I am working on a building with air handling units on each floor. Interior zones are served by the AHU while exterior zones are served by the AHU as well as FC unit which provides furthur heating and cooling. I modeled the system as a Power Induction Unit with series PIU to represent the FC units. I used a reheat delta T determined from AHU and FC's spec'd heating capacity and air flow rates and allowed eQUEST to autosize and distribute airflow. Thanks to the advice given from members on this list I was able to reduce my unmet hours to a reasonable range.
I am working on the baseline model and am again having issues with unmet hours. As mentioned the heat capacity of VAV systems are determined by the design flow rate and the reheat delta T. In order to reduce unmet hours I would increase flow rates to particular zones by manually increasing Min design flow rates with my reheat delta T set at 20F which is what is required by ASHRAE. I've been at this for a while and my building is basically a wind tunnel, I have floors with supply cfm upwards of 100,000 CFM and I still have thousands of unmet hours. (my throttling range are at 6)
Am I allowed to change reheat_delta_T to a larger value?
For a power induction unit with series PIU boxes, is there any way for the boxes to provide zone cooling? Looking at hourly reports for "zone coil cooling" I have 0's.
Much of this might be brought about by the fact that my building heating and cooling load has doubled in the baseline model.
Any advice would be much appreciated.
Date: Mon, 27 Aug 2012 09:40:41 -0400