Furnace Capacity |
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Applicability |
Systems with a furnace |
Definition |
The full load heating capacity of the unit |
Units |
Btu/h |
Input Restrictions |
As designed. Adjust the capacity if the number of unmet load hours exceeds 300. |
Baseline Rules |
Autosize with an oversizing factor of 25% (let the software determine heating capacity based on the building loads). If the number of unmet load hours for the baseline exceeds 300, increase the furnace capacity as described in Chapter 2. |
Furnace Fuel Heating Efficiency |
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Applicability |
Systems with a furnace |
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Definition |
The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows: (Equation 3.7.6-1) $$E_{t}=(0.0051427\cdot AFUE)+0.3989$$ where
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Units |
Fraction |
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Input Restrictions |
As designed |
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Baseline Rules |
See the values below:
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Furnace Fuel Heating Part Load Efficiency Curve |
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Applicability |
Systems with furnaces |
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Definition |
An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows: (Equation 3.7.6-2) $$Fuel_{partload}=Fuel_{rated}\times FHeatPLC$$ (Equation 3.7.6-3) $$FHeatPLC=a+b\cdot\ \frac{Q_{partload}}{Q_{rated}}+c \cdot (\frac{Q_{partload}}{Q_{rated}})^{2}$$ Where
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Units |
Data structure |
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Input Restrictions |
As designed when data is available, otherwise use the default values are provided above. |
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Baseline Rules |
The defaults shall be used. |
Furnace Fuel Heating Pilot |
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Applicability |
Systems that use a furnace for heating |
Definition |
The fuel input for a pilot light on a furnace |
Units |
Btu/h |
Input Restrictions |
As designed |
Baseline Rules |
Zero (pilotless ignition) |
Furnace Fuel Heating Fan/Auxiliary |
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Applicability |
Systems that use a furnace for heating and have an auxiliary fan for combustion air. |
Definition |
The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps |
Units |
Kilowatts (kW) |
Input Restrictions |
As designed |
Baseline Rules |
Not applicable |