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Why is the efficiency of a steam generator important?

Normally when buying a new steam boiler, one of the first parameters that are evaluated is its efficiency.
This is because it represents the effectiveness of transforming the energy of the burned gas into steam.

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However, the single boiler&#;s efficiency is not everything.

If you either need to decide which boiler is the best fit or achieve a reasonable improvement in performance and therefore savings in consumption, you must evaluate the overall efficiency of the thermal power plant.

But let&#;s go in order and see what the efficiency of a steam boiler is.

Index:

1. What is the efficiency of a steam generator?
2. Why is boiler efficiency important?
3. Calculation of the average yield and savings on gas consumption:
   a. The real efficiency;
   b. Start with demand profiles
   c. How to save with performance
4. Conclusions

1. What is the efficiency of a steam generator?

When it comes to calculating the efficiency of a steam generator, there are many variables to consider.
It is not very intuitive and some clarifications are needed, before going any further.

Let&#;s start from the basics:
What is meant by the efficiency of a steam generator? How is it calculated? Why is it classified as the most important parameter of a thermal power plant?

Let&#;s go in order and answer the first question: what is meant by the efficiency of a steam generator?

The efficiency of a steam generator is nothing more than a measure of its energy efficiency: it is the percentage of energy generated by combustion, energy which is then transferred to the water to evaporate it. In the calculation, it is also necessary to take into consideration the energy lost in dissipations, and fumes deriving from combustion.
As the dissipations and the temperature of the fumes decrease, the efficiency will always be higher: it will tend to 100%, without ever reaching it.
For the principles of thermodynamics, the 100% efficiency is impossible to achieve, as the heat generated by combustion would be transferred entirely to the water, without causing the slightest dispersion.

It is intuitive to say that, as the efficiency of a steam generator increases, the amount of fuel (e.g. natural gas) required to produce it will decrease.

After having made an overview on the meaning of efficiency, let&#;s move on to the study of a practical case, in which we show its correlation with methane consumption, and then go on to understand how to decrease it.

2. Why is boiler efficiency important?

In order to understand how important the calculation of the steam generator real efficiency is, we analysed the operating costs of a thermal power plant in its first 10 years of life.
We then divided all costs into the initial investment, natural gas consumption, electricity, water and maintenance costs.

This is what we found out.

What is noticeable at first glance, is the preponderance of methane costs compared to all the others.
In this case, about 68% of the total costs are represented by methane; and it is precisely here that we want to dwell.

Since efficiency is the ability to transfer the heat produced by combustion to water, and then transform it into steam, the higher the yield, the less volume of methane is needed to produce a certain amount of steam.

Since methane is the highest cost item for a heating system, and since efficiency is the parameter that most affects its consumption, it is now clear why is so important when choosing the new boiler.
Let&#;s see how it is calculated and how the boiler manufacturers use it in their favor, not behaving in a completely transparent way.

3. Calculation of the average yield and savings on methane consumption

The efficiency of a steam boiler is always provided by the manufacturer. All of them though calculate the efficiency under particular conditions that not always match the real ones.
So the question now is, what are those conditions? How does the efficiency vary based on mine?

Often, the customer who decides to buy or replace a boiler is not aware of the fact that the data provided by the manufacturing company is processed in the laboratory under specific loading conditions.

A bit like the automotive market, where the promised consumptions are almost impossible to achieve in our everyday life. The same thing happens in the world of industrial steam boilers.

So how do we move between unrealistic returns and technical specifications that are not entirely authentic, and not calculated based on our system?

Here are some tips.

a. The real efficiency

As mentioned in the previous paragraph, the yield provided by the manufacturer is calculated based on certain conditions recreated in their laboratory

Normally those parameters are, power close to 100%, ambient temperatures around 25 degrees and feed water temperatures close to 80 degrees.

As these conditions change, the efficiency of the steam generator varies accordingly.

So what do you need to do?

It becomes crucial to know and calculate efficiency according to the actual working conditions for your thermal plant.

This will allow you to simulate the cost of your system and find solutions to contain them.

b. Start with demand profiles

Normally steam requests throughout the working day or season vary following demands from production lines.

Here in the chart below, we have studied this variation on the specific case of one of our customers, in which it is seen how the flow of steam and its pressure vary throughout the day.

In addition to these data, to calculate the efficiency of our generator it will be necessary to detect the ambient and inlet water temperatures, in this way we will be able to calculate the true efficiency of the heating system and therefore the methane consumption.

