Zero Liquid Discharge Wastewater Treatment

Zero-liquid discharge (ZLD) is a water treatment process in which all waste water is purified and recycled; therefore, leaving zero discharge at the end of the treatment cycle. ZLD is an advanced wastewater treatment method that includes ultrafiltration, reverse osmosis, evaporation/crystallization, and fractional electro deionization.

Applications of ZLD:

  • Plant Discharge Compliance
  • Cooling Tower Blowdown
  • Flue Gas Desulphurization (FGD)
  • Gasification Wastewater
  • Coal to Chemicals (CTX) waste
  • IGCC Plant treatment

ZLD Technologies:

  • Falling Film Brine Concentrators
  • Forced Circulation Crystallizer
  • Horizontal Spray Film Evaporator
  • Hybrid Systems with Membrane Pre-Concentrators
  • Biological Treatment
  • Solids Waste Handling

Different ZLD systems:

For over 30 years vapor compression evaporation has been the most useful technology to achieve zero liquid discharge. Evaporation recovers about 95 % of a wastewater as distillate for reuse. Waste brine can then be reduced to solids in a crystallizer/dewatering device. However, evaporation alone can be an expensive option when flow rates are considerable.

One way to solve this problem is to integrate membrane processes with evaporation. These technologies are nowadays often combined to provide complete ZLD-systems. The most common membrane processes used so far are reverse osmosis (RO) and electrodialysis reversal (EDR). By combining these technologies with evaporation and crystallization ZLD systems have become less expensive. They are however combined differently depending on the circumstances. Together with these components, a variety of other well-known water treatment technologies are used in ZLD-systems for pre-treatment and polishing treatment. These treatments are:

  • pH adjustment
  • degasifier
  • mixed/separate bed
  • oil/water separator
  • neutralization
  • oxidation (UV, ozone, sodium hypochlorite) 4
  • dissolved air flotation (DAF)
  • carbon adsorption
  • anaerobic or aerobic digestion

The variation of ZLD-systems are endless

Designing a ZLD System:

Characterizing the waste stream is difficult yet essential when designing a ZLD-system. It is important to start off with a realistic estimate of composition, feed chemistry and flow rate. A poorly described waste stream will likely lead to a design which is far from its optimum.

The system will either be too large and expensive or too small to achieve the required separation. The selection of the waste water flow rate typically determines the size and therefore the initial capital cost of the ZLD-system.

But how does one characterize a waste stream? For existing plants, waste stream compositions can be measured directly, preferably on multiple occasions to characterize a range of compositions.

Depending on the process, the feed chemistry may change occasionally, and it is of great importance that one has this in consideration. The most common measurements today include organics, for example, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic carbon (TOC) and inorganics (anions, cations, silica).

General Guidelines:

If the water flow rate is small, not many components are necessary. The following general guidelines are accepted today:

  • Below 10 gpm of feed – crystallizers and/or spray dyers can be combined.
  • 10 – 50 gpm of feed – use a crystallizer alone.
  • 50 – 100 gpm of unsaturated feed – use an RO/EDR/crystallizer combination.
  • 50 – 100 gpm of saturated feed – use an evaporator/crystallizer combination.
  • 100 – 500 gpm of feed – either an RO/crystallizer or an evaporator/crystallizer combination may be the most economical.
  • 500 – 1000 gpm of feed – all three should be used.

Zero liquid discharge technologies help plants meet discharge and water reuse requirements, enabling your business to:

  • Meet stringent cooling tower blowdown and flue gas desulfurization (FGD) discharge regulations
  • Treat and recover valuable products from waste streams
  • Better manage produced water

Panorama offers complete thermal and non-thermal ZLD solutions to manage tough-to-treat wastewaters. Panorama’s solutions can help recover more than 95% of your plant’s wastewater.

Water reclamation systems design

Urban water reuse is a term generally applied to the use of reclaimed water for the beneficial irrigation of areas that are intended to be accessible to the public, such as golf courses, residential & commercial landscaping, parks, athletic fields, roadway medians, etc.

Expanded uses for reclaimed water may also include fire protection, aesthetic purposes (landscape impoundments and fountains), industrial uses and some agricultural irrigation.

