Air Handling Units

Demand for underfloor air conditioning systems, which are far more flexible and adaptable than ceiling-based systems, has risen as developers and landlords scramble to reconfigure office spaces in the wake of the coronavirus pandemic. Experts have predicted a 50% reduction in office occupancy, as millions embrace working from home. What is underfloor air conditioning? A zonal underfloor air conditioning system makes use of the raised floor void as a plenum for the distribution of air. Supply and return channels are created under the floor, and zone units serving areas of up to 300m2 are suitably located throughout the office space to generate conditioned air locally to serve the needs of the space. Underfloor air conditioning goes further than displacement systems, offering full function control of the indoor environment Individually controlled fan terminals of either recessed or floor standing configuration are let into the floor over supply plena. These terminals introduce air into the space above in accordance with the dictates of their own on-board temperature sensors and controls system. Users can adjust fan speed and set point temperature individually. Return air grilles are positioned in the floor over return plena. The whole system is controlled by means of the electronic management system controlling the operation of the zone units and the associated fan terminals permitting centralized monitoring and control. Underfloor systems are inherently compartmentalised and offer highly effective solutions in multi-tenant areas and other environmentally challenging applications.  Many low-height refurbished spaces suffer from high levels of user complaint due mainly to draft from ceiling mounted outlets positioned too close to the user. The changing work environment At AET Flexible Space, we have seen increased demand, both from existing clients looking to reconfigure their office space, and new clients looking for a flexible air conditioning which can help to future-proof their office. A huge benefit of an underfloor air conditioning system is that they are inherently flexible, and can be changed to suit new room layouts within minutes. Our unique Fantile™ units are installed to sit in-line with the finished floor, and can be easily repositioned at any time without the need for the significant, and costly, building works usually involved in repositioning ceiling-based ductwork. A huge benefit of an underfloor air conditioning system is that they are inherently flexible We are already seeing that COVID-19 has accelerated the trend towards more flexible, future-proofed, and sustainable office space. We have been seeing an increase in demand for our underfloor systems for some time, but the coronavirus lockdown has certainly made more people consider the end-users of this office space, and how they can be best served Workplace wellness is also an increasing concern, and may be a key element for encouraging workers back into the office. The Workplace Wellness Study conducted by Future Workforce found that workplace environment is more important to employee satisfaction, engagement and productivity than most organizations realize. 67% of employees said they are more productive in workplaces that promote a healthy environment. One-third said they lose at least an hour of productivity each day due to office environments that don’t support their daily health. Beyond the inherent flexibility of underfloor air conditioning systems, they also offer high levels of energy efficiency, sustainability, and air quality. As there is no ductwork with an underfloor system, individual zones operate at very low-pressure encouraging energy efficiency. AET’s systems have helped attract LEED and BREEAM and other Green Building points, and can provide up to 30% savings in energy costs and a 29% reduction in C02 emissions when compared to ceiling systems. Cost savings Cost savings are also a key concern for everyone in the post-COVID world, and the flexibility and economy of an underfloor system across the lifetime of a building is increasingly attractive. The British Council for Offices (BCO) indicates that underfloor air conditioning can offer dramatic savings in overall cost, but it requires a co-ordinated team approach to achieve the optimum result. The flexibility and economy of an underfloor system across the lifetime of a building is increasingly attractive In the past the only way to reduce ceiling-based HVAC costs has been to reduce the specification and downsize plant, or reduce flexibility by increasing the size of terminal outlets and reducing numbers. However, these solutions often result in increased complaints of end-users about draughts and noise, which necessitates a costly and environmentally unfriendly re-design. Ceiling-based systems also demand service and maintenance from within the work space, from the simple task of changing filters in fan-coils or cassettes, to more complicated reconfigurations of pipework and ducts to suit a new layout below. Not only do these refits mean significant hidden cost, but they also cause disruption, and have a high risk of damage from condensate leakage. Construction Considerations In order to maximize the benefits of underfloor air conditioning, it must be introduced into the overall design philosophy at an early stage. When incorporated into the overall building design, savings can be made to curtain wall costs, all other height-related savings such as elevator shafts, columns, stairwells, riser shafts, and vertical services such as mains pipe-work and electrical risers. The Swedish National Pension Fund has reported overall cost savings of between 5% and 7% in buildings using underfloor air conditioning. In order to maximize the benefits of underfloor air conditioning, it must be introduced into the overall design Good quality underfloor air conditioning systems are similar in price to conventional good quality fan coil systems, but underfloor systems also reduce the cost of construction and offer tax advantages. The average office building costs in UK are in the region of £1000 to £2000 per square meter. Therefore, a 5% saving in overall cost could range from £50 to £100 per square meter. The average cost of any AC system is in the region of £120 to £200 per square meter, and so an overall saving in construction equates to something in the region of 50% of the AC system. As we move forward into 2021 and beyond, commercial construction is going to require sustainable and cost-effective design. With so many benefits, it is clear why so many in the construction industry are now turning to underfloor air conditioning solutions.

