AIR-HANDLING UNIT (AHU) DESIGN GUIDELINE

1 Introduction and Notice

This manual provides guidelines and notices for the design and use of the AHU (Air Handling Unit) interface unit.

This guideline details various examples of typical applications for AHU controllers and their accompanying units. It should be used in conjunction with the PAC-IF013B-E/PAC-SIF013B-E installation manual and Modbus manual for correct operation.

This interface unit connects Mr. SLIM inverter outdoor units of MITSUBISHI ELECTRIC to local applications. Please check the following guidelines when designing the local system.

MITSUBISHI ELECTRIC does not take responsibility for local system design or failures (including outdoor unit failures) caused by local AHU and system design.

Conformity to regulations and laws must be confirmed on your system.

2 Basic Specifications and Connectable Outdoor Unit Models

2.1 Basic specifications of the interface unit

2.2 Connectable outdoor unit models

*1. Refer to "4. Function - System list".

3 System

The system can be configured using different step modes (Manual, Auto) and controls.

*1. It is recommended to select Intelligent multiple outdoor unit control. Design local AHU controller to ensure the following:

• Minimum capacity request should be 20% or more of total capacity.
• Operate all outdoor units when outdoor temperature is below -15 °C.

3.1 System configuration (Single outdoor unit)

(1-1) Manual step mode *1

Figure 3.1.1 illustrates a manual step mode system configuration. This mode involves an interface unit (1), a remote controller (2), an outdoor unit (3), various thermistors (4-7), an Air-Handling Unit (AHU) (8), and an AHU local controller (9). The system also includes a direct expansion (DX) coil (10), and local supply components like target air temp. thermistor (11), louver (12), air filter (13), heat recovery (14), and fan (15).

*1. Manual step mode: Variable capacity request signals for heat pump need to be calculated by the AHU local controller. The AHU local controller can send "Capacity steps" via non-voltage contact signals, analog signals, or Modbus signal to the interface unit. Operation mode can be set by remote controller, external input, DIP switch, or Modbus signal.

*2. If the outdoor unit is a PUHZ-SHW model, this thermistor is not needed.

(1-2) Auto step mode *3 & Supply air temp. control

Figure 3.1.2 depicts the Auto step mode with supply air temperature control. Similar to manual mode, it includes the interface unit (1), remote controller (2), outdoor unit (3), thermistors (4-7), AHU (8), and AHU local controller (9), along with DX coil (10) and local supply components (11-15).

*3. Auto step mode: In this mode, the outdoor unit's capacity step is automatically controlled to reach the target temperature. Set temperature and operation mode can be adjusted via remote controller, DIP switch, or Modbus signal.

Note: Auto change over function between cooling and heating mode is NOT available in this system.

*4. If the outdoor unit is a PUHZ-SHW model, this thermistor is not needed.

(1-3) Auto step mode *5 & Return/ Room air temp. control

Figure 3.1.3 illustrates the Auto step mode with return/room air temperature control. The system components are similar to the supply air control mode.

*5. Auto step mode: Similar to *3, capacity step is automatically controlled to reach the target temperature. Set temperature and operation mode can be set via remote controller, DIP switch, or Modbus signal.

Note: Auto change over function between cooling and heating mode is available ONLY when this system is selected and the input selection of capacity setting (DIP SW1 and SW6) is "No input (Auto step mode)".

*6. If the outdoor unit is a PUHZ-SHW model, this thermistor is not needed.

3.2 System configuration (Intelligent multiple outdoor unit control *1)

(2-1) Manual step mode (example)

Figure 3.2.1 shows an example of a manual step mode system configuration using intelligent multiple outdoor unit control (IMOUC). This setup involves multiple interface units connected to outdoor units, with one designated as the main interface unit connected to the AHU local controller and a remote controller.

*1. The interface system receives step request signals corresponding to the total capacity of outdoor units and automatically calculates the necessary capacity for each outdoor unit.

