BCBC Client Comfort System (CCS) - Design Manual


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9.0    OPTIMIZATION GUIDELINES

9.1    GENERAL OPTIMIZATION GUIDELINES

This section has been published as a draft. We feel that it will generate discussion and feedback that will allow it to be improved and become more useful.

Introduction

The sections following are arranged in rough chronological order for your convenience. The System Protection items should be considered during the seven day test procedure, while the Client Comfort section could be implemented after the building has been occupied or during move-in. The Energy/Operational items could be considered after the building has been occupied for some time and some operating experience has been gained. These lists of ideas are not meant to be exhaustive nor all-inclusive. If there are items missing that you feel should be included, please send the information back to us so that a more comprehensive list can be assembled in the future.

9.1.1    Pre-Occupancy Optimization SYSTEM PROTECTION

.1        Check ramp for MAD to ensure it opens slowly enough to prevent freeze protection from tripping during morning
           start-up in cold weather.
.2        Install Night Setback routines to allow equipment shut-down and still provide for building protection
.3        Set-up amperage points so that a broken belt or coupling will show OFF status.
.4        Check for good outside and return air mixing in economizer section of air handlers.
.5        Install routines to keep units off after freeze thermostat triggered, until reset by operator.
.6        Program alarms as required for building safety and operator preference.
.7        Ensure heating coil pumps are on when outside air temperature is below freezing or valve open.
.8        Ensure ramps on ASDs are set up to be slow enough to prevent overloading, and that all the parameters are set up.

9.1.2   Post-Occupancy Optimization CLIENT COMFORT

.1        Ensure that there is an adequate deadband between heating and cooling setpoints to prevent cycling.
.2        Set room temperature setpoint to match occupants’ expectations.
.3        Enhance SAT setpoint calculations with additional feedback.
.4        Check to see if VAV boxes should have increased airflow to solve stratification when reheat on.
.5        Ensure that overrides are set up for appropriate duration.
.6        Check for noisy or drafty diffusers in occupied areas.

9.1.3    Post-Occupancy Optimization ENERGY/OPERATIONAL

.1        Shut off any energy using devices for as long as possible. Consider optimal start.
.2        Install Dynamic Control Strategies in medium and large mass buildings.
.3        Optimize lighting off times through off-sweeps or other methods.
.4        Upgrade graphics to operators requirements.
.5        Optimize all heating and cooling to prevent/reduce chances of reheating/recooling.
.6        Ensure that when devices are off that setpoints concur with that action.
.7        Ensure that all software controllers are set up to reduce hunting and cycling.
.8        Input holidays into an annual schedule and incorporate year into point name. Eg. "SCH96_AS".
.9        Consider getting low use rooms up to temperature in morning and shutting off for rest of day, or widening deadbands,
           but only if occupants can restart when required. Note must be put in area.
.10      If information metering is installed, set up daily energy accounting routines.
.11      Ensure that heating coil pumps are only on when below freezing outside or here is a heating demand and off at other
           times.
.12      Set up building so that it operates on outside air for cooling if possible and bring on mechanical cooling only when
           required.
.13      Ensure that there is an adequate deadband between heating and cooling setpoints.
.14      Ensure that overrides are set up for appropriate durations.
.15      Find the areas of the building that are driving the setpoints and make changes to minimize their impact.

9.2    SYSTEM OPTIMIZATION GUIDELINES

Introduction

The generic startup logic used in the Client Comfort System Design Manual has been purposely simplified to allow commissioning and start up to be straight forward. The format and linking of the output orientated code with graphic icons, has put in place a system that will allow this code to be easily optimized and documented. The following guidelines provide a check list of optimization concepts that should be considered for each system. Chapter 38, Building Operating Dynamics and Strategies, of the 1995 ASHRAE Handbook HVAC Applications should be reviewed to provide background and rationale for optimization.

Optimization is a process of providing the optimum fit of the new CCS with the actual installed mechanical system’s limitations and the building characteristics. This process can only be completed when the building is occupied and used for its intended purpose. Trend data gathered by the CCS strongly suggests the areas in which optimization will be most effective. Analyzing the trend data will quickly identify system problems and opportunities for optimization. Trend graphics will also allow us to judge the success of our optimization strategies.

General Concepts

The optimization concepts are organized to match the output orientated code for all systems as outlined in Section 5 of the manual. The basic optimization concept is presented with supporting information. Exact generic code has not been provided as the actual implementation of the concepts are building and CCS vendor dependent. The lists of optimization concepts should be treated as the minimum optimization concepts to be applied to each system. Each project will present its own optimization opportunities and no attempt has been made to document these.

9C    OPTIMIZATION COOLING SYSTEMS

BCBC Single Centrifugal Chiller Type D (C:D)

Chiller Optimization Concepts

PG 3 Chiller
Reduce chiller runtime to the lowest possible number of hours in the most effective operating range.

.1    Control from actual space temperature demand not only outdoor air temperature.
.2    Use dynamic calculation as a lock out to prevent unnecessary chiller operation.
.3    Use room temperature average or return air temperature for stability.
.4    Avoid starting chiller for only one area of building. Solve hot spot problems so that they require cooling at approximately
       the same time as the rest of the building.

PG 3 Chiller Vane Program
Ramp chiller slowly on start up.

.1    When the chiller starts the complete loop is usually warm. If the chiller is not ramped over a period longer than the loop
       pull down, the chiller will go to full capacity to cool. This may exceed the condensing capacity of the system, causing the
       unit to trip on high head pressure or potentially establish a new electrical demand penalty. The highest value of the ramp
       should be limited during shoulder months to reduce electrical demand. Tune start up coding to match application.

