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]

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

[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]

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]

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]

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? :confused:

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.

[protech]

See here: http://www.fsec.ucf.edu/en/industry/resources/solar_thermal/manual/documents/Section_2_SolarWaterHeating.pdf

Go to the section entitled "1. Active Direct Systems"

Look at "Figure 2 Additional system components" to see a basic drawing of an active-direct system (A type of open loop system)


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.

[protech]

You'll notice that a pressure only relief valve is used up on the panel while a T/P relief valve is used on the tank. This is FSEC here. These guys are at the for front of solar.

[flamefix]

So no Temperature relief valve on the collector then as all agreed to.

This active system I just don't like the idea of domestic cold water supply circulating around a panel into the tank and then on to my shower or tap personally. I can understand having the collector direct to the store but I'd rather have my hot water indirect. I think I would have a plate to plate heat exchanger connected top to bottom of the store with a pump. Triggered by a flow switch on the cold inlet side which when a hot tap is opened causes the heat from the store to heat the hot water. Or as I said earlier on the solar side, and keep the store as the tank of hot water. But I am digressing rather from the topic.

you can see why I was confused by the words active..
http://www.solar-trade.org.uk/solarenergy/howwork.htm

What's the typical install cost of one of these active systems if I may ask?

[protech]

About the lowest you can get one here before you get your rebates and incentives back is $3500 for the smallest system under the most ideal circumstances. Most people will end up paying in the mid 4 thousands for a system sized for 2-4 people installed on a single story shingle roof. Bigger systems, multiple stories and tile roofing all make the price go up. The high end of the spectrum would be $8000ish.

This is of course for active-direct systems. Indirect systems cost even more and put out less heat (size for size). If you live south of Ocala Fl there is no need to have an indirect system unless you are both paranoid about freezing and like to spend extra money for no reason. If you do live north of that point, then I would recommend an indirect system.



So no Temperature relief valve on the collector then as all agreed to.

This active system I just don't like the idea of domestic cold water supply circulating around a panel into the tank and then on to my shower or tap personally. I can understand having the collector direct to the store but I'd rather have my hot water indirect. I think I would have a plate to plate heat exchanger connected top to bottom of the store with a pump. Triggered by a flow switch on the cold inlet side which when a hot tap is opened causes the heat from the store to heat the hot water. Or as I said earlier on the solar side, and keep the store as the tank of hot water. But I am digressing rather from the topic.

you can see why I was confused by the words active..
http://www.solar-trade.org.uk/solarenergy/howwork.htm

What's the typical install cost of one of these active systems if I may ask?

[Alphacarina]

Why would you really want to use a potable loop it seems to me that it is cheaper perhaps?Another good reason we use it is because it's more efficient . . . . we get more hot water

So long as freezing isn't a problem (or can be dealt with) there's no real reason to use an indirect loop

Don

[flamefix]

Another good reason we use it is because it's more efficient . . . . we get more hot water

So long as freezing isn't a problem (or can be dealt with) there's no real reason to use an indirect loop

Don

But in a southerly latitude efficiency is the least of your problems surely? and You can't get more hot water you can only get it quicker albeit if you draw it off and it reheats quicker you can get more but you are limiting your store temperature to 120F correct? With an indirect sealed system you could run the store higher and mix it down to 120F thereby increasing the amount of hot water you can draw off anyway.

I can accept the no need to have an internal tank arrangement and have a system like this for example..
I'll not link direct to them but you can work it out as I am not advocating their product just citing it as an example.

The cost of something like that is far cheaper more in the region of $1500

3*w.eliotsolar.com/solar_hot_water.htm

[Alphacarina]

You can't get more hot water you can only get it quicker albeit if you draw it off and it reheats quicker you can get more but you are limiting your store temperature to 120F correct? With an indirect sealed system you could run the store higher and mix it down to 120F thereby increasing the amount of hot water you can draw off anyway

No - My tank temperature will go as high as 150 degrees on a really good day . . . . but 125 to 135 is more typical

I have a single 4 by 10 AET panel feeding two Sears Best 55 gallon electric water heaters for storage. I have a T&P valve on each tank and one at the top of the collector

