Duct losses were included in these simulations to account for typical system conduction losses when supply air ducts are located in unconditioned spaces.
Duct losses can be eliminated or reduced when VRF systems are specified.
Savings for VRF systems are expected in three categories: 1) elimination or reduction of duct losses, 2) fan energy savings when compared to constant-volume systems, and 3) heating energy savings due to higher heating COP over conventional gas heating equipment.
Multizone systems do not have the high static duct losses
seen in high pressure systems.
Good sources say that duct losses
are typically high--15 percent to 30 percent on average of your heated air from the furnace is lost through cracks and openings at the duct joints.
The power used to compute EER does not include the fan power required to overcome duct losses
or high performance filters.
Further, SEEM closely tracks duct losses
to user specified zones (inside, outside, crawl, attic) and accurately models their impacts.
The temperature differences between the house and the crawl space and between the house and the belly space both increased postretrofit, reflecting fewer duct losses to the spaces.
Because of the reduction of duct losses due to retrofit, both the crawl space and belly appear to be "more outside" following the retrofit.
This points to the importance of using measured buffer space temperatures or modeling buffer space temperatures, including the impact of duct losses to the space.
The VRF essentially eliminates duct losses, which are often estimated to be between 10% to 20% of total airflow in a ducted system.
The more subtle energy efficiency advantages of VRF systems, such as the reduction in duct losses, the ease of electrical submetering, and even the higher part load efficiency, frequently are overlooked.