Monday, 11 November 2013

Peak oil technical challenge report.

Peak oil Technical report: Krampus Challenge 2013

Problem – The re-communalising of cooking 

Modern industrial civilization is incredibly wealthy, not just on the societal level but also at the level of the individual. This has had significant consequences, some of which have changed society in drastic ways. One marker/consequence of this incredible wealth is that individual households have baths and kitchens, someone that is almost unheard of historically for urban societies (outside of the houses of the elite). Public baths, for example, existed until the 16th century in England before the Puritans got rid of them and are still used by many cultures today, a Korean friend used public baths here in Melbourne. Cooking & eating is still partly a communal (as in not done on an individual or family level) activity, think fast food joints, restaurants or cafes. but this is often more as a special thing than a normal activity.

Fast food is itself incredible ancient, it dates back to ancient Persia (Iran) and it existed largely because most urban people didn’t have their own kitchens, the average Roman loved fast food (Viegas 2007).  To give you an idea of how common fast food was in urban settings, for every 60 residents of Pompeii there was 1 Thermopolium (fast food joint) along with Tavernes (cafe) and Popinas (wine bar, often a breakfast of vegetable stew or wine soaked bread was served). Now, there are large differences between modern and ancient fast food, the ancient fast food was less processed while also containing less meat but they otherwise share similar criteria; cheap, quick to prepare en mass and filling. Also Street vendors are a very old tradition, one that is still strong in Asia (think Malaysian hawkers) and it has its own style of food while still sharing the same criteria. 

The food served at these places varied; Paella, curries, nuts, a pot of soup mix, stew and so on were served. Traditionally, only the rich don’t eat this food in cities (since they could afford kitchens and/or servants) and the otherwise there would be a kitchen & dining room in the apartment buildings (Bed and Board), with the owner or staff cooking food. It is only really in modern Industrial civilization that these options aren’t standard for people living in urban settings.

The economic reasons for this are fairly simple, just as its more energy efficient to heat up one large bath than lots of small ones, its more energy efficient to cook large amounts of food at once in one place than in multiple small kitchens. By doing these things communally, energy is saved, less equipment is needed, appropriate economics of scale are achieved and benefits of specialization are achieved that family or individual kitchens just don’t provide. And, importantly, fuel, a scare and precious resource, is saved which since it was commonly wood also lessens the impact of cooking on the environment. We know these systems of cooking are economically viable in low energy settings and they will be perfectly viable in the future, no matter what decline may bring.  Eating, along with a few other activities, will become a far more communal affair in the future than it currently is now. Note, I’m not referring to any specific economic or political system, communal here refers more to large groups of non-family related people eating in the same place rather than as small family units, whether its under a Roman style economy or Maoist communal kitchens.

And here is one of the many problems that will exist in the near future; how to bring this change about in the best way possible. How do we take advantage of this model of cooking while fuelling it with renewable energy? After all, most renewable energy sources produce mechanical energy (wind and hydro for example), while the main historical source of renewable heat (biomass) is likely to be scarce and large scale use of wood in the cities would lead to devastating deforestation. Where can the energy for this cooking model come from and how could it best be put to use in a sustainable manner?

Overview of a Solution - Concentrated solar power

Only a few renewable energy sources produce heat; geothermal, solar and biomass. Geothermal is impractical outside of a few scattered areas and biomass already suffers depletion problems in the third world, adding depletion problems to the first world won’t be very helpful, which leaves solar power. Since this is using heat in the 100-600oC range, kitchens are generally inside buildings and these specific kitchens will be running for the majority of their time, the system will require; solar concentrators, a heat transfer mechanism and thermal storage at a minimum in addition to the specialized cooking equipment. A few more things can be added, excess heat is available after all, and some provision for mobile vendors would be useful but the core system is enough to begin with. Importantly, this system is not like current solar cookers in that it isn’t a standalone piece of equipment, but an entire building and includes a system that is only now being incorporated into regular solar cookers, thermal storage.

Also, while I am talking about this system as a replacement for standard restaurants and eateries, that isn't the only option available. Instead the system used in some college campuses can be copied/modified. Where each floor has a small kitchen units, more for snacks or small meals, and the building has a single big kitchen area, most likely the big kitchen could be the easiest part to adapt. There are a few options in how the system could be arranged, specific districts could be built instead (like shopping districts), and that would in turn affect what technologies are used.



