Overview

In this module, you can apply re-tuning control measures to your baseline building and observe the impact on the building, in terms of changes in energy, cost, and occupant comfort. These changes can be viewed in tabular form for a set of different measures, and each measure can be investigated in terms of its impact graphically.

Re-tuning measures can be applied singularly, or as part of a package of measures applied together. The dashboard works by importing the baseline control settings affecting the application of each potential re-tuning measure on one side of the screen, and allowing the user to specify a new control scheme for that measure on the other side of the screen. Any number of re-tuning measures can be applied to a new simulation through a check-box on the left. The tool will run the new simulation, compile the results, then add the latest run to a table of results.

A total of 28 potential re-tuning control measures are available for investigation, as well as 3 O&M measures and 7 capital project measures.

In-Depth

The 28 potential re-tuning measures are listed below, along with details on each measure. The measures are broken down into 4 savings categories/principles: “Turn-it-off”, “Turn-it-down”, “Mitigate Simultaneous Heating and Cooling”, and “Reduce Infiltration and Excess Outdoor Air.”

“Turn-it-off” Measures

• Reduce HVAC Schedules: The HVAC schedules govern the control of the air-handling unit, allowing it to turn-off after-hours when zone temperatures remain in range of the heating and cooling night setback setpoints. This measure allows the user to adjust the baseline HVAC operation schedule.
• Reduce Lighting Schedules: Lighting schedules are hourly fractions of the design lighting level, which create a load profile for lighting. This measure allows the user to change the Master lighting schedule. Some zones may connect to alternate lighting schedules that will not be changed by this measure.
• Cooling System Outdoor Air Enable: This measure locks out all of the cooling coils in the building when the outdoor air temperature falls below a lockout setpoint. This also has the effect of shutting off the plant-side generator (chillers, district cooling, etc), as well as the pumps, unless the user specifies that the chilled water pumps run during no-load conditions.
• Heating System Outdoor Air Enable: This measure locks out all of the heating coils in the building when the outdoor air temperature falls below a lockout setpoint. This also has the effect of shutting off the plant-side generator (boilers, district heating, etc), as well as the pumps, unless the user specifies that the hot water pumps run during no-load conditions.
• Holiday Scheduling: This measure allows the user to adjust the list of holidays in the BAS. Specifying a day as a holiday has the effect of running the building schedules according to Sunday schedules.
• Optimal Start: Optimal start is a measure that applies a machine learning algorithm to start up the air-handler at a variable time every morning. The algorithm determines how long it takes to warm up a space based on the recovery rate (change in space temperature per hour during warm-up) and the deviation of zone temperature in the coldest zone from the occupied heating setpoint (or deviation of zone temperature in the warmest zone from the occupied cooling setpoint). The optimal start requires the following parameter inputs from the user:
  • Maximum Early Start: The maximum number of hours that the AHU can start up Prior to the AHU schedule’s start time for the given day. 2-3 hours is typical for this measure
  • Recovery Rate: The expected rate of change in zone temperatures during warm-up and cool-down operations
  • Weekday latest start time: This is the latest start time (in military time hours) allowable on weekdays. Best practice is to make this time ½ hour prior to scheduled building occupancy to ensure a buffer of conditioning prior to occupancy.
  • Saturday latest start time: This is the latest start time (in military time hours) allowable on Saturday.
  • Sunday latest start time: This is the latest start time (in military time hours) allowable on Sunday.
  Note that correct implementation of Optimal start usually requires a paired change in the HVAC operation schedule. The HVAC schedule needs to be changed to reflect the latest start times defined in the algorithm (they should be equal to or later than the latest start time parameters in the measure).
• Pump Shutdown When there is No Load: This measure allows the user to change the change the operation scheme of the chilled water and/or hot water building loop pumps according to whether the pumps run all the time. Options include:
  • TRUE (Pumps run all the time)
  • FALSE (Pumps run only when there is a load that requires them to operate)
  • OA Lockout (Pumps run when there is no load, but only when the outdoor air temperature is below a threshold for hot water pumps or above a threshold for chilled water pumps
    • OA Lockout setpoint
• Turn Fans off During Night Heating Cycles: This measure allows the user to change the operation scheme of the AHUs during night setback heating cycles to either turn he AHU back on, or to keep the AHU off and allow zone-level heating equipment to operate independently to maintain night setback thermostat setpoints.

