In this article, we’ll explain the inner workings of both Active and Passive Solar Water Heaters, examining their advantages, disadvantages, and real-world applications.
Active Solar Water Heaters are a marvel of engineering that relies on fluid circulation, advanced controls, and the tireless power of pumps to efficiently warm water for diverse applications in commercial and residential buildings. On the flip side, Passive Solar Water Heaters takes a more elegant, simplified approach, using nature’s thermosyphon principle to create a self-sustaining flow of warm water.
Solar water heaters are described by the type of solar collector and circulation system that they use.
Active Solar Water Heaters
Active solar water heaters come in two main types: direct circulation systems and indirect circulation systems. These systems harness solar energy to heat water for various applications, such as domestic hot water, space heating, or industrial processes. Let’s delve into the specifics of each type:
Active Solar Water Heating System
Direct Circulation Systems
Direct circulation systems, also known as open-loop systems, involve the direct transfer of water from the collector to the end-use application without an intermediate heat transfer fluid. This simplicity makes them suitable for regions with mild climates where freezing is not a concern.
Direct Circulation Solar Water Heating Diagram
Indirect Circulation Systems
Indirect circulation systems, also known as closed-loop systems, use an intermediate heat transfer fluid to transfer thermal energy from the solar collectors to the water in the storage tank. This allows them to operate in colder climates without the risk of freezing.
Passive Solar Water Heaters
A Passive Solar Water Heater operates without the need for mechanical pumps or electrical components. These systems are less expensive than Active systems but are usually not as efficient. Without the need for moving parts, these systems can be more reliable and last longer.
Passive Solar Water Heating System
Thermosyphon Systems
Like an active system, a passive system relies on a solar collector to absorb sunlight. This collector is often a dark-colored, heat-absorbing material like metal or special coatings on a surface. In a passive system, the sunlight heats the water directly without the use of a separate fluid. The collector absorbs the solar energy, and this heat is transferred directly to the water circulating through or stored in the system.
Thermosyphon Principle
The core principle behind passive solar water heaters is thermosiphon. As water absorbs heat, it becomes lighter and rises. Simultaneously, colder, denser water descends to replace it. This creates a natural circulation of water through the system.
Evacuated Tube Solar Collector
The heated water typically rises from the collector to a storage tank located at a higher elevation. This tank is positioned above the collector to facilitate the thermosiphon effect. The warm water is stored in this tank until it is needed.
When hot water is required, it is drawn from the storage tank. The cold water that enters the collector to replace it completes the natural circulation loop, creating a continuous flow of warm water if there is sunlight.
Passive solar water heaters are characterized by their simplicity and reliance on natural processes. They are often used in residential and small-scale applications, providing a cost-effective and energy-efficient way to obtain hot water. While they may not be as suitable for large-scale commercial projects, the principles of passive solar design can still be applied to aspects of building construction to enhance energy efficiency and reduce reliance on traditional heating systems.
Storage Tanks and Solar Collectors
Most solar water heaters require a properly insulated storage tank. These tanks typically feature an extra outlet and inlet that are linked to the collector. In two-tank configurations, the solar water heater heats the water in advance of it entering the standard water heater. Conversely, in one-tank setups, the backup heater is integrated with the solar storage within a single tank.
Collector Types for Solar Water Heaters
Solar water heaters for residential properties usually use three different types of collectors to capture sunlight and convert it into heat for heating water. These collectors are critical components that determine the efficiency and performance of the system. Here are the main types of collectors used in solar water heaters:
Flat-Plate Collectors
Flat-plate collectors are the most common type and consist of a flat, insulated box with a transparent cover (usually glass) on top. Inside the box is a dark absorber plate, typically made of metal or other materials with high thermal conductivity.
Sunlight passes through the transparent cover and strikes the absorber plate, which absorbs the solar energy and converts it into heat. The heat is then transferred to a fluid (usually water or a heat transfer fluid) flowing through tubes attached to the absorber plate.
