Boiling it Down
What types of boilers are more commonly specified, how do engineers sort through different manufacturer options and in what direction are boiler controls heading? These are a few questions that a panel of boiler experts have set out to deal with in this month's M/E Roundtable.CONSULTING-SPECIFYING ENGINEER (CSE): What kinds of trends have you seen with different types of boilers?PARKER: T...
What types of boilers are more commonly specified, how do engineers sort through different manufacturer options and in what direction are boiler controls heading? These are a few questions that a panel of boiler experts have set out to deal with in this month’s M/E Roundtable.
CONSULTING-SPECIFYING ENGINEER (CSE): What kinds of trends have you seen with different types of boilers?
PARKER : The main driver in specifying one type of boiler over another remains more a function of project size and scope. For example, water-tube boilers are more prevalent in larger projects or for projects that require higher pressures or temperatures, while fire-tube boilers are used in smaller applications, usually less than 30,000 pph.
FASTABEND : In Virginia, we’ve seen the opposite. Many of the larger steam boilers in industrial and institutional facilities installed prior to 1960 were coal-fired, high-pressure water-tube boilers. As a result of environmental issues and lower capital costs, these boilers are now being replaced with packaged fire-tube boilers fired with natural gas or No. 2 fuel oil.
SPAGNOLO : Boiler specifications also depend on the market, with choice driven by the heating medium—whether it’s hot water or steam—the available fuel, the client and the type of project—as well as equipment replacement, renovation or new construction. If we were to identify one general trend, it would be modular boilers—mostly the copper-tube type.
FASTABEND : That is especially true for small commercial applications. The gas-fired condensing modular boilers show a lot of promise due to their compact size, sealed combustion and ease of handling the flue gas discharge. Another benefit is the higher efficiency realized due to an ability to recover the latent heat of vaporization from the condensation of the water vapor in the flue gas.
SPAGNOLO : In designing mechanical systems for commercial buildings, K-12 schools and universities—all sites where natural gas is typically available—smaller boilers are more versatile than their larger cousins and usually operate at a higher efficiency.
And from an engineering perspective, it is possible to design systems with lower return-water temperature, which allows for reducing the flow and consequently the pipe size. In addition to heating the building, these modular boilers are often used to generate domestic hot water. The overall flexibility, efficiency and operating features of the modular boiler are making it the choice of the future.
CSE: On the topic of control strategies, what are the latest developments in boiler controls and what would you like to see happen?
PARKER : Multiple boiler installations are being used to effectively match load conditions. Consequently, control strategies are being used to stage on boilers.
SPAGNOLO : Boiler controls have changed dramatically in recent years, largely reflecting advances in microprocessing. Older boilers that we are now replacing used to operate with a lot of human intervention.
However, today’s modular boilers are typically specified with the manufacturers’ controller. These devices cover most needs, from controlling the temperature of the water as it exits to sequencing the number of boilers that are firing. Today, most owners are more interested in monitoring than controlling boiler operations, which indicates they don’t care how the boiler does its job, just that it is doing it.
Safety is another reason for limiting the external control interface to the tasks of enabling the boiler and monitoring its operation. While it is beneficial for building master control systems to monitor operations, it is also important that firing and safety controls are handled locally, without unintentional overrides from the building control system.
FASTABEND : I personally prefer that boiler controls come from the boiler manufacturer, not building-automation system manufacturers. Building controls should monitor the operation of the boiler, but the control of the fuel, air, etc., should remain with the boiler manufacturer.
CSE: Speaking of manufacturers, how do you evaluate different product offerings?
PARKER : We compare operating efficiencies, maintenance history and physical size, which is critical when specifying equipment to be installed in an existing plant.
SPAGNOLO : Service is the discriminator. If manufacturers don’t answer our questions, it makes it difficult to specify their product. Other things we look at include efficiency, control options and the ability of the manufacturer to meet the owner’s insurance company requirements.
FASTABEND : Several factors enter the equation. First of all, does the unit fit the space and meet the system demands, hour-to-hour and season-to-season? Fortunately, almost all manufacturers comply with American Society of Mechanical Engineers standards, which insure a relatively high level of quality. However, we also look for burner-safety controls to meet the requirements of National Fire Protection Association, Factory Mutual or Industrial Risk Insurers.
Other important features are availability of parts and service. If the manufacturer has many installations within a reasonable geographic area, there is a better likelihood of receiving a good response if a problem develops. And finally, but not least, is the installed cost for both labor and materials. Does the labor required to install the unit match the availability of the local contractors? If contractors are limited, a unit with more factory-installed features rather than field fabrication may be more appealing.
CSE: As a result of the shaky economy, have you seen any noticeable effects on boiler pricing and product offerings?
PARKER : No. In general the bidding on overall projects may have become a little more aggressive. However, I have not seen any noticeable effects on specific component pricing or availability.
SPAGNOLO : While the economy is decidedly uncertain now, we do not see the downturn as having been long enough yet to affect boiler pricing or product offerings in our markets.