Note: This intelligent multiple outdoor unit control function is available only when Manual step mode is selected. Up to 6 outdoor units can be connected. Two different types of outdoor units (capacity and/or series) can be mixed, but connecting the same capacity outdoor units is highly recommended. Reference address setting on each outdoor unit is required. The interface unit connected to Ref. address 0 outdoor unit becomes the main interface unit. Connect the AHU local controller (Part No. 9) to the main interface unit. Connect ONE remote controller (Part No. 2) to the interface unit. Connect between interface units with a remote controller (daisy chain), with a maximum length of 500m.

*2. If the outdoor unit is a PUHZ-SHW model, this thermistor is not needed.

3.3 Operation range

(1) Operation range

Ensure operation is kept within the specified ranges:

(2) Set temperature range in Auto step mode *1

Note: *1. If the DX coil's capacity does not match the outdoor unit's capacity, the air temperature may not reach the set temperature, or ON-OFF cycling may occur. Design the DX coil to match the outdoor unit's capacity (refer to "6.2 Standard conditions"). *2. This function is available ONLY when capacity setting (DIP SW1 and SW6) is "No input (Auto step mode)" and return/room air temp. control is selected.

4 Function - System list

This section details various functions and their availability across different step modes, input types, and system configurations.

*1. As for system configuration, see the following page. *2. These functions are available ONLY with adaptable outdoor unit. Refer to "2.2 Connectable outdoor unit models". *3. Only reading is available.

Note on System Configuration Table: The table above lists various system configurations (Manual, Auto, Modbus) and their corresponding availability (✓) for different functions. The specific columns (A-F, Use, Not use) refer to different system setup types as detailed in the document.

4.1 Example of system configuration

The document illustrates several system configuration examples (A through F) showing how interface units, outdoor units, remote controllers, and AHU local controllers are connected.

• System A: Outdoor unit connected to Interface, which connects to AHU local controller.
• System B: Outdoor unit connected to Interface, which connects to AHU local controller and a Remote controller.
• System C (Manual step mode - IMOUC): Multiple outdoor units (Ref. address 0, 1, 2) connected via Interfaces to an AHU local controller. One interface also connects to a Remote controller.
• System D: Multiple outdoor units connected via Interfaces, each with a Remote controller, all feeding into an AHU local controller.
• System E: Multiple outdoor units connected via Interfaces to an AHU local controller.
• System F (Auto step mode - Group): Multiple outdoor units (Ref. address 0, 1, 2) connected via Interfaces to an AHU local controller. One interface also connects to a Remote controller.

5 Input and Output

5.1. Input and output

This table details the inputs and outputs for the interface unit, along with their availability.

*1. If connected outdoor unit is PUHZ-SHW model, it is not needed. (PUHZ-SHW models include high-pressure sensor instead.)

*2. This output is ON when compressor becomes OFF to protect outdoor unit because condition is out of operation range. (As for operation range, refer to "3.3 Operation range".)

*3. This output is ON more than one minute before defrost starts.

*4. This function is available ONLY with adaptable outdoor unit. Refer to "2.2 Connected outdoor unit models".

5.2. Requirements and guides regarding input, output, and settings

5.2.1 Requirements on capacity step input to the interface unit (Only manual step mode)

1. Do NOT input STEP 0 for 3 minutes after compressor is ON. (Keep compressor ON for 3 minutes at least.)
2. Regarding timing of capacity step changes, follow the note below. Note: Input next capacity step input after supply air temperature becomes stable. If this note is difficult to follow by local controller:
• The change must be within 5 steps in a single request with at least 5 minutes interval between every change.
• For 6 step changing or more (such as on start-up of operation), the interval between every change needs to be at least 10 minutes. (See figure 5-1.)

Figure 5.1 shows examples of capacity step changes over time. One graph depicts changes within 5 steps over 5-minute intervals, while another shows changes over 10-minute intervals.

5.2.2 Requirements and guides regarding defrost and pre-defrost signal

1. Do NOT input STEP 0 during defrost operation and while pre-defrost signal is ON.
2. After pre-defrost signal becomes ON, do NOT change capacity step request until defrost operation finishes. If you change capacity step after pre-defrost signal is ON, the outdoor unit may stop starting defrosting and frost may become big.
3. Pre-defrost signal becomes OFF before defrost operation finishes. Using both OUT4 (Defrost signal) and OUT8 (Pre-defrost signal) is recommended if you use pre-defrost signal. (See figure 5-2.)

