The new heat pumps will transfer heat from the homes, via water mains, to an existing underground water reservoir. The water from this storage facility will also be used in homes throughout the post. As temperatures and water use rise in the summer months, the lost water will be replaced by cooler water which increases the efficiency of the system. In the winter months, heat is drawn from the reservoir and the flat roof of the storage facility adds heat back into the water.

Subsurface ground-water temperatures average 75 degrees Fahrenheit year round at Fort Irwin. The system will switch over to a heat pump mode in the winter and will draw heat from the warm ground water into the homes. On-site tests conducted by the local utility, Southern California Edison, have shown a 50 percent reduction in energy costs utilizing the ground source heat pump technology.

Distributed Residential Ground Source Heat Pump System
Fort Irwin, California

Rene J Quinones
U.S. Army

The United States Army utilizing a patent furnished by DeMarco Energy Systems of America Inc., Austin Texas, is currently operating a Distributed Ground Source Heat Pump System (DGSHPS) to dnve 220 individual Water Fumace ground source heat pump units. The preliminary design and funding was provided by the local Utility company, Southern California Edison (SCE).

This design utilizes a municipal water system for it's heat sink. An existing one million gallon underground water reservoir constructed in 1943 was adapted to supplement the system. The design utilizes a closed loop and open loop system to feed water to the individual ground source heat pumps (GSHP) located in each home. The system taps into a twelve inch domestic water main which is the sole feed/output to the reservoir and then moves the water through two parallel double wall heat exchangers and returns the water to the reservoir (Open Loop).

The pump house uses one constant speed 15 hp motor to circulate the open loop water which has a vertical movement of less than 15 feet (4.5 meters). The closed loop system which circulates treated water is moved by one of two 50 hp variable speed motor. Backup motors are in parallel and are exercised by timers. The speed of the motors is regulated by a pressure sensing transducer located about 1/2 mile downstream (.8 km).

As demand increases in the homes the individual GSHP draws water from the feed side/main and circulates it in the unit. It then returns the water to a return water main which flows to the pump house and moves through the heat exchanger at speeds ranging from 300 GPM to 1,100 GPM. The speed of the motor/pump system is determined by the pressure in the main. As demand increase pressure drops and the pump speeds up to compensate. The constant speed, ( 15 hp) pump is designed to move water in the heat exchanger at flows of 825 GPM to 1,100 GPM.

The home units are standard design (off the shelf) units ranging in size from 2.5 to 3.5 ton GSHP. There was no mod)fication needed to any unit. The feed lines are copper, 1" (2.5 cm) with no splices or connections allowed unda the concrete slab or footings. The PVC mains in the street range in size from 8" (20 cm) to 4" (10 cm) at the end points. Isolation valves and cross overpoints were installed to ensure minimal impact on occupants in the event of a break.

The variable speed motors use off the shelf inverters, (Toshiba), along with all the other parts that are off the shelf items. There were no parts or pieces of equipment that were unique to this design.

Fort Irwin, California, is located in the lVIojave Desert at an altitude of 2,300 ft (707 m). Average rainfall is less than six inches (2.4 cm). Temperatures range from an average low of 25 degrees f (-3.8 C) to a high of 115 degrees F (46 C).

The project consists of 220 duplex homes ranging in size 900 sf (276 sm) to 1,400 sf (430 sm) constructed between March 1994 and December 1995.

Each home was fitted with a Water Furnace unit located in the garage. Water lines were laid in a common trench, standard PVC pipe. Laterals were laid to each unit, coiled copper pipe. Sand was used to backfill the trenches.

The tonnage for each unit matched what would have been used if a DX air conditioner were used. Since the use of GSHP was new to the Army Corps of Engineers it had been decided to maintain the tonnage in lieu of downsizing a half ton as recommended by the design engineers. Sizes ranged from 2.5 to 3.5 tons.

The pump house was located next to the existing underground water reservoir which was located at the south end of the project. Approximately one mile of water main was laid throughout the project for the GSHP system.