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SPC heat pipes – HVR Feature October 2005 – Industrial Space Heating

Warm air curtains are vital where external doors need to remain closed during the heating season, but with high pedestrian or goods traffic, or an “open door” policy to increased business, the doors must remain open.

Energy losses can be substantial in such areas with no air curtain. An Airdor® warm air curtain effectively reduces energy loss by up to 80%, whilst minimizing temperature fluctuations and providing immediate comfort warmth on entry. Airdors® complement the heating system already in operation. Added advantages include prevention of ingress of traffic fumes or insects, pollen or dust which makes a more pleasant and safe working environment for the building occupants .

A correctly specified Airdor® breaks the natural convection air currents through an open door, thus reducing the heat loss, whilst reducing the effect of pressure differentials across the doorway (e.g wind). The maximum pressure differential for an air curtain is 3 metres or 5 Pascal. It is advantageous to design the air curtain into the building at design stage, to avoid complications in positioning, suspension, width required, etc. It is essential that all factors affecting the doorway are considered, including normal pressure load due to temperature difference, any through draft or tunnel effect, whether a chimney effect exists and any wind or draught pressure load. Incorrectly specified air curtains can increase heat loss – the correct air velocity and volume must be achieved to ensure maximum benefit is obtained from the air curtain. Airdors® should be used to keep heat in, so are most effectively mounted within the heated area. Heated Airdors® in a cold air intake situation can still feel cool.

A common mistake is to fit an air curtain which is the same size as the doorway – however , for maximum efficiency , the warm air curtain should extend beyond the width of the door by a minimum of 100mm at each side. Horizontal Airdors® make no use of floor space and are suspended from the ceiling or wall – suspension kits are available to suit all models, in a variety of styles – or can be concealed in the ceiling, with only grilles visible, although this is more common in commercial applications.. Vertical Airdors, on the other hand, are floor-standing and require no additional fixing systems , so are easier to retro-fit. Normally vertical units will have a higher velocity and volume capability, and may be more energy efficient..

In industrial applications, a variety of solutions are available, including vertical and horizontal units. A “combi” version allows the unit to operate conventionally as a warm air curtain, but also to swivel and function as apace heater for a given time period, before returning to it’s air curtain position. Ambient (unheated) air versions of air curtains are available for use within chilled areas, such as food and dairy processing areas, flower storage areas or any other chilled area where frequent access is a necessity. Such a curtain permits the removal of the conventional heavy plastic strips which for many years have been utilized in such areas, and makes entry and exit much easier for vehicular and pedestrian traffic.

Inside the building, it is possible to utilise radiant ceiling panels to provide heating . This can be within a standard t-bar grid arrangement, where available, or suspended below the ceiling in a “sail” arrangement. Because the radiant panels operate using electro-magnetic radiation, such as we receive everyday from the sun, it travels in a straight line and warms the people below, not the air it travels through. Additional spot heating can be provided over specific areas if required. Inclined panels can be provided for “apex” style ceilings, but this requirement should be made clear at the design stage to allow correct orientation of the copper tubes which carry the heating medium.

This method of heating allows full usage of floor space and avoids any potential damage to wall or floor mounted units, and provides a “cone effect”, with a small amount of convection from the panel. The overall effect is a much more even spread of heating than, for example hot radiant tubes, which show peak temperature rises directly below the unit and less effect as you move away from the unit. The operation is silent and requires no maintenance once installed. With simple connection by push on hoses, the installation of radiant panels is much simpler than other types of radiant system.

SPC’s Thermatile Plus utilizes a patented aluminium sandwich type material as the main carrier plate, onto the back of which are mounted aluminium extrusions which carry the 10mm od copper tubes for the heating medium. The panel is extremely rigid, but lightweight, and can be provided with acoustic drilling and lining for rooms which require improved sound attenuation, such as conference rooms and the like.

Although normally supplied in a white finish, the panels can be colour co-ordinated to any RAL colour to match architecturally designed features, or with textured finish. Sails, mounted below the ceiling where there is no suspended t-bar frame, can be straight or shaped, even curved, and can be joined together to provide a stylish feature such as in an entrance lobby or a display showroom. Lighting can be accommodated within the panel, or suspended from the panel , giving probably the widest range of options to the heating designer to match the flair of the architect.

In industrial heating, very often there is no facility for radiant ceilings to be incorporated, and unit heaters are considered as an effective way of providing heat into a large area. Models are available for steam or hot water; coil selection and motor speeds allow for a wide variety of different outputs and leaving air temperatures to suit particular environments and applications.

The working environment will often determine, or limit, the choice of unit heater available with acceptable sound levels, for instance, downstream unit heaters are inherently noisier, and would normally not be used in areas such as laboratories, gymnasia, sports halls, etc. Assembly workshops, light engineering workshops, engineering machine shops, and heavy engineering workshops are other normal areas where unit heaters tend to be favoured, again, noise levels play a part and should be checked against the selection made.

Mounting heights will also play an important part in the selection of the correct unit heater, as well as the heat output required. If ventilation or ducting are involved, the air volume flow rate and added resistance of all ductwork, grilles, etc must also be taken into consideration. Air stream temperature is a key factor in the effectiveness of the heating installation, since a leaving air temperature which is too low will cause draughts and discomfort. Too high will cause patchy heating, air stratification, high temperature gradients and high roof heat losses. A suggested leaving air temperature between 35-52 deg C is normally satisfactory for a large proportion of installations. The unit heater should always be sized on the basis of actual entering air temperature, i.e ambient temperature at heater level and not on the ambient air temperature desired to be maintained at the working level.

It is inadvisable to design a system where different unit heaters give different air stream temperatures in the same area. Where some units have fresh-air inlets and others re-circulating air, it is advisable to minimize the differences between air stream temperatures by selecting different heat exchangers.

Email: spc@spcoils.co.uk