In considering the energy provided and consumed through a Steam distribution system as a billable commodity, accurate measurement is critical to provide justifiable cost statements. As discussed in the previous article, practice has been to measure the steam provided to a given point-of-use location and bill on the total energy contained in the steam even though a large portion (20+)% is not consumed or utilized once it condenses from steam to condensate. If it were possible to accurately measure and quantify the residual energy would it be beneficial? At 20% or more of the total energy provided this answer should be, Yes!
So, how exactly do we accurately make this measurement? The answer is to measure condensate, condensate temperature, and the temperature of the saturated steam provided at the point-of-use. With these three measurements it is possible to determine the Latent Heat provided to the Point-of-use, the Sensible Heat left over in the condensate, and the Total Heat as a sum of the other two (Latent Heat + Sensible Heat).
By measuring the condensate volume and taking a dynamic temperature reading of the condensate at the measurement point it is possible to accurately and repeatability measure the Lbs of condensate consumed. Since flow technology exists with extremely high accuracy combined with enormous turndown capability, this is a much more accurate and reliable way to measure the energy usage. By adding a dynamic temperature reading of the saturated steam pressure at the point-of-use, and feeding this parameter into a flow computer with the other two variables (Condensate volume and temperature) it is feasible to calculate both components of the Total Heat provided (Latent Heat and Sensible Heat). Latent Heat provides the energy as BTU’s and BTU’s/Hr consumed at the Point-of-Use and the truly billable or captured portion of the Total Heat. Sensible Heat is the residual energy or energy remaining in BTU’s or BTU’s/Hr that is not used and recoverable to the energy provider or perhaps recoverable to the end user through another Heat/Energy recovery process.