Convert thermosyphon to pumped.

[r.bartlett]

Many thanks

so you understand me.

I live here in San Miguel Tenerife. I moved from the UK 2 years ago as part of my retirement plan I run/own a small air conditioning company. I had one in the Uk for the last 30 years.The solar setup was part of a deal with a customer who had it installed but was made to take it down by the authorities.



I will try to reply within the text below..

The performance of thermosiphon type solar water heaters can potentially be improved by adding a circulating pump, but usually not a whole lot. Sometimes such a change can produce the opposite of the desired effect and/or cause unintended consequences and outcomes.

the issue as I see it is the TS effect relies on a temperature difference. As that temperature difference drops -the water heating up- the effect slows. In hot sunny days this doesn't matter as the sheer amount of heat available means plenty of hot water. in less sunny days this -could be??- a double whammy. less heat available and less flow.

Until the water circulation rate in a forced circulation (pumped) system reaches a point where the flow through the collector risers starts to becomes turbulent, and provided the systems are functioning properly, adding a pump will do little to increase system performance. To get to a flowrate where the flow through the collectors starts to become turbulent requires some information about the collector design that is not immediately apparent from the product spec sheets, but I'd take a SWAG and say maybe a pump that would provide a flowrate of, very approximately about 3 - 5 gal./min (~ 0.19 to ~ 0.32 l/sec) ought to get you there. That's probably an order of magnitude or two more than a thermosiphon system will produce. Once there, expect a performance improvement as measured by increased energy output to be very approximately something like 10 % over the prior thermosiphon performance. Again that's an increase over normal and expected performance. If the current unit is fouled, blocking flow in some parts of the collectors or plumbing, performance of any system, but particularly thermosiphon systems, will suffer as the blockages have more of an effect on the flowrate of gravity induced (thermosiphon) supplied systems.

difficult to get any information from Chromagen. they are notoriously bad at replying and I am no exception. However if the tank was below the tank then a pump becomes a must. I guess I am only trying to replicate that.

The increases in fouling will also lower the heat transfer coefficients in the collectors for either type system, but while related, that's a somewhat separate subject to how flowrate affects heat transfer.

see above

If you add a pump, and it's not a relatively big one, that may well be counterproductive to your goal. If your current system is working nominally, and it's not too old (fouling being somewhat a f(time in service)), adding a pump will probably destroy any thermocline (temperature stratification) in the tank that's attainable with thermosiphon systems, and a big part of what contributes to their thermal performance. Unless the pump is of a pretty healthy size to meet a circulation rate as described above, what you'll do is increase output a small amount - but not much, but in the process, destroy any temp. stratification in the storage tank which contributes to the current system's performance, whatever that may be, increase the collectors operating temp., and so increase heat loss to the ambient conditions which will decrease performance.

Before you do anything I'd suggest you get the system checked out for proper operation and design. Sometimes folks unfamiliar w/gravity systems are unaware of some of the finer points of such systems, such as the need and placement of thermosiphon loops or check valves, etc.

I am eager to learn the finer points but I have yet to find a 'dummies guide to TS solar' . Please can you forward details . I will get some better pictures of my set up for comment.



BTW: Have you noticed a performance change recently or over time ? Or have your hot water demands increased ? Or ??

I suspect, again, providing the system is functioning nominally, and the idea that, being outside the U.S, you're not a grossly profligate waster of just about everything notwithstanding, that what's going on is the demands on the system are more than the system can meet. I guess that's a sort of no brainer, but the task is to find out why. A 200 l system is OK, but without backup by a relatively quick recovery (read fossil fuel fired) backup system, a long shower or big laundry load or combination loads will quickly bring system shortcoming to the surface.

From the product blubs, I notice that the gas backup available is an instantaneous type with a rate substantial input, but the electric backup is only 2.3 kW - that's not much. What are your backup arrangements to meet hot water demand ?

