When a nonprofit rehab facility in Boise needed to expand, officials elected to stick with the previous building's geothermal approach. The new version, chosen largely for its simplicity and cost advantages, heats the hospital's 156,000-sq-ft space well. In fact, from special heat exchangers for therapeutic pools to other touches including filtration, the whole system coalesces to provide comfort for the convalescing.

For more than 50 years, Idaho Elks Rehabilitation Hospital has been providing rehabilitation services to people in the Boise area. The hospital was established in 1947 to offer convalescent care for children recovering from polio. Over the years, the hospital added other programs that required more space, so numerous additions were made to the original one-story hospital.

By the late 1990s, it was no longer feasible to keep adding to the original structure, and it was determined that another hospital had to be built. Consequently, construction on a new hospital commenced, and the state-of-the-art facility was dedicated in May 2001. The $25 million, four story building consists of approximately 156,000 sq ft, with each floor measuring in at around 39,000 sq ft.

The old hospital used a geothermal system to heat the facility, and it was decided that the same type of system should be used for the new building. The rationale was that the engineering staff already knew how the system worked, so it would be a simple transition. In addition, geothermal systems are incredibly energy efficient, so the nonprofit hospital would see the savings reflected in its bottom line.

UNUSUAL CITY OFFERING

It's no surprise that engineers don't normally consider geothermal systems when they're designing mechanical systems for hospitals. The reason for that usually boils down to cost: The first cost of a standalone geothermal system (as opposed to one being served by a heating district) can be four to five times that of a traditional boiler plant, and hospitals usually don't have the cash to invest in such an expensive system.

First cost wasn't really an issue for the Elks hospital, though. That's because the City of Boise operates a geothermal heating district that serves the city's downtown area, The city delivers hot geothermal water to buildings at 155[degrees]F to 165[degrees] and collects the water from customers after the heat is removed. The system currently serves 50 buildings, heating over two million square feet of floor space.

Boise's pricing structure is set to ensure an energy cost savings of 30% over natural gas, based on a comparison of energy usage of geothermal equipment taking 50[degrees] out of the geothermal water and a gas boiler with 75% boiler efficiency. If the geothermal equipment is designed to take more than 50[degrees] from the geothermal water, the savings is even greater.

Charles Paulin, P.E. with Musgrove Engineering (Boise, ID) was the project manager and principal engineer in charge of the Elks hospital design. He noted that whenever his firm does a project within the downtown vicinity, they always take a look at the opportunity to use geothermal.

He said it is very cost-efficient, because it is not necessary to bury miles of pipe somewhere. "The city brings the water to the facility and amortizes the cost over the life of the installation. So in this case, it was a no-cost option for the Elks, because they know they'll recoup that money fairly quickly."

Gregg Heyn, the hospital's director of engineering, noted that the initial cost of the equipment was a little more expensive than a set of packaged hot water boilers. "It also requires a more sophisticated control system. But we wouldn't have the energy savings, which is why we wanted to stay with the geothermal."

The water is delivered to the hospital already pressurized, so there's no need for a pumping system. As Musgrove noted, "We take their water and distribute it through several plate-and-frame heat exchangers, and from there, we just run the building systems through the other sides of the plate-and-frames. It's very cost effective to install."

Depletion of the aquifer has caused the City of Boise to place a moratorium on the use of its high-temperature geothermal district for new buildings (sidebar). Fortunately, the hospital was able to be grandfathered in, due to the fact that it was on the city's geothermal district in its previous facility.

Paulin noted that the city also provides a low-temperature geothermal system that runs through downtown, which uses the wastewater from the facilities using the high-temperature system. "Facilities typically take 50[degrees] or 60[degrees] out of the water, so a lot of times, water is being returned at 110[degrees] to 115[degrees]. The city lets us tap this water for hydronic heat pump systems, which we have been installing in a lot of the downtown office buildings."

MULTIPURPOSE SYSTEM

The hospital uses its geothermal system for heating and domestic hot water purposes. One plate-and-frame heat exchanger is used for the building's heating system and another is used for the domestic hot water. These Alfa Laval heat exchangers were constructed with Type 316 stainless steel.