Comfort Zone: Improving HVAC System Performance

Comfort Zone: Improving HVAC System Performance

You want to improve the performance of your HVAC system, but it’s so complex. One way to tackle this problem is to start at the zone level (conditioned space) and work your way back to major system components. Going in this direction allows you to take advantage of downstream savings before taking on more complicated (and costly) projects.

As an example of this approach, repairing corroded dampers will ensure that they open and close properly, reducing energy waste and increasing comfort. This fix may also reveal additional savings opportunities, such as resetting controls or rightsizing equipment.


Optimizing zone-level performance

Zone-level equipment includes mixing dampers, reheat coils and thermostats that control the conditioned space. As facilities age, this equipment can fall into disrepair or out of calibration, reducing overall system performance. Fixing problems in the zone can save energy and increase occupant comfort. Measures you can take at the zone level include:

Inspect dampers. Without regular maintenance, dampers often become frozen in position, rendering them ineffective at regulating air flow and saving energy. Locating and repairing nonfunctioning dampers can be time-consuming and expensive, but it can pay dividends in increased system efficiency and enhanced comfort.

Recalibrate thermostats. In systems with pneumatic controls, recalibrate thermostats every six to 12 months to ensure that the temperature is regulated accurately and efficiently. Although you should check calibration in response to a problem or complaint, proactive maintenance can optimize system efficiency and energy savings.

Maintain reheat coils. Inspect reheat valves and coils to ensure that they respond appropriately to control system commands. Verify the capacity of an electric reheat coil by measuring its power input with an amp probe and comparing it to the nameplate value. If the measured value is significantly lower than the nameplate value, replace the coil.

Shut off reheat systems in summer. If your facility includes a constant-volume reheat system, consider disabling it during the cooling season. With electric reheat systems, it’s possible to power off reheat coils at the breaker, saving energy. In certain situations, it may be necessary to leave some reheat coil breakers active to maintain comfort.

Control static pressure (resistance to airflow). Dual-duct systems typically include air balancing dampers to regulate static pressure in hot and cold ducts in response to zone demands. Over time, these dampers can fall into disrepair and fail, resulting in wasted energy and reduced comfort. Regular inspection and repair will help optimize system performance.

Ensure airflow. Vacuum the coils of ceiling-mounted chilled beams and variable-refrigerant flow (VRF) cassettes annually to maintain a free path for air through the heat exchanger. For VRF cassettes, clean the internal air filter each month, and make sure grilles and diffusers are not blocked.

Now you’re ready to tackle the big picture. Examine major HVAC system components and look for issues such as outdated or oversized equipment. Consider an energy assessment of your facility. A qualified professional can help you target the most effective cost-saving opportunities.

Tests Prove Benefits of Rooftop HVAC Controls

Tests Prove Benefits of Rooftop HVAC Controls

Tests Prove Benefits of Rooftop HVAC Controls

Tests Prove Benefits of Rooftop HVAC Controls

You know the cost-saving benefits that advanced HVAC controls can bring to commercial and industrial facilities. Without some hard data, however, it may sound to some like you’re just blowing a lot of hot air. Real-world testing of rooftop units by the U.S. Department of Energy (DOE) may just provide you with the evidence you need to convince the most skeptical decision maker.


Testing advanced controls

DOE researchers retrofitted packaged rooftop units (RTUs) with three control technologies not typically used with such units:

  • Integrated air-side economizer controls
  • Multi-speed controls on variable frequency drive supply fans
  • Demand-control ventilation (DCV)

In the multi-year study, advanced controls were tested on 66 RTUs atop eight different buildings in eight different climate locations. Of the units included, 49 were packaged air conditioners with gas heat, and the rest were heat pumps.

Two operating modes were evaluated. In standard operation, the supply fans ran continuously at full speed, and the economizers weren’t connected to the cooling system. In advanced mode, fans operated at different speeds (based on demand), and the economizers were integrated with mechanical cooling. For a fair comparison in similar climate conditions, each unit was switched daily between operating modes.


Energy savings and a quick payback

What did the researchers learn? For starters, the advanced controls reduced HVAC energy use by an average of 57 percent, with savings ranging from 22 to 91 percent. Other key findings included:

  • Average payback time for a control retrofit was three years.
  • Payback periods varied by unit type and utility rate, some in as little as nine months.
  • Utility incentives can significantly reduce payback periods.
  • Total building energy savings from the RTU retrofits ranged from six to 12 percent.
  • Fan energy savings represented the majority of energy savings.
  • The longer the operating time and the larger the unit size, the higher the energy savings.
  • Greater savings are expected in more extreme climates where economizers can have a greater impact.
  • Demand reduction from controls could have a significant impact on savings and payback in certain applications.

Armed with this information, you can demonstrate how advanced control retrofits can reduce energy bills and provide a reasonable return on investment. For more details, see Advanced Rooftop Control Retrofit: Field-Test Results.

Customized Comfort? Socially Driven HVAC Systems

Customized Comfort: Socially Driven HVAC systems

Customized Comfort? Socially Driven HVAC Systems

Customized Comfort? Socially Driven HVAC Systems

Saving energy while maximizing occupant comfort is a challenging goal for many facilities. However, a potential solution to this age-old problem has surfaced — socially driven HVAC optimization. In tests, this user-based system resulted in 20% cooling energy savings and 47% heating savings, while significantly reducing hot and cold concerns among building occupants.

