3.8.1 Inventory and assessment of pumping systems
The first step towards identifying applicable energy savings measures and optimising a pumping system is to establish an inventory of the pumping systems in the installation with the key operating characteristics. The inventory can be established in two phases (see Section 2.15.1 and Annex 7.7.3):
basic system description: this consists of consulting company records or carrying out simple measurements, in order to assemble the following data:
●list of, e.g. the 50 largest pumps consuming energy (by total pump power rating): size and type
●function of each pumps
●power consumption of each of these pumps
●demand profile: estimated variation during day/week
●type of control system
●operating hours/year, and hence annual energy consumption
●problems or maintenance issues specific to the pump.
In many organisations, most or all of these data could be assembled by in-house staff.
documentation and measurement of the system's operating parameters: documenting or measuring the following elements is desirable for all pumping systems, and is essential for large systems (over 100 kW). Collection of these data will require a significant level of technical expertise, either from in-house engineering staff or from a third party.
Because of the large variety of pumping systems, it is not possible to give a definitive list of points to look for in the assessment, but Sections 3.8.2 to 3.8.6 detail a useful list of key issues to address.
3.8.2 Pump selection
The pump is the heart of the pumping system. Its choice is driven by the need of the process which could be, first of all, a static head and a flowrate. The choice also depends on the system, the liquid, the characteristic of the atmosphere, etc.
In order to obtain an efficient pumping system, the choice of the pump has to be done so as to have an operating point as close as possible to the best efficiency point as indicated in Figure 3.35.
Figure 3.36 shows the ranges of total head as a function of the pump capacity for a given speed in different types of pumps.
It is estimated that 75 % of pumping systems are oversized, many by more than 20 %. Oversized pumps represent the largest single source of wasted pump energy.
When choosing a pump, oversizing is neither cost nor energy efficient as:
●the capital cost is high
●the energy cost is high because more flow is pumped at a higher pressure than required. Energy is wasted from excessive throttling, large by passed f lows, or operation of unnecessary pumps.
Where oversized pumps are identified, their replacement must be evaluated in relation to other possible methods to reduce capacity, such as trimming or changing impellers and/or using variable speed controls. Trimming centrifugal pump impellers is the lowest cost method to correct oversized pumps. The head can be reduced 10 to 50 percent by trimming or changing the pump impeller diameter within the vendor's recommended size limits for the pump casing.
The energy requirements of the overall system can be reduced by the use of a booster pump to provide the high pressure flow to a selected user and allow the remainder of the system to operate a lower pressure and reduced power.
The applicability of particular measures, and the extent of cost savings depend upon the size and specific nature of the installation and system. Only an assessment of a system and the installation needs can determine which measures provide the correct cost-benefit. This could be done by a qualified pumping system service provider or by qualified in-house engineering staff.
The assessment conclusions will identify the measures that are applicable to a system, and will include an estimate of the savings, the cost of the measure, as well as the payback time.
Pumping systems often have a lifespan of 15 to 20 years, so a consideration of lifetime costs against initial (purchase) costs are important.
Pumps are typically purchased as individual components, although they provide a service only when operating as part of the system, so a consideration of the system is important to enable a proper assessment of the cost-benefit.
Energy Efficiency (2009) 3.8.1、3.8.2