Radiant heating – for economy and versatility

Radiant tube heating is among the most economical forms of space heating on the market. It is clean, energy-lean and responsive. Howard Marfleet looks at the options and applications for radiant heating.

Faced with the challenge of selecting a new or replacement heating system for a large space building, specifiers or building energy managers seeking to minimise fuel consumption should automatically look at the options for heating by radiant tube.

This form of high performance heating is effective in a wide range of applications where even heat coverage, rapid warm-up, quick heat recovery and flexibility of operation are required – for example, in sports halls, aircraft hangars, warehouses, automotive workshops, transport maintenance sheds and factories.

Typically, radiant heating will reduce running costs by 25-60% in retro-fit applications, although this is occasionally beaten. In a recent heating decentralisation project for the MoD, energy cost savings of 64% where achieved by replacing a boiler and high temperature hot water system with gas fired radiant tubes from AmbiRad.

Low operating costs are achieved by concentrating the heat at low level, where it is most needed, without heating the volume of air in the building. Rapid response times reduce running costs still further. Such flexibility means that warmth is felt by people in the building within minutes of start-up on cold mornings – no fuel is wasted bringing the air to a comfortable temperature. By contrast, some conventional convection systems may take up to an hour to reach comfort conditions.

Similarly, when external doorways are opened – periodically or for long stretches of time – people working in a building heated by a radiant system continue to feel warm and once the doors are shut again, comfort temperatures are restored almost instantly. A minimal amount of heat is lost through the doorway, or through the roof.

Should a facility be down-sized, or activity confined to only one or selected areas of the building, radiant heating can be configured to heat only the part(s) required. This is called zone control and is a further energy-saving measure. It is particularly useful where activity takes place in different parts of the building on a daily basis – such as in an aircraft maintenance hangar. The building will not be fully utilised all the time, but selected areas will be occupied when planes are brought in for service and repair at different times.

Most importantly for many applications, especially environments where small particles and dust may be present in the air, radiant systems heat without air movement. In this context, radiant may be a trouble-free option for heating, where the air movement association with a convection system would tend to disturb particles in the air.

Since a radiant system burns fuel at the point of use, there are no distribution losses to take into account. Gas fired radiant tube heaters need to have a net thermal efficiency of 86% and a minimum radiant efficiency of 60% for inclusion on the Government’s Energy Technology List, in order to be eligible for Enhanced Capital Allowances.

Radiant tube heating is mounted overhead, often at very high level - normally between 4 and 12 metres, although mounting heights of 25metres are not uncommon (for example, to accommodate cranes). The gas burner fires a flame along the inside of a black steel tube causing it to heat up. The external surface temperature of the tube can reach 400–700°C, at which point it is emitting radiant heat. This is reflected downwards by a highly polished reflector.

Types of radiant heater
Linear or U- tube
These ‘straight line’ heaters are positioned at strategic points to provide excellent heat coverage around the building. Most commonly used in high bay factories or aircraft hangars for maximum effectiveness and flexibility, they can also have unusual ‘tailored’ applications.

At Interlink Express’ national distribution centre in Smethwick, for example, where around 110,000 parcels are processed every night, a total of 27 AR22SL linear radiant tube heaters were positioned over the 92 doorways at approximately 3.5m from ground level. The system effectively and economically heats the area immediately around the 95 loading bay doors while they remain open during the night.

Continuous radiant tube
Continuous radiant tube offers all-round, low intensity warmth in a variety of settings. It is particularly suited to sports halls where it can be set to a lower temperature than would be normally required, yet still achieve the required feeling of warmth for both athletes and spectators.

At Bath University Sports Training Village, a new university/community sports facility, Nor-Ray-Vac continuous radiant tube heating with a total of 24 burners ranging from 24 to 38kW output was installed in the Tennis halls and Multi-Purpose Sports Hall to provide even, low intensity heat at a constant 16-18°C.

Continuous radiant tube has the advantage of being quiet, aesthetically in keeping with the surroundings, convenient (in that it does not take up valuable floor space) and safe.

Packaged compact units
The latest type of radiant heater to come on to the market is the packaged unit, such as the Vision Compact from AmbiRad. This heater arrives on site in shrink-wrapped packaging which can be left on when the heater is installed to protect the unit from dirt, knocks and scrapes during non-related building work. The packaging can simply be removed at commissioning stage.

Radiant wall plaque heaters
Suitable for high roof buildings that suffer frequent air changes, or for spot heating applications, wall-mounted ceramic plaque heaters provide ‘instant’ heat exactly where it is needed. This small unit offers all the advantages of larger radiant models - quick warm-up (the Solarglow from AmbiRad can reach 1000°C in just two minutes), minimal air movement and a high level of comfort. Economically, it offers lower running costs, lower capital costs and lower installation costs due to its lightweight construction and ease of handling.

Web: www.ambirad.co.uk