How it works

Rather than relying on simple thermostats, socially driven HVAC optimization uses sophisticated software to allow individual control of the heating or cooling system. Using a computer or handheld device, occupants can indicate if they’re too hot, too cold or comfortable. This feedback is sent to the building automation system (BAS), which immediately adjusts airflow and temperature to improve comfort. After a short period, airflow and temperature return to energy-saving settings, awaiting more feedback from building occupants.

Over time, socially driven HVAC systems learn — by gathering and analyzing data — how to keep occupants comfortable and save energy, while relaxing temperature set points in unoccupied spaces. The technology is ideal for variable air volume (VAV) systems that are controlled by digital energy management, but it can be adapted to other HVAC systems.

Does it work?

The U.S. Department of Energy (DOE) evaluated socially driven HVAC optimization in a federal office and courthouse. The eight-story, 289,000-square-foot building has about 350 occupants and a digitally controlled VAV system.

The test evaluated whether the system saved on energy and maintenance costs (by reducing service calls due to occupant temperature complaints) and increased occupant comfort. The results indicated that the socially driven system:

  • Reduced cooling costs by 20%
  • Saved 47% on heating costs
  • Reduced hot and cold calls by 59%

In a survey of building occupants, 83% of respondents said they were more comfortable after the socially driven system was installed. The annual energy cost savings from the socially driven HVAC system were estimated to be $6,700, a significant amount, but not enough to justify the cost of the technology. However, the study didn’t consider additional savings from the decreased use of personal appliances, such as fans and space heaters. Building staff also pointed out such noneconomic benefits as increased comfort and control for occupants.

Overall, the report concluded the technology should be considered for facilities where thermal comfort is a priority, and where there is a significant amount of space with varying occupancy.



Best Practices in HVAC Commissioning

Best Practices in HVAC Commissioning

HVAC systems are critical to building comfort, but they’re also the biggest energy user in a typical commercial building. Proper operation affects employee health and productivity, as well as customer purchasing behavior.

A new HVAC installation may not operate as intended, however. People make mistakes, microprocessor controls are complex and different equipment brands are often intermixed. Commissioning can help you meet owner project requirement and avoid potentially costly problems, such as callbacks and repairs.

What is commissioning (Cx)? According to ASHRAE Guideline 0, The Commissioning Process, Cx makes sure the facility and all of its systems and assemblies are planned, designed, installed, tested, operated and maintained to meet the owner’s project requirements. HVAC Cx is essentially quality assurance, preparing the HVAC system to succeed, and setting the stage for long-term operations and maintenance (O&M). Cx for HVAC does cost money, but if done right, it’s money well spent.

A four-step process

Ideally, HVAC Cx is conducted through four phases of building construction.

1. Pre-design stage. Document the building owner’s expectations of how the system will operate. This includes measurable performance criteria such as kilowatt power draw per ton of cooling (kW/ton) and outside air flow rates. The initial Cx plan (processes and procedures) is drafted and the Cx team is assembled.

2. Design phase. The HVAC concepts, calculations, decisions and product selections are made. Specific codes are referenced, weather assumptions are made and usage assumptions are documented. It’s important at this stage to notify the mechanical contractor about the Cx requirements.

3. Construction phase. HVAC equipment verification should be conducted to determine what was actually delivered to the site. Pay special attention to substitutions and proposed deviations from the contract documents. Develop step-by-step test procedures and involve the local authority having jurisdiction as necessary.

4. Occupancy phase. Make sure the HVAC O&M manual has been created and knowledge transfer has occurred through training, which should encompass electrical, mechanical, plumbing and control systems. Trend logs should be kept to document long-term performance.

The following are some specific items to check during the commissioning process:

  • Validate air and hydronic flows
  • Building envelope tests
  • Static pressure, air leakage, thermal barrier performance
  • Required (ASHRAE 62.1) fresh air achieved
  • Equipment is accessible
  • Sequences of operation
  • Test all phases of operation, including emergency
  • Point-to-point and sensor calibration test
  • Train and coach O&M staff

Choose an experienced and accredited Cx agent for your project.

HVAC Cx can also help you promote the sustainability of your projects. It’s a prerequisite for LEED green building certification.

Cool Apps for HVAC Pros

Cool Apps for HVAC Pros

Cool Apps for HVAC Pros

Cool Apps for HVAC Pros

With the widespread use of mobile devices, it seems like there’s an app for everything. In the HVAC arena, there are apps for unit conversion, duct sizing, calculating boiler efficiency and more. The following are just a few examples of apps designed to help HVAC professionals work smarter and more efficiently.

Duct Calculator Elite is designed to simplify the job of duct sizing. It allows users to calculate duct size, velocity, pressure drop, and flow rate for ductwork.

HVAC Toolkit is a combination of 11 individual apps costing $24 in total. The toolkit includes apps for duct and pipe sizing, steam tables, refrigerant charge, psychometrics and more.

Fullsteam HVAC enables rapid sizing of low-flow rate steam and condensate pipes. Calculations include steam properties, pipe weights, as well as expansion and heat transfer.

Engineering Cookbook is a free reference guide for mechanical designers, providing access to frequently needed information, including heating and cooling load estimating, system trouble shooting, design guidelines, formulas and conversion factors.

Refrigerant Slider is a pressure-to-temperature refrigerant converter. The tool covers 69 different refrigerants, including natural refrigerants. The Global Warming Potential (GWP) and Ozone Depleting Potential (ODP) of each refrigerant is included.

HVAC Buddy Load Calc for iOS allows you to enter all the construction characteristics relating to heat gains and losses to calculate building heating and cooling loads. Opening areas for walls with attached doors and windows are automatically calculated and subtracted.

With these and other free and low-cost apps, you can make quick calculations, develop estimates on the go or connect with suppliers wherever you are.