Description:

The deep retrofit package includes the following measures, and estimates for these measures come from the Department of Energy's Advanced Energy Retrofit Guide:

Retrofit interior fixtures to reduce lighting power density by 11%

Overhead interior lighting accounts for a significant portion of overall energy use in a typical office building. Utilizing more energy efficient lighting technologies to reduce the amount of energy devoted to the lighting enduse can result in significant whole building energy savings.

This measure may not apply to smaller buildings or partial building tenants.

Available lighting efficiencies have steadily increased over the last few decades. Minimum efficiencies prescribed in building energy codes and federal regulations are frequently increased to keep pace with these improved efficiencies.

When evaluating lighting technologies, other factors should be considered in relation to cost besides energy savings and first cost. These include:

• Human productivity. The new lights should provide at least the same level of quality as the existing lights.
• Lamp replacement frequency and costs, including labor costs.

A lighting retrofit requires lighting design to achieve appropriate illumination with minimal energy usage. The design should evaluate the existing lighting system in terms of lighting orientation, layout, type, and control. It should evaluate each activity area and fixture individually, accommodate future changes in activities and space layout, and stress visual quality.

An efficient lighting system consists of efficient lamps, fixtures, control, and light path. All four of these should be considered as part of lighting design for a retrofit.

Lighting power density reduction goals can be met by replacement of existing lamps and ballasts with the latest current technology.

Install occupancy sensors to control interior lighting

Since lighting is typically required only when people are present, fixed lighting operating schedules may use more energy than necessary in zones with intermittent occupancy. Installing occupancy sensors in applicable zones will automatically match the lighting operation with occupancy. This helps minimize lighting run time and saves energy when compared with fixed operating schedules

Special Considerations

• Occupancy sensors work best in locations where there will be a minimal amount of false triggering, and where the lighting fixtures can respond (turn on) quickly
• The most common occupancy sensor types are ultrasonic (motion detection) and passive infrared (heat detection). In general, ultrasonic sensors are more suited for larger areas, and passive infrared sensors are more suited for smaller areas, within a 15-foot range.
• Occupancy sensors are most cost-effective when they serve spaces that are intermittently occupied, such as open offices, closed offices, conference rooms, restrooms, stairwells, and break rooms.

 

Install daylight harvesting sensors

Daylight harvesting sensors require the installation of photocells to sense the space lighting level and control the overhead lighting in the perimeter zones to maintain a constant light level in the space. This measure also includes replacing the overhead lighting with dimmable ballasts, since dimmable ballasts are necessary to realize energy savings.

Special Considerations

• The lighting next to the exterior windows needs to be on a separate circuit from the other lighting, so that these lights can be controlled separate from the interior zone lights.
• The design of a daylight harvesting system should account for sensor location, sensor orientation, and number of sensors. During installation, the light sensitivity settings need to be adjusted so that the desired lighting level is maintained in the space. Also, the system should be periodically tested for proper functionality.

 

Add advanced on/off control of office equipment

Office equipment; including computers, monitors, printers, and copiers; make up 9% of a typical office building’s overall energy usage. Office equipment typically consumes over half of the overall plug load for a typical office building. Besides the electric power draw of these loads, they also have an impact on the building’s HVAC system, creating an internal heat gain on the system.

Technologies are available to turn off plug loads when they’re not in use. These include:

• Adding computer power management software to optimize the energy performance of computers
• Rewiring electric circuits and implementing controls to shut off office appliances such as printers and copy machines based on sensed occupancy from motion sensors.
• Using “smart” power strips that use personal occupancy sensors to turn off task lighting when spaces are unoccupied
• Adding VendingMiser, CoolMiser, and SnackMiser controls on vending machines
• Adding time switches to turn off water coolers and coffee makers

Reducing the power draw of plug loads can also reduce the overall HVAC system energy usage.

 

Special Considerations

• Since significant energy savings can be realized from reducing computer and monitor usage, a company’s information technology (IT) department should be engaged in evaluating technologies. Server rooms, while typically small in floor area, can consume a significant amount of energy, so server equipment should be evaluated for energy savings opportunities as well.

 

Retrofit exterior lighting fixtures to reduce lighting power density (LPD) and exterior lighting control

This measure involves replacing a facility’s parking area lighting fixtures with more efficient fixtures that will deliver the same illumination at reduced power draw, and reducing the lighting level during unoccupied periods. Parking areas are traditionally lit with high-intensity discharge (HID) lighting fixtures, typically metal halide or high pressure sodium lights. Replacing these fixtures with newer, more efficient technologies such as light-emitting diodes (LED) will yield energy savings.

