Bad experience with evacuated tubes.

[J.P.M.]

Well JPM I have to say with all the problems I have had and heard of I would think you are correct but, when you see the amount of energy you get out of Solar Evacuated Tubes it is impressive. Even with my system compromised I see 100 degree water at 9am. I am quite surprised they have not resolved this problem sooner. In my research I found that the flat plates lose a lot of energy compared to the EV tubes and don't get hot till later in the morning. My system is on my roof with a long run of pipe so heat loss from the panels would just be adding to the loss specially in the Northern climates. Flat Panels do have their place for sure but, I am trying to get heat to heat my house as well as my hot water and my system is doing that already just not as well as it could until the pipes are fixed.



00

The idea is to meet the needs of an application in the safest, most cost effective way, while making it as serviceable and robust as possible. All this with some regard for aesthetics. Except for safety, all the goals are somewhat interdependent.

One approach often used is to make things as simple as possible (or no more complicated than required). Another way to say that, particularly in the case of solar water heating, is to use appropriate technology.

Some solar water heating applications may require higher working temperatures and thus make the best all around use of the higher efficiencies that evacuated tube units can achieve at higher temperatures. Such applications usually have working temps. above, say, 60 deg. C. or so. Another application might be in severely cold climates where the lower (thermal) loss coeff. of evac. tube units will allow heat collection when/where (fluid temps.- amb. temps. ) commonly exceed 40 to 50 deg. C. or more.

All that however, comes at a price. At lower delta t's, a reasonably well designed flat plate collector may well outperform an evacuated tube unit. The overall loss coeff. will be higher than evac. tube, but the temp. diff. will also be lower. The small extra amount of heat gain from the evac. tube comes at a price premium, and due to added complexity, more maint. and increased probability of problems.

Usually, flat plate is a more appropriate technology (dumber) for heating water than evac. tube. Evac. tubes may be good (appropriate) for some process heating applications. DWH is low tech stuff.

Do not confuse temperature with quantity of heat. It's easier to heat 1000 kg of H2O from 20 deg. C to 60 deg. C. than it is to heat 500 kg. of H2O from 20 C. to 100 C. with either flat plate or evac. tube. The quantity of heat is the same, the quality of the energy is different. The evac. tube is probably better for the 2d application. The flat plate better for the first. Using evac. tubes for DHW applications is overkill.

You want 100 deg. (F., I assume) water in the A.M., insulate the crap out of any storage tanks. Long pipe runs that cannot be made shorter by design can be insulated more heavily. Each application has different design challenges. There are lots of tricks available before evac. tubes, most of them more cost effective.

To paraphrase your statement, evac. tubes have their place for sure, just not usually for domestic residential applications. Usually, When I see evac. tubes for DHW use, I have often found after speaking with the owners, it was done out of solar ignorance.

[russ]

To paraphrase your statement, evac. tubes have their place for sure, just not usually for domestic residential applications. Usually, When I see evac. tubes for DHW use, I have often found after speaking with the owners, it was done out of solar ignorance.

100% correct - for residential the vac tube types seem to do better in partly cloudy or colder situations as I remember.

The total heat collected by both types per day is really quite close.

[LucMan]

As stated above flat plate panels are the simplest most reliable way to heat residential domestic water. If you need more heat add an additional panel.
The foremost reason solar thermal underperforms in northern climates is not because of the type of panel used but the lack of sunshine on the panels.
The low path of the sun limits sun exposure at best to a few hours per day if there is no cloud cover.
Flat plates shed snow more easily than evacuated tubes.
Evacuated tubes with intact vacuums will frost in cold weather delaying heat output for several hours.
The research between flat plate and evacuated tube systems overall efficiencies are available online, as are the failure rates for both systems.

[J.P.M.]

100% correct - for residential the vac tube types seem to do better in partly cloudy or colder situations as I remember.

The total heat collected by both types per day is really quite close.

And, collecting 50 % of the available energy of a 60% cloudy day with evac. tubes may not be worth the extra $$ over collecting 30% of the same 60% cloudy day's energy with a flat plate.

