Wind of change

Commercial kitchens need ventilation and innovation is vital in order to improve energy efficiency, tackle fire prevention and fit design aesthetics. Jim Banks looks under the hood

Manufacturers of ventilation systems operate in a highly competitive industry and constantly seek to be the best at meeting their customers’ changing needs. They also have to respond to a regulatory environment that is pushing to improve safety standards. Hood designs have to be safer, more efficient, more flexible, more intelligent and pleasing to the eye.

The biggest innovation is demand control ventilation, which responds to the needs of the kitchen as different appliances are used on the cook line.

“Customers’ needs are not changing greatly, as the natural gas cookers that have been in use for years produce a lot of heat, and although more efficient equipment may need less ventilation we’re not seeing that yet. The real change is in integrated controls and more economical demand control ventilation. More hoods now have a level of intelligence,” says Russell Robison, Director of Engineering at Gaylord Ventilation and member of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) technical committee on commercial kitchens.

“In the past, exhaust rates would be set at a given level and left there. They may have been fine-tuned by engineers to achieve a known level of energy efficiency, but demand control ventilation and smart hood technology is changing that. Now, there is an effort to maximise the use of transfer air – the air brought into the dining space – that used to be exhausted out of the building. The kitchen can be an exit point for that air to minimise the burden on the supply side for the kitchen ventilation system,” he adds.

However, intelligence often has to play second fiddle to beauty, particularly with the trend for front-of-house cooking.

“Equipment manufacturers have done a good job in decreasing the air volumes their ventilation systems use and in improving safety, but the challenge is always the initial cost,” says Len Bundy FCSI, principal of restaurant management consultancy George E Bundy & Associates. “Manufacturers are looking closely at how customers work to design the most efficient systems with fewer hoods, but this is not always easy with restaurants that use display cooking. There is more focus on aesthetics than on efficiency, although reliability is always the priority.”

Adam Irving, Sales Engineer at Vianen Kitchen Ventilation, reckons: “The area in which customers’ needs are changing is in aesthetic considerations, as there is a lot more front-of-house cooking these days, which means the kitchen is more visible to customers, so ventilation canopies have to fit the style of the restaurant. At Vianen we focus on the top end of the market so we already have systems that look clean because there are no visible fixings.

“Also, systems now need to follow the cook line, and in Jimmy Spices restaurants, for instance, we have put lights in the hoods to illuminate the different elements in the cook line,” he says. “Front of house cooking tends to involve a lot of smoke and grease, particularly wok cooking, so there can be no compromise on the performance of the ventilation system.”

Performance is increasingly measured in terms of energy efficiency, and more transparent standards are emerging by which new systems can be compared.

“Third party visualisation techniques use a scientific approach to reducing the air volumes used by exhaust and HVAC systems so less cooling is needed, therefore, less energy,” says Robison.

Engineering and consulting firm Fisher Nickel provides open access to data that can be used to assess individual systems against competing technologies, and this has fast become an essential tool for the validation of new equipment.

“Ventilation is a heavy user of energy when you combine the operation of fans and hoods with the heating and cooling of air,” adds Robison. “In institutional and business operations, where kitchens provide services to another profit centre, then total cost of ownership is a priority and they will readily pay for energy efficiency up front.

“You now have an ‘air war’ – a battle to reduce the volume of air required over a given piece of equipment. The aim is to reduce ventilation rates and the noise the ventilation system creates in the kitchen.”

In independent restaurants the desire or the ability to pay a higher upfront cost for more efficient ventilation technology may not be as great. The smaller the operation the less likely it is that energy efficiency, which has a long-term payback, will be at the top of the agenda.

“Energy efficiency is important, although clients might not necessarily see it as a key factor at first. It becomes important when we sit down with them because ventilation is a massive feature of long-term economies as energy prices rise. To clean the air in a kitchen you need to draw in and throw away a lot of air from the restaurant,” says Irving.

“A lot of work is being done now to segregate treated make-up air and untreated air that is drawn in and heated, because there are big savings to be made by separating those two volumes of air. Intelligent control is also becoming more important, and we have different systems that monitor areas of the cook line to detect when no cooking is happening, at which point the fans can start to run at 10-15% power. When a heat or vapour detector senses cooking is happening it can then ramp up the fan,” he adds.

