This is our first summer with central air conditioning since we had the geothermal system installed, and the hydronic radiators and boiler removed.
Our air conditioned space has remained no warmer than 72 deg.F, no matter what the temperature outside.
Earlier this spring, when the temperature had cooled after a warm spell, we opened our windows to cool the house. That is natural ventilation. However, after 3 days of this, our noses were stuffy and heads full from the allergens brought in on the breeze. Our air conditioning not only cools the air, it also filters the air. We have a MERV 7 filter on the water furnace heat pump. MERV is a rating of size particles that pass thru the filter, from 1 to 16. Some of the more common filters for residential systems are MERV 1 to 4. A MERV 7 filter will filter 70% to 80% of particles 3 to 10 microns in size. This includes the pollens, dust mites and carpet fiber, all larger than 3 microns. I think we will keep the windows closed next time.
Then, about a week ago, the evening temperature was cooling, about 72 degrees, the same as inside. But when I went outside, extremely humid. We kept the windows closed and the humidity out. Air conditioning also dehumidifies the air.
Conclusion: That natural ventilation may not be a savings. When the windows are opened, the filtered and dehumidified air escapes out the window.
Please note that at this time, we have an older home that is not airtight, and are not concerned about getting enough fresh air.
