How to prevent overheating?

[Guido in Boston]

You're most welcome.

I'd expect 3 valves plus a couple of drain cocks ought to do it but I'd still respectfully suggest getting a licensed plumber to do the work and also run it by the AHJ before you start.
Just don't skimp on valve quality - that's little more than foot shooting false economy.
While you're at it, add a check valve that works or at least change out the one you may have. If it's more than a couple of years old, you'll most likely find that it's failed partially open from fouling due to mineral deposits and become useless.

Yea, a lot of folks are not favorably inclined toward the AHJ's and often look n them as an impediment to progress. Unfortunately or not, if/when a disaster takes a property or any part of it, insurance carriers usually look for unpermitted improvements as a possible reason to deny a claim.
More just sayin' stuff.
Besides, a lot of times AHJ's do actually know some stuff, like most jurisdictions not liking non-code or otherwise inappropriate stuff from the automotive world for residential service that probably isn't ASME rated and probably also not suitable for potable water service.
A lot of times they can be a source of probably correct, pertinent and practical information.
After dealing with all kinds of code inspectors, including my own QC people, I found an inspector is like a Marine in at least one respect: the inspector can be your best friend or your worst enemy and you get to choose which.

Off topic, my wife's a retired Nurse-Practitioner who specialized in heart transplant and early lvad implementation and applications. She got to work with a lot of manufacturers and designers of medical equipment back in the early days of Lvad's.
We've had some interesting discussions over the years about the similarities between fluid mechanical systems and the human cardio-vascular system. We've both learned a lot from the discussions.
WAY back in the day (as an advisor-assigned side project during grad school days) I got to contribute to the design of one of the first blood heat exchangers used in open heart surgery applications. My part was as one member of the team that did some fairly extensive measurement work on the transport properties of human blood which, curiously enough, had not been extensively investigated up to that time, but essential to heat exchanger design. Most of it was pretty boring but one interesting thing we found and quantified - that was pretty much already known but had not yet been well quantified for heat exchanger design - was that human blood is thixotropic. Fun stuff that with 5 bucks will now buy me a cheap Starbucks.
FWIW, I believe the result of all our work might still be on display in the SUNYAB engineering library.

Yes, licensed plumber for sure. I will sweat a fitting or 2 for a repair, or tape some threaded fittings but would not do an installation. Not sure I have a check valve. I have an air-vent at the top of the panel to allow refilling. Where would check valve be located? what is the purpose? Wish I could get rid of the CPVC but Cu doesn't do well when concrete is poured around it.

One of the other engineers I used to work with sent me this today. Promising but electronic. The analog has a max on time of 10 s so I'm asking about the (undocumented) digital one - WTFM completely, I say.

https://www.grainger.com/product/13X528?gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231&gclid=Cj0KCQjw06-oBhC6ARIsAGuzdw2amutcaao0Oh9Fqsjf5Y3a3rgs_dvtX2oQcxYUlBrL9Oa-b1ih4E4aAnpjEALw_wcB&gclsrc=aw.ds

No insurance here in the hurricane zone - cost is 50% of property value per year - hahaha. Naked is more financially responsible unless you are a business.

I used to work at a defcon on Peacekeeper/MX even way farther back in the day. Tell me about QC and DCAS. But we won and the Ruskies lost the USSR. And it was decommissioned so even better.

Sounds like your wife might have worked with Abiomed - have good friends there. Cheers!

[J.P.M.]

Yes, licensed plumber for sure. I will sweat a fitting or 2 for a repair, or tape some threaded fittings but would not do an installation. Not sure I have a check valve. I have an air-vent at the top of the panel to allow refilling. Where would check valve be located? what is the purpose? Wish I could get rid of the CPVC but Cu doesn't do well when concrete is poured around it.

One of the other engineers I used to work with sent me this today. Promising but electronic. The analog has a max on time of 10 s so I'm asking about the (undocumented) digital one - WTFM completely, I say.
https://www.grainger.com/product/13X...p;gclsrc=aw.ds

No insurance here in the hurricane zone - cost is 50% of property value per year - hahaha. Naked is more financially responsible unless you are a business.

I used to work at a defcon on Peacekeeper/MX even way farther back in the day. Tell me about QC and DCAS. But we won and the Ruskies lost the USSR. And it was decommissioned so even better.

Sounds like your wife might have worked with Abiomed - have good friends there. Cheers!

