ASHRAE/IECC Baseline VAV Fan Curves and Min Flow Fraction

asked 2019-07-18 17:58:04 -0500

updated 2019-07-19 10:29:08 -0500

What are the appropriate fan curve coefficients and Fan Power Minimum Flow Fraction for the Fan:VariableVolume objects in an ASHRAE 90.1 PRM baseline model (System 5)?

I ask because there are some discrepancies between the ASHRAE/IECC code language and the Commercial Prototype Building Models. As noted in a previous Unmet Hours post, the prototype models use coefficients representing "Good SP Reset VSD Fan", which differ from the coefficients from 90.1 App G Method 2. Is this because the prototypes assume zone-level DDC where a SP reset would be required?

Regarding the "Fan Power Minimum Flow Fraction" field, both ASHRAE 90.1-2013 (6.5.3.2.1) and IECC 2015 (C403.4.1.1) state: "Low or minimum speed shall not exceed 66% of full speed. At low or minimum speed, the fan system shall draw no more than 40% of the fan power at full fan speed." I interpret this as meaning the baseline "Fan Power Minimum Flow Fraction" should be 0.66. However, the prototype models use a fraction of 0.25. What is the appropriate Fan Power Minimum Flow Fraction for a PRM baseline?

Another unrelated discrepancy I found in the prototype models for System 5 (used in medium office). ASHRAE (G3.1.1-4 Baseline System Descriptions) lists hot water boiler heating, whereas the prototypes use gas furnace heating. Are the ASHRAE prototype models not intended to represent ASHRAE PRM baseline models?

edit retag flag offensive close merge delete