Water heating is a luxury we have become quite accustomed to in developed nations and probably never really have thought about the vast amount of energy this demands. Our consumption of hot water comes at a cascading fossil fuel price through the electricity or the natural gas we employ. We may not think of hot water as such, but I feel having hot water on demand is one of the ways in which humans have increased their life expectancy. Hygiene has improved because who wants to take a cold shower when its cold out. Also reheating the body in the winter is such a beneficial approach to keeping the immune system robust. However, as always with the burning of fossil fuels, sunlight stored of ancient times, there is a fallout of negative impacts from air quality where it’s burnt to water quality where the fuel source is mined.
Consequently, this heating of water is one of the first appropriate technologies many will implement in a permaculture built environment. The systems are less complex than the electricity producing and storing ones (solar PV and batteries for example) and it helps to reduce your electric demand if wanting to go with renewables or go completely off grid. Whether it is showering or washing dishes or laundry (just do laundry in cold water), your hot water needs can be met through appropriate technologies.
I could throw a lot of numbers and conversion rates at you to provide more substantial evidence that heating water is energy intensive. If you do a web search of “how much energy does it take to heat water”, you will find the conversion factors. This shows the amount of energy and its relationship to the cost of electricity and it is actually pretty astounding how much the cost of hot water is. Furthermore, the amount of total energy used in a household for water heating is quite astonishing and see the graph below. With an average in 2015 in the USA of nearly 20%, this is a critical factor of societal energy consumption or production.
Interestingly enough, Nature produces its own hot water on demand in the form of hot springs. Warmed by underlying volcanic/geologic figures, humans once did pilgrimages to source this heat and mineral rich waters. Now we simply open a tap and voila; no real thought on energy. Thus part of this articles desired outcome is for readers to simply even think about hot water and what that implies. Sitting in hot springs is my top pilgrimage choice and am grateful for this blessing of the earth.
Fortunately, a way in which technology has advanced with water heating is to have insulated water tanks. If you heat the thermal mass laden water and then all that heat escapes slowly, you pay even more and so does the environment. So having insulated water tanks are mandatory in case you are doing a DIY system. The insulated tank with warm water is essentially your battery or storage of the energy. Thus you must protect this with an insulated layer to ensure efficiency. Moreover, there are more technologies beyond the ones presented below but here are a handful.
Water Heating: Solar Thermal Unit
This system is a panel composed of tubing, which traps the sun’s heat and transfers it to water. The tubes are usually made of either glass or copper, and in the letter case have black painted surfaces to increase heat absorption. The abundantly produced hot water is stored in an insulated tank for later use. The panels can be sited far from the storage tank, or even below it in height, as according to the laws of thermodynamics the hot water will travel upwards. The hot water is used within household systems and can also be directed into heating systems for radiant heat. Another function for the hot water is the irrigation of certain seedlings, like tomatoes and peppers, to create an extension of the growing season in temperate climates. A solar thermal system can be homemade or purchased commercially and grants often apply. This system is one people often start with, because it can be self made and offers a good relationship between price point and rate of return. This appropriate technology is extremely efficient and can make a wide range of different contexts become more energy independent.
Water Heating: Wetbacks
These systems, called many different names, utilize piping connected to a wood stove to circulate the heat generated and possibly lost to a hot water tank storage. So as you are space heating or cooking, the pipes are heated and the energy is transferred to the insulated tank and used later. There is a time lag but in cold climates, wood burning stoves run quiet frequently. Also in Slovakia we had a much simpler system, which was all the food we cooked was done with their traditional wood burning stoves. We always had a pot on top of the stove top which was filled with water and constantly heating. This was used in the cooking, dishwashing, and if you needed to bring water to a boil quickly this already heated water was put in an electric kettle. In this way the water took less time, thus less energy, to come to a boil because of its preheating as it was quite cold straight out of the tap.
Shower Heating Rocket Stove
In several places around the world I have utilized showers that are directly powered by firewood. Essentially they are like rocket stoves underneath the steel tank. The fire box is under the tank, which transfers heat upwards to the tank. Twigs and smaller diameter branches are added to create intense flames and abundant heat transfer. This system really shows just how much energy it takes to heat water and is a fascinating design. Where I taught PDC’s in Slovakia from 2015 to 2017, we had this system and for everyone to shower it took a couple of hours of consistent burning. As people would shower, the hot water was consumed and cold water would be sucked into the tank and begin to get heated. The hot water rises and is ready to use with a hot and cold mix regulator. You do have to be careful to monitor the temperature and know how much wood to put in because otherwise the tank can get too hot and explode. Similarly bush baths or some sort of water heating transfer systems are created for hot tubs as well.
Compost Heated Shower
Jean Pain made the compost heating and energy producing compost famous years ago in France. He addressed several of his homesteads energy inputs and did brilliant energy cycling along the way. His system of chipping underbrush to protect against fire in the South of France, produced huge compost piles rich in Nitrogen. The system produced heat and methane, which he captured for numerous fuel sources. You too can heat water through this fascinating anaerobic compost process that I have also seen heat garden beds in cold temperate locations (see article). The process is fairly straight forward, which is to build a large compost pile, at least nine cubic meters or yards in size and if in a cold climate insulate this with a ring of straw bales. You begin to build the pile and as you go you add in about 100 yards or meters length of black plastic piping. You continue to add compost materials as you lace piping this through the pile. The piping is connected to a pump that goes to the shower thus cycling the heat that builds in the pile. At first it may spike to over 160° F or 70° C but then will remain at around 131° F or 55° C. This is due to it being an anaerobic pile as it is not turned and you continue to add in materials high in nitrogen. Materials should be chopped fine and have proper moisture just like a hot compost pile. Additionally, a cold/hot water regulator is needed as the hot water that comes from this is simply too hot. The materials can one day be utilized for mulching of trees or better yet put into a hot compost pile to let them break down aerobically.
Renewable Electric Energy Dump
I don’t recommend heating water through electric sources but if excess energy is being created and you can’t sell it back to the grid, then you can dump it into hot water through a electric coil. For example in Argentina we used the firewood heating shower I describe above at a very remote site I worked at. Wood was sparse in this dry region but sufficient enough for our needs. That wood could have gone to mulching if we had utilized a bit more wiring from our micro hydro electric system. The system produced so much energy that the excess was dumped into a hot water tank at the electric station and was wasted. It could have been directed into the domestic system or we could have walked the descent distance to the hydro station and had outdoor showers there. Furthermore, geothermal provides an opportunity to heat water especially where hot springs exist. This integration in these special areas is becoming more the norm to take advantage of natures free hot water. I have seen this employed throughout the world in my hot springs travel as it one of my main nature retreats for health pilgrimages.
All in all there are numerous technologies that directly use the sun or its stored sunlight of modernity in the form of biomass. Permaculture dictates to have multiple elements for the important function so as a site grows in size you may have to employ numerous of these systems for specific needs. We all love a hot shower especially after a long days work with sore muscles. Leverage technology with natural abundance and you will have a hot shower that is lighter on the earth.
Written by Doug Crouch
Header Art by Nathan Maggard