Flat-plate collectors are versatile and used in both residential and commercial solar water heating systems. They are suitable for moderate climates and are effective for domestic hot water applications.
Evacuated Tube Collectors
Evacuated tube collectors consist of rows of glass tubes with an outer and inner tube. The air is evacuated from the space between the tubes to create a vacuum, reducing heat loss through conduction and convection.
Evacuated Tube Heat Pipe Collector
Like flat-plate collectors, sunlight passes through the outer glass tube and strikes an absorber within the inner tube. The absorber transfers the heat to a fluid circulating within the tube.
Evacuated tube collectors are more efficient than flat-plate collectors, especially in colder climates. The vacuum insulation minimizes heat loss, allowing them to capture solar energy even on cloudy days.
Evacuated tube collectors are commonly used in colder climates and are suitable for both residential and commercial applications.
Integral Collector Storage (ICS) Systems (Passive System)
ICS systems, also known as batch or breadbox collectors, integrate the solar collector and the storage tank into one unit. The collector is a black tank with a transparent cover, or dark tubes in an insulated tank. Water is heated directly in the collector, eliminating the need for separate pipes or heat exchangers. The heated water is stored in the same unit until it is used.
ICS systems are simple and cost-effective, often used in residential settings for domestic hot water applications. There should be a tempering valve that allows cold water to be mixed with the hot water coming from the tank.
They are used in open loop systems and aren’t suitable for cold climates.
The choice of collector depends on factors such as climate, available space, and the specific requirements of the solar water heating system. Each type of collector has its advantages and disadvantages, and the selection is often tailored to meet the needs of the project.
In hospital construction, isolation rooms play a crucial role in preventing the spread of infectious diseases and protecting both patients and healthcare professionals. There are positive and negative pressure room designs depending on the patient’s condition.
If the patient needs to be protected from possible contamination because of a compromised immune system, the room is put under positive pressure. If the patient has a contagious disease, then the room will be under negative pressure to prevent the spread of that disease. We’ll show you four different isolation room configurations. Here are key aspects of how a hospital isolation room typically works:
If you prefer to watch the video version of this presentation, then scroll to the bottom.
Positive Pressure Isolation Room
In hospital construction, positive pressure isolation rooms are designed to protect patients who are particularly susceptible to infections because of a reduced immune system.
The key characteristic of a positive pressure isolation room is that the air pressure inside the room is maintained at a higher level than that in the surrounding areas. This prevents external contaminants from entering the room.Â
Positive Pressure Isolation Room
In our example the supply air is delivered by a constant volume terminal with a reheat coil. The supply air has been calculated at 12 air changes per hour in accordance with ASHRAE Standard 170, which equates to 400 CFM (190 L/s). The toilet room will consume 60 CFM of that, while the return air will use a valve to ensure that there is always a 100 CFM difference. This additional 100 CFM creates a positive pressure within the room and ensures that nothing enters from the corridor.
Positive pressure rooms have a dedicated air supply system that provides filtered and clean air into the room. The ventilation system often includes HEPA filters to remove airborne particles and pathogens, ensuring that the air entering the room is of high quality.
The direction of airflow is carefully controlled to maintain positive pressure. Air generally flows from the isolation room towards adjacent spaces, minimizing the risk of contaminants entering the room.
Monitoring Systems
Pressure Monitoring: Continuous monitoring of air pressure differentials is essential. If the pressure drops, alarms are triggered to alert healthcare staff to take corrective action. The monitor can be connected to a building automation system.Â
Hospital Isolation Room Monitor
Located in the hallway outside the room is a monitor that reveals what is happening with the pressure differential, temperature, air changes per hour, and many other metrics. The monitor will have sensors located in the room and in the corridor to track the pressure differential.
Access to positive pressure isolation rooms is restricted to authorized personnel to minimize the risk of contamination.
