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MIXIT may be set into overheat protection state via the following methods having equal priority:

Via external digital input at DI4

Via BACnet/Modbus at BO,3/00101.4

Via internal detection

The digital input may for example be used with an electrical bimetal switch as an extra layer of safety.

5.2

Signal flow diagram for the radiator and underfloor heating applications

The signal diagram for the underfloor heating application is shown in Figure 20 with the most relevant BACnet
object numbers. Their description and corresponding Modbus registers are listed in Table 7.

Figure 20: MIXIT used with floor heating application.

Action

BACnet

Modbus

Persistent setting?

Object for
setting

Object for
status

Set start

BO,1 = 1

BI,2

00101.1 = 1

00201.3

Set stop

BO,1 = 0

BI,2

00101.1 = 0

00201.3

Set overheat risk/
Overheat risk
detected

BO,3 = 1

BI,6

00101.4

00212 = 6

Set setpoint from
fieldbus

AO,0

AI,0

00102

00311

Temperature
control enabled

BI,1

00201.4

, supply temp.

AI,17

00314

, flow temp.

AI,16

00313

, return temp

AI,21

00322

Valve opening

AI,19

00319

Table 7: Most relevant datapoints associated with the underfloor and radiator heating applications.

The data points associated with the overheat protection are only relevant for the underfloor heating
application.

Summary of Contents for MIXIT

Page 1: ...MIXIT integration Guide Application guide JAN2022 ...

Page 2: ...gration of MIXIT in AHU control with MIXIT configured for the heating coil application 8 4 3 1 AHU sequencing with safety functions for heating coil 8 4 3 2 Signal diagram of AHU 12 4 3 3 Signal diagram of AHU with MIXIT configured with the heating coil application 14 4 4 Integration of MIXIT in AHU control with MIXIT configured for the radiator heating application 16 5 MIXIT with radiators and un...

Page 3: ...it can interface to MIXIT s fieldbus profile 3 Interface to a programmable controller that only supports analogue I O Use case 1 is the common situation for large systems Use case 2 is sometimes used in smaller buildings Use case 3 can be encountered if the integration task you face is for retrofit with an older BMS system If facing use case 1 sections 3 and 4 are of relevance if integrating with ...

Page 4: ...eld level reflects the case for an air handling unit AHU 1 1 Alternative option for interfacing MIXIT to a dedicated controller If MIXIT cannot be connected at the automation level in use case 2 for example because no spare analogue outputs are available or there is no BACnet MS TP or Modbus RTU fieldbus master available at automation level there is one additional way of interfacing MIXIT to the d...

Page 5: ...ture control loop of MIXIT The tuning of the dedicated control shall be slower than that of the MIXIT controller otherwise there is a risk that the overall control will oscillate and therefore the recommended option is to transfer the setpoints from the dedicated controller to MIXIT via the automation layer as shown in Figure 2 The source for the start stop signal that shall be given at a digital ...

Page 6: ...or BUS control this is a persistent configuration and shall only be set once The configurations are described by Table 2 Action BACnet Modbus Persistent setting Object for setting Object for status Register for setting Register for status Config set point from fieldbus MV 0 3 MV 0 00117 2 00117 Yes Set setpoint from fieldbus AO 0 AI 0 00102 00311 No Set bus control state BO 0 1 BI 0 00101 0 1 0020...

Page 7: ...s the fluid temperature flowing towards the coil The difference between the two are briefly described below In either case local setpoints sequencing and safety functions can be managed by the AHU controller The application selection is done via the Grundfos GO app 4 1 MIXIT AHU control of discharge air temperature heating coil application Figure 4 shows the simplified cascaded control loops assoc...

Page 8: ...water temperature that is supplied to the coil MIXIT controls therefore the water temperature TF out of the mixing loop according to the setpoint The AHU controller is responsible for setting the appropriate water temperature setpoint such that the air temperature leaving the coil is at its appropriate setpoint for TA Figure 6 Alternative AHU control loops with MIXIT The drawbacks of this way of i...

Page 9: ...r Figure 7 shows the state diagram of MIXIT with the integrated coil preheat and frost protection functions enabled The shown states are as follows READY If a start signal is not given MIXIT is in the READY state The pump is stopped and the valve is closed PREHEAT When a start signal is given the PREHEAT state is entered e g see section 4 3 1 2 TEMPERATURE CONTROL When the coil has been preheated ...

Page 10: ...th the preheat function disabled Even simpler if the internal frost protection function has also been disabled the only thing that can bring MIXIT to the frost state is either a signal on the fieldbus BACnet BO 4 Modbus 00101 7 or a signal at a digital input from a frost thermostat Figure 9 shows how to interface to MIXIT when the coil preheat function in MIXIT is enabled The example in the figure...

