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Monday, December 23, 2024
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DDC Control of an Air Handler

MEP Academy Instructor
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DDC Control of an Air Handler

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.

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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
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.

DDC Control Points for an Air Handling Unit

How your House Plumbing Works

MEP Academy Instructor
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How your House Plumbing Works

In this article we’ll cover the workings of a typical household plumbing system, which is also applicable to some commercial buildings. Practically everything we do relies on plumbing, whether it’s washing your car, clothes, or dishes, and/or brushing your teeth before bedtime. The backbone of these activities is your home’s plumbing system, consisting of four key elements: waste drains, waste vents, potable water, and rainwater management.

Let’s explore each system individually and understand their functions. 

If you prefer to watch the video of this presentation, then scroll to the bottom.

Waste and Vent Sewer System

In most homes the sewer waste system is installed using ABS, PVC, or cast-iron drainpipes and vents. These pipes interconnect with fixtures like toilets, sinks, bathtubs, and showers. When a fixture is used, waste travels through these drainpipes, which are required to be sloped to keep things moving. The waste will ultimately reach the municipalities main drain beneath the street.

House Plumbing Diagram of Potable Water, Waste & Vent, and Rainwater.
House Plumbing Diagram of Potable Water, Waste & Vent, and Rainwater.

Periodically, you’ll come across clean-outs, like this one. These provide access to the inside of the pipes in case of a blockage and are required by your local code. In the United States, many homes have these cleanouts located outside for easier access by plumbers.

Fixture Units

Plumbing pipe sizes are based on what is called “Fixture Units”. Each type of fixture is given a fixture unit value that corresponds to a pipe size. The code contains a chart listing these values. See our other video on “How to Size Plumbing Water Pipes using Fixtures Units” as the process is similar for waste pipes. Main stacks range from three to four inches, depending on code requirements and municipal regulations. 

However, some homes lack municipal wastewater treatment services. In such cases, waste disposal is straightforward. The main drainpipe, which would typically lead to the municipal sewers, connects to a septic tank instead, often made of concrete or polyethylene. This tank separates solids from liquids before directing them to a leach field or drain field in the ground for natural solid filtration. Periodic pumping by a vacuum truck is necessary to ensure proper functionality.

Septic Tank for Homes without Municipal Sewer Systems
Septic Tank for Homes without Municipal Sewer Systems

Now, let’s delve into venting. For the effective operation of these fixtures and drains, a well-designed venting system is essential. When a toilet is flushed, for instance, the water’s downstream flow induces negative pressure. Vents play a crucial role in equalizing this pressure change, preventing issues such as gurgling and the siphoning out of water in pee traps. This prevention is vital to avoid the infiltration of sewer gases into your home.

These vents draw in air from the roof, and it’s imperative to keep them clear of bird nests and debris, or complications are guaranteed. 

Potable Drinking Water

Regarding potable water, it originates from the municipal water main buried in the street, like other services, and typically maintains a pressure range of 40 to 80 PSI. Every residence connected to this city’s water supply must feature an outdoor water meter and shut-off valve, like the one shown. This allows the city to determine how much water is consumed and to shut off services in cases of emergency or if service is discontinued. The incoming copper line is usually 3/4 to 1 inch in diameter, depending on the size of the home. The pipe enters the basement through the concrete slab, or through the first floor. This usually leads to another shut-off valve that is more accessible to the homeowner.

In the basement, first floor, or garage, we encounter the hot water heater and storage tank. Other designs may use tankless water heaters. Whether electric or gas-fed, this tank receives cold water, heating it before distributing it throughout the house, courtesy of the city’s water pressure. While some homes still use copper lines, new construction projects often utilize PEX piping due to its reliability and rapid installation. Some older homes may have galvanized pipe and fittings that tend to become clogged over time. We will suggest re-piping if you have old, galvanized pipes.

Private Well Water

How does one obtain water in the absence of municipal services? In rural regions, individuals rely on wells. A well is essentially a vertically drilled hole deep in the ground to tap into groundwater, which is pumped up. The pumped water undergoes a series of processes and filtration to ensure its drinkability. 

Private Well Water is used by 13 million US households
Private Well Water is used by 13 million US households

Public water systems comprise 90% of all water supplied. In areas without municipal services, wells are common. About 13 million US households get their water from private wells. 

