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Importance of Performance Testing in HVAC Systems

Optimal and energy efficient performance is a factor of serious concern in present scenario of IoT and AI related with HVAC. It is important to evaluate and inspect a system regularly to make sure that it is at optimal performance and to check its energy efficiency. Undoubtedly, HVAC systems are no exception to this rule. Now that fall is around the corner, it is a good time for homeowners in Lufkin, Texas, to have performance testing done on their HVAC systems. Performance testing is vital for finding problems HVAC system may have developed over the summer.

Performance Testing for HVAC Systems

Testing, adjusting and balancing (TAB) is necessary to confirm that an HVAC system is performing optimally to offer occupants with the most comfort at the lowest cost. Different performance tests evaluate different functions of an HVAC system. Here are some of the performance tests user should regularly and periodically conduct for his or her HVAC system:

  • Energy Efficiency Testing: An energy efficiency test will check an HVAC system to make sure that energy usage is as low as possible without hindering maximum comfort of the occupant. If energy bills are too high, user may want to order an energy efficiency test.
  • Acoustical and Airflow Testing: The acoustical and airflow test will check the airflow within home to determine whether HVAC system is performing optimally.
  • Air Cleaner Testing: HVAC system cleanses the air to keep indoor air quality ideal. Homeowners who have young children with asthma should have a test performed to evaluate the effectiveness of their system’s air filter or cleaner.

Importance of Performance Testing

Performance testing allows homeowners to identify issues with their HVAC systems. That way, homeowners will be able to have these issues resolved before they get worse and costlier to repair. For example, if the user’s air conditioner is inefficient when it comes to cleansing the air, even if the user changes the filter, it may suggest a more serious problem. Performance testing allows homeowners to deal with issues while they are small and easy to repair.

In preparation for the winter, user should have performance testing done for HVAC system. For more information about performance testing, user should not hesitate to contact a skilled technician.

Functional Performance Testing of HVAC System

Functional Performance Testing (FPT) is the process of putting the Direct Digital Control (DDC) IIoT system through its paces by manipulating every possible condition the HVAC controls and equipment will ever experience. FPT is an important part of the building commissioning process. Only by testing how the DDC system controls respond to switching from cooling to heating or economiser mode, occupied to unoccupied mode, satisfied to unsatisfied temperatures, or normal power to emergency power, can the building owner know the system will function properly when the contractors leave and the building is handed over. The tests force user to work through the controls sequence language created by the design engineer in a sequential order. As the author gains experience as a commissioning engineer, FPT allows him to better understand the brains behind why equipment performs and reacts as it does. To make sure, a piece of equipment works as intended and can provide the expected performance is the main reason to functionally test HVAC systems.

DDC Screen Shot – Parking Garage Ventilation showing how are Functional Performance Tests Created.

Depending on how the building is used and what the building owner wants, the control sequences can vary significantly among different types of buildings. For example, an office building is going to have different operating hours than a hotel and a warehouse is going to have different comfort requirements than an office. In addition, all buildings will have different sequences depending on the system types and specific equipment chosen by the engineer and owner (e.g., rooftop units versus heat pumps, central plant versus stand-alone equipment).

The tests are created by using a workflow diagram: start with the systems running and change setpoints or fail components to see how the system responds. Does the backup pump turn on when the user manually disconnects the main pump? Does the chiller turn off when the user manually overwrites the water temperature below the chiller setpoint? Does the emergency power turn on all of the equipment if the building experiences a power failure? The tests are written to walk through the design engineer’s controls sequences step by step and ensure the components are responding as designed.

How FPT can call attention to and fix issues?

When user starts picking apart the control sequences to create these tests and then performs the tests in the field, there is a lot of opportunity to find potential issues that could affect the overall performance of a system. The issues can vary in severity, from a small change in the programming of the system, to a larger scale item in which a piece of equipment or component can’t perform the way it was intended.

FPT Flowchart example for Occupied Heating Mode of a Heat Pump.

Here are few examples of issues and possible repercussions that were found during the recent functional performance testing of an office building.

Issue: An exhaust fan sensor wasn’t working correctly and prevented the fan from turning on when intended. The sensor was fixed and the equipment was retested successfully.

Repercussion: The fan wouldn’t turn ON, therefore, inhibiting air from being exhausted out of the space.

Issue: The CO2 sensors, which control the amount of fresh air from being provided into spaces, were not calibrated correctly and were reading very high false levels. The sensors were fixed in these spaces to read more accurate CO2 levels.

Repercussion: The heat pumps and energy recovery units were operating unnecessarily to provide fresh air to unoccupied spaces. Any energy savings attributable to the CO2 sensors were not being realised.