Reclaimed water is domestic wastewater or a combination of domestic and industrial wastewater that has been treated to stringent effluent limitations such that the reclaimed water is suitable for use in areas of unrestricted public access. Since most areas where reclaimed water is to be used are designated for public access, protection of public health is the primary concern. Although utilization of reclaimed water will be beneficial, there is no guarantee that this source will provide all the water that is needed or desired.

Highly treated reclaimed water that meets the requirements of these guidelines is a valuable water resource. Wastewater treated to urban water reuse standards may be used in lieu of potable water for agricultural irrigation (feed crops), residential/commercial landscape irrigation, dust control, etc. The reclaimed water system is an integral part of the utility system and provides benefits to both the potable water and wastewater utilities.

Some of the substances that can be removed from wastewater include:

  • Suspended solids
  • Volatile organics
  • Semi-volatile organics
  • Oil and grease
  • Hydrocarbons
  • Metals
  • BOD
  • COD
  • Color
  • Odor
  • Hardness
  • Minerals

Reclamation processes:

Wastewater must pass through numerous systems before being returned to the environment. Here is a partial listing from one particular plant system:

  • Barscreens – Barscreens remove large solids that are sent into a grinder. All solids are then dumped into a sewer pipe at a Treatment Plant.
  • Primary Settling Tanks – Readily settable and floatable solids are removed from the wastewater. These solids are skimmed from the top and bottom of the tanks and sent to the Treatment Plant where it’ll be turned into fertilizer.
  • Biological Treatment – The wastewater is cleaned through a biological treatment method that uses microorganisms, bacteria which digest the sludge and reduce the nutrient content. Air bubbles up to keep the organisms suspended and to supply oxygen to the aerobic bacteria so they can metabolize the food, convert it to energy, CO2, and water, and reproduce more microorganisms. This helps to remove ammonia also through nitrification.
  • Secondary Settling Tanks – The force of the flow slows down as sewage enters these tanks, allowing the microorganisms to settle to the bottom. As they settle, other small particles suspended in the water are picked up, leaving behind clear wastewater. Some of the microorganisms that settle to the bottom are returned to the system to be used again.
  • Tertiary Treatment – Deep-bed, single-media, gravity sand filters receive water from the secondary basins and filter out the remaining solids. As this is the final process to remove solids, the water in these filters is almost completely clear.
  • Chlorine Contact Tanks – Three chlorine contact tanks disinfect the water to decrease the risks associated with discharging wastewater containing human pathogens. This step protects the quality of the waters that receive the wastewater discharge.

At various stages in the multistage treatment process, unwanted constituents are separated using

  • Vacuum or pressure filtration,
  • Centrifugation,
  • Membrane-based separation,
  • Distillation,
  • Carbon-based and zeolite-based adsorption, and
  • Advanced oxidation treatments.

Activated carbon is a highly adsorbent form of carbon that is produced when charcoal is heated. It removes impurities via adsorption from both aqueous and gaseous waste.

Membranes allow materials of a certain size or smaller to pass through but block the passage of larger materials. Imaginative arrays of membrane materials in innovative physical configurations are used to separate unwanted solids and dissolved chemicals from tainted water. During operation, purified water diffuses through the micro-porous membranes and collects on one side of the membrane, while impurities are captured and concentrated on the other side.

Today, membranes made from cellulose acetate, ceramics, and polymers are widely used. The applications come in a variety of innovative designs, including tubular, hollow-fiber, plate-and-frame, and spiral-wound configurations. The goals of membrane design are to

  • Maximize the available surface area,
  • Reduce membrane pore size (to allow for the more precise removal of smaller contaminants),
  • Minimize the pressure drop the fluid will experience when flowing through the unit, and
  • Identify more cost-effective system designs.

The addition of oxidizing agents—chemical ions that accept electrons—has proven effective against these microorganisms like waterborne viruses, bacteria, and intestinal protozoa. Today, a variety of advanced oxidation techniques kill such disease agents and disinfect water, thanks to ongoing developments pioneered by the chemical engineering community.

