converting from low profile to tank above..

[r.bartlett]

chaps,

location :Tenerife Latitude 28 deg.

my solar water heater has been very hit and miss for the last year or so. Diagnosing why it sometimes works has been very difficult but I have suspected the floating ball in the NRV not letting the flow properly or perhaps an airlock.

Anyhoo from my understanding if the height between the tank and top of panel is over 200mm then no NRV is required.

So me being me thought why not have a play. so I took the panel off and dropped it down under the tank and lashed up (yes I know an understatement) to see how it goes.
pipe dia is 22mm which is standard over here. I have never seen bigger only smaller at 15mm


My thinking is any restriction in the heater flow (ie NRV) will drop the efficiency.
if the top of the tank is level with the panel then it will only heat up to a certain level. ie the level of the cold water inlet. This is the 'balance' point for the thermosyphon. so the panel only heats 2/3rds of the panel and the top half of the tank.??
is this correct?

I also guess I need to angle the panel up to around 35 deg for better efficiency during the winter. ?
the panel is now facing west from it's original south facing position.


solar.jpg

solar2.jpg


based on your responses I shall upgrade the piping etc.

Thanks

Richard

[LucMan]

From what I can see from your pictures the tank is now casting a shadow on the panel reducing capacity. The panel should be mounted true south for best performance, tilt can be adjusted for optimum winter performance.
The #1 issue with thermosyphon system performance is scale build up!

[r.bartlett]

From what I can see from your pictures the tank is now casting a shadow on the panel reducing capacity. The panel should be mounted true south for best performance, tilt can be adjusted for optimum winter performance.
The #1 issue with thermosyphon system performance is scale build up!

Thanks for the reply

no the sun is from the south so the tank being 'north' of the setup cannot shadow the panel. (if there is a shadow it's just me taking the picture.)

However as I say it's the theory of dropping the panel well below the tank which is what I am looking at. I am trying to understand if the tank position affects efficiency and flow rates

so far as luck would have it after 10 days of clear blue skies it's gone cloudy which kills my comparative testing.

However i did note the top of the panel the water outlet is cooler which I suspect means there is better flow through the panel. (before dropping the panel the water was actually boiling. which to me indicated meant the water was stagnated?)

once I am happy it's working properly I will turn the panel round 90 deg again .

[r.bartlett]

jumped on the roof and turned the panel round.. Interested in seeing how it performs. solid sunshine today so should be interesting,
IMG_20191222_122911134.jpg

[J.P.M.]

jumped on the roof and turned the panel round.. Interested in seeing how it performs. solid sunshine today so should be interesting,
IMG_20191222_122911134.jpg

You ought to find that the shown and equator facing panel orientation with less panel shading will improve performance.

At you latitude and climate, lower tilt angles - probably 20 - 30 deg. or so - produce larger output/m^2 of surface than higher tilts. That lower tilt makes the panel azimuth, while still important, somewhat less critical, but all else being equal, equator facing, or close to it +/- 10-15 deg. or so, is still the most productive.

In the limit, the interaction between and the influence of tilt and azimuth on one another for production purposes disappears at a horizontal tilt and tends to a max. at 90 deg.(vertical) panel tilt.

I suspect the shading that Lucman noted was probably contributing as much or maybe more to the lowered production as the less than optimal azimuth.

[r.bartlett]

You ought to find that the shown and equator facing panel orientation with less panel shading will improve performance.

At you latitude and climate, lower tilt angles - probably 20 - 30 deg. or so - produce larger output/m^2 of surface than higher tilts. That lower tilt makes the panel azimuth, while still important, somewhat less critical, but all else being equal, equator facing, or close to it +/- 10-15 deg. or so, is still the most productive.

In the limit, the interaction between and the influence of tilt and azimuth on one another for production purposes disappears at a horizontal tilt and tends to a max. at 90 deg.(vertical) panel tilt.

I suspect the shading that Lucman noted was probably contributing as much or maybe more to the lowered production as the less than optimal azimuth.

as I say there wasn't any shading by the tank as the sun is behind me when the pictures are taken but the panel facing west and almost flat meant little direct sun was hitting it c/w some clouds.
now I have moved it and will see.
in order to get a 35 deg angle whilst maintaining 250mm height difference means the tanke needs to go up almost 1m which is going to be tricky

thanks great input though as I need to study and understand far more than I do

[J.P.M.]

as I say there wasn't any shading by the tank as the sun is behind me when the pictures are taken but the panel facing west and almost flat meant little direct sun was hitting it c/w some clouds.
now I have moved it and will see.
in order to get a 35 deg angle whilst maintaining 250mm height difference means the tanke needs to go up almost 1m which is going to be tricky

thanks great input though as I need to study and understand far more than I do

As you had it, a west facing panel got shading from the tank before noon.