Anterooms
Some positive pressure rooms may have an airlock system with two sets of doors to further reduce the risk of air exchange with the external environment. You can see that the volume of air is the same, except now there is an extra door and small ante room.Â
Positive Pressure Hospital Isolation Room with Ante Room
We could also pressurize the Ante Room by putting a supply air grille in the room. An additional exhaust grille is added to the isolation room. The V-1 terminal valve will adjust as needed to maintain the required pressure differential.
Positive Pressure Ante Room in Isolation Room
Negative Isolation Room
A negative isolation room is also referred to as Airborne Infection Isolation (AII) Room. Negative Pressure Isolation rooms are designed with negative air pressure relative to surrounding areas to quarantine patients with infectious disease. This helps prevent small airborne contaminants from escaping the room and spreading to other parts of the facility.
Negative Isolation Patient Room in Hospital with Ante Room
High-efficiency particulate air (HEPA) filters are used to capture and filter out airborne pathogens. The ventilation system ensures a controlled flow of air to maintain the required air changes per hour (ACH) for the specific isolation room.
Exhaust valve V2 is used to pull air in from the corridor and the patient room into the Ante Room. This provides an additional barrier to contamination when entering or exiting the room. The Ante Room is provided with 10 air changes per hour to create a negative pressure. Valve V1 will maintain the proper pressure differential.
Monitoring and Alarm Systems
Continuous monitoring of temperature, humidity, and pressure differentials ensures that the isolation room is operating within the specified parameters. An alarm system alerts staff to any deviations from the desired conditions, prompting quick response and correction.
Choosing the Right HVAC System: When to Use VAV vs. Constant Volume Systems
Selecting the appropriate HVAC (Heating, Ventilation, and Air Conditioning) system for your building is a critical decision that can impact energy efficiency, occupant comfort, and operating costs. Two common options are Variable Air Volume (VAV) systems and Constant Volume systems. In this video, we’ll help you understand when it’s best to use a VAV system or a Constant Volume system, depending on your specific requirements and goals.
If you prefer to watch the video version of this presentation, then scroll to the bottom.
VAV vs. Constant Volume Zoning Differences
Efficient zoning can make a world of difference in terms of energy consumption, comfort, and cost savings. When comparing Variable Air Volume (VAV) systems to Constant Volume systems, it’s essential to understand the significant zoning differences between these two approaches. In this video, we’ll delve into the nuances of zoning in VAV and Constant Volume systems and how they impact your building’s HVAC performance.
VAV vs Constant Volume HVAC Systems
Zoning in Constant Volume and VAV Systems
VAV Individual Zone Control
Variable Air Volume (VAV) systems excel in providing precise zoning control. Here’s how zoning works in VAV systems:
VAV systems allow for individual temperature control in various zones or spaces within a building. Each zone has its own VAV box, which modulates the airflow to meet specific heating and cooling demands. As you can see in this diagram each room has its own controller and can determine whether they want heating or cooling.
Zoning in Constant Volume Systems
Constant Volume systems have limitations when it comes to zoning:
In Constant Volume systems, the same airflow is delivered to all zones simultaneously. This lack of individual control can lead to variations in temperature and comfort levels. Constant Volume systems struggle to adapt to changes in occupancy and temperature requirements within different zones. They are less suited for buildings with diverse thermal loads. You can see in this diagram that all rooms have to be in either cooling or heating mode, there is no option foe one room to be in cooling while another is in heating mode.
Temperature and Air Volume Control
With a VAV system the temperature and occupancy sensors continuously monitor conditions in each zone. The VAV system adjusts airflow and temperature, ensuring that comfort levels are maintained in each separate zone.
VAV System Minimum Zoning Layout – Additional Zone can be added to cover corner offices
With a constant volume system, the controller is in one of the spaces which can cause problems for other spaces if the room with the controller is unoccupied. This is when comfort complaints occur.
Energy Efficiency
Zoning in VAV systems contributes to energy efficiency by delivering conditioned air precisely where and when it’s needed, reducing unnecessary heating and cooling.
Constant Volume systems maintain a consistent airflow, even when zones require less heating or cooling. This inefficiency can lead to higher energy consumption and costs.