Historically, chlorine-based oxidation has been the most widely used, and it is very effective. However, the transportation, storage, and use of chlorine (which is highly toxic) present significant potential health and safety risks during water-treatment operations. To address these concerns chemical engineers and others have developed a variety of alternative oxidation treatments that are inherently safer, and in many cases more effective, than chlorination. These include Ultraviolet light,Hydrogen peroxide, and Ozone, each of these powerful oxidizing agents destroys unwanted organic contaminants and disinfects the treated water without the risks associated with chlorine use.

Considerations for constructing a water reclamation system:

In planning for urban reuse there are three major issues that must be considered prior to developing such a system.
The first issue is that year round wastewater treatment and disposal are required when designing any wastewater treatment facility. A water balance for the reclaimed water service area is needed to determine how much wastewater will be generated and how much irrigation demand there is for the reclaimed water. The wastewater generated may exceed the reclaimed water demand during portions of any given year. Therefore, a discharge permit, additional storage, or a designated land application site may be required.

The second issue which must be considered is the constituents (e.g. salts) that may be present in the reclaimed water and what effect(s) they may have on the cover crops that will be irrigated. For specialized users such as golf courses, nurseries, etc., a detailed evaluation of the effluent constituents may be necessary in order to determine whether or not they are candidates for urban reuse irrigation.

Third, Urban Water Reuse is not suitable for all wastewater treatment applications. The manpower requirements and permit reporting can make a reuse facility expensive for a small operation. The facility’s operator in responsible charge shall be a Class I Biological Wastewater Operator. Operation of reclaimed water systems requires on-site operation by a Class II Biological Wastewater Operator or higher operator 8 hours per day, 7 days per week. If the operator can monitor from a remote location and receive immediate notification for alarms, a reduced schedule for on-site operation by a Class II Biological Wastewater Operator or higher operator may be considered on a case-by-case basis.

Deciding how best to use wastewater begins with a laboratory analysis of the substances present in the water. Engineers work with each client to specify the laboratory tests that should be performed. Once that information has been obtained, our engineers and the client:

  • Identify the various ways the water can be used in the specific facility
  • Identify the substances to be removed from the water to make it suitable for each use
  • Determine the process needed to re-condition the wastewater for each use
  • Estimate how much water consumption would be saved by recycling and calculate the annual cost of the water
  • Obtain a cost estimate for the required treatment system
  • Compare the cost savings of reduced water consumption to the capital and operating expenses of the treatment system to determine whether the investment in recycling is cost-effective

Why wait? Start building your water reclamation systems design from the best water reclamation design companies now; get help & assistance from the top highly skilled & technical experts.

Plant & Equipment Relocation Services

In challenging economic times, some manufacturing companies are faced with difficult decisions regarding the location of their manufacturing facilities. Sometimes the reason being to reduce operational costs or for enhanced Business growth and/or new product lines may be pressing companies to move their operations to larger facilities to keep up with increasing demand. Other companies may simply be responding to changing market pressures by relocating closer to their customers or supplier network.

Regardless of these reasons for relocating a manufacturing facility, when that final decision to relocate is made, it’s up to the plant engineering company and its supporting team to execute the project. Since each relocation project comes with unique challenges, detailed planning and communication in the beginning have higher turnaround ratio for being successful projects.


Often, facility and equipment layout drawings are neglected. However, accurate and detailed layout drawings of the current facility location are essential to plan for the equipment relocation to another facility.

The accuracy of these drawings should be checked and missing elements should be replaced before any design effort begins. Items such as building column locations, equipment quantities, equipment identification and sizes, utility locations, pits, trenches and aisle sizes should be confirmed by spot checking. Don’t miss to note overhead equipment such as conveyors or cranes that may not appear on layouts.

