Springhill Suites in Pensacola Beach, Fla., uses a geothermal system in conjunction with a closed-loop evaporative fluid cooler.

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By Albert R. Barfield, Member ASH RAE

Designing an HVAC system for a beachfront hotel can be chal­

lenging because ofthe hot, humid, and salt-laden atmosphere.

In a premium barrier island location , the expense of the real estate

means that system size is also a consideration. Because potable

water must be piped from the mainland and sewer processing is

a challenge, water and sewer is expensive on the island. At the

80,145 ft2 (7 446m2) Springhill Suites in Pensacola Beach, Fla., de-

signers used a hybrid geothermal system to address these issues.

Top priorities in system selections were guest comfort, appropriate outside air ventilation levels for acceptable in-

48 ASHRAE Journal

door air quality, good humidity control within the hotel, equipment li fe, and energy efficiency.

ashrae.org

System Selection HVAC system selec­

tion was narrowed to a four-pipe, centra l plant chi ller and boiler or a geothermal ground-

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coupled heat pump system. According to contractor estimates, the geothermal ground-coupled system was less expen­sive than the four-pipe system. Additional advantages of the geothermal system were a smaller central plant footprint, minimal water consumption without an open cooling tower, and a ground loop life expectancy of more than 50 years.

Due to a restricted loop field area, there was only room for 98 boreholes

About the Author Albert R. Barfield is an employee of Gulf Power

Company in Pensacola, Fla.

June 2008

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(about I 00 tons (350 kW) of heat rejec­tion capacity). Given this complication, a fully ground-coupled geothermal system was not used. The contractor se­lected a 150 ton (528 kW) closed-loop evaporative fluid cooler to supplement the loop field during the seven months of peak season heat rejection. This fluid cooler was configured in parallel with the loop field, which offered some considerable heat rejection control and redundancy, forming a hybrid geother­mal system (Figure 1).

In addition to more than 300 tons (1055 kW) of space conditioning heat pumps, the geothermal closed loop serves the domestic water heating heat pumps, the heat pump pool and spa heaters, I 00% outside air rooftop heat pumps, and the water-cooled ice ma­chines throughout the hotel.

The hotel opened in July 2002 and submetering of system components was performed from May 2003 through April 2004. Submetering included do­mestic water heat pump energy and gal­lons of hot water consumption, outside air heat pump energy, main geothermal loop pump energy, pool and spa heat pump energy, first floor ice machine energy, closed loop evaporative fluid cooler energy and water consumption, average monthly closed loop return water temperatures and total building monthly electric energy consumption. In addition, annual propane energy consumption was gathered for the in-house laundry dryers, and water

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consumption data was gathered for the Figure 1: Hotel hybrid geothermal system. ozone fed laundry washers . Indoor tem-perature, relative humidity and perceived indoor air quality also were observed during the submetering period.

System Performance Performance of the various hotel systems is good. Conditioned

areas checked around the hotel maintained 72°F to 74°F (22°C to 23°C) dry bulb with 45% to 50% relative humidity in cooling and 68°F to 70°F (20°C to 21 °C) dry bulb with 30% to 50% relative humidity in heating. Preconditioned, zone neutral temperature out­side air is delivered from the rooftop heat pumps directly into each guestroom and into the common area of the hotel. The exhaust air balance is such that the building has a positive pressure. Occupants have been pleased with the indoor air quality.

The two rooftop 100% outside air, modified geothermal heat pumps delivered 7,630 cfm (3600 Lis) of zone neutral air at an

June 2008

annual energy performance of 15.7 wh/cfm (0.033 kWh/L·s - 1). Annual geothermal loop pumping consumed 290,925 kWh (I million MJ) for the main loop pumps, although these pumps did not use variable speed drives. The closed loop evaporative fluid cooler operated about seven months of the year and annual return loop water temperature averaged 85°F (29°C). Energy consumption for the fluid cooler tower was 40, I 07 kWh ( 1.4 mil­lion MJ) annually, while the evaporative tower consumed only about 482,000 gallons (1.8 million L) of water for the year.

The geothermally cooled ice machines keep the interior areas around the ice machines cooler and quieter, while reducing the energy to produce ice by 23% below air-cooled equipment.

Outdoor pool and spa annual heating energy consumption to heat more than 3,000 ft2 (279 m2) of outdoor pools and spas was 93 ,745 kWh (337 482 MJ). Pool temperatures were at 85°F

ASHRAE Journal 49

(29°C), with an estimated annual heating COP of 6.5 for the geothermal heat pump pool heaters.

Domestic water heating was supplied by geothermal heat pump water heaters to heat approximately 600,000 gallons (2.3 million L) of water at an annual energy consumption of33,850 kWh (121 860 MJ) and at an estimated annual COP of2.38 efficiency.

An ozone laundry washing process is used, which reduces laundry hot water consumption by 90% while reducing laundry water consumption by 22%. Propane dryers in the laundry opera­tion consumed 4, 719 gallons (17 863 L) of propane annually.

Ceiling fluorescent and compact fluorescent interior lighting in the hotel reduced annual lighting energy consumption by more than 70% from the incandescent lighting option.

Because only a nominal amount ofHV AC system components are exposed to the harsh salt atmosphere at this site, annual system maintenance has been greatly reduced compared to air source HVAC configurations on this island. Geothermal ground loop components have a life expectancy of more than 50 years, improving this geothermal system's ability to be sustained well into the future.

Total building electrical consumption was 1.74 million kWh (6.3 million MJ) for 2003 - 04. This annual electrical consumption, together with the 4, 719 gallons (17 863 L) of annual propane energy consumption indicates an overall site

50

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ASHRAE Journal

energy intensity of79,000 Btu!ft2 (897 MJ/m2) annually. When compared with the 1995 Department of Energy (CBECS) survey intensity, for the lodging segment, national average of 125,000 Btu/ft2 (1420 MJ/m2) , this hotel operates at 37% below the average.

Conclusion The annual data for this hybrid geothermal hotel shows the

match of hybrid geothermal HVAC technology to this hotel site achieved excellent results. The owners, operators, and guests of this hotel benefit from the tightly controlled temperature, humidity and good indoor air quality. Other benefits include low maintenance cost, high energy efficiency, reduced water consumption, and consistent system performance and avail­ability. Owner payback for the initial investment in this hybrid geothermal system is not considered here because the hybrid system was less expensive than the optional HVAC system considered. As noted, the energy intensity ( 1 ,000 Btu/ft2) for this hotel was 37% below the 1995 DOE (CBECS) survey average intensity for the national lodging segment. Finally, with only a few of the hybrid geothermal system components exposed to the harsh ocean salt atmosphere, expensive compo­nent replacement is reduced along with substantial life-cycle cost reduction.•

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