For office buildings, exterior lighting typically consists of parking area, walkway, and building façade lighting. This lighting is typically turned on at sunset and turned off at sunrise, based on photosensor or astronomical timeclock control. Energy savings can be realized by lowering the exterior lighting level below full load power during times when nobody is present.

This measure may not apply to smaller buildings or partial building tenants.

Special Considerations

• Overall lighting system efficiency, fixture life, light output depreciation, maintenance, environmental impact, and controllability should all be considered when replacing lighting fixtures.

 

Add roof insulation

Roofs can be a significant source of heat loss in cold climates and heat gain in warm climates. For roofing systems that have insulation entirely above the deck surface, which is a common roof arrangement in commercial office buildings, it’s relatively simple to add insulation to reduce heat transfer into or out of the building. Adding insulation to the roof will likely require the removal of the existing membrane. Most owners may consider this measure when the existing roof is in need of replacement. Also, replacing the membrane with reflective coatings, such as a cool roof, at the time of the insulation installation may also help to decrease overall cooling loads in hot climates.

Widen zone temperature deadband and add conference room standby control (DDC zone controls)

Deadband is the difference between the zone heating and cooling temperature setpoints. Widening the zone temperature deadband of the HVAC distribution system (e.g., piping, ductwork, terminal units) will result in measurable energy savings at the HVAC central equipment (e.g., boilers, chillers, air handlers). Putting the HVAC system in standby mode for zones that are unoccupied will also result in energy savings. Specific zone control energy conservation modifications will vary by HVAC system type and the specific needs and capabilities of each facility. In general, for centralized HVAC systems, it’s important to integrate the controls of both the central equipment and the distribution system for maximum energy efficiency and occupant comfort.

Special Considerations

• For hybrid systems (digital control at the plant, pneumatic at the zones), extending DDC control to the distribution level and providing enough capacity in the DDC system to allow for communication between the central equipment and the distribution system paves the way for implementing advanced control sequences that will help minimize energy consumption of the HVAC system, especially during non-peak heating and cooling periods. Extending digital control to the distribution level also allows operators to monitor performance of these systems and troubleshoot issues faster.

 

Lower variable air volume (VAV) box minimum flow setpoints and reset duct static pressure (digital zone controls)

For HVAC systems with variable air volume (VAV) systems, reducing the zone supply airflow during periods of low cooling and heating load will result in measurable energy savings at the central equipment (e.g., boilers, chillers, air handlers). In addition, reducing or resetting the duct static pressure setpoint will also result in energy savings. Specific zone control energy conservation modifications will vary by HVAC system type and the specific needs and capabilities of each facility. In general, for centralized HVAC systems, it’s important to integrate the controls of both the central equipment and the distribution system for maximum energy efficiency and occupant comfort.

Special Considerations

• Lowering the VAV box minimum flow setpoints mostly involves TAB (testing, adjusting and balancing) work. If a system already has DDC control at the distribution level, the minimum flow setpoints can be lowered at the main operator workstation.
• Prior to lowering the duct static pressure setpoint or implementing an automatic reset strategy, it’s a good idea to verify the integrity of the duct system. Check to see if there is excessive leakage in the system. If a certain area has recurrent comfort complaints, check to see if there are obstructions in the ductwork (e.g., duct liner that has peeled away from the duct, closed fire dampers). Also check to see if there are an excessive number of duct elbows in the ductwork serving that area.
• VAV box damper position is a good input variable to use for resetting the duct static pressure setpoint: raise the setpoint if a certain number of dampers are 100% open, lower the setpoint if most of the dampers are less than 100% open.

 

Add demand control ventilation

Adequate ventilation air, or outside air, is required to maintain acceptable indoor air quality. In general, the greater number of people in a space, the greater the amount of ventilation air required. This ventilation air increases the energy used by an HVAC system due to the energy required to heat, cool, humidify, and dehumidify the ventilation air, depending on the outdoor conditions and the needs of the space.

