room temperature to force load	REAL	59.0	°F	32.0	120.0
TRUnld	Room temperature to force unload	REAL	35.0	°C	0.0	50.0
TRUnld	Room temperature to force unload	REAL	95.0	°F	32.0	120.0
EnTOaCal	Enable outside air temperature calculation	BOOL	0	No, Yes
TOa	Outside temperature	REAL	20.0	°C	-50.0	80.0
TOa	Outside temperature	REAL	68.0	°F	-60.0	180.0
TOaVld	Outside air temperature valid	BOOL	1	No, Yes
TOaHys	Outside temperature for switching hysteresis	REAL	0.5	K	0.0	10.0
TOaHys	Outside temperature for switching hysteresis	REAL	1.0	°F	0.0	18.0
TOaLd	Outside air temperature to force load	REAL	0.0	°C	-50.0	80.0
TOaLd	Outside air temperature to force load	REAL	32.0	°F	-60.0	180.0
TOaUnld	Outside air temperature to force unload	REAL	30.0	°C	-50.0	80.0
TOaUnld	Outside air temperature to force unload	REAL	86.0	°F	-60.0	180.0
Reset	Reset	BOOL	0	No, Yes

Output values

Pin	Description	Data type	Standard value	Engineering unit or text group	Min.	Max.
ThLdCnd	Thermal load condition	INT	3	Load, Unload	1	3
LdDmdCnd	Thermal load demand condition	INT	3	Load, Unload	1	3
LdTRCnd	Thermal load room temperature condition	INT	3	Load, Unload	1	3
LdTOaCnd	Recent heating demand	INT	3	Load, Unload	1	3
RctCDmd	Recent cooling demand	BOOL	0	No, Yes
RctHDmd	Recent heating demand	BOOL	0	No, Yes
TiCDmd	Time of recent cooling demand	TIME	T#0D_0H_0M_0S_0MS
TiHDmd	Time of recent heating demand	TIME	T#0D_0H_0M_0S_0MS
DmdChg	Number of recent demand changes	INT	0	---	0	32767
DTRC	Room temperature difference cooling	REAL	20.0	K	-3.402822E38	3.402822E38
DTRC	Room temperature difference cooling	REAL	68.0	°F	-3.402822E38	3.402822E38
DTRH	Room temperature difference heating	REAL	20.0	K	-3.402822E38	3.402822E38
DTRH	Room temperature difference heating	REAL	68.0	°F	-3.402822E38	3.402822E38
TiDTRC	Time of minimum room temperature difference cooling	DATE_AND_TIME	DT#2011-1-1-0:0:0.0
TiDTRH	Time of minimum room temperature difference heating	DATE_AND_TIME	DT#2011-1-1-0:0:0.0
TiRec	Time of recorded data	TIME	T#0D_0H_0M_0S_0MS

Engineering

Typical interconnection

Pin	Use
CDmd	The block is informed of the present cooling demand of the room or zone via this input.
HDmd	The block is informed of the present heating demand of the room or zone via this input.
TR	The block is informed of the present room temperature via this input.
TRVld	The block is informed of the validity of the present room temperature via this input.
SpCCmf	The present comfort room temperature setpoint for cooling is interconnected to this input.
SpHCmf	The present comfort room temperature setpoint for heating is interconnected to this input.
TOa	The block is informed of the outside temperature via this input.
TOaVld	The block is informed of the validity of the present outside temperature via this input.
ThLdCnd	This output is further interconnected to the control logic on the electrical and mechanical installation with free cooling or heating, e.g. blinds or energy recovery.

Application

The function was developed for use on HVAC applications that include systems that support heating and cooling where operation is (nearly) free of charge. Such systems may include blinds or energy recovery units in a ventilation plant.

At present heating and cooling demand, the function ensures that such systems support present demand.

In addition, the function also allows for supporting such systems when no present heating or cooling demand exists.

Application examples

Energy efficient blinds control

Energy efficient blinds control are typically used in a room or building that is unoccupied. Blinds control contributes to minimizing heating and cooling demand for HVAC systems such as radiators or chilled ceilings. THLOAD can, for example, be configured as follows:

[TiPrd] = 24hr: Considers the previous day.
[SbstNeut] = Unload: If neutral is not supported, this state will be replaced with unload.
[EnDmdCal] = Yes, [EnDmdChg] = No, [TiMinDmd]= 15min: Recent heating and cooling demand is considered (continuing for at least 15 minutes), for changing heating and cooling demand within [TiPrd], a future demand is not anticipated.
[EnTRCal] = Yes, [TRLd] = 18 degC, [TRUnld] = 30 degC: Room temperature is considered, force of load and unload takes place at the appropriate room temperatures.
[EnTOaCal] = Yes, [TOaLd] = 12 degC, [TOaUnld] = 26 degC, [TOaHys] = 1 K: The outside temperature is considered, force of load and unload takes place at the appropriate outside temperatures.

