Solar collector t&p valve excessive tripping

[joe smith 100]

I have a new 4x10 solar collector with a t&p valve installed on it and a new 82 gallon solar water heater with its own t&p valve. This is an active system and the collector t&p valve cycles open about every 10 minutes and dumps steaming water to the ground. The tank t&p valve does not cycle. The pressure in the system goes to about 70psi and drops to about 55psi when the valve cycles. The city water pressure is about 55psi and a expansion tank is pressurized to 55psi. The thermometer attached to the line at the tank coming from the collector indicates a high temp reading of 180 degrees just before the t&p collector cycles and drops as the cold water entering the tak is picked up by the circulating pump.Any help would be appreciated.

 

[Master Plumber Mark]

not enough flow

usually that would mean that you are not moving
the water through the panel quick enough...
its getting way too hotcause it is going to slow


if you have put into your system a way to either throttel down or up the flow through the panels, then kick it open all the way and pump the water quicker through the panels

 

[Sponsor]

 

[Scuba_Dave]

Where are you located?
I have a greenhouse that will go up over 110 degrees on a 70 degree day. The T&P valve is doing its job, the water is being overheated

 

[protech]

You shouldn't have a t/p valve on the collector loop. Remove it and put a pressure relief valve in. That's pressure only. If you replace if with another t/p valve it will just fail again. t/ps should not go on the solar loop because everytime the collector stagnates the valve will go off.

 

[Master Plumber Mark]

Stress in the panels....

You shouldn't have a t/p valve on the collector loop. Remove it and put a pressure relief valve in. That's pressure only. If you replace if with another t/p valve it will just fail again. t/ps should not go on the solar loop because everytime the collector stagnates the valve will go off.

you sound like you know generally what you are talking about.

I am just wondering if a panel stagnates with no flow through it, how much pressure stress can the copper panel take???

I would think that at some point it could turn to steam if their was not some sort of pressure release on them....

have you ever run into one that got a stress crack in the welds ??

 

[protech]

When a flat plate glazed panel stagnates it will not boil the water in most cases because the water is under pressure already which raises it's boiling point. In the event that the pressure is very low the panel may make some steam but it doesn't matter because it will be cooled when it is injected into the tank upon circulation. Remember that the pressure can't go above the set point of the pressure relief valve because if it does the valve will relieve the pressure. The reason the tank must have a T/P valve is that if the tank temp goes above the boiling point at atmospheric pressure the water will flash boil off when it exits the aerator or tub spout causing an explosion of scalding water. The other reason the tank uses a T/P and the panel uses a pressure only is that the panel can only heat the water to a certain point(stagnation temp) where the water heater has elements that can heat the water past it's boiling point at elevated system pressure and the temp can exceed the tanks design limits (more than 500F).

 

[joe smith 100]

When a flat plate glazed panel stagnates it will not boil the water in most cases because the water is under pressure already which raises it's boiling point. In the event that the pressure is very low the panel may make some steam but it doesn't matter because it will be cooled when it is injected into the tank upon circulation. Remember that the pressure can't go above the set point of the pressure relief valve because if it does the valve will relieve the pressure. The reason the tank must have a T/P valve is that if the tank temp goes above the boiling point at atmospheric pressure the water will flash boil off when it exits the aerator or tub spout causing an explosion of scalding water. The other reason the tank uses a T/P and the panel uses a pressure only is that the panel can only heat the water to a certain point(stagnation temp) where the water heater has elements that can heat the water past it's boiling point at elevated system pressure and the temp can exceed the tanks design limits (more than 500F).

I live in florida.The MARCH pump is rated at 4.5 GPM and runs all day and shuts off in the evening. You state that panel can heat waterto stagnation temp. and can this be true with water circulating all the time? Thank you for your reply.

 

[hj]

T&P valve

The collector should have a pressure only relief valve, because once circulation stops the temperature will almost always rise to the point where a temperature relief valve will discharge.

 

[protech]

If you have little or no usage for a day the whole system will reach above 215F and BOTH t/p valves will start to relieve in the case of a timer controlled system.

