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Air Handling Units (AHUs) – Time Schedules

Site overview

Three storey office accommodation for large banking group in Colchester.

The Problem

  1. During an energy audit of this building, it was observed that the two primary AHUs were being enabled three hours a day, prior to general occupation of the offices.

  2. The software was back engineered and the cause was located as an error in the software. The AHUs were being triggered by the optimum start function, rather than the fixed-time start trigger.

The Solution

  1. The software triggering the AHUs was modified to use the fixed-time trigger.

  2. Based on the additional run hours and the motor sizes the saving was calculated at £6,000 per year giving a return on investment of one month.

  3. This calculation did not include the additional energy saving associated with the AHU process (Low Pressure Hot Water (LPHW) and Chilled Water (CHW) usage within the AHU and the additional load on the heating systems).

Measurement of Savings Achieved

Annual Energy Reduction = 75,000kWh Annual CO2 Reduction = 41 tonnes Annual Cost saving = £6,000 Cost of implementation = £500

Return on Investment

Payback period = 1 month


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