How does it work? 
The high velocity system is an energy efficient high pressure air delivery system that can be designed to provide heating, cooling, filtration, ventilation, humidification and dehumidification. The small duct high velocity system works on the principle of pressure rather than air velocity. It is quite different than a conventional furnace, the main difference being that the supply duct work is all “small diameter” or “mini duct” providing comfort, value and preservation of the architectural integrity of your home.

What makes it different? 
The high velocity uses pressurized small duct to condition the air differently than conventional forced air systems. With the use of a high pressure area to low pressure area, where the air is continuously being mixed, creating even temperatures from floor to ceiling. Because the plenum duct is pressurized, dust build-up within the duct work is eliminated in comparison to forced air furnaces where you would be paying duct cleaning services on yearly basis. With continuous air circulation from the constant fan, airborne dust and other allergens can be easily filtered out of the air. Air from outlets is mixed thoroughly, eliminating “hot and cold spots” commonly found with conventional systems.

Other considerable benefits of installing a high velocity heating and cooling system are:

• Quiet Performance – The system outperforms conventional heating and cooling systems by utilizing a patented high velocity stream of air. This air is delivered quietly and seamlessly into the room using small outlets or diffusers.
• Draft-Free, Even Temperatures – by eliminating drafts and removing 30% more relative humidity the high velocity system delivers superior comfort over traditional HVAC.
• Fits in Any Space – without compromising design or architectural integrity of your home where conventional colling and heating systems can’t be put to use.

https://www.impressiveclimate.com/furnaces-heating/heating-alternatives/high-velocity/