Phoenix Journal · Ventilation & Energy
Extract and cooling are two ends of the same air. Over-extract and the AC pays to replace what you threw out. The mechanism, the numbers, and the levers that cut both bills.
Airflow and cooling
It sounds back to front, but the fan pulling air out of your kitchen is one of the biggest things setting your air conditioning bill. Extract and cooling are not two separate systems - they are two ends of the same air, and when the extract is wrong, the AC pays for it.
In an air-conditioned kitchen, every cubic metre you pull out through the canopy has to be replaced by a cubic metre coming in. If the air leaving was cooled, you have just paid to condition it and thrown it away; the air replacing it has to be conditioned in turn. Get the airflow right and the cooling load falls out of it. Here is the mechanism, and the levers that move it.
The mechanism
A kitchen canopy is a one-way door for air. It removes heat, steam and grease-laden air from over the cookline - which it must do. But the building has to make that air up from somewhere. Make-up air is either drawn in deliberately through a supply system or pulled in through every gap in the building, and in a conditioned space both routes cost money.
Over-extract - a fan running harder or longer than the cooking actually needs - and you drag conditioned air straight out and force the cooling system to treat a fresh lungful of outside air behind it. The energy your make-up air system spends conditioning that replacement air tracks almost one-for-one with how much you extract. So the single most effective thing you can do for the cooling load is to stop moving more air than the cooking requires.
The middle figure is the one operators underestimate. Because fan power rises with the cube of speed, trimming fan speed to match a quieter service is not a linear saving - a 20 percent reduction roughly halves the power. Matching airflow to demand is the highest-leverage move on the list.
The hidden multiplier
There is a second, quieter way extraction inflates the cooling load, and it is the one an operator can fix cheapest. Grease builds up in the canopy, on the filters and inside the ductwork, and as it does the system moves less air for the same fan power - a heavily loaded system can lose 30 to 50 percent of its design airflow.
That does two things to your cooling bill at once:
So a grease-loaded extract quietly loads two bills: the fan's, and the AC's behind it. It is also why the link between a dirty extraction and higher energy bills is more direct than it looks. Restoring design airflow with a proper clean is maintenance you owe the fire risk assessment anyway - the cooling saving comes free with it.
The levers
None of this is a refit. It is control, balance and maintenance, in rough order of payback:
Because cooling and ventilation together account for something like a fifth to a quarter of a restaurant's energy, and because the loads compound, tackling the airflow tends to move more than its share of the bill.
Questions
Every cubic metre extracted must be replaced by make-up air, and in a conditioned space that replacement air has to be heated or cooled. Over-extraction drags conditioned air straight out and forces the cooling system to treat fresh outside air behind it, so the make-up air conditioning energy tracks closely with how much you extract.
Yes. A grease-loaded system loses design airflow, so the fan works harder for less effect and poor capture lets cooking heat spill into the room - which the air conditioning then has to remove. Restoring design airflow with a proper clean lightens both loads, and it is maintenance the fire risk assessment requires anyway.
No. Running flat out regardless of what is cooking is the most common ventilation waste. Because fan power rises with the cube of speed, matching the fan to demand - a 20 percent speed cut roughly halves the power - saves far more than most operators expect, and cuts the make-up air conditioning load with it.
Phoenix Duct Clean · by the numbers
A grease-loaded extract runs harder, moves less air and dumps cooking heat back into the room for the AC to remove. We restore design airflow to TR19 Grease so both bills come down - UK-wide, overnight, certificated.