One of the cornerstones of an energy efficient building is an air tight envelope.  Any leak in the building envelope will allow heat and moisture to exit in the winter, and enter in the summer.  The tighter the building envelope is, the less energy is needed to condition the indoor environment (because we are not losing the conditioned air to the outside).  While a "perfectly sealed" building if more efficient for heating and cooling, it is not good for occupants.  We need to bring fresh air in and exhaust both stale air and airborne contaminates in order to provide a healthy indoor environment.  We accomplish this in our SIP/modular hybrid using a combination of both spot and central ventilation equipment. 

For spot ventilation in each bathroom we have employed Panasonic WhisperGreen bath fans.  The WhisperGreen bath fans are designed for continuous operation on low speed (40CFM).  An occupancy sensor in each fan increases the fan speed to a higher setting (adjustable) when activated, and keeps the fan running on high for a set period of time  Personally, I feel that having each bath fan continuously pump 40CFM of conditioned air to the outside is ludicrous.  First, we already paid to condition the air we are exhausting.  Second, to keep pressure balance we need to bring in 40CFM of make-up air, which we then need to condition again.  While these fans are Energy Star rated (presumably for the energy efficient operation of their DC motors), I take serious issue with the fact that they can not be turned off when not needed.  I spent a little time fixing that!

Since the fans are rated for continuous duty, the two fans in the second floor baths are hard wired (no on/off wall switch).  Rather than waste energy by dumping a lot of air directly to the outside, the ducts from these units are connected to the energy recovery ventilator (ERV), where heat and moisture can be recaptured or rejected depending on the season, before the stale air is exhausted to the outside.  The full bath and half bath on the first floor are too far away to be economically connected to the ERV, and are therefore directly vented to the outside.  Rather than having these two units run continuously, they are connected to an on/off switch with a built in motion sensor.  Unless the sensor at the switch detects motion in the room, the fans are off.  When motion is detected, the fans run on high (at 80 CFM) for approximately 20 minutes and then shut off automatically.

The first thing you will (or won't) notice is the noise coming from these bath fans.  Even on high, these fans are super quiet!  This is a huge plus since my wife hates the usual noise typical bath fans make and will usually not use them if given a choice.  In this house, we must use the bath fans, otherwise moisture will promote mold growth and odors will linger.  Since all our fans operate automatically, no one ever has to think about using these fans in our house.  Moisure and foul odors are automagically eliminated.

The second thing you will notice about these fans is the annoying blinking green LED from the fan's built-in motion sensor.  During the day, you would swear it was a recording video camera.  At night, it emits an eerie green glow.  Since neither is pleasant, we have taken measures to cover the LED with foil tape and block the emitted light.  I contacted Panasonic to see if there was a way to disable the LED and I was told, "no."

In general, we are very pleased with these fans.  They are quiet, powerful and when modified so they don't run constantly, very energy efficient.  On high, the air in each of our bathrooms is turned over a few times during one 20 minute cycle.  My wife has commented that even the hottest showers do not fog up the mirrors.  At first, the plumbing inspector didn't believe that they were operating because he could not hear them.

Here is a link to the manufacturer's website: http://www2.panasonic.com/consumer-electronics/shop/Building-Products/Ventilation-Systems/Ceiling-Insert-Fans/

We purchased our fans from Energy Federation Incorporated (EFI).  See http://www.efi.org for more details.