Pressure Sensors Optimize Building Performance

    Posted on Mon,Nov 05, 2018 @ 12:44 PM

    HVAC system performance and comfort rely on accurate measurement and control of differential pressure.  Effective air distribution is achieved by closely monitoring and controlling air pressure.  By monitoring the airflow pressure across dampers, filters, fans, and between rooms, the HVAC system can efficiently and economically optimize building performance and reduce energy consumption.

    AHU_Sensors_noblueSensors from Belimo offer superior reliability, easy installation and commissioning, and seamless integration.

    Belimo pressure sensors are designed for air applications with a focus on low pressure for high accuracy, stability and zero drift for critical environmental applications.with major Building Automation Systems (BAS). They are the result of over four decades of experience, research, and a focus on providing value-adding technologies.

    Belimo differential air pressure sensors feature:

    • Eight field selectable pressure ranges in one unit helping to reduce inventory and support on-site range selection
    • Excellent zero-point stability and high accuracy ensuring optimal performance and repeatability.
    • Optional true auto-zero calibration ensures all measurements are accurate and drift free, no need for manual maintenance or on-site visits
    • Modbus communication protocol provides superior application data access and enables easy commissioning and parameterization
    • Snap-on housing allowing for quick installation and easy commissioning
    • Modular conduit fitting enables various mounting and cable configurations to meet a variety of applications
    • Spring-loaded removable terminal block creates a connection that offers resistance to vibration and maximum pull-out force, saving time during wiring and ensuring contact reliability
    • Output protection provides reverse-polarity protection, which minimizes the risk of damage caused by incorrect wiring
    • Detachable mounting plate designed as a drill template for easy and faster installation
    • NEMA 4X / IP65 and UL compliance enclosure tested to withstand harsh indoor and outdoor conditions, including exposure to dirt, dust, humidity, condensation, rain, and snow
    • Accurate and reliable readings backed with a 5-year warranty

    Discover the advantages

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    Tags: Belimo News, Technical Tips, Sensors

    Pressure Independent Valves a Good Solution for Water Source Heat Pump Application

    Posted on Thu,Oct 18, 2018 @ 09:00 AM

    In a water source heat pump (WSHP) application, a variable or constant speed pump accomplishes water distribution. The primary function of valves in a WSHP application is to allow a predetermined volume of water to enter each unit through either a water-to-refrigerant coil, water-to-air coil, or a water-to-water coil. The valves used are typically on/off control for full design flow when the WSHP starts. In most applications they are not required to control the amount of flow as in a traditional HVAC hydronic system.

    The benefits of using a pressure independent valve (PIV) for a water source heat pump:

    • Dynamically balances the system by responding to changes in differential pressure
    • Maintains design flow at part load and during morning start-up when all loops become critical
    • Each terminal receives the required flow, no overflow or underflow
    • Dynamic balancing allows a mechanic to easily commission a building and eliminates the need for rebalancing when alterations have been made to the hydronic system
    • Improves overall comfort and saves on pumping energy

    To select the right pressure independent valve determine the appropriate flow required for your heat pump and select the valve that satisfies this flow. Belimo’s pressure independent valve ranges from ½” to 6” with up to 713 GPM. This combination of pressure independent valve and variable-frequency drive (VFD) enables savings of pumping energy up to 90% of the time when the building load is less than full. More information on pressure independent control valves can be found online.

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    Tags: Belimo News, Technical Tips, Pressure Independent Valves

    Critical Zone Reset Logic Increases Pumping Efficiency

    Posted on Thu,Oct 04, 2018 @ 08:47 AM

    Hydronic variable flow systems may reset supply water temperature, pump static pressure, or a combination of both to reduce plant energy consumption and to comply with building codes and standards. The information below illustrates how valve position feedback to the Building Automation System (BAS) is used to reset the pump pressure setpoint in accordance with ASHRAE 90.1 and California Title 24.

