Investment in energy-efficient HVAC can contribute substantially to minimising the costs for very large hangars and warehouses
Nick Winton, Nor-Ray-Vac divisional manager at Nortek Global HVAC UK, believes the HVAC industry is now equal to the challenge and can deliver solutions that are both effective and economical to run.
Challenges & Action
Specific building requirements
Hangar design depends on the type and size of aircraft it is intended to house, but it is frequently the case that the roof is constructed to allow the complete tail plane within the structure. As a result, the roof height can vary from 10m to 30m, and the main doors – as well as measuring the complete width of the hangar – can be virtually as tall as the roof.
Being such large spaces, hangars contain a large volume of air and are prone to high air change rates. Since the doors are frequently open, air infiltration can severely disrupt comfort levels. In many areas of the UK the challenge is compounded by the fact that airfields tend to be sited in extremely exposed locations.
A heating solution therefore needs to be able to sustain a comfortable environment and, in particular, provide rapid recovery to full operating temperatures once the doors are closed.
The fact that hangars house very expensive equipment which can contain highly explosive fuel or armaments, makes it essential that the heating system complies with the prevailing authority’s mandatory fire regulations.
Hangars are often used at irregular time intervals and are rarely fully occupied. To ensure efficient use of energy the ideal HVAC solution should be capable of being configured to heat specific areas of the structure, in designated zones, as and when required.
Choosing a HVAC solution
An aircraft hangar environment is simply too hostile for many types of heating solution. Warm air heating, for example, would not only consume fuel attempting to heat the entire volume of air in the space, but would also give rise to enormous temperature stratification.
When the doors open to allow aircraft movement, the volume of warm air within the hangar would be replaced instantly with colder air from outside. Many commercial aircraft maintenance operations are scheduled at night, so the temperature fluctuations would be considerable.
Key advantages of radiant heat
Accepted as one of the most energy-efficient forms of space heating on the market, radiant tube heating has evolved to address the requirements of heating all sizes of aircraft hangar. Burning fuel (natural gas or LPG) at the point of use means there is no loss of efficiency in distributing heat around the building. Most importantly, the degree of warmth felt by personnel is less affected by cold air influx through the hangar doors opening and closing. The ability of a radiant heating system to respond rapidly to changed conditions is also a key factor.
Since radiant systems emit infra-red rays that warm only the people and objects in their path, as opposed to heating the volume of air in the building or the roof space, no fuel is consumed wastefully. Meanwhile, the occupants remain warm regardless of fluctuating air temperatures when the hangar doors are opened and closed. Focussing heat exactly where it is needed ensures people feel comfortably warm at all times, while the intense chill is taken off the aircraft structure preventing the build-up of potentially hazardous condensation.
When operatives are working in just one area of the hangar, which is often the case with aircraft maintenance, zoning enables other parts of the system to be switched off. Over time, this produces considerable fuel economies and substantial cost reductions. Since there is no requirement for a separate plant room, this is a further benefit of radiant tube heating that helps to keep operational costs low.
Continuous radiant tube heating offers several advantages over linear radiant tubes. The number of burners and roof or wall penetrations required can be kept to a minimum and it can be zoned to fulfil local heating requirements. By providing low intensity, even heat coverage over very large areas, the system is economical, energy-efficient and quiet to operate. Reduced energy bills and carbon emissions
Lessons & Results
Natural gas is, on balance, the most efficient, environmentally friendly form of energy. Although slightly less efficient at the point of use than electricity, natural gas produces almost 2¾ times less greenhouse emissions and is on average only one quarter of the cost.
Based on a case study comprising three RAF type C hangars measuring 92m (length) by 47m (width) by 14m (height), a gas-fired radiant tube heating system delivered a 64% energy saving compared to HTHW panels, whereas warm air re-circulating radiant system showed a 36% saving compared to HTHW panels.
In terms of energy use, natural gas is the most cost-effective, clean fuel for aircraft hangars and makes a substantial contribution to minimising the impact of the Climate Change Levy. Radiant tube systems such as the Nor-Ray-Vac can be designed to a thermal efficiency of >92%. At this thermal efficiency such systems are eligible for the Enhanced Capital Allowance (ECA) Scheme.
In the first year of operation ECA allows organisations to claim 100% of the equipment and installation costs as a capital allowance against taxable profits, providing a welcome upfront tax relief.
Effective, low-cost operation
Ryanair switched the specification for its new Prestwick hangar from under-floor heating to an overhead continuous radiant tube heating system because from experience at other locations it was found that working on a warm floor for long periods of time was uncomfortable to the ankle joint. Against a backdrop of high fuel prices and given the requirement to minimise greenhouse gas emissions, it makes sound financial and environmental sense for operators of civil establishments to reduce their fuel burden. With radiant heating it is possible to do so without compromising the comfort of the hangar’s occupants or the safety of the operation.