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Sam Thomas Prism Engineering Ltd

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Introduction

Prism Engineering provides consulting services to address technical, behavioural and

• rganizational aspects of

Energy Management We design and implement cost effective approaches to address comfort, efficiency and reliability.

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The context...

• Why try to optimize our building

control systems?

–Energy –Greenhouse gas emission reduction –Comfort –Equipment reliability –Reduced maintenance –….

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Terminology

• Re-commissioning (RCx)
• Retro-commissioning
• Continuous Optimization

https://www.bchydro.com/powersmart/business/programs/continuous-optimization/program-results.html

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Common RCx Measures

Item Measure

1 Reduce Equipment Runtime 2 Optimize Economizer Operation 3 Eliminate Simultaneous Heating and Cooling 4 Optimize Supply Air Temperature 5 Optimize Zone Temperature Setpoints 6 Eliminate Unnecessary Lighting Hours 7 Optimize Ventilation Rates 8 Volume Control for Pumps and Fans 9 Add / Improve Chilled Water Temperature Reset 10 Eliminate Passing (leaky) Valves

Schedules Sequences Sequences Sequences Sequences Setpoints Setpoints Setpoints O&M Schedules

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Eliminating Energy Waste with DDC

• Schedules
• Setpoints
• Sequences

Use DDC strategies to match the need!!

• 1. SC

SCHE HEDUL ULES

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Equipment Operating Schedules

• Weekly Schedules
• Occupancy Feedback
• Exception Schedules

–Holidays –After Hours Use –Special Events (ie Voting Day)

• Optimum Start

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Scheduling Example

• Graph shows natural gas savings.
• 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

• ccasional use. We changed that

schedule from 8-16:00h Sat and Sunday to 9-12:00h

1,000 GJ savings in last 12 months Municipal Hall

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Schedule was in hand “on” so fans operated continuously for 5 months

DDC Schedules May Not Result in Savings!!!

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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

Healthcare

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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.

Healthcare

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Holiday Calendar

Several holidays were not populated into the holiday calendar. Missing holidays are identified in red.

School

• 2. SE

SETPOI OINT NTS

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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

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Setpoints: Limits to Space Setpoints

Office

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).

• 3. SE

SEQU QUENC NCES

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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

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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

• ccupants
• 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

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Reset of Radiation Supply Water Temperature

MURB

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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 temperature Solution: reset based on CCV position

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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)

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Outdoor Air Damper Switchover

Municipal

Outdoor air temperature is greater than return temperature

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Minimum Damper in Heating

School

Problem: The operators should be sequenced such that the heating valve is fully closed prior to the initiation of economizer mode. The

• bserved overlap is the result of improper

sequencing in the program code, which

• perates 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 without overlap (one control loop).

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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

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D) Simultaneous Heating & Cooling

Office Problem: Independent control for heating and cooling valves

Fully open reheat coil valve Fully open cooling coil valve Fully open cooling coil valve

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E) Excessive Heating Coil Pump Operation

School

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

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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 CO2 transmitters and provide feedback to modulate
• utside air damper
• Under periods of low occupancy, reduce outside air rate
• Works best for spaces with variable occupancy (gymnasiums,

auditoriums, etc.)

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200 400 600 800 1000 1200 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

CFM Outside Air

Constant flow DDC Scheduling DCV

*Energy use is proportional to the area under the graph

Demand Control Ventilation

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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!

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Multiple Boiler Sequencing

• 7 @ forced draft boilers
• Problem: Boilers sequenced based on
• ne 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!

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Achieve Boiler Condensing

Observation: Boiler RWT is much higher than system RWT Problem: Secondary flow lower than primary

Office

Cause: low speed and fixed throttling valves

Solution: Lower SWT will increase valves opening, will result in higher secondary flow

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Achieve Boiler Condensing - Results

Pre retrofit RWT Post retrofit RWT

Office

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Heat Recovery – or NOT!

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Chiller Plant

• Chiller enabled at low

OAT (12C) and when at least one cooling valve is

• pen
• 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

Healthcare

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Q & A

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Thank you.

Sam Thomas, BSc, CEM, CPEnMS(I)

Tel: 250-687-4406 sam@prismengineering.com www.prismengineering.com 320 - 3605 Gilmore Way, Burnaby, BC V5G 4X5

@Prism_Eng