The Geothermal in This Building Helps Fight Fires
It has been repeated time and again that churches drive many worthy and valuable efforts, and when they get behind something, people listen. I wrote about a church in Tampa that has had geothermal HVAC since 1949, and had their first equipment upgrade in 2013 while still operating on the original geothermal wells. The Catholic Church has been in the news with remarkable sustainable efforts. Here is a peak at the 683,000 square foot Mormon Church Office Building in Salt Lake City, heated and cooled by geothermal sourced heat pump chillers since 1972.
Building Characteristics
The headquarters building of the Church of Jesus Christ of Latter-Day Saints (LDS) is a 28-story office tower plus penthouse and two 4-story wings to the east and west. The building was occupied in 1972. Construction is concrete. The entire complex has 683,000 net square feet of office space and houses 1,600+ employees. Three levels below ground contain the cafeteria, mail room, print shop, maintenance shop, and parking for 1,400 cars. The Genealogy Library is on the main floor of the west wing. A 335-seat auditorium is on the main floor of the tower. The interior of the building is designed on 5-foot square modules. This permits separate control of lighting and air-conditioning for each module. On the building’s exterior, T-shaped columns help shade the windows to reduce the cooling load. The windows are double glazed, and rotate so that external cleaning is not necessary.
Geothermal Source Description
The geothermal source is provided by four wells. Two of the wells are 390 feet deep and the other two approximately 635 feet deep. The two shallower wells are approximately 67ºF and the two deeper wells are ca 75ºF. During normal winter operation, water is pumped from the warmer wells and injected into the cooler wells. During the summer, the production and injection are reversed. This results in a greater than normal Δt between the wells and improves operating efficiency. Well number one is equipped with a 250-hp line shaft pump with the other three wells being fitted with 200-hp line shaft pumps. Total flow during any period of operation is 4,600 gpm. The facility has permission to produce up to 6,285 gpm and inject up to 5,280 gpm. Total production capacity of the four wells is 8,130 gpm.
Geothermal HVAC Systems Design
The central heat pump plant consists of three 750-ton York units connected in series. Two heat pumps can cover peak load and, in most instances, one heat pump will carry the entire building load. Each of the heat pumps consists of a turbo-compressor, condenser, cooler, and liquid intercooler, and is powered by an 800-hp General Dynamics squirrel-cage motor with geared-speed increaser. The central system is controlled through the use of a Honeywell Master Control Center. In utilizing the hot and cold water produced in the refrigeration cycle, two main air heating and cooling systems are used. The larger induction system is employed around the periphery of the building to balance heat loss and gain through the windows, while a dual duct, “high velocity” system is used in the interior to balance the net occupancy and lighting load. In the induction system, both hot and cold water is delivered to separate primary coils in a series arrangement in air streams within a common enclosure. These units, including 14 main air handlers, are located on the 13th floor of the tower and the 4th floor of the east and west wings.
Firefighting Needs Drive Selection of the Geothermal Heat Pump System
In 1953, the church leadership expressed concerns that existing city water service was inadequate to provide necessary firefighting capabilities for the historic buildings on Temple Square. In 1954, the church began to construct a 440,000-gallon, underground, concrete storage tank and two deep water wells and pump stations to feed fire hydrants on Temple Square. In 1957, the city proposed to meet their obligations for fire protection by constructing an 8 inch dedicated underground fire line with fire hydrants at strategic locations. In 1959, the church began to consider what should be done with the storage tank. Consulting engineers proposed the feasibility of using water from wells number one and two for air-conditioning purposes. In 1960, the feasibility study was started and submittals were sent to the state for revised use of the water. In 1962, the studies were completed and it was determined that two additional wells were needed for injection. The state water engineers gave approval and wells number 3 was completed in 1963 and well number 4 in 1964. In 1968, the construction of the new church administration building was started and it was completed in 1972. The system was also designed to provide pre-cool assist to the HVAC system of the Relief Society Building.
Operating History
Church Office Building Mechanical
Since going into operation in 1972, the system has performed very well with few major operational or maintenance problems beyond what would be anticipated during 43 years of operation. According to the maintenance staff, the average life of the York units is 25 years, and that they have now exceeded that and expect several additional years of life before major replacement is required.
System Economics
The system has always been extremely cost effective for the church. It was calculated that the system had a four year payback although it had cost one-third more than a more conventional system based on boilers and chiller with cooling tower. However, it should be remembered that two of the wells were drilled for other purposes and are not included in the first cost of the system. In 1982, the electrical cost for the building was estimated to be 0.03¢ per square foot, of which an estimated 50 percent was for lighting and the remainder for mechanical equipment.
Satisfaction with the Geothermal Heat Pump System
Church personnel seem to be extremely pleased with the overall operation and maintenance requirements. In fact, the head of maintenance said, “great system, would recommend again.”
Jay Egg is a geothermal consultant, writer, and the owner of EggGeothermal. He has co-authored two textbooks on geothermal HVAC systems published by McGraw-Hill Professional. He can be reached at jayegg.geo@gmail.com.
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