The only recommendation about air velocity from geothermal manufacturers is that the ductwork system be sized to handle 400 cfm per ton.

Without regard to the technology supplying the heat/cold air, Man D recommends no more than 700 fps at the supply registers.

Hope this helps.

Best regards,

Bill

I'm away from my copy of Manual D at the moment, but I recall it recommends supply duct velocity no greater than 700 FPM. Given that the face area of a register is substantially more than the cross sectional area of its connected runout duct, I would expect the face velocity to be well below 700 FPM.

Register face velocity considerations include noise, pressure loss, throw, adequate mixing (avoiding stagnation and stratification) of room air while not subjecting occupants to air velocities resulting in sensation of draftiness. Placement of the register within the room must also be considered.

ACCA Manual T addresses these issues.

Every system's design should employ Manuals J, D, S, and T

Thanks for your replies. I thought they might be lower than conventional design specs for hot air heat, because of the lower temp delivered by geo.
Thanks again.

Comfort depends on supply air temperature, air velocity and to a somewhat lesser degree, humidity, so it is a bit hard to quantify.

Our experience in commercial office buildings is that when people sit in a draft of >50ft/minute (velocity), they will probably feel uncomfortable.  Over this velocity, diffuser noise may be a problem, too.  In my opinion, a duct velocity of 700 ft/min is the max from an acousitical standpoint with a very good ductwork job.  500 ft/minute is better (with ductwork in a plenum return ceiling).  Unless there is fan powered equipment in the ceiling, we like an NC 35 acoustical enviromnent.  With fan powered equipment in the ceiling, we would aim for an NC 40.

This may be less of a problem for residential where you are not chained to a desk for 8+ hours /day.

For you geo guys, what is the normal supply air temp you would expect in heating mode?

Bruce

20 - 30 higher than return

My system is running right now. The return air temp is 71° the supply is 96°

Geodean, What temp are you maintaining at the thermostat? Somewhere around 70-72 degrees? Dave

  My thermostat is set at 72°  with a 3° differential.