Texas Hospital. Central Plant Redesign. Central Utility Plant SECOND PLACE HEALTH CARE FACILITIES, EXISTING 2013 ASHRAE TECHNOLOGY AWARD CASE STUDIES

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1 This article was published in ASHRAE Journal, January Copyright 2014 ASHRAE. Posted at www. ashrae.org. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about ASHRAE Journal, visit SECOND PLACE HEALTH CARE FACILITIES, EXISTING A new research institute at Houston Methodist Hospital prompted an expansion of the central utility plant. New high efficiency equipment included a gas turbine-driven electrical generator with duct burner and high pressure heat recovery steam generator with aqueous ammonia selective catalytic reduction. Texas Hospital Central Plant Redesign BY BRUCE L. FLANIKEN, P.E., MEMBER ASHRAE BUILDING AT A GLANCE Central Utility Plant Cogeneration CHP Upgrade Location: Houston Owner: Houston Methodist Hospital Principal Use: Existing Hospital CUP Includes: Two natural gas-fired, high pressure steam boilers; five electric drive water-cooled centrifugal chillers; two steam-driven, water-cooled centrifugal chillers including ancillary equipment (cooling towers, condenser/chiller water pumps) and electrical switchgear; gas turbine-driven electrical generator with duct burner and high-pressure heat recovery steam generator with aqueous ammonia selective catalytic reduction (SCR). The CUP now serves existing 1,000-bed hospital and 1.1 million ft 2 research facility. Employees/Occupants: 450 Gross Square Footage: 1.2 Million Conditioned Space Square Footage: 1.1 Million Substantial Completion/Occupancy: January 2011 Occupancy: 100% A new 1.1 million ft 2 ( m 2 ) research institute building at Houston Methodist Hospital (HMH) prompted an expansion of its existing central utility plant (CUP). The steam demand on the CUP required operation of the two existing natural gas 60,000 lb/h (7560 g/s) high-pressure steam boilers, leaving the plant without a standby unit. Although the CUP had sufficient chiller capacity, it was deficient in the necessary cooling tower capacity to support operation of all seven of the installed centrifugal chillers simultaneously. Auxiliary equipment for the one existing steam-driven chiller and/or ancillary equipment of any of the electric drive chillers (cooling towers, condenser/chiller water pumps) were not connected to standby power. ABOUT THE AUTHOR Bruce L. Flaniken, P.E., is design & construction manager of engineering at the Houston Methodist Hospital. 36 ASHRAE JOURNAL ashrae.org JANUARY 2014

2 ABOVE Cogeneration system with new and existing cooling tower and power house. LEFT Cogeneration system looking north. Therefore, they could not provide emergency cooling, which was required by the new research building as well as being necessary to care for patients during major storms and hurricanes that cause utility outages in Texas. The installation of the cogeneration turbine with duct burner and high-pressure steam thermal energy recovery unit makes HMH the only hospital in the Texas Gulf Coast area that can operate during hurricane-type power grid outages. The system incremental cost and estimated energy savings using simple payback had been projected to pay back in 3.5 years or less. The CUP upgrade project directly addressed the cooling tower deficiency by installing an additional 6,800 tons (23,915 kw) of cooling tower capacity in the form of seven additional cells. The standby steam and power concerns were addressed by the installation of a 200 psig (1379 kpa) natural gas turbine-generator combined heat and power (CHP) unit to increase overall thermal efficiency and produce steam via a combination heat recovery steam generator and natural gas-fired duct burner of standby power at 4,160 V via a natural gas-turbine generator. (Note: the actual capacity of the 4.3 MW cogeneration unit varies depending upon outside air temperature and percent relative humidity. Initial capacity rating is given at ISO inlet air conditions of 60 F [15.5 C] DB/60% RH. Ambient inlet air becomes de-rated to approximately 3.8 MW at 100 F [38 C] DB/60% RH.) The CHP unit was installed to address standby power and emergency cooling capability concerns. This unit allows HMH to generate its own electrical power and take advantage of reduced energy mix cost, and increase CHP thermal efficiency while in the CHP mode. The installation of the higher cost low NO X output CHP turbine with aqueous ammonia selective catalytic reduction (SCR) significantly decreased NO X emissions. It also reduced the overall permit application time in an EPA non-attainment zone (by submitting it to EPA using best available control technologies, which reduced overall NO X output substantially). Existing chilled water emergency cooling concerns were addressed through the addition of a 2,800 ton (9847 kw) steam turbine-driven chiller and by revising the existing electrical power distribution, feeding standby power to other electric chillers and their auxiliary equipment. This provides for 6,800 tons ( kw) of emergency cooling capability in cogeneration island mode (stand-alone mode) when all power is lost to the facility. Additional pump piping cross connections and manual bypass/isolation valves also were installed to allow dedicated chilled and condenser water pumps to cross connect to other nearby chillers to the greatest extent possible. Variable frequency drives (VFDs) were added to all cooling tower fans and chilled water and condenser water pumps to improve system response and wire-towater efficiency. The installation of a 2,000 ton (7034 kw) steam turbine chiller in 2004 was undertaken as part of an energy initiative rebate available from the local utility company. Another separate chilled water distribution upgrade project involved adding differential pressure sensors to control secondary chilled water distribution pumps driven by VFDs. This was done primarily to improve system DT that was 2 F to 3 F (4 C to 5 C) lower than designed for in the original chiller selections. It is an ongoing goal to achieve a standardized DT of 12 F (22 C) throughout all buildings on site served by our district CHP. The CUP now produces up to a total of 12,800 tons of chilled water through five 2,000 ton (7034 kw) electric chillers, one 2,000 ton (7034 kw) steam-driven centrifugal chiller and the new 2,800 ton (9847 kw) steam-driven centrifugal chiller in an N+1 configuration throughout. JANUARY 2014 ashrae.org ASHRAE JOURNAL 37

