VR-II Refrigerant Charge Calculator
This article explains how to calculate the total refrigerant charge for a VR-II system using up to three outdoor units.
Quick Answer
- Total refrigerant charge = A + B + C
- A = Total factory charge of all connected outdoor units
- B = Total additional charge for the selected outdoor units
- C = Additional refrigerant for liquid-line pipe length
- 1/4 in. pipe: 0.021 kg/m
- 3/8 in. pipe: 0.058 kg/m
- 1/2 in. pipe: 0.114 kg/m
- 5/8 in. pipe: 0.178 kg/m
- 3/4 in. pipe: 0.268 kg/m
Calculation Structure
| Section | Description |
|---|---|
| A | Combined factory refrigerant charge for Outdoor 1 (Master), Outdoor 2 (Slave 1) and Outdoor 3 (Slave 2), where applicable |
| B | Combined additional charge for the selected outdoor units |
| C | Additional refrigerant calculated from the total liquid-line pipe lengths |
Formula
Total Refrigerant Charge (kg) = A + B + C
Total Refrigerant Charge (kg) = A + B + C
Step 1 - Select the Outdoor Units
Select the applicable outdoor unit models in the calculator:
- Outdoor 1 - Master
- Outdoor 2 - Slave 1, where fitted
- Outdoor 3 - Slave 2, where fitted
The calculator provides the factory charge and any additional outdoor-unit charge for each selected unit.
Step 2 - Calculate Section A
A = Outdoor 1 Factory Charge + Outdoor 2 Factory Charge + Outdoor 3 Factory Charge
If only one or two outdoor units are installed, unused outdoor unit positions remain at zero.
Step 3 - Calculate Section B
B = Outdoor 1 Additional Charge + Outdoor 2 Additional Charge + Outdoor 3 Additional Charge
Step 4 - Enter Liquid-Line Pipe Lengths
Enter the total applicable liquid-line pipe length in metres for each pipe size.
| Pipe Size | Additional Charge Rate | Calculation |
|---|---|---|
| 1/4 in. | 0.021 kg/m | Length (m) x 0.021 |
| 3/8 in. | 0.058 kg/m | Length (m) x 0.058 |
| 1/2 in. | 0.114 kg/m | Length (m) x 0.114 |
| 5/8 in. | 0.178 kg/m | Length (m) x 0.178 |
| 3/4 in. | 0.268 kg/m | Length (m) x 0.268 |
Add the calculated charge for all pipe sizes together. This becomes Section C.
Example Shown in the Calculator
The screenshot shows the following entered pipe lengths:
| Pipe Size | Length | Calculated Charge |
|---|---|---|
| 1/4 in. | 48 m | 1.008 kg |
| 3/8 in. | 26 m | 1.508 kg |
| 1/2 in. | 40 m | 4.560 kg |
| 5/8 in. | 0 m | 0 kg |
| 3/4 in. | 0 m | 0 kg |
Total additional pipe charge (C):
1.008 + 1.508 + 4.560 = 7.076 kg
The calculator displays this rounded as 7.08 kg.
Maximum System Charge
| Outdoor Unit Configuration | Maximum System Charge |
|---|---|
| 1 Outdoor Unit | 35 kg |
| 2 Outdoor Units | 70 kg |
| 3 Outdoor Units | 105 kg |
Maximum charge check: The final A + B + C quantity must not exceed the maximum permitted refrigerant charge for the number of connected outdoor units.
Technician Checklist
- Select the correct Master and Slave outdoor unit models.
- Confirm the factory charge for each outdoor unit.
- Add the factory charges to calculate Section A.
- Add any outdoor-unit additional charges to calculate Section B.
- Measure the applicable 1/4, 3/8, 1/2, 5/8 and 3/4 in. liquid-line lengths.
- Calculate the charge for each pipe size and add them together to calculate Section C.
- Calculate the total system charge using A + B + C.
- Confirm the final charge is below the applicable maximum system charge.
- Record the final refrigerant charge on the commissioning documentation.
Source: VR-II Refrigerant Charge Calculator supplied in the service reference material.