Ventilation rate question

RonV_2

I would like some advice on what rate to set the air distribution in my house. It is a new house and this is part of my fine-tuning the setup. Before I ask for your advice, here is a description of the system configuration. I have a Unico air handler that is used for air conditioning. (The heating system is in-floor radiant and completely independent of the air system). The AC setup uses the Unico high velocity tubing to deliver air to rooms through the ceiling, and then conventional under-floor ducting via baseboards for return air. There is a Heat Recovery Ventilator in this system as well. The HRV pulls air from the house in the conventional way, using separate ducts from various points in the house, primarily bathrooms, laundry and pantry. The replacement air that is pulled from outdoors is pushed into the return on the AC air handler and returned to the rooms via the AC ducting. The AC fan can be run at low speed to push this air throughout the house, or I can leave the fan off and expect that this fresh air eventually gets pulled into the living space via the AC ducting, most likely through the return ducts.

We are in a cool climate so AC cooling (with fan at a high speed) runs only in the peak summer months. So, I am trying to decide what rate to set the AC fan during the rest of the year, or whether to simply leave it off. The HRV unit is running at 85 CFM (which is appropriate for the size of the house) full time, and gears up to 230 CFM when the bathroom exhaust timers (so called POSH timers) are turned on to exhaust a bathroom, usually for 30 minutes. I'm wondering what the most appropriate setting for the AC fan low speed should be. It can be varied to pretty much any airflow I want.

The default setting for the AC fan on low speed, after the installers left, was 430 CFM which I found noisy and excessive except during peak summer cooling season. I have adjusted the flow down to 230 CFM for now because this matches the HRV maximum air flow . It is very quiet at this setting, but air movement in the family room still feels a bit too drafty for those cold winter months, so I'm considering setting the AC fan down to about 85 CFM, just enough to match the airflow coming from the HRV at its constant low speed setting.

What speed do you think would be most appropriate?

Zman

You might consider putting a small hydronic coil in the AC duct to temper the changed air in the winter.
Not enough to heat the house, just enough to eliminate the draft.