Cooling the Wellcome building more efficiently

Summary

Changes to the software controlling the cooling system of the Wellcome Trust Centre for Human Genetics have greatly reduced its energy consumption and carbon emissions. Similar improvements could be made relatively easily across much of the University estate, and the Environmental Sustainability team are keen to work with building users to do this.

The challenge

Until recently, the Wellcome Centre’s cooling system used an old design that relied on continuously pumping chilled water constantly round a central loop, and then opening and closing the valves leading off that loop to allow it to flow into areas that need cooling.

This meant the central pump was working flat out most of the time to move cold water around the main circuit, even when little or no cooling was needed. This wasted energy and put unnecessary strain on the building’s pipework, shortening its life.

Martin Taylor, the Sustainability Engineer who led the project, likens it to keeping a car’s accelerator pressed to the floor while continuously applying the brakes to control its speed.

The solution

Martin worked with the building’s users, with Estates Services colleagues including Building Services mechanical engineers, and with external contractors Hoare Lea to understand how energy was being used to cool the building and how this could be improved. After analysing a year’s data, they put a more efficient system in place by changing how the pump and valves were operating.

Now, the pump varies its speed to match the demand for cooling, working only as hard as it needs to in order to drive cold water where it is needed. A lot of the time – at night, for example – it does very little.

Even minor reductions in how fast the pump is working save a lot of energy – the laws of mean a 20% speed reduction will generally cut energy consumption in half. The savings are even more pronounced in this case because most of the energy that was being wasted running the pump unnecessarily was being lost into the cooling fluid, heating it up and forcing the building’s chillers to work harder.

Moving to the new set-up was not a major project and caused little disruption to building users. This is because all these changes were made simply by changing the Wellcome Centre’s Building Management System (BMS) – there was no need to change the pump and valves themselves, as the BMS could be used to make them work in a different way.

The result

Even though the changes were quick and easy to make, they are already delivering major benefits.

Beforehand, cooling the building used an average of 93.7 killowatt hours (kWh) per day; that has now fallen to 12.3kWh. This 81.4kWh reduction equates to saving around £3,000 a year, and avoiding 10.4 tonnes of carbon dioxide emissions. Because the changes could be made in the building’s software, with no need to replace valves or pipework, the project’s total cost was only around £1,200.

By reducing the pressure the cooling system operates at, the changes will also greatly lessen the strain on the pump, valves and pipework, increasing its life and reducing maintenance costs – Martin estimates a saving of around 50%. Lower pressure will also mean less water is lost from any leaks that do occur.

The graph shows what a dramatic difference the changes have made to the cooling system’s power use – beforehand it was averaging just over 4kW, while now it is less than a quarter of that. The purple triangle represents the point at which the changes were made.

Wellcome trust building data

Martin says similar techniques could be bring major benefits to buildings all over the estate; it can work on heating as well as cooling systems. In fact the old design was still being used until very recently. Any heating and cooling systems that were installed more than around five years ago may be candidates for improvement. He is now leading a major project to examine the energy consumption of all electric pumps and motors across the estate.

It is a potentially fertile field for efficiency savings. An estimated 45% of all the electricity that is generated worldwide is used to power electric motors of one kind or another; on the estate, these motors are found in chillers, fans, heating systems, air conditioning units. Moving to a more modern design in which a motor doesn’t run at high speed for most of the time would be expected to cut its power usage by around half, at least. Variations on the new design could be used even when buildings have no BMS.

If you think a similar project could benefit your building, please contact martin.taylor@admin.ox.ac.uk.