Selecting the best-suited HVAC system depends on factors such as: cost and availability of the energy source; appliance or system efficiency; cost to purchase, install, and maintain the appliance or system; and environmental impacts associated with the fuel. Energy prices vary because of type of fuel, market pressures, supply availability, production capacity, weather, season, and politics. They tend to vary somewhat by geographic location. A common way to compare heating energy costs at a geographical location is by determining the delivered heating cost, expressed in consistent units (i.e., cost per million Btu, $/MMBtu), based on the cost of the fuel ($/unit), heating value of the fuel (HV), and seasonal efficiency of the system or appliance (η_hs), expressed in decimal form (i.e., 80% = 0.80):Compute the delivered heating cost ($/MMBtu) for the following fuels burned in a modern biomass heating unit (i.e., furnace or boiler) with a seasonal efficiency of 75%:
a. Wood pellets based on a heating value of 8000 Btu/ lb and a cost of $0.10/lb.
b. Shelled corn (15% moisture content based on a heating value of 7000 Btu/lb) and a cost of $0.04/lb.
(Shelled corn has had kernels removed from cob.
Cost is based on $2.0/bushel. A typical bushel of corn weighs 56 lb/25.4 kg and contains 72 800 kernels.)
c. BioHeat (5 to 20% biodiesel with heating oil) based on a heating value of 126 000 Btu/gal and a cost of
$2.90/gal.

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Delivered Heating Cost ($/MMBtu) = ($/unit 1 000 000 Btu/MMBtu)/(nhs. HV)