The water you receive from your faucet might originate from distant sources spanning hundreds of miles. Public water systems commonly derive their supply from either surface water, like lakes and rivers, or from groundwater. The drinking water can be stored behind a dam, or in tanks before being pumped to your home. 

Rainwater Storm Systems

The final aspect is rainwater management. Historically, rainwater and sewage were combined, meaning rainwater and household waste flowed into the same sewer. However, modern practices have separated them to streamline water management. So, when it rains, the question arises: where does all this water go?

Rain falling on the house’s roof travels into the gutters. The primary role of gutters is to redirect water away from the house, preventing water infiltration. There may also be pool deck and area drain’s that drain to the streets storm drain system.

Alternatively, some people opt to collect the rainwater from the roof gutters into rainwater barrels for non-potable use, such as watering plants and flowers. 

Rainwater Collection system using barrels
Rainwater Collection system using barrels

Sewer Waste Treatment

Now, where does all the waste and rainwater go once it leaves your home?

The municipal waste and storm drain mains usually follow the road. The wastewater main will eventually reach a lifting station that pumps the wastewater back up to prevent it from going too deep into the ground. This is because the system is pitched downward to keep everything moving by gravity. The longer the distance from your home, the deeper the main gets, which is referred to as its invert elevation. 

Waste and Storm Drain Diagram
Waste and Storm Drain Diagram

In the context of underground plumbing mains, the term “invert elevation” refers to the elevation or height of the inside bottom surface of a pipe. It is the lowest point inside the pipe where the flow of wastewater or sewage is present. The invert elevation is a crucial measurement as it helps determine the slope or gradient of the sewer line.

The wastewater is sent to a treatment plant where the nasty stuff is filtered out before being dumped into a lake, river, or ocean.

Unfiltered Rainwater Storm Drain

The Rainwater storm drain flows into a nearby river, lake, or ocean without being filtered or treated. According to the EPA, rainwater runoff picks up fertilizer, oil, pesticides, dirt, bacteria, and other pollutants as it makes its way through storm drains and ditches – untreated – to our streams, rivers, lakes, and the ocean. Polluted runoff is one of the greatest threats to clean water in the U.S. That’s why it’s important not to dump anything in the storm drain that you wouldn’t want to be swimming in the lake or ocean with, or drinking. 

In essence, this is the fundamental process of how your plumbing system operates.

How your House Plumbing Systems Work

Automatic Transfer Switch

MEP Academy Instructor
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Automatic Transfer Switch

Maintaining uninterrupted electrical power is very important for some facilities and processes. Think of a hospital. What would happen if the power went out during a surgery? What would happen to a patient connected to oxygen or life support machine dependent on electricity?

If you prefer to watch the video of this presentation, the scroll to the bottom.

Whether it’s a hospital, a laboratory, a manufacturing facility, or any other critical infrastructure, a sudden utility power outage can have severe consequences. This is where Automatic Transfer Switches (ATS) can ensure the seamless transition to backup power sources. In this article, we’ll explore how ATS is employed to maintain power during utility outages and why they are a fundamental part of various construction projects.

How Automatic Transfer Switches Work

Automatic Transfer Switches are devices that monitor the quality of the primary power source, which is typically the utility grid, and automatically switch to an alternative power source when an outage is detected. Here’s how they work:

Automatic Transfer Switch (ATS) Wiring Diagram
Automatic Transfer Switch (ATS) Wiring Diagram

An ATS system is designed to connect to two power sources: the primary utility power and a secondary backup power source, often a generator. 

During normal operation, the ATS connects the load to the primary power source. The controller keeps a close eye on the quality of this power source.

ATS systems are equipped with sensing devices that continuously monitor the voltage and frequency of the primary power source.  When the controller detects an interruption in the primary power supply, it automatically initiates a transfer to the secondary source, typically a generator. This swift response is critical for critical applications such as hospitals and data centers. This transfer occurs in less than 1 second.

Switch Mechanism

The heart of the ATS is its switch mechanism, which is responsible for making and breaking electrical connections. It ensures that only one power source can be connected at a time, preventing any back feeding of power.

