What each one actually does
An open refrigerated case holds product cold with a curtain of chilled air falling down its open face. Aerofoil Energy, who make the blades, put about 70 per cent of that cabinet's energy into making and holding the curtain. At each shelf edge the curtain turns turbulent and part of it drops into the aisle, and the case pulls in warm store air to replace what it lost.
An Aerofoil is a profiled blade that clips onto the shelf lip in place of the ticket strip. It smooths the flow at the edge so the curtain stays attached down the face of the case. Nothing is powered, nothing moves, and the case keeps trading while the blades go on.
A door removes the open face instead. The cold stays in, but every opening empties some of it out and pulls warm air in behind it, which is why door performance in a busy store never matches the laboratory number.
Why the store meter disagrees with the cabinet meter
Doors win on the cabinet. That is not in dispute, and it is why they get specified. The argument is about what the building does next.
An open case is, in effect, cooling the aisle for free. Take that away and the store air conditioning picks the load up. In a warm climate that can cancel most of what the cabinet just saved, which is why a doors business case built on cabinet readings alone tends to disappoint on the electricity bill.
We have monitored both routes on Australian sites. On a Queensland store where doors went on, the cabinets themselves dropped more than 60 per cent, from about 110 to 41 kWh a day, but the whole building meter rose about 3 per cent, from 363.8 to 373.8 kWh a day, with the outdoor average sitting near 28 degrees. On the NSW sites where we fitted Aerofoils, the full year refrigeration reduction settled at about 20 per cent with no offsetting rise elsewhere. Both sets of readings were taken by Nube iO, independently of us.
| Aerofoil blades | Fitting doors | |
|---|---|---|
| Saving at the cabinet | 15 to 25 per cent typical, manufacturer published | Larger. More than 60 per cent at unit level on the Queensland site we monitored |
| Effect on store air conditioning | None. The spill it stops was never cooling the store usefully | Picks up the load the open case had been carrying |
| What the building meter shows | The cabinet saving, near enough intact | Can go up. On one Queensland site we monitored it rose about 3 per cent while the cabinets used 69 kWh a day less |
| Install cost | About one third of doors on the same cabinets | The baseline |
| Ongoing cost | None | Gaskets, hinges and seals for the life of the door |
What doors cost to keep
A door is a moving part in a high traffic retail environment, opening as often as once a minute on a busy aisle. Gaskets tear, hinges wear and seals stop sealing, and a door that no longer seals is worse than no door because it leaks cold continuously while the store still believes the problem is solved.
Industry estimates put annual maintenance on a door equipped unit at $300 to $750, with an emergency repair for a torn gasket or a failed hinge at $1,200 to $1,500 each. Across an estate, over five years, that is a real number and it belongs in the comparison rather than in next year's reactive budget.
Some retailers add a wiper seal along the base or side of the door to catch what the gasket misses. Aerofoil Energy, who make both door and open case products, list the seal's own failure record: a high failure rate, an expensive part to replace, a visibly worn strip along a customer facing door, and mould growth where moisture collects behind it, which is a health issue on a food fixture, not just an appearance one.
Aerofoils have no equivalent line. There is no power, nothing that moves and no inspection schedule, so the saving that shows up in year one is still there in year five.
What doors do to sales
This is the part that rarely makes it into an energy business case, and it is usually the largest number in it.
Shopping Behaviour Xplained filmed shoppers in chilled aisles in 2017, against a behaviour database of more than 65,000 shoppers. Behind doors, the share of shoppers who read a pack in detail fell from 31 per cent to about 9 per cent, the proportion going on to buy fell by 29 per cent, and grab and go purchases fell 13 per cent.
The mechanism is mundane. A shopper with a basket in one hand and a phone in the other has no spare hand for a door, so they walk past. On an impulse category that is a direct revenue question, and it will dwarf the power bill either way.
Where doors are the right answer
Doors are not a bad product, and anyone selling you only one side of this is selling. Frozen food cabinets are doored almost everywhere for good reason: the temperature difference is far larger, so the case cannot hold a curtain against it. Low traffic aisles change the arithmetic too, because the bellows effect of constant opening is what erodes the door saving.
A doored cabinet has its own leak, at the gap between the doors rather than the shelf edge. Air moving inside the fridge creates a Venturi effect that draws warm outside air in through that gap, which is what a wiper seal is trying and often failing to stop. If an estate already has doored cabinets, the question is not doors or blades at all. Aerofoil Energy's JetSeal is built to block that same gap using the fridge's own airflow, so a mixed estate can be treated under one program rather than two.
How to settle it on your own stores
Neither a brochure figure nor this guide describes your cabinets. Case age, how the existing air curtain is set, aisle traffic, the store's own air conditioning and the local climate all move the result.
The step that settles it is small: instrument one store, take air velocity and temperature at the cabinets and the energy at the meter, fit one aisle, and read the same things again. Independent monitoring across an equal period before and after, controlled for outdoor temperature and case load, gives a number that belongs to your estate. Then stage the rest of it against that.
If the readings do not support the spend at your stores, that is a useful answer too, and it costs one store to find out instead of forty.
