Commercial heating
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Warm air heating in a commercial setting
Combined warm air heating and ventilation solutions have been on the market for many years. The technology has been developed to the point that they now offer optimum energy efficiency while improving air quality. Dravo’s Chris Boroughs explains the benefits
C
ombined warm air heating and ventilation solutions rely on a degree of fresh air intake to operate. Dravo’s range of indirect gas-fired
units, for example, provide both fresh and warm air in the building. Indirect fired units work on a patented air recirculation system which supplies the amount of fresh air required to meet the changing requirements of the building, while maintaining a constant supply of fresh air into the burner. When fresh air is required, ventilation is quickly
achieved as the dampers automatically adjust to provide the required amount of tempered outside air. The effect is almost instant as the fresh air is distributed evenly around the building. Since fresh air is delivered faster than it
can escape by natural ventilation, these units slightly pressurise the air inside the building. Pressurisation causes the air to distribute evenly throughout, eliminating temperature stratification or ‘cold spots’ and ensuring every part of the building is usable at all times. Once optimum conditions have been reached, the system modulates the fresh air input and utilises up to 90% recirculated air for maximum economy. When temperatures within the building change,
a combined heating and ventilation system can respond very quickly, soon returning the interior to comfort conditions. Heat recovery is fast becoming the norm for such
ventilation systems, reducing both running costs and harmful CO2 emissions into the atmosphere. This method of heating and ventilating premises is ideal for buildings requiring summer ventilation and regular air changes to maintain good air quality.
Combining the heating and ventilation functions
gives optimum control and avoids the problems of co-ordinating and balancing separate heating and ventilation units. The combined system also has significant benefits on the operation of the heating, since the system utilises a large air volume/low discharge temperature principle. A modulating burner and damper system,
controlled electronically, ensures full co-ordination of the heating and ventilation functions. Between 10% and 100% fresh air may be utilised together with up to 90% recirculated air. The 90/10 operation ensures excellent performance and low emissions. Dravo designs and installs bespoke heating,
ventilation and cooling system solutions for wide ranging applications, by providing reliable,
12 March 2023
consistent and comfortable temperature inside all of the new distribution centre.
Benefits of AHUs
¡ Up to 109% efficiency ¡ Low NOx <30ppm ¡ High pressure of up to 2500pa ¡ Extruded aluminium or galvanised painted pentapost frame construction ¡ Double skinned insulated panels of 50mm thickness ¡ Outer skin manufactured from plastisol ¡ High-efficiency, direct-coupled plug fan mounted on its own base frame and isolated from the structure via antivibration mounts Accessories: bag and panel filters, cooling and heating coils, thermal wheels and other options available to suit the application.
High velocity ductwork systems
The nature of the high-pressure fans provide a large available external static pressure, allowing the air to be distributed at high velocity through the systems, hence minimising the size of the distribution ductwork. The ductwork is all spiral wound galvanised steel, which is light, quick to install, and far cheaper than tailor made rectangular ducts. Standard size pre-fabricated ductwork is used which is readily available and installations can be started very quickly and completed whilst plant is being manufactured.
Above: Chris Boroughs, Dravo
Primary heated air is discharged into the building at high level via multiple nozzle outlets. The velocity is such that the surrounding air is continually entrained by a venture type effect resulting in large quantities of quality tempered air arriving at floor level at low velocity, providing uniform temperature throughout. The advantages of this type of distribution system
over conventional heating schemes are many and summarised below. ¡ Reduced temperature gradients to approaching 0.3C per metre rise, thus reducing normally high roof heat losses from static hot air, resulting in fuel savings in the order of 20%. ¡ Reclaims resultant heat gains from machinery, lighting and personnel. ¡ The central station air handling unit provides ease of service and maintenance with no moving parts at high level. ¡ The distribution system is quiet and aesthetically pleasing, with high velocity primary air allowing small diameter ductwork, either insulated or uninsulated to be used. ¡ Multiple points of air input reclaim warm air from high level increasing air movements by greater than 1:1 for better distribution and comfort. ¡ Lightweight air distribution system reduces building structure loadings and is easier to install. ¡ Lower noise levels than other types of induction air systems, due to lower nozzle outlet velocities. These bespoke air handing units and high velocity
systems can be supplied to meet all air heating requirements and the Dravo technical experts are always available to advise on unit selection.
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