CSE: What about from the standpoint of end users? Have tighter budgets had any considerable influence on boiler design?
SPAGNOLO : We are always careful when dealing with the client’s budget, regardless of economic conditions. Our engineers put forth their best design effort; we look at the clients’ goals, and then develop our own. Once we understand what the client wants to achieve, we develop solutions to fit the budget.
PARKER : The overall goal when designing a system is still to give the client the most bang for the buck while ensuring that all design needs are met, so tighter budgets have not changed the design of boiler systems.
Permits, no small matter
CSE: Have emissions restrictions and permitting rules made boiler specifications more challenging? If so, in what ways?
SPAGNOLO : Again, it depends on the type of project. Most boilers we specify are not affected by emissions regulations. Some jurisdictions require complete paperwork at permitting, requesting such information as the manufacturer’s name and boiler model, serial number, number of boilers, quantity of fuel per year, fuel type, hours of operation and information about the stack.
Gas-fired boilers tend to be the easiest to permit. When oil is required as the primary or standby fuel, additional requirements can apply, depending on the grade of fuel. The size of the plant can also make a difference as large plants serving hospitals or campuses typically have additional requirements. Early in the design, it is important to contact the agency and office responsible for permitting to get the latest requirements. Environmental regulations can be extremely dynamic, reacting to changes in technology, as well as the political environment.
PARKER : We’ve experienced some more concrete cases. For example, for emissions and non-attainment areas, in the Dallas/Fort Worth area, and restrictions in NO x emissions, we’ve had to specify low and ultra-low NO x burners.
CSE: What are the most common mistakes made when specifying boilers?
PARKER : Specifying boilers based on maximum load without taking into consideration minimum load and available turndown.
FASTABEND : The complexity of the controls should be compatible with the operators’ technical ability. We often see well designed, but complicated control systems that are not properly utilized because the operators do not have the time or technical background to maintain them properly. Another problem is boiler systems installed in areas lacking space for proper maintenance. Large, clean and appropriately lighted equipment rooms encourage good maintenance.
SPAGNOLO : Working with boilers is serious business, as it is a life-safety issue. Recent code changes, such as requiring high-low intakes for combustion air, can easily be overlooked in a renovation design if one isn’t careful, and it is becoming more common to see design mistakes. Tying into existing exhaust stacks and chimneys is another design consideration that requires careful evaluation of existing conditions and capacities. We have also seen operators, in trying to comply with a code or owner ventilation requirement, put exhaust fans in boiler rooms to give the room a negative pressure, and ultimately prevent a proper draft.
Our quality-control solution has been to normally start with a time-proven, office master specification. We also work with a few experienced manufacturers’ representatives, and perform independent peer reviews of our work.
Raising the bar
CSE: Has the industry come close to hitting the ceiling as far as operating efficiency goes? If so, in what ways can boilers or their related systems be improved?
FASTABEND : I would say that the conventional boiler/burner system probably has achieved top efficiency, but fuel cell technology being developed shows promise.
SPAGNOLO : We are definitely seeing some boiler manufacturers claim higher efficiencies for their units, but we still do not believe we have neared the top yet. Owners have an ongoing interest in equipment efficiency because boilers continue to be big consumers of HVAC energy. As utility deregulation increases and oil prices rise, owners will stay keenly interested in how to reduce operating costs. Further, we believe better efficiencies are possible from heating plants.
PARKER : Efficiencies have gotten pretty high with the use of economizers. Improvements in boiler/burner turndown are becoming an important factor to allow more efficient design and use of boiler systems.
M/E Roundtable Participants
Bill Fastabend , P.E., Vice President, Wiley & Wilson, Inc., Lynchburg, Va.
Gregg Spagnolo , P.E., CIPE, Head Mechanical Engineer, Hayes, Seay, Mattern & Mattern, Inc., Washington, D.C.
Tom Parker , P.E., Associate and Senior Mechanical Engineer, Carter & Burgess, Inc., Energy Services Unit, Fort Worth, Texas
Barbara Horwitz , moderator
Of Boilers, Controls and Interoperability
In the long term, it is quite beneficial for the industry to push for boilers and other equipment to be compatible with BACnet, LonWorks or some other industry standard or communications protocol. But even though interoperability remains a big buzzword, many owners are reluctantly tied to long-term relationships with single control vendors. These owners frequently ask if there is something we can do, as specifying engineers, to work toward some universal standard that will break the single-source suppliers’ grip.
The computer revolution has developed quickly, forcing adoption of industry standards to promote continued growth. And while the boiler industry is much older, it has been slow to embrace new technology. Someday, a building engineer will realize that when he or she gets a call at home at night, that individual can access his or her building’s control system via the Internet, assess the situation and perhaps even fix the problem online. Further down that road, we might be able to introduce the plug-and-play convenience of PCs. Imagine plugging in a piece of equipment—say, a new boiler—the control system would automatically identify it and all the operator would have to do is program the control system how to use it.
There is, we believe, ample room for improvement in the industry … and specifying engineers can play a significant role in that process.