For 9 or 10 months of the year, solar provides 100% of my hot water and only in the dead of winter is any electricity applied . . . . and even then, it's just to the top of the supply tank (the one with the thermal mixing valve on it) and only for 30 minutes in the morning before the sun comes up so that we have the normal temperature water for morning showers - The electricity is only used to raise the temp of the top half of the supply tank up to 120 degrees, which is what the mixing valve is adjusted for

I like having 110 gallons of really hot water . . . . it doesn't cool off much overnight and we can take a half hour shower in the morning, knowing it's basically all FREE

Don

[protech]

I have a similar setup as Alphacarina. I have a 4'x10' flat plate collector and an 80 gallon 5 port solar tank with 3 dip tubes. I installed a kilowatt hour meter on my old electric 40 gallon tank for a year before I installed my solar setup. it was costing me $55 and some change every month to feed electricity into that heater and that was back when rates were at $0.12 per KWA. I've had the solar setup on the same meter now for about 2 years and it's running at 95% solar fraction. That also includes the energy used to circulate the water. I've cut my water heating costs by 95%.

[flamefix]

No - My tank temperature will go as high as 150 degrees on a really good day . . . . but 125 to 135 is more typical

I like having 110 gallons of really hot water . . . . it doesn't cool off much overnight and we can take a half hour shower in the morning, knowing it's basically all FREE

Don

But Don you'll easily acheive that with an indirect system. In fact the systems I install can reach 80 -85c before limits cut in those limits can cut in at 60c or 50c what ever you wish.

However Jimbo from this site informed me the following in a separate post "perhaps the other thing which weighs heavliy on our procedures is the well know law firm of Dewey, Cheatham, and Howe. ALL water heater manufacturers, and many of our plumbing codes, SPECIFY that water heaters should NOT be set higher than 120ºF ( about 50ºC) for the reason that if someone gets scalded, the plumber and the manufacturer will get sued." that doesn't sit with solar systems achieving higher temps than this.
However as Long as you have a thermostatic blending valve then upper store temps don't matter within reason.

I'm not trying to Diss your installation or your system or antagonise you, I just don't follow your logic for having a system soley based on efficiency, and then not to store the heat at higher upper temperatures than you currently do possible with a fully stratified store and have it direct connected to your cold water mains supply. This side of the pond we simply would not be allowed to.

Given your solar radiation levels at your latitudes then the efficiencies you may gain from a direct system is to me fractions if at all over the indirect system.

Plus I suspect that an evacuated tube design would provide you more hot water in your winter season also.

[protech]

It very simple. Per dollar invested an indirect system puts out less heat than a direct system. If I install a 40 square foot collector ran direct and you install the same size collector indirect with both tanks containing the same volume and dimensions, my system will put out about 10% more heat than yours will. It also does not require the heat transfer fluid to be replaced every 4-5 years. In short, if you live in an area that rarely freezes, it makes good economic sense to install a direct system. I know from talking with the folks on the navitron forums that to get the same output over in the UK you end up spending more than twice what we do in Florida. Some of that is due to exchange rates and some due to our southern latitude, but it's also because we run direct flat plates and you tend to run vac tubes indirect.


But Don you'll easily acheive that with an indirect system. In fact the systems I install can reach 80 -85c before limits cut in those limits can cut in at 60c or 50c what ever you wish.

However Jimbo from this site informed me the following in a separate post "perhaps the other thing which weighs heavliy on our procedures is the well know law firm of Dewey, Cheatham, and Howe. ALL water heater manufacturers, and many of our plumbing codes, SPECIFY that water heaters should NOT be set higher than 120ºF ( about 50ºC) for the reason that if someone gets scalded, the plumber and the manufacturer will get sued." that doesn't sit with solar systems achieving higher temps than this.
However as Long as you have a thermostatic blending valve then upper store temps don't matter within reason.

I'm not trying to Diss your installation or your system or antagonise you, I just don't follow your logic for having a system soley based on efficiency, and then not to store the heat at higher upper temperatures than you currently do possible with a fully stratified store and have it direct connected to your cold water mains supply. This side of the pond we simply would not be allowed to.

