Integrating Direct Digital Control for VRF Improves User Control

ACES integrated the school's VRF with Alerton’s Visual Logic Display 362 programmable wall sensor displays.

ACES integrated the school’s VRF with Alerton’s Visual Logic Display 362 programmable wall sensor displays.

Popular in Asia and Europe, variable refrigerant flow (VRF) heating and cooling systems have been deployed in the U.S. over the past several years. The benefits of VRF, according to the U.S. General Services Administration (GSA), include up to 34-percent energy savings compared to code-compliant HVAC, and the ability to retrofit older buildings that do not have space for ductwork.

When the York County School Division renovated its Magruder Elementary School in Williamsburg, Va., in 2015, it chose to install a Mitsubishi VRF for energy efficiency and since the system was the most economical solution for the 15-year old building.

Although variable refrigerant flow systems offer energy savings benefits, consulting engineers describe shortfalls in the fully self-contained operation of VRF systems. Notably, manufacturer-supplied wall controllers lack:

  • Dual set points, which can lead to excess equipment run time as the VRF works to reach a single temperature point instead of a range
  • Night setbacks, resulting in potentially inefficient energy use at unscheduled times
  • Consistent interoperability across competing systems

The VRF specified for Magruder Elementary faced these same limits, which restricted the school division’s ability to fulfill its energy management protocols. Additionally, the VRF manufacturer had changed its wall controller in the middle of the school division’s last VRF retrofit, making it difficult to standardize their system controllers throughout the school district.

To provide more consistent wall controllers, the HVAC solutions provider/dealer, Air Conditioning Equipment Sales Inc. (ACES) of Richmond, Va., integrated the variable refrigerant flow with Alerton’s Visual Logic Display (VLD) 362 programmable wall sensor displays. The BACnet-enabled VLD provides the direct digital control (DDC) that was lacking with VRF wall sensor displays.

The integrated solution ACES developed addressed the above mentioned limits of the VRF wall units. Further, because the VLD is programmable, unlike some VRF manufacturer supplied wall controllers, the VLD opens the possibility to control a host of HVAC equipment, along with site lighting, exhaust fans, heaters and other energy loads.

“The VLD units allow us to apply our energy management protocols to the VRF,” said Russell Payne, supervisor of resource and security control for the York County School Division. “These include 73-79 F cooling and 64-70 F heating set point ranges, night setback and more.”

“Some mechanical engineers thought this couldn’t be done, but our controls programmer has developed a way to provide DDC for VRF,” said Paul Butler, sales engineer with ACES. “We’re not replacing the VRF control panel, but are using a powerful and adaptable wall controller to manipulate the VRF’s programmable data.”

The Alerton VLD-362 is a combined sensor/controller with temperature and humidity sensors and an interface and digital display. The units enable a wide range of sensing and control options than is typically possible with variable refrigerant flow manufacturers’ wall units, including:

  • Customizable set points (single or dual range)
  • Fan speed control
  • Schedule overrides in 30 minute increments
  • Ability to add CO2 monitoring and extra inputs and outputs

The VLD’s programmability also provides user flexibility notes Butler. “With VRF manufacturer’s wall units, we usually can’t customize the displays the way users want. For example, one school district might want its teachers to see temperature, time and set points, while another only wants the wall units to display temperature. With the VLD, we can provide each customer with what they want.”

With the VLD units installed in each classroom at Magruder Elementary, teachers are able to control their individual room temperatures, within the set points programmed by the district. Plus, teachers like the display, because it looks like the ones in their homes, notes Payne. “The VLD allows the user to have a seamless experience from space to space regardless of the equipment we are controlling, whether it is bathroom heaters, large rooftop units for gyms and cafeterias or small indoor VRF units located in the classroom ceiling grid.”

The 12,000-student York County School Division has deployed this DDC for VRF integration solution in its last three school HVAC renovations and additions, and plans to implement it in three more schools in 2016 within its Williamsburg, and Yorktown, Va., service area. In addition to improved building control, the Alerton products play a role in providing data to a thermograph floor plan the district has developed for each school, which allows the facility managers to see the temperature of every room and the equipment status. Eventually, the school district plans to show all of the schools on one display for comprehensive energy management.

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