    • ASHRAE 90.1 (2016) Section 6.5.4.4 states “Where DDC is used to control valves, the set point shall be reset based on valve positions until one valve is nearly wide open or setpoint limits of the system equipment or application have been reached.”
    • California Title 24 (2016) Section 140.4 (k) B.ii. states “For systems with direct digital control of individual coils with a central control panel, the static pressure set point shall be reset based on the valve requiring the most pressure, and the setpoint shall be no less than 80 percent open.”Capture-10
    When using the control valve position to reset the pump pressure setpoint the term “Critical Zone Reset” (CZR) is used to describe the BAS automated demand response logic as illustrated in the chart. Under normal operation, the speed of the pump is controlled by the position of the actuators.  One of the valves needs to be almost 100% open to satisfy the load – this is the critical zone.

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    Only the ePIV or Belimo Energy Valve position feedback signal will work as intended when fully open causes the CZR logic to increase the pump pressure. In response, the critical zone’s ePIV or Energy Valve actuator will move the valve position to less than full open for all load conditions, including design load. In contrast, a pressure dependent control valve or mechanical pressure independent valve (PIV) will stay fully open at design load, regardless of increased pump pressure, which would increase energy cost.

    Critical zone reset systems require an advanced BAS installation that can analyze and quickly communicate the actuator position of the ePIV or Energy Valve. However, one anomalous feedback signal can upset the whole system. Any outlier zones should be corrected during the commissioning process or deleted from the CZR algorithm. Additionally, the BAS should remove valves from the CZR logic when the AHU is off, i.e., chilled water valves may be commanded full open under low-temperature conditions to mitigate freezing risk.  Otherwise, the variable speed system will run at maximum speed; energy will be wasted, and the pump head pressure will be high.

    The ePIV and Energy Valve's position feedback signal is uniquely suited to reset pump pressure.  They are the only control valves that behave just like a VAV box actuator in AHU systems.

    Tags: Belimo News, Technical Tips, Energy Valve, ePIV

    District Cooling and the Effects of Low Delta T

    Posted on Mon,Mar 05, 2018 @ 09:36 AM

    new-chiller-1.jpgDistrict cooling is the centralized production and distribution of cooling energy. Chilled water is delivered from a centralized energy plant through an underground pipeline to commercial, industrial, and residential buildings to air-condition using chilled water.  Excess heat is extracted from the building by the air conditioning systems’ heat exchangers. The water is then returned to the central energy plant.

    District cooling plants operate to meet the cooling energy demand of their customers, which could be dozens of buildings in a college campus or municipality. District cooling systems offer lower up-front construction costs and eliminate the need for chiller plant maintenance at the building level.

    Customers of a district cooling plant pay for the volume of chilled water delivered to their building and may pay other charges as well.  A peak demand charge may be assessed and penalties for returning water below the design or contracted temperature due to poor heat exchange. Our industry has proven that lower return water temperatures and low delta T decrease the efficiency of the entire chilled water system.  This condition is known as “Low Delta T Syndrome.”  Low Delta T syndrome is the result of the inefficient use of chilled water at the point of consumption.  Belimo is sponsoring a webinar with High Performance Building on District Cooling and the effects of low Delta T.  This webinar will provide a review of district chilled water system design and how low Delta T impacts both the chillers and the buildings the chillers are serving. We will also cover low Delta T and how it impacts pumping, causes of low Delta T, attempts to correct low Delta T and the relationship between low Delta T and chiller capacity. In conclusion, we will review a study of a building where “Low Delta T Syndrome” was corrected at the point of water to air heat transfer.

    Webinar Objectives:

    • Identifying the importance of system design and pumping arrangements
    • Understanding the relationship between GPM and Delta T
    • How to calculate Btu and Tons
    • The types of district cooling building connections
    • Why maintaining Delta T is important in a district cooling system

    Register today!

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    Tags: Belimo News, Technical Tips, Online Learning Resources & Tools

    Belimo Energy Valve™:  Making Systems Energy Efficient, Easier to Control and More Transparent

    Posted on Tue,Feb 21, 2017 @ 11:15 AM

    The Belimo Energy Valve is an advanced pressure independent control valve that can drastically reduce the amount of water used to cool or heat a space.  By increasing the overall efficiency of the heat transfer, energy savings can be achieved.  In addition, the Belimo Energy Valve provides unparalleled transparency to the system and can drastically improve the controllability of complex hydronic systems.

