Sit down at your keyboard. Unwrap the new CD. Pop it into the drive. Half an hour later, you've finished sketching a rough concept for a new combined heating-and-power (CHP) plant. You've picked appropriate hardware, calculated the price tag, and projected how soon it will pay back.

Pure fantasy? Not anymore. CHP software tools can help you explore the viability of proposed CHP scenarios, working out for you some approximate parameters and even (at the high end) guiding you onward to conceptual designs with AutoCAD. And coming right over the horizon is a new crop of software enabling operators of CHP plants to optimize efficiency, hour by hour.

More on that development as it comes; the more immediate news concerns screening tools, with several powerful innovations hitting the field this year.

Screening refers, of course, to finding out whether there's merit in a given cogen proposal. Proper screening qualifies an idea to determine if it's worth being pursued with a full-scale engineering study (costing, say, $50,000). You get a yes-or-no answer. Because the assessment is preliminary and investigatory in nature, the software for it should be both affordable and easy to use for novices. On the other hand, the answer (often factoring together hundreds or thousands of input variables) should be reasonably correct: The result is carrying big stakes. Hence, there's a tradeoff to be struck between ease of use and accuracy. Fortunately, there's now a growing toolkit of proposed solutions offering both.

Dominating this array, of late, is the US Department of Energy (DOE), which has taken the lead in software R&D as a result of the strategic importance of CHPs. DOE's Office of Distributed Energy (ODE), under the leadership of Patricia Hoffman, is underwriting development costs through its partner facility, Oak Ridge National Laboratory (ORNL). Most screening tools are now available (many for free) or soon will be.

Screening Tools:
What They Do, How They Work
The current lineup of programs ranges from older, simple ones—still appropriate in some contexts—to robust ones able to process thousands of inputs. What distinguishes one from another? Randy Hudson, of ORNL's CHP group, explains that the differences lie not so much in the basic calculation of formulas, but in the level of data refinement, especially in newer tools. Various vendors have made differing assumptions regarding what factors are critical, which are less so, “and how to slice and dice,” for example, “the pricing inputs for fuel, electricity, heat, and capital equipment costs.” Consequently, some programs have been beefed-up in complexity. Others “are still very, very simple, requiring only three to five pieces of input” in order to yield an answer, says Hudson, who wrote a 2003 report for DOE on nine cogen screening tools.

In terms of how they're used, most programs follow a common approach. Users are offered various menus of options from which they point-and-click the needed input parameters. For example, you might specify data on heat and electric loads, and then select whether the proposed CHP system will yield process steam, hot water, chilled water, or combinations thereof. The screen may prompt you for such building specs as square footage or give you another drop-down list of types as models—say, a hospital, an office, a hotel, a school, or a retail site.

Based on these inputs, a mathematical calculation may result, suggesting a tentative answer on CHP hardware requirements.

Next, you might see lists of specific HVAC equipment options matching your load needs. You select size or type. The software incorporates data libraries of turbine models, costs, and output characteristics.

Once you've input all your parameters and loads, arriving at tentative hardware specs, you click again to read about costs. Many programs offer multiple assortments of added financial views: standard cash flow, simple payback, net present value, internal rate of return, operating costs, and even capital and tax-related cash flows. You may get a specific number on grid-power savings. Several tools also provide statements on the proposed system's physical outputs such as mass flows—steam, water, CO2, NO2—and specific power and heat production/consumption.

How They're Being Improved
From this overview it's apparent that greater accuracy will come from having more numerous and precise data inputs. This means grappling with more data fields. As these numbers have soared into hundreds and thousands, the programs growing proportionally complex, there's also been a corresponding need for users to obtain online help—and, happily, developers are responding: Tips, popup wizards, default values, and lists of good choices, along with bundle-in value tables and suggestions, are now being augmented. Instead of having to collect it yourself, reference data are at your fingertips. Finally, good tools typically flag any contradictory inputs, prompting for corrections.

