Resource Utilization Efficiency
A popular basis for the comparison of energy alternatives is ‘point of use seasonal efficiency.’ This measures the amount of useful heat delivered per unit of energy consumed at the point of use (i.e. in the home). Typical values for various heating systems are:
Typical values for various heating systems
|Mid-efficiency gas furnace
|High-efficiency gas furnace
|Electric furnace or base board
|Electric heat pump
Unfortunately these numbers have no real significance in themselves. For example, even though an electric heat pump is almost twice as efficient as a high-efficiency gas furnace, the two systems have comparable fuel costs since electricity is about twice as expensive as gas. Similarly, in order to identify how much of our resources are being used up, the ‘point of use seasonal efficiency’ must be combined with the resource utilization efficiency or RUE.
The RUE is a measure of how much energy must be used up in order to deliver a specific amount of energy at the point of use. For example, to generate electricity for winter home heating from coal, these steps must be followed:
Coal must be mined using up energy to power machinery
Coal must be transported to the generating station again using energy and incurring some losses due to spillage, wind, and weathering
Coal must be processed prior to being burned
The efficiency of a generating station using coal is 36.5%
The transmission efficiency of electricity is 92.6%
Combining all these items it is found that the RUE for coal-generated electricity is only 31%. In other words 323 units of energy are depleted up to deliver 100 units of energy to the home.
Because Ontario Hydro uses a combination of hydro and nuclear energy for base load, and fossil fuel generation for winter peaks, one can consider electricity for home heating in winter can be considered coal-generated electricity. Thus the RUE for electricity for heating is 31%.
This is an incremental analysis. Another approach is to take the overall RUE as the weighted average of the RUE of coal, nuclear, and hydro electrical generation.
The natural gas supply system is much simpler than the electricity supply system. The gas is extracted from the ground, processed to remove trace constituents such as propane, butane, and sulphur. Then it is compressed and transported to Ontario through pipelines. The RUE to deliver gas to consumers in Ontario is 84.5%.
By combining point of use efficiency with RUE it is possible to determine the overall efficiency of a heating system.
Provide the RUE/Point of use and Overall units of system
|Overall Units of
to deliver 100 units
to the home
Probably the best way to interpret overall system efficiency is to view it as a measure of how efficiently we are using our non-renewable energy resources. In other words, how much are we conserving for the future.
Clearly, all natural gas heating systems conserve more non-renewable energy than electrical heating systems. A homeowner conserves 27.5% to 60.6% less non-renewable resources simply by choosing a gas heating system over an electric one. This act alone reduces environmental loadings by reducing total CO2 emissions as well as reducing other harmful emissions from coal fired electrical generating plants.
Gas is a more efficient form of energy than electricity for space heating.
Gas is a more environmentally form of energy than electricity for space heating.