NECB-2017 Article 8.4.4.17 & Article 8.4.4.18
The following should be noted:
· If an exhaust fan exists in the proposed model (5.2.3.1(2) and 5.2.10.1(3)) then it is modelled identically in the reference building. This can be included/excluded manually by the user.
· Reference systems 1 to 5 & 7 shall be modelled with a supply fan that has a static pressure of 640Pa and a combined fan-motor efficiency of 40% (8.4.4.18.(3b))
· Reference systems 1 to 5 & 7 shall be modelled with no return fan (8.4.4.18.(3c))
· Reference system 6 shall be modelled with a supply fan that has a static pressure of 1000Pa and a combined fan-motor efficiency of 55% (8.4.4.18.(4b))
· Reference system 6 shall be modelled with a return fan that has a static pressure of 250Pa and a combined fan-motor efficiency of 30% (8.4.4.18.(4c))
· NECB-2017 Section 5.2.3 discusses the minimum performance requirements of constant-volume and variable-volume fans. While the proposed design should be modeled to reflect the actual design fan performance curves, the baseline building should reflect the performance characteristics stated in this section i.e.
o The power demand of constant volume fans (supply & return) should not exceed 1.6W per L/s of supply air delivered using the equation shown in section 5.2.3.2
o The power demand of variable volume fans (supply & return) should not exceed 2.65W per L/s of supply air delivered using the equation shown in section 5.2.3.2
o If a variable fan (supply, relief or return) is between 7.5kW and 25kW, then the fan power demand will be no more than 55% of the design wattage at 50% of the design air volume
o If a variable fan (supply, relief or return) is greater than 25kW, then the fan power demand will be no more than 30% of the design wattage at 50% of the design air volume
· Finally section 8.4.4.17 details the equations and coefficients (Table 8.4.4.17) used in calculating the power versus flow rate performance
o Except as stated in the next two points Individual fans shall be modeled as airfoil or backward inclined riding fan curve
o Where variable-air-volume fans are used, individual fans having a fan power greater than 7.5 kW and less than 25 kW shall be modeled as airfoil or backward inclined with inlet vanes
o Where variable-air-volume fans are used, individual fans having a fan power greater than or equal to 25 kW shall be modeled as forward curved with inlet vanes
In the ApacheHVAC NECB systems library the fans have been setup to match the fan control specified in Table 8.4.4.7.B. The static pressure and efficiency have been included by default to match the requirements of 8.4.4.18 and the resulting fan power should match that obtained by using the power equation in section 5.2.3.
For variable volume fan control the part-load fan parameters have been setup to match the ‘fan power greater than 7.5 kW and less than 25 kW’ case. If the resulting fan power is greater than 25kW then the part load performance will have to be manually updated by the user to match the requirements in section 5.2.3 & article 8.4.4.17.
