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.This 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.Note 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. The 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.With 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.We 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. It 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.
The definition of active controls that meet the requirements in LEED-CI 2009 EA credit 1.3, and clarifications on what non-VAV systems are eligible for active controls are listed below. Active control is the control capable of sensing space occupancy and adjusting the HVAC system demand based on the changes in space occupancy, which does not equal a thermostat or a separate thermal zone for each space. For VAV systems and non-VAV systems, active controls typically regulate the required outdoor air flow for ventilation, such as using demand controlled ventilation with CO2 sensors in each private office and specialty occupancy space, or regulate temperature set point based on occupancy by adjusting the HVAC system to operate under the unoccupied set back when occupant sensors indicate that the space is unoccupied.Alternatively, VAV systems meeting all the requirements in LEED Interpretation 5273 are also eligible. However, those systems which do not modulate the system level supply air flow but only redirect the excess air back to the ceiling void or return air duct under low demand conditions are not eligible for this alternative compliance path. For a VRF system or another constant volume system with separate thermal zones for each specialty occupancy or private office, the following active controls would be considered sufficient to meet the credit criteria:PRIVATE OFFICES: Occupant sensor controls or CO2 sensors in each private office sense space occupancy, and modulate the HVAC temperature set points when the space is detected as unoccupied. Additionally, the fan coil serving the room has the fans set to cycle on and off with loads or to operate on the lowest multi-speed setting for multi-speed fans when the space is detected as unoccupied.SPECIALTY USE SPACES: Conference rooms and other specialty use spaces have CO2 sensors or occupant sensor controls, which modulate the HVAC temperature set points when the space is detected as unoccupied. Additionally, demand control ventilation is used to limit the outdoor air supplied to the space based on CO2 levels or space occupancy. Please note, although the VRF system as described can vary the amount of refrigerant supply to the project spaces and save energy, the thermostat controls described are not considered active controls due to the following two reasons: 1. The system is controlled based only on thermostats. For private offices and specialty occupancies where the occupancy varies during the occupied period, thermostat control is not sensitive to the change of occupancy and therefore is not capable adjusting the VRF system to respond to the change, because occupant load is not a major load of the perimeter zones, and is also likely not very significant compared to the cooling load from lighting and equipment in the internal zones. When the occupants are absent or reduced, the HVAC system cannot effectively respond to the change and reduce heating and cooling supply, and/or the ventilation rate. 2. The VRF system is a constant volume system. It cannot reduce airflow to respond to the load change. Please note that the alternative compliance path in LEED Interpretation 5273 requires the system achieve significant supply flow reduction at both the system and zone levels. To achieve this, the system must have fan static pressure reset, and especially, for the spaces where the minimum outdoor air exceeds the required minimum supply volumes, some form of occupant sensing or demand controlled ventilation must be employed to allow the minimum supply volumes to be met. This requires projects to use either CO2 sensors or occupancy sensors in conference rooms or other specialty occupancies, because the room airflow in these spaces cannot typically be reduced to the required percentage of the peak supply volumes while still maintaining the ASHRAE 62.1 ventilation requirements associated with peak occupancy. With variable refrigerant flow and heat recovery which essentially allows for heat exchange between spaces under cooling mode and spaces under heating mode, the VRF system has high cooling and heating efficiency and can achieve high part-load energy performance. This may qualify the project for Option 1 - Equipment Efficiency. Please consider attempting this option in lieu of the option for active zoning and controls, if active controls will not be used with the VRF system.