Figure 5.2 illustrates the timing of defrost signals. It shows the pre-defrost signal (OUT8) becoming ON more than 1 minute before the defrost operation begins, and the defrost signal (OUT4) becoming ON during the defrost operation.

Regarding the delayed (balanced) defrost function and the pre-defrost signal, if you change the outdoor unit from a non-adaptable to an adaptable model, initialization of the function setting on the remote controller is necessary:

• First, select "Menu" → "Service" → "Check" → "Request code" on the remote controller.
• Second, set the refrigerant address of the outdoor unit that has been changed from non-adaptable to adaptable.
• Third, select the "Request code" item with the F1 or F2 button and set "200" with the F3 or F4 button.
• Then, press the [check mark button]. The function settings are initialized.

Note: You have to set the function settings after this initialization, if necessary.

5.2.3 Requirement regarding operation mode setting

1. Do NOT change operation mode frequently.

5.3. Requirements and guides when intelligent multiple outdoor unit control (IMOUC) is used

5.3.1 Power input timing when intelligent multiple outdoor unit control (IMOUC) is used

When IMOUC is used, supply power to the first interface unit, then the second interface unit within 1 minute. Otherwise, a system error will occur. (See figure 5-3.)

Figure 5.3 contrasts correct (OK) and incorrect (NOT OK) power input timing for IMOUC. The OK scenario shows sequential power-up of interface units (Main and Sub), while NOT OK shows simultaneous or incorrect power-up leading to errors.

5.3.2 Connection and setting when intelligent multiple outdoor unit control (IMOUC) is used

(1) When IMOUC is used, the following input connections to sub interface unit(s) are necessary:

• Thermistor: Target air temp. (TH1) input is not necessary because IMOUC is only in manual step mode. Coil on air temp. (TH11), Liquid ref. temp. (TH2), and 2-phase ref. temp. (TH5) inputs to sub interface(s) are necessary. (*1: Not necessary for PUHZ-SHW models).
• Input for capacity request (Analog signal): Input to sub interface(s) is not necessary.
• Modbus: Input to sub interface(s) is necessary only for monitoring sub interface(s).
• Remote switch: Input to sub interface(s) is not necessary.
• Other inputs: Forced compressor OFF (IN1) input to sub interface(s) is necessary if used. Fixed operation mode (Cooling/Heating) (IN2) input to sub interface(s) is not necessary.
• Remote controller: Daisy chain wiring among interfaces is necessary.

(2) When IMOUC is used, the following output connections to sub interface unit(s) are necessary:

• Operation: It can be monitored via main interface.
• Error: Output connection is necessary if you monitor error information of sub interface(s).
• Compressor ON: Output connection is necessary if you monitor this information of sub interface(s).
• Defrost: Output connection is necessary if you monitor this information of sub interface(s).
• Cooling mode: It can be monitored via main interface.
• Heating mode: It can be monitored via main interface.
• Self protection: Output connection is necessary if you monitor this information of sub interface(s).
• Pre-defrost *1: Output connection is necessary if you monitor this information of sub interface(s). (*1: Available ONLY with adaptable outdoor unit.)

(3) When IMOUC is used, the following DIP switch settings of sub interface unit(s) are necessary:

• Input selection (1-1 to 1-3): Setting of main interface is only necessary.
• Thermistor (TH11, TH5) (1-4 to 1-5): Setting of each sub interface(s) is necessary.
• Time stamp for SD card (1-6): Setting of each sub interface(s) is necessary, if you use this function.
• Position of TH1 (1-7): Setting is not necessary because IMOUC is manual step mode.
• IMOUC (1-8): Setting of each sub interface(s) is necessary.
• Fixed operation mode (2-1 to 2-2): Setting of main interface is only necessary, if you use this function.
• Fixed set temp. (2-3 to 2-5): Setting is not necessary because IMOUC is manual step mode.
• Thermistor (TH2, TH1) (2-7 to 2-8): Setting of each sub interface(s) is necessary.
• LED display setting (3-1 to 3-3): Setting of each sub interface(s) is necessary, if you use this function.
• Thermo differential (Auto step mode) (3-4 to 3-5): Setting is not necessary because IMOUC is manual step mode.
• Baud rate of Modbus (3-6 to 3-8): Setting of each sub interface(s) is necessary, if you use Modbus connection to sub interface(s).
• Settings for Modbus (4-1 to 4-8): Setting of each sub interface(s) is necessary, if you use Modbus connection to sub interface(s).
• Input selection (6-1 to 6-2): Setting of main interface is only necessary.

