Solar DHW system shutting down - Overtemp

alex_elsom

My solar dhw system over the last few days has currently shut down during the day. When I checked the controller it said that the solar array temp was 349 deg. against a limit of 270 deg. This evening when the temp showed 240 the pump was running and the return temp sensor on the controller had raised 10 deg, however the flow temp sensor had not. The opertional pressure of the system is 2 bar (30 psi), I recall it was higher than this, probably 3.5 bar (75 psi). My question is whether I have suffered a significant fluid loss in the system and how easy will it be to rectify the problem.

My solar DHW system comprises of the following components and was installed in 2011, I have done nothing to it since it was installed, so my inactiveness may have a part to play.

2# SunMaxx VHP30 arrays, a SunMaxx DHW controller, a Vaughan S80SRW20145 tank, a Beacon Morris HB-204 fan coil unit and a Solar Varem 25L 6.0 bar pressure vessel.

Hoping somebody can shed some light in my direction, the installer is no longer active and suggested a good plumber may suffice. Thank you. Alex

Jamie Hall

Four broad possibilities. First, you are not getting enough flow because the pump is failing. Second, you are not able to dump enough heat -- although if it has been working up until recently that seems unlikely. Third, you have lost some circulating fluid -- although that may be a result rather than a cause. Fourth the controller or one of its sensors is not working properly and thinking that it is overheating when it is not (I'm thinking of the flow temp sensor).

There may be others...

Your installer may no longer be active, but it appears that SunMaxx still is, and you could and probably should check with them for service.

psb75

It's getting hard to find people who will work on solar thermal systems. Support for parts and technical help is also getting sparse. A system like yours sounds like it was done well and they generally can be quite robust. But, things wear out. Some amount of maintenance attention is required--certainly after 10 years of service.
Someone needs to attend on site. There are too many variables that must be checked out. Jamie Hall has touched upon some of the main culprits. I will hazard to say that not just 'any plumber' will be willing and able to attend to your needs. You should search in the 'green' realm. And the best portal to that of course is the internet.

Zman

Some pictures of the system might help. I think you should learn as much as you can about your system. With limited options on service companies, the more you understand, the better.

Larry Weingarten

Hi @alex_elsom , Probably the most common fault is something to do with sensors. The connections get corroded, the sensor wire gets UV degradation, animals chew up the wire... I'd check the sensors and check control function as well, if you have or can get the tools to do that. The control might have allowed overheating, leading to fluid loss, leading to air in the system so the pump doesn't work well. Next in line is a burned out pump so you're doing the right thing now by looking at it. Photos really would be nice!

Yours, Larry

alex_elsom

Thank you all for your responses, it gave me some get up and go. I will takes photos over the weekend and post here for you all to admire or admonish. Thanks to Jamie Hall, I had a live chat with SunMaxx this afternoon, I have what I call a mongrel system, not everything is supplied by SunMaxx, but I believe I have the most important parts from them. They are looking into a response. I took some advise from Zman, and found a copy of the Instruction Manual for Residential Solar Water Heating Systems, and read through. An interesting document to go through, some hints on what to do and how to do it. Feeling a bit more confident. In response to PSB75, I have located 2 contractors, both at least ninety minutes drive from their premises to my home, but I have also spoken to a mechanical engineer who installed his own geo thermal heating system many years ago using a pond in his garden. He completely baffled me, but he is a source of encouragement too. Again I have spoken with a friend who works for CBRE, they seem to manage work for various companies, and he is asking some questions too. And last but not least on this round is Larry W, I am going to determine the values of all of my PT sensors and measure them, including the one on the array (should be fun on the roof), unless I measure that one from the control panel and calculate the value of the cable. I didnot realise that the flow and return sensors on the control panel where clip on. I didnot know that I can test the pH of the fluid by getting some fluid out of the air scoop. I have some other questions too, but that is for the weekend, pertaing to fluid volumes. Once again many thanks to you all.

psb75

You should be able to test the values of your roof sensor on the wire leads at the control panel. Adjust for likely expected temperature for time of day and conditions IF you get any pertinent values. Clip on/clamp on sensors are fairly common. And can lose contact after 10 years in the weather. Often the wire is "not so robust."

Larry Weingarten

Hi, An old trick for "measuring" sensors is to take them out of the system and immerse just the copper part of the sensors into a cup of water. Give them a few minutes of soaking so they are at the same temp. Now use your ohm meter to measure resistance through them. They should be just about identical. If not, you know at least one is off. A test to do before that is to do what @psb75 says and see how they read in place. I wouldn't be surprised if you get a strange reading from the roof sensor. Also, "freeze sensors" may have been used. This is essentially a snap switch that trips and makes the control think the collectors are too cold (or too hot). These sensors can fail too. Hopefully, your instructions will give you sensor wiring and also resistance ratings for a range of temperatures, so you can tell if the sensors are reading correctly.

Yours, Larry

alex_elsom

Update #1. I tested sensor 1 on the array with my trusty Fluke (yes a real one) and it read 1545 ohms. So I re-checked it again using my very cheap meter and that read 1556 ohms. On comparing that against the European DIN or IEC and the American standards, both of these figures seem to imply that the sensor is well and truly stuffed. I also swapped over the flow and return temperature sensors last evening when the pump was running and the readings of both sensors swapped their values, so they seem to work. I also runup the dump fcu by temp. wiring it up to an outlet, before re-connecting it back to the controller, so that works as well. The only thing that I have not been able to test is the 3 port valve, but I suppose that as that is fed from R2 it is 110v and therefore I could temp. connect that to an outlet to see if it drives from n/c to n/o. Stiil please keep reading, I have a couple of questions to ask.

alex_elsom

Bearing in mind that the system is ten years old and has never been maintained I was thinking of doing the following:-

Test the pH of the fluid to see if it is still within acceptable limits;
Cover the collectors with a dark tarp, to reduce the amount of daylight being received by the tubes;
Drain the system and flush with well water as that is what we have;
Hopefully if I do this the day after putting on the tarps, I will prevent thermal shock to the tubes;
Fill the system will well water to pressure test the system to see if there are any leaks;
Drain the system again if there are no leaks;
Re-fill the system with 50/50 propylene glycol/distilled water mix totalling ? USG (another question coming up) removing all air and finally re-pressurising the system;
Switch it on, cross my fingers and toes, remove the tarps and see if it works.

Q1. Can I the system empty of fluid overnight with the air valves open.
Q2. Can somebody help me with the amount of fluid needed to recharge the system. I have estimated the length of the system to about 140ft, comprising 58ft for the length with S1 sensor on the collector and 82ft for the other length which connects to the furthest part of the collector. The stainless steel pipes between the collector, controller, storage tank and dump fcu are all 3/4". The expansion tank is 25L and the heat exchanger of the 80G Vaughan tank is 20ft2 (this is the bit I don't understand, where does this figure come from).

Once again, thanks for your help/ advice/ input. Best wishes. Alex

alex_elsom

Update 2. Photos.