In a differential controlled there is usually a max temp setting on the controller that will stop circulation when the tank reaches a set temp. At that point the pump will shut down and the panel will stagnate and your panel t/p valve will relieve.

Trust me, go with a pressure only valve.

I live in florida.The MARCH pump is rated at 4.5 GPM and runs all day and shuts off in the evening. You state that panel can heat waterto stagnation temp. and can this be true with water circulating all the time? Thank you for your reply.

 

[flamefix]

I have a new 4x10 solar collector with a t&p valve installed on it and a new 82 gallon solar water heater with its own t&p valve. This is an active system and the collector t&p valve cycles open about every 10 minutes and dumps steaming water to the ground. The tank t&p valve does not cycle. The pressure in the system goes to about 70psi and drops to about 55psi when the valve cycles. The city water pressure is about 55psi and a expansion tank is pressurized to 55psi. The thermometer attached to the line at the tank coming from the collector indicates a high temp reading of 180 degrees just before the t&p collector cycles and drops as the cold water entering the tak is picked up by the circulating pump.Any help would be appreciated.

I'm interested to know how the solar circuit is replenished if it is a sealed system? are you manually replenishing the solar fluid if so with glycol or water? the pressures you talk about are they the solar circuit pressure or the cylinder pressure?

As others have posted the only relieving valve you should have is a pressure rated one at 6bar. The temperature and pressure valve should be on the cylinder if is unvented and would relieve at 90c and 6bar. If your cylinder is dumping via the TPR valve shut the system down and get it investigated. Your cylinder is a potential bomb.

You should shut your solar down and have it checked also, but if it is a TPR valve on the solar side then it will go off whenever your solar circuit goes into stagnation.

With a cold cylinder heating from scratch how long does it take to heat up and how long till the system blows off? if it does so before the cylinder has heated then it could be a blockage in your solar circuit causing the stagnation to occur prematurely.

 

[protech]

I guess you are assuming it's an indirect system flamefix? There is such a thing as a direct system that uses potable water in the collector circuit. Also known as "open loop" system. Very common in central and south Florida as well as central America.

 

[Alphacarina]

The MARCH pump is rated at 4.5 GPM and runs all day and shuts off in the evening. You state that panel can heat waterto stagnation temp. and can this be true with water circulating all the time?

I'll bet you don't have a flowmeter in your system??

You're assuming you have 4.5 GPM flowing because your pump is rated for that but in actuality, you have almost no flow at all because if you did, you wouldn't have such high collector temps

I would keep your pressure/temp valve on the collector where it is - When your system is operating properly, it will never trip . . . . and it's a nice safety valve for when your system isn't working correctly . . . . like now

Don

 

[Mikey]

A related overtemp issue

My system in central FL uses a single 4x10 collector, potable water loop, 82 gallon storage tank, and a solar-powered circulating pump. On a good day with little use, I see 160+° water at the kitchen tap. Every once in a while, during a cloudy stretch, the water gets cooler, well below the electric thermostat setting (130°).T he first time it happened, it was because we had forgotten to turn on the circuit breaker after installation. The 2nd time, though, I found the CB ON, and thought uh-oh, but quickly found that the overtemp limit switch had tripped, cutting off the backup electric power. This has happened several times, most recently sometime in the last week, 'cause it was a chilly shower tonight. It looks like during a long hot and clear spell, the water in the tank gets hot enough to trip the thermostat limit switch but not hot enough to trip the T&P valve. We never notice it until the water in the tank has cooled to the point we notice that something's wrong (around 110°). I think of this as a power saving feature, rather than a bug, but the downside is that if the tank temperature stays low for very long, we start to get the classic hot-water stink. At the first whiff of this, now, I check the overtemp switch and reset it.

 

[protech]

How do you know that he just didn't use any water for that day and the system is over heating?