3 The CUP can produce up to a total demand of 99,500 lb/h ( g/s), 210 psig (1448 kpa) steam through a 24,500 lb/h (3087 g/s) heat recovery steam generator, a 25,000 lb/h (3150 g/s) natural gas-fired duct burner and two high-pressure steam boilers rated at 50,000 lb/h (6300 g/s) in a N+1 configuration and with a boiler operated in standby low-fire mode for quick steam demand response to CHP systems shutdown, reducing energy consumption and emissions of NO X. A new 200 psig (1379 kpa) natural gas main from the local utility company that included a high-pressure natural gas pressure regulating station was installed to serve CHP and boiler loads while improving system performance and reliability. A rooftop ammonia storage tank and an at-grade fill station were installed to support the aqueous ammonia SCR emission controls system. A CHP continuous emissions monitoring system had to be installed and operational at the time of start-up, which required HMH to update all facilities overall air quality compliance forms to meet state and federal emission requirements. The BAS originally installed in the CUP was upgraded to increase the degree of automation and optimization that could be achieved to reduce staffing requirements while improving systems reliability, record keeping and maintenance. This will allow optimization of all CUP chillers, pumps, cooling towers, CHP electrical generation, CHP thermal energy recovery (heat recovery steam generator) and high-pressure steam boilers integration in our efforts to maximize wire-to-water efficiencies. Energy Efficiency Installing a new 2,800 ton (9847 kw) high efficiency R-134a steam-driven centrifugal chiller to replace the existing 2,000 ton (7034 kw) asynchronous electric motor-driven centrifugal R-22 chiller rated for kw/ton reduced electrical demand by 1,600 kw. Also, a modeled offset of nearly 1.5 million kwh of electrical consumption was realized. The optimized operation of the primary chilled water supply loop and the secondary chilled water loops systems has been greatly enhanced by the building automation system, which ASHRAE JOURNAL ashrae.org JANUARY 2014

4 When designing health care HVAC, expert guidance is essential. HVAC Design Manual for Hospitals and Clinics Now in a NeW, revised and updated second edition. This second edition provides in-depth design recommendations from consulting and hospital engineers with experience in the design, construction, and operation of health care facilities. It offers low-cost, highly reliable solutions, with a focus on what's different about health care HVAC. The manual contains essential guidance on: environmental comfort infection control energy conservation life safety operation and maintenance disaster planning strategies available in print or digital Format Price: $129 ($109 ASHRAE Member) best practice recommendations on temperature, humidity, air exchange, and pressure requirements for various types of rooms found in hospitals