Given your solar radiation levels at your latitudes then the efficiencies you may gain from a direct system is to me fractions if at all over the indirect system.

Plus I suspect that an evacuated tube design would provide you more hot water in your winter season also.

[protech]

For a southern latitude, and per dollar invested, that statment would be incorrect.


But Don you'll easily acheive that with an indirect system. In fact the systems I install can reach 80 -85c before limits cut in those limits can cut in at 60c or 50c what ever you wish.

However Jimbo from this site informed me the following in a separate post "perhaps the other thing which weighs heavliy on our procedures is the well know law firm of Dewey, Cheatham, and Howe. ALL water heater manufacturers, and many of our plumbing codes, SPECIFY that water heaters should NOT be set higher than 120ºF ( about 50ºC) for the reason that if someone gets scalded, the plumber and the manufacturer will get sued." that doesn't sit with solar systems achieving higher temps than this.
However as Long as you have a thermostatic blending valve then upper store temps don't matter within reason.

I'm not trying to Diss your installation or your system or antagonise you, I just don't follow your logic for having a system soley based on efficiency, and then not to store the heat at higher upper temperatures than you currently do possible with a fully stratified store and have it direct connected to your cold water mains supply. This side of the pond we simply would not be allowed to.

Given your solar radiation levels at your latitudes then the efficiencies you may gain from a direct system is to me fractions if at all over the indirect system.

Plus I suspect that an evacuated tube design would provide you more hot water in your winter season also.

[Alphacarina]

Yeah, my system is over 3 years old now and I suspect it's about paid for itself already . . . . I got a whopping tax writeoff back when I installed it - I put in new high efficiency windows that same year and I wound up not paying any tax at all!!

I guess the main reason that I went with a direct system is because it was MUCH cheaper and MUCH simpler . . . . and because we have water with next to no mineral content - So why not?? To buy a 'correct' 82 gallon solar tank was just a ton of money and then a bunch more for shipping. I bought all my big parts locally so there were no shipping charges. I don't recall the exact number, but I have a little less than $2500 in the entire system, and after 3 + years of operation, I'm VERY pleased with it - Assuming I'm saving the about the same $50 per month you mentioned, they've already saved me $1800 or so . . . . and I got about a $1500 writeoff, so I'm way ahead already

My tanks are standard water heaters with a full 3 inches of foam insulation. When I was designing the system, I had planned on installing another foot of fiberglass insulation around them . . . . . but, when they are full of 150 degree water, the outside cover of the tank still feels cool to the touch, so they aren't radiating away much heat

To be honest, I don't understand why millions more people don't have solar water heating installed - Of all the 'green' energy concepts out there, it's the most refined and perfected of them all and it also has the quickest payback of about anything else you can do

Don

[flamefix]

A 300litre twin coil solar cylinder stainless steel cylinder 2.1m tall and 5m2 of flat serpentine coiled high efficiency plate would cost £1442 +£2300 =£3742 = $5987 This is branded european produced with all the pumps and controls. That's full list. Vaillant/Viessmann product. Others would be cheaper maybe 20-25% and cheaper again if you look at the chinese product, maybe 30- 33%

You'd be able to get that for upto 40% trade/ internet prices off = $3592 plus installation and pipe between plate and cylinder.

So then plus your rebates perhaps not much more than you're spending just so you know.


The thrust of the point I am discussing is the direct connection between the cold water provision and your store coupled to the collectors. We couldn't do that here water regs would prevent that even with backflow prevention.

[protech]

To get the same output, one would only spend about $4000 in florida before rebates and incentives. That price is for everything. Materials, installation, permit.

Do you see what I mean about vac tubes not being economical in Florida?

[Mikey]

There was a discussion in another thread arguing that hot water should be stored at 140°F or higher to ensure various disease-causing organisms are killed, rather than just suppressed. The most notable is probably Legionella.


