Solar collector t&p valve excessive tripping

[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 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 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/...9-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/...9-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.