25 January 2002: The following report by Bob Melvin submitted 25 January 2002 summarizes the findings of investigations by several consultants that formed the basis of the subsequent redesign and replacement of the Ground Source Heat Pump system in the Mechanical Room. (Bob Cowherd)
Nick Orio of Water Energy Distributors visited today (at my pleading) to help us diagnose the problems with our self-destructing heat pumps. He found both electrolysis (which speeds corrosion) and excessive pressure drops (which speed erosion). Either one of these problems would be sufficient to destroy a heat pump in short order.
With both problems present, it's a wonder our heat pumps lasted as long as they did. I attribute our "good luck" to several serious problems with the well pumps. Before July of this year, we were running on a single well pump instead of three. This caused reduced pressure that muted the erosion problem. When we fixed the well pumps, we began to blast gritty water through heat exchanger walls that had been weakened by years of corrosion - and the heat pumps began dropping like flies.
The corrosion problem was indicated by a DC voltage differential of 0.3 volts between the heat pump cabinets (which are allegedly connected to the building ground) and the water circulating to and from the wells. This DC voltage is present whether or not the equipment is operating. There is no AC component. Electrical current is flowing from the equipment in the Mechanical Room into the well water and from there into the ground. This current strips the copper from the interior walls of the heat exchanger inside the heat pumps. Further proof was provided by Water Testing results. According to Nick Orio, the water test (done in 8/2000) found unusually high levels of copper. He believes this copper was stripped from the inside of the heat pumps.
REMEDY 'A': To correct the electrolysis problem, we need to enlist the services of an electrician (I'd suggest the top guy at Medford/Wellington, who says he is a Master Electrician). First, we need to determine where the heat pump chassis ground wires go. They should be connected to a common ground in the Mechanical Room electrical panel. Then, we want to determine where and how that panel is grounded. Our goal is to ensure that this panel - and in fact, the whole building - is grounded directly to the well casings. We need to provide the path of least resistance between the building and the wells and thus prevent electrical current from flowing through the heat pumps and into the water. This is how the building should be grounded, according to the current Mass. Building Code. Obviously, our building is not built according to the current Code. We may find that the heat pumps aren't connected to the panel's common ground (less likely), or that the panel isn't connected to the building ground (plausible) or that the building ground is not sufficient (also plausible).
...The erosion problem was indicated by measuring the pressure drop across the well side of a heat pump. Nick Orio measured 20 psi on the inlet side and 0 psi on the outlet side, for a differential pressure of 20 psi. A normal pressure drop is 4 or 5 psi. The maximum allowable pressure drop is 8 psi, at which point the water is blasting through the heat exchanger and erosion starts to become dangerous. We're at 250% of the maximum (or more! see below). This is not a good thing - to put it mildly.
The overpressurization may be worse than Nick measured. A couple of months ago, I had measured 24 psi. This may be more accurate because the equipment I was using (the kit that we purchased for HVAC balancing) was able to measure the negative pressure at the outlet. (The vacuum is due to the weight of the water being returned to the well.) When I reported my 24 psi measurement to Nick on the phone, he thought I was surely mistaken.
REMEDY 'B': The Hays flow-control valves that we were planning to install on the heat pumps would curb this problem. The valves cost $300 each and we'd need eight of them. The pipes are PVC, so the plumbing work is relatively simple. Probably two guys, one day - or about $1,600. Total cost estimate is $4,000. (Bob Melvin, 25 January 2002)
15 March 2002: Ed Conley of Corrosion Resolutions (<EdwrdCnly@aol.com> 24 Cold Spring Road, Westford MA 01886; 978 692-3255; fax: 978 692-3255; www.CorrosionResolutions.com) performed an extensive investigation of the several causes of premature corrossion in the ground source heat pump system. While the focus of immediate efforts was to replace the stainless steel well drop pipes with PVC drop pipes his report also included the following findings on the evidence that electrolysis might be contributing to corrossion in the heat pump heat exchangers. (Bob Cowherd)
4) Due to the relatively high dissolved copper concentration in the groundwater, I suspect that there may be another galvanic cell operating in the GSHP system. This galvanic cell would be created by electroless deposition of copper from the groundwater onto all wetted carbon steel component surfaces. The galvanic cell would consist of myriads of metallic copper platelets that would be attached to the affected carbon steel component surfaces. Galvanic attack of the components would be focused upon all immediate copper platelet-component interfacial areas. The potential difference between the two different metals in each of these numerous mini-sized galvanic cells would be approximately 300 mv. ...
6) It is necessary to analytically confirm or deny whether this galvanic corrosion cause is/is not occurring because this corrosion mechanism has a potential to significantly impact all wetted carbon steel system components in the mid-term. Corrosion Resolutions would propose the use of energy dispersive spectroscopy (EDS) to determine if galvanically active copper deposits are present in the GSHP system. Please contact me if you are interested in pursuing this matter further.
7) If galvanic activity confirmation is obtained, it is possible that sequestering the dissolved copper in the groundwater could mitigate this problem. This corrective action would prevent electroless copper deposition on wetted carbon steel components and; therefore, the adverse impact of galvanic corrosion would be eliminated.
