By monitoring the HVAC services of a large distribution warehouse, we were able to measure the negative effect dirty filters had on the operation of the HVAC system and the substantial energy savings that could be realised through an improved maintenance plan.
Fourteen 210kW Temperzone rooftop package units are used to service this large distribution warehouse, each unit features a pressure differential sensor which provides tangible insight into the status of the air stream filters. These units have Modbus enabled EC plug fans and an onboard Carel c PCO controller which connects directly to the filter sensor. Over time the degradation of the filter cleanliness was determined by the pressure drop readout as represented in the time series graph.
It was observed that the onboard filters become very dirty over a short space of time. In fact, after 30 days of 24/7 operation the filter pressure drop increased 29%, while the power consumption of the fans increased 15%.
The increased operational costs of dirty filters were substantial. Each unit on the site consumed on average an extra 50kWh per day, due to dirty filters. Over the year this could result in 18,250kWh of unnecessary energy consumption across the entire site, and at an energy tariff of 10 cents per kWh would result in an extra $25,550* in total energy costs.
There are also compelling environmental considerations of maintaining clean filters. Given the sites locations carbon emissions factor from energy generation*, we can observe that each unit would annually prevent 18.4 tonnes of C02 emissions from energy generation by maintaining clean filters at 43pa.
Reviewing historical data, the biggest change in pressure drop occurs every 6 months when filters are either cleaned or replaced. Observing the real-world costs of running a unit with dirty filters it would be ideal to increase the frequency of filter maintenance to monthly.
By including a differential air pressure sensor alongside the onboard unit controller, data can be ingested from the BMS and leveraged across system componentry, like the indoor fans, to better understand maintenance requirements. This strategy if developed correctly can help design service level agreements which improve quality of maintenance while reducing building operational costs.
* Carbon Positive Australia Emissions Calculator
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