The Importance of Providing a Proper Antifreeze Solution for Geothermal Installations By Jeff Persons CGD / Geo Source One Inc.

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1 The Importance of Providing a Proper Antifreeze Solution for Geothermal Installations By Jeff Persons CGD / Geo Source One Inc. As I look back on my past, I m grateful for the many opportunities I ve had with geology, water chemistry, the National Ground Water Association, and the geothermal heat pump industries. One of my earliest assignments in these ventures was to study the effects of water chemistry as it related to scaling incrustation and corrosion of piping systems. Early on I learned the importance of the Galvanic Series (Figure 1). The Galvanic Series is a guideline to indicate the susceptibility of dissimilar metals to form a battery cell which will corrode a less noble metal and deposit it on a metal which is higher on the galvanic scale. Lessons learned from investigating failures of a multiple number of piping situations taught me to avoid the use of ferrous metals in Open Systems. If working with an Open System containing natural water or well water, the materials of choice were always polyethylene, PVC, copper, brass, or stainless. To use galvanized or black iron fittings, which are very low on the galvanic series, was simply asking for a failure Figure 1 Illustration from HARDI Journal April 2009 within a few years. It is this same knowledge that the majority of geothermal heat pump manufacturers have imparted into their piping materials suggestions. Yet to my knowledge, no manufacturer has taken time to caution or educate contractors to the consequences that may result if lower cost dissimilar metal fittings are used. Nor have they mentioned that when ferrous metals are used; as is the case for cast iron body loop pumps, or for that matter; commercial systems where the building is piped with black iron pipe, that proper loop fluid chemistry is critical for longevity of the system. The same can be said for the type of antifreeze and the method by which the antifreeze is mixed. Low cost antifreeze solutions typically lack the needed corrosion inhibitors to prevent galvanic corrosion. Premium grade antifreeze solutions are often double the cost of uninhibited antifreeze. The extra cost buys broad spectrum corrosion inhibitors that protect a wide range of metals within the 1

2 system. Inhibitors alone will not provide total protection. Ultimately, the behavior of an antifreeze solution and its ability to protect or corrode a system depends upon the type of antifreeze, its corrosion inhibitors and the quality / purity of the make-up solution. Low purity make-up solutions will quickly deplete even the best inhibitors and render an other-wise safe antifreeze corrosive. Contractors working with geothermal equipment have a great deal to gain if they provide a complete package for the system which includes a water treatment / corrosion inhibitor solution when needed for southern climates and an inhibited antifreeze for those northern climate installations which need freeze protection. The value added for this service can be as much as $300 to $800 per residential system and into the tens of thousands for large commercial systems. If this function is not provided by the installing contractor, the end result is contaminated systems, dissatisfied customers and repeat warranty claims. When water chemistry is ignored on commercial installations the outcome will typically result in an insurance claim or lawsuit of major proportion. When this happens, both the contractor and the customer are saddled with substantial lost time, money and declining consumer confidence! Installing contractors and particularly loop installers who provide the system flush and fill function, need to know why certain water treatment solutions are used and the importance of maintaining a proper solution concentration. Loop installers must understand the consequences and liabilities to which they are exposed when not using the recommended system fill. In addition it is important to understand what actions may be needed to recover a system if the solution becomes corrosive. Figure 2 lists a variety of system solutions I ve encountered and their suitability for use with geothermal loops. Figure 2. Illustration condensed from HARDI Journal April

3 Case Histories: I prefer teaching from examples rather than cut and dried tables of rules and regulations. There is a great deal to be learned from the experiences of others and how they were resolved. The following is a series of four case histories of systems gone sour due to a lack of knowledge on the part of the installing contractor. Hopefully you may identify with one or more of these cases and discover a solution to avoid similar misfortune in the future for yourselves and your customers. 1. Commercial Office Building: In this instance we have a commercial two story office building of 25,000 sq. feet. The vertical geothermal loops are all fusion welded polybutylene, manifolded to a welded black iron building piping system. The piping system serves 22 geothermal units. Each system is isolated from the building loop with brass valves and rubber flexhose connectors. The system antifreeze fill was made with Methanol mixed 20% with city water. 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 and the need for an antifreeze solution was no longer a concern. The building first encountered problems approximately 8 years after completion when it was noted that a series of leak sites had developed at threaded connections between the Rubber flex hose connectors, brass valves and black iron interior loop piping. Oddly we also noted that the black rubber flex hose connectors between the geothermal systems and the building piping had become brittle and had a crunchy feel when flexed. Repairs to replace the leaking fittings required the use of liquid carbon dioxide freezing cuffs to isolate the leak sites, remove the leaking valves, cut and rethread the black iron pipe and restore the system into operation, (Figure 3). 3

