| Natural gas is a fossil fuel composed of a mixture of | | | | correction factor formula is: 1.025 x 1.170 or 1.199. |
| hydrocarbon gases. The primary components are | | | | Result is: $/therm x therms consumed x 1.199 = billing |
| methane, ethane and propane, however the | | | | for gas used. |
| remaining gases and their percentage of the overall | | | | The energy value of the gas in BTU's is normally |
| composition can vary greatly. For example, the trace | | | | reliable, provided the utility company measures this |
| levels of H2S in the mixture sometimes lead to the | | | | value throughout the year and integrates it over |
| natural gas being labeled as "sweet" or "sour". | | | | time. However, the gas density due to pressure |
| Natural gas is often measured in British Thermal Units | | | | makes up the largest portion of the billing or thermal |
| (BTUs). One BTU is equal to the amount of heat | | | | correction, and this is the most likely area for billing |
| required to raise the temperature of one pound of | | | | mistakes from the local gas utility. Consider the |
| water one degree Fahrenheit at atmospheric | | | | following example: |
| pressure. One cubic foot of natural gas has an | | | | The consumer is supplied natural gas at 0.25 PSIG but |
| average heating capacity of approximately 1000 | | | | is billed at a pressure of 2.5 PSIG. How much is he |
| BTUs. The actual heating capacity varies across the | | | | being overcharged? |
| country, and from time to time at any given location, | | | | 2.5 + 14.7 / (0.25 + 14.7) = 1.151 or 15.1% overcharge |
| due to variations in the gas mixture. It is typical to | | | | on his utility bill. |
| see variations of +/- 5%-10% in BTU content. | | | | Could this really happen? Not only can it happen, but |
| The utility company's meter at the building exterior | | | | it happens daily throughout the country! Depending |
| measures the consumed volume in hundreds of cubic | | | | on the total monthly usage, these discrepancies can |
| feet (CCF), however the consumer's bill normally | | | | be significant, resulting in artificially and inaccurately |
| measures the consumption in therms, where one | | | | high overall operating costs. |
| therm is equal to 100,000 BTUs. | | | | Submetering the natural gas usage at strategically |
| Customers are billed by taking the gas meter reading | | | | selected points in a facility shows how much gas is |
| in cubic feet and converting this value to therms and | | | | actually used at each metered location or work area |
| applying a thermal factor that is the product of the | | | | and provides an overall total for the facility. This total |
| heat value of the gas times the gas density. | | | | is compared to the utility's billing total as a means of |
| The formula for therms is: therms = cubic feet x | | | | verifying or disputing the charges. The key element in |
| 1000 BTU's per cubic foot / 100,000 | | | | efficient submetering is a flowmeter that measures |
| Assume that the heat value is 1025 BTU's per cubic | | | | the natural gas flow accurately without duplicating the |
| foot at 2.5 PSIG: 1025/1000 = 1.025 multiplier due to | | | | utility company's need for complicated and potentially |
| gas heat (energy) value; (2.5 + 14.7) / 14.7 = 1.170 | | | | erroneous corrections based on actual gas |
| multiplier due to gas density. The billing (or thermal) | | | | temperature and pressure. |