By Nicole Imeson, P.L.(Eng.)
Decarbonizing through Existing Building Commissioning (EBCx) is a great opportunity for building owners to reduce energy consumption and lower operating costs. Last month’s checklist article outlined the energy analysis process and the importance of utility bills and weather data to help commissioning providers (CxP) and owners identify simple measures to reduce energy. Depending on the existing systems, type of occupancy, and owners’ goals for the project, there are likely several different energy conservation measures (ECMs) suitable for the building. This article explores a few of the commonly implemented measures explored through EBCx projects.
Air Handling Units
An air handler operating 24/7/365 in an office building where occupants are not there overnight or on the weekends indicates an area for potential savings. If the air handler is the main source of heat for the building, it may need to operate in some capacity to maintain temperature during winter months. Still, when the building is empty, the temperature can float further from the setpoint to reduce energy. If there are other sources of heat, the air handler may be able to be turned off during unoccupied hours and only turn back on if the temperature has veered too far from the set point. There are several building-specific factors requiring further review and discussion by the commissioning team to determine if and how this measure could be implemented. Implementing a reset schedule, nighttime setback, or occupancy schedule to an air handler is a simple solution when the building has a BAS but becomes more complicated when the air handler operates as a standalone unit. The commissioning team would need to explore the capabilities of the system to determine how this measure could be implemented and compare those costs to the operating costs of the unit.
Failed dampers are also another opportunity to implement energy savings. Especially if the damper serves the outdoor air supply. When an outdoor air damper has failed in the fully open position, a significant amount more energy is required to heat/cool 100% outdoor air than would be required to heat/cool 25% outdoor air mixed with return air from the building. In addition, repairing damper actuators is typically a simple, low-cost repair. Depending on the abilities of the building operations team, this repair may be completed in-house.
In large buildings, even where the lights have been upgraded to LED, there may be a significant opportunity for savings by installing occupancy sensors or an operating schedule to turn the lights off when the space is empty — although a handful of lights will need to remain on for emergency purposes. In a small office or retail park with minimal lights, turning off LEDs during unoccupied hours may not net high savings, but in large facilities such as office towers or warehouses, the savings start to add up.
The potential savings are calculated using energy consumption from the lights, the current and projected energy rates, and expected unoccupied hours to determine the current operating costs. Those costs are then compared against the cost of installing sensors. If the payback period is short enough to justify the sensor installation cost to the owner, the measure will likely be implemented.
A boiler plant operating at the maximum heating water supply temperature year-round indicates an area for potential energy savings and improved occupant comfort. Implementing an outdoor air reset schedule into the boiler control sequence — modulating the heating water supply temperature relative to the outdoor temperature — allows the system to better match the heat loss of the structure. If the system is operating at maximum heating temperature when the demand is small, the space temperature will be satisfied very quickly or may overshoot the setpoint. Similarly, a nighttime setback can be introduced to the boiler plant to reduce the heating water supply temperature at night when the building is empty.
Lowering the water temperature when the loads are small will provide more gradual adjustments, which mitigate cycling and is more comfortable for the occupant. Rapid cycling leads to several issues within the boiler, such as stress and corrosion fractures from rapid heating and cooling of the burner or short run times. Also, the gas valves serving the burner are not manufactured for short cycling, which can lead to reduced life span.
Figure 1 – Common Hydronic Outdoor Air Reset Schedule Used in Calgary, Alberta, Canada. (Note: Heating Supply Temperatures are based on condensing boilers.)
This measure is typically simple to implement, even in a building without a building automation system (BAS). An outdoor air sensor is required, if not already installed in the building, to measure the temperature outside. Through the BAS or onboard boiler controller, the settings are adjusted to modulate the heating supply water setpoint based on the corresponding outdoor air temperature. In a nighttime setback scenario, the heating water supply temperature modulates down during unoccupied hours. Care should be taken to increase the heating water supply temperature and overall building temperature early enough so it’s back to the occupied setpoint before occupants arrive.
While the costs to implement this measure are relatively low, it should be noted the savings for this measure will be much larger in geographic regions with large temperature swings throughout the year. In the northern US and Canada, where temperatures can swing from -40°F to 95°F throughout the course of a year, the savings are more significant than in the southern US with moderate, short winters.
Pumps can use a surprising amount of energy. In older systems, constant volume pumps in lead/lag or duty/standby operation were common. As the zone valves closed, the pressure in the system increased, and a control valve modulated open on the system bypass to circulate flow within the mechanical room and maintain consistent pressure in the system. Conversely, as the zone valves opened and the pressure in the system decreased, the bypass valve modulated closed. The pumps would be running at 100% throughout these fluctuations. By replacing constant volume pumps with variable speed pumps, the flow rate can be reduced as the system pressure starts to climb, and only open the bypass when the pumps are at minimum speed, and the pressure is still climbing.
Similar to the other measures discussed, the cost to implement this measure must be compared to the current and projected operating costs of the existing constant volume pumps. If there are issues with the current pumps requiring regular maintenance or they are due for replacement soon, this measure becomes much more appealing because the cost to implement is easier to justify. The larger the pumps and the more hours they operate per year, the higher the savings will be. However, savings can still be realized on smaller systems since the cost of replacing smaller pumps will be less.
There are several possible energy conservation measures requiring consideration and exploration in each building. The types of measures possible and feasibility will depend on many factors, such as energy bills, operating characteristics, and implementation costs. Each building is unique. Therefore, each measure will need to be explored and savings calculated to determine if the measure is within the goals of the project and if the payback period is adequate for the owner. CxPs have the expertise to evaluate the building, find ECMs, calculate the potential energy savings, and work with the owner to implement the best measures for the building and project.