HVAC System

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Introduction

HVAC (heating, ventilation and air conditioning) refers to the equipment, distribution network and terminals that provide heating, ventilation and/or air conditioning to a building. HVAC accounts for 40% to 60% of the energy used in commercial and institutional buildings, and 12% to 15% in industrial facilities. This represents an opportunity for substantial energy savings using proven technologies and design concepts. A recent study estimates that California commercial businesses alone have the potential to save 46% of their energy costs through cooling and ventilation energy efficiency efforts by 2011.

Technology Options

HVAC systems are typically replaced or upgraded when they have reached the end of their useful life. Because HVAC systems are expensive, it may not be cost-effective to replace them on the basis of improved performance or estimated annual energy savings alone. To optimize the purchase and selection of these systems, perform an energy analysis and review the purchasing tips provided below.

When early retirement of the HVAC system is not an option, there are two general guidelines for improving the energy performance of existing HVAC systems:

  • Make the system as efficient as possible.
  • Control the system as efficiently as possible.

Routine maintenance of an HVAC system should be performed at least annually. Inspect motors, belts and steam traps, and rebuild or replace them as necessary. Filters should be replaced, dampers adjusted to ensure a tight seal, and linkages, boiler heat transfer surfaces and coils should be cleaned. Other low-cost improvements to improve your HVAC unit's efficiency include:

  • Install tight-sealing, insulated dampers. The outside air and the exhaust dampers should have edge and jamb seals. The damper between the return air duct and the outside air duct should be tightly sealed.
  • Insulate duct system. Supply ductwork and ductwork that is exposed to outside air — including the mixed air duct, exhaust duct and outside air duct — should be insulated.
  • Seal duct joints. Duct joints should be sealed with mastic.
  • Balance air-handling systems. Air-handling systems should be balanced so that each zone receives the design air flow. The returns registers should also pull as much as air back as is supplied.
  • Control ventilation to match occupancy of facility/building. Heating and cooling of outside air prior to its delivery to occupied spaces should be controlled to match the occupied hours of the building.
  • Control heating to match occupancy of facility/building. During unoccupied periods, the heating temperature can be reduced by 10°F to 15°F.
  • Adopt an "optimal start" strategy. Many systems are controlled by a time clock or an energy management system to begin regular operation. An optimal start strategy utilizes a database and outside temperature measurements to determine when the system should resume heating or cooling.
  • Control the air-handling unit to match occupancy of facility/building. Program the air-handling unit to cycle off during unoccupied periods.


More extensive and expensive system improvements can be considered as well, such as:
  • An Economizer: An economizer system uses large quantities of outside air to meet the cooling load rather than operating the mechanical cooling system. This involves providing the following: additional controls to evaluate outside versus indoor air, ductwork to allow up to 100% outside air to be brought into the building, and an exhaust or relief fan.
  • Variable Air Volume: A variable air volume (VAV) system maintains a constant supply air temperature and varies the amount of air delivered to each space. Therefore, spaces requiring less cooling receive less airflow, while those requiring more cooling receive greater airflow.
  • Heat Recovery: Heat recovery is a general term relating to the useful application of heat that normally would be wasted or exhausted from a building. Heat recovery is often cost-effective in industrial facilities, but is not usually cost-effective in commercial buildings because of the low temperature and small quantity of exhaust from them. One exception is commercial or restaurant kitchens, where exhaust from the kitchen often can be used for heat recovery.
  • Thermal Energy Storage (TES): TES systems are ice-making systems that are employed at night to produce ice that can then be melted during the day to provide a chilled-water source for air conditioning. Energy demand is shifted, since the air conditioning load changes from standard hours to late night. In some cases, thermal storage systems actually use more energy than conventional systems, since making ice is more energy-intensive than producing chilled water. However, since the system operates at night (during off-peak periods), this strategy is less expensive when lower off-peak power rates are available.
  • Part-Load Boilers and Chillers: HVAC systems are selected to meet the building's heat loss and gain during the coldest and hottest times of the year. For this reason, individual boilers and chillers tend to be oversized for most of their operating times. Many engineers are now designing systems with multiple boilers and chillers. One unit can be sized for 75% to 80% of the design load, while another is sized for part-load performance, or roughly 30% to 40% of the full load. This allows the operator to select which unit to operate based on energy efficiency performance.

