Basic Installation Guide
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Invisible.AC Limited St John’s Innovation Centre Cowley Road, Cambridge CB4 0WS United Kingdom T +44 (0)870 9619661 E nfo@invisible.ac i W www.invisible.ac Basic Installation Guide November 2016 This instruction is a summary of the basic rules and applies to most Invisible.AC applications. The Invisible.AC System is a pressure-duct based technology and operates on a design airflow of 36l/s per kW [UK applications assume a 27/19.5C (50% RH) air-on temperature] using our proprietary 66mm diameter acoustic mini-duct. Jet Outlets – the allowable airflow range per outlet is 15l/s to 30l/s. Target design airflow per outlet is 22.5l/s – giving an air-rush noise for an average room type of NR30 [much quieter designs are possible using more outlets with a lower air-jet velocity]. Example – say to achieve say 30l/s airflow at the outlet the measured figure [using a Davies Turbo-meter hard against the universal connector] is 9m/s [or this device 17.5 knots]. This equates to say a reading of 4.5m/s on a foam slotted outlet and 3.8m/s with the Turbo-meter held hard against the centre of the 25mm slot. Mini-duct – this comes in standard 3.5m lengths. Older North American technology generally had all outlets with the same standard length of duct to provide similar outlet velocity at each outlet. With the Invisible.AC 1m silencer /damper component the velocity [air-flow] can be adjusted – so mini-ducts can be much shorter in length [e.g. damper adjusted 35deg off of fully open makes this 1m duct equivalent to a 3.5m standard mini-duct]. 10% Rule – for mini-ducts longer than 3.5 meters the air is reduced in that run by 10% for every 1.5 meter over the 3.5 meters. For example, an 9.5 meter mini-duct run is equivalent to 60% of a standard outlet that is 3.5meters long - yielding a reduction of 40% in air-flow (9.5 – 3.5 = 6.0, 6.0 ÷ 1.5 = 4, 4 ×10 = 40%). Example: if you required 3kW total cooling in one particular room; you would normally need 3 x 36 = 108l/s of air delivered into the room. If 3.5mm standard mini-duct lengths are used you need 108/22.5 = 4.8[5] outlets. If the room was some distance away and had 9.5 meter duct runs you would need 40% more outlets, 5/0.6 = 8 outlets to deliver that same 3kW duty! Consider Traffic Patterns – locate outlets out of traffic pattern. A corner, 130 mm from each wall is a good location as are ceilings along walls avoiding open doorways. With say the 30l/s airflow the outlet normally pulls-in air from a 4 meter radius. Consider round floor outlets [with screens] for systems located in basements. Our 25mm slotted outlets can be used in walls, ceilings and floors – 130mm off – these fit in smaller voids [no mini-duct bending is needed]. Allow for Aspiration – locate outlets so the air stream does not impinge on any objects or people – at least 1m away. Our standard outlets have a directional nozzle as standard – that can be useful. Minimize Length, Minimize Restriction – generally keep the mini-duct length as standard close to 3.5m or use the 1meter silencer /damper as a minimum. Use the fewest number of bends as possible. Maximize the radius of any bends making sure the bend in the mini-duct near the outlet is at least 150mm. If not

Invisible.AC Limited St John’s Innovation Centre Cowley Road, Cambridge CB4 0WS United Kingdom T +44 (0)870 9619661 E nfo@invisible.ac i W www.invisible.ac Plenum Maximize Length, Minimize Restriction – run plenum duct as long as possible; it is better to lengthen the plenum if you can shorten even two outlet runs. Use full-flow tees and full flow elbows. The maximum total plenum length is nominally 45 meters; consider the first tee equal to 9 meters and elbows equal to 4.5 meters. 60/40 Rule – when using a tee split the flow as close to 50/50 as possible – no more than 60/40. Always use a...

Invisible.AC Limited St John’s Innovation Centre Cowley Road, Cambridge CB4 0WS United Kingdom Sound Acoustic Mini-Duct – always use acoustic mini-duct of at least 1 meter at the end of each run. You can use any duct of say 70mm diameter prior to that or you can use acoustic mini-duct for the entire run. The Invisible.AC 1 meter silencer /damper component is the best most flexible option. Return Air Duct Attenuation – use Invisible.AC acoustic Return Air Duct, duct-board, or sheet metal with acoustical duct liner. Never use flex duct with a solid plastic liner. Isolation – isolate the air...