Equipment condition review

  1. A detailed equipment review and condition assessment is required prior to relocation planning. The plant engineering company and supporting team should document the conditions and make recommendations as to whether the equipment’s condition warrants direct relocation, refurbishment or abandonment.
  2. Often, it costs more to repair, upgrade and relocate the out-of-condition equipment than it does to replace it. For equipment that will be moved, operation and maintenance manuals, maintenance records, spare parts inventories, PLC program data and structural information should be gathered and identified for each specific machine.
  3. If accurate layout drawings are not available, as-built drawings should be developed. The as-built drawing clearly indicate the building column grid, critical utility connections and equipment slated to be relocated. The equipment should be properly identified to include the equipment type, department or area, manufacturer, asset identification number, motor plate data, weight and utility requirements.
  4. High resolution, digital photographs are particularly helpful for equipment documentation. Photograph the equipment from all sides, paying particular attention to utility connection points and external control panels. Check if the facility has special foundations, pits or trenches. Provide detailed dimensions of the pit including depth, length and width, and note any utilities in the pit.
  5. Determine if the equipment from the current facility meets codes in the new location. Check control cabinets and panels for UL, NEC or comparable approvals. Check state permit requirements for boilers and pressure vessels as well.

Equipment database and identification

All equipment information gathered in the field should be added to an equipment spreadsheet or database. Equipment not clearly identified with an asset tag or ID that can be easily read should be manually tagged. During the physical relocation, all of the utility and controls tie points and connections on the equipment should be clearly identified, documented and tagged by the relocation contractor.

Utility and structural requirements

The plant engineering company coordinates with design disciplines to confirm that the utilities are installed in the correct location based on new drawings as well as at the correct time.

Coordination of pit, trench and foundation information requires coordination with a structural engineer. Overhead requirements such as cranes, monorails, conveyors and tooling rails also require structural coordination.

If the relocation is taking place within a “hot” facility (operational) or from a “hot” facility to a “cold” facility (non-operational), temporary or redundant utilities may be required to maintain operations. The plant engineering company will have to identify and coordinate these issues with the correct design disciplines to size the temporary utilities and design the required tie points.

Scheduling, evolution planning

The schedule being the most critical aspect of relocation may have to consider time for ramping down production at the current location while ramping up production at the new facility, which may require sequencing specific equipment and infrastructure to meet this requirement.

The plant engineering company will have to coordinate with manufacturing operations to develop the sequence and schedule of removal and relocation. This information will also be required by the facilities design team to schedule design, procurement and installation of utilities and structural requirements. Testing and commissioning requirements and durations should be included in the schedule. Detailed schedules should be developed and tracked using project scheduling software.

Equipment relocation work instructions

Equipment relocation work instructions (ERWI) or similar documents should be used which are detailed documents that contain all necessary information about the relocation & its specifics.

Installation coordination

The plant engineering company coordinates & syncs up with the utilities installer and the relation contractor to ensure the arriving equipment is ready to be installed and that the utility tie points are valid and available.

The relocation contractor performs a preliminary test once the equipment and utilities are connected to verify all motor rotations are working properly. Once these tests are complete, the equipment is considered mechanically functional & complete. Before turning the equipment over to manufacturing, the plant engineering company performs an inspection and checks the quality of the installation.

Testing, commissioning

Since each company has different requirements for testing and commissioning, the amount of plant engineering involvement with testing should be clear and agreed upon between the plant engineering company and his or her manufacturing organization early in the project. An ERWI containing the elements of testing & commissioning should be included if the relocation contractor has included support during this phase.

Looking for the best plant & equipment relocation experts? Talk to us & know more about how we can help you to successfully complete plant & equipment relocation ensuring minimal waste, eco-friendly ways &maximum efficiency in less time!

Clean steam systems in the Pharmaceutical Industry in India

What is clean steam?

Clean steam is used in the pharmaceutical and healthcare industries in processes where the steam or its condensate can come into contact with a pharmaceutical or medical product and cause contamination. In such cases, steam from a conventional boiler(often called utility or plant steam)is unsuitable because it may contain boiler additives, rust or other undesirable materials.

The use of clean steam is determined by the rules of Good Manufacturing Practice (GMP). These are general rules applicable to pharmaceutical manufacture,detailed in the Code of Federal Regulations(CFR Title 21,Part 211). They do not provide any specific recommendations regarding steam, but do present the general requirements offacilities, systems, equipment and operation needed to prevent contamination of pharmaceutical products during their manufacture.