“Turn-it-down” Measures

• Static Pressure Reset: Static pressure reset saves energy by reducing the duct static pressure setpoint during times of low airflow demand. There are control types, each with their own set of control parameters
  • Constant setpoint
  • Setpoint
  • Linear Reset: A linear reset makes a linear adjustment to the control variable (in this case duct static pressure) between a minimum and maximum value based on the span of a feedback variable between its specified minimum and maximum values (or vice versa; an inverse linear relationship). Outside of the two specified values for the feedback variable, the setpoint will remain at a minimum or maximum value. There are four parameters for the reset
    • Feedback variable: Choices for feedback variables include outdoor air temperature (OAT), Zone cooling demand, zone heating demand, maximum zone damper, average zone damper, fan speed, and return air temperature
    • Minimum for feedback variable
    • Maximum for feedback variable
    • SP at minimum feedback variable: A minimum (or maximum) value of the static pressure setpoint associated with the minimum value for the feedback variable)
    • SP at maximum feedback variable: A minimum (or maximum) value of the static pressure setpoint associated with the maximum value for the feedback variable)
  • Trim and Respond: A trim and respond strategy adjusts the static pressure setpoint in order to maintain a feedback variable at a target value. When the feedback variable drifts in one direction from the target, the static pressure will increase at the next time interval, while if the feedback variable drifts in the other direction, the static pressure will decrease at the next time interval. A minimum and maximum value for the static pressure setpoint bounds the reset.
    • Feedback Variable: Choices for the feedback variable include Zone cooling demand, zone heating demand, maximum zone damper, average zone damper, fan speed, and return air temperature
    • Maintain Feedback Variable at: The value for the feedback variable that trim and respond algorithm is targeting.
    • Change Rate (per hour): The rate of change of the static pressure with respect to time when the feedback variable drifts from the target. For example, if the static pressure is adjusted by 0.05” w.c. at 10 minute intervals, the rate of change is 0.3”/hr
    • Minimum SP: Lower limit for the static pressure
    • Maximum SP: Upper limit for the static pressure
  • Scheduled: A scheduled strategy allows the user to fill out a schedule for the static pressure setpoint
• Night Setback: The night setback measure allows the user to adjust the night setback heating and cooling setpoints. If the setpoints were originally set zone-by-zone, this will reset each zone to use a new unified set of night setback heating and cooling setpoints.
• Chilled Water Differential Pressure Reset:
• Condenser Water Temperature Reset: This measure allows the user to change the control of the condenser water temperature setpoint. This may involve either adding a reset or adjusting an existing reset. There is only one common reset strategy for condenser water temperature reset, and it involves setting the condenser water temperature as a constant offset from the outdoor air wet bulb temperature.
  Condenser water temperature reset can save energy relative to a constant high condenser temperature setpoint by allowing the condenser water temperature to go lower when appropriate, lowering the compressor lift and reducing chiller power consumption. It can also save energy relative to a constant low condenser water temperature setpoint by allowing the cooling tower fans to operate at part speed when appropriate.
  The three parameters for the reset are
  • Constant offset from outdoor air wetbulb temperature. A typical range of offset temperatures is 5-12 degrees F.
  • Minimum condenser water temperature setpoint (consider the minimum limits of the chiller. 60-65 degrees is typical
  • Maximum condenser water temperature setpoint (80-85 degrees is typical)
• Chilled Water Temperature Reset
• Hot Water Differential Pressure Reset:
• Hot Water Temperature Reset: Hot water temperature reset is most applicable for buildings using condensing boilers, as these boilers have more efficient operating points at lower hot water temperatures. For these boilers, the reset should feature low-end setpoints below 120°F and ideally, closer to 100°F to take full advantage of these efficiency gains.
