ENERGY EFFICIENCY CASE STUDY
Win 3:Ensure the chillers run only when cooling is needed
system until the outside temperature rises above 15C. ‘We found that where maintenance had been carried out these had been set to zero on some floors, so the sensor was always calling for cooling,’ Camsell says. With the hold-off points reset, chiller operating times were significantly reduced. However, the chillers were still coming on at 7am every morning, running for a short time, and then turning off again. The problem was narrowed down to one
However, even though the chillers were no longer running at night, they were still running when they should not have been, for example during a winter’s day while it was snowing
Kevin Barrett was on the roof one winter’s night to carry out an audit when he noticed the chillers were running. There are five one-mega-watt chillers, and they were using a lot of energy to cool an empty building in the middle of winter. He told the maintenance team. They claimed to have solved the problem but when Camsell made a nocturnal visit to the roof several weeks later, he noticed the chillers were still running. Camsell and Barrett set about resolving problem. First they found some rogue time schedules in the BMS system, which were calling for the chillers to run 24 hours. They removed these and the chillers ceased running at night. ‘That removed 12 hours running costs every single day,’ says Camsell. However, even though the chillers were
no longer running at night they were still running when they should not have been, for example during a winter’s day while it was snowing. Camsell and Barrett turned their attention to the ‘hold-off’ temperatures for each floor. These should ‘hold-off’ the cooling
outside air sensor linked to the hold-off control for one particular floor. This sensor had been relocated so that it was positioned inside the fresh air intake on the floor’s air handling unit. The problem was that the air handling unit was turned off at night. As a result the sensor warmed up so that in the morning it was calling for cooling. As soon as the air handling unit started working, cold outside air was pulled across the sensor, cooling it so that it no longer called for cooling. To resolve the issue, the sensor was relocated. ‘The chillers now run only when there is
a genuine demand,’ says Camsell. A glance at the building’s energy figures shows the impact the initiative has had on energy usage. In November 2010, before the works, the building consumed 88,973 kWh. In March after the issues had been resolved, this had dropped to 22,106 kWh. What’s more there was no capital investment needed, just time. ‘We did it all in house and the savings are phenomenal,’ he says.
Win 4:Ensure pumps have been Win 5: commissioned correctly
When Camsell and Barrett first arrived at Portland House three years ago the tenants were complaining about the noise of water in the radiator system. They were also unhappy about the radiators’ thermostatic values, which had a tendency to spring open making the rooms overheat. The system had been in place for two years.
It was designed to slow the circulating pumps as the thermostatic valves start to close to match the reduced demand for heat. ‘When we looked at the system, we found the circulating pumps were running at full speed, forcing water through the system, making it noisy and
42 CIBSE Journal November 2011
increasing wear on pipework and valves,’ says Camsell. He suspected the run-away pumps were also forcing open the thermostatic valves. The solution: When the pump was being commissioned a jump-wire had been placed between two control terminals to make it run flat-out. The wire had never been removed. With the wire disconnected, the system performed as designed. The thermostatic valves now work properly, which means the load on the boilers has been reduced, saving gas, while the pump’s reduced speed saves electricity. ‘We had assumed everyone had done their job correctly,’ says Barrett.
Turn everything off
The plant is scheduled to turn off at 7pm. However, Camsell now turns it off at 6pm, which saves one hour’s running time a day. ‘No one has even noticed,’ he says.
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