September 5th, 2007
A fine choice: in March of 2004, Starwood Hotels was looking for ways to mitigate the penalties imposed by the Southern California Air Quality Management Division for a boiler at its Westin hotel in Long Beach that failed to meet rigorous state standards. This is the story of facing three retrofit choices and choosing the high road to lower NOx
The Long Beach Westin is located less than a mile from the Pacific Ocean and offers 460 guest rooms and 41,000 sq ft of indoor meeting space. The city of Long Beach enjoys a temperate climate, with winter temperatures averaging 55[degrees]F and summer in March of 2004; the property was sold in January of 2006.
Independent boiler plants met the facility’s heating and DHW needs. The two boilers designed for the DHW loop each had a 1.7-MMBtu capacity and fed a 750-gal hot water storage tank. The building heat loop was fed by a 4-MMBtu boiler with a second 4-MMBtu boiler to provide redundancy.
Given the temperature climate, the property had little need for the full 4 MMBtu of heat the boilers were designed to provide. Although occupant demand calls for heating to be available almost year-around, the actual energy consumption is quite low. Indeed, the demand on the existing building heat loop was so low, the boilers were not subject to the SCAQMD’s demanding emissions standards as neither boiler used more than 9,000 Therm/yr. Additionally, the low demand allowed the building engineers to isolate the unused boiler and therefore avoid a situation where the second boiler radiated unnecessary heat back into the building.
Any boiler using more than 9,000 Therm/yr is subject to SCAQMD’s inspection. If the boiler produces more than 35 ppm of nitrogen oxide (NOx), SCAQMD issues a citation and levies a fine for failure to comply with state standards. Given that the boilers were original to the building, it is doubtful that either could have passed inspection by the state had they been utilized at full capacity. On the other hand, the boilers feeding the DHW loop exceeded the 9,000 Therm/yr threshold. As the latest inspection revealed that the DHW boilers were producing more than 33 ppm of NOx, the property was fined and a citation was issued by SCAQMD.
Recent changes to the operation of the property included the installation of ozone systems for the laundry functions, which significantly reduced the DHW load in the facility and brought it well below the specifications of the original design. As a result, the boilers dedicated to meeting the DHW demands were also operating at well below their capacity.
Both boiler loops were operating at approximately 1% of their annual capacity. Given the similar operational efficiency of the two systems and allowing for calculation Errors at a factor of five, the seasonal efficiency of the boiler plant still would not surpass 30%. Nevertheless, operating costs for the boiler plants were not prohibitive and demand was met adequately, a threshold of operational functionality that is satisfactory by moat standards.
DESIGNING FOR THE FUTURE
The single motivation for a re-evaluation of the boiler plants at the Westin Long Beach was the citation from SCAQMD. Starwood invited an outside energy management consulting firm, Energy Management Strategies, Inc. (EMSI), to evaluate the property and propose solutions to bring the DHW boilers into compliance with California state standards.
Only three options made sense. First, they could simply retrofit the existing boilers to reduce NOx emissions, because the efficiency of the boiler loop would have dropped as well. The advantage of retrofitting the boilers is the low cost of the solution and the retrofitting process has the least impact on the operations of the facility.
The second option was to exchange the original boilers with new boilers on a one-for-one basis. This would reduce the NOx emissions, and would be relatively inexpensive as a one-for-one exchange requires little reengineering and no analysis.
The final option was to redesign the boiler plant in its entirety. This would address the NOx issue as well as producing a right sized boiler plant that met the real-time needs of the facility. The overall efficiency of the boiler plant would increase dramatically, from only 1% to over 95%. However, a complete redesign of the boiler plant meant the most disruption to the facility itself, as well as the largest investment of any of the three options.
[FIGURE 2 OMITTED]
Starwood decided they would take the holistic approach to the facility’s needs and opt to redesign the boiler plants in their entirety. EMSI returned a proposal that combined the two boiler plants and replaced 11.4 MMBtu of heating capacity with capacity more in keeping with the facility’s real-time demand.
After performing an investment-grade audit of the existing system, a full study of the alternatives, and a complete financial analysis, EMSI returned with both the plan for renovation and the financial analysis to justify a complete reconfiguration of the existing boiler plant. Extensive building simulations indicated that the facility’s demand peaked at 4 MMBtu.
[FIGURE 3 OMITTED]
The design for the new boiler plant was based on the detailed analysis and due diligence performed by EMSI. Right-sized at 5 MMBtu, the new boiler plant is designed with 1-MMBtu modular boilers, which allow the plant to ramp up according to building demand, but also to scale back when demand is low. The modular design builds redundancy into the system with the fifth 1-MMBtu boiler.