Furnace Capacity 


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 


Applicability 
Systems with a furnace 

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 3.7.61) $$E_{t}=(0.0051427\cdot AFUE)+0.3989$$ where


Units 
Fraction 

Input Restrictions 
As designed 

Baseline Rules 
See the values below:

Furnace Fuel Heating Part Load Efficiency Curve 


Applicability 
Systems with furnaces 

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 3.7.62) $$Fuel_{partload}=Fuel_{rated}\times FHeatPLC$$ (Equation 3.7.63) $$FHeatPLC=a+b\cdot\ \frac{Q_{partload}}{Q_{rated}}+c \cdot (\frac{Q_{partload}}{Q_{rated}})^{2}$$ Where


Units 
Data structure 

Input Restrictions 
As designed when data is available, otherwise use the default values are provided above. 

Baseline Rules 
The defaults shall be used. 
Furnace Fuel Heating Pilot 


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 


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 fuelfired heat pumps 
Units 
Kilowatts (kW) 
Input Restrictions 
As designed 
Baseline Rules 
Not applicable 