VAV System Benefits of Effective Zoning
Efficient zoning, as seen in VAV systems, offers several advantages:
Customized Comfort
Occupants enjoy personalized comfort levels in each zone, enhancing satisfaction and productivity.
Energy Savings
Zoning reduces unnecessary energy consumption, leading to lower utility bills and a reduced carbon footprint.
Optimized Equipment Lifespan
HVAC equipment experiences less wear and tear when only operating as needed, potentially extending its lifespan.
Improved Air Quality
Better control over airflow can contribute to improved indoor air quality by minimizing temperature variations and balancing humidity levels.
When to Use a VAV System
Variable Air Volume (VAV) systems are versatile and energy-efficient, making them a popular choice for various applications:
1. Large and Diverse Spaces: VAV systems shine in buildings with multiple zones and varying occupancy levels, such as office buildings, shopping centers, or hotels. They can adapt airflow and temperature settings to meet specific zone requirements.
2. Energy Efficiency Goals: When prioritizing energy efficiency and sustainability, VAV systems are the preferred option. They minimize energy consumption by supplying only the necessary airflow to each zone, reducing operating costs and carbon emissions.
3. Occupant Comfort Matters: If maintaining precise temperature control and occupant comfort is crucial, VAV systems offer superior performance, ensuring consistent comfort levels throughout the building.
4. Cost Savings Over Time: While VAV systems may have a higher initial cost due to their complexity, they offer substantial long-term savings through reduced energy bills and extended equipment lifespan.
When to Use a Constant Volume System
Constant Volume systems have their place in certain scenarios:
Smaller and Simpler Spaces
In smaller buildings or spaces with consistent occupancy and minimal temperature variations, Constant Volume systems can be cost-effective and straightforward to install.
Limited Budget
If you have budget constraints and the building’s requirements align with the capabilities of a Constant Volume system, it may be a more economical choice upfront.
Minimal Zone Control Needed
Buildings with uniform temperature and airflow requirements throughout can benefit from the simplicity of Constant Volume systems.
Ease of Maintenance
Constant Volume systems tend to have lower maintenance costs due to their straightforward design, making them suitable for facilities with limited maintenance resources.
Making the Right Choice
Selecting between VAV and Constant Volume systems involves a careful analysis of your building’s specific needs, goals, and constraints. Here’s a step-by-step approach to help you make the right choice:
1. Evaluate Building Size and Complexity: Assess the size, layout, and diversity of your building’s zones to determine whether VAV or Constant Volume systems are better suited.
2. Define Energy Efficiency Objectives: If energy efficiency and sustainability are top priorities, VAV systems are likely the better choice.
3. Consider Comfort Requirements: Think about occupant comfort expectations. VAV systems excel in delivering precise comfort control.
4. Analyze Initial Budget and Long-Term Costs: Compare the initial investment and long-term operating costs of both systems to make an informed financial decision.
5. Consult with HVAC Experts: Seek guidance from HVAC professionals who can provide tailored recommendations based on your building’s unique characteristics.
Choosing the Right Zoning Approach
When deciding between VAV and Constant Volume systems, consider your building’s size, layout, occupancy patterns, and energy efficiency goals. Effective zoning is a critical factor in creating a comfortable, cost-effective, and environmentally friendly indoor environment.
While Constant Volume systems may have their place in smaller, simpler buildings, VAV systems offer superior zoning capabilities for larger, more complex structures with diverse temperature needs. Consulting with HVAC professionals can help you make an informed decision and optimize your zoning strategy to achieve maximum comfort and energy efficiency.
Conclusion
The decision of whether to use a VAV or Constant Volume system should align with your building’s specific needs, budget, and sustainability goals. Both systems have their strengths and weaknesses, so careful consideration and expert guidance will lead you to the HVAC solution that best serves your facility and its occupants.