Issue: The pumps for the ground sources system were starting up when any heat pump in the building started, even through the building loop temperature was within its proper range and not temperature conditioning was required. The controls sequence was reprogrammed and retested successfully.

Repercussion: The pumps were turning on unnecessarily, therefore, decreasing the lifetime of the equipment and increasing energy consumption.

If functional testing isn’t performed, issues such as the examples above may have never been noticed. All system types can generate different issues and functional performance testing offers reassurance to the building owner that the systems are working correctly and as intended.

Image 1: Typical commercial office building energy use (Images courtesy of Bell & Gossett)

Testing HVAC System Efficiency

The Energy Improvement Project consists of three primary steps: conducting an initial energy assessment of the hydronic system, updating the system with technologically advanced pumps and controls and adjusting the system in real time to evaluate the effects of the HVAC modifications.

The impact of energy efficiency improvements is often difficult to demonstrate at the individual system level because buildings typically get billed for energy use at the building level. According to Luke Falk, Assistant Vice President at Related and an adjunct Professor at Columbia University, the partnership among the water technology company, building manager and Columbia University allowed stakeholders to gain a granular understanding of exactly how much energy they would save by implementing a complex HVAC enhancement.

The key finding from the testing was that right-sized pumps paired with variable frequency drives (VFDs) powering the chilled water portion of a hydraulically balanced system can deliver a 95 per cent reduction in pumping energy, far exceeding the team’s expectations.

Image 2: Original system schematic

As noted by the Columbia research team, “The pumping electricity reduction with VFDs was far more significant than the effects of (reduced pump size and pressure-independent control valves): Annual replacement of the chilled water (ChW) distribution pump electricity was 92 per cent lower with VFDs than without. “When comparing the combined effects of the replacement pumps and the VFDs, the ChW distribution pumping electricity reduction was 95 per cent.”

Coupled with the findings in an American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Journal article that concluded energy improvements in the HVAC system could substantially influence 43 per cent of a building’s total energy, this has a dramatic impact on the overall building energy footprint (see Image 1).

Using data collected during the initial energy assessment, Columbia University researchers and water technology company engineers jointly reviewed the data. Researchers then calculated potential energy savings and tracked key system parameters following the renovation of the chilled and hot water systems, developing a mathematical model from the data. This prescriptive pathway to assess performance offers relevant technical data that, before now, has been extrapolated solely from laboratory test results or obtained through time-consuming proprietary energy assessments.

Image 3: Post-retrofit system schematic

Test Subject

Astor Place was developed by Related Companies and completed in 2005. It includes 39 residential units with commercial space on the building’s first and second floors. The HVAC system uses hydronic space heating through boilers and cooling with central absorption chillers. Fan-coil units provide HVAC to residential floors; HVAC in the common and commercial spaces employs air-handling units. Only the central plant equipment and air handling equipment in the commercial and common spaces were included in the retrofit and subsequent evaluation. The approach to the ChW and hot water (HW) systems was nearly identical, though monitoring was more comprehensive on the ChW systems, the details of which are outlined here.

On the cooling side, the original 30-horsepower (hp) condenser water pumps were replaced with lower horsepower but more technologically advanced pumps. The new pumps immediately delivered savings in electricity use—from 25.3 kilowatts (kW) to 18.0 kW.

Other modifications included new piping to create primary or secondary chilled water loops out of the original primary only system and the addition of 7.5 hp primary pumps. Constant primary chilled water flow optimises chiller performance. Decoupling the loops in the original one-loop system allowed for the installation of variable flow technologies on the secondary loop. New 15-hp pumps replaced the original 20-hp distribution pumps and were outfitted with VFDs.

Image 4: Pump electricity versus cooling load (hourly resolution).

The head losses were lower than expected, so the team was able to use smaller replacement pumps. This created more energy savings potential with the VFDs than on the larger pumps. Savings from dynamic adjustment using VFDs offset additional electricity required to operate the new primary pumps.

In providing their expertise, along with the pumps, drives and monitoring equipment for the project, the water technology company engineers obtained specific real-time data on pump and system performance.

The engineers simulate real-world conditions in laboratory testing, but they do not often get the chance to follow the pumps into the field to track performance data. The intent was to improve the energy efficiency of the system without modifying the heating and cooling loads. In the lab, manufacturers can test the efficiency of a pump, but in the real world there are often unexpected variables and more complex behaviour within the system that affect efficiency.

Columbia University’s Michael Waite, a post-doctoral research scientist in professor Vijay Modi’s Sustainable Engineering Lab, predicated a research thesis on a new mathematical model to assess a building’s energy profile that was derived from the research data. “There is a clear research gap for the evaluation of hydronic systems for large buildings,” Waite said. “Their complex systems demand a different mathematical model and approach to predict energy use. You also need to get into the building to see how (it has) responded to the energy conservation measures you have made.”