Efficiency Benefits

Between Pacific Gas and Electric (PG&E), Southern California Edison (SCE) and San Diego Gas and Electric (SDG&E), there is a total of 2432 GWh and 1069 MW of savings potential for cooling and ventilation alone. This is particularly important in terms of peak demand. Energy efficiency measures addressing high-efficiency chillers and packaged units, as well as chiller tune-ups and controls, make up a large share of total potential savings in this area. There also are potential savings from improving the performance of existing package and chiller units through better maintenance and operating practices as described above.

The following table shows savings as a percentage of total commercial sector energy consumption and peak demand for the three utilities across HVAC potential measures, aggregated across market segments and utilities in California.

Levelized
Measures GWH
Savings
Cumulative
GWH Savings
Energy
Cost $/kWH
Percent
Savings
HE Chiller 478 1,990 $0.017 2%
HE DX 246 769 $120 4%
Prog. T-Stat 46 815 $135 4%
Chiller Pumps 73 1,572 $224 9%
Cool Tune-ups 186 2,394 $372 13%
HE Vent. Motor 28 2,422 $397 13%
Pre-Cooler 95 3,396 $587 19%
Vent. VSD 26 3,422 $596 19%

Levelized
Measures MW
Savings
Cumulative
MW Savings
Demand
Cost $/kW
Percent
Savings
HE Chiller 315 315 $26 2%
Prog. T-Stat 277 2,616 $0.022 3%
Vent. VSD 453 5,251 $0.034 7%
HE DX 445 9,658 $0.066 12%
HE Vent. Motor 156 9,814 $0.071 12%
Chiller Pumps 110 11,802 $0.148 15%
Cool Tune-ups 308 12,110 $0.225 15%
Pre-Cooler 170 14,444 $0.326 18%

Manufacturers

The annual HVACR Directory & Source Guide for HVAC contractors, wholesalers, reps and engineers has a comprehensive list of manufacturers.

Some of the largest HVAC manufacturers include:

Purchasing Tips

When purchasing new equipment, several items need to be evaluated before proceeding. Specify the highest-efficiency boiler, furnace, chiller, air handler and rooftop unit that your wallet allows. In determining an acceptable cost limit, take into account the achievable energy savings over the life of the equipment.

Evaluate thermal loads as well before installing equipment, since changes to the building are likely to have occurred since the original equipment was purchased. Downsizing equipment can save substantial energy when replacement cooling or ventilating equipment is needed. Other efficiency measures such as reducing lighting levels, sealing duct leaks, installing low-emissive (low-e) windows and integrating building operations with an energy management system may allow smaller equipment to cool and ventilate your building.

The U.S. Department of Energy maintains a directory of HVAC software tools. Specialized design and analysis tools are available to help you select optimal HVAC systems:

American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE)
Publishes a set of four handbooks focused on HVAC systems.

Co$tWorks98
Offers an HVAC cost comparison program that calculates annual heating and cooling costs for a building and simple payback between two heating/cooling systems with different efficiencies or fuel types. It includes weather data for more than two hundred U.S. cities, and it remembers fuel rates for your location from use to use.

APACHE
APACHE (Applications Program for Air-Conditioning and Heating Engineers) is a comprehensive program for analyzing the thermal performance and energy use of buildings. It covers a wide range of requirements from basic design to detailed simulations of HVAC systems.

Building Energy Analyzer
Provides quick economic analysis of commercial and industrial buildings. This program estimates annual and monthly loads and costs associated with air conditioning, heating, on-site power generation, thermal storage and heat recovery systems for a given building and location.

CL4M Commercial Cooling and Heating Loads
Uses ASHRAE methods and algorithms to calculate cooling loads, heating loads and air requirements for each space in commercial buildings, as well as coil specifications.

Energy Trainer for Energy Managers HVAC Module
Contains about 4 hours of instruction on HVAC energy efficiency, and focuses on HVAC system operations and maintenance in existing buildings.

Emerging Technology

Advanced technologies have already demonstrated success in increasing the energy efficiency of heating, cooling and ventilation, without compromising occupant comfort or equipment performance. Yet the opportunity for further energy efficiency improvements remains large. There are several related advances that affect HVAC usage as well, such as cool roofs and evaporative pre-coolers. At this time, costs and savings estimates are less certain for these measures.

One direction pursued by Department of Energy (DOE) research and development is improved performance in chiller systems used in cooling large commercial facilities. Another promising direction is advanced combined, heat and power (CHP) systems that use waste heat to cool and heat buildings, significantly increasing system efficiency. According to DOE officials, integrated CHP systems can offer up to a 30% to 40% improvement in building efficiency. DOE goals for CHP development include helping manufacturers integrate their components into packages and ready them for the marketplace.