    Join us for this webinar to understand the practical science behind the improved performance and the potential gains that can be realized in your buildings. The webinar will cover:

    Why Hydronic Design Models Don’t Match Building Performance

    Modelling softwares make a few faulty assumptions about basic hydronic behavior which can lead to disappointing building performance.  By selecting and installing proper equipment, engineers and contractors can be successful in achieving the modelled results.

    Understanding and Improving Heat Transfer at the Coil

    By understanding the thermodynamics behind the heat transfer at coils and heat-exchangers, we can devise better control strategies to better match the water flows to the specific loads in the space.  When done properly, most buildings can use far less water to heat and cool, and thus save large amounts pumping and plant energy.

    Static vs. Dynamic Balancing

    Until examined closely, the true benefits of advanced control valve technology, may be overlooked from a control and comfort standpoint.  By exploring dynamically balanced systems, we can see how we can hope to have more stable loops and more comfortable spaces.

    Belimo Energy Valve

    The Belimo Energy Valve is an electronically pressure independent valve with a fully integrated BTU meter.  It has the ability to control flow, manage Delta T, monitor system glycol percentage and fully expose the performance of the equipment.  With advanced communication platforms, which include BACnet, MODbus, IP and cloud based optimization, the Belimo Energy Valve provides unparalleled access to all of the data.

    Case Study Review

    See results from actual Belimo Energy Valve installations.

    Register Now!

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    Tags: Belimo News, Free Items, Green Building Technology, Online Learning Resources & Tools, Technical Tips

    Energy Cost Savings Can Be Achieved Through Better Compliance

    Posted on Thu,Oct 20, 2016 @ 09:15 AM

    A recent Department of Energy study1 conducted by Pacific Northwest National Laboratory (PNNL) investigated the lost energy savings in small commercial buildings that were not in compliance with the current energy code, in this case, IECC 2012. In energy codes, air economizers are required on most commercial air systems, whether packaged or split system. However, just having an economizer damper and associated control doesn’t result in automatic compliance. There are many subset requirements for economizers today (economizer requirements for details).Capture2.png

    Although this DOE study focused oncompliance verification, it identified a common problem, 100% of economizer controls reviewed had their high-limit shutoff not in agreement with the setpoints as prescribed by the IECC for climate zone 4C. This is not a new problem. The California Energy Commission in 2003 identified that 72% of the economizers investigated had improper high-limit shutoff settings. What’s new, PNNL was able to use the US DOE commercial prototype building model to determine energy effectiveness of specific code requirements and lost energy savings for this incorrect setting. Calculations showed that the wrong high limit setting would result in additional electrical usage of $3.56 / ton per year to as much as$14.18 / ton per year. Also highlighted in the report was the difficulty in verifying if the control was set to the correct high-limit shutoff in accordance with energy codes. It was noted that systems often found in small to medium-sized commercial buildings, didn’t meet the size requirements of the IECC to trigger mandatory commissioning. The verifier was well experienced in economizer controls, but still had challenges identifying setting and operation of the installed controls. In this study, thirty minutes of time was attributed to verifying the economizer control setup.

    Download the complete study, An Approach to Assessing Potential Energy Cost Savings from Increased Energy Code Compliance in Commercial Buildings” by Michael Rosenberg, Reid Hart, Rahul Athalye, & Jian Zhang, Pacific Northwest National Laboratory, David Cohan, United States Department of Energy. This paper presents the results and many lessons learned on how to increase ourbuilding performance.

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    In summary, improper setup of an economizer leads to lost savings, and verification to validate the settings is an additional cost. With the ZIP Economizer by BELIMO, just enter the ZIP code of the building, and the economizer will automatically set the high-limit shutoff values as required in the latest energy codes.You can visually verify the climate zone and the high-limit value set by the ZIP code. (see how easy it is)

    The ZIP Economizer is also equipped with other energy saving and system projection features and meets all the latest economizer control code requirements.