The height difference is what drives the flow in a thermosiphon system. Some is necessary. Zero height diff. between top of tank and top of collector will tend to reduce flow rate to something close to zero. Too much height will need more insulation thk. for the lines to avoid allowing line losses to reduce the fluid density gradients and slow things down and reduce thermal efficiency.

Thermosiphon systems are pretty elegant in theory. In practice however, things that are not as worrisome in a pumped system - where the power of the pump tends to overwhelm and mask small(er) worries - can easily kill performance.

To the point about thermosiphon systems and details: One thing I just noticed. Looking at the latest photo, a question: Where are the collector inlet and outlet ? Looks like they are on west (same) side of the collector to me. If so, to the degree that the top and bottom sides of the collector are not level (horizontal), that out of plumb will cause problems with the flow distribution and so the collector efficiency. Unless there are good reasons to do it otherwise, common and good practice usually puts single collector system inlets and outlets at opposite corners for most any single collector system, pumped or thermosiphon, but particularly for thermosiphon systems.

[r.bartlett]

As you had it, a west facing panel got shading from the tank before noon.

The height difference is what drives the flow in a thermosiphon system. Some is necessary. Zero height diff. between top of tank and top of collector will tend to reduce flow rate to something close to zero. Too much height will need more insulation thk. for the lines to avoid allowing line losses to reduce the fluid density gradients and slow things down and reduce thermal efficiency.

Thermosiphon systems are pretty elegant in theory. In practice however, things that are not as worrisome in a pumped system - where the power of the pump tends to overwhelm and mask small(er) worries - can easily kill performance.

To the point about thermosiphon systems and details: One thing I just noticed. Looking at the latest photo, a question: Where are the collector inlet and outlet ? Looks like they are on west (same) side of the collector to me. If so, to the degree that the top and bottom sides of the collector are not level (horizontal), that out of plumb will cause problems with the flow distribution and so the collector efficiency. Unless there are good reasons to do it otherwise, common and good practice usually puts single collector system inlets and outlets at opposite corners for most any single collector system, pumped or thermosiphon, but particularly for thermosiphon systems.

Ok no point in arguing but as I say at this time of the year the sun doesn't go as high as summer. The tank is exactly side on facing south. With the panel below it and slightly to the south no shading was occurring.

Any hoo. I was considering a small flow pump which I have in my garage as the next stage. Possibly controlled by a digital thermostat on the panel outlet.
The other point regarding the in out connections. This is how it was from factory. It's no biggy to swap one over to promote cross flow.
Also this is what they call a low profile set up whereby the tank and panel are at the same height
I have concerns that these sacrifice efficiency for looks

Equipos-ACS-compactos-Chromagen-merkasol_m.jpg

[LucMan]

To the point about thermosiphon systems and details: One thing I just noticed. Looking at the latest photo, a question: Where are the collector inlet and outlet ? Looks like they are on west (same) side of the collector to me. If so, to the degree that the top and bottom sides of the collector are not level (horizontal), that out of plumb will cause problems with the flow distribution and so the collector efficiency. Unless there are good reasons to do it otherwise, common and good practice usually puts single collector system inlets and outlets at opposite corners for most any single collector system, pumped or thermosiphon, but particularly for thermosiphon systems.

Excellent point.
Piping in this configuration will short circuit the water flow. That's why you had excessive temps in the panel and low capacity.

[r.bartlett]

Excellent point.
Piping in this configuration will short circuit the water flow. That's why you had excessive temps in the panel and low capacity.

how do you measure capacity in a thermosyphon system?

[J.P.M.]

how do you measure capacity in a thermosyphon system?

Not ragging on Lucman, but capacity isn't a word I'd use. A perhaps better term might be "efficiency".

First off, are the inlet and outlet on the same side of the collector ?

A definition of efficiency = = energy output/energy input.

Energy output == energy input - energy losses to the environment.

Energy input = solar insolation incident in the plane of the collector.

To a first approx., energy losses to the environment are mostly proportional to the difference between collector operating temps. - ambient air temps., and site conditions such as wind.

If both your inlet and outlet are on the same side of the collector, when the solar energy input is great enough to overcome the system thermal losses - which losses are roughly proportional to the diff. between the collector temp. and the ambient temp. - useful energy will be collected with any left over and "available" solar energy converted to heat by the solar thermal collector and that heat is then transferred to the water.

The heated water then expands and its volume per unit mass increases. That results in what's called a density gradient. That heated (and now less dense) water rises and that's what makes the fluid in a thermosiphon collector move against, and opposite to, an external force field (in this case, gravity). Basically, the sun is the pump.

Now, when a fluid (water) is passing through the collector, pumped or thermosiphon, it will always take the path of least resistance. For most thermal collectors that means the shortest path from inlet to outlet, and also probably the one with the fewest pressure drop inducing elbows, tees or changes in direction for the flow. That usually means the first or second riser in a liquid cooled flat plate collector with inlet and outlet on the same side of the collector. With inlet and outlet on the same side of the collector, the fluid flow will tend to stay on that side of the collector.