In cloudy climates, there is often not enough sunshine to justify the cost diff. - there just ain't enough energy to collect. In sunny climates, the high temp. performance due to lower loss coeff. is not needed, so paying for performance you don't need is cost ineffective.

[RJM]

I am not sure why people say evacuated tubes are complicated...all the header is, is a pipe plane and simple, the beauty of the Solar Tubes is if any should break the system still functions and each tube can be replaced easily. Surely the assembly process is a little more complicated but the system itself is pretty basic.

The issues with Solar Tubes is frost and snow accumulation and the reason for that is because they are so efficient they don't lose enough heat to shed even the frost in the early mornings. I am looking into ways to remedy this possibly with the use of heat tape. Another advantage is a South facing unit captures sun as it rises and sets....I can still generate heat for my house till about 5pm after the tank has captured all it can. I am in a cold climate and using them for heat and hot water so maximizing energy capture is my main objective.

The reason flat plate collectors shed snow is because of heat loss which is not a good thing to maximize heat capture. I have read comparison that sound like they capture the same amount of energy but, I also noticed they compared from times when the Flat Panel is active which starts later in the day than evacuated tubes by at least an hour on either end of the day.

One design flaw I discovered in the basic set up of most systems is they do not optimize the heat from the collector as an example: Say your system heats your storage tank to 120 Degrees F and the differential is 10 Degrees which means it has to get to 130 Degrees+ to add additional heat but that water could be used to heat your house or basement. To solve this problem I added a 3 way bypass valve and Heat Exchanger with Fan to continue to circulate the water after the tank to extract that wasted heat. In order to get the system to continue circulating the water I take out the bottom tank sensor to trick it into believing the tank temp is cooler than it actually is. This way I can continue to circulate water even at temperatures around 100 Degrees which yields roughly 80 - 85 degree air coming through the exchanger heating my house while still maintaining the heat in the upper portion of the tank. Does anyone know if there are two stage pumping stations out there?

And, collecting 50 % of the available energy of a 60% cloudy day with evac. tubes may not be worth the extra $$ over collecting 30% of the same 60% cloudy day's energy with a flat plate.

In cloudy climates, there is often not enough sunshine to justify the cost diff. - there just ain't enough energy to collect. In sunny climates, the high temp. performance due to lower loss coeff. is not needed, so paying for performance you don't need is cost ineffective.

[LucMan]

I am not sure why people say evacuated tubes are complicated...all the header is, is a pipe plane and simple, the beauty of the Solar Tubes is if any should break the system still functions and each tube can be replaced easily. Surely the assembly process is a little more complicated but the system itself is pretty basic.

The issues with Solar Tubes is frost and snow accumulation and the reason for that is because they are so efficient they don't lose enough heat to shed even the frost in the early mornings. I am looking into ways to remedy this possibly with the use of heat tape. Another advantage is a South facing unit captures sun as it rises and sets....I can still generate heat for my house till about 5pm after the tank has captured all it can. I am in a cold climate and using them for heat and hot water so maximizing energy capture is my main objective.

The reason flat plate collectors shed snow is because of heat loss which is not a good thing to maximize heat capture. I have read comparison that sound like they capture the same amount of energy but, I also noticed they compared from times when the Flat Panel is active which starts later in the day than evacuated tubes by at least an hour on either end of the day.

One design flaw I discovered in the basic set up of most systems is they do not optimize the heat from the collector as an example: Say your system heats your storage tank to 120 Degrees F and the differential is 10 Degrees which means it has to get to 130 Degrees+ to add additional heat but that water could be used to heat your house or basement. To solve this problem I added a 3 way bypass valve and Heat Exchanger with Fan to continue to circulate the water after the tank to extract that wasted heat. In order to get the system to continue circulating the water I take out the bottom tank sensor to trick it into believing the tank temp is cooler than it actually is. This way I can continue to circulate water even at temperatures around 100 Degrees which yields roughly 80 - 85 degree air coming through the exchanger heating my house while still maintaining the heat in the upper portion of the tank. Does anyone know if there are two stage pumping stations out there?

