WCEC tested variable capacity compressor and variable speed blower technologies and evaluated duct losses for single zone and multi-zone residences.
Estimates of degradation in EER of 10% to 55% (Mowris 2016) included: 3 to 12% for low air flow, 4 to 7% for evaporator blockage, 7 to 36% for duct losses and 4 to 56% for refrigerant mischarging.
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.
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.
* Exhaust duct losses
: 2.0 kPa (0.02 bar), assuming heat recovery
The power used to compute EER does not include the fan power required to overcome duct losses
or high performance filters.
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.
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.