The simple answer is you do need a mechanical ventilation system for a SIP house because it is a very air tight form of construction. There will be times when opening a window for ventilation isn't appropriate eg when it is very cold outside. What is required is the removal of the stale and damp air from the house and replacement with fresh air from outside the house. The issue is heat loss with the extract air. By including a heat recovery ventilation system in your SIP build you can capture the heat before it leaves the building. The way this works is the the warm stale air within the house is extracted out via a heat recovery unit which transfers the heat to the cold fresh air coming into the house. A good heat recovery system combined with a highly insulated and air tight build which SIP builds are can drastically reduce and possibly eliminate the need for home heating.

This might be well known to everyone, but just wanted to point out that by using SIPs for walls and roof you can expect a very air-tight structure, which makes it easier for the ventilation system to exchange air. So by separating external from internal, the control of air quality, humidity and temperature becomes much easier.

If you are concerned about the humidity and temperature of air in your home I suggest you monitor the quality using one of simple rh meters like below. Target temperature should be between 21-23deg and humidity between 25%-60%.

ZEHNDER COMFOAIR Q

Any experience with particular products or brands of ventilation systems?

I think it makes sense to have a balanced ventilation system.