Evacuated tubes are prone to vacuum loss, heat pipe failure from freezing, and rubber seal failure at the header depending on the tube type.
Multiply that by the number of tubes in an array and you have many possible points of failure.
Here in NY state most pro installers won't install an evacuated tube system because NSERDA (the state subsidy authority) requires certified contractors to guarantee the complete system for a period of 5 yrs. That is along time to keep an evacuated tube system online with out any issues. Larger array's can cook the glycol because of the extreme temperatures generated during the summer month's. This requires glycol replacement as the glycol becomes degraded and loses it protection properties, and it's viscosity.

As far as a 2 stage pump, Grunfoss (Apha) and Taco make variable speed pumps that can be set to a specific delta T and may be what you are looking for.

[russ]

The simple fact that total heat collected by a similar foot print flat plate or a vac tube system is about the same means that for most applications it makes no sense to go for complexity.

[RJM]

If the heat tubes are filled with an appropriate solution to prevent freezing there will be no failure as it is a sealed copper pipe. Not sure why the rubber seal would fail...maybe the earlier versions used the wrong material but that failure should have little to no affect on the system as it is the copper pipe going into the header where all the energy is transferred.

The probable reason for not guaranteeing the system is most likely because of the heat pipe failures so until that issue is resolved it will be hard to guarantee..once that issues is fixed there should be no problem.

It is true that the systems can get very hot which once again proves how much more efficient the Solar Tubes are since you apparently never have that problem with Flat Plate collectors...you just settled that argument.

Many take to covering the system and using heat dumps to vent off the excess heat BUT if you can use that excess heat for other purposes such as cooling, a process called "Absorption Cooling" check out this link http://www.technologyreview.com/news...ool-buildings/ or helping to dry Fire Wood an idea I thought of since my location is very damp and takes a long time to season my wood. I am sure there are other ways to utilize that heat.

Thank you for the info on the pumps but, what I am looking for is the equivalent of two Pumping Stations in one. Stage one would circulate the water from the Array through the tank and back but once the differential is met and stage one shuts down, stage two would kick in and circulate the water from the array through the heat exchanger to heat the house. Right now the system need to be tricked into continuing the circulation by pulling out the sensor from the bottom of the storage tank.

I myself am a product designer and look to solve any and all problems as they arise...I believe the current systems even the flat plate could use a two stage system to better utilize the heat generated.

Evacuated tubes are prone to vacuum loss, heat pipe failure from freezing, and rubber seal failure at the header depending on the tube type.
Multiply that by the number of tubes in an array and you have many possible points of failure.
Here in NY state most pro installers won't install an evacuated tube system because NSERDA (the state subsidy authority) requires certified contractors to guarantee the complete system for a period of 5 yrs. That is along time to keep an evacuated tube system online with out any issues. Larger array's can cook the glycol because of the extreme temperatures generated during the summer month's. This requires glycol replacement as the glycol becomes degraded and loses it protection properties, and it's viscosity.

As far as a 2 stage pump, Grunfoss (Apha) and Taco make variable speed pumps that can be set to a specific delta T and may be what you are looking for.

[russ]

RJM - This is an old, old topic that has been gone over many times. New to you as we can see by your comments.

A flat plate collector heats a larger volume of water to a lower temp - The "getting hotter" means squat. You proved nothing except that you do not understand heat collection units. The total heat units collected by both types is close - proven by many agencies over time.

Have fun tilting your windmills.

[LucMan]

Thank you for the info on the pumps but, what I am looking for is the equivalent of two Pumping Stations in one. Stage one would circulate the water from the Array through the tank and back but once the differential is met and stage one shuts down, stage two would kick in and circulate the water from the array through the heat exchanger to heat the house. Right now the system need to be tricked into continuing the circulation by pulling out the sensor from the bottom of the storage tank.

I myself am a product designer and look to solve any and all problems as they arise...I believe the current systems even the flat plate could use a two stage system to better utilize the heat generated.

What you are looking for is s differential controller with multiple sensors that can control a 3 way valve to change the water flow circuiting ($200) to the heat exchanger.
Vs a pump pack $600 plus. These controllers are readily available. I have one one in stock.
You must be a newby to solar. I suggest you start doing some extensive research before continuing your project as you will be wasting lots of money and effort.

[J.P.M.]

