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Case study: Optimising HVAC systems

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article image Danfoss AB-QM pressure independent balancing and control valve

Danfoss (Australia) partnered with Devex Systems to conduct a test case at the UTS in Sydney to assess the performance of the Danfoss AB-QM pressure independent balancing and control valve (PIBCV) in optimising an HVAC system. 

Despite several innovations in the field of HVAC efficiencies, it is still challenging to optimise HVAC systems so that they are consistently able to operate at their optimum efficiency. 

The Danfoss AB-QM pressure independent balancing and control valve (PIBCV) enables HVAC systems to stay automatically optimised delivering significant energy savings. The AB-QM control valves also make system commissioning quick and easy for the installer and help reduce the overall capital cost of HVAC systems.

A test case was conducted by Devex Systems and Danfoss comparing two rooms positioned side by side.

Room C1.11 and Room C1.13 in Building 5 (Business School) on the Ultimo Campus at the UTS were identical in size and heat load. Each room was serviced with its own (identical) fan coil unit located above the ceiling space in the adjoining corridor.

While the AB-QM valve was applied to room C1.11, the Classic control (control valve plus manual balancing valve) already operating in room C1.13, remained untouched.

The HVAC system consisted of a primary secondary system with conventional chillers using air-cooled condensers, along with a primary chilled water system featuring a series of 12 air handling and 190 fan coil units, chilled water supply temperature at 6 degrees, and two high load demand chillers and two low load demand chillers.

A central air handling unit provided pre-cooled fresh air and the space above the suspended ceiling was used for air distribution from the central air handling unit to the fan coil units.

The fan coil units in rooms C1.11 and C1.13 had a total air supply capacity of 520l/s, with return air from room (340l/s) blended with fresh air from hallway (180l/s). The estimated design cooling load was around 10kW.

Test case results:

The test results were logged using a Danfoss CCR2/CCR3 hydronic analyser. The data was recorded in 5-minute intervals and stored on an SD card, which was later analysed with a tool developed specifically for the analyser.

The AB-QM DN32 valve used in Room C1.11 had a capacity (Qmax) of 0.89L/S, and was set at 40%, or 0.36L/S.

The data comparing the two rooms was gathered over a period of two weeks in March 2012, and the following observations were made:

The AB-QM achieved a narrower range of room temperature of 2°C while the Classic control oscillated within a 4.5°C range over a typical day. 

At observed capacity, the AB-QM potentially saved 45% pumping power. 

The AB-QM achieved a chilled water temperature differential of 50% higher than the Classic control.

Estimated savings per annum combining chiller, control and pumping costs are in excess of $95,000 with an estimated payback of less than three years on a conservative capital investment to retrofit.

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