I'm running multiple model runs with all parameters held constant except for the central AC. I've noticed that when I use the same furnace with SEER 14 and SEER 15 Central AC I get identical therms / year output for the furnace. However, the same furnace will increase about 15% in therms / year when I use a SEER 17 or SEER 24.5 AC. What is changing in the model that causes the same furnace to use more gas when the AC system changes from SEER 15 to SEER 17? Is it the two stage compressor?
The attached picture shows this happen twice, once with an 80% AFUE furnace cycle through SEER 14,15,17,24.5 AC's and the 4 bars on the right show the same progression with a 90% AFUE furnace
Thanks!