What you are looking for is s differential controller with multiple sensors that can control a 3 way valve to change the water flow circuiting ($200) to the heat exchanger.
Vs a pump pack $600 plus. These controllers are readily available. I have one one in stock.
You must be a newby to solar. I suggest you start doing some extensive research before continuing your project as you will be wasting lots of money and effort.

+1 on the research part. There will always be problems. Heading off the most obvious ones before they occur through process and product knowledge is perhaps a better start and a bit more proactive on heading off problems rather than simply meeting all challenges as they appear. If nothing else, you'll get blindsided less.

[RJM]

Russ, I didn't make this up myself:

From Bob Nape: http://blog.heatspring.com/which-is-...be-collectors/

"Flat plate collectors can only heat water up to 170-180 degrees Fahrenheit, which means there is very little risk of overheating. Evacuated tubes, on the other hand, can heat water to well over 250 degrees. For this reason, they are much more likely to overheat than flat plates, and you need to be more concise with your design. If you’re using evacuated tubes, it’s always better to oversize your storage tank rather than under-size it for this reason. Evacuated tubes are also used more in colder climates because they are more efficient than flat plates in extremely cold temperatures. In extremely warm climates, evacuated tubes have a very high chance of overheating, so be careful if you’re in the southern states."

Before you point out his side by side comparison remember the systems are not of equal surface area as he mentions.

From Solar Panels Plus which sells both flat plate & evac tubes: http://www.solarpanelsplus.com/evacu...be-collectors/

"While evacuated tube technology clearly surpasses flat panels for nearly all water heating applications, the advantages are truly dramatic when used for solar air conditioning, heating or commercial process.

That’s because evacuated tube heat pipe collectors can more easily attain the higher temperatures needed, they can collect and retain heat even when it is very cold outside, and due to their superior Incidence Angle Modifier they collect solar energy more evenly throughout the day resulting in a lower buffer or thermal storage requirement. There are many other advantages as well."

I did a great deal of research a number of years ago and purchased a system but was only able to install it recently. I thought I would share my thoughts with others on how we ALL can improve on the systems and hear from others on how to improve mine....didn't mean to ruffle feathers but, I will stand up for myself when dismissed.

RJM - This is an old, old topic that has been gone over many times. New to you as we can see by your comments.

A flat plate collector heats a larger volume of water to a lower temp - The "getting hotter" means squat. You proved nothing except that you do not understand heat collection units. The total heat units collected by both types is close - proven by many agencies over time.

Have fun tilting your windmills.

[RJM]

Thank you for that information, had heard about them but not seen any as of yet. I tried to find a capable installer to no avail in Ulster County NY. The system is up and running already and generating heat, this is the first winter installed in the Fall. My problem has been with the burst heat pipes, found remedies for that but looking for replacements which would be preferable. I felt the basic piping design had room for improvement and it is working as I planned using a manual 3 way valve. Would like to see the capabilities of the differential controller you speak of can you give me more info on who makes it? Thanks.

What you are looking for is s differential controller with multiple sensors that can control a 3 way valve to change the water flow circuiting ($200) to the heat exchanger.
Vs a pump pack $600 plus. These controllers are readily available. I have one one in stock.
You must be a newby to solar. I suggest you start doing some extensive research before continuing your project as you will be wasting lots of money and effort.

[LucMan]

Search Resol solar controllers

[Chipper5783]

Repairing heat pipes - the saga continues

David,

Who is your supplier and will they sell heat tubes to others who may need replacements? Since this seems to be such a problem I would think someone would be able to supply them as long as they are better than the originals. Thanks.

My appologies RJM - I have not checked this thread in a while. My supplier has vanished! Their web site is still up, but many phone calls and e-mails later - no reply. So I repaired 88 tubes (adding to the ~15 good originals) and I operated through the summer. My performance was much better. I finally got some more of my system connected, so now I can also pre-heat my domestic hot water (as well as the underslab in my work shop). In the past week I got back to the task, as of today I finally have my full compliment of 120 tubes (104 with acetone). Likely there are still a few that are failed, so I am waiting for a frost event (see my earlier description) and hope to be able to identify any additional failed heat pipes.

Regards, David