Uses of clean steam:

The main use of clean steaming pharmaceutical manufacturing is for the sterilization of products or, more usually, equipment. Steam sterilization is encountered in the following processes:

  • Manufacture of injectable or parenteral solutions, which are always sterile.
  • Bio-pharmaceutical manufacturing, where a sterile environment must be created to grow the biological production organism(bacterium, yeast or animal cell).
  • Manufacture of sterile solutions,such as ophthalmic products.

Typically in these processes, clean steam is injected into equipmentor piping to create a sterile environment, or into autoclaves where loose equipment, components (such as vials and ampoules)or products are sterilized.

Clean steam may be used for some other functions where conventional utility steam might cause contamination, such as:

  • Humidification in some clean rooms.
  • Injection into high purity water for heating prior to Clean-in-Place (CIP) operations.

Fundamentals of clean steam system design:

Avoidance of corrosion

Unlike utility steam, clean steam has no corrosion inhibitors. Also, low conductivity water or condensate is hungry for ions, causing it to be corrosive to many materials commonly used in utility steam systems. Carbon steel,gunmetal and bronze, all commonly found in utility steam components, would all be rapidly corroded. Metal components for clean steam systems are therefore usually AISI 316 L stainless steel, or sometimes titanium. Non-metallic materials used include EPDM and PTFE.

Then eed to avoid corrosion is not only necessary for safeguarding the integrity of equipment. Corrosion products entering the clean steam could potentially cause contamination of the pharmaceutical product, either as chemical or particulate contamination.

Even where 316l stainless steel is used, a particular form of corrosion, called “rouging”, is often encountered in clean steam systems. The passive layer on the steel surface is disrupted and a red/brown/black film develops over time. Often this film is stable and does not pose a threat to the pharmaceutical product. Sometimes a powdery film develops and this can detach from the steel surface and cause discoloration of equipment which the steam contacts.
If this occurs, and the manufacturer feels that there is a risk of contamination or discoloration of the product, then the clean steam generator or even the full distribution system may be cleaned (“derouging”).

A variety of methods are used, but they all involve a chemical treatment to remove the surface layer of steel – this is essentially an etching process. After de-rouging, a passivation process must be used to restore the passive layer on the steel surface, since it is the passive layer that is responsible for corrosion resistance.

Preventing entry of contaminants into the system

Clean steam must be free of contaminants at the point of use. Chemical and microbial contaminants can enter steam systems in a variety of ways, and in the design of clean steam systems this must be avoided. Pathways for contamination include leakage, air being pulled into the system and “grow through” from a contaminated external environment.

Preventing microbial growth in the system

Steam at typical operating pressures will kill bacteria and their spores, so the parts of a clean system that are continuously exposed to steam will be sterile. However, if condensate is allowed to collect in the system, and it cools, then stagnant water can provide a suitable environment for bacterial growth. Though these bacteria may be killed when the condensate is discharged into equipment, followed by steam, their breakdown products, including endo toxins, may still be present. Endo toxins are not destroyed by typical clean steam system temperatures.

Looking for a clean steam system design consultant? Look no more, contact Panorama now!

Energy audit in India – Chemical Industry

Chemical industry is one of the oldest industries in India. Indian chemical sector has grown a long way since its early days of independence.

The chemical industry forms the backbone of the industrial and agricultural development in India and also provides building blocks for downstream industries. This industry is a significant contributor to India’s national economic growth. To know the extent of energy being wasted it is essential to know the amount of energy being consumed.

Energy audit is an inspection, survey and analysis of energy flows for energy conservation to reduce the amount of energy input into the system without negatively affecting the output. The energy audit is the key for decision-making in the area of energy management.

Energy Audit in India – Projections

India is projected to sustain the world’s second-highest rate of gross domestic product (GDP) growth, averaging 5.6 percent per year from 2006 to 2030 (Annual report, 2007 and GOI, 2006 and 2010).

India’s economic growth over the next 25 years is expected to derive more from light manufacturing and services than from heavy industry, so that the industrial share of total energy consumption falls from 72 per cent in 2006 to 64 percent in 2030.

The changes are accompanied by shifts in India’s industrial fuel mix, with electricity use growing more rapidly than coal use in the industrial sector. The Indian chemical industry was the 5th largest in the world, and 2nd largest in Asia, after China. The volume of major chemicals produced in India amounted to 8.3 million metric tons (MMT) in 2011-12.

