Flat solar thermal panels or evacuated tube?

[russ]

are you using a heat exchanger or directly using the water you heat? Is this a pumped system or working off of a thermosyphon? If you are using a heat exchanger, how big is the reservoir? If not, i agree with other posts that it is dangerous to use this water for domestic purposes due to bacteria you are surely growing in this perfect environment.

The other points are good plus how much water is consumed daily.

The point about 'dangerous to use this water for domestic purposes due to bacteria' is totally off the mark.

[mtmtntop]

are you using a heat exchanger or directly using the water you heat? Is this a pumped system or working off of a thermosyphon? If you are using a heat exchanger, how big is the reservoir? If not, i agree with other posts that it is dangerous to use this water for domestic purposes due to bacteria you are surely growing in this perfect environment.

[emarq]

Low water temperature on evacuated tubes system

Hi guys,

I need a help. I live in Brazil ( lat. 23.5 South) and I have a thermal reservoir (110gl or 400 liters) and 25 evacuated tubes (2m (6.5ft) long each tube) installed in thermosiphon system in a 25

[russ]

What about Legionella bacteria in your water? The water should be heated up to 60 C once a day to kill them off? Are you using the water for domestic use??

Using the water for domestic use - legionella - one of my more minor concerns - such as in no interest.

[russ]

What tilt are the tubes? What latitude are you at? If the neighbour had his tubes tilted for winter bias it would reduce the overheat in summer. All the info I have seen recommends about +20 degrees above latitude. I am at 38 degrees south so will tilt mine to 45 degrees for more heat in winter and take the edge off summer heat

They are on the roof so it is a bit difficult plus a lot of ugly of the tilt is changed.

[Peter69_56]

Just had an issue today.A competitor called with-an ET problem. Seems they have a 120Gallon Rheem tank with wraparound heat exchanger. 50 tubes. Tank temp 110 F manifold temp 250 F What do you think is wrong? i know the answer but throwing it out for comment. We are at 39 north latitude.

Circulating pump failed? or blockage so no circulation flow?

[Peter69_56]

Like Roscho04 says - depends on your location and requirements.

Both types of collectors can collect similar amounts of heat - flat plates are better for low temperature applications (such as household use hot water) in temperate climates while evacuated tube types do better when higher temperature water is required, in cloudy situations and during the winter in cold areas.

I have the flat plate type - mild climate here. A neighbor has a big bank of evacuated tube types and keeps a good portion covered all summer.

Roscho04 is just the reverse of my situation - for his location the evacuated tube type is better.

What tilt are the tubes? What latitude are you at? If the neighbour had his tubes tilted for winter bias it would reduce the overheat in summer. All the info I have seen recommends about +20 degrees above latitude. I am at 38 degrees south so will tilt mine to 45 degrees for more heat in winter and take the edge off summer heat

[Peter69_56]

Heat sink paste

[QUOTE=roscho04;33026]Hello Stone hope all is well:
I really don

[Peter69_56]

Legionella

[QUOTE=russ;17152]Those are the common claims made by manufacturers but - observations I have made from my system and my thoughts have trouble with their statement. I collect power readings from four meters every morning and hot water system data about every hour. Solar insolation is collected from my Davis weather station both Global solar radiation and UV are recorded.

1) I consider that my system is functional for about 85% of available light. The very early morning and late evening light no system will pickup. If the insolation for a day is 2000 watts/m2 then you really have 1700 watts to work with. Even if the vacuum tube collectors extend the day you might say 50% of nothin is still nothin.

2) My hot water system electrical backup is set for 50 degrees. I don't need or want water hotter - now for a radiator heating system OK hotter is needed. For in floor radiant heating I have the temperature set at 35

[Peter69_56]

Plate vs tube

There's a lot of good information contained in this thread. I work for a manufacture where we distribute both flat plates and evacuated tubes.

It all comes down to value - which system produces the most in your area for what you spend. However, there are a few general pros and cons for each technology to consider.

Evacuated tubes produce more on cloudy / overcast days than flat plates. They also produce higher internal temperatures (our manifolds generally stay around 160-170F during the day), and are easier to maintain.

The internal temperatures will not burn anyone or cause a hazard - the heat is inside the glass tubes, and the vacuum insulation makes the outside the same temperature as it is outside.

If damage occurs - such as in a storm - a tube can be replaced easily and with minimal expense, and without draining the system or messing with any piping or components. Most manufactures will pack in a few extra spare tubes with each collector - however, replacement tubes cost around $25/each.

Evacuated tubes are also modular - they come in separate pieces that are assembled on the roof. Therefore, it's generally easier to install from a labor standpoint.

The cons, are that evacuated tubes are generally about 20% more expensive than their flat plate counterparts. They also can get very hot - and generate too much heat, so a form of heat dissipation is needed, especially in the summer months. This adds about 10% extra cost in components.

In a closed loop system (or a drain back), this is the only real difference in cost versus a flat plate. Flat plates have the same general components - controls, tanks, pumps, glycol, etc - other than dissipation and the valve that controls them.

The real point to consider is it it worth the extra $300 to $500 in system costs for an evacuated tube versus a flat plate for what you receive in return?

