A storage heater, nightstore (New Zealand) or heat bank (Australia) is an electrical heater which stores thermal energy during the evening, or at night, when electricity is available at lower cost, and releases the heat during the day as required. Alternatively, solar storage heaters are designed to store solar energy as heat, to be released during the night or other periods where it is required, often making it more cost effective than selling surplus electricity to the grid and buying it back at night.
Principle of operation Storage heaters are typically composed of clay bricks or other ceramic material (grog), of concrete walls, or of water containers. There are also special materials such as feolite. This material serves as a heat storage medium. There are electrical heating elements embedded in the material which can be switched on to heat the storage medium and thus to store energy. The stored heat is given off continuously (through thermal radiation and convection). To speed up the heat transfer, storage heaters may come equipped with mechanical fans that can move air through the heater; see the section on fan-assisted storage heaters.
Types of storage heater
High heat retention storage heaters High heat retention storage heaters (HHRSH) are the newest and most advanced storage heaters on the market. High heat retention storage heaters are able to retain more heat than traditional storage heaters, with a minimum of 45% heat retention 24 hours after a full charge. This significantly reduces the heat wasted during the day, and is achieved through improved insulation. High heat retention storage heaters also include smart controls and monitor climatic conditions to estimate future heat demand, making them much more responsive to changes in their environment than traditional storage heaters. All high heat retention storage heaters are also Lot 20 compliant, in line with the EcoDesign regulations which came into force on 1 January 2018.
Regulations Lot 20 is an EU legislation that was designed to remove inefficient heating technologies from the market and reduce the energy used by products that heat our homes. The goal of the legislation is to achieve the UK's overall carbon reduction targets and has been in place since 1 January 2018. It states that all installed electric heating products manufactured from 1 January 2018 must have an electronic thermostat with a 24-hour, 7-day timer with either adaptive start or an open window sensor. Storage heaters must include: an electronic heat charge control with room and/or outdoor temperature feedback or controlled by energy supplier, an electronic room temperature control plus week timer and a fan assisted output. Optional additional compliance features are distance control, adaptive start and open window detection. Non-compliant stock that was manufactured before this date may still be sold. From an environmental health point of view, asbestos has been used in night storage heaters for many years, the fibers of which can get into the air and pose considerable negative health impact.
Application
Storage heaters are usually used in conjunction with a two-tariff electricity meter which records separately the electricity used during the off-peak period so that it can be billed at a lower rate. In order to enjoy the lower rates, the house must be on a special electricity tariff. In most countries, storage heaters are only economical (compared to other forms of heating) when used with such a special tariff. In the United Kingdom the Economy 7 tariff is appropriate. Storage heaters usually have two controls: a charge control (often called "input"), which controls the amount of heat stored, and the draught control (often called "output"), which controls the rate at which heat is released. These controls may be controlled by the user, or may operate automatically once the user selects the target room temperature on a thermostat. Storage heaters may also incorporate an electric heater (utilizing either resistance heaters or heat pumps), which can be used to increase heat output. Such added heating, if it is resistance heating, is expensive, as it occurs during the high-tariff time of day.
Comparison to other heating systems
Advantages Storage heaters, while often still more expensive than equivalent gas- or oil-fired heating systems, are cheaper than running the same amount of electrical heating using electricity at regular daytime rates. Users of gas central heating and some other systems often turn off the heating during the night as an economy measure, with the result that the house is cold at night and early morning; but because night storage heaters are on at night, the house is still warm at those times. Using storage heaters allows houses to be sited in areas where natural-gas distribution systems are not available, without requiring the homeowners to pay higher daytime electrical-heating bills. The capital cost of night storage heating is relatively low, and installation is far easier than the initial installation of gas-fired boilers, piping and radiators, or electric heat pumps. This is an important advantage when renovating old buildings without existing central heating. As compared to gas central heating systems, night storage heaters have next to no maintenance costs.
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