The Boiler Down Below
There is a very large potential to harness and use the thermal energy sitting below.
My job takes me to many unique and interesting locations across the U.S. and Canada. After many decades of participating in this industry, I continue to be amazed at the clever jobs and applications I see. I jump at any opportunity to visit a jobsite or mechanical room; much can be learned from observing how modern hydronics are installed and designed. Not to say that older mechanical spaces are not interesting, also. I like to see how the latest high efficiency boilers, pumps, and equipment are combined into a system. Renewable energy utilization is at the top of my list, and I never miss an invitation to visit these sites and installations.
A recent trip brought me to Reno, Nev., bunking down at the Peppermill Resort. Frank Sterzinar, a manufacturer’s rep from Osborne Co., and I were traveling together on a training trip, and he was able to get us a tour of the central mechanical plant for the resort. In addition to 2,000 rooms, the property has multiple pools, spas, a fitness center, restaurants and shops that are all heated and cooled by the central plant.
Several years back, the owners of the property decided to take a multi-million dollar gamble and drill a well into the hot water aquifers below the parking lot. The property sits on 50 acres on the edge of the Moana Geothermal Resource. The goal was to have a pool of 200 F water, which could be used to provide heating, domestic hot water (DHW) and power generation. To generate electricity, 200 F fluid is put in contact with a heat exchange fluid with a lower boiling point; steam is generated to spin a turbine for power generation. There are several sites in the Reno area that generate electricity via the deep thermal wells.
The GEO that I am more familiar with involves installing loops of PE tube into a well or trench. A fluid circulates through the tube to transfer the energy from the ground or well source through a heat exchanger in the heat pump, for instance. With the tube in a well or in the ground, you first need to transfer the energy through the wall of the tube, so you have some exchange efficiency losses. The GEO source water at the Peppermill system transfers directly into the system via a large plate and frame heat exchanger, so the fluid has only one exchange surface within the stainless plates.
At about the 4,400 foot level they hit a supply of water at 174 F. The decision was made to stay with this well and temperature to cover heating and DHW production. On the day we toured the plant, the well was being pumped at 834 gpm. Across the parking lot a reinjection well returned the water into the same aquifer at about 130 F. At peak loads, the well will supply 1,200 gpm. The production pump has the capacity to pump 2,000 gpm, if required. A very large plate and frame heat exchanger transferred GEO energy into the hyfdronic piping. The GEO water is used for various pool heat exchangers before being reinjected at 130 F down a well across the parking lot.
The plant was well maintained, clean and virtually leak free. Four 24 million BTU/hr. Clever Brooks boilers were still on line to take over if the well or pumping equipment failed, which it did several years ago around Christmas when a 400-hp reinjection pump failed. After that experience, they now keep a spare custom-built pump in inventory. One boiler is maintained at temperature to roll online within minutes if the GEO goes down. Smaller wells are scattered across the property and have provided pool loads and smaller contributions to the property’s thermal loads over the years. The smaller wells have been taken out of service with the higher flow well now online.
Water quality and scaling had been a concern. The water is tested monthly and after four years of operation the heat exchanger maintenance has not been an issue or a maintenance challenge.
The GEO system eliminates the need to run the boilers for heating and DHW production, eliminating the $1.7 million cost to operate the boilers. The ROI was reached at 3.2 years on the system.
There are several areas of the Intermountain West that have access to these thermal aquifers. With adequate temperature and flow, absorption chillers could be powered by the thermal to provide cooling and refrigeration, also.
It is not so easy to get access to these large building facilities these days and thanks to Sterzinar for arranging the visit and to the maintenance team for guiding us and allowing our group to tour and take pictures.
On this trip, I also met John Phillips, who taught a GEO plant operators course at a local community college. Several of the GEO facilities in the area have students who have completed Phillips' course and are involved in the plants’ operation. There is a very large potential to harness and use the thermal energy sitting below this area of North America. For the past 10 years, government grants have provided some momentum to this quest for GEO thermal energy. Unfortunately, the recent tax credit extension for renewable energy did not include GEO. Hopefully that can be addressed and help further the research and development of this clean, renewable, accessible energy source below our feet.
Bob “Hot Rod” Rohr has been a plumbing, radiant heat and solar contractor and installer for 30 years. Rohr is a longtime RPA member and Plumbing Engineer and PHC News columnist. Bob joined Caleffi North America as manager of training and education. He can be reached at firstname.lastname@example.org.