  Other boilers and hot water loops interfacing with district heating can also utilize hot water temperature reset to save energy through reduced convective heat losses from pipes, fittings, and other hot water loop components, especially as they transverse mechanical rooms, chases, plenums, and other unconditioned spaces. The reset can also potentially save energy through reduced plant-side simultaneous heating and cooling (transfer of heat between hot water and chilled water loops- in some buildings) There are two control options for hot water temperature; a constant temperature setpoint and a linear reset.
  Linear Reset: A linear reset makes a linear adjustment to the control variable (in this case duct static pressure reset) between a minimum and maximum value based on the span of a feedback variable between its specified minimum and maximum values (or vice versa; an inverse linear relationship). Outside of the two specified values for the feedback variable, the setpoint will remain at a minimum or maximum value. There are four parameters for the reset
  • Feedback variable: Choices for feedback variables include outdoor air temperature and average hot water valve command.
  • Minimum for feedback variable
  • Maximum for feedback variable
  • Hot water temperature setpoint at minimum feedback variable: A minimum (or maximum) value of the hot water temperature setpoint associated with the minimum value for the feedback variable. Note that a minimum value for hot water temperature setpoint should be around 150°F for non-condensing boilers (unless there is a separate building loop that can go lower), and as low as 100° for condensing boilers.
  • Hot water temperature setpoint at maximum feedback variable: A minimum (or maximum) value of the hot water temperature setpoint associated with the maximum value for the feedback variable)
• Chiller Staging: This is a measure that is applicable to multiple-chiller systems using variable speed chillers. This measure saves energy for most modern chillers that have peak efficiencies in the range of 40% to 75% part load ratio. By staging on a second chiller earlier (e.g. when all running chillers reach 75% speed instead of 100% speed), it is possible to keep all chillers in their most efficient operating part load range.
  For each stage, the user should specify the part load ratio for stage-up and for stage down. For example, in stage 2, this would apply when the first two chillers are running. The stage-up value would indicate which speed the two running chillers would have to rise to in order to stage-up to stage 3 (3 chillers). The stage-down value would indicate which speed the two running chillers would have to fall to, in order to stage down to a single chiller. The user should leave a buffer between stage-up and stage-down commands. For example, if the stage-down threshold in Stage 2 were set at 50% and the stage-up threshold in stage 1 were set at 80%, two running chillers at 50% would stage down to a single running chiller at 100%, which would then force an immediate stage-up back to 2 chillers. A smarter staging scheme would be a stage-down from Stage 2 at 30%, then a stage-up from Stage 1 to 2 at 75%.
• Secondary Pump Staging: Building loop (typically “secondary loop”) pumps are often staged in parallel (or lead-lag). Pump power often increases exponentially with increasing part load ratio, such that is can reduce overall system pump power to have multiple pumps running at part load, rather than a single pump running at or near full load.
  For each stage, the user should specify the part load ratio for stage-up and for stage down. For example, in stage 2, this would apply when the first two pumps are running. The stage-up value would indicate which speed the two running pumps would have to rise to in order to stage-up to stage 3 (3 pumps). The stage-down value would indicate which speed the two running pumps would have to fall to, in order to stage down to a single pump. The user should leave a buffer between stage-up and stage-down commands. For example, if the stage-down threshold in Stage 2 were set at 50% and the stage-up threshold in stage 1 were set at 80%, two running pumps at 50% would stage down to a single running pump at 100%, which would then force an immediate stage-up back to 2 pumps. A smarter staging scheme would be a stage-down from Stage 2 at 30%, then a stage-up from Stage 1 to 2 at 75%.