    Latest Code Economizer Requirements

    • 100% Outside Air – Economizers shall modulate and have the capability to provide up to 100% of supply air with outdoor air when needed to meet the cooling load.
    • Pressure Relief – Means of relieving the additional outside air shall be provided to prevent building over-pressurization. Typically provided by a barometric damper or powered exhaust.
    • Integrated Cooling – which is to provide mechanical cooling with Free Cooling with the damper remaining at 100% outdoor air position and requires a 2 stage thermostat to comply.
    • Class 1 Motorized Dampers – Dampers shall have leakage no greater than 4cfm/ft2 in accordance with AMCA 500D and tested and labeled by an approved agency.
    • Economizer Fault Detection and Diagnostics (FDD) – requiring an advanced digital economizer control providing system information, status, and fault notification.

    Citations:

    An Approach to Assessing Potential Energy Cost Savings from Increased Energy Code Compliance in Commercial Buildings - PNNL- 24979

    Small HVAC Problems and Potential Savings Reports

    International Code Council

    Tags: Technical Tips

    ASHRAE Supplier Sponsor Webinar on Dynamic Balancing

    Posted on Tue,Aug 23, 2016 @ 09:00 PM

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    Pressure Independent Valves offer system stability, improved efficiency and overall versatility that can only be achieved in a dynamically balanced hydronic system. During this webinar you will learn how partial loads can wreak havoc on statically balanced systems and how static balancing devices under perform the majority of the time. See how pressure independent valves can keep your system balanced at all loads and flow, eliminate overflows, and achieve perfect valve authority.

    Join us on Thursday, September 15th at 11:00AM PDT / 2:00PM EDT as Dick Hubbell, Regional Application Consultant for Belimo America discusses why design and modeling data doesn't always match a building’s actual performance.

    Energy and performance models make a few faulty assumptions about hydronic performance. By understanding these assumptions, we can have a better view of actual performance. This presentation will examine the performance impact of improper valve sizing, unstable system pressures and balancing device selection. We will also examine the physical effects of valve authority and coil degradation in hydronic systems.
    In this session we will discuss:

    • Design and Modeling Assumptions

    • Hydronic Heat Transfer at the Coil

    • Hydronic Performance Problems

    • Valve Sizing

    • Static vs. Dynamic Balancing

    • Coil Performance

    • Optimize Potential Performance Solutions

    Register Now.

    Tags: Belimo News, Technical Tips, Online Learning Resources & Tools

    Belimo Highlights: National Conference on Building Commissioning

    Posted on Fri,Jun 19, 2015 @ 10:00 AM

    2015 National Conference on Building Commissioning (NCBC); “Gateway to the Future of Commissioning”; is designed by the Building Commissioning (Cx) Association (BCA) to advance state-of-the-art building commissioning and the professionals within a forum for sharing the cost-effective processes for optimizing building performance, reducing energy use, and improving indoor air quality, occupancy comfort, and productivity.

    At this year’s national conference William ‘Bill’ McMullen, President, Business Unit Manager, Energy Solutions, Dewberry announces that the BCA will be launching a University. The university is in the development stages and more information will be released online when it comes available.

    Big Data was a central theme of this year conference.  A highlight of a few of the sessions covered:

    The Value of Submeter Data in Energy Information Systems Implementations: Andrea Salazar, Senior Engineer at EMI Consulting 

    Our industry is evolving with the use of the internet to allow for Energy Information Systems (EIS) to develop instant access to information such as fuel cost, weather, and sub metered data to enable us to make smarter operating decisions for lower cost and more efficient building operation. 

