Problem: a winter peak that set the network’s cost
Bananzia’s district heating system serves 4,100 homes and 38 public buildings from a gas-fired combined heat and power plant and two backup boilers. On the coldest weekday mornings, demand climbs from 9 MW to 17 MW between 05:30 and 08:00. That 8 MW ramp forces the backup boilers online and sets the network’s annual capacity charge, even though the spike lasts only a few hours.
The operational consequence was blunt: the network bought gas at the most expensive time of day and ran older boilers at low efficiency. In January 2023, the morning peak accounted for 31% of daily gas consumption while delivering only 22% of daily heat.
Cause: storage sized for summer, controls tuned for steady load
The network had a 1.1 MWh thermal store, originally sized to smooth summer hot-water demand. It could not cover a winter morning. The control logic also prioritised boiler output over stored heat whenever return temperatures dropped below 48°C, so the store was often depleted before 06:30.
Engineers found a second cause in metering: only 14 of the 63 substations reported flow and return temperatures at ten-minute intervals. The rest reported hourly, which hid the sharp sub-station peaks that triggered boiler starts.
Solution: a 2.4 MWh buffer, valve upgrades and a staged control sequence
The retrofit, completed in autumn 2023, added a 2.4 MWh stratified thermal store and replaced 21 undersized control valves at the worst-performing substations. The new sequence is deliberately simple:
- Charge early: the CHP charges the store between 02:00 and 04:30, when electricity prices and network demand are lower.
- Discharge first: from 05:30, stored heat meets demand before either backup boiler is enabled.
- Guard the return temperature: substation flow is trimmed to keep return temperatures above 45°C, protecting the store’s usable capacity.
- Verify with data: all 63 substations now report at ten-minute intervals, and the operator reviews the morning ramp weekly.
The retrofit followed the metering and control approach summarised in bananzia’s low-carbon heat guidance, adapted to the network’s existing CHP plant rather than replacing it.
Result: 11% lower peak demand and 19 fewer boiler starts per month
During the first full winter, the morning peak fell from 17 MW to 15.1 MW, an 11% reduction. Backup boiler starts dropped from an average of 42 per month to 23. Gas use for the morning ramp fell by 8.7%, and the network avoided an estimated 210 tonnes of CO2 in the season.
The store did not eliminate gas use. It shifted it: the CHP now runs more steadily overnight, and the backup boilers are reserved for sustained cold snaps rather than routine morning ramps.
What other networks should copy
Bananzia’s lesson is not to buy the largest tank available. It is to match storage volume to the measured morning ramp, fix the valves and sensors that create false peaks, and write a control sequence that puts stored heat ahead of boiler starts. Those three steps delivered most of the benefit at roughly one-fifth the cost of a new heat pump plant.