The answer to the question is that it depends on really where you live. In warmer climates where the outside air temperature stays fairly warm (70F+), and the weather is fairly consistently sunny, the flat plates can be a better value overall, as they will perform as well as the evacuated tubes. So in areas like Florida, Texas, Arizona, etc, most contractors and homeowners tend to opt for flat plates.

In cooler and/or cloudy climates, the evacuated tubes out perform the flat plates. So if your temperature in the winter and shoulder months stays 50F or lower, or you have rainy/cloudy seasons, most contractors and homeowners tend to opt for evacuated tubes.

The other thing to keep in mind and consider is that some flat plates can be very inexpensive and cheaply made - and some evacuated tubes can be very expensively priced. I have seen a flat plate sell for $450 or so, and an evacuated tube collector sell for $3500. Therefore, at times, when people compare costs, they run across prices like these and get an idea that tubes are vastly more expensive.

My recommendation would be to shop around and ensure you get the best value for your money. Look at the SRCC certificates and see what kind of production you get for the price you pay, and make sure you get nothing less than a 10 year warranty on either technology.

Our flat plates generally sell to a contractor for around $950 or so and the evacuated tubes that we manufacture in the states generally sell for around $1250 or so - and other manufactures will generally be around the same price or so.

Hope this information helps!

Thank you for the "first" unbiased report I have seen on plate vs tube. Most are either plate or tube sellers and so are clearly biased. This thread was good in that you have no barrow to push in either direction. I totally agree with your assesment. Each has their good and bad, and your location and weather conditions, as well as ability to purchase at resonable cost all needs to be taken into account.

Well done

[Naptown]

Just had an issue today.A competitor called with-an ET problem. Seems they have a 120Gallon Rheem tank with wraparound heat exchanger. 50 tubes. Tank temp 110 F manifold temp 250 F What do you think is wrong? i know the answer but throwing it out for comment. We are at 39 north latitude.

[Peter69_56]

Hotter Water Not Total Heat

Perfect Solution Mountain!

Your temperature loss problem can be solved by insulation.

The quantity of water you need to recirculate you are not going to get from solar panels unless you have a lot of them.

Vacuum tube only has the capability to produce hotter water - not more total heat. Your location - winter time you are never going to get 200 liters per panel per day from solar panels.

I am not sure what you are saying here. Surley if one adds more tubes the temperature will rise, and if one then puts more tubes in parrallel, say 3 parallel banks of 30, then one will have both heat and temperaure. In series for temperature increase, and parallel for volume of heat?

[Peter69_56]

Array tilt

re evacuated tubes and radiant floor and my prior post. my 75 tube array shares a boiler loop with a backup boiler. on this loop is a radiant loop for 450 sq ft, a heat exchanger for a 2700 gallon endless pool (indoors) and heat exchanger for dhw. the tubes run during the day. the boiler runs after the sun sets to catch up if there is a need. I only let the pool take boiler heat for an hour max via a wiring setup and relay i have with the pool circ pump.

the boiler turns off at 8am and cools to prevent thermal shock from the tubes that start circulating about 10 am this time of year.

the solar gain(south facing, mostly glass) in this room along with the floor heat keep this room at 66. i have turned off the boiler on a really cold night (-20) to see what happened and the room temp fell to 59 so the floor holds alot of heat .(The floor has a 2" "mudpack" base under ceramic tile.)

i am running glycol as this is a closed system, not a drainback.

once the loop is warmed, even now when the sun is low the panel loop will continuously run about 120-125, and heats the pool and the floor as long as they are calling for heat.

although i have run the array at 170, it does not run that hot continuously except in the long days of the summer. I find that i can harvest the most heat running it with a differential setpoint controller set at 135/115.

i am still working on the dhw as i have a standalone hw heater for now. it has been problematic getting the aquastat to call correctly as there is no port for it on the conventional tanks. this may have to wait for the how water heater to be replaced.

finally, i have my array at 70 degrees to maximize the low winter sun. the array runs less efficiently in the summer. I rarely dump heat even in the summer with this setup.

What is your latitude? I am at 38 degrees 08 minutes South (Melbourne Australia), and am considering tilting my array to 55 degrees for more winter bias and less summer heating so I have more overall heating but still have unboosted hot water from spring to autumn.

[Peter69_56]

Hot tubes

I don't think there is really a right answer because there are different factors.

1. tubes are more efficient, but cost a lot more. The lower efficiency of panels isn't necessarily a problem, since the sun is effectively unlimited, so you can put up more panels (unless you have limited space). So you need to know the specific costs of each compared to the amount of water they heat; this varies with suppliers, but in many cases, tubes will be cheaper.

2. how robust they are. Tubes can be a little fragile, where as you can usually jump on a panel without damaging it. So are you likely to get anyone throwing rocks?

3. how accessible they are; tubes can get extremely hot. You don't want children or animals touching them.

This is not correct, unless the vacuum has been lost in the tubes. If the tubes are working they are like a thermos, hot inside and cool outside. With the vacuum lost they can then be hot on the outside and will not function as designed then. If you have hot tubes, have them replaced.

[Naptown]

[QUOTE=roscho04;33026]Hello Stone hope all is well:
I really don