T/P valves are not a good idea on a collector because it's very common for the collector to stagnate (home owner is away for the weekend, power goes out in an AC powered pump system, etc etc). It really doesn't hurt anything for the collector loop to stagnate on an open loop system unless it's an everyday event. There is no logical reason to have a t/p relief valve in place of a pressure only relief valve. Over pressure is what is dangerous in the solar loop, not over temp. If the pump was to continue circulating on an already thermally saturated tank, the tank t/p would vent the excess heat. Therefore, an extra thermal relief serves no purpose on the collector loop but does provide for a faulty system that will need to be serviced frequently. When people have to constantly have service done on a heater, they end up deciding to go with a more "conventional" heater and have the solar system removed.

In short, a collector t/p valve only causes problems and solves none. Use a pressure only relief valve. Don't trust my opinion? Look around at the prepackaged active direct systems from various suppliers (like leveredge, www.theleveredge.com) and see if they package a t/p valve or a pressure only valve. All of my suppliers use a pressure only. These guys have been installing systems for more than 30 years. They have learned a few things along the way.

Make sense?

I'll bet you don't have a flowmeter in your system??

You're assuming you have 4.5 GPM flowing because your pump is rated for that but in actuality, you have almost no flow at all because if you did, you wouldn't have such high collector temps

I would keep your pressure/temp valve on the collector where it is - When your system is operating properly, it will never trip . . . . and it's a nice safety valve for when your system isn't working correctly . . . . like now

Don

 

[protech]

There are a few things that will cause that condition to occur. I know of a plumber in central Florida that specializes in that sort of thing. You should give him a call. <whistling and twittles his thumbs>

My system in central FL uses a single 4x10 collector, potable water loop, 82 gallon storage tank, and a solar-powered circulating pump. On a good day with little use, I see 160+° water at the kitchen tap. Every once in a while, during a cloudy stretch, the water gets cooler, well below the electric thermostat setting (130°).T he first time it happened, it was because we had forgotten to turn on the circuit breaker after installation. The 2nd time, though, I found the CB ON, and thought uh-oh, but quickly found that the overtemp limit switch had tripped, cutting off the backup electric power. This has happened several times, most recently sometime in the last week, 'cause it was a chilly shower tonight. It looks like during a long hot and clear spell, the water in the tank gets hot enough to trip the thermostat limit switch but not hot enough to trip the T&P valve. We never notice it until the water in the tank has cooled to the point we notice that something's wrong (around 110°). I think of this as a power saving feature, rather than a bug, but the downside is that if the tank temperature stays low for very long, we start to get the classic hot-water stink. At the first whiff of this, now, I check the overtemp switch and reset it.

 

[Mikey]

There are a few things that will cause that condition to occur. I know of a plumber in central Florida that specializes in that sort of thing. You should give him a call. <whistling and twittles his thumbs>

I might do that -- it's a local call... but I'm busily occupied getting ready for a long trip Up North for my <insert big number here>th High School Reunion, so it'll be a couple of weeks.

 

[Cookie]

10th, I bet...

 

[flamefix]

I guess you are assuming it's an indirect system flamefix? There is such a thing as a direct system that uses potable water in the collector circuit. Also known as "open loop" system. Very common in central and south Florida as well as central America.

Yes I did but I was questioning it.

Why would you really want to use a potable loop it seems to me that it is cheaper perhaps? even in Greece and Cyprus (95%) solar energy heated sytems the indirect method is used.

To have that loop direct to the tap with no regulation is that normal? Surely the supply side is regulated to the taps with a blender valve TMV set to 50c say?

I'm beginning to see now why a TPR valve might be used as the cylinder is the pressurised vessel subject to temperature also so if it didn't blow on pressure the cylinder could reach stagnation itself possible?.

Perhaps you could send me a link to read about the systems you are installing I'd like to read up on them, thanks.


Perhaps make it a indirect circuit and fix a plate to plate heatexchanger between the tank and the collector and pump both sides triggered by the temp of the store and the flow from the collector.

 

[Mikey]

Close, but no see-gar. Thank you, thank you.

 

[Cookie]

can't be 20 no sir...
but then again, I got my teachers 31 years ago, lol. lordy, that is a long time.