PG 3 Chiller Vane Program
Reset chilled water to highest possible temperature.

.1    Actual space demand should be fed back to the chilled water reset to insure that the warmest possible chilled water is
       being used to meet the load. A safety low minimum should be set as well as a high limit, which when reached should stop
       the chiller.

PG 22 Cooling Tower
Reset condenser water to lowest possible temperature.

.1    Actual chiller machine design will determine the lowest possible water temperature that can be operated. Achieve
       condenser water control by cycling the condenser or cooling tower fans, or control output capacity not bypass condenser
       water.

9V    OPTIMIZATION VARIABLE VOLUME AIR SYSTEMS

PG 2.2 Return Fan or Exhaust Air Pressurization Control
Maintain optimum positive building pressure.

.1    Building pressure should be maintained positive to reduce infiltration. If setpoint is too high air movement at doors could
       be a problem and exhaust air volume may be restricted. Too low a setpoint will allow building to go negative. Outside air
       reset may be required to offset pressurization changes caused by the stack effect as building thermocline reverses from
       winter to summer. In some systems return fan will be able to be shut off when system is on a high percentage of
       recirculation.

PG 4.3 Cooling
Reduce cooling run hours as low as possible.

.1    Prohibit mechanical cooling if Cold Day = YES. Cold Day is calculated in Temperature Predictor program.
.2    If the supply air is too cold with one stage of DX, hold off cooling start decision or increase air flow to warm area. In
       severe conditions you may have to increase minimum flow to solve low temperature or provide a false load with mixed air.
.3    For direct expansion systems if discharge air temperature drops too low with two stages of cooling hold off second stage
       until supply air increases above setpoint.

PG 5.2 Heating
Review original design intent for heating.

.1    Insure that heating is meeting the original design intent. If early morning warm up is included provide programming. Use
       optimum start to start fan and heating. Insure mix is set to 0% for warm up.
.2    Optimization of heating will require a clear understanding of actual heating performance. Most systems have heating coils
       to heat minimum ventilation air at extreme cold ambient temperatures.

PG 6.2 Evaporative Cooling
Maximize evaporative cooling to reduce mechanical cooling.

.1    Trend a start cycle of evaporative cooling. Note response time effect of cold water as it fills. An interlock will be required
       to prevent outside air on mix from closing down. If outside air on mix is reduced, humidity in space will rise rapidly.
       Discharge control may have to be implemented to prevent over cooling. Rapid cycling of pump or valve can usually
       achieve some control. Each system will be unique.

PG 11.3 Supply Air Temperature

.1     Add high and low temperature adjust to supply air temperature calculation.
    
   Generic Start Up Code
        SAT_SP = 18 - ((RT_AVG - RT_SP) * 4) ADD B + C

        Add:
        IF MAX_RT > 23.5 THEN B = (23.5 - MAX_RT) * 3 ELSE B = 0
        IF MIN_RT < 21 THEN C = (21 - MIN_RT * 3 ELSE C = 0

        Tune algorithm to match actual conditions.

.2    Add minimum ventilation calculation.
       Calculate the maximum supply air temperature (ventilation air temperature setpoint VAT_SP) that will still insure minimum
       ventilation is being met.
       SAT_SP = LSEL(SAT_SP, VAT_ST)
       When cooling is started:
       VAT_SP = SAT_SP
       If heating is used consider using mixed air temperature rather than supply air. If mixed air is not stable hold fixed minimum
       position with damper analog out.
       Ventilation air temperature setpoint = ((Minimum CFM * Outside Air Temp) + ((Total Air Flow - Minimum CFM) *
       Return Air Temp)/Total Air Flow)
       If no flow measurement exists estimate flow from ASD position speed calculation and fan curves.
       Review BCBC Adequate Ventilation Document.

.3    Optimize supply air temperature and ventilation fan volume.
       Example: If ASD > 80 reset supply air temperature setpoint down. If ASD < 60 reset supply air temperature setpoint up.
       Limit will be required. Keep air flow high enough to meet minimum air flow and ventilation requirements. Reset must be
       timed to prevent cycling.

PG 12.3 Supply Air Pressure
Implement terminal regulated air volume control (TRAV).

.1    Insure that at least one terminal VAV box is completely open and temperature parameters cannot be met before
       increasing fan static pressure.
.2    Identify boxes that can never achieve temperature or air volume setpoint and take corrective action.
       Eg:    - increasing air flow,
                - removing duct restrictions,
                - improve diffusion,
                - increase static and lower supply air only as a last resort because total energy will be increased.

 

EXAMPLE OF
CLIENT COMFORT SYSTEM
OPTIMIZATION MATRIX

Project:_________________________              Date:______________      Prepared by:______________

Building A B C D
System SZ VAV VAV1 VAV2 GYM SZ SZ1 SZ2 SZ3 SZ4 SZ1 SZ2
Implementation of Temperature Predictor Program X X X X X X X X X X X
Feedback to boiler reset program   X         X     X  
Night setback of space temperature X                 X X
Fan shut off at night     X   X X X X X    
Fan slow down at night   X   X              
VAV box control - night mode   X   X              
Reheat valve control - night mode X   X   X X X X X X X
Room temperature control of SAT_SP X X X X X X X X X X X
Reheat flush at 6:00 when cold day   X X X X X X X X X X
Return fan off when not required   X X X              
Exhaust fan control X   X   X X X X X    
Loss of box volume alarm   X X X              
Overrides push buttons     X X X X X X X X X
2nd pump operation X       X X X X X X X
Set up alarms X X X X X X X X X X X
Energy Accounting implemented by building                      

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                                                                                    Updated: 97/05/28 by KWS
                                                                   
Copyright British Columbia Buildings Corporation, September 1994