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Hot and Cold Comfort

Recent advances in boiler and chiller technologies

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Credit: RENTECH
Modular boiler designs offer ease of transportation, delivery, and installation, all of which reduce overall cost.
What could be more boring than a mature, established, and widely used technology? What could be easier to take for granted? We tend to get blasé about technical advances that our ancestors would have found to be amazing, even magical. Take something as commonplace and obvious as heating and cooling a building.

First envisioned by the inventor of the steam engine, James Watt, advances in radiant steam heating slowly took hold and became popular in the 19th century. This century saw the invention and widespread use (at least in large buildings and government offices) of steam radiators, draft regulators, automatic water valves, and the vacuum-return steam heating system, among others. For smaller buildings and residences, hot water (or “hydronic” systems) would replace or supplement traditional fireplaces, chimneys, and wood-burning stoves.

With high-pressure hot water systems becoming popular, additional advances continued in the design of registers, boilers, and radiators. These included sectional boilers, steel-encased furnaces, and cast-iron boilers replacing earlier models encased in brick, installation of direct radiators providing heat to individual rooms, and thermostats to finely adjust levels of heat output. At first heated by loads of manually fed coal delivered by horse-drawn wagon or truck to individual homes, heating systems would be powered first by electrical coal stokers operated by thermostats and then by oil and natural gas burners using fuel piped into the home. Driven by intense free market competition and ever-increasing demand, this nascent industry experienced the kind of growth, diversification, and innovation found today in Silicon Valley.

This technology plateaued and marked time by the late 20th century, experiencing refinements, improved efficiencies, and wider use, but no major technological breakthroughs like the explosion of innovation experienced in the previous century. The same has been said about many other industries.

The question is: what exactly are the disruptors of this industry? What technology advances and operational practices are making boilers and chillers increasingly efficient today? But before we can know where we are going, we have to look back at where we have been and determine exactly where this technology stands.

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Building Boiler Systems: The Current State of the Industry
Boiler heating systems are typically used for larger, multi-unit apartments, hotels, office spaces, factories, and for large commercial buildings in general. The heat generated by the boiler and carried by the conveyance pipes is measured in British Thermal Units (BTUs—defined as the amount of heat necessary to raise 1 pound of water 1°F). Given an average wall height for each room, there is a given number of BTUs per square foot of floor area needed to achieve the desired ambient air temperature required for the safety and comfort of the occupants. These heating requirements have been enshrined in building codes and industrial specifications. The amount of heat required per square foot depends on the climate of the building’s location. The amount of heating required is typically 50 BTU per square foot of interior space in a cold climate, 35 BTU per square foot in a moderate climate, and 20 BTU per square foot in a hot climate.

(Source: The US Department of Energy’s Office of Energy Efficiency and Renewable Energy [DOE-EERE])
The size of the current boiler market in the US is substantial, providing considerable incentive for further technological improvements. The US Department of Energy’s office of Energy Efficiency and Renewable Energy (DOE-EERE) categorizes commercial and residential boiler use in the US in Table 1.

In addition to output, boilers are rated by overall operational efficiency. This is measured by the Annual Fuel Utilization Efficiency rating (AFUE) developed by the DOE. It compares the amount of heat actually generated by the boiler with the potential heat in the fuel used to heat the boiler. For example, burner fuel oil (No. 2 oil) has a heat content of 140,000 BTUs per gallon. If a boiler burns a gallon of fuel oil and generates 120,000 BTUs of room heating, the boiler system has an AFUE of almost 87%. The standard efficiency for new boilers is an AFUE rating higher than 95%.

Unlike the forced hot air system utilized for small residential units and buildings, boiler systems utilize the heat from steam which is carried throughout the building by a series of conveyance pipes. The pipe network connects the steam flow to each room in the building where it is used to heat the rooms either via heated floors, baseboard heaters, or free-standing radiators. Hot water or steam enters the radiator structure, radiates heat into the room, and then exits via a return pipeline. These return pipes carry the now-cooled water back to the boiler to be reheated. These systems form a complete circuit connecting boilers to conveyance pipes to radiators to return pipes and back to the boiler again. Each individual component of the system has its own unique design characteristics.