5 allows improved wire-to-water transfer of energy, reducing overall energy consumption considerably Energy Mix Energy Mix Innovation The use of a natural gas turbinedriven CHP/heat recovery steam generator/duct burner to provide for the base steam demand, and that required to run the steam-driven chiller, has resulted in a substantial shift in demand from the existing utility power grid to the natural gas utility and allowed us to produce up to 2,800 tons (9847 kw) of chilled water from free steam for only the cost associated with running the condenser-chilled water pumps and cooling tower fans. HMH can produce up to 6,800 tons ( kw) of emergency cooling in the cogeneration (CHP) island mode if all power is lost due to rolling brownouts or storm damage. This upgrades the ability to operate a significant portion of the campus while maintaining patient care and research demands while reducing dependence on the local power grid. The hospital s steam demand profile requires producing approximately 20,700 lb/h (2608 g/s) of steam to meet heating, sterilizing, humidification, domestic hot water steam loads, along with the steam demand of a 2,800 ton (9847 kw) steam-driven centrifugal chiller (requiring 25,300 lb/h [3188 g/s] of high-pressure steam). This allows us to base load the CHP for electrical power generation and recovered thermal energy while rarely having to fire the high NO X steam boilers. Operation & Maintenance Existing reliability, redundancy and other O&M issues addressed during the project design and construction phase included adding cooling tower capacity, along with system piping and electrical system modifications that provided a higher degree of overall functionality and reliability. We have achieved cold weather operation of the CUP using one 2,800 ton (9847 kw) steam-driven chiller Electricity MMBtu Gas MMBtu FIGURE 1 Cogeneration decreased the dependency on electricity, reducing electric consumption and avoiding $1.85 million in net expense over 12 months. This cogeneration project is expected to return investment in fewer than two years. Blended $/MMBtu Blended $/MMBtu Blended $/MMBtu 0 Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Jan. FIGURE 2 Year-over-year change. Due to the reduction in electricity use (a higher expense energy source) the overall $MMBtu was reduced significantly and savings are higher than modeled. where previously it took a minimum of two 2,000 ton (7034 kw) chillers. This was achieved by improving AHU coil design DT to match the original design of 12 F (22 C) DT and adding UVC lights to keep cooling coils clean when replacing old low DT air-handling units, by adding UVC lamps to existing cleaned and refurbished AHU coils, and by better secondary and primary chilled water systems differential pressure and VFD control. The addition of the CHP and associated protective switchgear has made the overall system much more complex, but the added BAS automation and increased O&M training required by the system have resulted in a more reliable and easier to troubleshoot overall central utility plant, and one that certainly can operate during extended power grid outages. Cost Effectiveness The natural gas-fired CHP cogeneration/heat recovery steam generator/duct burner units were installed to address both power capacity and emergency cooling capability concerns. This gives HMH the ability to 40 ASHRAE JOURNAL ashrae.org JANUARY 2014

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7 self-generate electrical power and achieve savings in energy costs while in the cogeneration mode. The $1 million annual estimated energy savings resulting from the overall increased thermal efficiency of the CHP (from 30% to approximately 88%) came from base loading of the CHP unit for both power and steam consumption (24/7/365). This completely offset the added cost of the upgrade from a new high-pressure steam boiler and a new 2.5 MW emergency diesel generator to the 4.3 MW gasfired cogeneration turbine/heat recovery steam generator/duct burner unit with a modeled payback between three and four years. The project achieved a 92.2%+ annual operating $2 Million $1.5 Million $1 Million $500,000 hours (8,079 hours of operation) for cogeneration (CHP) and used the free steam to run a steam-driven chiller 8,456 hours during this period, making maximum use of the free thermal energy recovered by the heat recovery steam generator. While we found it difficult to compute the exact savings derived from cogeneration due to dramatic utility cost fluctuations that occurred during $0 $(500,000) Actual Net Savings: $1.85 Million Avoided Utility Free Stream Increased Standby Gas Increased Maintenance Feb. Mar. Apr. May Jun. Jul Aug. Sep. Oct. Nov. Dec. Jan. FIGURE 3 Shift of energy expense due to cogeneration (from ). While installation of the cogeneration operation increased maintenance and standby gas expense, the benefit of avoided utility expense of more than $1.3 million and more than $800,000 of free steam generation established this project as a best practice standard for reducing expense and lowering carbon footprint. the project, we were able to calculate energy cost savings of approximately $1.85 million mainly due to the added thermal energy recovery (Figure 1). We averaged electrical and natural gas use and cost via a blended $/MMBtu (Figure 2). This translates to a total annual gross savings of $2.2 million from Feb ASHRAE JOURNAL ashrae.org JANUARY 2014

