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Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating.
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Radiation vs. convection
In practice, the term "radiator" refers to any of a number of devices in which a fluid circulates through exposed pipes (often with fins or other means of increasing surface area), notwithstanding that such devices tend to transfer heat mainly by convection and might logically be called convectors.
The term "convector" refers to a class of devices in which the source of heat is not directly exposed. As domestic safety and the supply from water heaters keeps temperatures relatively low, radiation is inefficient in comparison to convection.
For homes with radiators, Energy Star recommends placing heat-resistant reflectors between radiators and exterior walls to help retain heat in a room. [1]
Types
Hot water
A hot-water radiator consists of a sealed hollow metal container filled with hot water by gravity feed, a pressure pump, or convection. As it gives out heat the hot water cools and sinks to the bottom of the radiator and is forced out of a pipe at the other end. Anti-hammer devices are often installed to prevent or minimize knocking in hot water radiator pipes.
Hot water baseboard
Traditional cast iron radiators are no longer common in new construction, replaced mostly with forced hot water baseboard style radiators. copper pipes which have aluminum fins to increase their surface area. In the U.K., modern domestic radiators tend to be of sheet steel construction (often with steel fins), though copper/aluminium is often found in industrial Air Handling System heat exchangers.
Steam
Steam has the advantage of flowing through the pipes under its own pressure without the need for pumping. For this reason, it was adopted earlier, before electric motors and pumps became available. Steam is also far easier to distribute than hot water throughout large, tall buildings like skyscrapers. However, the higher temperatures at which steam systems operate make them inherently less efficient, as unwanted heat loss is inevitably greater.
Steam pipes and radiators are prone to producing banging sounds often incorrectly called water hammer. The bang is created if condensate fails to drain properly; this is often caused by buildings settling and the resultant pooling of condensate in pipes and radiators that no longer tilt slightly back towards the boiler.
Fan assisted heat exchanger
A fan-assisted radiator contains a heat exchanger fed by hot water from the heating system. A thermostatic switch energises an electric fan which blows air over the heat exchanger to circulate it in a room.
Its advantages are small relative size and even distribution of heat. Disadvantages are fan noise and the need for both a source of heat and a separate electrical supply.
Underfloor
The current trend in radiant heating is towards underfloor heating, where a network of pipes, tubing or heating cables is buried in or attached beneath a floor, allowing a gentle heat to rise into the room. Best results are had with conductive flooring materials such as tile. The large surface area of such room-sized radiators allows them to be kept just a few degrees above desired room temperature, minimizing convection. Such systems offer a high level of comfort, but are more expensive in new construction than less efficient systems and generally difficult to retrofit into existing buildings.
The Roman hypocaust employed a similar principle of operation.
Electric baseboard
Similar in configuration to forced hot water baseboard - low profile units running along the base of a wall with a central heating element surrounded by radiating fins - electric baseboard heaters are inexpensive to produce and install. They offer instant heat and great reliability, but may be more or less cost-effective relative to other forms of heat depending on electricity prices.
Portable
Electrically powered portable radiators come in two basic forms:
- Electric elements, which either heat directly or radiate heat to a heat-conducting solid such as quartz
- Liquid filled, which employ an electric element to warm a fluid such as oil held within metal tubing, which circulates via convection.
See also
- Coolant
- Heater core
- Heat-resistant reflector
- Underfloor heating
- Bleed screw
- Thermostatic Radiator Valve
Radiator Reflector
External links
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Wikimedia Commons has media related to: Radiators |
References
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