Image 5: Chilled water distribution annual pumping electricity

Energy-Savings Opportunity

Prior to the retrofit, nearly 30 per cent of the building’s common system utility costs were for pumping electricity, due primarily to the pumps being oversized for the demands of the system and the constant speed operation at partial loads. Oversized pumps were found to cause unnecessarily high-pressure differentials and flow rates in the system.

Oversizing pumps is a common industry practice. There are a number of reasons why, including adding safety margins beyond those factored into the design by pump manufacturers and accounting for marginal over performance at system peak loads. However, this common practice comes at a cost—namely increases in the system’s operation, maintenance and capital costs over the system’s lifecycle.

When considering both heating and cooling, the retrofit resulted in a computed annual pumping electricity usage of 316-megawatt hour (MWh), a 41 per cent improvement in pumping energy requirements and an estimated 12 per cent reduction in the building’s central operations’ energy bills.

Image 6: Total annual cooling system pumping energy

Commercial buildings account for 36 per cent of all US electricity consumption and cost more than USD 190 billion in energy every year, according to the US Department of Energy. With more than 80 per cent of the existing commercial and institutional buildings in the US expected to operate beyond 2030, as reported by the Colorado-based Rocky Mountain Institute, demand for HVAC system retrofits will be great.

The existing environment presents an opportunity for saving energy, creating better value for building owners and promoting sustainability.

In addition, the populous states of New York and California have in place some of the country’s most stringent environmental policies—much stricter than existing federal rules—dictating that efficiency will continue to be a major consideration in selecting equipment for retrofit projects, regardless of potential federal policy changes.

VFD Story

Centrifugal pumps installed in HVAC systems typically operate in variable load applications that see a fluctuation of flow requirements based on the heating or cooling load of a building at any given time. The original pumps specified for Astor Place were running at constant speed along with being oversized for the true operational demands of the building.

VFDs were the perfect solution to address the pump oversizing. Even at peak cooling load, electricity reduction was more than 50 per cent compared to constant-speed pumps, according to the test data. VFDs do bring the most benefit in terms of energy consumption. The pumps consumed just enough energy to provide proper service for that part of the cooling loop. In addition to the VFD testing, the research team set up four retrofit combinations to collect additional data to assess the energy savings contribution of the various retrofit measures installed at the same time. The following scenarios were analysed:

  • VFD and pressure independent control valves (PICVs) in operation (final post-retrofit condition)
  • VFD in operation; original air handling unit (AHU) valves
  • VFD bypassed; PICVs in operation
  • VFD bypassed; original AHU valves (replacement pumps and primary-secondary loop modification only)

The combination of VFDs and PICVs provided the most savings in terms of electricity consumption, detailed in images 4 through 6. “A robust monitoring effort was essential to developing these fundamental understandings and the data needed to form analyses and to develop energy conservation measures,” Waite said.

“This study further illustrates that replacing constant speed pumps with more appropriately sized equipment can significantly reduce their energy usage. Replacing the constant speed, constant flow primary HW and condenser water (CW) pumps provided estimated annual electricity savings of 20 per cent in primary HW pumping and 29 per cent in CW pumping,” Waite said in his thesis.

Doing the Math: With all retrofits considered, the total annual cooling pumping energy reduction was computed to be 36.1 percent compared to the original system (see Image 6).

The data analysis of the pre- and post-retrofit conditions formed the basis for the mathematical model to assess energy consumption, calculating the following:

  • pump power at thermal loads within monitoring range
  • pump power at loads beyond monitoring range
  • system hydraulic behaviour
  • pump power

The mathematical model can provide a fast and accurate energy assessment of a hydronic system. From there, the team can install sensors at various points and recommend specific system improvements that can immediately reduce energy consumption and costs.

Monitoring system behaviour at Astor Place yielded three primary benefits: determine if equipment was operating as designed; assess the amount of energy being used and the dynamic adjustments to the load’s demands; and gain a broader understanding of system behaviour, the last of which is most intriguing for Waite.

“This will allow us to develop theories on how systems behave as a whole rather than a collection of individual parts,” Waite said.

For Related Management Company, the granular focus of the project was insightful. The project gave the company the opportunity to establish a clear chain of cause and effect when dealing with energy efficiency while driving value to the condo owners through energy savings.

Future Implications

As owners seek to improve efficiency of building systems, HVAC upgrades are often last on the list due to perceived high upfront costs. The results from the Astor Place Energy Improvement Project can help inform decisions about new equipment and the potential for energy savings.

“It’s not cost effective to replace a large pump as a stand-alone efficiency measure,” Waite said. “But if your BMS tells you that over a decade a 25 hp pump never operated over 15 hp, you can replace it with properly sized equipment that’s both cost effective and energy efficient.”