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CS-2009 EAp2:Minimum Energy Performance

control of PIU fans for System 8

Shall the PIU fans of System 8 cycle according to paragraph G3.1.2.4? In EneryPlus you can impose the "Fan On Flow Fraction", which is defined as: The fraction of the primary air flow at which fan turns on. In the parallel PIU the fan operation is intermittent. If the primary air flow is above this fraction of the maximum, the fan is off. Otherwise the secondary fan will run according to the Availability Schedule specified in the Fan:ConstantVolume object (see Fan Name below), unless it is overridden by an availability manager (ref. AvailabilityManager:NightCycle and others). Could the "Fan On Flow Fraction" be equal to 0.5 and the fans be always available? In this way they are continuously on during the winter season and they turn off sometimes during the summer season (when more primary air is required).

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 08/16/2016 - 17:50

The PIU fans should not cycle according to G3.1.2.4. This applies to the main fans in the air handling units. The PIU fans should operate when the primary air flow has reached the minimum setting. The minimum flow is 30% as indicated in G3.1.3.14. So the fraction should be 0.3.

Wed, 08/17/2016 - 18:29

It means that during the winter season (when no cooling is requested) the PIU fan shall operate 24 hours/day, doesn't it?
Profile picture for user sheffer
Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Mon, 08/22/2016 - 20:48

It shouldn't. The PIU fan should cycle based on the temperature in the space. It should also be off when the space is unoccupied unless there is a call for heat. The main air handler fans should operate during occupied to meet the minimum outside air requirements. This document on pages 3.97 to 3.98 explains how the system fan control should operate. http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-25130.pdf

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