    Previous research into benefits of sub metering indicated:

    • Energy Reduction 5%-46%
    • Cost $0.02-$0.25 per sq. ft.
    • Simple Payback 10 Months – 3.5 years

    A recent study was conducted by EMI Consulting referencing 27 commercial buildings with EIS.  The results indicate more sub metering (data) = more savings. When energy is metered at the building, system, and equipment level and integrated with sensors and building automation systems, the savings were measured up to 20% (Building + System + Equipment + Sensors + BAS Integration = 20%). Even more enlightening is that a higher level of integration resulted in lower incremental cost. However, technology and systems are new so cost/benefit is still evolving.

    Lawrence Berkley National Lab (LBNL) hosts a site of EIS tools and research located at http://eis.lbl.gov/. The LBNL has worked with the California Energy Commission and the Department of Energy to evaluate and improve performance monitoring tools for energy savings in commercial buildings.  This website covers all prior, recent and current LBNL work in energy information systems and types of performance monitoring and analysis technologies. The site also contains links to project-specific pages documenting DOE and CEC-funded work from 2008 to present, links to research publications, and presentations.

    CX Mission Critical Facilities for Safety and Resiliency: Rachel Rueckert, PE, LEED-AP, QCxP and; Dave Guberud, QCxP, Ring & DuChateau, LLP

    This presentation provided an in-depth understanding of resiliency including related threats and underlying principles. Commissioning of mission critical facilities for safety and resiliency is important in keeping the critical space at varying degrees of negative pressure. This requires not only a well-controlled and sealed air distribution system, but also envelopes that can pass a variety of tests.  The ability of measuring direction of flow, redundancy of systems, and quick and tight damper control are some of the important HVAC functions.

    Data Analysis in the Cx Process: Ryan Stroupe, PG&E Pacific Energy Center; and William E. Koran, PE, Director of Energy Analytics, Northwrite, Inc.

    We were introduced to two different but powerful tools that enhance the visualization of measured building data to enable identification of proper operating trends and areas for improvements that can save energy.  Both of these tools, ECAM and Universal Translator are free to download and use. 

    ECAM is a Microsoft Excel®-based tool that facilitates the examination of energy information from buildings and reduces the time spent analyzing utility meter data and system operational data. Starting from time-series data, ECAM automates a wide array of charting and analysis functionality to provide the ability to complete pre and post energy efficiency project regression analyses of utility interval meter data against outdoor air temperature. ECAM offers additional applications that can be used independently: analysis of a building’s load profile, creating per-square-foot metrics of building energy use, and developing scatter charts based on occupancy or time of day. These applications can ultimately be used to better understand a building’s energy use patterns and inform the selection of energy efficiency measures with the highest potential for savings. Learn more online at http://cacx.org/PIER/ecam/.

    The Universal Translator (UT) is a tool that was developed for building energy maintenance professionals that allows a Cx agent to take measured data and normalize it and put it in nice graphical form. The program is for anyone who works with “real world” data. Problem data might be data that comes from different data loggers where the clocks are not synchronized or from data loggers that recorded at different intervals. Calibration errors might be another source. The UT also has additional analysis functions to help analyze data. It includes modules to analyze economizers, light and plug loads, equipment runtime and set point analysis. Spending hours with a spreadsheet trying to take problem data and make it into something usable is a real task. The UT could save hours of work.

    "Big Data", Better Choices: Data Tools for EBCx Impact: Terry Bickham, CEM, LEED AP, CDSM,CSDP; Director, Energy Services and Solutions, TraneCost of Ownership

    Continuing the topic of visualizing “Big Data”, Terry Bickham of Trane presented how visualization of data can communicate opportunities for optimization of operation to reduce building operating cost.  Data from the National Institute of Building Sciences(NIBS) indicate in the life cycle expenses of a building operating costs account for 60-85%  compared to 5-10% for construction. 

    A study by LBNL indicates opportunity to save energy as the building gets older using retro commissioning, ongoing commissioning, operational optimization, and analytics of available data.  Available data displayed to building occupants can be used as behavior modification resulting in lower energy use.  LBNL scientists are also developing methods of applying Fault Detection and Diagnostics (FDD) to rapidly diagnose problems in buildings and inform human operators what needs to be fixed before they turn into bigger problems. The ultimate differentiator is in maintenance gains and setting building professionals up to further optimize performance. Many of the same visualization techniques can be applied to the ongoing operation. Combining visualization with automated analytics allows for ongoing commissioning at a glance – simple, sustainable, and with measurable impact.

