Modern Building Services

26 MODERN BUILDING SERVICES MARCH 2023 FEATURE PIPED SERVICES, PUMPS ANDWATER Optimising pump systems for improved energy efficiency GaryWilde , Technical Services Officer at the British Pump Manufacturers Association (BPMA), offers some basic information and guidance on purchasing, maintaining and designing pump systems for optimum energy efficiency, CO 2 reduction and capital expenditure payback time. G iven the global rise in energy costs, there has never been a better time to review and assess the efficiency of your pumping systems whatever their size, complexity or indeed sphere of operation. Pump systems account for 20% of the worlds electrical energy demand and between 25% - 50% of the electrical energy usage in certain applications. Pumps are the single largest user of electricity within industry across the European continent, consuming over 300 TWhpa of electricity, which in turn accounts for over 65 Mton of CO 2 emissions. It is also well documented that rotodynamic pumps which account for 80% of the installed base are between 20-30% oversized. There is therefore a major potential to save energy if rotodynamic pumps are properly sized and operated. Where to start - assess the potential for savings Understand your pumping system: To identify if a pumping system is sized correctly make the following checks; • Are you wasting liquid flow? • Are you creating additional pressure? • What is the monitoring & controls philosophy? • Are there any oversized pumps installed for your required duty? • Are there any significantly old pumps employed in the system? • Is there excessive noise in the system? • Are there any throttling valves installed in the system? • Have you the correct size of pipework installed? • Inadequate maintenance lowers pump system efficiency, so what maintenance procedures are in place? • Are you adopting a proactive equipment replacement programme to current EU legislation? System Design - making the right choices The vast majority of pump systems operating today were not originally designed with energy conservation as a major consideration. If pump systems are initially designed on an energy efficient basis and pumps are correctly applied and sized the energy savings will often be in excess of 50%. To design an energy efficient pump system all the following criteria should be considered: • Basic plant layout • Pipe size, configuration, and restrictions to limited pipework losses • Information on the liquid, (viscosity, density, aggressiveness, temperature) • System characteristics and pump selection • Pump/System control • Avoid oversizing of the pump units • Selecting the most energy efficient pumps at the best efficient point • Fitting VSD’s to match the system design & demand Low energy costs are a direct result of knowing what is the minimum flow and pressure that the system requires to operate successfully (system demand) and then selecting the correct sized pump and matching it to the system. When selecting a pump, it is important to determine the required flow and pressure to be generated by the pump. The flow may be determined by a process requirement, by the heating or cooling required in the system or by the peak water demand for utilities. The pressure required may be to elevate the liquid within the system or to overcome the pressure losses in the system created as liquid passes through it. It is important to know as much about the pump system as possible and to create a pressure/ flow profile for the system. The energy required to drive the pump is directly related to the flow and pressure required. To generate high pressures generally leads to designs that may be inefficient and therefore it is important that neither the flow nor the pressure is over specified. Pump Control It is now readily accepted that significant energy savings have already been made by using variable speed drives and high efficiency motors. Generally, VSDs are used to continually adjust the speed of the pump to the demand. The savings can be determined by the affinity laws: Q= Flow, H= Head, P = Power and n = Rotational Speed When building a new pumping system, most pumps are selected with a safety factor in play to satisfy potential future uprates or to allow for wear in the pump or fouling of the system. Often there are many different parties involved in specifying and building a system and the safety factor can grow exponentially. This results in the pump deliveringmuch higher flows than required. Theremay also be the need to vary the flow due to process conditions or varying heating and cooling needs within buildings. Q 2 Q 1 n 2 n 1 = H 2 H 1 n 2 n 1 = 2 P 2 P 1 n 2 n 1 = 3