Which CHP tool is right for a particular job? Which will work best for you? Several factors apply in making the decision. Two primary ones, says Hudson, are how much work you wish to put into the data-collection and how much sophistication you require in the preliminary stage of screening—some screens being “coarse” and some “fine.” A third selection factor is the user's level of CHP sophistication.

From the dozen or so good products out there, here are four of particular interest—being either free or relatively low in cost and equipped with DOE's newest simulation engine.

Process Heating Screening Tool
Developed for ORNL by E3M Inc. (www.e3minc.com); anticipated free or low-cost download from DoE Midwest Regional Application Center websites (www.chpcentermw.org) and other RACs.

Released in mid-2004 by DOE's R&D lab at Oak Ridge, this software does a quick assessment of usable heat from any of 1,000 models of turbines in its database. The heat-centered analysis is aimed at potential reuse in direct process heating as well as heat-recovery boilers.

“I like to think of it,” says the tool's creator Arvind C. Thekdi, who is president of E3M Inc., “as a ‘window-shopping' tool. You can look at a turbine, and if you like the numbers, you can go inside the ‘shop' and analyze it in detail.” That is, one can decide whether to hire engineers to do a detailed study.

Three kinds of process-heat recycling can be scrutinized by PHST: fluid (i.e., liquids, air, and other gas), heating in ovens (say, for drying processes), and reuse of the residual oxygen from the turbine exhaust.

Prior to deciding to write PHST, Thekdi and the Oak Ridge staff searched for other software capable of doing this particular spectrum of heat analysis, finding only programs for measuring steam generation. DOE saw a significant potential for advancing industrial CHP by developing PHST for download at its new regional application centers (www.chpcentermw.org; click ‘evaluation tools').

A user starts by selecting from multiple menus of turbines (sized 28 kilowatts up to 20 MW), and then chooses assorted heat-exhaust characteristics to be explored. Other key elements, such as current energy consumption, are inputted. When selections are completed, the tool sizes a turbine, tells you how much you'll save with it, estimates the installation cost, and projects payback. Results can be generated, says Thekdi, “in as little as 30 minutes.”

PHST is primarily aimed at industries having relatively continuous heat processes with large fuel consumption—such as petroleum, chemical, steel processing, mining, and cement plants. Sites where heat loads fluctuate should probably use one of the more flexible heat-and-power modelers shown below.

BCHP Screening Tool
Developed by GARD Analytics (Park Ridge, IL) for the US Department of Energy; available on CD by contacting Steven Fischer at Oak Ridge National Laboratory (fischersk@ornl.gov)

Also brand-new—and in some ways complementing the Process Heating Screening Tool just described—is a powerful and important new hourly simulation tool for calculating electrical and thermal loads in commercial buildings. Bundled with the industry-standard DOE-2.1E load modeler is a big database on daily weather and power rates nationwide.

ORNL's Steven Fischer, who oversaw its development, describes BCHP-ST as “a screening tool where you don't need a great deal of experience or background in the field to do the calculations.” First, a user inputs assorted building specs, and the program pulls from its database the appropriate meteorological weather-year data needed to calculate the heating, cooling, ventilation, and electrical loads. These values are then matched with the parameters of various heating and cooling systems on the market as well as power-and-heat–recovery technology. Users select various combinations of generators and absorption chillers from pull-down menus. “There are few programs that do all of that,” Fischer notes.

But the really big difference is that competing tools require users to specify thermal and electric loads—a task both laborious and fraught with the potential for errors. By contrast, BCHP Screening Tool has already done most of the legwork and linked a hefty database to the input fields. “We have both gas and electric utility rates that you can tap into,” Fischer says. You select your city or utility from the list; a second list indicates all of the esoteric rate structures nationally—more than 3,000 of them, adding up to “about 60 megs of data” with documentation.

Having such voluminous rate- and meteorological-forecast data (based on three-year weather averages), the tool can then figure all of your projected loads.

