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maximoney1

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Posts: 28
Reply with quote  #1 
Greetings and salutations from Scotland folks. Just happened onto this forum recently (seems i'm a bit late to the party) but just thought i would share my solar thermal project with you. I have two solar systems installed, a 2.59KWp PV system which had to be installed by an MCS certified installer in order for me to qualify for the government backed Feed in Tariff, (see pic 1) mounted on upper roof.jims_solar_001resized.jpg 
The lower panel you can see in pic 1 is the solar thermal panel i constructed myself. This is basically a copper serpentine design over aluminium spreader plates. The pump is an EL Sid dc pump, powered by the two small pv panel to be seen at the extreme right hand side of the thermal panel. The control of the MPglycol through the 300ltr Tank lower coil 'finned heat exchanger' is done by a solar controller activating 3 way diverter valves. See closer pic 2 of solar thermal panel. 002resized.jpg 
So basically, if the sun is shining, then the glycol is being pumped(makes sense that the higher the intensity of sun, then the higher the pump runs, thus delivering more heat to the exchange coil. The way i have set up my control and themostats is, my first thermostat doesn't measure the temp of the collector(which is really of no interest to me), it measures the temp of the pipe right before the diverter valve to input into the tank. In this way, it takes account of all the pipe heat loses etc etc and gives an accurate indication of the temp of fluid about to enter the lower coil within the tank. There is no point setting your controller to panel temps if heat loses along the way are going to drop the fluid to a lower temp. My 2nd thermostat is about six inches from the bottom of the tank, thus giving me an idea of the baseline temp for the solar input to work on. My third thermostat is about 3 inches from the top of the tank. This gives me my maximum ' danger temp' incase of overheating. How ive set it up, is the warmed fluid is delivered up to the first diverter valve, if the temp is higher than the lower thermostat, then it is diverted through the tank heat exchanger. If the temp is lower, it diverts past the tank heat exchanger, back to the thermal panel to pick up more heat. As the heat in the tank rises it is statified to the top of the tank, thus the cooler water at the bottom allows maximum extraction of heat from the panel. The flow rate being goverened by the dc pump which is goverened by light intensity, means that in low sun conditions, the fluid remains in the panel for longer picking up more heat and thus it is still possible to extract heat even on cold days, especially if the incoming water supply is close to 4-5 deg centigrade. If on the other hand, during mid summer, the tank starts to over heat, at a temp of 98deg centigrade, a second diverter valve activates to stop the solar fluid going through the tank coil and is directed to a radiator heat dump. This heat dump radiator is within the confines of the well insulated boiler room, thus keeping the ambient surrounding air temp higher(so it is not completely wasted). Thus, the fluid in the panel is always moving in full sun and doesnt stagnate as such, preventing premature deterioration of the solar fluid. We do get temps down to minus 10deg centigrade on a few occasions, hence the glycol instead of water. I do lose a percentage of heat using the glycol, which i suppose i could swap out for water in summertime if i could be bothered, but my boiler rarely comes on in summer anyway. Unvented tank resized.jpg 

Incidentally, the boiler back up, operates through the higher coil on a completely independant thermostat(see pic 3) on the middle of the tank. This is set to check tank temp, a couple of hours before we rise and top up the tank temp if necessary.  Safety radiator resized.jpg 
Pic 4 showing heat dump radiator plumbed to diverter valve 2.

With the tank being an unvented one, the plumbing of the boiler and all safety fitments on the tank(prv etc etc), had to be installed by a certified installer. Because the solar thermal panel only has an impact on the lower solar coil, this could be done by any competant person.

Pic 5 shows the boiler and conections boiler resized.jpg 

pic 6 shows expansion vessel and extra insulation around the tank prior to me removing it for photos. exp vessel resized.jpg 

pic 7 shows solar controller display solar controller display resized.jpg 
The following pics are simply showing some of the materials used... 007resized.jpg  008resized.jpg  Sid dc pump resized.jpg

I have only on one occasion had the second diverter valve operate to dump heat(98deg centigrade), you could hear it gurgling in the lower coil and it was in the initial stages of set up, whereby i think i might have had a brief airlock which allowed the fluid to stagnate very breifly in the collector, before being sent through the tank exchanger, but have never acheived it again.  It will quite happily produce 70deg centigrade water for long periods during the summer and adequately heats the whole tank during the warmest summer months. I tend to just check the bottom tank temp performance from time to time, plus the sum total of maintainence is to occasionally top up the gravity feed header tank. It really is great, being a set up and forget system. Unlike my boiler which is getting due its annual service [frown]
The winter time performance, on the thermal panel however is rather poor, only really helping on clear days. This is where i wished i could have installed a refridgerant system to pick up more heat.