Most office building HVAC systems, especially older systems, are designed to deliver a constant amount of ventilation air during occupied periods, regardless of how many people are in the space. Energy savings can be realized by controlling the amount of ventilation air provided based on the ventilation needs of the space. For office buildings, this is typically accomplished by sensing the CO2 concentration in the space, and adjusting the amount of ventilation air accordingly between preset maximum and minimum values. When using this method, it’s important to consult and consider ventilation rate standards such as ASHRAE 62.1 – Ventilation for Acceptable Indoor Air Quality. This standard covers demand-controlled ventilation strategies.

Demand-controlled ventilation is most cost-effective in buildings that have highly variable occupancies or high minimum outside airflow rates. In buildings that schedule their HVAC system to operate according to the building’s main occupancy schedule, there’s typically not enough variation in occupancy during equipment operation to make demand-controlled ventilation cost-effective. However, this measure is worth evaluating for any facility, as there may be enough HVAC system operating hours during partial occupancy to make this measure cost-effective.

Special Considerations

• Calculating the necessary ventilation rate is usually easier than controlling the HVAC system to maintain that ventilation rate. It’s not as great a challenge with constant air volume systems (compared to VAV systems), but it’s still something to consider. With constant volume systems, even though the minimum outside airflow rate should not vary significantly, it’s important to recognize that the percent that the outside air damper is open probably does not correlate directly with the outside airflow percentage, due to damper performance characteristics.
• With VAV systems that use a fixed minimum outside air damper position, the outside airflow rate will change depending on the amount of system supply and return airflow. Directly measuring the outside airflow rate is the preferred method of maintaining minimum airflow rates with VAV systems, even though this requires regular calibration of the outside airflow sensors.
• For systems serving multiple zones, it’s preferred to sense the CO2 concentration in multiple spaces, not just in the return air duct, for a more accurate representation of space ventilation needs. As with other HVAC sensors, CO2 sensors are prone to drift out of calibration, and thus require periodic maintenance.
• For VAV systems that operate often in economizer mode, it may be cost-effective to reset the VAV box minimum airflow settings downward during economizer operation based on sensed CO2 concentration in the space, for fan energy savings. VAV boxes have minimum airflow settings for maintaining adequate ventilation to the space, and these settings are typically based on minimum outside air operation. Since the supply air during economizer operation has a higher percentage of outside air than during non-economizer operation, the minimum airflow can be reduced while still providing adequate ventilation to the space. This strategy can realistically only be accomplished if the zones are DDC-controlled.
• Energy recovery ventilators, which transfer energy between the outgoing exhaust/relief and incoming outside air streams, can help reduce energy usage. These systems are more cost-effective in extreme climates, with hot, humid summer and/or cold winters.

 

Replace supply fan motor and variable frequency drive

This measure involves replacing a facility’s supply fan motors and VFDs with premium efficiency motors and VFDs with current technology. Standard motor efficiencies have steadily increased over the last few decades due to improvements in motor design and manufacturing, and VFD efficiencies have increased greatly over the past 10 years. Minimum motor efficiencies prescribed in building energy codes and federal regulations are frequently increased to keep pace with these improved efficiencies.

Special Considerations

• Most facilities do not consider upgrading motors or VFDs with higher efficiency models until the existing motors or VFDs need to be replaced due to failure or system replacement/reconfiguration. However, it may be worth replacing large, old VFD/motor combinations that operate frequently with more efficient models even before failure.

 

Shut down heating plant when there is no heating load

Facilities often run their heating plants throughout the year, even on warm days. This is often done to satisfy year-round reheat loads that are inherent in multi-zone VAV systems commonly used in large office building. Summertime reheat loads can occur in zones that require ventilation yet have relatively low cooling requirements. Reheat is provided to prevent overcooling these zones, which are typically interior zones. In humid climates, reheat may also be required at the air handler level to reheat the air after dehumidification.

If the reheat load can be reduced, then there is less need for heating plant operation and energy can be saved. If the reheat load can be eliminated altogether, greater savings can be achieved by shutting off the entire heating plant (boilers and pumps) to reduce standby and distribution losses, and to reduce auxiliary equipment operation.

Special Considerations

• A common strategy for implementing this measure is to shut down the heating plant when the outside air temperature is above a certain value, e.g., 75°F. To be able to do this, though, reheat loads above this temperature must be eliminated or, at least, greatly reduced. Many HVAC systems in large commercial buildings operate with a certain amount of simultaneous heating and cooling, due to the nature of the systems. Minimizing this paves the way for shutting off the heating equipment.
• In addition to energy savings, this measure should result in increased equipment life due to less run hours for the heating plant.

