Back to basics with air movement
Thermal destratification, the recycling of rising hot air, which has been described as the missing piece to the HVAC puzzle, is simple, effective and remarkably economical says Stephen Bridges of Airius.
The only reason why this technique, which can offer savings on heating and cooling costs of between 20 and 50%, is not more widespread is that there is little awareness of how adaptable it is for use in virtually any space, with ceiling heights ranging from a normal office to a high-bay warehouse.
Contrary to popular perception, destratification is not the preserve of big spaces because if your ceiling is 2.5m high or more, you can benefit from destratification fans that are really no more complicated to install than a light fitting. The same simplicity applies even to a 38m aircraft hangar.
Most of us live and work in a space within two metres from the floor – any space above that is potentially a heat sink. I became a convert when I saw destratification fans at work in the USA, and consequently brought the latest thinking in this technology across the Atlantic. The innovations had been developed by a plastics injection moulding firm, which needed to find ways of making dramatic savings in energy costs if it was to resist overseas competition – a story that will resonate with many business managers these days.
Recycle and re-use
Everyone knows that hot air rises, and then it has to be replaced to keep the working space at or near ground level within a comfortable, efficient working range – even more galling when you are actually generating heat as part of a production process or from computers or freezer cabinets, only to lose it to the roof space. The higher the ceiling, the greater the heat gradient and potential heat loss, but nevertheless, the principal applies in any space. Recycle and re-use the heat that rises and the savings are going to be immediate.
Of course, manufacturers always quote the best figures, and the ‘up to 50%’ figures relate to high ceilinged spaces. However, even a low ceilinged, insulated building can expect savings of 20 to 30% on space heating costs and that is not insignificant in today’s energy markets. Maximising savings made will, of course, depend on the technology chosen – and we’ve come a long way from the days of a box fan blasting air down.
So what do you look for to get the comfort right and the savings maximised? The goal is to equalise the temperature throughout the space, minimising convective heat loss from the working area – in other words, to destratify the air space. The way to do this turns out to be remarkably simple, involving no complex programming of a building energy management system, no need for extra ACI units that need regular statutory inspections, or ductwork that will need cleaning and exhausting.
A degree of destratification can be achieved by simple paddle designs or basic box fans. However, designs that neutralise the turbulence that is created by the turning vanes will enable significantly higher throughput in return for the same electrical input – up to 60% more. These designs will also ‘reach’ right to the floor. The boosted throughput is achieved by special multi-vane stators, patented by Airius, which neutralise the turbulence created by the fan blades. This means air is projected straight downwards in an even, predictable column, that will spread when it reaches resistance at the floor, quickly equalising heat distribution and eliminating hot and cold spots.
Airius engineers describe the column as an invisible duct, and what is often surprising to people not used to destratification, is how gentle the downward air flow can be. People walking through the column of air will feel barely a ruffle in their hair. Suffice to say that these fans are used in retail environments where significant downdraughts would be wholly unacceptable for the customer experience. Engineers are delighted to find these fans require no special supply (single phase), draw from 12W for an office-style unit, 42W for a warehouse, to no more than 400W for a 38m high aircraft hangar.
A degree of planning is required to ensure the full area is adequately covered, but a single fan can cover a surprisingly large area. In return for 31W input, a space with a floor area of approximately 100sqm can be equalised. At the top of the range, one fan will suffice for a floor area of over 300sqm.
So who is using this technology and is it working for them? Lush Cosmetics reported a ROI of 26 days at their Poole factory. Morrisons supermarkets turned to Airius to resolve the problem of having too-chilly food aisles alongside too-warm household aisles. At the Genentech temperature controlled pharmaceutical warehouse in Louisville, Kentucky, a major commercial disaster was averted after the US Food and Drug Administration found the higher warehouse bays were too warm to be fit for purpose. Airius destratification fans resolved the issue within days.
Destratification, it seems, really is the missing piece in the HVAC puzzle.
Destratification in action
Anyone who has shopped in a Morrison’s supermarket recently will have felt the benefits of destratification – although they wouldn’t have realised because the air flow of the air column is barely perceivable,
Morrisons, the fourth largest supermarket chain in the UK, is always looking for ways to reduce their energy costs and carbon footprint and ways to increase customer comfort.
In fact supermarket operators and their HVAC consultants have been trying to resolve the age old problem of cold chiller aisles and uncomfortably warm clothing aisles for many years. Costly and inefficient ducting systems, under cabinet heaters and heat retrieval systems have failed to solve the problem to date.
Mitton Mechanical, a Morrisons contractor, approached Airius in late 2007 to conduct a trial in the Morrisons Knottingly store in Wakefield. Airius units were placed at four metre intervals in three chiller aisles in the hope of reducing the stratification from 6-8ºC to 1-2ºC thus making the chiller aisles more comfortable (without adversely affecting the chiller units). More comfortable chiller aisles should increase the aisle spend, as shoppers rush through when the aisle is too cold and dwell longer when it is comfortable. Another advantage of destratification is that it eliminates freezer/cabinet fogging.
The trial was hugely successful and over 100 Morrisons stores have now been retrofitted with the Airius units. The Airius units are now on the standard specification list for all new stores and are being retrofitted as part of the normal refurbishment programme.