Mitigate Simultaneous Heating and Cooling

• Supply Air Temperature Reset (Single-duct, cold deck and hot deck): Supply Air Temperature Reset saves energy during cold weather by increasing the discharge air temperature as much as possible without driving a significant number of VAV boxes into cooling mode (Avoids use of zone-level heating. Warmer DAT temperature is brought about generally through more return air, rather than mechanical heating.) During warm weather, supply air temperature reset cab save energy by decreasing the discharge air temperature as much as possible without driving a significant number of boxes into heating mode. This helps to minimize the fan system power consumption as the same cooling load can be met at lower airflow rates by using a lower discharge temperature. Several options are available for SAT control
  • Constant setpoint
  • Linear Reset: A linear reset makes a linear adjustment to the control variable (in this case SAT setpoint) between a minimum and maximum value based on the span of a feedback variable between its specified minimum and maximum values (or vice versa; an inverse linear relationship). Outside of the two specified values for the feedback variable, the setpoint will remain at a minimum or maximum value. There are four parameters for the reset
    • Feedback variable: Choices for feedback variables include outdoor air temperature (OAT), Zone cooling demand, zone heating demand, zone cooling minus zone heating demand, maximum zone damper, average zone damper, fan speed, and return air temperature
    • Minimum for feedback variable
    • Maximum for feedback variable
    • SAT at minimum feedback variable: A minimum (or maximum) value of the SAT setpoint associated with the minimum value for the feedback variable)
    • SAT at maximum feedback variable: A minimum (or maximum) value of the SAT setpoint associated with the maximum value for the feedback variable)
  • Trim and Respond: A trim and respond strategy adjusts the SAT setpoint in order to maintain a feedback variable at a target value. When the feedback variable drifts in one direction from the target, the SAT setpoint will increase at the next time interval, while if the feedback variable drifts in the other direction, the SAT setpoint will decrease at the next time interval. A minimum and maximum value for the SAT setpoint bounds the reset.
    • Feedback Variable: Choices for the feedback variable include Zone cooling demand, zone heating demand, zone cooling minus zone heating demand, maximum zone damper, average zone damper, fan speed, and maximum cooling demand
    • Maintain Feedback Variable at: The value for the feedback variable that trim and respond algorithm is targeting.
    • Change Rate (per hour): The rate of change of the SAT with respect to time when the feedback variable drifts from the target. For example, if the SAT setpoint is adjusted by 0.5°F at 10 minute intervals, the rate of change is 3°F/hr
    • Minimum SAT: Lower limit for the SAT
    • Maximum SAT: Upper limit for the SAT
    • Variable SAT Limits: If No, the constant minimum and maximum SAT setpoints bound the reset at all times. If Yes, the minimum and maximum SAT setpoints are themselves reset based on outdoor air temperature using a linear reset. This is a 6-parameter reset
      • OATLow: low- outdoor air temperature associated with low temperature bounds for the minimum and maximum SAT
      • OATlow-SATMax: Maximum SAT at low outdoor air conditions
      • OATlow-SATMin: Minimum SAT at low outdoor air conditions
      • OATHigh: high outdoor air temperature associated with high temperature bounds for the minimum and maximum SAT
      • OATHigh-SATMax: Maximum SAT at high outdoor air conditions
      • OATHigh-SATMin: Minimum SAT at high outdoor air conditions
• Reduce VAV Box Minimum Airflow Setpoints: Minimum VAV airflow setpoints are about ensuring adequate zone ventilation at all times. Minimum airflow setpoints are generally determined based on design occupancy assumptions, meaning zones can end up being over ventilated for significant periods of the time. When zones become heavily occupied, internal heat loads rise, leading VAV boxes to go into cooling mode, which drives up airflow, providing increased ventilation. In addition, air mixes extensively throughout buildings. This approach allows ventilation to be metered at the OA damper and not controlled as tightly at the zone level. High minimum VAV airflow setpoints create excess energy consumption in two ways:
