Increase Profits and Reduce Warranty Returns with Proper Antifreeze Mix

1. Commercial Office Building: In this instance, we have a commercial two-story office building of 25,000 sq. feet. The geothermal loops are all fusion-welded polyethylene, manifolded to a welded black iron building piping system. The piping system serves 22 geothermal units with brass valves and flex-hose connectors at the equipment locations. System antifreeze fill was 80% city water with methanol as the system antifreeze. The original system operated with a minimum return fluid temperature from the loop of 40 degrees. Over the years, the cooling dominant nature of the application caused the minimum return temperature to rise above 60 degrees. The building first encountered problems approximately eight years after completion when a series of leak sites developed at threaded connections between brass valves and black iron interior loop piping. Repairs required using liquid carbon dioxide freezing cuffs to isolate the leak sites, removing the leaking valves, cutting and rethreading the black iron pipe, and restoring the system into operation. After analyzing the failure sites, we determined that the methanol solution was highly corrosive. Methanol is an excellent solvent and a primary reason that NASCAR crews need to replace the fuel cells (gas tanks) in the cars they maintain. The mixture of methanol with city tap water made for a conductive solution and a galvanic cell between the brass valves and black iron pipe. The need for repairs continued until the system was completely flushed and cleaned, and refilled with water containing industrial boiler/tower water inhibitors and sacrificial anodes to help protect the system piping, much as the anode in a hot water tank helps protect the steel shell of a water heater. The cost for these repairs ran into the $20,000+ range but saved complete replacement of the piping system for the short term.

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   Figure 3

   Residential horizontal closed loop for a 5-ton geothermal system: (Figure 3) The geothermal loop is filled with softened well water and 20 percent methanol. The owner experienced three loop pump failures in fewer than eight years. He replaced two failures under product warranty. The third failure occurred out of warranty and cost the owner more than $1,800. By this time, the customer had lost confidence in the installing contractor and contacted our office to remedy the situation when he experienced a fourth failure. Upon inspection, we discovered that methanol in combination with the high-sodium softened water had eaten through the pump bodies. As fluid leaked from the system, the pumps became air-locked, overheated and burned out. To clean the system, we first replaced the flow center and pumps, and flushed the loops with tap water, followed by 120 gallons of deionized water which we circulated for several days, followed by another 120 gallons of deionized water and 24 gallons of inhibited propylene glycol antifreeze to attain a freeze point of 20 degrees. The total cost for flow center replacement and a complete system cleanup flush and fill was nearly $5,000. Had the contractor flushed and filled the system with an inhibited antifreeze solution during installation, the proper antifreeze solution would have added $450 to the total cost. In hindsight, the installing contractor's decision to use softened site water with methanol cost more than $10,000 in additional warranty materials, labor and cleanup costs plus the total loss of consumer confidence and any opportunity for repeat referrals for an otherwise very nice installation.

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   Figure 4

   Residential 10-ton geothermal system: (Figure 4) Vertical closed loop of +/- 20-year age, shared between two 5-ton geothermal units. This system functioned reasonably well for 20 years with little maintenance until a contractor, with minimal knowledge of the system's history, replaced one of two 5-ton systems. The original equipment, it appears, was totally sealed and filled with calcium chloride mixed with city tap water. It appears the solution was likely “in equilibrium” with the loop piping and had not created any major corrosion issues. When the contractor replaced the defective machine, he also installed two self-purging, atmospheric flow centers. He must have been oblivious to the fact that the clear fluid in the system was calcium chloride, which becomes extremely aggressive with the presence of oxygen. Now you have atmospheric flow centers that incorporate an open but capped solution tank. To further compound the problem, the contractor compensated for lost fluid by adding methanol as the makeup solution. The combination of air contact in the atmospheric tank plus the methanol created a toxic corrosive cocktail that destroyed and ate out six loop pumps within a two-year period. Correcting the problem resulted in a lawsuit, considerable lost time on the part of the distributor, installing contractor and homeowner. The cost to replace the corroded flow centers and completely flush the system with deionized water plus add inhibited propylene glycol as the solution fill amounted to nearly $10,000. If we were to factor in the expenses for failed loop pumps, labor and legal fees, the expenses to the installing contractor were likely in the $30,000 range.