Apologies for being longwinded, but i hope some of it was of interest.

Regards, Jim from Scotland.


stmbtwle

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Reply with quote  #2 
I'm impressed! That's a very attractive, well thought out system, thanks for sharing!

A question though, how do you avoid pumping cold water into storage when the system starts up in cold weather? We have sensors (or snap switches) in the collector to ensure the system does not start up until the collector is heated. Before I installed a switch, my setup would start pumping before the collector reached the necessary temperature, thus actually COOLING the storage for a while. Possibly my PV panel was too large?

I definitely like your heat dump setup, I need something like that to prevent stagnation.

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Willie, Tampa Bay
netttech

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Posts: 720
Reply with quote  #3 
Welcome Jim,

Great looking panel & a major project!

Is this the first year for the solar thermal? It would be interesting reading the performance of the panel.

Being serpentiened copper, it should perform well. I'm in the middle of re-configuring my hot water panel, which has serpentiened copper also.

Can you give details: Glazing type, diverter valve manufactor, etc. I've always thought having a divert valve (based on temp) would be beneficial. Being able to re-circulate the glycol thru the panel again to gather more heat would be a benefit in my opinion.

Jeff
Central IL
Solar Air & Water
maximoney1

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Posts: 28
Reply with quote  #4 
Quote:
Originally Posted by stmbtwle
I'm impressed! That's a very attractive, well thought out system, thanks for sharing! A question though, how do you avoid pumping cold water into storage when the system starts up in cold weather? We have sensors (or snap switches) in the collector to ensure the system does not start up until the collector is heated. Before I installed a switch, my setup would start pumping before the collector reached the necessary temperature, thus actually COOLING the storage for a while. Possibly my PV panel was too large? I definitely like your heat dump setup, I need something like that to prevent stagnation.


Hi stmbtwle,

Even in cold weather, if the fluid temp right at the first diverter valve is higher than the bottom of tank temp, then there is a heat gain to be had, therefore it is diverted thro the coil. It is irrelevant if higher up the tank the temp is higher since the work/heat is being extracted at the lower level and stratifies accordingly. The first initial glug of cold water in the pipes will simply pass thro the diverter to the recycle side and only when the temp rises above the preset differential level, will it then go thro the coil.
Hope ive explained it ok, but feel free to ask other questions.
maximoney1

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Posts: 28
Reply with quote  #5 
Quote:
Originally Posted by netttech
Welcome Jim,

Great looking panel & a major project!

Is this the first year for the solar thermal? It would be interesting reading the performance of the panel.

Being serpentiened copper, it should perform well. I'm in the middle of re-configuring my hot water panel, which has serpentiened copper also.

Can you give details: Glazing type, diverter valve manufactor, etc. I've always thought having a divert valve (based on temp) would be beneficial. Being able to re-circulate the glycol thru the panel again to gather more heat would be a benefit in my opinion.

Jeff
Central IL
Solar Air & Water


Hi jeff,

It has been installed since 2010. It was my first venture into solar, but there are a few things i'm looking at which could improve it. The trouble is, over in UK, is everything is so very expensive to buy, my set up cost me approx $1600 to build, which means on savings alone, i'm probably looking at around a 10 year plus payback. I can't give you performance figures, because i don't have any. I built it mainly as a learning curve, so i was all a bit 'suck it and see' so probably not as efficient as it might have been with detailed calcs etc. I would love to have a workshop and access to cheap materials as i love experimenting with things.
The serpentine pipework is 12mm(approx 43meters length), but to mitigate long run length and pressure probs, i installed my pump slightly higher than my panel, but obviously a good bit lower than the gravity feed header tank. This way it is not really attempting to push fluid up hill, simply push it around the circuit. The solar coil in the tank is 22mm finned stainless steel(at the time it was the highest thermal transfer properties i could find), so this slows the fluid down a little giving a greater time to dissipate the heat.
The glazing is UV stabilised twinwall polycarbonate. I have a much lesser degree of space between the heat absorber and glazing than most folks reccommend, relying on the twinwall characteristics to provide the thermal barrier to heat loss. I use honeywell 3port diverters.
Recirculation of the glycol is only taking place when the bottom of the tank is to warm to do work on, which means the little gain you have already made in the panel is not entirely lost. There is nearly always the possibility of transferring some heat gain to the tank. Every time someone run the hot tap, cold floods the bottom of the tank providing plenty of thermal capacity to work on.

