Considerations for Building Controls

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Betty Freeman
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1 Considerations for Building Controls Does Nighttime Setback really save energy? Natalia Camblor, CEM Project Engineer Sustainable Engineering Group LLC

2 AIA Quality Assurance Learning Objectives 1. Recognize the operational challenges with night setback 2. Understand the energy impact of typical solutions to the operational challenges

3 Night-time Building Setback - Definition Widely used control strategy in which the system is cycled off during unoccupied hours, and the temperature in each zone is allowed to drift away from the occupied setpoint.

during unoccupied hours, and the temperature in each

4 Night-time Building Setback - Definition

5 The Reason for Night-time Building Setback Allowing the indoor temperature to drift saves energy by reducing the temperature difference between the ambient and the indoors.

6 Typically Good Setback Candidates K-12 Schools Office buildings Places of worship Courthouses Government buildings Strip malls Most higher education buildings

7 Typically Poor Setback Candidates Hospitals Nursing Homes Dormitories Art Museums Prisons & Jails Transportation Terminals Public Safety Buildings

8 Energy Model Building Description Location: Madison, WI Size: 60,000 ft 2 Construction Year: 1997 Facility Type: Middle School Systems: Natural Gas HW VAV with DX cooling Hours: 7:00 am 6:00 pm DDC system

9 Energy Model 3-D Rendering

10 Correctly Programmed Setbacks Save $ 8ºF Setback No Setback (Baseline) 9% Savings

11 Consequences of Setbacks Building envelope is cooled down during setback period Building air temperature may be recovered in most spaces within 1 or 2 hours Envelope and furniture temperature takes longer to recover

may be recovered in most spaces within 1 or 2 hours

12 Air Temperature vs. Radiant Temperature

13 Perceived Temperature Perceived temperature is roughly the average of the mean radiant (surface) temperature and the air temperature.

14 The Untold Reality of Setbacks Some spaces do not reach temperature setpoint when occupants start using the space Most spaces have low radiant temperature causing the perceived temperature to be outside the comfort zone This causes COMPLAINTS!!!

Most spaces have low radiant temperature causing the

15 The NUMBER 1 Solution Put Air Handling Units (AHUs) into Occupied Mode one to ten hours earlier, never mind the added ventilation Complaints typically go away. Everyone is happy!

16 Three Hours Earlier Start Time Breakeven Point 3 Additional Hours Occupied Mode No Setback (Baseline) All savings from setbacks disappear

17 The NUMBER 2 Solution When everything else fails, put AHUs into Occupied Mode 24/7 Dampers What Dampers?

18 The NUMBER 2 Solution Complaints ALWAYS go away. But what about the BILL???

19 24 Hour Occupied Mode Operation 24 Hour Occupied Mode No Setback (Baseline) 30% Cost Increase

20 Other Observed Solutions Increase boiler supply water temperature Increase speed of boiler VFD Portable electric heaters

21 Recommended Solutions Improve warm-up sequence Utilize DDC to close outdoor air dampers Reduce night setback temperature If there is no DDC, reduce or eliminate setback

22 Nighttime Setback Requirements Night setback can save energy IF: o Warm-up sequence does NOT ventilate (no open OA dampers!) o All occupied spaces are able to recover during warm-up period o All occupants are comfortable even though the perceived temperatures may be below setpoint In practice, this is very difficult to accomplish

23 Conclusions Night setback is perhaps even more complicated than economizer sequencing Only 3 hours extra operation in Wisconsin climate for a school wipes out ALL energy savings Night setback is NOT recommended unless the building will be closely monitored by a skilled professional, as it often increases the energy usage of the building

24 AIA Quality Assurance Portland Energy Conservation, Inc is a registered provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-aia members are available on request. This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

25 Thank you! Natalia Camblor, CEM

Using Time-of-Day Scheduling To Save Energy

Using Time-of-Day Scheduling To Save Energy The following article was published in ASHRAE Journal, May 29. Copyright 29 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is presented for educational purposes only.