The primary purpose of the air bleed valve at the top of a system is to allow trapped air that's evolved out as the water heats up to escape and so avoid an air lock at the top of the system as the air accumulates over time and so completely stops or at least impedes the flow. A temperature stagnated collector system is the result.
An air bleed will also, as you write, make the system easier to fill (and drain) but a simple ball valve will do the same thing for many years without failing.

A check valve is a usually necessary and essential component of most flat plate, fluid circulating solar water heating (or other liquid) systems where the storage tank is below the level of the flat plate collector(s).
It's a one way valve that prevents water from flowing in the opposite direction from the way the pump is pushing the water.
Without a check valve, most, or all, or more than all of the thermal energy gained when the system is heating water can and will be lost beginning when the pump stops due to thermosiphoning.

Check valves are usually placed in fluid circuits near pump outlets in such a way that reverse thermosiphoning will be prevented - at least until the check valve develops a bypass leak from fouling and then it needs to be serviced or replaced as I mentioned in a prior post.
Question: What's the elevation of your storage tank relative to the bottom of your collector(s) ?

On copper and concrete, the way I learned it, unless the concrete has a lot of fly ash or somehow has a lot of sulfur in it, copper and copper tubing (both annealed and drawn types) usually get along well with concrete as lots of old, large and still operating radiant slab hydronic heating systems with copper tubing will attest.
Concrete poured around copper piping systems or ornamental work will bubble off some H2 gas but that's usually not much of a problem as long as the H2 evolves out of the pour.
The bigger problem with copper tubing embedded or set in concrete is most often that the differential thermal expansion of the copper tubing is not properly accounted for and stress corrosion cracking of the copper is the usual result. Plumbing codes handle that situation well for residential applications.

You may be thinking of aluminum in contact with concrete which requires some considerations.
Aluminum reacts with the alkalis in portland cement type concrete and big time hydrogen gas evolution is the result.
Over time this causes the aluminum to corrode and the aluminum oxide material, has a larger volume than the aluminum it evolved from. That greater volume must be accommodated for somehow and nature takes it by cracking or spalling the concrete. In addition, any trapped and evolved hydrogen gas that gets stuck in the concrete can do the same.
Now since concrete has poor strength properties in tension, the concrete runs a real risk of structural failure from either spalls or cracks or both.
Another possibility is that aluminum in contact or close proximity to other metals (rebar, clamps, etc.), especially if there are any chlorides in the mix (think chlorinated H2O to mix the concrete), will result in galvanic corrosion of the aluminum with more volume changes and other associated corrosion problems.

Bottom line, IMO only you'll be safer if you get your system examined by a knowledgeable solar pro and talk to the AHJ.
Or, better and safer yet, if you still want to fool around with alternate energy, stop throwing good money after bad, scrap the solar water heater, quit fooling around with stuff above your pay grade and get a PV system/ You'll be $$ ahead for a lot less PITA.

[Guido in Boston]

Thank for the very educational post. Would love to install PV and expect to do so in the next decade once grid-connected PV is permitted. Yes, now that you say the check valve is fluidically after the circulator pump, I do have one.

The panel is 2 stories above the HW tank, on the standing seam roof. Not accessible without a 2 story ladder and good sticky shoes.

Mismatched tempco was the bane of my existance for more than a year - major failure analysis program on MX. Did you ever read the old Design News magazine "Sherlock Ohms" column? I wrote a good one about that subject for them, among others.

Since you seem quite knowledgable, got any background in residential/small-community scale pyrolysis of waste plastic (washed up on beach) to make liquid or gaseous fuels? Not enough mass/time for a waste to energy plant...

[J.P.M.]

Thank for the very educational post. Would love to install PV and expect to do so in the next decade once grid-connected PV is permitted. Yes, now that you say the check valve is fluidically after the circulator pump, I do have one.

The panel is 2 stories above the HW tank, on the standing seam roof. Not accessible without a 2 story ladder and good sticky shoes.

Mismatched tempco was the bane of my existance for more than a year - major failure analysis program on MX. Did you ever read the old Design News magazine "Sherlock Ohms" column? I wrote a good one about that subject for them, among others.

Since you seem quite knowledgable, got any background in residential/small-community scale pyrolysis of waste plastic (washed up on beach) to make liquid or gaseous fuels? Not enough mass/time for a waste to energy plant...

