Variable Water Flow system (VWF)
Carrier Variable Water Flow
Recommended by Carrier, the AquaSnap can be equipped with one or two variable-speed pumps to save signiﬁcant pumping energy cost (more than two-thirds), ensure tighter water ﬂow control, and improved overall system reliability. Operating mode at part load Pro-Dialog+ includes three part-load operating modes: - Fixed speed control - Constant delta P control - Constant delta T control. 1 - Fixed speed The control continuously ensures a constant pump speed based on compressor capacity. When the compressor capacity is equal to zero, the pump speed can be automatically reduced to a second setpoint (adjustable down to 60%) to save energy during low occupancy periods. This solution is suitable for traditional installations with constant water ﬂow and terminal units equipped with threeway valves. This solution reduces pumping energy costs especially when the ﬂow can be reduced during night-time periods. 2 - Constant delta P control The control continuously acts on the pump speed to ensure a constant delta P. This solution is suitable for installations with two-way valves. When these close, the water speed will accelerate in the system branches that are still open. For a ﬁxed-speed pump this results in an unnecessary increase of the pressure at the pump outlet. The constant delta P control mode ensures that each circuit branch always has a uniform supply, without unnecessary energy waste. In industrial processes such as plastic injection molding, this solution ensures that each terminal unit has the correct pressure supply. 3 - Constant delta T control The VWF algorithm maintains a constant delta T no matter what the unit load, reducing the ﬂow rate to the minimum. It is suitable for the majority of comfort applications.
Carrier Variable Water Flow (VWF) is a hydronic control function package that permits control of the water ﬂow rate. The Carrier VWF not only ensures control at full load, a speciﬁc Carrier algorithm linked to an electronic frequency converter also continuously modulates the ﬂow rate to minimise pump consumption at full load as well as part load. The Carrier hydronic module includes pressure transducers that permit intelligent measurement of the water ﬂow rate and real-time display on the Pro-Dialog+ or Touch Pilot user interface. All adjustments can be made directly on the interface, speeding up start-up and maintenance. As Carrier VWF acts directly on the pump, the system no longer requires the control valve at the unit outlet. However, for applications with two-way valves a bypass system must be kept to guarantee the minimum ﬂow rate.
Full-load set point The ﬂow rate control at full load uses the Pro-Dialog+ or Touch Pilot user interface, reducing the pump speed. This ﬁrst control saves energy that would normally be dissipated in the control valve. For example, if the pressure supplied by the pump is reduced by 20% the power consumption of the pump is reduced by the same ratio, compared to a traditional installation.