The pics below show the height difference between the dc pump above the top of radiator height/above height of top of panel/above height of highest point in tank coil. The second pic shows the height difference up to the gravity feed header tank.
pump and rad resized.jpg  header tank and pump resized.jpg 

Garage_Hermit

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Posts: 2,240
Reply with quote  #6 
Hi, Jim,

Thanks for the nice read !

Just wondering, is that a gas boiler, or electric ? (gas I suppose, since U talk of "yearly maintenance").

Other question, what is your angle of tilt on the hydronic panel ?

For maximum effect, it should be about equal to your latitude + 15°.
Perhaps you could check out this link: http://www.builditsolar.com/References/SolRad/SolRadTables.htm
  and see what your panel should be picking up, in BTU per square foot per day:

so for example if U live nearest to 53° N, you would select the tables for "56 North"

and your panel would be set for (53)+(15) = 68 degrees (or thereabouts)

Using the table, say, for 21st February, you would see that a panel inclined at 66 degrees (nearest to yours) will theoretically pick up 1742 BTU for the WHOLE DAY per square foot of panel...  (Otherwise U can work out the arithmetic average, such as between between 56 and 66 degrees of collector tilt, to get your actual pro-rata inclination value) (the same as U would do for the dates, in fact...)

If your panel is , say, (to my "untrained eye" [biggrin] 14 x 2.5 ft), that gives 35 square foot, x 1742 = 60,970 BTU for the day...

Divide that by 3412 and U get the kW - 17.8 kW.

However, since the panel will only be around 50 percent efficient (due to reflected light, leaks etc.), U will "likely" only get one-half of that, therefore 9 kilowatts...

(still better than nothing!) (and far better than a coal-fired powerstation, for example...) (33%)

On the same page, for the same date, you will see a value of 1986 BTUH - this is for a collector in full sun, with the sun hitting the panel dead on (normal, 90° angle of incidence), which it won't do for very long) but does give an idea...

Good luck with the numbers and tuning the panel !

G_H



__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
maximoney1

Registered:
Posts: 28
Reply with quote  #7 
Quote:
Originally Posted by Garage_Hermit
Hi, Jim,

Thanks for the nice read !

Just wondering, is that a gas boiler, or electric ? (gas I suppose, since U talk of "yearly maintenance").

Other question, what is your angle of tilt on the hydronic panel ?

For maximum effect, it should be about equal to your latitude + 15°.
Perhaps you could check out this link: http://www.builditsolar.com/References/SolRad/SolRadTables.htm  and see what your panel should be picking up, in BTU per square foot per day:

so for example if U live nearest to 53° N, you would select the tables for "56 North"

and your panel would be set for (53)+(15) = 68 degrees (or thereabouts)

Using the table, say, for 21st February, you would see that a panel inclined at 66 degrees (nearest to yours) will theoretically pick up 1742 BTU for the WHOLE DAY per square foot of panel...  (Otherwise U can work out the arithmetic average, such as between between 56 and 66 degrees of collector tilt, to get your actual pro-rata inclination value) (the same as U would do for the dates, in fact...)

If your panel is , say, (to my "untrained eye" [biggrin] 14 x 2.5 ft), that gives 35 square foot, x 1742 = 60,970 BTU for the day...

Divide that by 3412 and U get the kW - 17.8 kW.

However, since the panel will only be around 50 percent efficient (due to reflected light, leaks etc.), U will "likely" only get one-half of that, therefore 9 kilowatts...

(still better than nothing!) (and far better than a coal-fired powerstation, for example...) (33%)

On the same page, for the same date, you will see a value of 1986 BTUH - this is for a collector in full sun, with the sun hitting the panel dead on (normal, 90° angle of incidence), which it won't do for very long) but does give an idea...