At 60 °C (140 °F) - Legionella dies instantly - pasteurisation (http://en.wikipedia.org/wiki/Pasteurisation) occurs.
At 55 °C (131 °F) - 95% die
50 to 55 °C (122 to 131 °F) - Can survive but do not multiply
35 to 46 °C (95 to 115 °F) - Ideal growth range

In Quebec, a study of 211 homes (178 electric water heaters, 33 oil or gas water heaters) found Legionella contamination in 40% of electric water heaters. No water heaters using fossil fuels were contaminated. The authors concluded that, because of design variables, use of an electric water heater was the most significant factor leading to Legionella contamination in hot water in the home.

Many references support the concept of keeping water hot in the water heater, and using tempering valves downstream to present non-scalding temperatures at fixtures.

[Alphacarina]

If you have a modern, high tech, very well insulated tank, then keeping water stored at 140 degrees continuously might only cost you a few bucks a month, over keeping it at the lowest temperature which will satisfy your needs . . . . typically 110 to 115 degrees - But if you don't have modern equipment, the heat lost to the ambient will be large and you'll be spending lots of extra money just to be sure all water borne disease microbes are killed - One more reason to buy the highest end, best insulated water heater available when the time comes . . . . especially if you're ever planning on anything solar

I guess it doesn't cost me anything extra, as my tanks typically get to at least 140 degrees a time or two each week without me doing anything. Needless to say, I have a mixing valve set to 115 to make sure none of that very hot water ever shows up at any tap

Don

[protech]

I'm not sure where you are going with all of this as most solar heaters produce water above 150F. I'm lost.........


There was a discussion in another thread arguing that hot water should be stored at 140°F or higher to ensure various disease-causing organisms are killed, rather than just suppressed. The most notable is probably Legionella.


At 60 °C (140 °F) - Legionella dies instantly - pasteurisation (http://en.wikipedia.org/wiki/Pasteurisation) occurs.
At 55 °C (131 °F) - 95% die
50 to 55 °C (122 to 131 °F) - Can survive but do not multiply
35 to 46 °C (95 to 115 °F) - Ideal growth range

In Quebec, a study of 211 homes (178 electric water heaters, 33 oil or gas water heaters) found Legionella contamination in 40% of electric water heaters. No water heaters using fossil fuels were contaminated. The authors concluded that, because of design variables, use of an electric water heater was the most significant factor leading to Legionella contamination in hot water in the home.

Many references support the concept of keeping water hot in the water heater, and using tempering valves downstream to present non-scalding temperatures at fixtures.

[protech]

And what exactly is the problem with a direct system again?


A 300litre twin coil solar cylinder stainless steel cylinder 2.1m tall and 5m2 of flat serpentine coiled high efficiency plate would cost £1442 +£2300 =£3742 = $5987 This is branded european produced with all the pumps and controls. That's full list. Vaillant/Viessmann product. Others would be cheaper maybe 20-25% and cheaper again if you look at the chinese product, maybe 30- 33%

You'd be able to get that for upto 40% trade/ internet prices off = $3592 plus installation and pipe between plate and cylinder.

So then plus your rebates perhaps not much more than you're spending just so you know.


The thrust of the point I am discussing is the direct connection between the cold water provision and your store coupled to the collectors. We couldn't do that here water regs would prevent that even with backflow prevention.

[flamefix]

I'm not sure where you are going with all of this as most solar heaters produce water above 150F. I'm lost.........

I am guessing he is referring to the storage of that water thereafter where at the temperatures listed legionellae can occur. And also it could occur in the collector itself during periods when it doesn't reach the higher temperatures.



And what exactly is the problem with a direct system again?

Well my understanding is that your cold water domestic supply is directly connected to the solar circuit, Which could result in back flow in the cold water supply main, and regardless of a check valve this would not be permitted here. The minimum backflow prevention that would be suitable would probably be a an air gap as formed from a header tank, with a ball cock valve arrangement.
But then in your direct system utilising that method would mean the water pressure would be at the gravity head supply of the header tank not mains water pressure.

There was mention of heat loss from from storage tanks at higher temperatures and I can tell you the calculated heat loss from a storage vessel used here is in the region of 1.8 to 2.4kW /24hrs from memory.



To get the same output, one would only spend about $4000 in florida before rebates and incentives. That price is for everything. Materials, installation, permit.