 

This measure may not apply to smaller buildings or partial building tenants.

Increase efficiency of condenser water pumping system

This measure applies to cooling plants that use water-cooled chillers, which is a common type of cooling plant for large office buildings. Condenser water pumps circulate water between the chiller and the cooling tower.

Most cooling plants use constant speed condenser water pumps piped in parallel, with one pump dedicated for each chiller. For systems that have multiple chillers, the condenser water system pumps are typically balanced when all of the chillers and condenser water pumps are operating. During part load conditions, however, when fewer chiller/pump combinations are running, these systems can be out of balance due to pressure characteristics of the common piping system.

Reducing the speed of the condenser water pumps at part load conditions (when chillers are shut off) to the design condenser water flow will yield energy savings.

Special Considerations

• For most HVAC applications, VFDs are controlled to maintain a setpoint of some measured variable, e.g., temperature or pressure. With the strategy outlined above, the ‘part load’ speed is a set speed. Continuing with the example above, when both chillers are operating, each condenser water pump would operate at 100% speed.
• When only one chiller operates, the speed of the one operating condenser water pump might be 80% speed. The ‘part load’ speed should be determined by measuring the condenser water flow, and manually adjusting the speed until the flow equals design flow.
• The discharge valves related to constant speed condenser water pumps are often throttled slightly, as a way to balance the system to design flow with all chillers operating. If VFDs are installed, these valves should be opened up for additional energy savings. Modulating condenser water pump speeds below design flow is typically not recommended for system performance, energy efficiency, and maintenance reasons

 

This measure may not apply to smaller buildings or partial building tenants.

Increase efficiency of condenser water system

Many large commercial office buildings use water-cooled chillers to transfer heat from the building to the outdoors. In these systems, heat is ultimately rejected at the cooling tower through the condenser water system. Two common measures that can be applied to condenser water systems to increase the energy efficiency of the system include adding VFDs to the cooling tower fans, and adding a condenser water supply temperature setpoint reset strategy. Many older cooling towers use constant speed (on/off) or two-speed (high/low/off) fans that cycle to maintain the condenser water supply temperature setpoint. Adding VFDs to the cooling tower fans and varying the speed of the fans to maintain the condenser water supply temperature setpoint yields energy savings with no associated pump penalty or sacrifice in performance. In most situations, chiller efficiency increases with decreasing condenser water temperature, typically by 1-1.5% per degree reduced (Doty, 2009). Therefore, lowering the condenser water supply temperature setpoint will reduce the energy consumption of the chiller. There is a tradeoff, though – to achieve that lower temperature, the cooling tower fans will need to run harder. This should be accounted for in determining the energy benefit related to resetting the condenser water supply temperature setpoint.

Special considerations

• To achieve maximum energy savings when adding VFDs to cooling tower fans, it’s more efficient to run multiple fans at the same low speed than to run one fan at a higher speed. Pumping energy and control should also be considered when determining the optimum number of fans to operate.
• Before implementing this measure, it’s necessary to verify that the existing chiller(s) will accept cooler condenser water temperatures. Some chillers, especially older models, will not operate correctly at cooler condenser water temperatures.

 

This measure may not apply to smaller buildings or partial building tenants.

Change cooling plant pumping system to variable primary

This measure applies to cooling plants that use chillers, which is a common type of cooling plant for large office buildings. Chilled water pumping systems generally fall into one of two categories: primary-only, and primary-secondary.

In primary-only systems, one set of pumps circulates chilled water between the chiller(s) and the air handler(s),. These systems can either be constant flow or variable flow. In primary-secondary systems, the primary pumps circulate chilled water through the chiller(s), and the secondary pumps draw from that loop to circulate chilled water to the air handler(s).

In general, primary-only variable flow systems use less energy than primary-only constant flow and primary-secondary systems, due to reduced pumping energy usage. However, they are usually more complex to design and operate. They are generally better suited for larger facilities with multiple chillers and sophisticated operating staff.