Good luck with the numbers and tuning the panel !

G_H




Hi G_H,

Yes it is a gas boiler. The panel angle can be changed to suit the month, by simply moving the feet out from the wall and sitting on bricks. When i can be bothered, i use the following chart(pic 1) solar angle calculator.gif 
Thanks for the calcs guide, i will have a go at calculating for november output. Im at 55.8deg latitude.
Panel is currently at 70deg angle

The glazing panels are 8ftx2ft(x3) = 48sqft

So for nov 21 @70deg i potentially have access to 1039btu x 48sqft = 49872btu for the whole day
divided by 3412 =14.6kw x potentially 50% efficiency = 7.3kw

I'm assuming my efficency will be even lower running on glycol, so potentially 5kw. Does this sound about right?

Garage_Hermit

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Reply with quote  #8 
Depends on your level of freeze-protection, I guess...
Your 43-meters of serpentine contains 3.7 liters - how much of that is glycol ?
 perhaps 40% ?  therefore 60% of 7.3 kW =  4.38 kW  (allowing for a poor antifreeze).
However, some antifreeze products have a very high heat capacity, (such as 3.6, for 4.1 for H2O at 20°C) so it might be not all that of a knock-down as U think...
(in that particular case, just 13% less...) cf.  http://www.roth-uk.com/files/SOL_Solar_Fluid.pdf

which would mean 87% of 7.3 = 6.35 kW actual power...
So the mid-point would be 5.3 kW theoretical...
======
To determine the actual performance of your collector, you'd need to measure it over a full collection day -- without running off any hot water !

Alternately, just connect the collector to a big barrel of cold water and measure the starting & finishing temps, and the number of liters, and that will give U the power, period !  You would also (presumably...) record the solar conditions (times of sun on collector, clouds etc. to ensure you stayed good per the Tables...) - you will soon develop the nose of a solar tester (for tips, just ask any of the Tester Heads on here...) [smile] (they know who they are...).

G_H

__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
maximoney1

Registered:
Posts: 28
Reply with quote  #9 
Quote:
Originally Posted by Garage_Hermit
Depends on your level of freeze-protection, I guess...
Your 43-meters of serpentine contains 3.7 liters - how much of that is glycol ?
 perhaps 40% ?  therefore 60% of 7.3 kW =  4.38 kW  (allowing for a poor antifreeze).
However, some antifreeze products have a very high heat capacity, (such as 3.6, for 4.1 for H2O at 20°C) so it might be not all that of a knock-down as U think...
(in that particular case, just 13% less...) cf.  http://www.roth-uk.com/files/SOL_Solar_Fluid.pdf

which would mean 87% of 7.3 = 6.35 kW actual power...
So the mid-point would be 5.3 kW theoretical...
======
To determine the actual performance of your collector, you'd need to measure it over a full collection day -- without running off any hot water !

Alternately, just connect the collector to a big barrel of cold water and measure the starting & finishing temps, and the number of liters, and that will give U the power, period !  You would also (presumably...) record the solar conditions (times of sun on collector, clouds etc. to ensure you stayed good per the Tables...) - you will soon develop the nose of a solar tester (for tips, just ask any of the Tester Heads on here...) [smile] (they know who they are...).

G_H


Hi G_H,

The glycol mix is 40% by volume, good to minus 20deg centigrade or up to 300deg centigrade for short stagnation periods, but simply states that it has high thermal efficiency. I dont have the data sheet info anymore and cant download it from their website [frown] 
From this i would have calculated it as (60% x 7.3kW =4.38kW) +(40% x 7.3kW x 87%=2.54kW) giving a total of 6.9kW ?

Also, could you explain the solar angle thingy as you stated the best angle to be latitude+15 deg, but if i look at the 'solar angle calculator' is basically ranges from about 10deg angle in winter to 58 deg in summer, taking accout of my latitude. Any idea's as to the discrepancy, since using your specified calculation would suggest 56+15 = 71deg !
stmbtwle

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Reply with quote  #10 
Thanks for the explanation Maximoney.  My collector switch does about the same job as your diverter-valve sensor, except that it turns on the pump instead of actuating a valve.
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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