Hello again!
Our project is in the final throws of appeal and we have been able to secure EAp2 and 4 points for energy efficiency. However, there has been some discourse with our review team regarding the method for modeling our exhaust fan and the limitations of the HAP model (or any model for that matter).

In the model, if the rooftop units are equipped with a default Power Exhaust Fan as a process load, the model presents an inaccurate picture of the actual function of the system. This is not the proper way to simulate a power exhaust fan (PEF). The PEF should only run during economizer operation. The PEF’s on the installed rooftop units actually consist of four (4) 1.0 HP fans. These fans cycle on to relieve building pressure as the economizer outside air dampers open. The economizer operation in the Boston area is limited to the shoulder periods of the year. When the economizers are in operation, the supply fan air flow is not at peak, so maximum pressurization will be limited. During most periods of economizer operation and average of 2-3 fans will run. We emailed Carrier to confirm that the HAP program cannot determine building pressurization and does not have the capability to properly simulate the operation of the PEF’s. We have confirmation from Carrier that our analysis is accurate.

We determined that a better way to simulate the PEF’s was to add an electrical load to miscellaneous Building Electrical Load in the program. This allowed us to attach a schedule to it. Both proposed and baseline buildings were simulated using the same input. However, our review team is stipulating that we cannot model the space in this manner.

The reviewer is assuming that the exhaust fan is being modeled in the baseline case and an additional PEF load. This is not how we have considered the model. We have removed the exhaust fan configuration from the baseline and proposed models and added the power consumption and schedule to the building electrical load in both the baseline and proposed cases.

Can you possibly explain to us why the reviewer is not allowing us to model the rooftop units in this way? And possibly direct us to a methodology that is acceptable that will recognize the modulating nature of the exhaust fan operation and its asynchronous operation against the supply fan?

Thank you!