Moreover, because the program uses hourly increments and matches these precisely with hourly utility charges, the resulting numbers will almost certainly be more accurate than if you had dug through your past billings for a whole year and attempted to project ahead from there. “It's a much more comprehensive calculation,” Fischer says.

Of course, as the years go by and the program ages, a user will need to reverify the utility rates periodically. On this point Hudson notes that a big database is “a two-edged sword.” He explains, “It's nice to have if you don't have anything else to use to plug in—but then again there's the question of how good is that info, and how recent. So it's potentially a good and bad thing at same time.”

How complicated is it to use? Fischer concedes, “There's a bit of a learning curve, so it takes some serious interest. It's not for the casual user.” As of the spring of 2004 about two-dozen copies had been delivered and were in use. “What we're discovering,” he says of this launch phase, “is that, to do the calculations right, you do need more experience than we expected.”

The BCHP Screening Tool, notes Fischer, “is likely to complement” the final tool in this brief survey, Cogen Ready Reckoner, “particularly in the area of commercial buildings where users have little or no a priori knowledge of their thermal loads.” First, though, comes a powerful new version of another modeling program.

Building Energy Analyzer (BEA)
Developed by InterEnergy Software (www.interenergysoftware.com) and the Gas Technology Institute. Cost: BEA $580, BEA PRO $780. Order from GTI (800) 883-7743.

BEA 2.2, a tool for screening CHP in commercial buildings, has just been released in a PRO version incorporating several “capital assessment components” and other powerful new features, notes GTI's manager of software development, Marek Czachorski.

The most important of these is probably the “retrofit wizard,” an improved way to calibrate modeling of the weather-influenced building energy consumption. Correct weather data is turning out to be increasingly critical to accurate cogen screening, Czachorski says. Changes in the weather will obviously impact building energy consumption as well as fuel and electricity costs. Even a moderately skewed long-term forecast will seriously distort the cogen model.

As its basis for climate data, BEA 2.2 PRO uses the National Renewable Energy Laboratory's (NRELs) Typical Meteorological Year (TMY2) database and DOE-2.1E simulation engine (as does DOE's BCHP Screening Tool). These are good, he says, so far as they go, but “so-called ‘typical weather' is still only artificial,” and hence the output is potentially less than satisfactory. For example, if you were to retrovert your CHP simulation model and compare the weather-influenced cost predictions to what you actually paid for fuel and power, chances are you'd come up with a mismatch. People find this discrepancy routinely in their models, he says, “and they are really scratching their heads trying to find out ‘what did I do wrong?'”

The answer is that TMY2 is, by definition, artificial/composite weather; thus, as one corrective, BEA 2.2 PRO now includes an additional database of actual cooling and heating days as well as minimum and maximum monthly temperatures spanning the last three years for 233 geographical locations in the US. “When modeled by BEA 2.2,” he explains, “building energy consumption and that from the actual energy bills are then normalized using cooling and heating days data from both databases and compared.” This greatly improves the level of confidence when interpreting modeling results and, if needed, guides the user's corrective action in adjusting the model.

Also similar to the DOE's BCHP Screening Tool, BEA 2.2 PRO uses 8,760 hourly increments for modeling a year. This means, says Czachorski, that “everything is happening in real time—which is especially important for proper calculation of cogen heat-recovery effectiveness.” Consequently, you don't risk making the large-scale errors inherent in longer time spans.

An added monitoring component for heating-and-cooling coil dynamics and energy consumption by end use permits you to look at 8,760 hours of data on metered elements—including, for instance, how much electricity went into the HVAC equipment, how much went into heating and the like, he says.

Finally, there's a module for predicting onsite and avoided emissions of CO2, CO, NOx, SOx, and particulates from various hardware layouts. Emissions levels can affect eligibility for credits, incentives, and permitting.

Cogen Ready Reckoner
DOE screening tool; see www.eere.energy.gov/der/chp/.

