Northfield Bakery: a single-SEU energy review and a baseline that flatters the plant
Northfield Bakery runs three baking lines on a 24/7 schedule. Gas-fired ovens supply 41% of site energy; electricity for proofers, refrigeration and compressed air supplies 55%; diesel supplies the rest, burned by nine delivery trucks that Northfield's own drivers operate daily under a three-year lease that includes fuel. The energy review was assembled by a maintenance planner from the site's twelve monthly utility invoices. It concludes that the whole site is one significant energy use, identifies no relevant variables, and states that future energy use will be 'approximately flat'. The EnPI is total site kWh per tonne of product and the energy baseline is calendar year 2022. Production was 18,400 t in 2022 and 17,900 t in 2024, while total energy fell from 62,000 MWh to 61,500 MWh. In March 2024 a new blast freezer was commissioned and gas oven 2 was rebuilt to a higher thermal efficiency. At the management review the plant manager said that 'consumption is below the baseline, so we have improved'.
1. Identify the deficiencies in this energy review against clause 6.3 and explain the consequence of each for the SEUs and the baseline.
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Analysis of energy use (6.3 a). Twelve site-level invoices are not an analysis of energy use. The standard requires analysis based on measurement and other data; without sub-metering of ovens, refrigeration and compressed air, the review cannot show where energy is used, so neither SEU identification nor improvement opportunities can be supported.
SEU identification (6.3 b). Declaring the whole site a single SEU is not a determination, it is an absence of one. SEUs are uses that account for substantial consumption and/or offer considerable improvement potential; a site-wide SEU cannot be targeted, owned or monitored.
Relevant variables (6.3 c). Production volume, product mix, oven loading and ambient temperature are not identified, so performance can never be normalised and every later comparison is ambiguous.
Current performance and future use (6.3 d, e). Performance of the SEUs is not determined, and 'approximately flat' has no basis in data, planned production or known projects.
Boundary error. Diesel is excluded because the trucks are leased. Ownership is not the test; the trucks are operated by Northfield's drivers within its operational control, so this energy use belongs inside the scope and the review.
Not updated (6.3). The new blast freezer and the oven rebuild are changes that should have triggered a review update.
2. Is the plant manager's conclusion supportable? Show the arithmetic and state what is needed before any improvement claim is made.
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The conclusion is not supportable.
- 2022 intensity: 62,000 MWh ÷ 18,400 t = 3.370 MWh/t
- 2024 intensity: 61,500 MWh ÷ 17,900 t = 3.436 MWh/t
Intensity is about 2% worse, not better. Absolute consumption fell 0.8% only because output fell 2.7%; output fell faster than energy. 'Below the baseline' is a statement about volume, not about energy performance.
Before any claim:
- Separate the EnPIs by energy type (gas per tonne, electricity per tonne); a single total-kWh ratio hides the fact that gas dominates and that the two carriers behave differently.
- Document the EnPI method (6.4) so the indicator, the denominator and the frequency are fixed in advance, not chosen after the result is known.
- Normalise for relevant variables - product mix, ambient temperature for refrigeration, oven loading.
- Handle the structural changes. The blast freezer adds load unrelated to efficiency, and the rebuilt oven reduces gas per tonne. Either normalise for them or adjust the baseline (6.5) and record why and how.
- State uncertainty, including meter class and any estimated data.
A defensible statement would be: 'gas intensity per tonne on Line 2 fell X% after the rebuild, after normalising for mix; site electricity intensity rose because of the new freezer.'
3. How should Northfield determine its SEUs, and what must happen before the baseline is re-established?
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Criteria first. Agree and record the criteria for significance - for example share of site energy above 5%, or any use with identified improvement potential above a stated threshold. Criteria chosen in advance stop the SEU list from becoming whatever is convenient.
Granular level. The SEU list must be fine enough to act on: ovens (per line), refrigeration and the new blast freezer, compressed air, proofers, and the delivery fleet. A use that cannot be assigned an owner and an operating criterion is too coarse.
Data before conclusions. Run a metering campaign as the data collection plan required by 6.6: temporary loggers on ovens and the freezer, a week of compressor logging, plus fuel-card data for the fleet. Four to eight weeks of interval data is normally enough to rank uses credibly.
Then the baseline. Re-establish the EnB (6.5) using data from the reviewed energy use, over a period that reflects normal operation. The existing 2022 calendar year can be retained only after adjustment for the freezer and the oven rebuild, with the adjustment method documented. Alternatively, use a post-metering 12-month period as the new baseline, and say plainly that earlier comparisons are no longer valid.
Reissue the review with relevant variables, current performance of each SEU, and a future-use estimate tied to production plan and known projects.