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Micro managing

The use of micro-sensors has enabled Pizza Hut to identify and control some major areas of hvac energy use, reports Damon Schünmann

When Pizza Hut asked consultant Aecom to check out its energy usage, it began a chain of events that ended up with a complete picture of how its restaurants were performing across its hvac sub-circuits. And pretty much all the rest as well. Enter Nowatt, which approached Aecom with a proposition to use its system of sensors that can provide a breakdown of electrical use across building services.

Nowatt director Mark Hillyard explains: “Our tool produces raw data on energy being used. It’s a mass of sensors that go into a building to give access to information in real-time over the internet.”

Circuits selected for monitoring have typically included the restaurant air conditioning, kitchen air conditioning, cooker hood supply and extract fans, lighting circuits, and walk-in fridge and freezers.

Since energy readings are commonly taken only every half hour, it makes it tricky to know where the energy is being used. Aecom needed something that showed this exactly. Once the sensors were fitted, the consultant was able to see that time clocks for air conditioning were not set, so it got an AC contractor to get that changed. The error had been wasting about 72 kWh per night and now it is saving about 17,000 kWh per year.

Aecom building engineer Richard Groves says: “We also discovered that one AC unit was not providing any cooling because of the constant 3 kW load on the kitchen AC sub-circuit, which we knew from the technical manual was the consumption of the fresh air fans. At the same time as fixing the time clock, we also requested the AC be fully repaired, which re-established comfortable conditions in the kitchen and staff areas.”

Mr Groves adds: “We looked at data for a Shrewsbury restaurant, and the walk-in freezer was using twice as much energy as it was rated at. That was particularly frustrating because it was supposed to be a low-energy site and, when it was working correctly, it should use half as much energy as a typical walk-in freezer. We would expect it to be using 60 kWh for the freezer and the fridge but it was using about 140 kWh.

“The fridge contractor found that the defrost heater was permanently engaged. It was fixed and was back to its low-energy operation. That site is now using about 30 per cent less energy. There are different configurations in each Pizza Hut, from standalone restaurants to those in retail parks and the one in [London’s] Brent Cross shopping centre. This benchmarking allows us to see what typical use should be for different restaurant type.”

Mr Hillyard says: “Each restaurant has 40 to 50 sensors providing in-depth analysis on how each business works. The micro-sensors feed data to a tracker or monitor and this passes them to an internet connection. This transmits the data and we collate it on a server where the client can log-in to view it.

“It provides a microsecond understanding of the electrical usage and itemises the electricity bill for a building into its component parts. It’s business payback data that allows sight of return on investment - it takes away the mystery of energy savings.”

The monitoring has resulted in a change in the specification for new-build walk-in fridges and freezers. Mr Groves says this came about when one restaurant had to be re-built following a fire. “We requested that the insulation of the walk-ins be increased from 75 mm to 100 mm, that the external condensers were moved from the rooftop plantwell - which is a sun trap and also has the other heat rejecting plant in it - to the rear wall directly behind the walk-ins, and the use of thick insulated curtains inside the doorway to the walk-ins.

“When compared with another site using the old configuration of walk-ins, the new one is saving approximately 20,000 kWh per year in energy consumption for the two walk-ins.

“Overall at this site, we made many energy-saving suggestions - some were used, some weren’t, but the re-built site is using approximately 30 per cent less energy than this time last year before it burnt down.”

Nowatt claims that its transducers measure at better than 95 per cent accuracy. While electricity billing meters measure at 100 per cent, Nowatt says that fitting them to get that level of accuracy would perhaps cost £50,000.

My Hillyard believes the hvac sector is often subjected to ‘green-wash’ because it is difficult to measure the breakdown of energy use. Aecom has been able to prove this by demonstrating that one so-called energy-saving product would not produce the results that were claimed in a real-life setting.

“One device purported to save energy on the fridge and freezer devices, and the company had all sorts of factory test data to prove how good their device was,” says Mr Groves. “We persuaded it to carry out a free trial, with the power consumption monitored on the circuits that the fridges and freezers were plugged into.

“The results of the trial were that the device actually led to the fridges and freezers using more power because the compressors were having to work harder to overcome the effects of the energy-saving device - something that the factory tests had not picked up. Our trial was based on real-life use of the fridges, not idealised factory tests.

“We also monitored appliance internal temperature, external temperature around the building, kitchen temperature and food sales to ensure that we spotted anything that could affect the results. In the end, we reported to Pizza Hut that it should not proceed with a full estate-wide roll out of this product as the device was not energy saving but increased the energy use.”


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