May-June 2004

Ten Years in Creative Design for Medical Campus Utility Demand

Provenant's 22,000-square-foot Surgical Center at Summit is available 24/7 for emergency, scheduled surgical and outpatient needs.

The year was 1992: Wayne's World was sweeping movie theaters; Nirvana still had a front man; Tiger Woods was a high school sophomore winning his second Junior Amateur title; greenhouse gases were at some of their highest recorded levels; and Provenant Health Partners of Denver, CO, was about to embark on a project to transform its semipermanent emergency room structure in Frisco, CO (altitude 9,200 ft.) into a larger, permanent surgical medical center - a project that would win national acclaim from the United States Department of Energy (DOE), the Colorado Energy Conservation Network, the American Council of Engineering Companies, and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), for its technological advancement of energy and environmental design. Summit Surgical Center's evaporative cooling system, designed by Beaudin Ganze Consulting Engineers Inc. (BGCE), continues to operate today - a demonstration of how creative synthesis of climatic conditions, functional requirements, and energy and environmental goals can produce better, cleaner, and cheaper mechanical electrical plumbing systems.

Provenant's importance comes into sharper focus when one considers that it serves four ski resorts in the valley and that the nearest hospital is a lengthy ambulance or helicopter ride away, not always a minor feat when subject to the extreme weather conditions frequent in the Rocky Mountains.

The challenge of the center's 1992 transformation included preserving the continuity of emergency medical services provided by the existing clinic, and was compounded by strict hospital guidelines for surgical suite temperature (65°F). The Colorado State Department of Health (CSDH) guidelines stated that operating rooms must be maintained at 50% relative humidity (RH). The site altitude of 9,200 ft. (2,804 m) above sea level and 50% RH requirement posed a potential for condensation on the operating room's exterior wall surfaces and glazing. BGCE's psychrometric analysis corroborated this concern, and a variance was submitted to and granted by CSDH to allow the maintenance of 35% RH; however, the mechanical system was designed to provide the 50% RH should the variance be changed by CSDH.

The center was designed with energy savings as its primary goal; consequently both the mechanical systems and the building envelope were designed to be energy misers. The original emergency room clinic had continual complaints of inadequate space-temperature comfort. Most were attributed to the age and unreliability of the equipment. The owner requested that an environmentally sound, energy-efficient heating and cooling system be designed and installed within construction and operating budgets. The mechanical and electrical systems enable the remote mountain surgical center to be completely self-sustaining for up to 14 days in the event of a utility outage.

The new indirect/direct evaporative air-conditioning system design is free of chlorofluorocarbon refrigerants. The approach was unique for a surgical facility. Utilizing the favorable high-altitude and climatic conditions of summer outdoor design temperature of 77°F (25°C) and the low RH of 31%, cooled air is provided to the surgical rooms at 54°F (12.2°C), meeting strict hospital guidelines.

The Heating, Ventilation, and Air Conditioning (HVAC) system air stream is evaporatively cooled in a two-stage process with both stages rejecting building heat. The first stage is an indirect process, during which airflow passes through a cooling coil containing evaporatively cooled water. The water is cooled by a rooftop cooling tower in an evaporative cooling process and then piped to the coil. The air stream does not come in contact with the water. In the second process, air comes in direct contact with cold, potable water that is evaporated in the air stream, further adiabatically cooling the air to 54°F (12.2°C). The air then is ducted to the surgical suites, resulting in a 65°F (18.3°C) air temperature at 50% RH.

Humidity is added to the air stream via an innovative method. The direct evaporative cooling section of the air handler is equipped with a sump heater, and during the winter months, when humidity must be added to the air stream, the evaporative-cooler sump water is heated and pumped through the evaporative pad. The air stream is filtered to 35% average efficiency per ASHRAE Standard 52-76 at the central air handler and to 90% at the operating rooms. This also meets the 1993 edition of the American Institute of Architects  "Guidelines for Construction and Equipment of Hospital and Medical Facilities."

The new-and-enlarged facility's single air handler supplies 17,500 cfm (8,258 L/s) to the building, while 5,100 cfm (2,407 L/s) (29.2%) is outside air. A slightly smaller airflow is continually exhausted from the substerile areas, the laboratory, and the restrooms for ventilation and to maintain positive building pressure. Air balancing was critical to ensure that the surgery suites maintained the proper space pressure with respect to adjoining areas. ASHRAE Standard 62-1989 is either met or exceeded in all areas of the facility as demonstrated in Table A.

The seven refrigeration compressors and seven condenser fans were replaced by one supply fan, two pumps, and a cooling tower fan, even though the facility's square footage nearly tripled. The old and unsightly air-conditioning units located on the ground were removed. The new mechanical equipment was contained in an enclosed building, and the clean lines of the cooling tower on top of the equipment room go virtually unnoticed from the ground level.

