Guidelines to Improve HVAC Efficiency

Written by  //  2019/07/08  //  Home Utility Management  //  No comments

HVAC can represent over 50% of energy consumption in buildings, especially in climate zones that demand plenty of space heating or air conditioning. Due to the high energy footprint of HVAC installations, design features that improve efficiency often yield an attractive return on investment. In addition, many energy efficiency measures can achieve synergy through smart design decisions.

To achieve optimal performance, HVAC systems should be specified with adequate equipment capacities according to the application, and the building envelope should minimize unwanted heat transfer. Automatic controls can ensure the available capacity is used efficiently.

Investing in High-Efficiency HVAC Equipment

HVAC systems are characterized by a wide range of available configurations, and energy efficiency metrics have been developed for each type of equipment. When specifying HVAC installations for a project, it is important to understand the meaning of each metric and the cases where it applies:

  • The Annual Fuel Utilization Efficiency (AFUE) applies for furnaces and boilers, and the most efficient units exceed 95%.
  • The Seasonal Energy Efficiency Ratio (SEER) applies for unitary air conditioners, as well as unitary heat pumps in cooling mode. This metric indicates BTUs of cooling per watt-hour, considering the entire cooling season, and the most efficient units offer a SEER of around 30.
  • The Integrated Energy Efficiency Ratio (IEER) is used in for larger systems in commercial and industrial applications, and it describes efficiency over a range of typical operating conditions. IEER values above 20 are common for the most efficient chillers and heat pumps.
  • The Heating Seasonal Performance Factor (HSPF) describes the performance of air-source heat pumps during the typical heating season, following a similar approach as the SEER. The top-performing units in the market have HSPF values of around 10.

The Energy Efficiency Ratio (EER) and Coefficient of Performance (COP) are also common metrics. However, they indicate performance for a specific operating condition, while the measures above are based on a range of possible conditions.

Increased efficiency comes with a higher price, but it reduces operating costs throughout the entire service life of equipment. However, even the most efficient HVAC equipment may suffer a performance drop if capacity is poorly matched with building needs.

Importance of an Efficient Building Envelope

Ideally, the building envelope should minimize summer heat gain and winter heat loss, reducing the workload on HVAC equipment. To reduce heat transfer effectively, the building must have adequate insulation and air-tightness. Increasing the number of windows reduces the building envelope performance, but the effect can be mitigated with low-emissivity and triple-pane glass. Effective use of shading and adequate window orientation can reduce direct sunshine, preventing glare and lowering heat gain in summer.

A high-performance building envelope can lower design loads for HVAC equipment, allowing reduced nameplate capacities. This not only reduces the operation and maintenance cost of HVAC installations, but also equipment prices.

The best opportunity to deploy a high-performance building envelope is during the initial construction. Upgrading the envelope of existing properties is possible, but much more expensive due to the scale of the modifications required. For example, installing high-performance windows in new constructions is simpler than replacing older windows.

Enhancing HVAC Performance with Automatic Controls

A high-performance building envelope and efficient HVAC equipment can be complemented with automatic controls to achieve the lowest possible operating cost. The most efficient HVAC units typically have these controls built in – variable refrigerant flow systems and helical rotary chillers with variable speed are two examples.

When an HVAC system includes components such as hydronic pumps, air handlers and cooling towers, a significant efficiency gain is possible with variable frequency drives. A building automation system can modulate all HVAC components according to load, to optimize the operating cost while keeping a suitable temperature and humidity.

Motor-driven equipment above 1 hp of nameplate capacity can normally use NEMA Premium Efficiency motors with variable frequency drives. In fractional horsepower applications, electronically commutated motors offer high efficiency and built-in speed control without an external drive.

Concluding Remarks

The energy performance of HVAC systems can be enhanced by selecting equipment of adequate capacity, ideally with a high nameplate efficiency. A high-performance building envelope and automatic controls complement the equipment selection, minimizing HVAC costs for building owners.

Considering that HVAC represents the largest share of energy consumption in most commercial buildings, measures that boost efficiency often offer a high return on investment. Industrial environments have larger loads than HVAC equipment, but the business case for energy efficiency remains favorable.

Michael Tobias is the founder and principal of Chicago Engineers, an Inc 5000 Fastest Growing Company in America. He leads a team of 30+ mechanical, electrical, plumbing, and fire protection engineers from the company headquarters in New York City; and has led over 1,000 projects in Chicago, New York, New Jersey, Pennsylvania, Connecticut, Florida, Maryland and California, as well as Singapore and Malaysia.

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