An old standby used by both DOE and ORNL, Cogen Ready Reckoner, says Fischer, “has been a valuable tool for industrial applications, which is seeing some use in evaluation of CHP in commercial applications.”

Originally developed in Australia, Ready Reckoner was then imported by the DOE and revised with US values and specs for applications here. Fischer and Hudson have used it for years, particularly Hudson. Unlike BCHP Screening Tool, Ready Reckoner permits only 12 incremental divisions (compared with the Screening Tool's 8,760). However, as Fischer points out, that capability still “lets you divide a day into first, second and third shifts for modeling and industrial systems.” You can also select representative days for modeling each season of the year or, alternatively, specify thermal loads for each shift or time period, or break the year down into periods matching production schedules. Whichever parameter you select, you are using a constant thermal load and constant utility rate for each period. Although that's not nearly as refined as an 8,760 analysis, it's often adequate. Hudson points out that when he's using Ready Reckoner head to head against a colleague running the BCHP Screening Tool on the same project, “we get pretty much the same answers.”

Why Not Several?
Hudson's last point suggests that it may be worthwhile to screen your next project with more than one tool—particularly since several of them are free and can produce rapid results. Thus, if two different tools or methods arrive at the same results, you've probably gained an even stronger indicator of accuracy. Conversely, if two tools or methods come up with disparate results, this might suggest some erroneous assumptions or “garbage in” occurring with one or both tools. Alternatively, you may want to use multiple tools to gain the benefit of their respective strengths, especially if a single tool seems lacking in something important.

Still another strategy for gauging tool and assessment accuracy would be to have two different users screen the same project using different tools. If results don't match, switch chairs and try again.

Even if you've settled on using just one tool, don't always rely on a single “black-or-white” or “conclusive” prediction as the basis of your cogen decision. Instead, Hudson suggests, using the tool to provide a range of estimates, including optimistic and pessimistic ones. “You can look at highs and lows and expected values for [fuel and energy] prices in the future,” he adds. Also, by taking multiple assumptions, you can “get some feel for how price-sensitive the project is,” or how close you may be to the ‘ragged edge' of not having a viable project,' he suggests.

Likewise, on a marginal CHP project in a weak cogen market, if you apply a fine-screening tool persuasively, you can “rescue” a proposal that otherwise wouldn't be salable.

Note, too, that the above tools are hardly an exhaustive list and that other excellent tools should not be overlooked. Pricier ones may offer very worthwhile advanced and needed features, especially for industrial facilities or district power. Several are capable of providing basic screening or full-bore, in-depth assessments (the latter of which none of the four tools above can do). Among a strong lineup of commercial products, Thermoflow Inc. offers three related tools: GT Pro, for highly detailed design of industrial gas-turbine applications with or without HRSG or combined cycle; a cogen screening product called Plant Design Expert; and a third, Recipro, for small cogen applications. A detailed 3D design simulator, HeatMap CHP, is offered by the Washington State University Cooperative Extension Energy Program. The Electric Power Research Institute (EPRI) has developed a product called SOAPP CT.25 geared for conceptual design of industrial gas turbines with or without HRSG. All are profiled in Hudson's market survey, which can be viewed online at ORNL.gov or at the Midwest RAC website noted above.

Besides all of these commercial offerings, there are in-house tools developed by CHP engineering firms. In addition, some of DOE's six regional application centers offer customized versions with built-in localized weather and utility-rate data.

No single tool has attained perfection, or even emerged as a favorite, but DOE's strategy of subsidizing multiple ones allows practitioners to mix and match easily, to do experimentation, and to meet a personal preference.

Finally, despite many improvements, critical gaps in data accuracy remain. Some are probably impossible to correct—particularly, long-range fuel and power pricing, which is inherently sensitive to everything from strange weather trends to world events impacting the supply side. “If we were able to predict that,” says Hudson, “we'd all be living well-off somewhere.”

Based in La Mesa, CA, writer DAVID ENGLE specializes in construction-related topics.

DE - March/April 2006