You're welcome.

If the air bleed and the check valve haven't been inspected or serviced in a while, I'd suggest they're at least due and probably causing problems.
If the air bleed is not bleeding air sufficiently, that may be the source of at least some of your overheating due to a vapor lock that forms and then comes/goes from slow/partial valve operation.
What's the collector surface area ?
Which El Sid pump do you have ? Seems like most of them are pretty low head for that much elevation change for one thing. Also, if it a low head pump, besides needing a bigger pump to overcome the elevation head when filling the system, it may produce insufficient head to maintain a decent flowrate.
It's neigh onto impossible to troubleshoot or analyze a plumbing system remotely with incomplete information.

Without editorializing: To your questions, the answer to both is no.

[Guido in Boston]

You're welcome.

If the air bleed and the check valve haven't been inspected or serviced in a while, I'd suggest they're at least due and probably causing problems.
If the air bleed is not bleeding air sufficiently, that may be the source of at least some of your overheating due to a vapor lock that forms and then comes/goes from slow/partial valve operation.
What's the collector surface area ?
Which El Sid pump do you have ? Seems like most of them are pretty low head for that much elevation change for one thing. Also, if it a low head pump, besides needing a bigger pump to overcome the elevation head when filling the system, it may produce insufficient head to maintain a decent flowrate.
It's neigh onto impossible to troubleshoot or analyze a plumbing system remotely with incomplete information.

Without editorializing: To your questions, the answer to both is no.

Collector is about 2 x 4 feet, very roughly. Never got up on the roof to measure it.

I have the model SID5PV pump. Curve below. Fluid dynamics was never my strong suit. Enlighten me, master (Midnight Diner music plays softly in the background).

[J.P.M.]

Collector is about 2 x 4 feet, very roughly. Never got up on the roof to measure it.

I have the model SID5PV pump. Curve below. Fluid dynamics was never my strong suit. Enlighten me, master (Midnight Diner music plays softly in the background).

Question or 2 on the relief valve that's lifting (operating):
1.) Where is that valve located ?
2.) Is there more than one relief valve on the system ?

On pump curves: Every manufactured pump has a pump curve plotted by the manufacturer as a 2 dimensional graph. The abscissa is the flow rate the pump will produce - usually in G.P.M. or litres/time period (sec., minute or hour depending on the application). The ordinate is the "head" or pressure drop that the pump will successfully work against to produce the flow rate shown from the graph at the point where the two parameters intersect on the pump curve.

For the SID5PV pump, the curve tells us it will sustain a flowrate of ~ 2.5 G.P.M, when the flow is frictionless (zero pressure drop) - an impossible situation but it's a base # so to speak. At the other end of the curve, the other limit is the maximum "head" or head pressure the pump will produce when operating under "deadhead" or zero flowrate conditions. You might visualize that as how high a standing column of water you'd see if the pump's outlet were to be plumbed to a clear vertical pipe of sufficient height so as not to overflow.
From the SID5PD pump curve, that water column looks to be something like maybe ~ 2.2 ft. in height - from looking at the point where the pump curve meets the ordinate axis at the left side of the graph.

Any other point on the curve represents the flowrate attainable by the pump given the pressure drop induced and that flowrate as the fluid is forced through the fluid conduit and all the associated valves, fittings, branches. tees, diverters, filters and other things that cause pressure drop.

All that comes down to my suspicion that, because you probably have at least a P.S.I . or so of friction loss even at a low flowrate (BTW, 1 P.S.I. of pressure drop ~ = 2.3 ft. of head). your system doesn't have too high a flowrate. However, if you have 30 gal. of hot water at something > 200 F from 8 ft^2 of collector surface, some things are not adding up. On a hot summer day in FL, your system - if it was operating at a good overall daily thermal efficiency of, say, 50% - which is a high dart throw estimate - might add something like 6,000 BTU of heat (a back of the envelope calc, but probably optimistic) to that water. But, low flowrates tend to deduce thermal efficiency and at close to stagnation flowrates, efficiengy approaches zero meaning no heat gain.
If things were running at 50% thermal efficiency, on a hot, sunny summer day in FL, that would raise the H2O in a 30 gal. tank by something like ~ 24 F or so before consideration of standby losses. So, where's the rest of the heat coming from ?
Does the tank have another energy source like electricity or natural gas ?
If so, what's that sources thermostat set at ?
Things are not making sense.

