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NC-2009 EAp2:Minimum Energy Performance

Energy modeling - ASHRAE §G3.1.2.4

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Julien Daclin
Head of Sustainability
Deerns France
LEEDuser Basic Member
24 thumbs up

Hi all, We are undertaking the energy modeling of an office building and the Baseline is using a System 7, climatic zone is 4a. The building is connected to a heating District Energy System. Could someone please help me to understand ASHRAE 90.1 §G3.1.2.4? The section states, “Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours. If the supply fan is modeled as cycling and fan energy is included in the energy-efficiency rating of the equipment, fan energy shall not be modeled explicitly.” In our case, the supply fan is modeled as the cycling fan. I cannot see how the supply fan should be modeled without taking into account its energy consumption. Should the extract fan be cycled too? Thanks for your help.

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
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Wed, 11/07/2012 - 16:16

The energy efficiency rating is not the same as the energy consumption. Some measures of efficiency (COP, EER, SEER) include the fan energy (see G3.1.2.1). The second sentence means that if the fans do cycle and the efficiency includes fan power you do not model extra fan power as it is already included. For example, a heating/cooling system that cycles with temperature that has a dedicated outside air system that runs continuously would not add more fan power than already included in the efficiency measurement for the heating/cooling system.. The extract fan would follow the same rules.

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