Heat-storage blocks

Press, Volume CXI, Issue 32587, 22 April 1971, Page 20

Heat-storage blocks

At a time when so many other fuels have been increasing in price, the price of one, off-peak electricity has remained more or less as it was. Indeed in some areas, the off-peak rate has actually been reduced to encourage additional sales of this relatively new and convenient source of power.

The changes in the off-peak tariff—-which have for the most part been of great benefit to the user of controlled storage electric central heating—are very similar to what has been happening in other parts of the world. Gunther Mohr, writing in “AEG Telefunken Progress” last year forecast that the amount of electricity available during off-peak periods would increase still further and this would make power supply authorities even keener to push off-peak sales.

To use off-peak electricity efficiently requires special storage equipment. Because low-cost off-peak power is only available at certain times of the day (and those are almost always the times when heating is not needed), some way must be found to draw power from the mains and store it in the form of controllable heat. One storage central heating system draws power from the mains, stores it in the form of heat and then, when a.thermostat is tripped or a switch is turned, it warms the area which requires heating. There is thus no waste during the charging period and instant response when heat is required.

The first units designed to use off-peak power were little more than blocks of concrete with wires through

them. When there was power available it heated the wires, which in turn heated the blocks.

Because of their ability to store heat, the surface of the blocks remained at a constant temperature and acted as a room heater. Units of this type were widely used in Europe in the early days of off peak power and for a country where the climate is relatively easy to forecast they are quite satisfactory. There are, however, certain obvious disadvantages to the simple uninsulated block storage system. Heat (and power) is wasted because it supplied heat continuously, regardless of whether it is required. The area which can be served by one heater is limited because it relied solely on natural air flows and radiation— the storage capacity was also very limited and this type of equipment is seldom satisfactory in areas where the climate is changeable. A further disadvantage is the high surface temperatures of this type of equipment and most manufacturers recommended that an air gap of at least two inches be left all round the unit.

The simple block storage unit has since been modified considerably so that the standard of control over the input charge is improved and most units now have a proper insulation system so that less of the original charge is wasted.

One manufacturer makes a controlled storage system using a heat exchanger and a thermostatically-controlled fan. This enables a room to be heated at the time when it is required, but having used off-peak electricity.