4 Figure 3. CO 2 Pipe freezing cuff to help isolate and allow repair of leaking section of black iron pipe at the threaded connections. A brass valve and corroded pipe thread fitting are seen at the right. Upon analysis of the multiple failure sites it was determined that the original fill solution of methanol mixed with city water had no corrosion inhibitors and was highly corrosive. Methanol is an excellent solvent and a primary reason top fuel race crews need to replace the fuel cells (Methanol 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, 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. As part of the system repair process we began removing brittle rubber connector hoses only to discover that the hoses were fine. Instead of a pending hose failure condition we discovered the hoses had thick scale deposits of precipitated iron. The highly conductive antifreeze solution had dissolved the iron from the piping system and re-deposited it on the interior wall of the rubber flex hoses. When the building owner Figure 4. Iron deposits from the rubber flex hose connectors. assigned a Boiler / Tower Chemical supplier to do a complete system clean-up; the pressure fluctuations that ensued during this clean-up process caused massive amounts of the iron precipitate to release itself from the hoses. As these large flakes of scale circulated through the 4

5 system, they plugged pump strainers and settled out in low velocity sections of the piping system and vertical loop heat exchangers. The cost for flushing and cleaning this system ran into the $20,000+ range but saved complete replacement of the piping; at least for the short term. 2. Residential horizontal closed loop for a 5-ton geothermal system: (Figure 5). Figure 5. Methanol corrosion in a loop pump ferrous metal body. This homeowner experienced 3 loop pump failures in less than 8 years time. Two failures were replaced under the product warranty. The third failure occurred out of warranty and cost the owner over $1,800. By this time, when the individual experienced a fourth pump failure, he contacted our office with the hope that we might find a solution to his problem. Upon inspection, we discovered the rubber connection flex hoses were crunchy when squeezed, the system had lost all pressure and the wall and floor were streaked with iron stain below the flow center pumps. Methanol; likely mixed with well 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 flushed the loops with tap water; then followed with a second flush using 120 gallons of deionized water which we circulated and filtered for several days. Once we were confident the system was clean and all debris from the old pumps had been removed, we followed with a third flush with another 120 gallons of deionized water and 24gallons of inhibited propylene glycol antifreeze to attain a freeze point of 20 degrees. The total cost for flow center replacement and a complete system clean-up flush and fill was nearly $5,000. Had the system been flushed and filled with deionized water and an inhibited antifreeze solution at the time it was installed, the proper antifreeze solution would have added $450 to the total cost of the system. In hind-sight, the installing contractor s decision to use well water with methanol cost over $10,000 in additional warranty materials, labor and cleanup costs plus the total loss of 5

6 consumer confidence and any opportunity for repeat referrals for an otherwise very nice installation. 3. Residential 10-ton geothermal system: (Figure 6) 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 one of two 5-ton systems was replaced by a contractor with minimal knowledge of the system history. The original equipment, it appears, was totally sealed and had been filled with calcium chloride mixed with city tap water. Figure 6. Pump body corrosion caused by a combination of Calcium Chloride, Methanol and Oxygen mixed with city water. It appears the solution was likely in equilibrium with the loop piping and had not created any major corrosion issues. When the defective machine was replaced, the contractor also replaced the loop flow centers for both machines. Oblivious to the fact that the clear fluid in the system was calcium chloride, and, that calcium chloride becomes extremely aggressive when oxygen is present, the new flow centers were installed as 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 make-up solution. The combination of air contact in the atmospheric tank plus the methanol created a toxic corrosive cocktail that destroyed 6 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 6

7 amounted to nearly $10,000. Considering the expenses for failed loop pumps, labor and legal fees, the expenses to the installing contractor were likely in the $30,000 range. 4. Office building 8-ton system: (Figure 7) 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 connection to a portable fill tank was needed to re-pressurize the old loop and locate the leak. Before reaching 10 psi. the face blew clean off the circulating pump. Figure 7. Pump body corrosion from a rancid ethylene glycol solution. Upon failure analysis, it appears the original system may have been filled with contaminated water, (possibly original vertical loop fill water from the drilling rig tank). (Bacteria love glycol and will reduce the glycol from antifreeze to something similar to vinegar or silage, if you choose to describe the foul odor it creates.) The resulting acidic solution slowly 7