A direct digital control (DDC) system, which also acts as a remote monitoring system, was installed, allowing the parent company, based 100 mi. away, to monitor it. The DDC system controls the daily flush for the evaporative-cooler sump to minimize biological contamination. It controls the tower drain-down function to prevent equipment freezing, a major concern in the mountain environment.

The new system addressed ASHRAE Standard 55 for occupant comfort and eliminated such complaints. The building shell exceeds ASHRAE Standard 90.1 by prescriptive method and is demonstrated in Table B. The only augmentation of the system was adding auxiliary cooling coils just to provide redundant coverage for the worst-case scenario days.

Costly, inefficient, and environmentally unsound refrigeration equipment was replaced with cost-effective equipment. The original clinic equipment used 1.4 kW of electricity per ton of cooling. The new system was designed for 0.3 kW/ton, or 5.9 kW (0.5-, 0.75-, and 3-hp motors) input, translating into a direct energy savings of 79% on a per-square-foot basis.

Review of the 1994-1995 electrical utility data (Table C) clearly demonstrates that summer cooling had virtually zero impact on the electrical demand and consumption. There is no historical electrical demand data for the facility since the previous electrical service was only metered for consumption (kilowatt-hours).

The indirect/direct evaporative cooling system serving this surgery facility provides not only operational cost-savings but also installation savings. This surgical facility addition/remodel was slated for 20 tons (70.4 kW) of cooling, but due to the altitude effects on equipment capacity duration, a 25-ton (88-kW) air-cooled chiller would have been required. Utilizing the indirect/direct evaporative cooling system resulted in an installation-cost avoidance of $10,500 when compared to a conventional system.

The new indirect/direct evaporatively cooled system is less complex and has far fewer moving parts, which results in less maintenance. The replacement of the original seven packaged, air-cooled, air-conditioning units with the evaporatively cooled system enabled the director of plant operations to reduce the number of site-maintenance personnel. The old air-cooled units demanded constant attention and required that a certified refrigerant technician be called upon if repairs dictated removal or replacement of refrigerant charges. The recommended replacement interval for the direct-cooling evaporative media is two to three years at a cost of $1,200. The indirect coil requires biannual waterside cleaning, which is a 12-hour job.

By all accounts, Summit Surgical Center was an example to be held up for other medical service providers to consider when upgrading their campuses. And so it was.

The year was 2002: Mike Meyers again was sweeping movie theaters but this time as Austin Powers; Nirvana now was something one sought at yoga class; Tiger Woods had become one of the biggest icons in the history of professional golf; greenhouse gases threatened the environment at ever-increasing levels, and another medical services provider, Arkansas Valley

Regional Medical Center (AVRMC) in La Junta, CO, was poised to launch its central plant renovation project - a project that would catapult it from the vestiges of its hodgepodge of systems, including a vintage 1950s plant, to twenty-first century operating capabilities and efficiencies, including allowances for a future cogen system and equipment, should effective utility rates warrant system conversions.

AVRMC is an amalgamation of an 80-bed hospital, a medical office building, and two nursing-home wings, the original facility having been added to at numerous junctures and the existing physical plant having been divided between two areas of the campus along the way. A more recent addition included adding mechanical/electrical physical plant capabilities to help serve the new wings but left the outdated physical plant to serve the existing buildings. The newer wing of the hospital was equipped with a 350-kVA emergency generator but received its heat from the outdated physical plant. The 1950s vintage plant, equipped with steam boilers, a single 300-kW cogeneration unit (a venture from the early '90s) and a 208-V emergency generator that served the hospital's emergency power load, had expended its useful life. So BGCE set off to merge the old and the new, once and for all.

The existing cogen unit engine carried a life expectancy of about 10,000 hours. With 8,760 hours in a year, that meant that their generator would barely make a year before they would have to take it down and rebuild it. The day they took it down for rebuild, their electric demand would spike, and they would set their electric rates for the next year. Since rates for the coming year are set based on current-year peak, they were not able to earn the lower rates their system should have been earning. If they had had a backup generator, even if it was not a cogen unit, they could have taken the cogen unit down and put this other one up to avoid those demand charges.

The team explored reutilizing existing cogen equipment and peak-shaving opportunities. The hospital's current gas and electric rates did not warrant the use of cogeneration; however, there were significant advantages to reusing the old generator instead of shipping it off to the salvage yard. It was adequate in size to power an electric chiller and thus provide peak shaving and demand avoidance to the medical campus. Also, should the main generator for providing emergency power lapse for whatever reason, that repurposed generator could offer additional backup. The goals of the new design included having a plant that could be set up to accommodate cogen functionality in the future should the gas and electric rate structure shift to make cogen economically desirable.

