- 4 buildings ranging in height from 4 to 6 storeys
- 137 apartments
- completed 2003
- 1 car park level
- outdoor pool (unheated)
- cross-ventilation designed into all units
- natural light and cross-ventilation used in all common areas
- rain water collection and storage for landscape irrigation
- native and low-water use plants in common area gardens
Mondrian installed carbon monoxide (CO) sensors to control the carpark ventilation fans at a cost of $7,800 plus GST. Energy consumption decreased on average by 40 kWh per day (7%) and the payback period is two years.
Why this project?
Mondrian participated in the City of Sydney Council’s Smart Green Apartments program. The energy audit identified that HVAC (Heating, Ventilation and Air-Conditioning) - of which the carpark ventilation system is a significant element - accounted for 36% of total common property energy consumption and recommended automatic controls for the system based on exhaust gas levels.
Existing system and operation
The car park ventilation system consists of an exhaust fan and two supply fans. They were controlled by a timer and ran from 7am to 9.30am and from 4pm to 7.30pm every day.
These fans have a high power rating (22 kW for the exhaust fan and 4 kW for each of the supply fans) and therefore accounted for large amounts of energy consumption even though they only operated for short periods. Moreover they operated during the times of the day when the electricity prices were higher and hence accounted for significant energy costs.
The upgrade process
An Energy Saving Action Plan, which was prepared as part of Mondrian’s participation in the Smart Green Apartments program and that forecast savings of $23,500 per year, was adopted at the Annual General Meeting. It contained a number of initiatives including the upgrade for the car park ventilation system. The sinking fund budget also included an estimate of all related costs.
The building manager sourced 3 quotations for Carbon Monoxide (CO) detectors and Variable Speed Drives (VSDs) for the exhaust and supply fans.
The proposed number of sensors varied from 6 to 9. Prices varied from $7,800 to $15,000 for the CO monitoring system, and from $25,000 to $32,500 when variable speed drives were included. (All prices are ex-GST).
Because it wasn’t possible to accurately predict how often CO levels would reach a level that necessitated operation of the ventilation system Mondrian’s committee decided not to install VSDs at the outset. They planned to monitor how often the ventilation system actually came on after CO detectors were installed.
After satisfying themselves that 6 sensors were sufficient and complaint with Australian Standard AS 1668, and that the supplier was professional and credible, Mondrian installed 6 sensors for a total cost of $7,800 plus GST. They also entered into a service and maintenance contract valued at $620 (plus GST) p.a. to ensure the detectors and control system continued to operate correctly. The service frequency is six-monthly, as recommended by the manufacturer and to comply with AS 1668.
The controller is configured to activate the exhaust and supply fans for 4 minutes run time when the CO level is 9 PPM (parts-per-million) or more for more than 4 minutes. The fans remain on if the CO level remains greater than 9 PPM. In the event of a system fault all ventilation fans will operate until the fault is rectified.
NOTE: Mondrian’s carpark is an “occupied space” because it’s also where the building manager’s office is located - so the system must trigger at a lower CO concentration. If no-one worked in the carpark, the system would only need to trigger at 15 PPM.
The system is serviced twice-yearly at a cost of $600 p.a.
The impact of the new system on energy demand throughout the day was immediately obvious:
Total daily consumption decreased on average 40 kWh per day.
The ventilation fans do come on several times a day, and as seen in the following examples the daily energy demand profile can vary significantly from day to day. The fans are responsible for the peaks in the graphs. It is also obvious that they’re needed throughout the day – not just ‘peak’ periods in the mornings and afternoons as previously assumed when the fans operated on a timer.
Mondrian initially hoped the fans wouldn’t come on at all once CO detectors were installed. They were surprised to learn how often they are still needed. The committee will now investigate installing variable speed drives to further reduce energy consumption.