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    The Future in Fire Protection and Life Safety Cx: David LeBlanc, PE, SFPE, Vice President, Jensen Hughes

    In this session, discussions on the development and relevance of two new NFPA standards (NFPA 3: Recommended Practice for Commissioning of Fire Protection and Life Safety Systems) and (NFPA 4: Standard for Integrated Fire Protection and Life Safety System Testing).  These standards were developed in response from a request from the NIBS for standardized methods to commissioning and test Fire Protection Systems to ensure performance in conformity with the design intent.

    The NFPA 3 outlines the commissioning process and integrated testing of fire protection and life safety systems, to ensure systems perform in conformity with the design intent. NFPA 3 address the recommended practice which covers procedures, methods, and documentation, giving stakeholders a reliable way to verify that active and passive safety systems are optimized to function as intended. It also defines a commissioning team and spells out qualifications for team members. The next edition of this standard is now open for Public Input (formerly proposals).

    The NFPA 4 standard provides the minimum requirements for testing of integrated fire protection and life safety systems where such testing is required by governing laws, codes, regulations, or standards. This standard would not provide requirements for the testing of individual systems. The standard would apply to new and existing systems. Free access to the 2015 edition of NFPA 4 (registration required).

    Throughout the conference additional Cx advancement in building codes were mentioned.  Here is a highlight of changes forthcoming. The International Code Council (ICC) incorporated System Commissioning Requirements in the International Energy Conservation Code (IECC 2012 section 408).  Buildings with total cooling capacity greater than 480,000 BTUs and heating capacity greater than 600,000 BTUs (exception: simple unitary systems serving dwelling units in hotels, motels, and similar) will need to have a commissioning plan, testing adjusting and balancing (TAB) of air and hydronic systems, functional performance testing of equipment, controls, and economizers. The ICC is developing a standard for commissioning (ICC 1000) and completed its first public draft review this spring. ICC 1000 first draft is available for download.

    Tags: Belimo News, Technical Tips

    Improving Chilled Beam Performance and Cost-Effectiveness

    Posted on Tue,Jun 02, 2015 @ 10:00 AM

    In recent years, sustainability and efficiency have made their way to the forefront of building design.  More so now than ever, owners and contractors are looking to take advantage of the most advanced climate control systems in an effort to lower energy costs, maximize space, and ensure the safe and comfortable use of their structure for many years to come.

    The use of chilled beams, in particular, has become a highly popular method of achieving these goals. Originally built to take the place of passive radiant cooling ceiling systems, they provide designers and engineers with the ability to make the most out of their space by dramatically reducing bulky supply and return air ductwork to the minimum size required to meet your ventilation requirements. Heating and cooling loads are served with smaller water pipes and more efficient hydronic systems.

    Chilled beams are an intelligent option for both new buildings and retrofits alike; and when used in conjunction with other state-of-the-art technologies like Belimo’s 6-way Characterized Control Valve (CCV), they help reduce life-cycle costs and improve climate-controlling capabilities in structures of nearly all shapes and sizes.

    The Belimo 6-way CCV is designed specifically for chilled beams and radiant ceilings. It can perform change over and modulating control for a single coil in a 4-pipe system with functionality equivalent to that of up to four 2-way control valves. This represents significant savings in terms of space, material, and installation time.

    Belimo CCV’s innovative ball design features hydraulically decoupled heating and cooling circuits, which means that each sequence is controlled individually by the rotary movement of a single actuator. As a result, one valve can support a coil with two different Cv values.

    In addition to substantially reducing wiring requirements, the use of only one actuator6-way characterized control valve simplifies building management system controls and enhances the ability of operators to manage indoor conditions. The 6-way valve is also highly compact and offers a 0% leakage in the closed position, helping prevent energy losses and reducing operating costs.