The source of the heat driving the system, the burner, is fed by fuel lines that transmit oil or gas to an ignition flare which generates the heat that creates the steam. Atomized by a fuel injector’s spray nozzle to maximize its oxygen content, the ignition is created by a spark assembly. Once ignited, the flame is adjusted by the rate of fuel injection. The flare is deflected by refractory bricks to focus on the heat exchanger. A heat exchanger consists of a series of metal tubes formed into a manifold and carrying its own internal volume of water acting as a working fluid to transfer the heat to inside the tank. Exhaust gases from the flare are vented separately to the outside air.

Boilers are basically enclosed water-filled tanks heated by an external energy source. This energy can come from the combustion of fossil fuels (coal, natural gas, or oil), electrical heating coils (typically for smaller buildings), or even concentrated sunlight. As the water within the tank heats up, it flashes to steam and its volume expands, increasing pressure within the tank. The result is an increase in pressure within the tank. Therefore, the tank’s structural components (joints, welds, fixtures, appurtenances, and the wall material itself) have to be designed and reinforced if necessary to withstand these anticipated operating pressures without rupturing. The steam or hot water created in the boiler becomes the working fluid that the system uses to convey heat throughout the building. Heat is transferred from the external energy source to the water within the tanks via fuel burners that ignite the incoming fossil fuel and a heat exchanger that carries this heat to the water. The hot water is then conveyed to the piping system by means of a circulating pump, whereas steam typically provides its own pressure for movement in the pipes.

The boiler operation is kept within design limits by expansion tanks, water pressure regulators, and safety release valves that allow steam exceeding the tanks’ rated containment pressure to safely escape. The entire operation is controlled by a thermostat that regulates the temperature in each room and provides feedback to the boiler to burn more fuel if the rooms are too cold, or less fuel if the rooms are too warm.

Connected to the boiler is a network of pipes that circulates the hot water or steam to different locations and rooms in the building and back again to the boiler. The overall structure resembles a loop that extends to the furthest part of the building. Attached to this loop is a system of automatic controls and regulators (emergency pressure relief valves, air purge vents, and backflow preventers). All of these are necessary to prevent potentially dangerous buildup of heat and pressure within the piping system.

The delivery point of the heat occurs at the radiators installed in each room and connected to the circulating pipe loop. Radiators are appliances that connect to the steam flow pipes, run the steam through their interior, and radiate the heat from the steam from exposed metal surfaces. The typical temperature for a hot water radiant system is a steady 180°F. The same temperature is used for steam systems, but these can be adjusted when a room temperature gets too cool by increasing the heat output of the burners to flash steam the boiler water to a temperature above 212°F. As such, steam systems don’t rely on the constant heating of steam, but on the cycling on and off of the burners to produce steam as needed. In addition to automatic controls, radiators are often equipped with individual manual shut-off valves.

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Photos: RENTECH
Installation of a high-pressure boiler unit.

Recent Advances in Boiler Technology
In real estate, the three most important factors are “location, location, location.” In the field of advanced boiler technology, the three most important factors are “efficiency, saving space, and zero waste”—and location, or at least properly matching the type of boiler application to the kind of facility utilizing the boiler heat. So where can additional efficiencies be squeezed out of a mature technology?

Overall boiler efficiency is not just about the cleaner burning of the fuel providing the heat. There are space savings which indirectly lead to improved operational efficiency. Space saving can be provided by modular designs which directly provide ease of transportation, delivery, and installation—all of which reduce the system’s overall costs. They also make retrofitting operations easier since they can be installed alongside existing large, single-unit boilers. This, again, results in considerable overall cost savings. By transitioning with side-by-side systems, the operational costs of replacing an older, less efficient system with a newer, more efficient boiler are reduced as well.

Modular boilers can be configured side by side for operational flexibility or stacked to save floor space.

