Case study · Food and cold storage
16% less temperature variation after door monitoring
Door sensors and alarms on a busy 12,000 m³ freezer at a UK food distribution depot. Three months after they went in, against the three months before, the freezer ran colder and steadier, with lower peaks and a complete record. Energy savings are estimated from the temperature data, not metered.
- Customer
- A 12,000 m³ freezer at a UK food distribution depot
- Sector
- Food and cold storage
- Rules it served
- Food safety and customer audit standards
- Traffic
- 1,200 to 1,600 door openings a day
- Compared
- Three months before door monitoring against three months after
The problem
A large freezer at a busy distribution depot sees constant traffic: 1,200 to 1,600 door openings a day. Every opening lets in warm, humid air. A door left open for a few minutes means a temperature rise, frost on the evaporator coils and a long pull-down for the refrigeration plant.
What we did
Door sensors went on the freezer doors, reporting to Sematics alongside the freezer's temperature sensors.
- A door left open raises an alarm, so it is closed promptly instead of being found later.
- Door events sit on the same record as the temperature, so a rise has a cause next to it.
- Staff know the doors are monitored and that the system will catch a door left open.
The result
Over the three months after, against the three months before, temperature variation fell by 16% (standard deviation 0.69 °C to 0.58 °C). The average went from −20.23 °C to −20.91 °C, and the highest reading from −15.93 °C to −16.45 °C. Data completeness rose from 96.5% to 100%.
Openings averaged about 11.5 seconds, 4 to 5 hours open in total a day across 1,200 to 1,600 openings: short openings, promptly closed.
A sensor on a door saves nothing on its own. The saving comes from what the monitoring makes happen: alarms get a door closed sooner, and, the biggest effect, people stop leaving doors open once they know the doors are watched.
Estimated, not metered: less warm air getting in means less work for the plant. Taking 12 kW of thermal load avoided, at a plant efficiency (COP) of 1.6, gives 7.5 kW of electrical demand. Over 8,760 hours that is about 65,700 kWh a year, about £9,900 a year at £0.15 per kWh, and about 8.6 t CO₂e a year at a DESNZ factor of 0.13096 kg CO₂e per kWh. These figures are estimated from the measured temperature data using UK average tariff and plant efficiency assumptions; they are not metered. Energy monitoring measures the real figure; the working is in the full report (PDF).
In figures
What changed, at a glance
- Door left openAn alarm is raised
- Closed soonerInstead of found later
- Habits changeStaff know doors are watched
- Less warm air inSteadier freezer, less frost, less work for the plant
16%
less temperature variation in a 12,000 m³ freezer after door monitoring (standard deviation 0.69 to 0.58 °C)
Three months before and after door monitoring
96.5% to 100%
data completeness, three months before and after door monitoring
Data completeness before and after
Related
If this sounds like your site
The full report (PDF)
The measured results and the energy estimate with its working, in three pages.
Read moreEnergy monitoring
Metered energy on refrigeration plant and incoming supplies, on the same dashboards as temperature.
Read moreDoor switches
Door contacts that report open and closed to Sematics, with the time each door was open.
Read moreFood distribution and cold storage
Monitoring for cold stores, depots and distribution sites.
Read more
Source: Measured: Sematics temperature and door data for one freezer, three months before door monitoring against three months after. Energy, cost and carbon figures are estimates from that data (12 kW thermal ÷ COP 1.6 = 7.5 kW; × 8,760 h; £0.15/kWh; 0.13096 kg CO₂e/kWh), not metered. Customer not named. The figure: Sematics data for a 12,000 m³ freezer at a UK food distribution depot, three months before door monitoring against three months after; customer not named.
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