    Using a single 6-way control valve to support chilled beam applications results in reduced installation requirements and minimal labor costs, and in the building sector where lean construction is becoming increasingly important, this is highly advantageous.

    Through all of its innovative features, the Belimo 6-way control valve can serve as a highly economical addition to chilled beam applications in a wide range of building designs, and as more and more owners and contractors look for new and effective ways to cut costs and improve the environmental-friendliness of their structure, technologies like it will become increasingly prominent.

    Download 6-way Product Brochure or go online to learn more.

     

     

     

    Tags: Product Review, Green Building Technology, Technical Tips

    Practical Tips to Achieve Excellence in Air and Water Control

    Posted on Tue,Nov 11, 2014 @ 10:00 AM

    When control loops are not properly tuned, actuators may fail prematurely, and the system can provide poor temperature or flow control.

    Three conditions are usually caused by poor control loop tuning: oscillation, hunting, and dithering. Oscillation is constant changes in position. Hunting is wide, constant swings in control signal. Dithering is small, sometimes imperceptible changes in signal. For floating actuators, the time and frequency of the pulse, rather than signal voltage, is the control output but the result is the same.

    Oscillating control loops caused by being over sensitive can result in more than a million actuator movements in just a few years and can cause actuator failures. In sluggish control loops, actuator movement does not occur or is too small to affect flow, resulting in extreme system overshoot and comfort problems.

    There is an easy trade-off between tight control and a reasonable number, and size, of actuator movements. Space temperature changes occur slowly in a stable process. When a room fills with people, it takes about 5 minutes for a 1 degree temperature change to occur. It may take another 5 minutes for a wall sensor to register the change. Fast movements of the actuator are not necessary.

    Mixed air control is also a very stable process. Rapid changes in outdoor air temperature or average return air temperatures are rare. On the other hand, discharge air temperature control with a hot water or chilled water valve is a fast process because the sensor is close to the coil.  A bare averaging thermistor sensor may respond in 30 seconds to a 1-degree change. Encapsulated sensors may take 2 minutes.

    During start-up of a system, more actuator movements may be necessary to find the correct operating condition, but the space is not occupied and there is time to stabilize the system without fast actuator responses. In an ideal control loop, each actuator movement is productive.

    Proportional constants (and also integral and derivative) should be set so that continuous oscillation of actuators does not occur. Actuator movement should not occur before the effects of previous movements have had time to affect the sensor. This may be 10 minutes for a space sensor or 1 minute for an air sensor. Movement of damper or valve actuator when air temperature is within .5 degrees of set point, or when mixed-air is within 1 degree of set point usually will yield stable control; attempts to achieve more precise control may result in unstable control and excessive actuator movement.

    When 3-point floating control is used, the total run-time of the actuator should be entered into the program logic. When the actuator is at either the fully open or fully closed position, continual pulsing of actuator against end-stops (end-stop dithering) should not occur. The actuator should either stop and hold or drive continuously against the end-stop.

    Each VAV box and actuator control loop should be individually tuned. Where high turbulence in the sensor flow control loop is causing dithering (rapid oscillation) of the actuator control loop, the sensor loop should be corrected mechanically or with software averaging. Where the control loop is not fully adjustable, it may be necessary to find a method unique to the individual controller.

    If an actuator is “chasing” a process which occurs faster than the actuator movements are able to correct, as may occur in the situation described above, the result will be many more actuator movements than are necessary to affect flow. The average flow should be adjusted, but turbulence is normal and should be ignored.

    VALVE SEQUENCING resized 600

    Potential Problems:
    • Hunting: wide oscillations
    • Dithering: small, unproductive movements of the actuator
    • End-Stop Dithering: the actuator or damper is at the end of its rotation, but the control loop continues to pulse.
    Possible Solutions:
    • Reduce the proportional or integral gain.
    • Use a deadband.
    • Add time delay.
    • Reset constants.
    • Shut down control when at end-stops.
    • Do not control process faster than components response.

    Tags: Technical Tips