Starting from these conditions, diverse solutions can be found to increase the average efficiency and decrease costs: for example, by increasing the modulation range of your boiler.
If you need support in calculating performance and analyzing plant data, fill out the form at the bottom of the page.

c. How to start saving with efficiency

At this point, we start to have a solid understanding of what is the steam boiler efficiency.
But how can we use this information to guide us in choosing a new generator? How does the choice of generator affect methane expenditure throughout its life?

Taking up the concept expressed at the beginning of the article, methane represents approximately 68% of the total costs of a heating system under the conditions established previously.

When we have to choose between different boilers, priority must be given to what allows us to reduce methane consumption as much as possible.

Often this translates into higher initial costs, but even just a 1% increase in efficiency will allow you to save around &#; 5-6,000 each year only on methane costs.

So what tools can you use to increase the average efficiency of your thermal power plant?

Considering the profiles of steam flow and pressure requirements, it is better to look for the boiler and burner that best modulate and &#;follow&#; the required load, thus avoiding unnecessary waste.
Depending on the pressure profile, it is also advisable to choose a system that can modulate the steam pressure supplied.

The higher the modulation ranges for the flow rate and the steam pressure, the higher the average efficiency of our system, with consequent savings in burnt methane.

The reduction in consumption often means more expensive technologies, but, almost always, widely justified by the economic savings received every year.

Conclusions

The efficiency of a steam boiler is undoubtedly the parameter that we all know best, as well as the most important, as it is the percentage of energy efficiency that a generator can achieve.
As the efficiency increases, the dissipations and dispersions will decrease and it will cost less and less to produce steam.

Given its importance and centrality, many boiler manufacturers &#;inflate&#; this number, by creating it in the laboratory conditions that are not easily replicable.
For this reason, it is important to collect the flow and pressure profiles of our system, to then calculate the efficiency according to your real conditions.

Starting from the analysis of these profiles, we can then identify the steam boiler with specifications that allow us to increase the average efficiency of the entire system and decrease methane consumption.

If you need further clarification on the calculation of your real efficiency, do not hesitate to contact us and request a free inspection.

Related Covered Product Categories

Small Commercial Boilers

Residential Gas Boilers

Link to Partedon Group

Commercial Gas Water Heaters

Residential Gas Furnaces

Find more Heating and Cooling Equipment efficiency requirements and a full list of covered product categories >>

The Federal Energy Management Program (FEMP) provides acquisition guidance for large commercial boilers, a product category covered by FEMP-designated efficiency requirements. 

FEMP's acquisition guidance and efficiency requirements apply to gas- or oil-fired, low-pressure hot water or steam boilers used in commercial space heating applications with a rated capacity above 2,500,000 and at or below 10,000,000 British thermal units per hour (Btu/h). High-pressure boilers (i.e., those used in industrial and cogeneration applications) are excluded, while residential boilers (i.e., those with a capacity less than 300,000 Btu/h) and small commercial boilers (above 300,000 Btu/h and at or below 2,500,000 Btu/h) are covered by the ENERGY STAR program.

This acquisition guidance was updated in June .

Find Product Efficiency Requirements

Federal purchases of commercial boilers must meet or exceed the minimum efficiency requirements and thermal efficiencies listed in Table 1. These efficiency levels can be voluntarily adopted by non-federal organizations, institutions, and purchasers.

Table 1. Efficiency Requirements for Large Commercial BoilersProduct ClassRated CapacityFuelHeating MediumEfficiency* (%)Large Gas-Fired Hot Water>2,500,000 Btu/h and &#;10,000,000 Btu/hGasHot WaterEc &#; 96.0Large Gas-Fired Steam>2,500,000 Btu/h and &#;10,000,000 Btu/hGasSteamEt &#; 83.7Large Oil-Fired Hot Water>2,500,000 Btu/h and &#;10,000,000 Btu/hOilHot WaterEc &#; 89.0Large Oil-Fired Steam>2,500,000 Btu/h and &#;10,000,000 Btu/hOilSteamEt &#; 85.8*Both thermal efficiency (Et) and combustion efficiency (Ec) are based on 10 CFR Part 431.86 - Uniform test method for the measurement of energy efficiency of commercial packaged boilers.