The System shall
  • Run entirely on non-biomass renewable energy 
  •  Only require backup heat sources in very unfavorable conditions 
  •  Have a backup power supply 
  •  Provide excess heat under normal operating conditions
    • If necessary during winter as well
  • Be operational in temperate areas
  • Pay for itself and provide a living for its operators 
  •  Provide any level of heat required for cooking 
  • Use less energy than conventional eateries 
  •  Able to use a variety of technologies
  • Serve as many or more people as a standard eatery 
  •  Be as technically simple as possible while still fulfilling operational needs
Core Sub-systems:

Solar concentrators

In order to get the necessary temperatures for cooking, especially at this scale, sunlight needs to be concentrated. This heat is not going to directly heat the food (as modern solar cookers do) but instead heats the fluid used in the heat transfer system. There are a variety of technologies available and it’ll depend on the buildings location and architecture which one is used. One promising project at RMIT is Micro Urban Solar integrated Collectors (MUSIC)(RMIT 2013), which aims to develop collector platforms that can be mounted on roofs and produces heat in the 100-400oC range. If this technology works out that would be a perfect option but there are other roof mounted technologies that can be used. 

Trays of parabolic mirrors are quite common in solar applications, parabolic mirrors are cheap, but Fresnel lens are being used in an MIT salt solar cooker, so Fresen Lenses are also an option. A tracking parabolic dish is also a possibility and so is a solar bowl, instead of a fixed spherical mirror with a tracking receiver, this technology is already used in a solar kitchen (Auroville, India). Scheffler reflectors are also an option and are used in quite a lot of solar cooking technologies and modified evacuated tubes could also provide hot or boiling water. 

And the solar concentrator component doesn't necessarily have to be mounted only on the roof, using a nearby open space is an option for some places, particularly rural ones. This system will be easier to implement away from city centers for the basic reason that the buildings can be wider and more land is available for sunlight harvesting. Otherwise the solar concentrators can be mounted on the roof, but sunlight could be deflected from nearby roofs or gardens (similar to how the Japanese put solar panels over fields) to increase the available sunlight. There will be a small range of technologies that work best for this application (I doubt that evacuated tubes will work), but the mixture used will depend on local conditions.

The main problem is likely to be the availability of sunlight and locations for solar collectors. Roof sharing is an option; the specific eatery could use neighboring roofs for solar collectors and the neighboring building gets free food or payment. Instead of building this solar restaurant only in one building a group of neighboring buildings could be linked up in a heat distribution network (like a microgrid) and pool their available space for sunlight collection. As it stands, architectural design would have to change to accommodate this along with construction techniques and urban planning.

Thermal storage

Most cooking isn’t done during the day (Magazine 2012), so heat is going to have to be stored. If enough heat is stored then a week or so of cloudy days won’t interrupt business. There are a variety of heat storage technologies; the most likely to be used are those that use oil, water or molten salt, though phase change materials could be used in the cooking equipment. Concrete, and some other solid materials like packed rocks, can also be used store heat, but liquid storage is likely better for this application. Thermal storage is an area in which research is still continuing, there’s a concrete thermocline method (John, Hale et al. 2013) that could turn out to be the most efficient option available, but it isn't the only developing heat storage technology out there.

The most efficient storage method is a large cylindrical tank (for liquid storage), since increasing volume decrease the surface area to volume ratio, the larger the better and this also applies for solid heat storage for the same reasons. However, for small vendors, and as a potential backup system, some form of portable heat batteries would be useful.  There would be two primary models; a small one for mobile vendors that is light enough for one person to move and a big one for stationary purposes. The big one doesn’t necessarily have to only power the eatery, it could be rented out for other uses; space heating, public baths, process heat, sterilization etc. This battery would most likely combine liquid heat storage (for lightness) and very strong insulation in order to function adequately.

However, since the bigger the thermal battery is the better it is, having shops that are close together sharing one large storage device makes a lot of sense. Another option is sharing the storage among a group of buildings or even a village/town. The main issue then is how to share the heat when the batteries are low.  

Thermal transfer system     

This is what connects all the other sub-systems together. None of the other components are actually connected to each other directly (that is an option however) and without this system a radically different architecture would be needed.  All this system has to do is move heat where it’s needed and when. Steam pipes are a good and traditional way of doing this and it’s likely the method that’ll be chosen.

If possible, this component should be powered by excess heat. Stirling engines could be used; they only produce mechanical power when enough heat is available, which is when you want the pumping done. This system could also be connected to a larger heat grid, mostly as a supplier, and this would provide benefits to surrounding heat users while adding an extra revenue stream for the eatery.

