Electric vs. Gas Cont...
Mr. Lindsay's March 1 letter (PUBLIC UTILITIES FORTNIGHTLY, p. 6) requires some further discussion. We do agree that reducing cooling seasonal peak electric demand is desirable. Lessening the electric infrastructure's environmental effects and electric system failures, as we witnessed in the summer of 1996, is to the public good. However, thermal storage systems have siting issues and the potential to run out of capacity at the worst possible time on peak days. Wouldn't a gas chiller, operating in the cooling season on the lightly loaded gas delivery system, be a simpler, more economical, and less environmentally damaging choice?
Mr. Lindsay's letter referenced the incomplete Total Equivalent Warming Index (TEWI) study, managed by the Department of Energy, but mainly funded by a group of electric chiller refrigerant manufacturers. This study still contains a number of issues. First, TEWI is not a comprehensive study of environmental issues. Only carbon dioxide emission and the impact of refrigerant release on global warming are studied. Not covered are such issues as sulfur emissions from coal-fired power plants, fuel disposal issues from nuclear power plants, nor any other impacts of electric infrastructure.
Even in this limited role, the TEWI study on cooling poses certain unresolved issues.
• Why does the electric calculation assume that no energy is used moving fuel from mine to power plant? Energy is used to extract, transport and distribute fuels. The TEWI report discusses losses for energy extraction of 4.5 percent for coal, which may be low, 8.9 percent for gas and 10.9 percent for oil fired plants. Oddly, these values are included in the gas cooling calculation, but not the electric cooling calculation.
• Why is the annual electric distribution loss used when chillers operate on overloaded summer distribution? According to the Electric Power Research Institute, electric distribution system losses during summer cooling periods are higher than the annual average losses (16 percent vs. 8 percent) due to higher loads on transmission lines. %n1%n The draft report even includes discussion of this, but fails to include the effect in the analysis.
• TEWI assumes a 35-percent to 45-percent annual average electric generating efficiency. This is very high. Thirty-three percent would be more realistic for an annual average. %n2%n In addition, why is TEWI assuming the annual average generating base? Peak summer demand for electricity is often met by operating inefficient older coal fired power plants, less-efficient simple cycle gas turbines, and supplemental boiler firing. This is the true generating base for summer peak demand, and electric air conditioning is the key summer peak demand. The effect of this alone can raise CO2 generated by power plants from 0.65 kg CO2/kWhe to 0.90 kg CO2/kWhe. %n3%n
• Refrigerant release levels at 0.5 percent from electric chillers seem very low. Maintenance is only required after a 15-percent release. %n4%n
• The electric chiller efficiencies (such as 0.48 to 0.50 kW/ton) represent the current best available equipment, which is a small fraction of all electric chillers sold.
• Engine chiller efficiencies used in the report are not the best available, and no allowance is made for heat recovery from the engines, which