Upon request, Corrosion Resolutions would offer the services of its Senior Water Treatment Consultant to conduct a sequestering feasibility study and evaluations of the groundwater treatment cost and the implementation practicality of this corrosion control approach in this specific application. Notes: 1) Performance of these engineering activities would not be warranted until corrosion mechanism activity has been confirmed as outlined in Item 7, above; and 2) Please contact me if you are interested in pursuing this analysis.
8) Significant corrosion of the Alloy 709 Cu-Ni heat exchanger tubing has also occurred. Based upon the information that you provided to me, I believe that it is virtually certain that the tubing failure mechanism is either erosion-corrosion or cavitation. Both of these corrosion processes are caused by designs that permit the occurrence of high water velocity in the heat exchanger tubes. Consequently, I recommend that you reduce pressure and lower water velocity to the lowest practical rate. Note: Alloy 709 is subject to erosion-corrosion/cavitation when water velocity exceeds approximately 7.5 fps in heat exchanger tubing.
2 May 2002: Bob Melvin's draft letter from Cambridge Cohousing to Water Energy summarized the electrolysis issue as follows.
The other major corrosion problem arises from dissimilar metals, electrically connected and submerged in an electrolytic solution (the well water). Stainless steel and regular steel have a galvanic potential difference that can cause serious corrosion. This is why a hole formed in the drop pipe for well number 2, next to where it attached to the stainless steel submersible pump. The drop pipe for that well was subsequently replaced with PVC. The other two drop pipes are likely to corrode similarly and will soon need to be replaced.
Our electrician did not find any source of stray DC current within the building. However, when well wires were disconnected and the submersible pump grounding wires were measured, he found that wells number 1 and 3 were not at the same DC potential as well number 2 (the well with the PVC drop pipe). The voltage differentials were approximately the same differential that Nick Orio measured (0.3 VDC). The corrosion consultant believes there may be two factors at work – the aforementioned corrosion cell; and a corrosion reaction between the water - which he believes is naturally high in copper compounds (e.g. copper sulfate), and the iron drop pipe. The likelihood is that the voltage we were originally concerned about is a product of an ongoing corrosion process in the wells, rather than a stray current that is driving the corrosion process.
May 2003: electrolysis consultant Scott Paul of CorrTech (508-435-0090) visited but his report is not in my records. (Bob Cowherd)
12 August 2004: Nick Orio of Water Energy, regional distributor of Climate Master heat pumps, visited Cambridge Cohousing and performed a series of tests. The first item tested as presented in the subsequent report was on the question of electrolysis caused by stray currents. (Bob Cowherd)
Using Water Energy's new specially-constructed test machine, Nick found absolutely no evidence of electrolysis.
[A 14 September 2004 letter from Ed Hofeller to Water Energy on behalf of Cambridge Cohousing referred to the CorrTech results, and Nick Orio's independent test both comfirming that the absence of any evidence of electrolysis.]
We are baffled by your warning regarding an electrolysis problem given your statement to Bob Melvin the day you took your readings that “I don’t know what you did, but there doesn’t seem to be any grounding issue…” Especially since your statement to Bob was consistent with the results of testing in May of 2003 by CorrTech that proved there was no stray current problem that could adversely affect the heat pumps. You seem to need reminding that it was you who discovered that it was water velocity on the source side that caused the destruction of the original heat pumps. Given the discrepancy between your verbal and written statements, the alarm you sound requires supporting evidence. Please return to the site and perform the testing so we may view for ourselves the results. ...
...We expect Water Energy to honor its agreement and to that end, I again ask that you provide us with your evidence of a “.4 volt difference to ground” and reproduce the test for our technicians to view.
28 October 2004: Stan Martin, lead counsel of Holland & Knight, LLP included the following passage on the Ground Source Heat Pump system in his "Claim of Cambridge Cohousing" (Bob Cowherd)
b. Heat Pump Subsystem: When the HVAC system was started up in the Winter of 2001-2002, with the well subsystem back at full strength, there were several more heat pump failures in rapid succession and the system had to be shut down. This time, water was found in the refrigerant lines (the presence of water can destroy components). The discovery of water suggested that one of the heat exchangers inside the heat pump had been perforated. It was clear at this point that there was either a systemic problem or a serious manufacturing defect.
On January 18, 2002, after two new heat pump failures were discovered, Water Energy Distributors was again consulted. By memo dated January 25, 2002, the consultant identified suspicious voltage differentials, supporting its theory that electrolysis (corrosion accelerated by a stray electrical current, probably due to faulty grounding) might be causing the damage. However, when (at CCH's insistence) Water Energy checked the pressure drop in the well subsystem (where it loops through the heat pump), it found that the pressure drop to be several times greater than normal, indicating excessive water velocity through the heat pump.
At this time CCH contacted Corrosion Resolutions and asked for a thorough evaluation of the situation. They concluded that the heat exchangers were almost certainly perforated by “erosion corrosion;” in other words, the speed of the well water looping through the heat pumps had worn away the metal piping.
To be certain that electrolysis was not playing any role, CCH hired a series of experts. First, CCH hired an electrician to test and evaluate the grounding of all the HVAC equipment. Then, CCH sought and hired a specialist in electrolysis, CorrTech, Inc. The conclusion of CorrTech and of every other expert was that there was no electrical problem.
15 June 2009: Ken McKeen discovered a leak in the heat exchanger of our heat pump #2 in an area of severe corrosion. (Bob Cowherd)