Fast & Efficient Multiple Site AHU Retrofit

AHU retrofitDarnells Limited, a mechanical and electrical specialist based in Oxford were awarded the contract for a multi-site AHU retrofit project. Three sites located in Bicester, Kidlington and Spiceball required multiple air handling units upgrading to futureproof their ventilation systems and to reduce energy consumption across the sites. Initially the sites HVAC systems featured 7 old, outdated, and inefficient belt driven centrifugal fans across plant rooms, basements, and roof tops. The client did not require an energy saving survey in this instance as prior to the tender specification it was confirmed that simply replacing the inefficient fans with plug fans with IE3 or better motors controlled by an inverter, would provide the levels of energy savings required.



AHU Retrofit Before

Site Surveys & Fan Selection


Our FanGrid specialist, Geoff Edwards visited all three sites to assess the ahu retrofit and fan requirements and any additional services that may have been needed prior to selection. Due to consideration of the cost and performance, coupled with the chamber lending itself to a standard induction configuration, the DKNB range of backward curved plug fans with aluminium impellers were chosen as the ideal solution. The DKNB was selected with a mounting stand configuration that would support the motors which weighted up to 100Kg, without additional modifications to the AHU housing. The durability of the pressure optimised B wheel could also withstand the conditions and achieve the duty easily.



AHU Retrofit Fan Selection


Enhanced Modifications

Due to the high duty required on one of the air handling units at the third site in Spiceball, a double fan configuration was required, featuring a modified bulkhead to accommodate and house two DKNB 450 diameter fans with 4kW IE3 standard induction motors. The new double configuration could achieve a duty of 15,840m3/h at 475Pa. All modifications were made by Axair’s supplier partner using their inhouse fabrication and modification centre while keeping to a very tight lead time and delivery schedule.


AHU Retrofit



Retrofit AHU

6 weeks for AHU retrofit



Competitive Lead Times

The project was completed within a 6-week period from the point of order to delivery of the fans, AV’s, flexi’s and modified bulkheads, with fabrications delivered in modular form to site to ensure easy and simple installation by the M&E team.

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