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   Figure 5

   Office building 8-ton system: (Figure 5) Vertical closed loop of +/- 20-year age. Likely system fill when installed was automotive antifreeze (ethylene glycol) mixed with drilling or site water. The office manager called one afternoon to announce the system was not cooling and there was a bad smell in the mechanical room. This type of call generally sets off all types of alarms and had me on the way immediately to find out what had happened. Upon arriving, I found the floor was wet around the base-mounted loop pump. A horrible stench filled the air and the system pressure was down, but I did not see a leak. A quick, temporary hose cross-connection to city supply would let me repressurize the old loop to help find the leak. Before reaching 10 psi, the face blew clean off the circulating pump. Upon failure analysis, it appears that contaminated water may have filled the original system. (Bacteria love glycol and will reduce it from antifreeze to something similar to vinegar or silage, however you choose to describe the foul odor it creates.) The resulting acidic solution had slowly dissolved the impeller and face of the pump until the failure occurred. Cleanup as with the previous examples involved replacing the pump and flushing the loop with deionized water. Only this time, the first flush had iodine added to it to help disinfect the loop. Once flushed, the system was refilled with deionized water and a 20% solution of inhibited propylene glycol. Annual monitoring will serve to verify if the antifreeze holds its strength and inhibitor balance. The replacement pump plus cleanup expenses for this system ran in the $7,000 range.

In each of these cases, methanol or a glycol mixed with site water was largely responsible for the failure of the loop pumps or piping system. In my experience, it appears that virtually all geothermal manufacturers as well as the International Ground Source Heat Pump Association (IGSHPA) provide pressure drop tables for designing closed loops using methanol as an antifreeze. In addition, every closed-loop drilling contractor we work with also uses methanol as their vertical loop fill solution. In each case, we find ourselves either providing deionized water to fill the loops on site, or we flush the loops with deionized water and test the electrical conductance of the return water to assure that all mineralized tap or drill rig water has been flushed from the system.

Methanol is in common usage as an antifreeze solution in the drilling industry. It is inexpensive and makes for easy freeze protection of rig water pumps and lines. However, like smoking, old habits are very hard to break. Methanol, or for that matter any antifreeze, either with or without inhibitors, when mixed with a mineralized or contaminated water source will act like a cancer to the geothermal piping and pumping system. There is no easy cure other than to clean it out completely, or take precautions in the beginning to see that it does not occur.

Mixing Antifreeze Solutions

Antifreeze suppliers provide guidelines for the allowable chemical content of city water to which you may add antifreeze. Rarely do I find a water supply in the field that meets these criteria. To maintain the best possible performance of the corrosion inhibitors, the antifreeze solution must be made from clean deionized or distilled water. The presence of bacteria, iron, calcium, magnesium or sodium (softened water) in makeup water will combine with corrosion inhibitors, rendering them ineffective and causing problems in the future.

Antifreeze solution is available as a premix or as concentrate and mixed with deionized water on-site. Deionized water should always be made from a chlorinated, bacteria-free city water supply. To use any other water source as a mix agent is to gamble away future time and profits. All major cities have water equipment and service providers who manage deionized water column rentals and exchange them on a regular basis. A conductivity lamp on the column discharge line will tell when the column has exhausted its resin capacity and is in need of replacement.

As product distributors, you are in the best position to educate your dealers on the methods for proper geothermal system solution fill. The loop solution will be as a boiler/tower fill in southern states using low or nontoxic corrosion inhibitors, or as an inhibited ethanol or propylene glycol in the northern states. After all, these solutions are a key part of the long-term dependability of all geothermal installations. As distributors, you might as well be a part of the merchandising chain rather than outsourcing this possible profit center to others or, worse yet, leaving the loop solution fill to chance and trusting that your dealers will understand water chemistry and take the initiative on their own. Failure to follow appropriate procedures for filling geothermal loops will create negative cash flow and erode consumer confidence in a technology we so desperately need.

Jeff Persons is president of Geo Source One Inc. near Plain City, OH (Columbus area). Contact Jeff at 614/873-1140, geosourceone@rrohio.com or visit www.geosourceone.com.