These reactive systems are becoming commonplace, though Vianen is also installing proactive systems that turn on the ventilation hood five seconds before combi ovens are programmed to open.

Regulatory changes have made safety as important as efficiency in the minds of equipment manufacturers.

“A major driver of ventilation equipment development has been the changes in codes in the US, which have been dramatic,” says Bundy. “They created a lot of challenges, and some things have wasted millions of dollars. For instance, many ovens now require type 1 grease-extracting hoods where type 2 hoods were previously acceptable. Another fire prevention requirement is for sensors that compare temperature in the room with temperature under the hood so the ventilation system comes on if there is a discrepancy. But this can lead to the hood operating even when the oven is off and cooling down.”

The potential for fires to spread through ventilation ducts to other parts of a building have focused R&D efforts on sophisticated automatic systems.

“Kitchen fires are all self-igniting and people are not used to it. We protect the ventilation duct and the hood, where combustible material in the form of grease residue collects. All these are under a hood and are ventilated, so the duct will have residues that could self-ignite,” says Jan Waldow, Product Manager for Tyco Fire Protection Products.

“Appliances usually overheat due to faults such as broken switches that allow the temperature to rise, and if the safety switch also fails then grease can heat up to 260°C, the point at which there is heavy smoke, and then up to 360°C, at which point the fire will self-ignite. If the smoke goes unnoticed, for instance if staff are in the storeroom or have their backs turned, then the fire could get started and may continue to get hotter as it is heated by the appliances,” he adds.

It may appear to be a rare combination of circumstances that would lead to these failures in these controls. Yet Waldow points to a German safety authority study that suggested around 79% of safety switches do not function as they should.

Given that there is a risk of fire, the first step in combating it is to take the energy out of it by turning off the cooking appliance.

“That cools the fire, and then you can use any one of three methods to put it out – remove the fuel, cut off the oxygen supply or remove the heat from the combustion process,” says Waldow.

If grease is burning then that means removing the grease, this is manageable if a small pan is on fire, but less so if it’s in a ventilation hood. In fire protection systems such as the ones we recommend, the preferred method is to cut off the air supply and cool the fire to below self-ignition temperature by spraying on a wet chemical solution.

“Water isn’t used because it would cause a fat explosion if poured onto hot grease, which would rapidly expand to 1,600% of its original volume. The wet chemical cuts off the oxygen supply, and our systems also automatically cut the power supply so there are no reignitions. We suffocate the fire then cool it down. The challenging issue in a commercial kitchen is to decide when the system should kick in,” says Waldow.

“It is all about detection and we have a very reliable method, which involves fusible links in the air stream within the ventilation duct. The system ensures there are very few false discharges. There may be systems that are quicker, but the quicker they are the more false discharges you have. Systems that work on ambient temperatures have problems because temperatures in a kitchen vary according to what equipment is on, how long it has been operating and what speed the ventilation system is working at,” he adds.

Systems based on fusible links are using an old technology that is tried and tested. Yet research and development is still a big part of what companies such as Tyco are doing to improve fire protection systems.

“We have to keep pace with new cooking technologies and practices. For instance, a few years ago the move from animal fats, which ignite at 260°C, to vegetable oils, which ignite at 360°C, was a big shift. It sounds as though that would make kitchens safer, but if a vegetable oil fire ignites there is much more energy in the fire, so it is more severe and harder to tackle. Also, better insulation in many appliances means that they don’t cool down as quickly, and some new appliances are harder to protect. We have to make sure our systems can tackle more severe fires,” says Waldow.

“It is also important to have self-contained systems that are independent from everything around them and work even if there is a power cut. Operators also have to ensure their fire protection systems are inspected and maintained by fully certified engineers.”

The cleanliness of ducts and hoods is also a big factor in safety, hence the rise of ‘clean in place’ technology.

“This kind of technology is popular in business and industry applications, universities and hospitals,” says Keven Hass, National Sales Manager at Gaylord Ventilation. “A water wash of the ventilation system can happen while the kitchen is in use, so there is no need to shut down operations. And you can do it while the ventilation duct is hot. Also, the new systems on the market use less water and less soap.”

Innovation continues on all fronts as all manufacturers grasp the need to design systems that suit the needs of an individual kitchen in terms of efficiency, performance, control and aesthetics. There is no doubt that ventilation is a buyer’s market.

Jim Banks

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