For designers, installers and operators of heating, ventilation and air-conditioning (HVAC) systems, energy efficiency is rightly the number one selection criteria. This applies particularly to fan motors. However, while EC fans - the popular solution that integrates a fan, motor and speed control – are regarded as something of a de-facto guarantee for efficiency, that is not always the case. When evaluating the efficiency of your fan, motor and speed control combination it is vital to consider the ‘wire to air’ efficiency.  Therefore, the total effect of both electrical and mechanical performance must be taken into account. Some EC fans have the motor mounted inside the fan wheel which disrupts the air flow. The result is decreased aerodynamic efficiency, and that impacts the overall efficiency of the fan unit. In contrast, a fan ‘package’ that comprises a high efficiency motor operating in combination with a variable frequency drive (VFD) that matches the motor speed with the required load could offer superior overall efficiency. Part-load efficiency is crucial In most cases, EC fans are fitted with brushless DC motors, known also as permanent magnet (PM) motors. When operating at full speed they can offer efficiency better than the IE4 standard. That sounds good until you consider that their motor efficiency can drop rapidly at part loads. In fact, they might not even deliver IE3 efficiency at speeds below 60 percent. This part-load efficiency is crucial since the majority of HVAC installations operate at less than 80 percent speed for 99 percent of the time. A more cost-effective, and energy-efficient, alternative can be to reduce the dimensions of the mechanical components such as air handling units (AHUs), ducting and auxiliary equipment to match the most common operating conditions. This approach must make provision to over-speed the fan motors to handle the 1 percent peak requirement, accepting that for this brief period there will be slightly lower efficiency and increased audible noise. EC fans cannot be over-speeded. Yet with VFDs it could, for example, be possible to over-speed a motor by up to 15 percent of its nominal speed. ABB EC Titanium™ motors are a highly efficient integrated motor drive solution for HVAC applications Power factor makes an important difference Harmonic currents are an additional energy efficiency consideration as they lower the total true power factor (PF) of the network by increasing the total line current. This extra current is not active current, but reactive current that results in higher system losses. Harmonics can result in added infrastructure costs due to the need to over-size equipment such as transformers, cables and fuses. Electricity bills might be increased while some utilities also impose penalties on their commercial customers with a low power factor. When evaluating the efficiency of your fan, motor and speed control combination it is vital to consider the ‘wire to air’ efficiency A traditional EC motor might have a power factor of around 0.78, drawing some 25 to 40 percent more current from the network than its actual load. That is why many EC fan systems require the installation of costly, centralized harmonic mitigation equipment. Instead, a fan package approach enables the use of a state-of-the-art VFD with active front end (AFE) technology that eliminates harmonics at source. The benefit is a power factor of 1, so that the motor draws only the current it actually needs. What happens when motors need replacing? There is also a sustainability issue regarding the ease of servicing and replacement of the fan motors. Should an EC fan fail it is not serviceable and the complete unit will need replacing, with implications for both costs and the lead time to get a suitable replacement. With a separate drive, motor and fan set up based on standard equipment, if the VFD fails it can be replaced the same day, with no need to go inside the AHU. If the motor fails it can also be replaced the same day.