Magdalena Patyna is an environmental engineer with the Passive House Institute (PHI). She has had several areas of interest while working at PHI, including building certification, lifecycle assessment, software and tools, and commercial kitchens. Patyna is now responsible for  developing a streamlined approach for the certification of buildings with commercial kitchens.

Patyna shared some of her invaluable knowledge about commercial kitchens in Passive House construction with Passive House Accelerator. The conversation has been edited for clarity and length.

PHA: And how is commercial kitchen typically defined?

MP: There is no universal definition, but it starts at approximately 200 meals per day. It’s worth mentioning that you can tell a "commercial" kitchen by the size and type of equipment, which are quite different from what you’d find in a residential kitchen.

PHA: You mentioned that you identified some pieces of equipment that help with efficiency. Can you provide some examples?

MP: I would like to divide it into two main sections: kitchen equipment and, later, ventilation systems. 

With efficient pieces of kitchen equipment, they are not just for passive buildings; they are worth considering in every commercial kitchen. We have this list full of kitchen equipment and which properties they should have in order to be considered efficient. There are of course a lot, but I’ll give you some examples.

We prefer enclosed devices. For enclosed devices, the best recommendation is that they are double walled. If the devices have glass fronts, then we recommend at least double glazing with a heat reflective coating. These properties not only help to improve the insulation of the devices but also ensure that less odor, moisture, fat, and hot air escape into the room. It is also best to use induction hoods. 

I don't know if you know what induction hoods are—they're also called compensation hoods—but they are really great [see an example here]. They pull air directly from outside into the cooking area, so it’s not preheated air that is moving through the hood, and it creates a suction that carries away the contaminated air from the cooking but removes way less of the clean air from the room. As a result, less air has to be heated or cooled again. Our research from 2012 shows that using induction hoods can reduce the required airflows by 27%. They are game changers. 

PHA: That is huge! Have any of these components, either the hoods or other kitchen equipment, been certified by the Passive House Institute?

MP: No. Because the equipment varies from kitchen to kitchen, our focus has been on providing guidelines on what makes most common equipment efficient. The main goal is to use as little energy as possible, but also to avoid having a really hot kitchen where you cannot work.

To reduce the overall energy demand per meal and prevent discomfort, we have a procedure:

1.      First, through efficient equipment and good kitchen planning, you should reduce the release of steam, grease, odors, or thermal loads to lower the exhaust air requirements. For example, by using devices with an enclosed design, as mentioned earlier. As an example for kitchen planning, don't put cooling devices next to heating devices. We also recommend more efficient LED lighting, also for cooling rooms. That is an easy choice.

2.      Now, you may need a piece of equipment that releases a lot of heat. If that’s the case, then you should seek to exhaust or reuse heat as locally as possible, so you don't have this hot air everywhere because people will really suffer. As an example, there’s a combination steamer. When it opens, a lot of steam comes out. However, there are devices known as condensation hoods that can be installed above the steamer and automatically turn on if you open the door. Inside the condensation hood, steam is captured and automatically cooled, condensing into water droplets that are drained away. This process reduces the escape of moisture and heat into the room.

3.      If that’s not possible or enough, place induction hoods close to the appliances. For example, you may have a grill. To contain the heat and keep it from spreading to the whole kitchen, you should place induction hoods as close as possible to the device.

Ultimately, you want to eliminate unwanted factors like grease and steam locally and reuse heat as much as possible in places where it’s easiest to implement. According to our proceedings document, these techniques can reduce the required airflows significantly and therefore reduce the energy demand per meal by up to 66% (calculated for a central European climate). 

PHA: I want to go back to not putting cooling devices next to heating devices. From the perspective of the kitchen worker, I imagine that you want your hot and cold sections separated, but then there’s something like a refrigerator that produces a lot of heat even though it's cold inside. Is there any recommendation for placement within the kitchen layout for these kinds of appliances? 

MP: If it's a little refrigerator, not really. However, there are also cooling and freezing rooms, and they're way more energy intensive. After analyzing several options, in a central European climate, we recommend putting the room in a bottom corner of the building, outside of the thermal envelope, and robust insulation for all remaining walls that are not adjacent to the thermal envelope. For hot climates, it should be checked if this still makes sense. The goal is to maximize efficiency while reducing the waste heat into the kitchen, and to take advantage of the existing thermal envelope. We also have some requirements for installation of the rooms, such as a U-value of about 0.15 W/(m²K) to keep the contents of the cooling or freezing room from getting warm.

