Alton Towers Resort in North Staffordshire is the largest theme park in the UK, including a waterpark, hotel complex and more. Open throughout the year, the park uses a substantial amount of energy in heating and cooling applications, as well as water filtration and operation of the rides themselves, such as Congo River Rapids (pictured). Operator Merlin Entertainments commissioned Centrica Business Solutions to review the overall energy use at the waterpark, and work to improve its efficiency. A major part of this task was a review of the 24 water pumps in the waterpark.
The pumps were largely Grundfos centrifugal types, which had been in place for a couple of decades. The initial suggestion was to replace the pumps with new, more efficient units. This would have saved energy in operation but was a significant investment. More importantly, it would have been disruptive, meaning that the park was likely to be out of action.
Central Group is a Merseyside-based supplier and installer of pumps, drives and motors, with an office in the Midlands. Centrica had previously worked with Central Group on several schemes, including a successful energy-saving project at Arrow Park Hospital, so it asked the firm to review the pumps and put forward a solution.
OVERSPECIFIED
Central Group’s account manager Gianfranco Colangeli went to Alton Towers, and found that much of the pumping gear had been overspecified. “At an initial design stage everything ends up being oversized,” he explains, and if a valve is introduced to control the flow “your pump ends up working harder to overcome the mechanical restriction”.
Colangeli came back with the information he needed to write an energy appraisal – and reckoned that the answer was not to change a single pump, but instead to fit variable-speed drives to the existing pumps. Most of the pumps could be run at a lower speed, while still providing adequate flow, but thanks to the cube law (see box, right) this could mean a substantial energy saving. Colangeli calculated that the measure would have a payback time of less than two years. The energy appraisal was so convincing that the scope of the job was increased, and a total of 64 pumps were identified as needing new drives.
Once the initial assessment process had been finished, the physical work of installation and testing throughout the park took two to three months – but crucially, “it had zero impact on the operation of the waterpark,” says Colangeli. The drive units could be wall-mounted and wired up while the park was operating, then connected to the pump motors at a more convenient time. “We were working odd hours, but we didn’t want to interfere,” he explains.
DRIVES
Most of the pumps are now driven with ABB’s ACH580 drives, which are optimised for HVAC applications: “It’s a simple drive for a simple application,” says Colangeli. “On the Master Blaster, we used the ACS880 model (pictured, above right) – you can do more programming, they have direct torque control and they are linked.”
One of the centrepieces of the waterpark, the Master Blaster is not just a conventional water slide; rather, it’s a ‘water coaster’ with three uphill sections where guests are pushed along by water flow at 5m/s. There are also ‘dark sections’ and the whole thing is 208m long. This was a critical application: the client was concerned that it should work completely predictably, just as it had before. Moreover, other suppliers had been unable to improve its efficiency.
“The pipework system was very strange,” says Colangeli. It operates using seven 55kW pumps, with five on duty at any time and two on standby. “And I noticed that all the valves were 50% closed – when you see that you know that you can make an energy saving.” This could be done without affecting the ride: “Once we had explained that it would have zero impact they were okay for us to go.”
Colangeli and his colleagues, including project engineer Anthony Daly, started at 5:30am every morning because any testing had to be done before the waterpark opened at 8am. Once they had fitted all seven pumps with inverter drives, they tested each one in turn: first, with the pump at full speed and the valve closed as before, they measured the water flow downstream of each valve with an ultrasonic flow meter. Then, with the valve fully open, they adjusted the drive speed until the water flow was measured to be the same as before. Finally, the physical ride testing process could begin. “They have a designated weight that they send around,” explains Colangeli. If that works to their satisfaction, “then they send one of their own people around”.
The total cost for 64 applications, including some new control gear and electrical repairs where needed, was around £215,000 – substantially less than the initial quotation for replacing fewer pumps. Most of the units had the speed cut by 10% as an initial measure, although Colangeli believes there is potential for further optimisation. There are other benefits, too: the pumps should require less maintenance, as the lower operating speeds mean less cavitation.
And the results were extraordinary: the energy savings were even better than predicted, saving Alton Towers 1.4m kwH per year, and the actual payback period turned out to be just over a year. The project even won Central Group ‘Project of the Year’ at the AEMT Awards 2018.