Remarks

Boiler Lockout from Outside Air

Generally, prohibit boiler operation above 60 degrees F. Suggested control would be to cut-in at 55 and cut-out at 60 degrees F outside air. This Is open loop control, but saves energy compared to "start based on demand" routines, since all it takes is one strong demand point to run the large machine for extended periods.

Chiller Lockout from Outside Air

Generally, prohibit chiller operation below 50 degrees F, and coordinate with air and water economizer settings. Suggested control would be to 'cut-in' at 55 and 'cut-out' at 50 degrees F outside air. This is open loop control, but saves energy compared to "start based on demand" routines, since all it takes is one strong demand point to run the large machine for extended periods

Load Limiting

Reducing demand for primary electrical HVAC equipment can save money on demand costs. This has application for chillers, large variable speed tans, and large variable speed pumps By load limiting to 90%, this keeps 90% of design capacity available but will reduce electric demand by 20-25%. Since 30-40% of the electric costs for large facilities are often from demand, this will create savings.

Outside Air Reset of Hot Water Converters

Compared to a constant temperature setting, this will reduce standby losses. In the cooling season, these losses are also unnecessary cooling loads.

Mid-Range Vestibule Temperature

For vestibule spaces, temper the space to a mid-range temperature, half way between indoor and outdoor temperatures.

Operable Window Interlock

Where operable windows are used, provide automatic control interlock to disable the HVAC serving that room, to avoid heating and cooling the great outdoors.

Roll-Up Door Interlock

Provide automatic control interlock to disable the HVAC serving interior area, to avoid heating and cooling the great outdoors when the door is up. This will encourage people to keep the door closed.

Staggered Heating and Cooing System Start-Up

(Buildings with demand charges)

After extended 'off periods, such as night set back, normal automatic control response will be to drive the heating and cooling equipment in order to reach the occupied set point. To avoid setting the utility maximum electrical demand value and subsequent higher demand charges coming out of unoccupied periods, bring large electrically driven heating and coolinq equipment loads on In segments for 30 minutes or until the process has "caught up:' and is no longer at full load . NOTE: this Is not in reference to inrush currents for starting motors.

For example, consider a buildinq heated bv electric resistance heat. Bv default, cominq out of unoccupied periods during winter will result in 100% of the heat being energized simultaneously. Controlling in 2 or more zones and allowing ample pull-up time for zone 1 to get to temperature and begin cycling normally before starting zone 2 will reduce the maximum demand for that day and, if done diligently through automation, will reduce the overall seasonal demand and demand charges

Examples:

Electric resistance heat (winter) • Packaged HVAC cooling equipment (summer)

Figure 22.16 Basic HVAC Control Applications (Concluded)
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