About the lowest you can get one here before you get your rebates and incentives back is $3500 for the smallest system under the most ideal circumstances.

Could you clarify the above as I thought the second statement taken from and earlier posting referred to an active system and the first statement refers to a indirect in which case aren't the two similarly priced? cheers

[protech]

#1 Legionellae can not grow in the collector or the tank because the longest amount of time the collector will go without reaching temps above 150f is about a week.

#2 What is it that your governing body is worried about that is going to back flow from the collector? In an active-direct system it's just potable water in the collector loop. We already discussed above that bacteria cannot grow in the collector loop because of the high temps. How is it any different than having a two story house with a hot water circulation loop?

#3 I'm not sure about the heat loss with the type of tank I install. I've never calculated it. I know that the tank temps can reach 200F and remain above 120F for about a week from experience. It's frequent that I get a service call about a week after the start of some gloomy weather (which is very infrequent here). The reason for this is because the homeowner will turn the circulation cut out temp up to high and the over heated water will trip the high limit thermodisk on the electrical backup heating. After a few months go by, we will get a spat of gloomy/rainy weather and it takes 3-5 days for the homeowner the run out of stored solar heat. That's including usage too, not just stand by losses.

#4 No, they aren't similar in price. The direct system is far cheaper (all things considered). You quoted $5987 just for the materials. I quoted $4000 for materials AND installation. Your system is twice the cost. How is that similar?



#1 I am guessing he is referring to the storage of that water thereafter where at the temperatures listed legionellae can occur. And also it could occur in the collector itself during periods when it doesn't reach the higher temperatures.



#2 Well my understanding is that your cold water domestic supply is directly connected to the solar circuit, Which could result in back flow in the cold water supply main, and regardless of a check valve this would not be permitted here. The minimum backflow prevention that would be suitable would probably be a an air gap as formed from a header tank, with a ball cock valve arrangement.
But then in your direct system utilising that method would mean the water pressure would be at the gravity head supply of the header tank not mains water pressure.

#3 There was mention of heat loss from from storage tanks at higher temperatures and I can tell you the calculated heat loss from a storage vessel used here is in the region of 1.8 to 2.4kW /24hrs from memory.



#4 Could you clarify the above as I thought the second statement taken from and earlier posting referred to an active system and the first statement refers to a indirect in which case aren't the two similarly priced? cheers

[flamefix]

#1 Legionellae can not grow in the collector or the tank because the longest amount of time the collector will go without reaching temps above 150f is about a week.


Legionellae can still develop, it's a bacteria and given the right conditions could rapidly develop. The Regs here will not allow any contamination or possible contamination to backflow into the cold water supply. so that could depend on the materials the water is sitting in ie the solar panel piping material, the storage tank


#2 What is it that your governing body is worried about that is going to back flow from the collector? In an active-direct system it's just potable water in the collector loop. We already discussed above that bacteria cannot grow in the collector loop because of the high temps. How is it any different than having a two story house with a hot water circulation loop?

The Regs here will not allow any contamination or possible contamination to backflow into the cold water supply. so that could depend on the materials the water is sitting in ie the solar panel piping material, the storage tank. A hotwater circulation loop (called a secondary return here) would form what is called the distribution circuit and the regs state the water should be stored at not less than 60c and distributed at not less than 55c. The recommendation on scalding grounds is that it should be 50c but that thermostatic mixing valves be used at every outlet to prevent harm to persons particularly the young/old, vulnerable, infirm and sensory challenged. So that shouldn't pose a problem here.




#4 No, they aren't similar in price. The direct system is far cheaper (all things considered). You quoted $5987 just for the materials. I quoted $4000 for materials AND installation. Your system is twice the cost. How is that similar?

Ahh but I quoted the price an installer or shrewd diy-er could buy it for also, and the installation cost would depend on local circumstances. Most hoses here are at least 2 story which is more risky to install on so it would cost more here. So the cost of $3592 +$1000 for installing it isn't far off your price of $4000 and this is for a premium branded product (not that i'm saying yours isn't). For a non branded system it would be up to $1000-$1200 less. I'm often under cut by £1000 - £1500 but their the people that phone up a year later when the company that installed it have done a runner or folded and reset up under a similar name without the liablities, with a system that was shodily installed and on the cheap, non solar rated components, such as central heating pump, pressure vessel soft soldered pipe work, heating pipe insulation, pressure relief into the house,... I'm sure you see your own horrors there.