Automatic Transfer Switch Sequence of Operation
Automatic Transfer Switch Sequence of Operation

Before making the transfer to the secondary source, the ATS ensures that the generator’s output matches the utility power in terms of voltage, frequency, and phase. This synchronization is vital to protect sensitive equipment from damage.

Once the utility power is restored and stable, the ATS automatically switches the load back to the primary source, ensuring that the backup source is used only when necessary.

The Role of ATS in Commercial Construction

1. Hospitals: In hospitals, where uninterrupted power is critical for life-saving equipment, ATS systems ensure that surgeries, intensive care units, and other essential functions continue without interruption during power outages.

2. Laboratories: Research facilities and laboratories rely on precise and stable power for experiments and sensitive equipment. ATS systems guarantee that experiments aren’t compromised due to power disruptions.

3. Manufacturing Facilities: Manufacturers can’t afford production downtime due to power outages. ATS keeps assembly lines running smoothly and avoids costly interruptions.

4. Data Centers: Data centers house mission-critical data, and even a brief power interruption can lead to data loss. ATS is essential in these facilities to maintain uninterrupted operation.

5. Hotels: In the hospitality industry, guest comfort and safety are top priorities. ATS systems ensure that guests aren’t inconvenienced by power disruptions.

Critical Power Backup options using an ATS
Critical Power Backup options using an ATS

Conclusion

Automatic Transfer Switches are unsung heroes in the world of commercial construction. They play a vital role in ensuring uninterrupted power in critical applications, from hospitals to laboratories, manufacturing facilities, data centers, and beyond. For those in the construction industry, understanding the importance of ATS systems is key to delivering projects that meet the highest standards of reliability and safety. These unassuming devices are the backbone of power continuity in our modern world, making sure that when the lights go out, the show goes on.

How an ATS Switch Works

Chilled Water Pumping Options

MEP Academy Instructor
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Chilled Water Pumping Options

In this article we’ll discuss the three different pumping methods used in a central plant for the distribution of chilled water. This includes primary variable flow, primary/secondary with distributed pumping, and primary/secondary variable flow with tertiary pumping. There are many other pumping configurations, but in this article we’ll cover the first three.

If you prefer to watch the video of this presentation, than scroll to the bottom.

Primary Variable Flow Chilled Water Pumping

In a primary-only variable flow chilled water system, the operation is centered around using only primary pumps to circulate chilled water through the entire system. The key feature of this system is the variation of flow rates in response to the cooling load. This provides a more energy-efficient operation. Here’s an overview of how the primary-only variable flow chilled water system pumping arrangement typically works:

Primary only variable chilled water pumping
Primary only variable chilled water pumping

Chillers

Chilled water is generated by one or more chillers in the system. There is a chilled water temperature sensor in the chilled water supply pipe leaving the chiller. The chiller cools the water to the desired chilled water supply temperature before it is sent to the cooling coils. 

The 3-way valve ensures that the chiller receives the minimum flow required by the chiller manufacturer. The 3-way valve bypasses the coil when the demand for cooling is reduced at this coil. This provides the chiller with a minimum amount of flow. There are better ways to do this that we’ll cover in another video.

The chilled water is then distributed to the various cooling loads, such as air handling units (AHUs), fan coil units (FCUs), or other cooling devices in the building. The chilled water is distributed using variable speed pumps.

Primary Chilled Water Pumps

The system relies on one or more primary chilled water pumps to circulate water through the chillers and the entire distribution system. These pumps are typically equipped with variable frequency drives (VFDs). The VFD’s adjust the pump speed and flow rates based on the demand. VFDs on the primary pumps allow for the adjustment of the pump speed to match the varying cooling load. Lower pump speeds during periods of lower demand contribute to energy savings. The demand is determined by a differential pressure sensor installed at a remote location.

Differential Pressure Sensor

The cooling coils have supply air temperature sensors that control the amount of chilled water flowing through the control valves. As demand in the space reduces, the 2-way valves modulate toward the closed position. This causes an increase in pressure within the chilled water system. This increase in pressure is sensed by the differential pressure sensor and is communicated to the VFD. The VFD then slows down the speed of the pump, which reduces the amount of chilled water circulated throughout the system.