With the Clean Energy Rule finalized in Spring , federal agencies must significantly reduce the use of on-site fossil fuels in new and majorly renovated facilities used for federal purposes. From FY to FY , federal entities must reduce the use of fossil fuels by 90% in facilities that are newly constructed or undergoing major renovation (exceeding a total cost threshold of $3.8 million in dollars for federally owned buildings). To comply, contracting officers should avoid purchases of commercial fossil fuel-fired boilers. Federal buyers are encouraged to consult the Clean Energy Rule webpage for further guidance. If no technically practicable alternative to a fossil-fueled product can be found that meets the mission requirements of the agency, an agency may obtain guidance, or request technical assistance, or petition for downward adjustment of the fossil fuel reduction target from FEMP by contacting the Clean Energy Rule team.

FEMP has calculated that a 3,000,000 Btu/h gas-fired hot water commercial boiler meeting the required combustion efficiency level of 96.0% Ec saves money if priced no more than $59,703 above the base model. The best available model saves the average user more: $66,839 in lifetime energy costs. Table 2 compares three types of product purchases and calculates the lifetime cost savings of purchasing efficient models. Federal purchasers can assume products that meet FEMP-designated efficiency requirements are life cycle cost-effective.

Table 2. Lifetime Savings for Efficient 3,000,000 Btu/h Gas-Fired, Hot Water BoilersPerformanceBest AvailableRequired ModelBase ModelCombustion Efficiency98.0%96.0%82.0%Annual Energy Use (therms/yr)35,,,000Annual Energy Cost ($/yr)$29,808$30,429$35,625Lifetime Energy Cost (25 year)$342,552$349,689$409,392Lifetime Energy Cost Savings$66,839$59,703======

• Performance Column

  Annual Energy Use: 1,400 full-load hours per year, for 25 years.

  Annual Energy Cost: Calculated based on an assumed natural gas price of 8.48¢ per therm, which is the average price at federal facilities in the United States (Site-Delivered Energy Use by End-Use Sector and Energy Type in Fiscal Year ).

  Lifetime Energy Cost: Future electricity price trends and a 3% discount rate are from the Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis &#; : Annual Supplement to NIST Handbook 135 and NBS Special Publication 709 (NISTIR 85--39).

  Lifetime Energy Cost Savings: The difference between the lifetime energy cost of the less efficient model and the lifetime energy cost of the required model or best available model.

  Best Available Model Column

  Calculated based on highest efficiency model identified in publicly provided manufacturer data as of June . Note that more efficient models may be introduced to the market after FEMP's acquisition guidance is posted.

  Required Model Column

  Calculated based on FEMP-designated efficiency requirements. Federal agencies must purchase products that meet or exceed FEMP-designated efficiency levels.

  Base Model Column

  Calculated based on the current federal minimum efficiency standard for this product type.

Determine When FEMP-Designated Products Are Cost-Effective

An efficient product is cost-effective when the lifetime energy savings (from avoided energy costs over the life of the product, discounted to present value) exceed the additional up-front cost (if any) compared to a less efficient option. FEMP considers up-front costs and lifetime energy savings when setting required efficiency levels. Federal purchasers can assume products that meet FEMP-designated efficiency requirements are life cycle cost-effective. In high-use applications or when energy rates are above the federal average, purchasers may save more if they specify products that exceed FEMP efficiency requirements (e.g., the best available model).

Purchasing Requirements

Federal laws and requirements mandate that agencies purchase ENERGY STAR-qualified products or FEMP-designated products in all product categories covered by these programs and in any acquisition actions that are not specifically exempted by law.

These mandatory requirements apply to all forms of procurement, including construction guide and project specifications; renovation, repair, energy service, and operation and maintenance (O&M) contracts; lease agreements; acquisitions made using purchase cards; and solicitations for offers.

FAR Contract Language

Federal Acquisition Regulation (FAR) Part 23.206 requires agencies to insert the clause at FAR section 52.223-15 into contracts and solicitations that deliver, acquire, furnish, or specify energy-consuming products for use in federal government facilities. 

To comply with FAR requirements, FEMP recommends that agencies incorporate efficiency requirements into technical specifications, the evaluation criteria of solicitations, and the evaluations of solicitation responses.

• Agencies may claim an exception to the Clean Energy Rule if no alternative to a fossil-fuel powered product is found that meets the technical needs and mission requirements of the agency. If an agency wishes to obtain further guidance, request technical assistance or petition for downward adjustment on the fossil fuel reduction target from FEMP, they may do so by contacting the Clean Energy Rule team and following the petition process. Contracting officers should still aim to purchase products that meet the ENERGY STAR or FEMP-designated requirements and minimize emissions as much as possible.

