Your Existing Rooftop Unit (RTU) Can Do More For You
Packaged Rooftop Units known as “RTUs” and other Air Handling Units (AHUs) are common in the majority of commercial buildings in Minnesota for Heating, Ventilation, and Air Conditioning (HVAC). They often have both natural gas for heating and electricity for fans, compressors, and damper operations, as well as cooling with condensers and refrigerants. RTUs may also be paired with separate condensers providing cooling, or condensers may be part of “split” system (e.g. paired with a furnace or fan coil unit). Components may be located on the roof, on the ground, or inside the building.
RTUs typically represent a significant portion of energy consumption for a building, especially if they are the primary means of heating and cooling. And, they likewise present several opportunities for energy conservation and savings. Further, you can realize lowered “peak demand” charges when lowering overall energy consumption and the monthly highest demand spikes which determine utility peak demand fees. And, while energy efficiency is a great reason to optimize your equipment, these updates can improve your tenants’ comfort, extend equipment life, and provide valuable operations and maintenance insights.
Maximizing Your Existing RTUs
Most RTUs and related equipment have an expected life of 15-20 years. If you have relatively new or midlife equipment, several retrofit opportunities can help to reduce your energy consumption and costs, often with incentives of utility rebates and grants available to help offset the cost of the system and installation.
Updating Controls and Components
Scheduling: Simply adding scheduled thermostats with aggressive temperature setbacks for unoccupied periods can make a major difference.
Advanced Sensing and Controls: However, even greater savings are available with more sophisticated building automation systems (BAS), which can help tie together multiple components in your system (vs. independent thermostats) for better management and orchestration. These advanced unified systems have evolved greatly in the past few years, and they have become more affordable and easy to retrofit to existing equipment, often with local wireless mesh networks to reduce wiring requirements and improve cross-device communications. Sub-zoning control can be added to help with more granular sensing and control of different spaces served by a single unit.
Outside Air Economizing Optimization: For RTUs and AHUs with functional Outside Air (OA) Economizers and actuators, two primary automated control sequences can contribute significantly to savings, and utility incentives can help. The following logic can enhance RTU efficiency in sensing and modulating Outside Air management.
Free Air Cooling with Outside Air: The system will monitor outside air temperature and humidity conditions in order to more precisely take advantage of the existing economizers of the AHUs. The system will employ logic across the units to maximize outside air for cooling, thereby minimizing compressor and fan-drive energy used for conditioning air (e.g. use early-morning cool air in summer to minimize morning cooldown, use Spring/Fall cool air for cooling in the “shoulder” seasons.)
Demand Control Ventilation (DCV) with CO2 Sensing: Ensures the optimal amount of energy is used to manage outside air to reach CO2 targets, for healthy and safe indoor air quality (IAQ), with precise sensing and control. Typically, systems are over-engineered to maximum-occupancy settings, calling for excessive outside air intake and corresponding conditioning (energy waste). In addition to energy-saving, maintaining healthy IAQ levels enhances comfort, health, and productivity.
Remote Management: While some Web-based or “Smart” Thermostats offer remote access and select alerts, more-advanced systems provide advanced scheduling, automation, performance monitoring, data, and diagnostics capabilities.
Data Trending & Insights: Provides an understanding of building system operations by aggregating data points. This is useful when analyzing system performance over time and service planning. ( e.g. system automatically analyzes the time required for individual spaces to reach the desired setpoint, and then self-adjusts the optimal start period in order to reach it). Additional information such as equipment runtime can assist in discovering existing potential conditioning issues in various spaces based on sensing.
System Alerts & Remote Diagnostics - Alerts can easily be set to contact appropriate facility personnel when select equipment is operating outside of normal ranges (e.g. discharge air temperature). The alert types can be simply customized in the settings including adding and removing team members. Having 24/7 remote access to the current and historical data of all of your major mechanical equipment helps the user quickly identify and begin the diagnostic process. Results are often reduced maintenance and operations costs by minimizing truck rolls and onsite assessments as well as prolonging equipment longevity through quick diagnosis and resolution of operational issues.
Indoor Air Quality (IAQ) Sensing & Management:
Sensing can now go well beyond temperature and humidity, to include CO2, Volatile Organic Compounds (VOCs). and other air quality indicators. Moving beyond sensing, you can retrofit your HVAC with active air purification solutions (such as UVC lighting or bipolar ionization) to improve the quality of the air, reducing pathogens, allergens, mold, mildew, and other detracting factors.
High-efficiency Motors
Upgrading the motors in your RTU to high-efficiency motors can have a significant energy use impact.
Variable Frequency Drives (VFDs):
VFDs offer the ability to modulate with greatly reduced energy consumption and more accuracy in fine-tuning fan and compressor operations.
Replacing Your RTUs
When the performance of your equipment declines and repair/maintenance costs become a recurring issue, you have several options for enhancements when looking to replace the units.
Revisit sizing and specs to match your space demand and requirements.
High Efficiency: While a new standard unit will be more efficient than its predecessor, seek out high-efficiency or ultra-high-efficiency units to achieve ratings and savings for the life of the equipment.
Go Heat Pump RTU! With the increasing costs of natural gas and the move toward electrification, an air-source heat pump is worth considering as an RTU replacement. We find adding this energy-efficient electric heat source adds value.
If you’re interested in assessing your current systems and exploring the benefits of enhanced controls systems, components, or replacement options, contact Minify Energy.