As I wrote, it's difficult to analyze what's going on without being there.
Get a plumber on site who knows something about solar water heating and have the system analyzed or as I suggesed get a PV system .
I'm not getting anywhere with this line of reasoning.

[Guido in Boston]

Question or 2 on the relief valve that's lifting (operating):
1.) Where is that valve located ?
2.) Is there more than one relief valve on the system ?

On pump curves: Every manufactured pump has a pump curve plotted by the manufacturer as a 2 dimensional graph. The abscissa is the flow rate the pump will produce - usually in G.P.M. or litres/time period (sec., minute or hour depending on the application). The ordinate is the "head" or pressure drop that the pump will successfully work against to produce the flow rate shown from the graph at the point where the two parameters intersect on the pump curve.

For the SID5PV pump, the curve tells us it will sustain a flowrate of ~ 2.5 G.P.M, when the flow is frictionless (zero pressure drop) - an impossible situation but it's a base # so to speak. At the other end of the curve, the other limit is the maximum "head" or head pressure the pump will produce when operating under "deadhead" or zero flowrate conditions. You might visualize that as how high a standing column of water you'd see if the pump's outlet were to be plumbed to a clear vertical pipe of sufficient height so as not to overflow.
From the SID5PD pump curve, that water column looks to be something like maybe ~ 2.2 ft. in height - from looking at the point where the pump curve meets the ordinate axis at the left side of the graph.

Any other point on the curve represents the flowrate attainable by the pump given the pressure drop induced and that flowrate as the fluid is forced through the fluid conduit and all the associated valves, fittings, branches. tees, diverters, filters and other things that cause pressure drop.

All that comes down to my suspicion that, because you probably have at least a P.S.I . or so of friction loss even at a low flowrate (BTW, 1 P.S.I. of pressure drop ~ = 2.3 ft. of head). your system doesn't have too high a flowrate. However, if you have 30 gal. of hot water at something > 200 F from 8 ft^2 of collector surface, some things are not adding up. On a hot summer day in FL, your system - if it was operating at a good overall daily thermal efficiency of, say, 50% - which is a high dart throw estimate - might add something like 6,000 BTU of heat (a back of the envelope calc, but probably optimistic) to that water. But, low flowrates tend to deduce thermal efficiency and at close to stagnation flowrates, efficiengy approaches zero meaning no heat gain.
If things were running at 50% thermal efficiency, on a hot, sunny summer day in FL, that would raise the H2O in a 30 gal. tank by something like ~ 24 F or so before consideration of standby losses. So, where's the rest of the heat coming from ?
Does the tank have another energy source like electricity or natural gas ?
If so, what's that sources thermostat set at ?
Things are not making sense.

As I wrote, it's difficult to analyze what's going on without being there.
Get a plumber on site who knows something about solar water heating and have the system analyzed or as I suggesed get a PV system .
I'm not getting anywhere with this line of reasoning.

For your questions, there are 2 (code) T&P valves - one on the tank and on on the top of the panel, next to the air bleed. Some years ago I left the system full and the pump off (my bad) and the T&P on the panel blew for some hours since nobody was home, eroded the elastomer seat and would no longer seal. Replaced.

So, 6000 BTU/hr or per sunny-day-length? The HW tank is a Lochinvar electric heat (1500W) one but the breaker is off.

[J.P.M.]

For your questions, there are 2 (code) T&P valves - one on the tank and on on the top of the panel, next to the air bleed. Some years ago I left the system full and the pump off (my bad) and the T&P on the panel blew for some hours since nobody was home, eroded the elastomer seat and would no longer seal. Replaced.

So, 6000 BTU/hr or per sunny-day-length? The HW tank is a Lochinvar electric heat (1500W) one but the breaker is off.

Which valve is operating (lifting)?

If it's the one at the top of the collector, my guess is it's probably doing so because the flow is either low or plugged for reasons previously described and so the water is just sitting there in the sun getting hot and going nowhere. The low flow or not flowing water then gets to the temperature set point of the valve and the valve lifts. Cooler water replaces the sewered water and the process continues.

Get the system checked out by someone knowledgeable in how solar flat plate water heaters work and if you choose to keep it, get it fixed. It's not functioning as intended and add-on devices won't change or fix it.