  1. They can force zones to accept a greater amount of relatively cool supply air than is required for zone conditioning. To compensate, the VAV box will activate its reheat coil. This can even occur in the summer for some zones (and is the leading cause of summer gas/steam use in buildings with VAV systems).
  2. By limiting certain zones to a higher-than-required minimum airflow rate, the total amount of air that must be delivered throughout the system is increased, increasing fan power consumption.
• Enable/Fix Economizers: Economizers often do not work to their full capacity because of control limitations. These include Inappropriately low maximum dry bulb economizer limits (e.g., 55 to 60°F), Inappropriately high minimum dry bulb economizer limits (e.g., >45°F). In most cases, it’s a good idea to switch from fixed dry bulb to differential dry bulb (dry climates) or differential enthalpy (humid climates) economizer strategy.
  This measure allows the user to revise the economizer strategy and the minimum and maximum outdoor air lockout setpoints previously set in the AHU configuration module.
• Thermostat Setpoints and Deadbands: This measure allows the user to adjust the occupied heating and cooling setpoints. The dashboard features a single heating and cooling setpoint. In the event the zones do not use a global setpoint, this measure will reset all zones to use the specified new global heating and cooling setpoints.
• DOAS: Supply Air Temperature Reset: This measure allows the user to adjust the supply air temperature setpoint at the discharge of the DOAS section of the AHU. This is often referred to as the conditioned outside air temperature/setpoint. This setpoint can be controlled to a constant setpoint, or an outdoor air temperature reset is available. Some guidelines for setting up effective resets on DOAS SAT setpoints are as follows:
  1. Direct-to-zone air delivery, no heat recovery:
     1. Create a range of outdoor air temperatures with no conditioning (i.e., 52-70°F).
     2. Above this range in humid climates, use the DOAS as the primary engine for dehumidification. Set DOAS supply air temperature to 52-53°F
     3. In dry climates, set DOAS supply temperature to 60-65°F above the no-conditioning range and allow zone-level cooling systems (if they exist) to be primarily responsible for cooling.
     4. Below the “no conditioning” range, set a low outdoor air temperature DOAS supply air temperature of between 55°F (heavy occupancy) and 65°F (light occupancy).
  2. Direct-to-zone air delivery, with heat recovery:
     1. Lock out heat recovery coil or wheel in “economizer range” of 55-70°F
     2. OR, in that economizing range, set the DOAS supply air temperature equal to the outdoor air temperature plus supply fan temperature rise (SAT control will modulate the heat recovery to an intermediate speed for some systems).
     3. Above economizer range, enable heat recovery and set the DOAS supply air temperature to 53°F (humid climates) or 55-60°F (dry climates).
     4. Below economizer range, enable heat recovery and set the DOAS supply air temperature to 65°F.
  3. DOAS-> AHU Outdoor Air Intake, with or without heat recovery
     1. Systems typically sized to provide maximum of around 20-30% outdoor air in aggregate to AHUs.
     2. In choosing DOAS supply air temperatures, work backwards from required AHU supply air temperature, accounting for the mixing of return air with conditioned outdoor air.
     3. For example, if during cool weather AHUs have 65°F SAT setpoints, return air temperatures are 72°F and DOAS systems provide 25% OA on aggregate, 44°F DOAS supply air temperature would be ideal for avoiding use of mechanical heating and cooling.
     4. Example DOAS SAT Reset: Reset from 45°F DOAS SAT at 45°F OAT to 55°F SAT at 55°F OAT.*
• Eliminate Fighting Thermostats: Among thermostats in adjacent zone, some variation in setpoints are acceptable to account for different occupant preferences, however wildly different setpoints among adjacent zones (where the difference is close to or greater than the deadband range) will cause simultaneous heating and cooling within the floor. This measure aims to correct fighting thermostats by setting high and low limits for the occupied heating and cooling setpoints, then adjusting thermostat setpoints that fall beyond those limits. As a general guide, the user should ensure that the maximum heating setpoint is at least 1 degree warmer than the minimum cooling setpoint among zone thermostats on the same floor.

