How plastic pipes can boost energy efficiency
Measuring the head losses and pump-duty requirements of plastic pipework revealed some amazing results. Des Dolan of Durapipe discusses the findings.
Energy efficiency has become increasingly important in the building-services industry, with contractors, consultants and specifiers looking to select products that can demonstrate clear energy savings. This applies to all products in the supply chain — with pumps and pipework no exception.
All modern buildings require large volumes of water to be supplied to each and every floor, and a reliable network of pumps and pipes is integral for the effective distribution and operation of water supplies. The energy efficiency of pipework systems is coming under increased scrutiny. While there is a belief that plastic pipe systems are more energy efficient than metal alternatives, there has previously been little evidence to confirm the theory.
As a result, Durapipe UK embarked on a joint project with Wilo, one of the UK’s leading pump manufacturers, to undertake research into the required energy to pump water through a plastic pipe network, compared with a traditional carbon-steel system.
The energy used to pump liquid around a pipe network all comes down to the level of frictional head loss. When a liquid flows through a pipe, friction between the pipe wall and the liquid causes a head loss, which is an irreversible loss of the fluid’s potential energy. Calculating this loss is fundamental to the design of any pipework system for HVAC applications, with the internal roughness of a pipe an important factor when considering friction loss.
The absolute roughness of a pipe material is provided in millimetres, with the smooth bore of plastic pipes providing a much lower surface roughness than carbon steel. The lower the surface roughness, the lower the frictional head loss experienced, which in turn means reduced pump duties and smaller pumps — ultimately resulting in energy and cost savings.
This research project compared the pump duty requirement using both plastic and steel pipe materials. The test was carried out based on a light commercial installation of 200 m of straight 32 mm pipe, 20 elbows and two isolation valves, assuming a flow rate of 1 l/s.
The results revealed a total frictional head loss of 8.23 m for the plastic pipe system, compared with 15.71 m for the steel installation. Due to the reduced power needed to operate a plastic pipe installation, a lower-duty, more cost effective pump can be selected to work with the pipe network. The cost for the most appropriate pump to effectively service this application was £1717 for the steel pipe system and £676 for the plastic pipe option — a cost saving of 60%.
More importantly, the smaller pump required for the plastic pipe network would achieve energy cost savings of 75% compared with the pump required for the carbon-steel pipe network. In addition to the initial reductions in installed costs, the energy cost savings with a plastic pipe material will grow over the lifetime of the system.
Suffering from scaling and corrosion, the surface of steel pipework deteriorates over time, which restricts flow through the pipework, increasing the pump duty needed to pump the liquid through the pipe, which in turn increases energy costs.
In comparison, the smooth bore of plastic pipe sees a consistent flow rate maintained over the lifetime of the system — offering stable pump energy costs, while also benefiting from reduced maintenance requirements and costs.
The energy efficiency of new buildings is typically thought about in relation to heating the building and the building fabric. Insulation, solar panels, windows and heating systems are always considered for their energy-efficient properties. However, it is important to remember that mechanical services, such as pump and pipe networks can offer significant energy cost savings over the lifetime of a building.
The building services landscape has changed dramatically over recent years, and incorporating energy-efficient products into project specifications has become integral to winning new projects, tenders and framework agreements. Every manufacturer in the supply chain needs to be able to communicate the energy-efficiency credentials of their products if they are to continue competing for new projects and not get left behind.
Des Dolan is building-services brand manager with Durapipe.