The energy conservation and utilization of renewable sources are essential factor to fulfill energy demand. Renewable energy and nuclear power are the world’s fastest-growing energy sources, each increasing by 2.5 per cent per year. Among the various sectors contributing to greenhouse gas (GHG) emissions, the contribution of the industrial sector was significant.

Thus, mitigating GHG emissions from the industrial sector offers the best means of reducing overall GHG emissions. Therefore, energy conservation means less reliance on energy imports and, thus, less GHG emissions. It can be achieved either by reducing total energy use or by increasing the production rate per unit of energy used. On the other hand, improving energy efficiency is the key to reducing GHG emissions (Export-Import Bank of India, 2013).

Energy audit is an inspection, survey and analysis of energy flows for energy conservation to reduce the amount of energy input into the system without negatively affecting the output.

Objective of Energy Audit in Chemical Industry:

The primary objective of energy auditing in chemical industry is to determine ways to reduce energy consumption per unit of product output or to lower its operating costs. The present scenario of energy demand in chemical industries is the indication of energy conservation and optimum utilization of renewable sources of energy (BEE).

Considering the scenario of the Indian industrial sector and its energy utilization efficiency, there is urgent need to review manufacturing technologies and the present energy management approach.

Owing to old and obsolete industrial technologies and machinery the extent of energy wastage is very high. Energy Conservation potential in the industrial sector of our nation has been projected between 30 to 40 %.

Good energy management begins with an energy audit. Effective management of energy-consuming systems can lead to significant cost and energy savings as well as increased comfort, lower maintenance costs, and extended equipment life.

A successful energy management program begins with a thorough energy audit. The energy audit evaluates the efficiency of all building and process systems that use energy. Energy audits don’t save money and energy for companies unless the recommendations are implemented.

Audit reports should be designed to encourage implementation, but often they impede it instead. In this paper, the discussion on the scope and objectives of energy audit, types of energy audit, contents of an energy audit, audit methodology and targets and benefits of the energy audit are presented.

Finally a typical case study of chemical industry for energy audit is discussed with a clear and consistent path toward introducing energy management and auditing. The methodology, tools used, results and difficulties encountered during the study are also discussed.

The energy crisis all over the world in the seventies warned mankind and forced it to think about the appropriate utilization of the energy resources on the earth for the sustainable development. In history, the energy crisis had led to many innovations as well as research and development programs in all sectors related to energy. It is well known that energy sector has its own impact on the progress and development of any nation.

The availability of various energy resources and in house capability to use it in the appropriate manner for productive development of a nation is a key factor in the economic growth of the country.

Role of energy audit:

To institute the correct energy efficiency programs, we have to know first which areas in our establishment unnecessarily consume too much energy. An energy audit identifies where energy is being consumed and assesses energy saving opportunities. In the factory, doing an energy audit increases awareness of energy issues among plant personnel, making them more knowledgeable about proper practices that will make them more productive. An energy audit in effect gauges the energy efficiency of plant against “best practices”. When used as a “baseline” for tracking yearly progress against targets, an energy audit becomes the best first step towards saving money in the production plant.


Key points:

  • Although most efforts should be focused on the application of economic, mature technologies there are arguments to support innovation in energy efficiency technology.
  • Public and private expenditure on energy efficiency innovation is increasing globally.
  • Innovation programmes should be long-term and consistent.
  • R&D programmes need to be driven by input from the customer industries.
  • Government support can be used to help bridge the twin valleys of death but care must be taken to ensure that innovations are really aimed at meeting real customer needs.
  • A wide spread of technologies is needed as the failure rate is high.

HVAC Controls & Automation Systems

HVAC (stands for Heating, Ventilation and Air Conditioning) equipment needs a control system to regulate the operation of a heating and/or air conditioning system. Usually a sensing device is used to compare the actual state (e.g. temperature) with a target state. Then the control system draws a conclusion what action has to be taken (e.g. start the blower).

The application of Heating, Ventilating, and Air-Conditioning (HVAC) controls starts with an understanding of the building and the use of the spaces to be conditioned and controlled. All control systems operate in accordance with few basic principles but before we discuss these, let’s address few fundamentals of the HVAC system first.