I'd suggest you consider seeing how/if/where you can cut back on hot water use. (Short) showers with low flow shower heads, flow restrictors in faucets, low water use appliances that sort of thing.

not sure it is fully functioning, we have a lot of hot sunshine which maybe disgusing poor set up. as regards back up. sadly the unit never came with a electric heater so atm it's on it's own. I have access to a small swimming pool HP rated at 2.7kw output which I was considering plumbing into the circuit but not sure where. There is a couple of 'drain back' plugs in the side but again I don't really know what they are all about.
IMG_20171204_080343 (3).jpgIMG_20171204_080349.jpg

[J.P.M.]

The performance of thermosiphon type solar water heaters can potentially be improved by adding a circulating pump, but usually not a whole lot. Sometimes such a change can produce the opposite of the desired effect and/or cause unintended consequences and outcomes.

Until the water circulation rate in a forced circulation (pumped) system reaches a point where the flow through the collector risers starts to becomes turbulent, and provided the systems are functioning properly, adding a pump will do little to increase system performance. To get to a flowrate where the flow through the collectors starts to become turbulent requires some information about the collector design that is not immediately apparent from the product spec sheets, but I'd take a SWAG and say maybe a pump that would provide a flowrate of, very approximately about 3 - 5 gal./min (~ 0.19 to ~ 0.32 l/sec) ought to get you there. That's probably an order of magnitude or two more than a thermosiphon system will produce. Once there, expect a performance improvement as measured by increased energy output to be very approximately something like 10 % over the prior thermosiphon performance. Again that's an increase over normal and expected performance. If the current unit is fouled, blocking flow in some parts of the collectors or plumbing, performance of any system, but particularly thermosiphon systems, will suffer as the blockages have more of an effect on the flowrate of gravity induced (thermosiphon) supplied systems.

The increases in fouling will also lower the heat transfer coefficients in the collectors for either type system, but while related, that's a somewhat separate subject to how flowrate affects heat transfer.

If you add a pump, and it's not a relatively big one, that may well be counterproductive to your goal. If your current system is working nominally, and it's not too old (fouling being somewhat a f(time in service)), adding a pump will probably destroy any thermocline (temperature stratification) in the tank that's attainable with thermosiphon systems, and a big part of what contributes to their thermal performance. Unless the pump is of a pretty healthy size to meet a circulation rate as described above, what you'll do is increase output a small amount - but not much, but in the process, destroy any temp. stratification in the storage tank which contributes to the current system's performance, whatever that may be, increase the collectors operating temp., and so increase heat loss to the ambient conditions which will decrease performance.

Before you do anything I'd suggest you get the system checked out for proper operation and design. Sometimes folks unfamiliar w/gravity systems are unaware of some of the finer points of such systems, such as the need and placement of thermosiphon loops or check valves, etc.

BTW: Have you noticed a performance change recently or over time ? Or have your hot water demands increased ? Or ??

I suspect, again, providing the system is functioning nominally, and the idea that, being outside the U.S, you're not a grossly profligate waster of just about everything notwithstanding, that what's going on is the demands on the system are more than the system can meet. I guess that's a sort of no brainer, but the task is to find out why. A 200 l system is OK, but without backup by a relatively quick recovery (read fossil fuel fired) backup system, a long shower or big laundry load or combination loads will quickly bring system shortcoming to the surface.

From the product blubs, I notice that the gas backup available is an instantaneous type with a rate substantial input, but the electric backup is only 2.3 kW - that's not much. What are your backup arrangements to meet hot water demand ?

I'd suggest you consider seeing how/if/where you can cut back on hot water use. (Short) showers with low flow shower heads, flow restrictors in faucets, low water use appliances that sort of thing.

[r.bartlett]

Chaps I have a std Chromagen 200L thermosyphon roof top system which although works I believe doesn't work to it's full potential/. The principle means there will always be cool water in the tank which amount will differ depending upon the amount of sunshine.(obviously). It appears on cooler days the panel is very hot but the return is cold water temperature.?


we quickly run out of hot water when I believe the panel still has potential to heat. I'd rather have a tank full of 50c than 1/3rd at 80c. If you get my drift..

My thought was to introduce a small pump in the solar loop regulated by a thermostat to ensure a flow through the panel when the top of the panel reaches a certain temperature (ie 70c) .

I live in Tenerife so we experience 300ish days of sunshine but it's the cooler months coming up when there are a lot cloudier days which is bothering me

TIA

Richard