Zoning differences between VAV and Constant Volume systems can significantly impact your building’s HVAC performance. Precise zoning in VAV systems ensures individual comfort control and energy efficiency, while Constant Volume systems struggle to adapt to varying zone requirements. By understanding these distinctions, you can make an informed choice that aligns with your building’s specific needs and sustainability objectives.
In this article we’ll show you some basic DDC control points used for the control of an air handler. Your situation may be different, but this will give you an idea of the optional points that can be used for various sequences of operation. The examples will build the DDC controls one point at a time and explain its purposes as we build the control diagram.
First we’ll start with a constant volume air handler that has a supply and return fan. Then, we’ll build this AHU to be a variable volume air handler. The advantage of a VAV air handler is that it can optimize the diversity of the zones to save energy by reducing fan speed. There are heating hot water and chilled water coils.
We’ll also build a controls points list as we add the various DDC components for controlling the air handler.
If you prefer to watch the video version of this presentation, then scroll to the bottom.
Control Dampers
Three dampers are added, which include the outside air, return air, and exhaust air dampers. These dampers will have actuators that will allow the DDC controls to adjust the damper positions to meet the system requirements. They will be actuated by 24 volts power. See Control Dampers on Amazon.
Temperature Sensors – DDC Controls
Return Air Temperature Sensor
The return air temperature sensor monitors the temperature of the air returning to the HVAC system from the conditioned space. This information is essential for assessing the thermal conditions within the building. The sensor provides input to the HVAC DDC controls, helping it to regulate the temperature by adjusting the heating or cooling output as needed. It contributes to the overall climate control strategy of the building.
Checkout
Mixed Air Temperature Sensor
The mixed air temperature sensor monitors the temperature of the air after it has been through the return air and outdoor air streams. This information is used to control the mixing of these two air streams to achieve the desired supply air temperature. In HVAC systems, maintaining the right temperature in the supply air is crucial for providing comfortable conditions within the building. The mixed air temperature sensor helps optimize the operation of heating and cooling components to achieve the desired supply air temperature.
By accurately measuring the mixed air temperature, the HVAC system can adjust the mixing ratio of return air and outdoor air to maximize energy efficiency. This is important in commercial buildings where energy costs are a significant consideration.
The mixed air temperature sensor plays a role in preventing issues such as coil freezing or overheating. By monitoring the temperature of the air entering the HVAC system, it helps ensure that the components, like heating or cooling coils, operate within safe temperature ranges.
Supply Air Temperature Sensor
The primary function of the supply air temperature sensor is to continuously monitor the temperature of the air being discharged from the air handler. This sensor provides real-time feedback on the actual temperature of the conditioned air.
The supply air temperature sensor is an integral part of the HVAC control system. The data from the sensor is used as input for the control algorithms that regulate the operation of heating or cooling components to achieve and maintain the desired supply air temperature.
The sensor’s feedback is crucial for the control system to adjust the operation of heating or cooling elements, such as coils or dampers, to achieve the setpoint supply air temperature. This regulation ensures that the conditioned air delivered to the occupied spaces meets the specified comfort requirements.
By accurately measuring the supply air temperature, the HVAC system can optimize its operation for energy efficiency. This is essential for managing energy consumption and operational costs in commercial buildings.
The supply air temperature sensor helps prevent issues such as overheating or underheating of the conditioned air. If the temperature deviates from the setpoint, the control system can take corrective actions to ensure the air supplied to the building is within the desired temperature range.
Outside Air Temperature Sensor
The outside air temperature sensor is crucial for the control of economizer systems in air handlers. Economizers utilize outdoor air for cooling when the outdoor conditions are favorable. The sensor helps determine whether the outdoor air is suitable for free cooling, allowing the system to reduce reliance on mechanical cooling and improve energy efficiency.
The sensor provides input for temperature reset strategies. The supply air temperature setpoint may be adjusted based on the outdoor air temperature to optimize the system’s efficiency. This can help achieve energy savings by adapting to varying external conditions.
In cold climates, the outside air temperature sensor is used to control preheating systems. It ensures that the incoming outdoor air is appropriately conditioned to prevent freezing and improve the efficiency of the HVAC system.
