LOW-TECH MAGAZINE

The Revenge of the Hot Water Bottle

Imagine a personal heating system that works indoors as well as outdoors, can be taken anywhere, requires little energy, and is independent of any infrastructure. It exists – and is hundreds of years old. The hot water bottle could save a great deal of energy and money without sacrificing thermal comfort.

Hot water bottles work both indoors and outdoors. Illustration: Marie Verdeil.

Thermoelectric Stoves: Ditch the Solar Panels?

Wood stoves can provide a household with thermal energy for cooking and for space and water heating. Wood stoves equipped with thermoelectric generators also produce electricity, which can be more sustainable, more reliable and less costly than power from solar panels.

Too Much Combustion, Too Little Fire

The fire – which we have used in our homes for over 400,000 years – remains the most versatile and sustainable household technology that humanity has ever known. The fire alone provided what we now get through a combination of modern appliances such as the oven and cooking hob, heating system, lights, refrigerator, freezer, hot water boiler, tumble dryer, and television. Unlike these newer technologies, the fire had no need for a central infrastructure to make it work, and it could be built locally from readily available materials.

Heat your House with a Mechanical Windmill

Renewable energy production is almost entirely aimed at the generation of electricity. However, we use more energy in the form of heat, which solar panels and wind turbines can produce only indirectly and relatively inefficiently. 

A solar thermal collector skips the conversion to electricity and supplies renewable thermal energy in a direct and more efficient way.

Much less known is that a mechanical windmill can do the same in a windy climate -- by oversizing its brake system, a windmill can generate lots of direct heat through friction. A mechanical  windmill can also be coupled to a mechanical heat pump, which can be cheaper than using a gas boiler or an electric heat pump driven by a wind turbine.

Ditch the Batteries: Off-Grid Compressed Air Energy Storage

Going off-grid? Think twice before you invest in a battery system. Compressed air energy storage is the sustainable and resilient alternative to batteries, with much longer life expectancy, lower life cycle costs, technical simplicity, and low maintenance. Designing a compressed air energy storage system that combines high efficiency with small storage size is not self-explanatory, but a growing number of researchers show that it can be done.

Heat Storage Hypocausts: Air Heating in the Middle Ages

Hot air vents in the floor of the Maulbronn monastery. Source: "Das Kloster Maulbronn. Geschichte und Baugeschichte.", Ulrick Knapp, 1997 / Via Spiegel 2016.

The Romans are credited with the invention of the first smoke-free heating system in Western Europe: the hypocaust. Until recently, historians had assumed that its technology was largely lost after the collapse of the Roman Empire. In fact, however, it lived on in large parts of Europe, and was further developed into the “heat storage hypocaust”, an underground furnace on top of which granite stones would be piled, to then release hot air through vents in the floor. By this means, a room could be kept warm for days with just one firing of the hypocaust's furnace.