The 6,000 BTU energy addition is a daylong estimate for the collector system, and to stress, is only a dart throw.
But since it looks like the system is not functioning, it doesn't make much difference.

[Guido in Boston]

Which valve is operating (lifting)?

If it's the one at the top of the collector, my guess is it's probably doing so because the flow is either low or plugged for reasons previously described and so the water is just sitting there in the sun getting hot and going nowhere. The low flow or not flowing water then gets to the temperature set point of the valve and the valve lifts. Cooler water replaces the sewered water and the process continues.

Get the system checked out by someone knowledgeable in how solar flat plate water heaters work and if you choose to keep it, get it fixed. It's not functioning as intended and add-on devices won't change or fix it.

The 6,000 BTU energy addition is a daylong estimate for the collector system, and to stress, is only a dart throw.
But since it looks like the system is not functioning, it doesn't make much difference.

No disrespect intended, but I think you misunderstood, or I poorly described my problem. The one time the panel-mounted T&P lifted was years ago, and as I said, my bad (pump off, system full). After the T&P was replaced all was fine. The problem I am trying to fix now is only a summer problem - winter performance is excellent.

In summer there is so much solar BTU input that in the course of a 9am-3pm sunny day the water reached 190 out of the faucets - I have not let it get any hotter for fear of something bad happening

[J.P.M.]

No disrespect intended, but I think you misunderstood, or I poorly described my problem. The one time the panel-mounted T&P lifted was years ago, and as I said, my bad (pump off, system full). After the T&P was replaced all was fine. The problem I am trying to fix now is only a summer problem - winter performance is excellent.

In summer there is so much solar BTU input that in the course of a 9am-3pm sunny day the water reached 190 out of the faucets - I have not let it get any hotter for fear of something bad happening

OK.
Bottom line and then I'm done.
Aside from replacing the system with PV, the simplest solution as I suggested previously is to cover part of the collector in the warm season.

I'm aware of your weather, but a properly secured, corrugated panel will most likely not take off in a hurricane. Secure it well and tether it
You'll just need to place and remove it in the fall and the spring.
I know, a PITA for access. Life is not perfect.
Access to equipment is one part of good design solar peddlers often don't consider.

Next workable solution is also as I previously suggested: To either get a bigger tank or another tank to act as a buffer.

I can't add anything else to the discussion other tan to get a decent undergraduate text on solar thermal processes if you're curious. Duffie and Beckman is probably the best bible for that purpose. A free online download is available.

Good luck in your search for a solution.

J.P.M.

[Guido in Boston]

Thanks for taking the time to work with me on my problem, JPM, and for providing some fine education at the same time. Very much appreciated. Will have a look at the text you recommend.
Kind regards,
Guido in Boston, PE

[J.P.M.]

Thanks for taking the time to work with me on my problem, JPM, and for providing some fine education at the same time. Very much appreciated. Will have a look at the text you recommend.
Kind regards,
Guido in Boston, PE

You're welcome.
I was taught and mentored by many engineers who shared many things with me.
One of them was an obligation to share what they'd learned and shoot straight.

Again,

Good Luck,

J.P.M.

[LucMan]

First thing that comes to my mind is that a 2 x 4 flat plate should not be able to overheat a 30 gallon storage tank. My first question is how old is the system? Second, is this a new problem or has overheating been an issue since the initial installation?

[Guido in Boston]

First thing that comes to my mind is that a 2 x 4 flat plate should not be able to overheat a 30 gallon storage tank. My first question is how old is the system? Second, is this a new problem or has overheating been an issue since the initial installation?

Installation was in 2017. Winter home, and this is only the 2nd summer I have been there. Same problem last summer but to a lesser degree.

[J.P.M.]

First thing that comes to my mind is that a 2 x 4 flat plate should not be able to overheat a 30 gallon storage tank.

Yea, I stated something along those lines in my 09/22,8:35 P.M. post when SWAGing about a 24 F. rise from what is perhaps something like a 6,000 BTU daylong input from an 8 ft.^2 collector to a 30 gal. tank but I didn't get a bite on that from the OP.
Also, with that much piping through a 2 story piping arrangement, I'd bet that pump wouldn't produce as much flow as a simple thermosiphon system would produce with the tank at the top of the collector.
Besides, it's an older system that probably needs service and my guess is it wasn't the best designed or high quality system to begin with peddled to someone who didn't have the necessary information to make a good decision.