8 through Jan with a net annual avoided cost of $1 million. One additional cost that had to be included was the cost of running one of the high-pressure steam boilers at low fire during cogeneration (CHP) mode so that in the event of cogeneration shutdown we could get the highpressure steam system operational in under an hour. That additional annual operation cost was $73,726. Also, we have added the calculated cost of chilled water demand load and power consumption savings on the CUP chilled water production by recovering 24,500 lb/h (3087 g/s) of high-pressure steam from the cogeneration heat recovery steam generator for an annual total of 294,000 lb/h (37043 g/s) of high-pressure steam (165,541.6 MMBtu). That steam is used to produce 21 million ton hours of cooling via the steam-driven centrifugal chillers at an estimated savings of $817,523 for a combined annual net savings of $1.8 million from Feb through Jan This puts the simple payback at 2.16 years versus four years as initially modeled. Systems overall heat transfer efficiency for the cogeneration (CHP) unit increased from around 30% for generation of electric power to slightly above 88% by using the heat recovery steam generator unit to capture the free waste heat and use it effectively to generate domestic hot water, heating hot water, sterilizer steam and/or chilled water in the manifolded high-pressure steam distribution system. The environmental impact from NO X emissions has been reduced by selecting a gas turbine-generator CHP unit using aqueous ammonia SCR with best available control technology rated to produce maximum 15 ppm NO X in lieu of high-pressure steam boilers. Using the EPA CHP emissions calculator, the CHP system will reduce NO X by a net reduction of 71% or tons/year (56.9 kg/year), SO 2 by a net reduction of 100% or tons/year (154 kg/year) and will reduce CO 2 by 10,511 tons/year (28,797 kg/year) or 28%. Expensive hurdles included site adaptation of the existing 50-year-old CUP roof structural support to install the equipment on the roof and getting a crane to set up the equipment without closing the hospital main patient drop-off. Others were limited working space access adjacent to the emergency entrance/ambulance drive and the ongoing construction of the new research building. JANUARY 2014 ashrae.org ASHRAE JOURNAL 43

9 Integrating the xisting plant BAS and CHP system controls, installing the chiller, cooling tower and piping cross connections without shutting down the existing CUP utilities had to be carefully planned and mitigated. The heat recovery steam generator can recover 24,500 lb/h (3087 g/s) of free high-pressure 210 psig (1448 kpa) steam from the turbine engine discharge gases. The duct burner was selected to generate an additional 25,000 lb/h (3150 g/s) of high-pressure 210 psig (1448 kpa) steam by injecting fuel to the closed gas turbine discharge where there was sufficient oxygen to get an extremely efficient burn with minimal heat loss. This allowed us to base load the heat recovery steam generator and recover high-pressure steam while running only one high-pressure steam boiler November through February. The recovery and use of this lower cost steam is what improved payback and pushed overall thermal efficiency to 88.1% while keeping loss of thermal efficiency to the flue stack to 11.9% of input gas ratings. HMH also base loaded the CHP electrical generation capacity so it would not have to negotiate interconnectivity fees with the local utility. HMH received a local utility rebate of approximately $450,000 for the kw demand displaced by the steam centrifugal chiller. A lesson learned was that we should have included the turbine inlet chilled water cooling coil to reduce entering air temperature to 57 F (14 C) ISO year-round to allow the turbine to operate at maximum efficiency due to denser, cooler air intake and produce the full 4.5 MW of power at all outside air temperatures. The cost to add that now as a separate project is about $1.2 million, while including it initially would have cost about $750,000, reducing the simple payback from nearly five years to about three years or less. In Houston, there are approximately 7,080 hours where the outside air temperature is above the 57 F (14 C) ISO temperature that allows the CHP turbine to produce 4.5 MW of power, in lieu of the de-rating to approximately 3.8 MW at 100 F (38 C) DB/60% RH of standby power at 4,160 V via a natural gas-turbine generator. Another lesson learned is that we should have set up the electrical systems protection relays to shut down the cogeneration unit, rather than the main power feed from the utility company as this is less disruptive of our side and still protects the utility and hospital systems as required. Made-to-order Heat Transfer Products: Your Complete Hydronic Solution Engineered Air is proud to be your comprehensive authority for all finned tube, convector and forced convection heating needs. With a full range of predesigned and fully customizable solutions, our exacting standards and history of perfection bring flexibility, precision and peace of mind to any sized project. Complete line of hydronic products manufactured for all applications. Custom ultra quiet fan coil units and classroom unit ventilators. Comprehensive build-to-order heating solutions for perimeter radiation, cabinet heaters, unit heaters, radiant panels and chilled beams. Engineered Air is the market leader for hydronic heating solutions in cold climates, with thousands of installations in some of North America s most recognizable buildings. Visit us online to learn more about what Engineered Air can do for you ASHRAE JOURNAL ashrae.org JANUARY 2014

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