Rating System

LEED ID+C: Commercial Interiors, LEED BD+C: Retail

Rating System Version

v3 - LEED 2009, v2 - LEED 2.0

Inquiry

We are seeking clarification on the definition of active controls for non-VAV systems. The response from USGBC to CIR 5273 states that thermal control is not sufficient alone if it does not include for variable central plant such as VAV AHU. In some versions of VAV, thermal control can be achieved without modulating the central plant and this delivers no energy savings. These systems deal with low flow situations by allowing the excess air to discharge back to the ceiling void or similar whilst keeping the AHU at a constant speed, which does not result in any energy savings. Thus for the case proposed by the design team on CIR 5273, it is possible to achieve an equipment configuration which does not realize any energy savings from thermal controls.\n\nThis inquiry refers to a Variable Refrigerant Flow (VRF) system. The VRF system operates by delivering refrigerant to the room device/terminal to deliver heating or cooling to the space. Each space has thermal control. The thermal control operates by varying the amount of refrigerant delivered to the room device/terminal and as such varying or modulating the central plant. This ability to vary the heating or cooling delivered to the space allows the central plant to modulate and match the instantaneous load in the space at any given time. This delivers energy savings in the central plant. Furthermore the VRF system also has heat recovery, which allows for heat taken from a space which is in cooling mode to be used in a space in heating mode and vice versa.\n\nNote that because of the closed-loop nature of the VRF system, it is not possible to operate the system in a mode, which does not save energy, as it is not possible to "vent" any excess refrigerant in low load situations. The variability of the system comes not from changing the amount of air into the space, but by varying the amount of refrigerant from the central system to the project space. \n\nThe requirement by the reviewers to provide demand controlled ventilation as part of the response to CIR 5273 is inappropriate for a VRF system, which - by definition - ramps up and down based on temperature readings, not air flow measurements. Since the trigger for a VRF system to ramp up and down is related to temperature, we believe that the thermal controls in each room are sufficient active controls for a VRF system, as they provide both individual control in the meeting rooms and private offices and realise energy savings resulting from individual controls.\n\nWith this system, we are still able to meet the requirements of ASHRAE 62.1 for the highest design occupancy and provide adequate ventilation to the project space.\nWe do not believe that the argument that the thermostat will not pick up on when a person leaves the room, as this may not be the major load in the space, is relevant. While this is correct, with a thermostat, the system will modulate to control the space regardless of what is generating the load, e.g. solar, people, equipment. The fact that the people load is not the significant load means that the control of the other loads is the more important element, therefore the system will respond to whatever changes the load, whether it is people, equipment, lighting or something else. \n\nIt was suggested that the proposed design also does not meet the intent of the credit, because of the lack of ability to vary the amount of fresh air into the space. However, feedback seems to suggest that occupancy and CO2 sensors would help achieve this credit, although it is unclear whether installing these in the system would achieve the credit or if this is only in the context of VAV systems.\n