The sensor plays a role in freeze protection strategies. If the outside air temperature drops to levels that could lead to freezing conditions, the system can take preventive measures, such as adjusting the heating elements or modulating the supply air temperature to avoid damage to components.
In systems with heat recovery units, the outside air temperature sensor helps optimize the efficiency of heat recovery. The sensor provides input for controlling the flow of outdoor and exhaust air to maximize energy transfer between the air streams.
The outside air temperature sensor may also be used in conjunction with cooling towers. It provides data to control the operation of cooling towers based on the outdoor conditions, ensuring efficient cooling when needed.
Outdoor air temperature can impact humidity levels. The outside air temperature sensor may contribute to humidity control strategies by influencing the operation of humidification or dehumidification systems based on external conditions.
Space Temperature Sensor
The primary function of the space temperature sensor is to continuously monitor the temperature within the occupied zone. This sensor provides real-time feedback on the actual temperature where building occupants are present.
The space temperature sensor is an integral part of the HVAC control system. The data from the sensor is used as input for the control algorithms that regulate the operation of heating or cooling components to achieve and maintain the desired space temperature.
The sensor’s feedback is crucial for the control system to adjust the operation of heating or cooling elements, such as terminal units or dampers, to achieve the setpoint temperature in the occupied zone. This regulation ensures that the space remains within the specified comfort range.
The space temperature sensor can be integrated with occupancy sensors to adjust the temperature based on occupancy status. During unoccupied periods, the system may enter setback modes to conserve energy, and the space temperature sensor plays a role in this strategy.
Current Transducer
The current transducer is used to confirm that the fan is running. The current transducer detects current flowing through the electrical power cables serving the fan. There will be one for the supply fan and another for the return fan. Checkout
Filter Differential Pressure Sensor
The filters differential pressure sensor monitors the pressure drop across air filters in the HVAC system. As filters accumulate dust and particulate matter, the pressure drop across them increases. An increase in pressure drop indicates that the air filters are becoming clogged with contaminants. The sensor provides real-time feedback on the differential pressure, serving as an indirect measure of filter cleanliness. Checkout Filter Differential Pressure Sensors on Amazon.
By continuously monitoring the differential pressure, the sensor helps determine when the air filters have reached a point where they need replacement or cleaning. This information is crucial for maintaining optimal system performance and indoor air quality.
Regularly changing or cleaning air filters in response to the information from the differential pressure sensor helps maintain the HVAC system’s energy efficiency. Clean filters allow for proper airflow, reducing the system’s energy consumption.
Control Valves – DDC Controls
The primary function of the chilled water control valve is to regulate the flow of chilled water through the system to achieve the desired cooling effect. It controls the amount of chilled water entering the cooling coils. Checkout Motorized Ball Valves on Amazon.
The chilled water control valve helps match the cooling capacity of the HVAC system to the building’s actual cooling load. This ensures that the system operates efficiently and doesn’t waste energy by overcooling spaces.
By modulating the flow of chilled water based on the cooling demand, the control valve contributes to energy efficiency. It helps prevent unnecessary energy consumption by delivering the right amount of cooling precisely when and where it’s needed.
Smoke Detector
The primary function of a smoke detector in an air handler is to detect the presence of smoke in the air circulating through the HVAC system. Early detection is crucial for initiating prompt responses to potential fire situations.
Smoke detectors in air handlers contribute to fire prevention by identifying the presence of smoke particles before an actual fire develops. This early warning allows for timely intervention to address potential fire hazards.
If the smoke detector detects smoke, it is typically integrated into the HVAC system’s control logic. Once activated, it can initiate an automatic shutdown of the air handler to prevent the spread of smoke throughout the building.
Smoke detectors are equipped with alarm signaling capabilities. When smoke is detected, the smoke detector can trigger audible and visual alarms, alerting building occupants and personnel to the potential fire hazard.
