We are now in what is likely to be the most difficult period of the Covid-19 pandemic, hunkered down as we await the full rollout of vaccines and endure a huge surge in infections and deaths. Among the hardest hit industries are foodservice establishments of all types. A restaurant business report describes an industry in free fall, with loss of 2.5 million jobs in the U.S. since the pandemic began, stressing family finances and the national economy alike.

Many of our beloved restaurants have closed, and many have pivoted to takeout service and outdoor dining options, as the coronavirus is much less likely to be spread outdoors. We have seen rapid growth of outdoor ‘parklets’ and beer gardens, and some municipalities have relaxed parking requirements to allow for more curbside dining. Of course, colder climates present some serious challenges, which we see are being met with a combination of ingenuity, determination and simple hardiness. For example, we have seen tiny ‘quarantine greenhouses’ along the canals of Amsterdam, and plastic bubble domes on rooftops and sidewalks of major cities (though these have received decidedly mixed reviews due the fact that they are largely enclosed). In Paris, famous for its sidewalk cafes, a planned ban on outdoor heaters was delayed due to the pandemic.

Considering CBE’s experience studying innovative and energy-efficient ways to provide comfort, in this Centerline post we share some ideas for keeping people warm as we get through this final (we hope) dark and cold pandemic winter.

Fundamentals First

First, we assume that safe outdoor dining should take place in well-ventilated spaces that are open on most of the sides, as required by some municipal codes. Although CBE’s comfort research has been geared towards indoor environments, many of the underlying fundamentals apply as well to outdoor winter dining. The primary comfort considerations include clothing or other types of insulation such as seat cushions, or blankets which are commonly provided for outdoor dining in cold locales such as Norway. While concerns about virus spreading may impede sharing materials that contact the skin, people could be encouraged to bring their own.

The other key comfort factors include air movement and the amount of thermal radiation landing on, or being emitted from, a person. (Air temperature, humidity and metabolic rate are also comfort parameters, but for a sedentary diner outdoors, we’ll have to accept these largely as givens.) Finally, we should keep in mind what we know from both research and common sense, that all body parts are not equal when it comes to thermal sensation, and that in cold environments our hands and feet have the greatest impact on our overall comfort.

Hacking Comfort Prototypes

Based on this knowledge about comfort, our research team has built numerous simple and low-cost ‘personal comfort’ prototypes, and tested them in our laboratory using human subjects and physical measurements. A key strategy in the design of these devices is to focus heating (or cooling in summer) on a person, rather than on the space surrounding them. Because such devices can be put together with simple materials and tools, we think that some of these ideas could be adapted by restaurants seeking to make dining al fresco more appealing, and without a great investment to be lost as these become less necessary post-pandemic.

Through extensive prototyping and testing, we found that we can provide comfort by using very low-powered heating elements, with reflecting materials arranged to reflect the heat towards our bodies. We tested this concept in several devices, including in chairs, and also in footwarmer and legwarmer prototypes that we built using foam sleeping pads, reflective attic insulation and other common materials. Some devices included a small heat lamp, enclosed in a cage for safety, and activated by a switch built into a footrest (see small images above). We also found that simple passive (non-electric) versions also worked well, and in an outdoor setting do much of the work by blocking drafts and reflecting body heat back to the user.

More recently, we made a simple prototype fitted to a common patio table, shown above, using a reflective foil attic insulation that resembles bubble wrap (see photo above right). This material is inexpensive and readily available at big-box hardware stores, and in this type of application can be reinforced with foam or wood stays. This simple device both blocks drafts and reflects back body heat, and is surprisingly effective. Combined with a seat cushion for additional insulation (and/or a blanket) it makes an inexpensive outdoor comfort hack.

For additional ideas to improve outdoor comfort, CBE’s team also sees inspiration in traditional ‘hooded’ chairs that enclose and shield a person’s back and head from drafts, and which could work as an effective reflecting surface in a modern adaption. Examples include the traditional woven Orkney chairs developed in the cold northern tip of Scotland, and the innovative Strandkorb beach chairs of Northern Europe.

Off-the-Shelf Products

While passive comfort devices may work in milder climates, in colder temperatures more active heating may be needed. Luckily, many commercial products are available for this. Keeping in mind the key strategy behind personal comfort devices, we should look for devices that directly heat the body, rather than heating the space around it. This approach is further reinforced by a CBE study on the effectiveness of personal heaters that considered both heating effectiveness and power use. A set of 12 electric personal heaters of three different types were evaluated: conductive, radiant and convective. In brief, the most efficient devices tested were conductive heaters — those which are in direct contact with the body, for example, as with a heated car seat. The conductive heaters were on average ten times more efficient than radiant heaters, the second-best option. While there are many heated seat covers available for as little as $50, getting power to seats may require some creativity and a few heavy-duty extension cords. For more luxurious establishments, one manufacturer offers heated, though pricey chairs and lounges. (Alternatively, a cordless and rechargeable heated patio chair cover appears to be a good option, however at the time of this writing it is not available).

The second-best types of heaters tested were radiant devices, which work primarily by radiant heat transfer (think of sitting in front of a fire on a cold night). The study evaluated dish and panel-shaped models, including products intended for desk and floor locations, which used from 150 to over 750 watts. With these devices, the angle and distance from the body were found to be critical, and of course care must be taken to prevent situations that can lead to burns, so it’s not clear how applicable these would be to restaurant settings in which furniture and people are constantly moving. Lastly, the study showed that convective heaters — those ubiquitous electric heating towers which heat and blow air towards the user, some using as much as 1500 watts — were the least efficient, in fact providing only 1/20th the heating effectiveness of heating through conduction (direct contact).

Finally, what about the effectiveness of the propane patio heaters that are already commonly in use (and targeted for eventual phasing out in Paris)? I recently had dinner outside with our ‘pod’ family, who had recently purchased one. This particular model had a tiltable top reflector that allowed for the heat to be directed towards the table, and it provided quite comfortable heat for our table of four. While these may already be largely ubiquitous in restaurants with outdoor dining, they can be cumbersome and require frequent refills of propane, if they not fitted with direct lines. Careful attention must also be paid to safety and health considerations as outlined in this NFPA fact sheet. Since overhead radiant heaters primarily heat the head and upper body, the devices above that keep legs and seat warm should ideally be combined with them.

While we hope the pandemic crisis will soon end, some of the patterns that have emerged — such as working from home, less travel and hours spent commuting — may have long term impacts, leading to a new normal. Perhaps dining in ‘parklets’ and patios, including during chilly months, will be part of it.


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