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Focus on System Efficiency by the AHRI Systems Steering Committee

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Figure 2: Commercial HVAC Efficiency Tech nical Limits Chart Based on Studies Conducted by Dick Lord

Historical Efficiency ImprovementsSignificant progress has been made to improve HVACR equipment efficiency since the 1970s, when regulations were established (see Figure 1). This has been done through minimum efficiency standards for equipment, such as ASHRAE 90.1 and federal appliance requirements established by the Department of Energy (DOE). The focus has been at an equipment and component level, and on the design full-load capacity rating point.

Recently, new metrics have been established — SEER, IPLV, IEER — that evaluate efficiency on a part-load or annual basis. These metrics are encouraging the development of new tech nologies such as inverter-driven chillers, rooftop systems with more stages of capacity, and speed control for indoor fans.

There are tech nological and economic limits to the amount of efficiency that can be obtained at the component level. Figure 2 shows how full- and part-load efficiencies are approaching these tech nological limits for chilled water systems. Similar curves can be created for other HVACR component efficiencies. There is room for further improvement on some products, but the potential for significant progress is limited — and costly. Many in the industry are now referring to this as “max-tech.”

Figure 1: USA New Commercial Construction Standard ASHRAE 90.1 Stringency 1975–2018 Based on Studies Conducted by PNNL

Future Efficiency ImprovementsWith the desire to achieve ongoing efficiency improvements, the industry will require new and different approaches to improve building efficiency and energy use. Work has already begun on these approaches. For example:

• AHRI — established the Systems Steering Committee• Alliance to Save Energy — established the Systems Efficiency Initiative• Europe — has embarked on significant efforts through the Second European Directive• Canada — has started work on whole-building metrics and tools for evaluating building energy• ASHRAE — established the bEQ (Building Energy Quotient)• Several other countries have developed similar metrics and initiatives. The common approach of all these initiatives is to evaluate a building’s heating and cooling as a system instead of as a group of components operating at full load. Studies have shown there are opportunities to improve building efficiencies using a systems approach, but current building efficiency standards are focused on a historical component approach, which is easier to control and inspect during construction — and easier for government agencies to regulate. Work is currently underway to explore and document potential improvements and opportunities.

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Understanding Commercial Building HVAC

Figure 4: Large Office: Baltimore (Zone 4a) Load Profile From Benchmark Building Models

Figure 5: Hospital: Baltimore (Zone 4a) Load Profile From Benchmark Building Models

ASHRAE, in conjunction with the Pacific Northwest National Laboratory (PNNL), has created 16 standardized benchmark buildings (as shown in Figure 3) that represent more than 80 percent of the commercial building market. These represent the EnergyPlus building models for all ASHRAE Standard 169-17 global climate zones, and are useful tools in understanding how commercial buildings operate and where energy use can be improved.

Figure 4 shows examples of building load profiles obtained from the PNNL models from a large office and hospital. Note there is very little operation at the full-load point used for most current efficiency metrics, with the majority of operation taking place at part-load and reduced ambient temperatures. These examples also reveal a significant amount of time where simultaneous heating and cooling occurs — another opportunity for energy recovery and reuse. This is particularly evident in the hospital example.

Figure 3: ASHRAE 90.1 Benchmark Building Models Developed by PNNL

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New InitiativesThe industry is evaluating several new initiatives:

1. Development and conversion to new part-load or annualized metrics, such as IPLV for chillers and IEER for rooftop units, split systems, and variable refrigerant flow (VRF) methods

2. Hybrid systems where two tech nologies are used in one unit with the development of new rating approaches such as AHRI Guideline V for rooftop units and energy recovery devices

3. Subsystem approaches (focus on parts and/or a complete HVACR system)

4. Whole-building system approaches (ASHRAE bEQ)

5. Defined commissioning requirements to ensure equipment runs correctly

6. Smart connected buildings that interface with the smart grid

7. Integrated fault detection (fault detection and diagnostics)

These initiatives are intended to not only improve design efficiency and energy use of the building’s HVACR system, but to ensure proper commissioning and operation of the building during its life cycle.

Systems and Subsystems ApproachOne of the AHRI initiatives is to look at HVACR equipment at the system or subsystem level on an annualized basis using typical building load and weather profiles. Figure 6 shows a typical chilled water system used in a large commercial building. The green dots represent components targeted by today’s efficiency regulations, while the red dots depict components that these regulations do not address. There are also no requirements for the overall system. For example, there are requirements for chiller efficiency and cooling tower fan efficiency, but there are no requirements for the cooling tower approach temperature, pumping power, or how these components work together.

Figure 7 depicts an example of a complete systems approach. The dotted line box defines the composite energy use on an annualized basis. In this model, targets would be established for the complete system instead of the components, and if the proposed approach can prove to use less energy than an industry defined baseline system, the complete system would be approved. This could also be used by rebate and higher tier guidelines.

Figure 6: Current ASHRAE 90.1 Regulations (Prescriptive Approach)

Figure 7: Possible Sub-Systems Option Approaches

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Supporting Changes to Technology and StandardsThe required tech nology and standards to support a systems and subsystems approach do not exist. The industry is undertaking several new initiatives to develop and demonstrate these standards.

• ASHRAE 205P — will facilitate standardization and sharing of equipment performance data for use in performance simulation by defining standard characteristics (such as data models, data formats and automation interfaces; will likely be released for advisory public review in early 2016.

• ASHRAE 90.1 Section 6 — allows for the use of alternative compliance paths. This approach previously existed, but was not used until the 2013 ASHRAE 90.1 standard was released with an alternative compliance path for data centers called power usage effectiveness (PUE). This is likely where system and subsystem approaches will be first implemented for HVACR systems.

• New system level tools and procedures — user-friendly tools capable of calculating system level energy on an annualized basis for a given building and for local climate conditions. It is important to compare the calculated proposed system with a baseline system that represents what ASHRAE 90.1 considers required minimum system efficiency standards. ASHRAE 205 models will be used along with ASHRAE benchmark buildings and climate zone benchmark cities.

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