Energy, Appliances and Utilities
Energy&Environment * EnergySTAR * Toyota PRIUS Myths, Facts, and Hype ...
Additional Resources: A Consumer’s Guide to Energy Efficiency * Alliance to Save Energy * American Council for an Energy-Efficient Economy * CEE
Utilities:
ComEd: www.ComEdCARE.com * www.ComEdservice.com
Jan '07 electricity cost $94.96/869kWh=$0.109/kWhr; NOTE, in August'08: $99.96/847kWh=$0.118/kWh)
NiCorGas: www.nicorgas.com/gascost
Jan '07 natural gas cost $96.53/116.7Therm=$0.827/Therm=$0.0282/kWhr (in the flier $0.67/Therm gas supply cost; see unit conversion below. NOTE, in August'08: $42.60/25.35Therms=$1.68/therm, about double Jan07-price per Therm);
NOTE, in Jan'07 the electricity was about 3.85 times more expensive than the gas energy above (now about 2 times), but considering the usual efficiencies the electrical heating cost would be about 3 times more (now about 50% more).
Appliances: (see unit conversion below)
Typical furnace: 1 therm/hr = 100000 BTU/hr = 29.3 kW(h) heating power
Typical A/C unit: 3.5 tonR = 12.3 kW(c) cooling power & 10 SEER value (see below)
P[kW]=12Q[tonR]/SEER=12*3.5/10 = 4.2 kW(e) electrical power
NOTE that in Chicago area climate a typical furnace heating power is about 3 times bigger (about 30 kW) than A/C cooling power (about 10 kW, corresponding to A/C compressor electrical power of about 3-4 kW depending on SEER value below, since the "relevant" indoor-outdoor temperature difference in winter (75-15) oF is about 3 times bigger than in summer (95-75) oF.
What is SEER? How does it apply to the energy efficiency of air conditioners?
Every air conditioning unit has an efficiency rating known as its “Seasonal Energy Efficiency Ratio” (SEER). The SEER is defined as the total cooling output (in British thermal units or BTU) provided by the A/C unit during its normal annual usage period (for an average U.S. climate) divided by its total energy input (in watt-hours) during the same period . The efficiency of central air conditioning units is governed by U.S. law and regulated by the U.S. Department of Energy (DOE). The minimum SEER value was recently increased from 10 to 13, and EnergySTAR A/C units have even higher values.
What is a Ton of Refrigeration?
One ton of refrigeration capacity (tonR) is equivalent to 12,000 BTU/hr cooling rate.
The cooling capacity of refrigeration units is often indicated in "tons of refrigeration". A ton of refrigeration (tonR) represents the heat energy absorbed when a ton (2000 lb) of ice melts during a 24-hour day at equilibrium (0 oC=32 oF) temperature. The ice is assumed to be initially solid at 32 oF (0 oC) and becomes liquid water at 32 oF (0 oC) at the end. The energy absorbed by the ice is the latent heat of ice times the total weight.
Today, refrigeration units are often rated in BTU/hr instead of tonR. The BTU/hr equivalent of one ton of refrigeration (tonR) is easy to calculate: multiply the weight of one ton of ice (2000 lb) by the latent heat of fusion (melting) of ice (144 BTU/lb), and then divide by 24 hours to convert into BTU/hr. Thus, one ton of refrigeration, 1 tonR = (2000X144)BTU/(24 hr) = 12,000 BTU/hr.