Each module is a separate boiler. They can be configured in a side-by-side floor layout for operational flexibility or vertically stacked to save floor space. Each boiler module provides a fixed percentage of the system’s overall heat load. With each module designed for maximum thermal efficiency, the result is a system that utilizes less area and emits fewer exhaust fumes. The operational flexibility inherent in a modular system allows the boiler to match a building’s operational profile both seasonally and across a typical work day. When load demand for heat is at its highest, all modules can be firing and providing heat. Lesser loads or disperse loads throughout a larger facility can be matched with fewer operating modules. With each module at its highest efficiency when operating, the system’s overall efficiency is maximized. Efficiency equals cost savings, and modular boilers provide this both in terms of facility layout and facility operations.

High-efficiency boilers from RENTECH are
custom-designed for each application.

The boiler itself is getting smarter with each advance in control technology, with artificial intelligence creating the “smart boiler.” Already most boilers utilize building automation systems (BAS) and programmable logic controls (PAL). Boiler engineers have built real-time monitoring and measurement of water use into their monitoring systems to allow operators to adjust boiler systems in real time. These systems can even suggest additional cost-saving efficiencies. Boilers can self-monitor for wear and tear of operating parts, notifying operators when maintenance is necessary and spare parts are required. This again provides an indirect cost savings by keeping parts and material inventories low.

In addition to modular design, boilers can be equipped with stack economizers. Basically, these recover waste heat from the hot flue gases from boilers and reuse this waste heat to preheat the boiler water. Essentially, these are not different from combined heat and power systems that recover heat from power systems and reuse it to heat office space. This may not sound significant at first, but a typical boiler loses up to 20% of its heat out the flue. Even recovering only half of this heat can push overall system efficiencies another 10% higher.

Building Chiller Systems: Current Practices
As a building needs heating in the winter, it also needs cooling in the summer. A chiller does not just cool a building; it also dehumidifies the air. Chillers not only provide comfort to building occupants; they are critical to the operation of energy-intensive, heat-generating systems such as computer servers. Chillers themselves require significant energy to operate. Depending on building location (and other external factors such as seasons, latitude, outside temperature, cloud cover, local wind and humidity, etc.) and its internal use (mechanical operations, heat gain from lighting, number of occupants, etc.), chillers can represent the building’s single largest consumer of electrical power, consuming over 50% of a building’s electrical power supply. In fact, over 20% of the electrical power generated in the US is consumed by chiller operations and up to 30% of our electrical energy inefficiency (US DOE data). The market is huge, with chiller inefficiency costing billions of dollars annually. And the potential for both efficiency improvements and technological disruptions is great.

A building chiller is essentially a large heat transfer system. It uses the principles of refrigeration to carry heat from inside a building to the external environment. Refrigeration utilizes vapor compression and vapor absorption of a coolant working fluid (whether simple water or chemicals like Freon). This coolant is provided in a continuously circulating flow from a cool exterior radiating point where the preferred temperature is about 50°F back into the building to absorb heat which it then carries out again.

Heat from the building interior is fed into the cooling system at an internal evaporator which turns the refrigerant into a low-pressure gas as it gains heat and increases temperature. In doing so, it reduces the temperature of the building’s internal spaces. The refrigerant is then piped to a compressor, which transforms the refrigerant into a high-pressure gas, still at higher temperature. From there, it is pumped to an external condenser which rejects the heat to the building’s outside environment. This reduces the refrigerant to a high-pressure liquid. From the condenser, the refrigerant passes through an expansion valve which changes it into a low-pressure liquid that is pumped back to the evaporator to start the cycle over again.

Though this is the basic operating principle of any chiller or refrigerator system, there are two different types of chillers: air-cooled and water-cooled. Air-cooled systems radiate heat from condensers that resemble room radiant heaters or automobile radiators. Air-cooled chillers typically require external ambient air temperatures of no more than 95°F to function properly. Rejection of heat by water-cooled condensers is a two-step process. The heat is first transferred to a tank of cooling water. This heats up the water which is then pumped separately to a cooling tower where it rejects the heat to the outside environment and subsequently returns to its coolant tank. Though more complicated, water cooler systems can be installed indoors, which provides protection from the elements and greatly increases their operational lifetimes. However, air cooling systems, being simpler, have fewer maintenance costs.