  Products meeting FEMP-designated efficiency requirements may not be life cycle cost-effective in certain low-use applications or in locations with very low rates for natural gas or fuel oil. However, for most applications, purchasers will find that energy-efficient products have the lowest life cycle cost.

  Agencies may claim an exception to federal purchasing requirements through a written finding that no FEMP-designated or ENERGY STAR-qualified product is available to meet functional requirements, or that no such product is life cycle cost-effective for the specific application. Learn more about federal product purchasing requirements.

Federal Supply Sources and Product Codes

The federal supply sources for energy-efficient products are the General Services Administration (GSA) and the Defense Logistics Agency (DLA). 

The U.S. Department of Agriculture (USDA) and U.S. Environmental Protection Agency (EPA) provide programs that help federal agencies buy products with positive environmental attributes.

Identification codes for product categories covered by sustainable acquisition requirements are provided by DLA and the United Nations Standard Products and Services Code (UNSPSC).

• Under the Multiple Award Schedule program, GSA issues long-term governmentwide contracts that provide access to commercial products, services, and solutions at pre-negotiated pricing.

  Federal buyers can use the GSA Multiple Award Schedules to find a vendor and pull up their latest price list. Alternatively, buyers can search for a specific product in GSA Advantage! or enter the product in GSA eBuy to get a quote from multiple vendors. Before purchasing a product through one of these channels or a preferred vendor, buyers should make sure the product meets the FEMP or ENERGY STAR efficiency requirements. For solicitations, buyers should include the relevant FAR clause and incorporate energy efficiency into the contract language and evaluation criteria to ensure compliance with the federal purchasing requirements.

  TAKE ACTION

  • Review the Multiple Award Schedule program.
     
  • Visit the GSA Advantage! online shopping network and associated acquisition tool GSA eBuy.
     
  • Learn about efficient, healthy buildings and environmentally responsible purchasing from the Sustainable Facilities (SF) Tool.

• DLA offers products through the Defense Supply Center Philadelphia and online through FedMall (formerly DOD EMALL).

  TAKE ACTION

  • Visit FedMall.

  Products sold through DLA are codified with a 13-digit National Stock Number (NSN) and, in some cases, a two-letter Environmental Attribute Code (ENAC). The ENAC identifies items that have positive environmental characteristics and meet standards set by an approved third party, such as FEMP and ENERGY STAR.

• USDA's BioPreferred Program was created to increase the purchase and use of biobased products. Federal law, the FAR, and Presidential Executive Orders direct that all federal agencies and their contractors purchase biobased products in categories identified by USDA. 

  TAKE ACTION

  • Review 139 categories of biobased products.

• EPA offers several resources for choosing which products to buy. The Environmentally Preferable Purchasing Program helps federal government purchasers utilize private sector standards and ecolabels to identify and procure environmentally preferable products and services.

  TAKE ACTION

  • Learn more about the Environmentally Preferable Purchasing Program.
     
  • Review federal purchasing specifications, standards, and ecolabels.
     
  • Get an overview of the Electronic Product Environmental Assessment Tool (EPEAT) and procuring environmentally preferable electronic products.

• UNSPSC is a worldwide classification system for e-commerce. It contains more than 50,000 commodities, including many used in the federal sector, each with a unique eight-digit, four-level identification code. Manufacturers and vendors are beginning to adopt the UNSPSC classification convention and electronic procurement systems are beginning to include UNSPSC tracking in their software packages. UNSPSCs can help the federal acquisition community identify product categories covered by sustainable acquisition requirements, track purchases of products within those categories, and report on progress toward meeting sustainable acquisition goals. 

  TAKE ACTION

  • Review FEMP's table of product codes for ENERGY STAR and FEMP-designated covered product categories.

Commercial Boilers Schedules and Product Codes

GSA offers commercial boilers through Multiple Award Schedule Industrial Products HVAC and C schedules.

DLA's ENAC for commercial boilers is "HF."

The UNSPSCs for commercial boilers are , , , , and .

Buyer Tips: Make Informed Product Purchases

A boiler system should be capable of meeting the building's peak heating demand and also operate efficiently at part-load conditions. Selecting the right system and properly sizing a boiler requires knowledge of both the peak demand and load profile. If building loads are highly variable, as is common in commercial buildings, designers should consider installing multiple small (modular) boilers in addition to boilers that have modulating burners. In periods of low demand, some of the boilers can be isolated from the other boilers and not incur any standby losses or cycling losses. They can also be automatically staged such that each boiler is running at its most efficient operating point without incurring additional cycling.

