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I'm assuming from what you said that in the zonal exhaust you've set the make up air source EXHAUST-SOURCE = AIR-HANDLER.

Two potential reasons for the increased airflow I can see are:

1. The economizer kicks in.
2. I would check the system's SIZING-RATIO as well as the COOL-SIZING-RATIO... The fact you're getting a closer to cooling setpoint (75°F instead of 76°F) suggests that you didn't have enough autosized airflow in the past to meet some peak cooling loads.

I suggest to start by disabling the economizer and see if the problems persists. Then move on to the checking how cooling and airflow interact in your given model.

Look at the zone THERMOSTAT-TYPE and throttle range too.

The key is to figure out what's causing the increase in airflow. Then as far as fan electricity is concerned, it's another matter. An increase in airflow tends to raise the consumption so here you're not comparing apples to apples. Also, considering you said you used a "part-load fan performance curve", I'm assuming you used FAN-CONTROL = FAN-EIR-PLR, but which default curve have you actually used? Have you actually plotted it to see what it looks like?

I'm assuming from what you said that in the zonal exhaust you've set the make up air source EXHAUST-SOURCE = AIR-HANDLER.

Two potential reasons for the increased airflow I can see are:

1. The economizer kicks in.
2. The airflow is increased to meet cooling load.

I suggest to start by disabling the economizer and see if the problems persists.

Then move on to the checking how cooling and airflow interact in your given model. I would check the system's SIZING-RATIO as well as the COOL-SIZING-RATIO... . The fact you're getting a closer temperature to cooling setpoint (75°F instead of 76°F) suggests that you didn't have enough autosized airflow in the past to meet some peak cooling loads.

I suggest to start by disabling the economizer loads. Also look at the zone THERMOSTAT-TYPE and see if the problems persists. Then move on to the checking how cooling and airflow interact in your given model.

Look at the zone THERMOSTAT-TYPE and throttle THROTTLING-RANGE range too.as well.

The key is to figure out what's causing the increase in airflow. Then Then, as far as fan electricity is concerned, it's another matter. An increase in airflow tends to raise the consumption so here you're not comparing apples to apples. Also, considering you said you used a "part-load fan performance curve", I'm assuming you used FAN-CONTROL = FAN-EIR-PLR, but which default curve have you actually used? Have you actually plotted it to see what it looks like?