Plus I also pointed out that you could install a simple indirect system for $1500

I can accept the no need to have an internal tank arrangement and have a system like this for example..
I'll not link direct to them but you can work it out as I am not advocating their product just citing it as an example.

The cost of something like that is far cheaper more in the region of $1500

3*w.eliotsolar.com/solar_hot_water.htm

[Alphacarina]

What I don't understand is . . . . how could a closed loop system prevent this from happening?

Your tank(s) could backflow just as easily as mine . . . . and since you're closed loop, the water in your tanks isn't as hot as mine. I'll bet virtually none of your neighbors have 140 degree water in their tanks either

I have a well, so it would have to back up a long ways to contaminate anyone else . . . . but then I don't understand how you could get enough backflow to get back past your water meter in a public system anyway???

I would hope your public officials have bigger/better things to worry about

Don

[flamefix]

What I don't understand is . . . . how could a closed loop system prevent this from happening?

Your tank(s) could backflow just as easily as mine . . . . and since you're closed loop, the water in your tanks isn't as hot as mine. I'll bet virtually none of your neighbors have 140 degree water in their tanks either

but then I don't understand how you could get enough backflow to get back past your water meter in a public system anyway???


Well a closed loop is not then directly connected to the water suppliers water main.

Yes the tank is, but as I have mentioned prior it is normal to keep tanks (cylinders here) at 60c here minimum but with the indirect systems the cylinder can be set to store at up to 90c before upper limits kick in.

Indirect systems here can easily reach 140F that you mention and in any case say in the winter months low solar days the cylinders have twin coils for after heater from a boiler or an electrical immersion heater element, to ensure the cylinder heats up to 60c.
Some of the controllers will even allow the whole store to be heated to 60c to ensure the cylinder is sterilised on a pre settable time period.

you can view a live feed from this http://www.seconsolar.com/DL2/Live%20data.html but you'll have to check the weather to see how the output is affected.

The water regs here are allowing for say a drop in supply pressure from the water main which would then allow the system to back flow into the water main. You could argue that a check valve would prevent that but they have 5 categories for water and the risk attached to them and the backflow prevention that each category of risk must be provided with.

the complete regulations are available here for those interested.

http://www.opsi.gov.uk/si/si1999/19991148.htm

and this guidance might be more helpful in explaining them

http://www.defra.gov.uk/environment/water/industry/wsregs99/waterregs99-guidance.pdf

[protech]

Your regulations (known as "codes" state side) make no sense.

You’re saying they don't want hot water (fluid category 2) from the open collector loop to be siphoned back into the municipal supply, so you should replace it with a more hazardous fluid (category 3)? That is the most backward logic I have heard in some time. You want to replace a fluid that MAY under very rare and ideal circumstances contain a pathogen with one that is ALWAYS hazardous and has a good chance of getting into the water supply at some point in its service life (closed solar loop leaks into potable hot water tank).

Those categories were taken right from your own code book http://www.defra.gov.uk/environment/water/industry/wsregs99/waterregs99-guidance.pdf

[protech]

I'm sorry flamefix, but I still fail to see how the solar loop can contain any more pathogens than the tank it self. Please explain a set of conditions that would allow this could occur.

[protech]

Look, let’s cut the crap here. Are you saying that YOU regularly install an active-indirect system sized for 2-4 people for the equivalent price of $4000 on a daily basis or not. Because I, and most of my legitimate competitors do. That's out the door. Materials, Labor, Building Permit, Delivery.........everything.

Yes, or no. If no, what's your average price for the above.