That means the other side of the collector will not have as much flow going through it and so will run hotter. Running hotter will increase the thermal losses as explained above and that will decrease the thermal efficiency with the results being less heat collected and the day long storage temp. increase will be less.

One reasonably workable solution to the problem of flow maldistribution caused by inlets and outlets on the same side of the collector,and one that's commonly employed for solar thermal flat plate collector systems, both thermosiphon and pumped, is to not do that. Instead, to get the flow more evenly distributed put an inlet at the bottom of one corner of a collector (call it bottom west) with the outlet at the top of the collector at the opposite corner (call that one top east). There will still be some reduced flow (maldistribution) at the top west and bottom east corners, but thermosiphon systems are somewhat forgiving and tend to be a bit self correcting in regards to flow distribution - just not enough to overcome $hit setups like inlets and outlets on the same side of the collector.

BTW, with respect to that somewhat self correcting flow distribution situation in thermosiphon systems, unless a thermosiphon system is very carefully designed, that tendency toward self correction of maldistribution of flow usually comes at the expense of a slight loss of efficiency vs. a pumped system of the same size and orientation and collector particulars, even when and after parasitic pumping costs are considered.

Bottom line, cooler collectors collect more useful heat and operate at a higher thermal efficiency because the thermal losses are less. The closer an entire collector surface operates to the inlet temp. of the collector coolant (water in this case), the more heat will be collected, and for any particular day, the higher will be the bulk storage temp. at the end of that day.

[LucMan]

BTUH= gallons of storage x 8.34 lbs per gallon x temp. rise in 1 hr will get you started. Your results will vary according to time of year, time of day as well as your panel orientation and fouling factor. Then go to the SRCC web site and see if your system is listed under OG 100 certified systems and compare your results.
Just remember that the SRCC results are under optimum conditions with new panels.

[J.P.M.]

Just remember that the SRCC results are under optimum conditions with new panels.

Thus, and for a lot of reasons, making any comparison of output on any random day pretty much useless and probably adding more confusion than help.

Conditions most likely don't match the assumed SRCC conditions.
There's probably no real way for the OP to even understand what's required for input much less get an estimate of that solar input.
That makes such comparisons least confusing and pretty much useless, and made more so by a collector that's most likely not being operated at the OG100 assumed flow configurations.

No more than FWIW, somewhat in the sprit of leading a horse to water, and assuming the OP is reasonably intelligent, I suggested the OP check out a solar energy text for particulars back on 12/14/2017.

Sending him, or anyone who's that solar ignorant off to compare a probably fouled and probably incorrectly plumbed system against some industry standards without knowing what they're doing or looking for will, IMO only, do little more than add to the confusion.

Richard: Do some homework. A little effort will answer most of your questions. You seem to be willing to do what's necessary, but lack basic information on the basics of why things are not working well. Reminds me of a steam locomotive with a full head of steam and so lots of motive potential, but no flanges on the driving wheels.

Take what you want of the above. Scrap the rest.

[r.bartlett]

"Now, when a fluid (water) is passing through the collector, pumped or thermosiphon, it will always take the path of least resistance. For most thermal collectors that means the shortest path from inlet to outlet, and also probably the one with the fewest pressure drop inducing elbows, tees or changes in direction for the flow. That usually means the first or second riser in a liquid cooled flat plate collector with inlet and outlet on the same side of the collector. With inlet and outlet on the same side of the collector, the fluid flow will tend to stay on that side of the collector."


This in an interesting topic in itself .
just thinking aloud..

If the flow is at the bottom left the water entering will be at it's coldest. Once in what is the process of it rising? Density of the water from the tank outlet to the panel inlet v the density of the water in the panel. IE the panel water is hotter and less dense.So we have a natural flow.

Then as the water enters the panel it will spread along the bottom by the same force. IE as it enters it will 'try' to go up the first available pipe to fill the 'partial vacuum' created by the rising water already in the pipe?

But the other tubes are also heating the water.Those columns of water will also be rising which also creates a partial vacuum at the bottom feeder tube. Each riser tube of water will be trying to rise by the same heating density process drawing the cooler water towards itself.. So it's possible the outlet being on the same side is not necessarily a factor?

I would like to measure each riser tube for temperature gradient but construction does not permit

So as a idea, by enlarging the tank outlet pipe to the panel inlet will allow greater volume of 'cooler' water to enter the panel increase flow rate and increase performance..??

thoughts ?

Oh and I was out all day . but just got back (all day 25c rock solid sunshine.) The panel water top outlet was hot and the bottom inlet warm to the touch, only had this once before in the old set up... The panel is working very very well atm (best i have had I suspect) but i still need to work harder on the layout.

[LucMan]

Solar Pathfinder Assistant can calculate the output capacity of your panel monthly. Download the evaluation version enter your panel model or dimensions, latitude, longitude, orientation, tilt, etc. The orientation and tilt can be changed in the software so that you can fine tune the output to your personal usage.