Reduce Outdoor Air and Infiltration

• Reduced Minimum Outdoor Air: This measure allows the user to adjust the minimum outdoor airflow rate or outdoor air fraction. Note that this measure is not applicable for AHUs that only have open/shut minimum outdoor air dampers that cannot modulate to an intermediate position and should not be applied to buildings with excess exhaust air that needs balancing. Also, a better approach may be an effective demand control ventilation measure, if appropriate CO₂ sensors are available.
  Determine rough compliance with ASHRAE 62.1-2013 and reduce any excess default ventilation rates. Many operational sequences are based on unrealistic design occupancy. For offices and most commercial spaces: 5 cfm/person + 0.06 cfm/ft2
• Demand Control Ventilation: DCV uses feedback from indoor air quality sensors to determine the ventilation rate or outdoor air damper position. DCV does not save energy. Why? It is often set up only to increase the ventilation rate above the normal baseline during times of under-ventilation and not vice versa. When implementing, make a corresponding lowering of baseline outdoor air damper commands or airflow setpoints.
  This measure is a linear reset from a minimum outdoor air damper fraction at a minimum return air CO₂ setpoint to a maximum outdoor air damper fraction at a maximum return air CO₂ setpoint. A recommended range of CO₂ setpoints in the reset is 800 to 1100 cfm.
• Building Pressurization Control: Proper pressure control balances building exhaust air sources (AHU relief air, dedicated exhaust fans) with outdoor air intake (DOAS, minimum outdoor air and economizer dampers, makeup air units).
  Excessive negative pressurization can pull outdoor air in through the envelope (poorly sealed doors and windows, rooftop penetrations, unused or improperly pressurized HVAC systems). This tends to cool (in the winter) spaces that need to be directly heated. When the air is brought in via outdoor air intakes (economizers or DOAS systems), some or all of that coolness can be used productively to temper warm return air and meet SAT setpoints. Excessive positive pressurization makes AHU fans work harder to push ventilation air into the building. The goal is a neutral to slightly positive pressure (0 to 0.05 in. w.c. static pressure)
  This measure attempts to correct building pressure issues by managing the return fan speed on the AHU. Usually the return fan speed is controlled using a fixed percentage offset from the supply fan speed. An alternative control scheme uses a linear reset to adjust the return fan speed. This reset uses a higher offset percentage at a minimum building pressure setpoint to a lower offset percentage at a maximum building pressure setpoint.
  
• Exhaust Fan Control/Scheduling: This measure allows the user to adjust the schedule applied to building exhaust fans. Often exhaust fans will run according to master HVAC schedules, when they only need to run during occupied hours, which may be shorter, especially if there is an extended morning warm-up period built-in to the HVAC schedule.
• Close OA Dampers at Night/Weekends/Morning Warm-Up: This measure allows the user to adjust the schedule that is applied to minimum outdoor air requirements. Often the outdoor air damper will run according to master HVAC schedules (or even 24/7), when they only need to run during occupied hours, which may be shorter, especially if there is an extended morning warm-up period built-in to the HVAC schedule.

O&M Measures

• Fix Leaking Heating Coil Valve: This measure allows the user to adjust the degree of leaking in heating coils. There are multiple heating coils available in the AHU configuration, so the dashboard for this measure shows the average heating coil leakage defined by the user, and allows the user to change that average. Note that this is a single-variable change within the dashboard, so the average value will be applied to all existing heating coils. In most cases, this measure will be applied by correcting all leakage to 0.
• Fix Leaking Cooling Coil Valve: There are multiple cooling coils available in the AHU configuration, so the dashboard for this measure shows the average cooling coil leakage defined by the user, and allows the user to change that average. Note that this is a single-variable change within the dashboard, so the average value will be applied to all existing heating coils. In most cases, this measure will be applied by correcting all leakage to 0.
• De-Lamping : This measure allows the user to apply a de-lamping percentage, which will reduce the design lighting density for each zone by the specified percentage

Capital Project Measures