8 dissolved the impeller and face of the pump until the failure occurred. Clean-up; 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 clean-up 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 IGSHPA (International Ground Source Heat Pump Association) documents provide pressure drop tables for designing closed loops using methanol as 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 has long been used 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 often 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 assure that problems will not occur. Mixing Antifreeze Solutions Antifreeze suppliers provide guidelines for the allowable chemical content of water that may be safely added to their antifreeze, (Figure 8). Figure 8 Dilution Water Quality (illustration by Interstate Chemical) 8

9 Rarely do I find a water supply in the field that meets the criteria for potable make up water that is found in Figure 8. To maintain the best possible performance of the corrosion inhibitors; an antifreeze solution must be made from clean deionized or distilled water. The presence of bacteria, iron, calcium, magnesium, or sodium (softened water) in make-up water can and will combine with corrosion inhibitors rendering them ineffective and cause problems in the future. You might be surprised at just how many commercial contracts ignore the importance of using distilled or deionized water and will still state to fill the system with potable water ; or for that matter the drawings will show a hydronic system pressure reducer valve and backflow device connected directly to the potable water supply with no provision for a deionized water column to protect the antifreeze that is already in the system. To exemplify the danger in mixing antifreeze with potable water I constructed an simple non-scientific experiment with sample containers filled with a piece of copper pipe and a sample of steel wool. My experiment has 16 sample solutions. Eight solutions each for both deionized water and city water. The samples are mixed as a plain solution, a plain solution with a corrosion inhibitor; (in this case Fernox F-1, a hydronic system corrosion inhibitor), and again, mixed with an FDA listed non-toxic inhibited propylene glycol, (Interstate P-323). Samples were also mixed with methanol as a plain solution and as a solution with the Fernox F-1 inhibitor added to verify if the inhibitor might provide corrosion protection with methanol solutions. (The results for eight of these samples are easily seen in Figure 10 at the end of this report.) The results of this study indicate that while deionized water by itself is corrosive. The solutions made using deionized water with an inhibitor or with inhibited antifreeze all remained crystal clear with no sign of corrosion. Whereas the samples made with city water; both with and without corrosion inhibitors, had significant corrosion, discoloration and sediment either due to the lack of corrosion inhibitors or from the precipitation of corrosion inhibitors due to minerals in the city water. This simple experiment serves to show that while city water is potable, not all city supplies are suitable for use as an antifreeze mix or system fill solution. This simple test method can be easily repeated with your own loop fill solutions. Should you encounter a problem project; it might be prudent to run an analysis on the fill water and test this water to see if corrosion inhibitors might be added to help buffer and make the sample less corrosive. If proper inhibitor concentration cannot be found, the situation may require a complete flush and fill process with a clean solution of deionized water and your favorite inhibited antifreeze. Antifreeze solutions may be ordered and shipped as a pre-mix or they may be ordered as concentrate and mixed with deionized water on site. Deionized water if made on-site should always be made from a chlorinated iron and bacteria free city water supply. Never use well water or an untreated water 9

10 source with a deionized water column. Should there be any bacteria present in the supply water, the bacteria can contaminate the deionizing column and carry themselves on to other systems just as drilling tools and fluids can carry bacterial iron from well to well. When it comes to the use of deionized water; 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. Typically these rented ion exchange columns are replaced with new tanks based on your usage and the mineral load removed from the supply source. A conductivity lamp on the DI column discharge line will tell when the column has exhausted its resin capacity and is in need of a replacement, (Figure 9). Figure 9. Typical Deionized water column with fluid quality indicator lamp on outlet piping from the column. As geothermal loop installers you re in the best position to educate your customers in the methods for proper geothermal system solution fill. The loop solution will be as a boiler tower fill in southern states using 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 loop contractors, you might as well be a part of the merchandising chain rather than let this possible profit center be outsourced to others or worse yet; leave the loop solution flush and fill process to chance and trust that the HVAC contractors you partner with 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. 10

11 Figure 10. Water Sample Comparison: City water with milky white precipitated corrosion inhibitor from propylene glycol Crystal clear solution of deionized water and inhibited propylene glycol Cloudy rusty solution of city water and Methanol Cloudy rusty solution of city water only 11

12 Figure 10 continued Cloudy rusty solution of deionized water and methanol Clear solution of deionized water and methanol with 0.5% corrosion inhibitor F-1 Rusty sediment in a deionized water sample (no corrosion inhibitor added) Crystal clear deionized water with 0.5% F-1 corrosion inhibitor References: Increase Profits and Reduce Warranty Returns with Proper Antifreeze Mix by Jeff Persons, HARDI HVACR Business Journal April 1, /14/