As you tighten and insulate the envelope (beyond code minimums), the “correct” throw diminishes in value.

Dale, you addressed ventilation and dehumidification, but what about filtration? I am just saying that a good forced-air system can provide all of these HVAC functions at a lower installed cost and better operating efficiency than having separate hydronic and forced-air systems for these functions.

Dale, I understand the need for “throw” in commercial systems serving large spaces, but is it really necessary for residential applications? Even if it is important, it is the velocity at the register that determines throw, not the velocity in the duct.

Mike,
So the Rheia system is basically a high velocity duct system like Unico. Is that correct?

Roy,
Yes handling air is necessary for dehumidification and for ventilation which is the proper job of dedicated ventilation and de-humidification systems.
Dehumidification is something that traditional hvac systems provide only as an side effect that is often at odds with sensible cooling. Ventilation is a function that conventional hvac systems don’t address at all. Or they do Mickey Mouse things like putting a duct from a furnace or heat pump return to the outside and call it ventilation. Pretty pathetic.

Neither application has a lot to do with heating and cooling. The real trick is to find ways of decoupling these otherwise disparate functions. That is what is done in commercial HVAC systems and what I practice in my work.

Roy
I don’t know what the flow rate is for the very small diameter ductwork they are showing but the duct size alone would dictate that the velocity in the duct be somewhat high. They do show an awful lot of such small diameter ductwork so maybe they are just dividing a larger flow into many parallel streams that converge at the register. Providing the registers with the appropriate flow to provide the correct throw and spread with low noise is the objective.

Dale, maybe you can heat and cool without moving air, but it is hard to dehumidify, ventilate, or filter without moving air. Thus, I am not a fan of hydronic radiant or baseboard systems.

Mike, thanks for the feedback. How does the cost compare?

Hi Dale: I don’t think Rheia is necessarily promoting “high velocity” ductwork like Unico, at least I don’t see that in their literature. I believe that they are saying that you can use more small ducts rather than fewer large ducts to make installation easier. I hope they are not promoting the high static pressures required by Unico systems.