Airflow Measuring Station
The airflow measuring station ensures that the proper amount of outside air enters the air handler by adjusting the outside air damper.
High Static Pressure Switch
High duct-static pressure poses challenges in the event of a building fire when fire dampers are activated. During a fire, the closure of fire dampers results in downstream duct sensors detecting a pressure drop. Subsequently, these duct pressure sensors transmit signals to increase the air handler’s speed even further to restore normal operation.
However, due to the closed fire dampers, the ramping up of the air handler causes an increase in duct pressure upstream of the fire dampers. This increase reaches a threshold where a high static pressure switch intervenes, cutting power to the Variable Frequency Drive (VFD) and transmitting a signal to the Direct Digital Control (DDC). Notably, switches in this specific application adhere to specifications, requiring manual reset and dual outputs: one for disengaging power to the VFD and another for signaling the DDC controls.
Variable Frequency Drives (VFD’s)
One of the primary functions of a VFD on the supply fan is to enhance energy efficiency. The VFD allows the speed of the fan motor to be adjusted based on the actual demand for airflow. This prevents the fan from running at full speed constantly, which can result in energy savings, especially during periods of partial load. Checkout Variable Frequency Drives on Amazon.
The VFD provides precise control over the speed of the supply fan, allowing for fine adjustments to the airflow. This is particularly beneficial in systems with variable air volume (VAV) requirements or in response to changing building loads. The ability to modulate the fan speed ensures that the system meets the specific ventilation and comfort needs of the space.
Soft Starts and Stops
VFDs enable soft starts and stops for the supply fan motor. This reduces mechanical stress on the motor and the associated components, extending the lifespan of the equipment. The gradual acceleration and deceleration also contribute to smoother operation.
In response to changes in the building’s heating or cooling requirements, the VFD adjusts the fan speed dynamically. This allows the HVAC system to respond quickly and efficiently to fluctuations in temperature or occupancy, maintaining optimal conditions within the building.
VFDs on supply fans can be integrated with building automation systems to control the air pressure within the HVAC system. This is particularly important in systems with variable air volume, where maintaining the right pressure helps optimize the performance of terminal units and other components.
The ability to adjust the speed of the supply fan based on demand contributes to significant energy cost savings over time. By avoiding unnecessary energy consumption during periods of low demand, a VFD helps keep operational costs in check.
Many energy codes and standards encourage or require the use of VFDs in HVAC systems to meet energy efficiency goals. By incorporating a VFD on the supply fan, a system can align with these codes and standards, ensuring compliance.
DDC Control Points for VFD
The specific Direct Digital Control (DDC) control points for a Variable Frequency Drive (VFD) on a supply fan in an HVAC system can vary based on the system design, the control strategy employed, and the building’s requirements. However, here are some common DDC control points associated with a VFD on a supply fan:
Setpoint Control: Fan Speed Setpoint: The desired speed or frequency at which the VFD should operate the supply fan. This setpoint can be adjusted based on the building’s heating, ventilation, and air conditioning needs.
Feedback Signals: Actual Fan Speed: The real-time speed of the supply fan as measured by sensors. This feedback signal allows the DDC controls to compare the actual speed with the setpoint for precise control.
Motor Current: Monitoring the current drawn by the fan motor provides information on the motor’s load. Abnormal current levels may indicate issues such as mechanical problems or belt tension.
Safety and Fault Monitoring: Motor Overload Protection: DDC controls can be programmed to monitor motor current and provide protection against overloads. If the current exceeds a specified threshold, the system can take corrective actions or initiate an alarm.
VFD Faults
Monitoring for faults in the VFD, such as overvoltage or overcurrent, and providing alerts or triggering safety protocols in case of a fault.
Soft Start and Stop Parameters: Acceleration/Deceleration Time: Controlling the rate at which the fan motor accelerates or decelerates to prevent sudden starts or stops, reducing stress on the equipment.
Pressure Control: Duct Pressure Setpoint: In systems with variable air volume (VAV), the DDC controls may control the VFD based on the desired pressure setpoint in the ductwork. This ensures proper air distribution and terminal unit performance.