Recent design innovations have yielded greater efficiency

Recent Chiller Design Innovations
As with boilers, chillers always have room for additional improvements in design, operation, and efficiency. Again, these efficiencies can either be direct improvements in heat utilization or indirect design changes that reduce the system’s overall operating costs. And these recent developments have been largely successful. As a result of their utilization, the peak load efficiencies of building chiller units are 25% higher than a decade ago and reach overall efficiencies of 95%. These improvements are designed to reduce maintenance, increase efficiency, and minimize greenhouse gas emissions. These may be small things, but small things add up.

Diagnostic tools and intelligent controls are a software and hardware team that ensures long-term peak efficiencies and fewer repairs. They allow a chiller system to self-examine its own operation while providing hard data in real time to system operators. The resultant performance data and energy utilization analyses provide the tools that operators need to adjust or even upgrade the system.

As with modular boilers, modular chillers can be used to provide space saving and flexible operations. These are separate chillers linked together as an operating unit but with each module equipped with its own compressors, pumps, fans, and valves. Each comes with independently operating controls functioning in accordance with software algorithms designed to optimize operational efficiency.

Advanced chillers can even be designed as heat recovery systems. As with a combined heat and power recovery system, a waste heat recovery chiller system uses the heat normally rejected by the condenser and puts it to work. The primary use is the heating of water: hot water supply, service water, process water, etc. By actively extracting heat from the condenser, the system reduces the overall work load of the condenser (referred to as a condenser “lift”) required to increase the refrigerant from a lower pressure to a higher pressure. By reducing the work load of the compressor,
the operator can reduce the electrical power utilized by the compressor motor—a significant cost savings. Add onboard intelligent control systems that can maximize simultaneous hot- and cold-water generation and further efficiencies can be achieved.

On the Horizon: Future Boiler and Chiller System Advances
On the cutting edge of boiler and chiller technology are new developments that will soon further transform the industry. These include:

Ice “Batteries.” These are designed to create reliable and simple energy storage systems at minimal cost. The overall result is an increase in system efficiency by storing energy in the form of ice blocks. The system creates ice during off-peak hours (for example, at night when a store or office building is not occupied). The ice is then used during the work day to enhance the overall cooling of the building. The larger system can provide ice cooling for a full eight-hour work day.

Utilizing the Earth’s Heat. Geothermal heat pumps have been around for a while. What is new is their full integration into a large building’s heating and cooling systems. They work off of the principle that earth at a certain depth tends to maintain a roughly constant temperature year round. In winter, geothermal pumps heat buildings by absorbing the heat from the earth by circulating water in buried pipeline loops and transferring this heat back up into the building. In summer, it acts as an auxiliary cooling system with the water flow reversed to carry heat from the building back down into the relatively cool earth. The trick with integrating geothermal pumps into commercial building systems is to properly size them so that they can provide a significant addition to the building’s heating and cooling operations, while avoiding installation problems. Installation can be a problem in urban environments where the building is underlain by a foundation structure and other pre-existing utilities. Studies have shown that improvement in geothermal pump performance for commercial building can be achieved at minimal additional cost by increasing the pipe length of the earth heat exchanger and by increasing borehole spacing around the building.

Smart Systems and Analytical Software. These rely on further improvements and sophistication of control system hardware and software. Improved operating algorithms can effectively remove the human operator from the decision-making loop. This relegates people to an oversight role while decision-making is performed by the software. The software not only makes its own operating adjustments, but it will also schedule maintenance based on date received from sensors analyzing the process, and can order and purchase spare parts when needed.

Zoning. This takes the modular concept a step further to the actual rooms being heated and cooled. Like geothermal heat pumps, zone HVAC has been around for a while. What is new is giving this operating system a level of intelligence that allows it to track room utilization and occupancy. This data can come from GPS chips embedded in employee ID badges that allow the system to track movement and analyze meeting room and auditorium schedules to evaluate the number of people that will be using these work spaces and when they will need them. For example, the system can prepare an appropriate level of comfort for a room that will hold a meeting of a dozen people at 2:00 in the afternoon. Zoned cooling and heating systems can be activated far enough ahead of time so that the room temperature is ready for its occupants just in time for the meeting, and then later deactivated when the meeting is over and the room is no longer needed.