Energy Efficiency

The system’s energy efficiency is enhanced by avoiding the need for secondary pumps and the associated energy consumption in a primary-secondary system. The variable flow nature ensures that the system operates at optimal conditions, minimizing energy wastage.

Dynamic Control in Central Plant

The system continuously adapts to changes in the cooling load. This provides dynamic control and improved efficiency over traditional constant flow systems.

This primary-only variable flow chilled water system offers a flexible and energy-efficient solution by adjusting the flow rates in the primary loop based on real-time cooling demand. It’s particularly suitable for applications where load variability is a significant factor.

Primary/Secondary with distributed Pumping

In a primary/secondary variable flow chilled water system with a distributed pumping arrangement, the operation involves two separate loops. There is a primary loop and a secondary loop. This design is often employed in larger and more complex chilled water systems, including more than one building. Here’s an overview of how the system typically operates:

Primary secondary with distributed pumping in Central Plant
Primary secondary with distributed pumping in Central Plant

Primary Chilled Water Pumps in Central Plant

One or more primary pumps circulate chilled water through the chillers and the primary loop. In this design there is a pump dedicated for each chiller. A common leg connects the primary and secondary loops. 

Secondary Chilled Water Pumps

The secondary pumps are outside the central plant and into the buildings, bringing them closer to the cooling coils. The pumps provide the pressure required to bring the water from the common leg through their most remote coil and back to the common leg. These pumps will also operate using VFD’s to match the load of the coils they serve.

Energy Efficiency in Chilled Water Central Plant

The primary/secondary design allows for more precise control over the distribution of chilled water to the loads. This avoids over pressurizing the secondary loop which can occur when the secondary pumps are located within the central plant.

By separating the loops, the system can adapt to changes in the secondary loop without affecting the primary loop. Thereby contributing to overall energy efficiency.

Distributed pumping offers redundancy and flexibility, allowing for continued operation even if one secondary pump is offline for maintenance or repair.

This primary/secondary variable flow chilled water system with a distributed pumping arrangement is a robust solution for larger commercial buildings. This allows for precise control, energy efficiency, and redundancy are critical considerations.

Primary/Secondary Variable Flow with Tertiary Pumping

In a primary/secondary variable flow chilled water system with tertiary pumping, the operation involves three separate loops. There is a primary loop, a secondary loop, and a tertiary loop. This design is employed in large and complex chilled water systems to optimize control and enhance energy efficiency. The primary and secondary pumps can be located in the central plant, thereby allowing the tertiary pumps to be located in the individual buildings where the cooling coils are located. Here’s an overview of how the system typically chilled water pumping operates in this system:

Primary secondary with tertiary pumping. Central Plant
Primary secondary with tertiary pumping. Central Plant

Chilled Water Pumping

Primary chilled water pumps circulate chilled water through the chillers and the primary loop within the central plant.

Secondary chilled water pumps in the central plant circulate chilled water through the secondary loop. The secondary pumps respond to fluctuations in the cooling load requirements within the system using VFD’s.

Tertiary pumps circulate chilled water through the tertiary loop within each building. Tertiary pumping loops are dedicated to specific loads or areas that have unique cooling requirements. You might find this system on the campus of your local University which has a central plant and buildings distributed throughout the campus.

These pumps are provided with VFD’s to regulate the flow based on the specific needs of the tertiary loads within the building.

Variable Frequency Drives (VFDs):

Primary, secondary, and tertiary pumps are typically equipped with variable frequency drives (VFDs) to adjust pump speed and flow rates based on real-time demand. This flexibility ensures that the system operates efficiently under varying conditions.

Energy Efficiency in Central Plant

The primary/secondary/tertiary design allows for precise control over the distribution of chilled water to different types of loads with varying cooling requirements. By separating the loops, the system can adapt to changes in each loop without affecting the others, as a result it contributes to overall energy efficiency.

Dynamic Control and Redundancy

The system provides dynamic control, adapting to changes in the cooling load in real time for each loop. The inclusion of a tertiary loop offers additional redundancy and flexibility for meeting specific cooling needs.

This configuration provides a high level of control and efficiency, making it suitable for large and diverse commercial buildings with complex cooling demands.

Central Plant Chilled Water Pumping Options
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