DUCTED VS. DUCTLESS AIR CON­DI­TION­ING SYS­TEMS

MEP Middle East - - KNOWLEDGE PARTNER - By Tariq Al Ghus­sein, chief ex­ec­u­tive of­fi­cer, Taqeef

The AC mar­ket in the re­gion was built on ductless AC units – in­deed, it was Fu­jitsu Gen­eral’s first ever desert spec­i­fied win­dow unit which orig­i­nated the AC mar­ket in the re­gion in 1972. Fol­low­ing this, split AC units – wall mounted ductless de­signs which of­fer di­rect and eas­ily con­trol­lable cool­ing for sin­gle or mul­ti­ple rooms or spa­ces – be­came the most pop­u­lar choice.

In more re­cent years, we’ve seen the mar­ket evolve, and wit­ness a move to­wards ducted de­signs which are largely hid­den in the walls and ceil­ings of a build­ing, with cool­ing de­liv­ered from a cen­tral air con­di­tioner via wall and ceil­ing vents. While many con­sider this to be the most aes­thet­i­cally un­ob­tru­sive cool­ing op­tion, it comes at con­sid­er­able cost. Ducted units are not usu­ally the most ef­fi­cient as im­proper in­stal­la­tion, in­su­la­tion and main­te­nance im­pact the safety, ef­fec­tive­ness and emis­sions of these de­signs.

Ducted Sys­tems

When opt­ing for a ducted sys­tem, sev­eral fac­tors need to be looked at to en­sure the best pos­si­ble out­come in terms of en­ergy ef­fi­ciency and main­tain­ing air in­tegrity. The first, and prob­a­bly the most im­por­tant of these, is the de­sign of the ducting it­self. Un­for­tu­nately, as a re­gion, we don’t rou­tinely spec­ify re­turn air ducting, which un­der­mines the ef­fi­cacy of the whole sys­tem. In sim­ple terms, con­trac­tors and spec­i­fiers often re­duce the amount of ducting they use as a cost-cut­ting mea­sure. This means that the dust that’s rou­tinely gen­er­ated by the sys­tem sim­ply col­lects within the false ceil­ing, com­pro­mis­ing air qual­ity and safety. And, while many of us rou­tinely have our ducts cleaned, false ceil­ings are tricky - if not im­pos­si­ble - to ac­cess, which means the prob­lem is an on­go­ing one.

Sim­pli­fy­ing the struc­ture of the ducting de­sign (through the use of shorter ducts and less bends) is also prefer­able – re­sult­ing in eas­ier clean­ing and main­te­nance of the units. Us­ing op­ti­mum spec­i­fi­ca­tion, pro­fes­sion­ally in­stalled in­su­la­tion also con­trib­utes to the ease with which the main­te­nance is car­ried out.

An­other is­sue re­lated to ducted de­signs is im­proper siz­ing and in­stal­la­tion; a pri­mary cause of high en­ergy bills, re­duced per­for­mance, poor in­door air qual­ity and ir­reg­u­lar air distri­bu­tion of cooled air. All these fac­tors can cul­mi­nate in un­com­fort­able hot and cold spots due to the un­even distri­bu­tion of cooled air.

A large per­cent­age (20%) of the air cir­cu­lated through the ducting sys­tem can be lost due to leaks and poor con­nec­tions. So, it’s im­per­a­tive that pro­fes­sional air duct seal­ing is com­pleted to avoid these is­sues. De­spite the ini­tial cost and in­con­ve­nience of the process, users will have in­creased en­ergy ef­fi­ciency and lower util­ity bills, mean­ing the ini­tial cost out­lay is re­cov­ered over time.

The in­ac­ces­si­bil­ity of ducts often causes a chal­lenge when it comes to main­te­nance and clean­ing. Not only do dust and al­ler­gens ac­cu­mu­late but the ducts can also pro­vide a haven for ver­min in­fes­ta­tion, which can be very ex­pen­sive to treat, all the while com­pro­mis­ing the health and well­be­ing of the res­i­dents. To avoid such is­sues, it’s im­por­tant that ducted sys­tems are prop­erly in­su­lated. In ad­di­tion to pro­tect­ing against mois­ture-re­lated prob­lems, duct in­su­la­tion will also im­prove en­ergy ef­fi­ciency by pre­vent­ing ex­ter­nal vari­able tem­per­a­tures from af­fect­ing the tem­per­a­ture in­side.

While the above looks at the ways to en­sure the best re­sults from a ducted sys­tem, re­search still points to un­ducted de­signs (i.e. wall mounted split units) as the most en­ergy ef­fi­cient and air pre­serv­ing method of cool­ing in harsh desert con­di­tions. A de­sign scheme where ducts are avoided - or at least re­duced - should al­ways be pro­moted as a man­age­able al­ter­na­tive as we pur­sue an en­ergy con­serv­ing stan­dard. And, while there will be some ex­cep­tions to this (for those chiller fan coil units which are larger and nois­ier, a com­plex ducted de­sign is often nec­es­sary) this should not be stan­dard prac­tice.

Ductless Sys­tems

Split ACs or ceil­ing con­cealed DX sys­tems work in a very dif­fer­ent and more di­rect way. They are eas­ily and in­stantly con­trol­lable, of­fer max­i­mum en­ergy ef­fi­ciency, and re­main the most pop­u­lar choices when it comes to units in­stalled in res­i­den­tial and com­mer­cial prop­er­ties.

The ben­e­fits of ductless sys­tems aren’t re­stricted to in­creased en­ergy ef­fi­ciency and reg­u­lated tem­per­a­ture con­trol. One of the most com­mon risks mit­i­gated by split units is the prob­lem of mold, which can be caused by in­tro­duc­ing cold air into a warm room and the re­sult­ing con­den­sa­tion.

Fore­go­ing a ducted sys­tem for a wall mounted unit not only al­le­vi­ates the prob­lems as­so­ci­ated with hav­ing to clean and in­su­late ducts, but also greatly im­pacts build­ing costs. By fore­go­ing the ad­di­tional space needed to ac­com­mo­date ducts, it pos­si­ble to re­duce build­ing costs by shav­ing up to 50cm off each floor. Ducting can be re­placed with a sleek and mod­ern unit de­sign (which can also be con­cealed in cup­board or al­cove if pre­ferred) re­sult­ing in higher ceil­ing and re­duced con­struc­tion height. On a 30-story build­ing this could mean as many as an ad­di­tional three floors.

The fu­ture

As an in­dus­try, we need to get bet­ter at de­sign­ing schemes with max­i­mum ef fi­ciency as a pri­or­ity. That means only us­ing ducted de­signs where and when they’re ab­so­lutely nec­es­sary – in large scale projects which re­quire bulky and noisy fan coil units where ducting is es­sen­tial to re­duce the noise. Other wise we should use wall mounted units or ceil­ing con­cealed as the stan­dard – as they do in Europe and Asia - en­sur­ing the ducting is suf­fi­cient (sup­ply and re­turn), min­imised in length by good de­sign and prop­erly in­su­lated.

Which­ever sys­tem is cho­sen, mind­ful con­sid­er­a­tion of en­vi­ron­men­tal im­pact should be a key driver. After all the best cool­ing should pro­vide com­fort that pro­motes a greener, cleaner world.

As an in­dus­try, we need to get bet­ter at de­sign­ing schemes with max­i­mum ef­fi­ciency as a pri­or­ity.″

Tariq Al Ghus­sein, chief ex­ec­u­tive of­fi­cer, Taqeef.

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