Occupancy and Schedule Control: Occupancy Status: Integration with occupancy sensors to adjust the fan speed based on the building’s occupancy status, optimizing energy usage.
Scheduling: Modifying the DDC Controls setpoint or operation schedule of the VFD based on the time of day or specific building requirements.
Energy Efficiency Measures: Demand-Based Control: Adjusting the fan speed based on the actual demand for conditioned air, optimizing energy usage.
Energy Monitoring: Tracking energy consumption and providing data for analysis to identify opportunities for further efficiency improvements.
Air Handler DDC Controls Points List
Return Air Relative Humidity Sensor
The primary function of the return air relative humidity sensor is to continuously monitor the relative humidity level of the air that is being drawn back into the HVAC system from the occupied spaces.
The sensor is an integral part of the HVAC DDC controls system. The data from the return air relative humidity sensor is used as input for control algorithms that regulate the operation of humidification or dehumidification components to achieve and maintain the desired indoor relative humidity level.
The feedback from the sensor is essential for the control system to adjust the operation of humidification or dehumidification elements, such as steam humidifiers or cooling coils, to achieve the setpoint relative humidity. This control is crucial for maintaining a comfortable and healthy indoor environment.
If the return air relative humidity sensor detects that the indoor air is becoming too humid, the control system can take corrective actions to prevent issues such as condensation, mold growth, or discomfort for occupants.
Conversely, if the indoor air is too dry, the return air relative humidity sensor helps the control system adjust humidification measures to prevent issues like dry skin, respiratory discomfort, or damage to sensitive equipment.
Maintaining an appropriate relative humidity level contributes significantly to occupant comfort. The return air relative humidity sensor ensures that the HVAC system responds effectively to changes in humidity, providing a comfortable indoor environment.
The return air relative humidity sensor often works in conjunction with other sensors, such as temperature sensors and occupancy sensors, to provide a comprehensive understanding of the indoor environment. Integrated control strategies can then be employed to balance temperature and humidity for optimal comfort and energy efficiency.
Outside Air Relative Humidity Sensor
The primary function of the outside air relative humidity sensor using DDC controls is to continuously monitor the relative humidity level of the outdoor air before it enters the HVAC system.
The sensor is an integral part of the HVAC control system. The data from the outside air relative humidity sensor is used as input for control algorithms that regulate the operation of humidification or dehumidification components to achieve and maintain the desired indoor relative humidity level.
The sensor helps in controlling the humidity levels of the outdoor air that is brought into the building for ventilation purposes. This is particularly important for maintaining a comfortable indoor environment and preventing issues associated with excessively high or low humidity.
High Relative Humidity
If the outside air relative humidity is too high, the control system can take preventive actions to avoid introducing excessively humid air into the building. This helps in preventing indoor humidity issues and contributes to occupant comfort and health.
Conversely, if the outside air is too dry, the sensor helps the control system adjust humidification measures to prevent introducing overly dry air into the building. This is important for preventing issues related to dry skin, respiratory discomfort, and static electricity.
By accurately monitoring and controlling the humidity levels of the outdoor air, the HVAC system can optimize its operation for energy efficiency. This is crucial for managing energy consumption and operational costs in commercial buildings.
The outside air relative humidity sensor may work in conjunction with other sensors, such as temperature sensors and airflow sensors. Integrated control strategies can be employed to balance temperature and humidity for optimal comfort and energy efficiency.
In air handling units that use outdoor air for cooling or ventilation, the outside air relative humidity sensor plays a role in adjusting the humidity level of the mixed air. This ensures that the air supplied to the building is within the desired relative humidity range.
Understanding the function of the outside air relative humidity sensor is crucial for designing and maintaining HVAC systems that prioritize indoor air quality and occupant comfort in commercial buildings. It helps ensure that the system responds effectively to variations in outdoor humidity, contributing to overall comfort and health within the building.