Why Automatic controls?

The capacity of the HVAC system is typically designed for extreme conditions. Most operation is part load/off design as variables such as solar loads, occupancy, ambient temperatures, equipment & lighting loads etc. keep on changing throughout the day. Deviation from design shall result in drastic swings or imbalance since design capacity is greater than the actual load in most operating scenarios. Without control system, the system will become unstable and HVAC would overheat or overcool spaces.

HVAC Systems:

HVAC systems are classified as either self-contained unit packages or as central systems. Unit package describes a single unit that converts a primary energy source (electricity or gas) and provides final heating and cooling to the space to be conditioned. Examples of self-contained unit packages are rooftop HVAC systems, air conditioning units for rooms, and air-to-air heat pumps. With central systems, the primary conversion from fuel such as gas or electricity takes place in a central location, with some form of thermal energy distributed throughout the building or facility. Central systems are a combination of central supply subsystem and multiple end use subsystems.

There are many variations of combined central supply and end use zone systems. The most frequently used combination is central hot and chilled water distributed to multiple fan systems.

The fan systems use water-to-air heat exchangers called coils to provide hot and/or cold air for the controlled spaces. End-use subsystems can be fan systems or terminal units. If the end use subsystems are fan systems, they can be single or multiple zone type.

The multiple end use zone systems are mixing boxes, usually called VAV boxes. Another combination central supply and end use zone system is a central chiller and boiler for the conversion of primary energy, as well as a central fan system to delivery hot and/or cold air.

The typical uses of central systems are in larger, multi-storeyed buildings where access to outside air is more restricted. Typically central systems have lower operating costs but have a complex control sequence.

Where are HVAC controls required?

The HVAC control system is typically distributed across three areas:

  1. The HVAC equipment and their controls located in the main mechanical room. Equipment includes chillers, boiler, hot water generator, heat exchangers, pumps etc.
  2. The weather maker or the “Air Handling Units (AHUs)” may heat, cool, humidify, dehumidify, ventilate, or filter the air and then distribute that air to a section of the building. AHUs are available in various configurations and can be placed in a dedicated room called secondary equipment room or may be located in an open area such as roof top air-handling units.
  3. The individual room controls depending on the HVAC system design. The equipment includes fan coil units, variable air volume systems, terminal reheat, unit ventilators, exhausters, zone temperature/humidistat devices etc.

Benefits of a control system:

Controls are required for one or more of the following reasons:

  1. Maintain thermal comfort conditions
  2. Maintain optimum indoor air quality
  3. Reduce energy use
  4. Safe plant operation
  5. To reduce manpower costs
  6. Identify maintenance problems
  7. Efficient plant operation to match the load
  8. Monitoring system performance

What is control?

In simplest term, the control is defined as the starting, stopping or regulation of heating, ventilating, and air conditioning system. Controlling an HVAC system involves three distinct steps:

  1. Measure a variable and collect data
  2. Process the data with other information
  3. Cause a control action

The above three functions are met through sensor, controller and the controlled device.

Elements of a control system:

HVAC control system, from the simplest room thermostat to the most complicated computerized control, has four basic elements: sensor, controller, controlled device and source of energy.

  1. Sensor measures actual value of controlled variable such as temperature, humidity or flow and provides information to the controller.
  2. Controller receives input from sensor, processes the input and then produces intelligent output signal for controlled device.
  3. Controlled device acts to modify controlled variable as directed by controller.
  4. Source of energy is needed to power the control system. Control systems use either a pneumatic or electric power supply.

Figure below illustrates a basic control loop for room heating. In this example the thermostat assembly contains both the sensor and the controller.

The purpose of this control loop is to maintain the controlled variable (room air temperature) to some desired value, called a setpoint. Heat energy necessary to accomplish the heating is provided by the radiator and the controlled device is the 2-way motorized or solenoid valve, which controls the flow of hot water to the radiator.


Panorama offers a wide variety of design solutions for HVAC Controls, including actuators, control panels, control sensors, current sensors and transducers, thermostats, and valves. Contact us for more information on HVAC Controls.