Heating and cooling costs are one of the most important variables when it comes to measuring a building’s overall operating expenses. An AHU’s heating, cooling, and fan performance can significantly impact the bottom line. And because these systems are responsible for temperature control and moisture regulation, ventilation, filtration, and building pressurization, they’re vital to the health and productivity of building occupants.
When your AHUs aren’t in optimal condition, they drive excess energy consumption or, even worse, potentially cause problems with indoor environmental quality (what is known as “sick building syndrome”).
Standard Variables for AHU Performance and Efficiency
Here are the standard variables measured to determine AHU performance and efficiency:
Temperature
In regular operation, systems may appear to operate correctly, but temperature setpoints and supply air temperatures may fluctuate under heavy load (at high or low temps). There are often capacity issues with heating and cooling coils, as well as issues with the sequence and controls. When these issues go unnoticed, the result is energy waste.
Moisture
Problems with temperature control can also lead to potential moisture issues that can cause serious problems with the environmental health of your facility. Moisture levels provide another key metric for understanding your AHU’s performance.
Energy Use
Energy efficiency packages, also called economizers in the industry, save energy through passive cooling using outside air. Systems based on the ASHRAE 90 are a code requirement for most AHU systems. When these systems aren’t properly calibrated, they can be the opposite of “economizers,” becoming a significant source of energy waste.
Ventilation
Ventilation is the amount of outside air that has to be moved inside a building. Ventilation requirements are determined by occupancy and square footage. In the US, the most widely applicable standard is ASHRAE Standard 62.1. Under-ventilation is problematic because it can lead to health and productivity concerns. On the other end of the spectrum, over-ventilation drives cost due to increased heating or cooling.
Fan Operation
Fan efficiency isn’t a factor that gets a lot of attention, but it can impact the overall efficiency and drive cost. After all, fans (and motors) are often the largest energy consumers in AHU systems. Fan systems should deliver an optimum pressure level. If those levels become too high or low, occupant health could be at risk, and heating and cooling may be uneven. In the case of overpressure, you could incur significant excess operating costs.
Compressors
For systems that include compressors, the efficiency of these components plays a big part in energy usage. Poorly designed systems can result in premature equipment failure and temperature instability. Oversized compressors can also affect latent cooling capabilities, which can cause moisture issues, while underpowered systems can be overworked, which can lead to system failure.
Measuring Basic AHU Performance and Efficiency Manually
You can measure AHU performance without using a software and sensor suite or installing a controller system. It’s not quick and easy, but it’s possible. Start by measuring temperature and humidity at both inlet and outlet. Then measure the barometric pressure. You can then use temperature and barometric pressure to calculate air density. Then you multiply density by volume flow rate to determine mass flow. Sensible heat duty can be determined by multiplying mass flow by temperature difference. Latent heat is a bit more complicated to calculate but it can be done by plotting inlet and outlet air conditions on a psychrometric chart and reading the delta in water content inlet to outlet and multiplying it by air mass flow to get the condensation rate. To arrive at latent duty, multiply the condensation rate by the latent heat of vaporization.
AHU Controllers
The modern approach to AHU performance optimization involves DDC controller systems. DDC Controllers rely on a series of sensors to measure temperature, moisture, energy use, ventilation, fan operation, and compressor duty cycles. Based on these inputs, these systems identify inefficiencies and provide alerts to allow personnel to make needed adjustments. Some systems have built-in intelligence to make basic operational adjustments automatically to keep systems within optimal operational parameters.
Why Optimize Your AHUs
Keeping AHUs operating at peak efficiencies in a commercial setting can be complicated, but the impacts can be significant in terms of overall energy savings. According to a 2009 Department of Energy study, the commercial sector spent $80.7 billion on energy for HVAC, and that figure represents more than 40% of overall energy expenditures. The impact of AHU optimization can run into the tens of thousands of dollars per year for an individual facility. There are also knock-on positives worth noting, including increased occupant comfort, improved work productivity, and reduced environmental impacts.
Kinetix Air Streamlines, Accelerates, and Cuts Costs of AHU Manufacturing
Custom air handler manufacturing is competitive, and traditional selection software only helps manufacturers do part of the job. The Kinetix Air AHU manufacturing platform unifies all aspects of custom AHU sales, design, manufacturing, shipping, service, workflow management, and much more. It automates repetitive and time-consuming parts of the process – cutting your level of effort and reducing risk from errors. Kinetix Air cuts design time by 75% and reduces validation, pricing, submittal, and BOM package time to near zero, saving you more than 20 hours per AHU for an average savings of $200K per year. With a unified, integrated solution like the Kinetix Air AHU selection software platform, you can design/select and price an air handling unit that meets any customer specification in less than an hour and quickly make changes to the model as they come up.
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