For guidance on boiler rightsizing and quality installation, consult the American National Standards Institute/Air Conditioning Contractors of America Standard 5: HVAC Quality Installations Specification (ANSI/ACCA 5 QI ).

Federal procurement officers and buyers should consider specifying boilers with the following features:

• Condensing: Hot water boilers include both condensing and non-condensing varieties. Condensing boilers that are able to extract heat from water vapor in the combustion gases for use in producing hot water are typically more efficient than non-condensing models. There are some tradeoffs to consider along with the efficiency improvements. Condensing boilers must be made of corrosion resistant materials which can increase their manufacturing cost. Although more expensive, condensing boilers' increased efficiency can significantly reduce energy costs to a point where savings exceeds the cost premium compared to a standard, non-condensing boiler. Hybrid systems are also useful particularly in retrofit applications to integrate new condensing boilers into an existing modular system with conventional boilers.
   
• Water temperature reset: Hot water boilers should have the capability for water temperature reset. This is typically based on the outdoor air temperature or the return water temperature. When the heating load is reduced, the supply water is set to a lower temperature.
   
• Modulating burners: It is recommended that boilers have the capability to vary their heating output by modulating the burner. Most of the time boilers operate at part load. To prevent excessive cycling and the losses that accompany them, specify boilers that have modulating capability. A minimum turndown ratio of 5:1 is recommended for gas-fired, hot-water boilers. This is particularly important in condensing boilers that run more efficiently at part load.
   
• Low mass: Because boilers cycle on and off and it takes time to bring a high-mass boiler up to operating temperature, using low-mass boilers will reduce energy consumption. In addition, some boilers can be brought online quickly, therefore avoiding the need to keep a boiler on hot standby.
   
• Remote monitoring capability: Remote monitoring capability is useful to manage boiler operation and to detect any malfunctions in a timely manner.
   
• Precise air-fuel ratio control: It is important to keep the air-fuel ratio at optimum levels at part-load operation as well as full-load operation. This is better accomplished by using sensor-driven servos rather than a mechanical linkage (e.g., jack shaft) between the gas input and the blower damper. Oxygen trim systems should be used on larger boilers. Oxygen trim systems monitor the oxygen in the flue gas and adjust the air-fuel ratio for optimum combustion efficiency.
   
• Optimum start control: An optimum start control fires up a boiler so that it fires just in time to heat up a building before it is occupied in the morning.
   
• Other enhancements: Other options to increase efficiency of the heating system include reusing heat from blow down and return condensate for steam boilers, using electronic ignition devices, and increasing boiler and piping insulation.

Many new energy consuming commercial boilers come equipped with Internet of Things (IoT) sensing components, and network connectivity. Making a new purchase or replacement represents a prime opportunity to evaluate the vulnerabilities of your network. All IoT-enabled devices introduce novel exposures to potential data breaches. Building controls and heating, ventilating, and air conditioning systems are no exception. Security can almost never be networked in after the fact, and so it is important to ensure that your networked devices are secure. Also, regularly testing for network vulnerabilities is key. For more information on how to build cybersecure networks of building technologies, consult FEMP&#;s Energy and Cybersecurity Integration resources and Cyber-Securing Facility Related Control Systems fact sheet.

User Tips: Use Products More Efficiently

Several diagnostic and maintenance procedures are important to maintain efficient boiler operation. Flue gas temperature monitoring is useful in detecting efficiency and operating problems. Maintaining steady excess air levels (with an oxygen trim sensor) ensures that burners will mix air and fuel properly. Low water levels can damage boilers, so water levels should be checked frequently as part of a regular maintenance program. Water treatment can prolong boiler life as well as increase efficiency. Waterside and fireside surfaces should be cleaned annually.

The Boiler Efficiency Institute provides maintenance and operation manuals for boilers and boiler control systems. To encourage quality operations and maintenance, building engineers can also refer to ASHRAE/ACCA Standard 180: Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems. In addition, the FEMP O&M Best Practices Guide, Release 3.0, Chapter 9 provides valuable information on operation and maintenance of boiler systems.

Lawrence Berkeley National Laboratory provided supporting analysis for this acquisition guidance.

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