Inputs for THLOAD can be interconnected as follows:

[CDmd] and [HDmd] are interconnected with the heating and cooling demand signals valid for the room or zone.
[TR] is interconnected with the room temperature. It may be a filtered room temperature.
[TRVld] is interconnected with the validity of the room temperature measurement. [TRVld] is eventually set to = No for exceptions, e.g. open windows (detected by window contacts).
[TOa] interconnected with the outside temperature or a filtered outside temperature.
[TOaVld] is interconnected with the validity of the outside temperature measurement.

The output [ThLdCnd] for THLOAD implements in one condition for blinds position – if energy-efficient blinds control is desired, for example, as follows:

If thermal load state is equal to load, blinds take advantage of solar radiation during the day (i.e. blinds should be opened as much as possible) and prevent heat flow from the room to the environment during the night (i.e. blinds should be closed as much as possible).
If thermal load state is equal to Unload, blinds prevent solar radiation during the day (i.e. blinds should be closed as much as possible) and permit heat flow from the room to the environment at night (i.e. blinds should be opened as much as possible).

Energy-efficient control of energy recovery in ventilation plants

Energy-efficient control of energy recovery in ventilation plants can be used, for example, for run-around coils or plate heat exchangers with bypass dampers. The goal is to minimize heat or cooling demand by controlling energy recovery. THLOAD can, for example, be configured as follows:

[TiPrd] = 24hr: Considers the previous day.
[SbstNeut] = Neutral: Supports the state neutral.
[EnDmdCal] = Yes, [EnDmdChg] = Ja, [TiMinDmd]= 15min: Recent heating and cooling demand is considered (continuing for at least 15 minutes), for changing heating and cooling demand within [TiPrd], a future demand is anticipated.
[EnTRCal] = No, [TRVld] = No: Room temperature is not considered.
[EnTOaCal] = No, [TOaVld] = No: The outside temperature is not considered.

Inputs for THLOAD can be interconnected as follows:

[CDmd] and [HDmd] are interconnected with heating and cooling demand signals of active heating and cooling elements in the ventilation plant (e.g. heating or cooling registers). Additional heating and cooling demand signals may eventually be considered from other heating and cooling equipment (e.g. radiators in the rooms) acting on the room ventilated by the ventilation plant.

Output [ThLdCnd] for THLOAD is then implemented as one condition for supply air temperature setpoint for energy recovery, for example, as follows:

The supply air temperature setpoint for energy recovery is set to the heating supply air temperature setpoint if the thermal load state is equal to load.
The supply air temperature setpoint for energy recovery is set to the cooling supply air temperature setpoint if the thermal load state is equal to unload.
The supply air temperature setpoint for energy recovery is set to the average of the heating supply air temperature setpoint and cooling supply air temperature setpoint if the thermal load state is equal to neutral.

Night cooling with mechanical ventilation

Night cooling with mechanical ventilation can be efficient if relatively cold outside temperature can be used at night to precool a building. Yet, setting control functions for night cooling is difficult: It is often unclear as to when night cooling is more beneficial than cooling during the day. In particular, night cooling should not cool unnecessarily. THLOAD can be used, configured, for example, as follows:

[TiPrd] = 24hr: Considers the previous day.
[SbstNeut] = Neutral: Supports the state neutral.
[EnDmdCal] = Yes, [EnDmdChg] = No, [TiMinDmd]= 15min: Recent heating and cooling demand is considered (continuing for at least 15 minutes), for changing heating and cooling demand within [TiPrd], a future demand is not anticipated.
[EnTRCal] = Yes, [TRLd] = 18 degC, [TRUnld] = 30 degC: Room temperature is considered, force of load and unload takes place at the appropriate room temperatures.
[EnTOaCal] = No, [TOaVld] = No: The outside temperature is not considered.

Inputs for THLOAD can be interconnected as follows:

[CDmd] and [HDmd] are interconnected with heating and cooling demand signals for active heating and cooling elements of the ventilation plant (e.g. heating and cooling registers) as well as additional heating and cooling demand signals from heating and cooling equipment (e.g. chilled ceilings in the rooms) acting on rooms ventilated by the ventilation plant.
[TR] is interconnected with the room temperature. It may be a filtered room temperature.
[TRVld] is interconnected with the validity of the room temperature measurement. In addition, [TRVld] is set to = No during the period for night cooling and then some time beyond, e.g. 1 hour.

The output [ThLdCnd] for THLOAD is then implemented as a condition for night cooling:

Night cooling is enabled if the thermal load state is equal to unload. Additional conditions must be met for night cooling to actually occur. The FB NGTC can be used here, for example.
Night cooling is not enabled if the thermal load state is not equal to unload.