Mi Minim imiz izin ing g Wa Wast ste Usi Using g you our Bu Buil ildi ding g Co Contr trol ol Sy Syst stem Sam Thomas Prism Engineering Ltd
Introduction Prism Engineering provides consulting services to address technical, behavioural and organizational aspects of Energy Management We design and implement cost effective approaches to address comfort, efficiency and reliability. 2 2
The context... • Why try to optimize our building control systems? – Energy – Greenhouse gas emission reduction – Comfort – Equipment reliability – Reduced maintenance – …. 3
Terminology • Re-commissioning (RCx) • Retro-commissioning • Continuous Optimization 4
https://www.bchydro.com/powersmart/business/programs/continuous-optimization/program-results.html
Common RCx Measures Item Measure Schedules 1 Reduce Equipment Runtime 2 Optimize Economizer Operation Sequences 3 Eliminate Simultaneous Heating and Cooling Sequences 4 Sequences Optimize Supply Air Temperature 5 Optimize Zone Temperature Setpoints Setpoints 6 Schedules Eliminate Unnecessary Lighting Hours Setpoints 7 Optimize Ventilation Rates 8 Volume Control for Pumps and Fans Setpoints 9 Add / Improve Chilled Water Temperature Reset Sequences 10 Eliminate Passing (leaky) Valves O&M 6
Eliminating Energy Waste with DDC • S chedules • S etpoints • S equences Use DDC strategies to match the need!! 7
1. SC SCHE HEDUL ULES 8
Equipment Operating Schedules • Weekly Schedules • Occupancy Feedback • Exception Schedules – Holidays – After Hours Use – Special Events (ie Voting Day) • Optimum Start 9
Scheduling Example • Graph shows natural gas savings. Municipal Hall • DDC changes made: – Monday start up time was 02:30h which we moved to 06:30h. – T-F weekday start up time for the building was at 04:30h on weekdays - we moved it 06:30h. – There was a schedule to heat the building on weekends for occasional use. We changed that schedule from 8-16:00h Sat and Sunday to 9-12:00h 1,000 GJ savings in last 12 months 10
DDC Schedules May Not Result in Savings!!! Schedule was in hand “on” so fans operated continuously for 5 months 11
Healthcare Add Weekly Schedule to Zones The AHU serving most of the building has to run continuously, but the hair salon and dental clinic are closed at night. A new schedule was created to control the reheat valves to only maintain night setback temperature at night, reducing reheat loads 12
Healthcare Add Weekly Schedule to Pumps POOL CIRCULATION PUMPs The Hydrotherapy pool circulation runs continuously. The pool is only used on weekdays, about 20 hours/week. A new schedule was created and the pumps (7.5hp & 3hp) were equipped with VFDs to run at 60% speed during unoccupied periods. 13
School Holiday Calendar Several holidays were not populated into the holiday calendar. Missing holidays are identified in red. 14
2. SE SETPOI OINT NTS 15
Setpoints: Meeting Occupant Comfort w/ Temperature, Humidity and Ventilation • MATCH THE NEED!! • Maintain energy efficient space temperatures with a deadband – Heat to 21°C – Cool to 24 ° C – Revise based on particular space needs within predefined limits • Maintain Humidity and Pressure – Meet requirements of space 16
Office Setpoints: Limits to Space Setpoints Comfort vs. Efficiency : we are cooling at the AHU to provide comfort to the zone requesting the most cooling. Are there cases where we may want to “limit” this setpoint (68F=20C). 17
3. SE SEQU QUENC NCES 19
Sequences – HVAC Systems A programmed set of instructions… A. Feedback and Reset Temperatures B. Damper controls C. Zone Isolation D. Simultaneous Heating and Cooling E. Control of pumps F. Demand Control Ventilation 20
A) Feedback and Reset Temperatures • Full recirculation mode for warm up / set back period – Reduce outside air that needs to be heated when there are no occupants • Automatic supply temperature reset on demand feedback – Varying reset with season & occupancy – Avoids unnecessary reheating during spring & fall – Typical savings of 3% of heating energy required • Reset of heating water temperature using outdoor air temp – Applies to heating water systems (boilers) and radiation systems – Reduces overheating – Can reduce boiler standby if boiler water temperature is also reduced 21
MURB Reset of Radiation Supply Water Temperature 22
DDC Trend Logs for SWT reset AHU cooling coil valves on each floor for a high rise building w/ central chiller plant Problem: low chilled water supply Solution: reset based on CCV position 23 temperature
B) Damper Controls Proper operation of mixing dampers – Bring in only as much outside air as is needed – Minimum outdoor air should be provided when in heating mode (unless required for CO2 control) 24
Municipal Outdoor Air Damper Switchover Outdoor air temperature is greater than return temperature 25
School Minimum Damper in Heating Problem: The operators should be sequenced such that the heating valve is fully closed prior to the initiation of economizer mode . The observed overlap is the result of improper sequencing in the program code, which operates according to the graph. A heating/economizer overlap occurs for supply air temperature controller outputs in the range of 20% to 50%. Solution: Use a split range control for control of the mixing dampers and heating coil valve 26 without overlap (one control loop).
