Altherma Hydrobox and well water - Heat exchanger corrosion

I have a client with a less than 3 year old Daikin Altherma installed and the Hydrobox heat exchanger has corroded internally and is leaking refrigerant into the water side.

It isn't one that I installed. Coincidentally, a couple of weeks prior to finding this problem I was speaking to an engineer who works for the company that installed it, he tells me they have had 4 heat exchangers recently that have had to be replaced. They have also had a number of pumps fail.

It is apparent that the system on which I am working is a retrofit on an oil boiler system and no power flushing of the system was undertaken before commissioning the Altherma. I also doubt that any inhibitor has been added to the system

To make matters worse the house is in a rural location and has only well water available from a borehole pump.

I have always added Fernox Protector to the systems I have installed, but I have explained to the client that in his case, simply changing the heat exchanger, then draining down and refilling the system and adding inhibitor may not be sufficient. Judging by the water colour and the magna clean filter the system is full of black iron and sludge.

We carried out a ph test and it was approximately 8.0, which under normal circumstances should be ok. Short of carrying out a full water analysis we are unsure of the water quality coming into the building, although we are aware it does carry silt and particles. The client is going install a filter to the incoming mains water supply. I suggest he speaks to the local company that deals with drilling boreholes for their advice.

If there are any pinholes elsewhere in the system, power flushing may move the sludge that is plugging any holes causing more leaks.

Does anyone have a suggestions as to the best inhibitor to use for well water, which has been drained through the soil and granite below, before being pump back out of the ground?

Hmmmm! As I thought, know one has a scooby and neither do we ;)

So today we installed the new heat exchanger and the plumber power flushed the system. The amount of iron and sludge that was removed needed to be seen to be believed. The plumber reckoned it was the dirtiest heating circuit he had seen and the thought the problem was not so much the well water but the fact that there was no corrosion inhibitor in the system.

The system has been dosed with inhibitor and is back up and running. Time will tell if it is successful. If it the heat exchanger does corrode through again that will leave a big question mark hanging over the quality of the heat exchanger. It is an Alfa Laval heat exchanger so I have no reason to believe it is a poor product. Then again maybe it is made to a Daikin specification.

Would it be worth fitting one of the "magnetic" in line filters to hopefully trap some of the debris?
Fernox make one similar to the type now recommended for use with the Mitsubishi Ecodan system. At least these are relatively easy to isolate and clean.
Hopefully the power flush will have got rid of most of the debris and the corrosion inhibitor will help to prevent such a build up again.

I would be running a sand filter to start with and the HX needs to be titanium/stainless, perhaps a shell/tube pool heating one of you can get one to meet the load. Pahlen may have the right one.

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Originally Posted by hyperion

Would it be worth fitting one of the "magnetic" in line filters to hopefully trap some of the debris?
Fernox make one similar to the type now recommended for use with the Mitsubishi Ecodan system. At least these are relatively easy to isolate and clean.
Hopefully the power flush will have got rid of most of the debris and the corrosion inhibitor will help to prevent such a build up again.

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A Magna Clean filter is already installed. The translucent bowl was/is black. We tried to clean the bowl with a scouring pad, but it is impossible to clean. That is what alerted us to the state of the system water.

As an aside the plumber reckons operating at these low water temperatures it is possible for a jelly like substance to grow in the water, I guess it is some kind of algae. He is now recommending Fernox AF10, which is a combine inhibitor and biocide agent.

A filter was installed last week. I assume it is a sand filter as I took advice from someone who is used to dealing with well water. The client took advice from the local irrigation/borehole contractor and I would suspect he got the same answer.

As an aside the plumber checked the incoming water and it had a ph of 6. Being well water this probably varies as the water table rises and falls.

The heat exchanger is an Alfa Laval that is made for Daikin. I haven't establish what is fabricated from, but I always assumed that they were stainless steel. It might be a nightmare to try to retrofit another manufacturer's heat exchanger into the box, and there is definitely insufficient room in the cupboard in which to install something external.

The job is complete and is operating, so it is a case of suck it and see. It should be good enough. I am sure it was the lack of flushing during the installation coupled with the failure of the contractor to add inhibitor that has done for this machine.

Check if there is any zinc coated steel piping in the heating circuit. The inner piping of the hydrobox is made of copper. Zinc with copper together in one heating circuit makes a disaster. So if the metals are mixed in the circuit, the problem could reoccur after some time.

Refrigerologist, is it a ground source heat pump, or it is an air to water HP? If it is an AtW HP, i'm just wondering what water from the well doing inside space hating circuit.