Ahh but I quoted the price an installer or shrewd diy-er could buy it for also, and the installation cost would depend on local circumstances. Most hoses here are at least 2 story which is more risky to install on so it would cost more here. So the cost of $3592 +$1000 for installing it isn't far off your price of $4000 and this is for a premium branded product (not that i'm saying yours isn't). For a non branded system it would be up to $1000-$1200 less. I'm often under cut by £1000 - £1500 but their the people that phone up a year later when the company that installed it have done a runner or folded and reset up under a similar name without the liablities, with a system that was shodily installed and on the cheap, non solar rated components, such as central heating pump, pressure vessel soft soldered pipe work, heating pipe insulation, pressure relief into the house,... I'm sure you see your own horrors there.

Plus I also pointed out that you could install a simple indirect system for $1500

[protech]

No, it can't. Well not in Florida anyway. The collector loop will not be in the ideal growth range for enough time for that to occur. We get just a few days out of the year that the loop isn't sterilized.


Legionellae can still develop, it's a bacteria and given the right conditions could rapidly develop. The Regs here will not allow any contamination or possible contamination to backflow into the cold water supply. so that could depend on the materials the water is sitting in ie the solar panel piping material, the storage tank

[flamefix]

Your regulations (known as "codes" state side) make no sense.

You’re saying they don't want hot water (fluid category 2) from the open collector loop to be siphoned back into the municipal supply, so you should replace it with a more hazardous fluid (category 3)?

I think you're misrepresenting or interpreting what I am saying. and to clarify some of your points I have posed the question to the regs here so some things i'll get back to you on, and if i'm right or wrong I'll freely admit it publicly however; I am talking about my opinion and the regs here in the UK and I am not saying you are wrong to do what you are doing in any way, I have only said It wouldn't be allowed here (which I am confirming) and I 'personally' don't see the need.

your point above doesn't make sense either because the collector and the cylinder are as one the fluid in the two freely circulate they could gravitate if the pump wasn't on and if there are check valves then these could fail.

Now an indirect system is less risk because there is a physical barrier between the two fluids, be it the coil a cylinder within a cylinder or a plate heat exchanger.
That said I have clearly stated the cylinder holding the hot water must be heated to 60c. or be capable of heating to 60c to kill any legionellae.

here is an article relating to preheated water that is heated by solar and either flows to a hot tap if at the required temperature or is then passed through a combi boiler on the cold inlet side to be heated by the boiler. Another system I am not a fan of however,
http://www.wras.co.uk/Preheated-Water.htm

[flamefix]

Look, let’s cut the crap here. Are you saying that YOU regularly install an active-indirect system sized for 2-4 people for the equivalent price of $4000 on a daily basis or not. Because I, and most of my legitimate competitors do. That's out the door. Materials, Labor, Building Permit, Delivery.........everything.

Yes, or no. If no, what's your average price for the above. no I am not saying that nor have I . I don't know what you purchase your system for and or your mark up for profit and labour content. All I have told you is the cost of the items as they are here, I am not saying what you can install them for and make the level of profit you require because I don't know your cost base. I have stated that you can buy an indirect system a lot cheaper than I believed you thought.
The systems here are integrated differently to the ones you have described in that they are connected to the central heating system, they are installed at height requiring safety platforms access towers and insurances and other factors are likely different here to there, so a true comparison on installed costs is difficult to compare equally, whereas the material cost isn't. I also don't know how local factors influence things for example It's cheaper for me to buy a Mac from the US than in the UK its the same bloody machine though. It might be you buying solar equipment is more or less expensive than buying it here.

However for your information a premium system with evacuated tubes 80 gallon cylinder (tank) as I described installed and warranted is $8600 a flat plate version is $7500 but equally a perfectly good quality system could be installed for $5750

That's based on my input costs but without your rebates, as I have no idea what they would be.

Why are you not also comparing your system to the integrated tank and collector system that you can get for far cheape,r than the system you fit that I have also given information on?



No, it can't. Well not in Florida anyway. The collector loop will not be in the ideal growth range for enough time for that to occur. We get just a few days out of the year that the loop isn't sterilized.

I'm not going to argue it's your professional opinion and I respect that, I am not fully convinced there is no risk, so personally I'd rather not take the risk given there is an alternative option.

[mkiernan]

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>
protech is very right, do not use a t&p valve any where near the collector.
t&p valves are set to go at 210f as per ipc.
you only need a pressure relief valve.