Page 11: ... Figure 9 MIXIT detects frost by the build in frost detection function It could also be signaled from the AHU control to MIXIT to go into FROST state This is done by setting frost risk BACnet BO 4 Modbus 00101 7 In that case MIXIT sets frost risk detected BACnet BI 7 1 Modbus 00204 4 1 as would happen when frost was detected by the build in frost detection function ...

Page 12: ...4 3 1 2 The build in preheat function The preheat function will warm up the coil until the water return temperature is above a certain threshold The threshold can only be set from Grundfos GO e g see Figure 10 The preheat function makes sure there is a flow in the shunt such that the return temperature sensor can be trusted That is it exists into the TEMPERATURE CONTROL state shown in Figure 9 whe...

Page 13: ...n for all is that heat recovery is needed and there are coils to control the temperature leaving the AHU It is for this temperature control MIXIT can be used In Europe air handling units often have a structure like the one shown in Figure 11 In the figure sensors and control loops relevant for control of the air temperature leaving the AHU are shown and sensors and control loops relevant for contr...

Page 14: ...controller have the following functions zone temp controller Calculates the reference for supply air temperature bases on the discharged air stream temperature and the outdoor temperature sequencing and defrost Decides which control loop runs and by which setpoint Priority for air heating is via the heat recovery system if such is present It also controls defrosting of the heat recovery system pre...

Page 15: ...st protection in the figure happens by a temperature switch with manual reset This can be used exclusively or alongside the build in frost protection function in MIXIT Figure 13 shows the same system but where setpoints and on off signals are read back and the flags for finished preheating of the coil BI 1 and frost risk detected BI 7 are used for appropriate sequencing with the rest of the AHU co...

Page 16: ...on fieldbus analogue signal internal variable Temperature control enabled BI 1 q air temp heating coil preheat and frost TF TS TR Valve opening AI 1 9 MI XI T AI 2 1 AI 1 7 AI 1 6 AI 2 7 AI 2 0 _ q ZONE TA Outdoor air Discharge air preheat temp controller air temp heating zone temp controller coil preheat and frost sequencing and defrost TZ TO TF TS TR Set start stop BO 1 Start stop read back BI 2...

Page 17: ...erature control loop Air inlet temperature control loops via heat recovery Setpoint for air inlet temperature control with coil Coordinating balance between heat regeneration and heat injection with mixing loop Defrosting of heat recovery system Controlled by MIXIT Direct control of the air temperature at the coils according to setpoint from AHU controller Safety functions o Heating coil preheat o...

Page 18: ...sor is integrated in the shunt so if using this datapoint from MIXIT to detect the preheat the water temperature towards the coil must be less than the water supply temperature to MIXIT otherwise there is no shunt flow and the instantaneous return temperature measured at the sensor in shunt is not correct in this case If using the heating coil application with the build in preheat function this pr...

Page 19: ...controller interaction with MIXIT when configured with the radiator heating application Figure 16 shows a signal diagram of MIXIT configured for the radiator heating application Table 5 list the associated control and status registers ...

Page 20: ...controller water temp control zone temp controller sequencing and defrost TZ TO TF TS TR on off BO 1 on off read back BI 2 setpoint AO 0 setpoint read back AI 0 damper ratio on off setpoint defrost TA valve opening AI 19 TZ TA reference AHU controller TZ reference AHU MI XI T signal available on fieldbus other signal internal variable AI 21 AI 17 AI 16 AI 20 _ ZONE 1 TA Outdoor air Discharge air T...

Page 21: ...aximum level This is to avoid triggering the overheat protection function in case of a small overshoot The control loop carried out by MIXIT is shown simplified in Figure 18 Figure 18 MIXIT control loop with setpoint limitation due to overheat protection function For example if the overheat protection function is set with a maximum level of 50 deg C and the given setpoint is above the 45 deg C MIX...

Page 22: ...s are listed in Table 7 Figure 20 MIXIT used with floor heating application Action BACnet Modbus Persistent setting Object for setting Object for status Register for setting Register for status Set start BO 1 1 BI 2 00101 1 1 00201 3 No Set stop BO 1 0 BI 2 00101 1 0 00201 3 No Set overheat risk Overheat risk detected BO 3 1 BI 6 00101 4 00212 6 No Set setpoint from fieldbus AO 0 AI 0 00102 00311 ...

Page 23: ... Pull DI5 up Input has internal pull up all applications Set setpoint CI01 Configure range and type in Grundfos GO all applications Temperature control enabled Relay 2 all applications Fault Relay 1 all applications Boiler setpoint CIO3 Voltage 0 10 corresponds to 0 100 deg C all applications Set overheat risk Pull DI4 up Input has internal pull down underfloor heating Remove overheat risk Pull DI...

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