Special Considerations

• For proper operation of a primary-only variable flow chilled water system, it’s especially important that:
  • The control sequences are designed and implemented to maximize energy efficiency without impacting performance
  • The control loops are tuned properly
  • The chilled water flow meter is calibrated regularly
• Complex control systems such as a primary-only variable flow chilled water system especially require proper setup and adequate maintenance to maintain performance and avoid chiller staging issues. Minimum required flow through the operating chillers must be maintained at all times, which is typically accomplished through use of a flow meter and bypass valve.
• If controls complexity is a barrier to implementing this measure, another measure worth considering is converting the primary-only constant flow system to a primary-secondary system. Changing to this type of system involves replacing and adding pumps (VFD-equipped for the secondary pumps), modifying the chilled water piping in the mechanical room, and modifying the controls. While this system would not save as much energy as a primary-only variable flow system, it’s less complex to operate, and would consume less energy than a primary-only constant flow system.
• BAS software overlays are available that will continually and automatically optimize the performance of a primary-only variable flow chilled water plant.

 

This measure may not apply to smaller buildings or partial building tenants.

Add a variable frequency drive (VFD) to one chiller

This measure applies to centrifugal chillers, which is a common type of cooling plant for large office buildings. At low load, the efficiency of these chillers is less than the full load efficiency. Also, these chillers have limited turndown capability. Part-load efficiency and turndown can be improved by converting the compressors from constant speed to variable speed through the addition of a VFD.

For cooling plants with multiple chillers, one chiller can be retrofit with a VFD and used as the lead, since it will operate most efficiently at part load. The other chillers in the plant can come online when the load increases beyond the load of the one chiller. Then the VFD-equipped chiller modulates to maintain the setpoint while the other chillers operate fully loaded.

This measure may not apply to smaller buildings or partial building tenants.

Special Considerations

• Not all centrifugal chiller compressors can be retrofitted with a VFD, due to refrigerant performance and torsional resonance. The chiller manufacturer should be consulted before adding VFDs to the compressors.
• The VFD retrofit should be designed for the particular chiller model, and installed by a qualified person. To maximize energy efficiency, the existing chiller staging strategy should be modified to allow part load operation of the VFD-equipped chiller and full load operation of the constant speed chillers.
• The energy savings related to this measure depends on the building cooling load profile and the number and size of chillers in the plant. The more variable the cooling load profile and the fewer number of chillers, the greater the energy savings potential. It may be more efficient to install a small chiller to handle low loads than to install a VFD on one of the existing compressors.

 

Replace boilers and change heating plant pumping system to variable flow primary

Most large office buildings, especially older facilities, use non-condensing boilers in a primary-only constant flow piping arrangement as their heating plant. Replacing the boilers with condensing boilers and converting the piping system to a variable flow primary system would reduce energy usage of the heating plant through increased boiler efficiency; reduced pumping energy due to VFDs installed on the pumps, and reduced heat loss through the secondary piping due to lower loop temperatures.

Unlike non-condensing boilers, condensing boilers are designed to allow the flue gases to condense in the boiler and flue. These boilers are more efficient than non-condensing boilers, and operate even more efficiently at lower return water temperatures. Lower water temperatures will also reduce piping conduction heat losses.

Implementation of this measure requires replacing the boilers and pumps, changing any 3-way heating coil control valves to 2-way valves, adding differential pressure sensors, and modifying the control of the heating water plant to keep the loop temperatures as low as possible while still satisfying the heating load.

This measure may not apply to smaller buildings or partial building tenants.

Special Considerations

• This measure is most suitable for facilities that operate at part load heating for a significant amount of time. Part load heating allows for reduced pump speeds and reduced heating water supply temperature, increasing the efficiency of the system.
• Lowering the heating water supply temperature, and thus the return water temperature, will increase the boiler efficiency. However, the performance of the existing heating coils must be evaluated at lowered heating water supply temperatures. In some instances, the coils may not perform adequately at lowered temperatures, especially with heating coils that have a low number of rows. In these instances, either the heating coils must be replaced, or the heating water supply temperature must be kept high enough to maintain adequate coil performance.
• Minimum flow rates must be maintained through the boiler(s). This is typically not a major issue, but is one that should be considered during design and operation of the system.
• Differential pressure-based pump speed control and heating water supply temperature setpoint reset are both strategies that increase the efficiency of the system, but care must be taken in implementing these strategies together as they often overlap. For example, for a given heating load, lowering the temperature setpoint will result in increased pump speeds since the heating valves will open in response to the lowered temperature setpoint.
• The pumps typically operate to maintain a constant differential pressure setpoint in the system. Resetting this setpoint based on an indication of load (e.g., heating water valve position) would result in more efficient operation.

See DOE’s Better Buildings Decarbonization Resource Hub for more information on energy efficient lighting, HVAC, and building envelope technologies that can help to cost-effectively decarbonize buildings.