Fujitsu Airstage - Cold Weather Heating

The design of a VRF system requires matching the capacity of the system to the heat load at a specific design temperature. When temperature drops below the design point, additional measures should be taken to improve the capacity and performance of the system.

1. Confirm the occupied space is free of any drafts, open windows, open dampers or any other problems that could bring untreated air into the building. In buildings with revolving doors, these should be used in place of regular doors that allow more air each time a person enters or leaves.
2. If capacity at peak load is a concern, the capacity of the indoor units should equal approximately 100%-110% of outdoor unit capacity.
3. When forecast predicts an extended period below design temperature, maintain occupied set point.
4. Set limits for all local controllers
5. Use snow shields to protect outdoor units
6. Use high heat setting
7. Limit the amount of outside air being introduced to the building and never bring untreated air directly to an indoor unit.
8. Confirm any ERV/HRV or DOAS is suited for extreme temperatures
9. Ensure that system was properly designed and installed. The creation of as-built drawings and proper refrigerant charge calculations are necessary to ensure proper performance.
10. If supplemental heat exists, ensure controls sequencing for on/off.
11. Understanding of all potential derates to performance: 

• Ambient Temperature                                                  
• Refrigerant Line Lengths
• Applied diversity
• Defrost
• Oil recovery

12. Proper training