This was proposed to me recently for a house that is currently being designed for me.
    Rather than using an air-to-air heat exchanger we'll just use the low speed air handler's fan to pressurize the house.  Put a motorized damper on an external intake and put the fan on a timer.  You would just dump the fresh air in to the cold air return.  The timer would cause the damper to open up  the intake and cause the fan to operate (if it's not already energized)
   "Even though it is a SIPs house, it will leak a bit."  So by pressurizing the house (with the timer) the air will be exchanged due to the leakage around windows and such.
   Now if this is feasible, I'm all in favor.  It would eliminate a $3000 cost for the air-to-air heat exchanger.
   Comments please.

Interesting idea. I'm not sure if the house/windows/doors would leak enough to get the number of air exchanges necessary... but along with normal air infiltration through opening/closing doors... it might be enough. Positive pressure in the house would probably also tend to cause your doors to slam shut whenever they're open... something to think about.

I too am designing a SIP home... and my designer and I were talking about ventilation. He mentioned there are windows that you can buy that have a built-in vent with some sort of sealing flap built into the window sill. If I remember, he was talking about drawing air into the house through these types of windows... the opposite of what your looking to do. Perhaps it's reversible?

Best of luck,
RAR
Spokane, WA

RAR,

If you have not seen the statement "Build tight, Ventilate right" before, you need to understand the fact that you cannot build too tight but you can underventilate. Pressurizing a home as described would only force water vapor into the walls, around doors and windows, etc. You are better off to spend the money to properly ventilate your home than try to make a bad system work because it is almost guaranteed to fail. I suggest you find a building science professional, i.e. energy rater or auditor and have the system designed for the energy efficiency of the structure. DO NOT RELY ON LEAKS FOR VENTILATION.

Curt

lkg907;

if your HVAC contractor is charging $3,000 for the exchanger, you are paying at least twice as much as you should

Build tight, Ventilate Right!
Curt is correct in that a pressurized house will push interior moisture into your thermal envelope.  In cold climates this will eventually condense, causing mold, rot, etc. 
Also "dumping" air in to the cold air return would create a location of condensation.  This may not rot anything structurally, but would create a prime area to grow mold and the ducted systems would spread the mold spores throughout your house.  In cold climates you are asking the furnace to work harder therefore reducing its efficiency.
There are forced air heating systems that combine the exchanger with the furnace.  We've seen some installation savings from using these.

I will have to choose a ventilator for my new SIP bungalow soon.
Here in Alberta swings in the winter can be from -35C to +5 in a few days ( also the opposite, unfortunately...) Summers are getting warmer too. We have very low relative humidity.
If I have it right, an HRV recovers heat, an ERV recovers heat and moisture. Yes?
Will an ERV freeze in the winter?
What types  are there? Is an ERV fundamentally different?
HVAC is a combo radiant floor and forced air. The place will be as tight as i can make it. Have foamed in all joints, windows, etc.
What brands are out there? Do some work better in a colder climate? This is where the saving would be most obvious- winter on the Steppes of North America...
Not so much ned for dehumidifying in the summer, i would think.

bob