With potential payback periods of under two years and typical energy savings of between 20 and 40%, Richard Johnston, National Business Development Manager at Elta Group Building Services, outlines why it’s time to take another look at destratification.
For many facilities managers, service operators and heating engineers, the large cavernous spaces typically found in entrance halls, warehouses and manufacturing sites present a challenge in terms of ensuring effective heating of the zone of occupation. While the implementation of advanced technologies including heat pumps, solar thermal and thermal storage have helped offset the costs of generating and storing heat, latest developments in a more traditional technology are resulting in major reductions in heat usage at a fraction of the cost.
Thermal destratification, or the effective redistribution of heat and air through large spaces, isn’t new, and anyone who has visited a manufacturing site or warehouse will be aware of the large number of box fans used to recirculate air. While used widely, the effectiveness of this technology in achieving its frequently stated 15% energy savings has been called into question. The concern lies with the fact that the air flow is released at an angle and spread over a wide area, rather than being directed to the area of occupation.
Despite this, with a typical floor to ceiling differential of 10 to 20°C in high ceilinged spaces, the ability to harness and redistribute hot air has long been seen as a key way to reduce energy consumption. As a rule of thumb, the temperature increases by 0.5 to 1°C for every metre in height. In practice this means that to achieve a temperature of 21°C at the ground, or occupied level, the ceiling of a 10m by 10m room would need to be heated in the region of 26 - 31°C. As well as reducing heating bills and wear on HVAC equipment, effective redistribution of this wasted heat energy could increase thermal comfort of workers by eliminating hot and cold spots, as well as reducing condensation on equipment through better air circulation.
Thankfully, through advances in the technology, it is now possible to achieve a temperature differential as low as 0.5 to 1°C from floor to ceiling and wall to wall. More importantly this has led to typical savings of 30 per cent on annual heating bills in even the most energy efficient buildings, with additional reductions in air conditioning requirements of up to 30 per cent. In the case of industries where heat is generated as part of the production process such as bakeries and printing presses, which have even more need of suitable destratification, savings of up to 50 per cent have been achieved. Overall, the greater the temperature difference from floor to ceiling, the bigger the savings. As a result destratification is now recommended as one of the Carbon Trust’s effective energy-saving strategies.
The step change has been realised through optimisation of design and operation of destratification focused towards the zone of occupancy (ZOO). The latest ZOO Fans available from Elta Group Building Services create a gentle column of hot air that is directed towards the floor. This allows previously wasted heat to be channelled to the area that it is needed most. As a result, thermostats switch off quicker and heating systems cycle off sooner, reducing wear and increasing the lifespan of HVAC equipment through reduced use. Additional benefits of this approach include the elimination of hot and cold spots, as well as reductions in condensation on concrete, chillers and windows, as a result of the fans delivering one air turn per hour, all of which has the added benefit of improving the comfort level for customers and employees.
Cutting costs in energy efficient buildings
The United States provides a number of good examples to UK practitioners in terms of energy savings. Pespi Co’s 1 million sqft facility in Wytheville, Virginia is one such example. The site was Leadership in Energy and Environmental Design (LEED) Gold Rated, one of the United States’ highest energy efficiency ratings and the equivalent to the more commonly used BREEAM here in the UK. Despite also having been classed as the most energy-efficient bottling plant in the world, heating costs dropped by 30 per cent within five weeks of installing ZOO Fans, with an added productivity gain of 5 per cent thanks to a more comfortable working environment.
Energy efficiency has been key to maximising returns. The typical destratification fan in Elta Group Building Services’ ZOO Fans range uses the same amount of energy as a 40 or 50 watt light bulb. Compared to the higher powered motors needed to power rooftop mounted Air Handling Units, or big plate fans conventionally used to push air through a building, destratification fans achieve a better result at a fraction of the operating cost. As the result of the technology’s low energy usage, small upfront cost and reduced heating bills investment pay back periods are typically under two years. The Centre for Advanced Energy Systems at Rutgers University in the U.S. examined 700 projects designed to “improve air circulation with destratification” under the U.S. Department of Energy and The Energy Efficiency & Renewable Energy Industrial Technology Program found an average payback period of 1.6 years.
The installation of destratification fans is also a lot less invasive than traditional air movement methods. Using a simple cable and grip method, ZOO Fans can be fitted in minutes and the self-contained design means that the fan won’t interfere with lighting or sprinkler systems. With limited pressure on the fan, it is also a fit and forget solution, with little to no maintenance requirements other than occasional cleaning of the blades in high pollution environments.
The effectiveness of destratification fans has even seen the technology start to replace outdated and inefficient ducting. Cleverly positioned fans help to redistribute heat and air at a fraction of the cost. This is increasingly being used to great effect where obstacles are preventing the effective distribution of heat, such as warehouses with large racking systems, where heat needs to be channelled down aisles to warm operatives.
With energy consumption a continuous battleground for building and facilities managers, and contractors tasked with reducing CO2 emissions, the effective use of destratification is an opportunity that cannot be missed. Taking into account low upfront costs, short payback periods and significant reductions in heating bills it is perhaps time the whole industry reassessed the potential impact of destratification.