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How the 75F System Works with VAV Systems

Apr 18, 2019 6:13:00 AM

Smart VAV with Reheat illustration

There's a lot of waste involved with VAV systems commonly used in office and commercial buildings. Typically, VAV systems operate with roof-top units (RTUs) in cool-only mode. The supply air temperature is held constant at 55°F and, when a zone falls below its setpoint, the damper closes and reheat is enabled. When a zone is above its setpoint, the damper opens fully to allow as much 55°F air as possible into the zone to cool the space quickly. This cycle often involves first cooling and then heating the same air. Since the RTU operates in cool-only mode, the 55°F air must again be reheated before it is discharged back into the space to keep the zone's air temperature in balance.

See the waste?

75F works to make existing VAV systems more efficient by installing wireless, pre-programmed VAV controls. The controls make the system smart and enables remote control and diagnostics via 75F® Facilisight™, our suite of web and mobile apps. The 75F Building Management System (BMS) front-end is automatic and the control system is self-commissioning, so the job is simple: Install the controllers and sensors, then power it up. No networking labor, no programming labor -- just instant, real-time performance data.

75F with VAV Systems - How It Works

The 75F Smart VAV with Reheat solution enhances the typical VAV with Reheat by adding airflow temperature sensors upstream and downstream from the heating coils for each zone. RTUs remain in auto mode, and they can add heat if all zones are calling for heat. When this occurs, the 75F solution begins to modulate the reheat valves open. This ensures that the air is treated appropriately so the RTU or reheating elements require less energy and increase occupant comfort.

Additionally, if a recirculating fan is present, available air in the plenum space can be used to minimize wasted reheat energy, making use of preconditioned plenum air.

Similar to some other VAV with Reheat systems, 75F doesn't maintain a constant temperature of 55°F on supply air. Rather, our system finds the optimal supply air temp for the system in coordination with the user's comfort and energy efficiency setpoints. The RTU can be optimized to provide "free cooling" when cool outside air is available and only use the cooling coil when absolutely necessary.

75F Smart Approach VAV with Reheat System illustration

How it Works with the 75F Suite

The 75F solution for VAV is part of a vertically-integrated suite that provides customers with complete building intelligence. The system is compatible with staged and modulating RTUs (connected to a Central Control Unit) and terminals (synced to 75F Smart Nodes), as well as our range of discreet, secure sensors. The system works seamlessly with:

Uniquely, 75F Smart VAV with Reheat is a continuous commissioning system that can be synchronized with our Outside Air Optimization solution for greater indoor air quality and energy efficiency. The 75F Smart Node makes automation, remote monitoring and control of your entire HVAC system accessible and affordable.

75F implements the ASHRAE "RP-1455 Advanced Control Sequences for HVAC Systems" out of the box and couples it with proactive, continuous commissioning. This allows you to maximize the energy efficiency and performance of your system, provide control stability and allows for real-time fault detection and diagnostics.

75F for VAV

 

 

To learn more -- such as the specific systems 75F with VAV controls, as well as more benefits and key differentiators, download our free PDF, 75F for VAV.

DOWNLOAD FREE PDF: 75F FOR VAV

 

Sarah Baker

Written by Sarah Baker

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