Major Suppliers
RENTECH Boiler Systems of Abilene, TX, is an international provider of high-quality, engineered industrial boiler systems in the form of complete, engineered solutions. These solutions are manufactured in their sprawling, 70-acre, state-of-the-art manufacturing plants. Each boiler system is custom-designed for and built for each customer’s unique applications. The company’s complete, integrated engineering solutions comprise packaged water tube boilers, modular heat recovery steam generators (HRSGs), waste heat boilers, and other specialty boilers. Their customers include the largest independent power producers, refining, petrochemical, and industrial companies in North America. They specialize in and are the largest supplier of HRSGs for high-efficiency gas turbines that operate in the 3- to 40-MW size range. Their expertise in high-fired applications incorporates full optimization of the duct-burner performance while utilizing catalytic oxidation and SCR for control of emissions from the entire system. RENTECH’s packaged boiler design often has been specified for critical industrial processes, turbine warm-up, and auxiliary boiler applications because of its rugged design and proven reliability. Their use of 100% membrane wall construction eliminates the need for refractory and enables quick startup to achieve full steam capacity of the boiler in less time than it takes with older designs. Their optimized boiler design results in lower emissions. RENTECH’s knowledge of low-emissions burner and catalytic reduction technologies enables their company to supply systems that fully comply with all performance criteria and are backed by single-source guarantees.

Credit: iStock/baona

Case Study: The Morning Star Packing Company Tomato Processing Plant Doubles Steam Output While Lowering Emissions
Morning Star Packing Company is a major producer and packager of tomato ingredient products. As part of a plant expansion initiative, it recently installed new boilers, combustion systems, and a Selective Catalytic Reduction (SCR) system at its facility in Williams, CA. This led to a boost in output while maintaining emissions within the required limits. “We increased steam generation capacity at the plant twofold while lowering NOx output,” says Jon Ikerd, Project Manager for Morning Star.

Since 1970, Morning Star has been serving the produce market and now accounts for over 25% of California’s tomato processing production. It supplies 40% of the US ingredient tomato paste and diced tomato markets with sales of approximately $350 million. “Morning Star is the world’s leading tomato ingredient processor, serving food processors throughout the world,” says Ikerd. Additional processing plants were added, expanding the company’ capabilities.

Credit: RENTECH
An industrial boiler installation

The company’s expansion brought new problems and challenges. The selected boiler for another Morning Star facility ran into issues related to installation and the welding of the steam drum. This meant it did not initially meet its guaranteed production levels. To solve this problem, the company opted for a solution consisting of multiple elements: two boilers from RENTECH Boiler Systems, with register burners and an SCR system.

All of this equipment plays a vital role in the facility’s production processes—the steam is used to boil, dehydrate, and concentrate the paste. “The success of the installation was very much a collaboration between our burner representatives and RENTECH,” according to Ikerd. The new burners were effective in narrowing the window of combustion in order to reduce NOx to below 15 ppm. However, this made boiler operation more finicky and less reliable.

So, a suitable alternative had to be found for ultra-low NOx burners. California is known for its tough environmental regulations. The Williams plant is not in a nonattainment district (where standards are very strict due to air pollution levels persistently exceeding Ambient Air Quality Standards); it still has to satisfy stringent state requirements. The county air quality control office set a strict limit of 25 tons per year of NOx for Morning Star. This made it difficult for the company to execute its expansion strategy. If it had opted for the same boilers and burners as usual, it would have greatly exceeded its NOx quota. Fortunately, the combination of the John Zink Hamworthy register burners and SCR, along with RENTECH boilers, meant that capacity could be greatly increased while remaining in compliance on emissions levels. The register burners selected for Williams brought NOx levels down to less than 30 ppm. The SCR then further reduced this to 5 ppm. The expansion project effectively doubled steam generating capacity at Williams.

The new boilers have raised capacity from around 680,000 pounds per hour to 1,360,000 pounds per hour. Boiler efficiency has also been raised from below 80% to around 85%. For a business whose highest operating cost is fuel, this equates to a welcome reduction in the cost of steam. “Our new RENTECH boilers have enabled us to double steam capacity while keeping total emissions well below the 25 tons per year limit,” says Ikerd. BE_bug_web

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