The extra energy required to pump this extra water may more than offset the energy you save by reducing the Table 1. It does no good to operate sprinklers at lower pressures than they were designed for if that destroys the distribution pattern, causing dry spots which can only be eliminated by over-watering the rest of the area. The remainder of this article will consider situations where it is reasonable to assume that pressure reductions will not cause any reductions in irrigation efficiency. Suppose a golf course with 100 acres of irrigated area was located in climate zone where 36 inches of irrigation were required annually. To see whether or not this is financially significant, you need to consider the type of fuel and the price of the fuel you use.
Different fuels contain different amounts of useful energy, and of course prices differ.
The amount of energy in different fuels can be summarized in a conversion factor that gives the number of BHP-HRS per unit of fuel. Commonly used conversion rates for different types of fuel are given in Table 2. Dividing the BHP-HRS saved by the conversion rate listed for your fuel will give the energy savings in units of fuel per year. Consider further the example of the golf course with 100 acres of irrigated area and an annual water application of 36 inches. As noted before, a one PSI reduction in pressure requirements saved 1360 BHP-HRS per year.