We also have recommendations for specific device types because there are several commercial dishwasher types like the under counter, the flight type dishwasher, and so on. We measure this in maximum liters per rack. If that's not met, then they're not efficient enough.

PHA: That’s very thorough! Let’s move on to ventilation.

MP: With commercial kitchens, you typically have a separate ventilation system. Some projects are very impressive and use cascade ventilation systems, but it's not that common. Overall, this topic is very important because our research from 2012 shows that approximately 40% of energy consumption in a commercial kitchen is due to the kitchen’s ventilation system. This is also because heat recovery is not that easy to do for kitchen ventilation systems. As you can imagine, the air in the kitchen has grease and a lot of particulates that can clog the recovery coils or create other problems. If these grease deposits accumulate in the ventilation system, they can burn easily, and we want to avoid having this buildup in the ducting.

Now, there are several methods for treating and cleaning the exhaust air. The first step is to go for simple and efficient grease separation, like using an exhaust hood designed to catch grease particles, as they stick to surfaces. It’s not perfect, but it’s easy to do and gets most of the job done. For further cleaning, there is a treatment with ozone: you put ozone inside the system, and then the grease burns, but it's rarely actually used. You can also use a heat recovery system normally, but to have less problems with clogging any pores, we recommend a rotation recovery system in place. These are better suited for kitchens in general.

Our findings also show that it's not necessary to have like 90% heat recovery in this case. Depending on the climate, the kitchen may even become too warm in the winter months.  The goal is therefore to find an optimal balance between comfort and heating demand. That said, any level of heat recovery is better than none at all.

PHA: If you've already designed a kitchen and a chef wants to add a piece of equipment like, say, a fryer, is there a way to easily boost ventilation?

MP: Of course. Typically, you will have a ventilation system that is not operating at 100% capacity. So, if it's operating at 66%, you can then increase it a little bit. That is usually the best way to get that boost: you have this buffer, and you can increase it afterwards. 

PHA: That is an excellent way of thinking about it! Are there any special mechanisms to efficiently improve exhaust that should be considered when designing a commercial kitchen?

MP: So that's a great question actually, because this is very Passive House related, and we have to look at this in two parts: the exhaust system itself, mostly through extraction hoods, and then we have to make sure we get some makeup air to compensate for the extraction.

As you know, Passive House projects are very airtight, so makeup air is essential—otherwise the exhaust hoods will not function correctly. The best is to have controlled openings in the commercial kitchen that automatically open when the extractor hoods are activated. There can be other solutions, but we don’t recommend any manual solutions like relying on opening windows for commercial kitchens.

We’ve also created a guide for kitchen extractor hoods, mainly focused on residential kitchens, but it can still provide useful insights for commercial kitchens as well.

PHA: I already asked about the harvesting heat, but are there devices that can take excess heat produced by, for example, a range or a fryer or a dishwasher, and then use that outside of the kitchen to help preheat anything? Or is that not really a technology that exists? 

MP: Usually, the goal is to get the excessive heat out as soon as possible, and reuse it for preheating incoming, fresh air. Using waste heat from kitchen air for other areas of the building is far too complex, so it’s better to focus on using more efficient equipment and reducing waste heat altogether. There are also some devices for recovering the heat from warm water in the kitchens, but they're usually used locally. 

PHA: What other considerations should designers prioritize when working on a commercial kitchen?

MP: If you inform PHI or your certifier that you are working on a commercial kitchen, we will send you the table I mentioned before. In this table, there are some tips about where to focus, like using an intelligent kitchen layout. We are working in this way to collect experiences and information to be able to set a streamlined process in the future and are happy to receive feedback.

Of course, the designer/energy consultant has to coordinate with kitchen designers, and, in the case of Passive House, you also have to estimate the kitchen’s energy demand for certification. It's crucial to have good contact with the kitchen designers because they can help tell you approximately the amount of power the devices use and how long they will be on (see What Planners Should Know).

PHA: Is there anything else that you'd like to add that you think people should know about?

MP: I guess my main message would be to choose equipment wisely and in such a way that the need for ventilation can be greatly reduced. That's the goal with commercial kitchens for the future.

For more information about commercial kitchens and Passive House design and construction, see the Passipedia page here.