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I predict in certain areas, "free cooling" systems will become the standard. These are system which do just what you talk about automatically. When there is a need for cooling and exterior air is cool enough, supplement supply air with air from the outside. This way your AC system load is reduced, or if cool enough, the compressor doesn't need to run at all to remove heat from your home by replacing it with cooler air from outside.

Free cooling is already part of many commercial AC systems, usually referred to as an "economizer".

2 comments

I wish I had a system like that and have thought about it a lot. I live in Calgary and today will be 28C and it will go down to 12C at night. I wish my system could just run a fan at 7am and draw in a ton of cool air to cool the house. Instead my AC runs for 30 minutes or whatever. Seems like a waste.

I'm working towards that with my Home Assistant installation, using inside and outside thermometers. You can trigger the fan based on the appropriate parameters, time of day, temps, etc.

Planning a similar system for the house we'll be completing on in the next few months.

Since we'll be renovating/refreshing the whole house I'll have the opportunity to do stuff I won't be able to do later without much more disruption.

I did a bit of reading after posting my comment and it looks like many HVAC technicians recommend against doing this in a residential setting due to humidity issues. Sounds like most HVAC economizers are for commercial settings.

I'm assuming this applies to high humidity areas? Seems in drier climates this would reduce humidity/mold risks

I've been wondering why my Nest thermostat doesn't already have an option to do this. I can turn on the fan manually, but it's not smart enough to do that automatically when it's cooler outside than it is inside.

Your system only exchanges heat with the outside (via a refrigerant). The fan only circulates air; on its own, it doesn't draw air from the outside (by design; you don't want to be cooling outside air).

The system would need to have a second mode and a fresh air intake, as well as wiring and support from your thermostat. It can be done, but HVAC is a slow-moving industry.