How to Buy an Energy-Efficient Commercial Boiler
Information about energy-efficient boilers in this section includes the following:
| Efficiency Recommendation Cost-Effectiveness Example Calculate Costs How to Select |
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Sizing Buyer Tips Maintenance and Operations Tips For More Information |
Also provided is a portable document format version of How to Buy an Energy-Efficient Commercial Boiler (PDF 253 KB). Download Adobe Reader.
| Efficiency Recommendationa | |||
|---|---|---|---|
| Product Type (Fuel/ Heat Medium) | Rated Capacity (Btu/h) | Recommended Thermal Efficiency (et)b | Best Availablec Thermal Efficiency (et) |
| Natural Gas Water | 300,000 - 2,500,000 | 80% et | 86.7% et |
| 2,500,001 - 10,000,000 | 80% et | 83.2% et | |
| Natural Gas Steam | 300,000 - 2,500,000 | 79% et | 81.9% et |
| 2,500,001 - 10,000,000 | 80% et | 81.2% et | |
| #2 Oil Water | 300,000 - 2,500,000 | 83% et | 87.7% et |
| 2,500,001 - 10,000,000 | 83% et | 85.5% et | |
| #2 Oil Steam | 300,000 - 2,500,000 | 83% et | 83.9% et |
| 2,500,001 - 10,000,000 | 83% et | 84.2% et | |
a This recommendation covers low- and medium-pressure boilers used primarily in commercial space heating applications. It does not apply to high-pressure boilers used in industrial processing and cogeneration applications.
b Thermal efficiency (et), also known as "boiler efficiency" or "overall efficiency," is the boiler's energy output divided by energy input, as defined by ANSI Z21.13. In contrast to combustion efficiency (ec), et accounts for radiation and convection losses through the boiler's shell.
c These "best available" efficiencies do not consider condensing boilers, which are generally more efficient but are not readily ratable with ANSI Z21.13.
| Cost-Effectiveness Example 5,000,000 Btu/h Gas-Fired Water Boiler | |||
|---|---|---|---|
| Performance | Base Model | Recommended Level | Best Available |
| Thermal Efficiency (et) | 78% | 80% | 83.2% |
| Annual Energy Use (therms) | 96,200 | 93,700 | 90,100 |
| Annual Energy Cost | $38,500 | $37,500 | $36,100 |
| Lifetime Energy Costa | $646,000 | $630,000 | $606,000 |
| Lifetime Energy Cost Savings | — | $16,000 | $40,000 |
a Lifetime energy cost is the sum of the discounted value of annual energy costs based on average usage and an assumed boiler life of 25 years. Future gas price trends and a discount rate of 3.4% are based on Federal guidelines (effective from April 2000 to March 2001).
Metric Conversions:
1 Ton = 12,000 Btu/h
1,000 Btu/h = 293 watts
°F = (1.8 * °C) + 32
1 Foot = 30.5 cm
Cost-Effectiveness Assumptions: Annual energy use in this example is based on 1,500 equivalent full-load hours per year. Boiler model: 5,000,000 Btu/h gas-fired water boiler. Assumed gas price: $0.40/therm, the Federal average gas price in the U.S.
Using the Cost-Effectiveness Table: In the example shown above, a 5,000,000 Btu/h gas-fired water boiler with a thermal efficiency of 80.0% is cost-effective if its purchase price is no more than $16,000 above the price of the base model. The best available model, with an efficiency of 83.2%, is cost-effective if its price is no more than $40,000 above the price of the base model.
Determine Your Own Project's Cost-Effectiveness
Try the energy cost calculator to compare the energy costs for your selection with FEMP-recommended and "best available" boiler models. You can model different scenarios by varying electricity cost, efficiency, and boiler type.
How to Select Energy-Efficient Boilers
Specify boilers with efficiency levels that meet this recommendation. Select only boilers rated under the certification program run by the Hydronics Institute of the Gas Appliances Manufacturers Association (GAMA). Although the HI directory reports only combustion efficiencies, thermal efficiencies can be calculated for model series listed without a pound sign by dividing gross output by input (using 140,000 Btu/gal. for #2 oil models).
Sizing and Part Load Performance
A boiler system should be capable of meeting the building's peak heating demand while also operating efficiently at the more common part-load conditions. Sizing and selecting a boiler system properly, therefore, requires a knowledge of the peak heating load, as well as an understanding of the load profile. If building loads are highly variable, as is common in commercial buildings, designers should consider installing multiple, smaller (modular) boilers. Modular systems are more efficient because they allow each boiler to operate at or close to full rated load most of the time, with reduced standby losses. Other efficient options for handling variable loads are modulating boilers, which can run at partial capacity (instead of cycling on and off), and condensing boilers.
Buyer Tips
While both water and steam models are covered in this recommendation, water boilers and distribution systems tend to have lower maintenance requirements. There is a broad array of options in boiler equipment and controls that can enhance energy performance: stack gas heat recovery equipment, such as air preheaters and economizers; condensing heat exchangers, which also utilize stack gas waste heat; turbulators (fin enhancers) to improve heat transfer and balance of gas flows between tube banks; water recovery equipment, to re-use heat from blowdown and water return condensate; outdoor temperature controls, which control the system loop temperature in accordance with outside temperatures; electronic ignition devices; increased boiler and piping insulation; and high performance (including "power") burners.
Maintenance and Operations Tips
Several diagnostic and preventive procedures are important to maintaining efficient operation. Flue gas temperature monitoring is useful in detecting efficiency and operation problems. Maintaining steady excess air levels (with an oxygen "trim" system) ensures that burners will mix air and fuel efficiently. The Boiler Efficiency Institute provides maintenance and operation manuals for boilers and boiler controls. Low water levels can damage boiler vessels, so water levels must be checked frequently. Water treatment prolongs the life of boilers, while increasing efficiency. Waterside and fireside surfaces should be cleaned annually. Steam boilers should be blowndown daily to remove sludge and sediment.
For More Information
- DOE's Office of Industrial Technologies' information clearinghouse provides publications on steam systems and helpful tips on improving boiler efficiencies.
Phone: (800) 862-2086 - American Council for an Energy-Efficient Economy (ACEEE) publishes the Guide to Energy Efficient Commercial Equipment which includes a chapter on HVAC systems.
Phone: (202) 429-0063 - GAMA's Hydronics Institute publishes the I=B=R Ratings for Boilers, Baseboard Radiation, and Finned Tube (Commercial) Radiation, a directory of commercial boilers with certified performance ratings.
Phone: (908) 464-8200 - American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) publishes the Cooling and Heating Load Calculation Manual.
Phone: (800) 527-4723 - American Boiler Manufacturers Association (ABMA) publishes a directory of commercial and industrial boiler manufacturers that offer equipment and services for boilers.
Phone: (703) 522-7350 - Boiler Efficiency Institute publishes maintenance and operating manuals on commercial and industrial boilers.
Phone: (800) 669-6948 - Lawrence Berkeley National Laboratory provided supporting analysis for this recommendation.
Phone: (202) 646-7950