The new construction project, to be completed in the spring of 2004, has included a new steam boiler plant, a new emergency generator for the site to handle all emergency loads, an absorption chiller coupled with an existing electric chiller, and reuse of an existing generator designed with power feed to serve the electric chiller. Additionally the chiller plant was selected to strategically utilize steam-absorption chillers and electric chillers so the owner could operate the plant to utilize the most cost-effective energy source, be it gas or electricity. With gas currently being the most economical fuel, the primary cooling for the expansive campus will be from the absorption chiller system. Any necessary additional cooling that the absorption chiller cannot handle will be addressed by the electric chiller, and that electric chiller will be powered by the onsite generator, thus avoiding the electrical demand charges of the electric chiller on peak cooling days. This unique strategy also allows for change to the chilled-water generation approach based on utility rates. Should electricity become a cheaper fuel source than gas, the electric chiller could be utilized at the first stage of cooling.

The decision of when to switch between the electric and the absorption chillers involves analysis of the constant and shifting loads. It is determining when there is enough load out there to baseload the absorption chiller. There are other buildings on the campus that use electricity but are not hooked to the central plant. They have refrigeration equipment and are going to utilize their equipment in the summer, so they are establishing some of the amount of electricity used for their air conditioning. In the wintertime, the load profile will shift such that a portion of the load is simply coming from different draws; therefore in wintertime the system only needs to shift for the fraction of the increased load to the system's plants. That is why we can run our central plants electrically for many months of the year. There is a certain point, however, when their loads start to climb. There is a certain cut-off point where we say, "All right, time to stop cooling with our electric chiller in the central plant."

The systems have been designed so if a big enough rate spread in gas to electric rates develops - i.e., if cogen makes sense - the owner easily could integrate the required equipment. The hospital is a good candidate for cogen since it has a variety of heating loads across all of the autoclaves, sterilizers, domestic hot water, and kitchen requirements - there are a lot of places to utilize waste heat - that add to produce a fairly solid baseload, but cogen should be sized to utilize all of the waste heat. This campus could benefit from a small cogen plant on the order of 240 kW. Cogen units are available in 60-kW units, so four 60-kW cogen units would work nicely. This also would respond to the lesson learned from the previous cogen equipment. It is nice to go with modular generators so if you lose one, you are still operating at 75% power. If you base your economic model on three out of four running, you can accommodate having one down for repair and avoid the load spikes that impact your annual rate contract.

There are some expenses associated with designing in the flexibility to convert to cogen. The biggest premium is in the space. You do not necessarily have to provide the space, but you at least must identify where to expand the building to create that space. AVRMC built in that extra space, as they had an immediate space available. The space is adjacent to the plant, so when the time comes, AVRMC can move its storage out, and it is easily able to recast the space and integrate the systems. Another cost associated with building in the flexibility to convert to cogen was planning for how the electrical switchboards were configured to allow for easy tie-in later.

The project has posed the complex challenge of constructing a new plant while maintaining the existing steam-heating and chilled-water systems. The old chilled-water system included electric chillers in the old wing and an electric chiller in the newer wing. The existing distribution was a confusing web between the existing plants and the various facilities connected to them throughout the campus development. The new distribution plan required increased capacities in some locations and design of new cutovers to pick up old loads electrically, steam-wise, and chilled-water–wise. Significant piping reconfigurations were necessary to consolidate the plant into one location, all the while keeping in mind the importance of minimizing hospital downtime. Consolidation of the emergency-generator loads required the use of temporary generators and reconfiguration of the power system to change over the system, again to minimize downtime. Plans also have entailed how to decommission the old plant and how to take it off-line, making sure that the new plant is really operational with no bugs or hiccups and that it really works as intended.

The next year will be a process of learning how to optimize the system, utilizing the DDC system with trend history and the optimization capabilities in the DDC programming. The first set-points and changeovers will be determined by engineering modeling. After that, the team will be trend logging, analyzing, and adjusting when to turn on the electric chiller, turn on the electric generator with the chiller, and so on. There are many variables in these algorithms. A lot of it is how the building actually responds, whether it is a weekend or a weekday, and what season it is - all of those real-life, real-time conditions that dynamically drive demand. For example, in the middle of wintertime, the team still might be able to run that electric chiller off the grid. There might be a certain point in time where the other 8 kilos on the campus are starting to ramp up and the team all of a sudden needs to stop using that big electric chiller and push right into the absorption chiller. Going forward, the team also will continue to analyze current utility rates and contracts for the opportunity to initiate cogen operations.

BGCE looks forward to the next 10 years as an opportunity to further creative development of systems for medical-campus utility design.