C) Zone Isolation • In unoccupied mode (schedule or occupancy sensor), set flow set to 0 CFM subject to temperature setpoints being met • Fan energy savings on AHU as VSD will run at a slower speed • For VAV or Dampers installed in ducts 27
Office D) Simultaneous Heating & Cooling Fully open cooling coil valve Fully open cooling coil valve Fully open reheat coil valve Problem: Independent control for heating and cooling valves 28
School E) Excessive Heating Coil Pump Operation Problem: Based on a review of the code, currently the coil pumps are enabled anytime the heating plant is online (i.e. below 15 ° C) regardless of whether there is a call for AHU heating. Solution We recommend revising the coil pump control to enable the pump only if the heating coil valve is open 29
F) Demand Control Ventilation • Air handling systems are designed to provide adequate fresh air to meet code and guidelines (ASHRAE 62.1) • Minimum damper setting should be sufficient to provide these ventilation requirements • Install CO 2 transmitters and provide feedback to modulate outside air damper • Under periods of low occupancy, reduce outside air rate • Works best for spaces with variable occupancy (gymnasiums, auditoriums, etc.) 30
Demand Control Ventilation 1200 1000 CFM Outside Air 800 Constant flow 600 DDC Scheduling DCV 400 200 0 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 *Energy use is proportional to the area under the graph 31
32
DDC Control of Heating Plants • Warm weather shut down: – Typical standby losses: 5-6% of rated input if boiler is pumped continuously – 1MBH boiler on hot standby: 60,000 BTU/h of losses • Multiple Boiler sequencing • Run boiler pumps only when boiler is firing • Optimize Condensing • Ensure heat recovery is recovering heat! 33
Multiple Boiler Sequencing • 7 @ forced draft boilers • Problem: Boilers sequenced based on one control loop – IF NOT HB~ITF_LWC AND (HB~IC_1002.I1 > 1) AND HB~IC_1002.S1 THEN – HB~ITF_STG1 = SWITCH(HB~ITF_STG1 , HB~ITF_BLR_CO , 14 , 10 ) – HB~ITF_STG2 = SWITCH(HB~ITF_STG2 , HB~ITF_BLR_CO , 28 , 16 ) – HB~ITF_STG3 = SWITCH(HB~ITF_STG3 , HB~ITF_BLR_CO , 42 , 22 ) – HB~ITF_STG4 = SWITCH(HB~ITF_STG5 , HB~ITF_BLR_CO , 56 , 36 ) – HB~ITF_STG5 = SWITCH(HB~ITF_STG5 , HB~ITF_BLR_CO , 70 , 50 ) – HB~ITF_STG6 = SWITCH(HB~ITF_STG6 , HB~ITF_BLR_CO , 84 , 64 ) – HB~ITF_STG7 = SWITCH(HB~ITF_STG7 , HB~ITF_BLR_CO , 98 , 78 ) • Outcome: No minimum on / off time, resulting in boilers cycling rapidly – Pre-purge and post-purge before / after each time the boilers cycle – Standby losses make the seasonal efficiency worse than an atmospheric boiler! 34
Office Achieve Boiler Condensing Observation: Boiler Problem: Secondary flow RWT is much higher lower than primary than system RWT Cause: low speed and fixed throttling valves Solution: Lower SWT will increase valves opening, will result in higher 35 secondary flow
Office Achieve Boiler Condensing - Results Pre retrofit RWT Post retrofit RWT 36
Heat Recovery – or NOT! 37
Healthcare Chiller Plant • Chiller enabled at low OAT (12C) and when at least one cooling valve is open • The CHW setpoint was reset based on OAT with a very restrictive range • Chiller running with very little load (look at delta T) Optimization Strategy: • Enable the chiller based on offset between room temperature VS setpoint • Reset CHW setpoint based on AHU cooling valve positions, not OAT • Increase the reset range to 5 to 11 °C 38
Q & A 39
Recommend
More recommend