5.4 SD card data logging

5.4.1 Time stamp function

The time stamp function enables logging of operation time. To use this function, set DIP SW (SW 1-6) of the interface unit to ON, connect the remote controller, and set the clock on the remote controller ("Menu" → "Initial setting" → "Clock").

6 Requirement on local AHU design

6.1 Air flow volume

This section provides standard air flow volumes for different outdoor unit capacities.

Ensure air flow volume is kept within the maximum and minimum limits.

(1) Maximum air volume

*1. 600% of selected outdoor unit's maximum standard air volume is available ONLY when 6 same capacity outdoor units are connected.

(2) Minimum air volume

Total amount of selected outdoor unit's minimum standard air volume is allowable.

6.2 Standard conditions

When calculating capacity for designing AHU DX (Direct expansion) coils, refer to the standard conditions below. It is recommended to keep nominal capacity within 90%-110% under the standard condition.

[1] COOLING

[2] HEATING

6.3 Requirement on DX (Direct expansion) coil

(1) Heat exchanger volume of DX coil

Ensure the DX coil capacity is within the following range. If the piping length is 30m or shorter, DX coil capacity can be increased as follows.

Note: Calculate by linear interpolation in case of other piping lengths not shown on this table.

(2) Structure of DX coil

When multiple outdoor units are connected, select one interlaced DX coil with multiple refrigerant circuits, or multiple coils in parallel to the air flow. If multiple coils are placed in series with the air flow, a maximum of 2 coils in series is acceptable. (See figure 6-1.)

Figure 6.1 illustrates examples of DX coil structures for multiple outdoor units: Interlaced, Parallel, 2 in series, and 3 in series. The '3 in series' configuration is marked as 'NOT OK'.

(3) Diameter of header

A larger header diameter can decrease refrigerant flow velocity, disturbing refrigerant oil circulation and potentially causing compressor damage. Use piping with an outside diameter less than the value shown in the table below.

(4) Withstanding pressure

The design pressure of the outdoor unit is 4.15 MPa. The burst pressure of the connecting application must be more than 12.45 MPa (3 times the design pressure).

(5) Contamination maintenance

1. Wash the heat exchanger to keep it clean. Rinse thoroughly to remove flux. Do not use chlorine detergent.
2. Ensure the amount of contamination per unit cubic content of the heat transfer pipe is less than the following amount. Example for ø9.52mm pipe: Residual water: 0.6 mg/m, Residual oil: 0.5 mg/m, Solid foreign object: 1.8 mg/m.

6.4 Thermistor position

< Target temp. thermistor (Locally supplied) > Put the thermistor where average supply or return air temperature can be detected. Avoid placing it where it picks up the temperature of the DX coil.

< Liquid refrigerant pipe thermistor (TH2) > Place the thermistor where liquid refrigerant pipe temperature can be detected. Protect it with heat insulating materials to prevent influence from ambient temperature. If the refrigerant is distributed by a distributor, position the thermistor before the distributor.

< 2-Phase temp. thermistor (TH5) > Position the thermistor where 2-phase temperature can be detected on the DX coil pipe, ideally in the middle of inlet and outlet ports. If there are multiple paths, locate it on the top. Protect with heat insulating materials.

< Target temp. thermistor (TH1) > Place the thermistor where average supply or return air temperature can be detected. Avoid placing it where it picks up the temperature of the DX coil.

< Coil on temp. thermistor (TH11) > Position the thermistor where average air temperature of the DX coil inlet can be detected. Avoid placing it where it picks up the temperature of the DX coil.

This product is designed and intended for use in the residential, commercial, and light-industrial environment.

MITSUBISHI ELECTRIC CORPORATION
HEAD OFFICE: TOKYO BUILDING, 2-7-3, MARUNOUCHI, CHIYODA-KU, TOKYO 100-8310, JAPAN