If possible, the pipes should be imbedded in heavily insulated walls and themselves be thick and heavily insulated. And if excess heat is being used to drive the system, consideration should be paid to lowering the required pumping power, there won't be much mechanical power to waste. there are two main ways of doing this (both surprisingly recent practices) are to make the pipes as straight as possible by placing the pipes before you place the equipment or making them as wide as possible to reduce friction. Also this system could be used for space heating of the eatery, small pipes that are normally closed could branch out from the central pipes and when space heating is required, while extra heat is in the pipes, they can simply be opened. It won't be highly responsive, but its an option to consider.

Cooking equipment
Since the heat is going to be delivered directly as steam, the cooking equipment will need to be specially designed. Ovens would have a surrounding cavity into which steam is pumped and a thermo-electric generator could power a fan when necessary. The rest of the equipment can be modified in similar ways; high pressure steam could be pumped underneath metal plates to heat them up, similar to how electric stoves work, coffee machines could extract the heat from the steam and the leftover heat from these processes can be used to keep things warm. It likely inadvisable to use the steam from the heat transfer system directly, so steam cookers will need a heat exchanger to swap the heat between the steam for cooking and the steam for heat transfer. 

Refrigeration unit

Refrigeration is quite useful for food storage and luckily the overall system will produce excess heat. This excess heat can be used in a vapour absorption cycle (Said, El-Shaarawi et al. 2012), or absorption refrigeration, to refrigerate. If the climate warrants it, this could also be expanded to provide cooling for the entire eatery. Absorption heat pumps are also worth looking into, along with any other similar technologies that use waste heat. Absorption refrigeration is quite an old technology and there are already designs out there that could be dropped into the system with minimal modification.

The main problem with absorption refrigeration is that ammonia is the best refrigerant for these cycles and it's toxic. This means that safety and the placement of the fridge needs to consciously looked at, so when a leak happens it causes the least harm possible and doesn't leak into the main dining area. Otherwise it's worth exploring if the refrigeration system should instead of being linked to the main system, be a physically separate system that has its own solar heat supply. Another is also how to deal with intermittency, is the fridge heavily insulated and cooled extra low so the system can deal with losing power for a few days, should it have a separate thermal battery to smooth out the heat supply or a combination of the two.

Peripheral/optional sub-systems:

Small/mobile vendors

Eateries that aren’t stationary or are too small for this system to be used are still fairly important. Whether it’s a mobile hot dog stand, a hawker cart or maybe a small store in a train station, the full system likely isn’t a viable option. That however, doesn’t mean that they can’t benefit from this system. As mention above, small thermal batteries could be used to power these stalls or there could be a heat grid and specific outlets where vendors can charge their batteries.

How this is done depends greatly on the running times of the stalls and vendors. At my local train station there’s a small coffee shop that’s only open for the morning and afternoon commute, it wouldn’t require a large battery and there’s a commercial area right next door, though this example could use a small solar system. Other places would require either multiple or larger batteries, though the option of installing a small and stripped down system is there.  As it stands, these stalls would already benefit because the demand for cooking fuel is reduced by the core system and this just extends the solution slightly. Besides, the mobile vendors and small stalls would generally be able to use standard solar cookers while using thermal storage as a backup.

Thermo-electric conversion

In this situation thermo-electric generators would be better than heat engines for producing electricity, despite the low energy efficiencies (typically around 8%), however as this is converting waste heat the low efficiencies aren't that important. As it stands, adding thermo-electric generators to cooking equipment is already being done and it turns out to be very worthwhile, see the BioLite stove or Powerpot. The best things to power are going to be the LED lights, kitchen fans and possible a radio for music + ambiance. After that comes customers micro-electronics (energy sippers), small batteries and possible energy efficient computers. Small vendors would greatly benefit from this system as it reduces the need for batteries (for lights and stuff) while letting them run certain electronics cheaply or mechanical applications (fans for improved combustion for example). 

The thermo-electric generators should be placed where heat flow is already happening or where you want to slow it down, so that you don't have to create a extra heat flow which adds extra costs of its own. Basic thermo-electric generators are technologically simple, but more advanced ones are available if necessary, and that would be the first place to start. One possibility is to use 3D printed thermo-electric generators (Roch 2013) which could be quite cheap and available in quantity, but the main advantage is that they could wrap around the heat transfer pipes rather than being large blocks, which makes placement easier.

Waste Heat

The system is quite likely to generate excess and waste heat. If enough is generated, not guaranteed, then some use for it should be found. The most immediate use would be for space heating or cooling (using absorption cycles), after that comes heating water and possible using steam for cleaning or sterilization. If a district heating distribution system is available then excess heat could be pumped into it, otherwise nearby buildings could use it for certain processes. It all depends on the form the waste heat is in (steam for example), how much is available and when is it available (randomly, periodically etc). And it will be a limited resource, budgeting it carefully will be crucial.  


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