Solar water preheater project based on builditsolar $1000 system - Page 6

strider3700 · 06-19-11, 07:20 PM

I was doing a little research and I'm thinking about going with a conventional 60 gallon water heater rather then one of those lifetime plastic heaters I had originally planned on. I can get a 60 6 year which will need some basic upgrades and better insulation for $370. upgrades will be about 100 with superinsulated box. a 12 year is $550 and will still need some more upgrades and more insulation. plastic lifetime tank is $1400...

I need to decide if a bottom inlet is better then top for the cold. I'm thinking it makes the plumbing a bit easier but this is without drawing it out.

strider3700 · 06-29-11, 11:34 PM

I'm getting ready to make some fins for my water heating collectors and was hoping to use a bunch of "old" aluminum I have lying around. I have some 12" roll flashing. some 18" valley flashing, some 12" L flashing, some 8" L flashing and a Bunch of 7.5" step flashings.

I was thinking just go with 6" cut the big stuff down to 6" and leave the 8" and 7.5" stuff big with some overlap but after forming it for my 1/2" pipe that means the width is going to be somewhere between 4 and 4.5" which seems tight. my glass which sets the collector size is 34"x76" so that's 8x76"(minus frame/gap/header) risers or 18x 34" risers depending on if I go vertical or horizontal for the glass. Horizontal is more stealth for my location(guerilla install) but it's a bunch more 1/2" 3/4" T's.

Any thoughts or suggestions?

GaryGary · 06-30-11, 09:54 AM

Quote:

Originally Posted by strider3700

I'm getting ready to make some fins for my water heating collectors and was hoping to use a bunch of "old" aluminum I have lying around. I have some 12" roll flashing. some 18" valley flashing, some 12" L flashing, some 8" L flashing and a Bunch of 7.5" step flashings.

I was thinking just go with 6" cut the big stuff down to 6" and leave the 8" and 7.5" stuff big with some overlap but after forming it for my 1/2" pipe that means the width is going to be somewhere between 4 and 4.5" which seems tight. my glass which sets the collector size is 34"x76" so that's 8x76"(minus frame/gap/header) risers or 18x 34" risers depending on if I go vertical or horizontal for the glass. Horizontal is more stealth for my location(guerilla install) but it's a bunch more 1/2" 3/4" T's.

Any thoughts or suggestions?

Hi,
Whether 4 or 5 inch total width is overkill or not depends on the thickness of your aluminum. You need about 0.018 thick aluminum to have an efficient fin that is 6 inches wide. You can run the fin efficiency for the alum you have here: FinEficCalc.xlsx

On the 3/4 by 1/2 T's, PEXSupply.com usually has a good price on the bags of 25. But, if the collector is not too wide, you really don't need 3/4 inch header -- a half inch header with standard half inch T's is fine -- like this one:
Experimental Solar Collector Using Hybrid Copper/Aluminum Construction

I tested the flow distribution for the half inch header collector and its fine:
Copper/Aluminum Solar Collector Flow Distribution Test

The test collector is only 4 ft wide, but I think you could go somewhat wider before needing the 3/4 inch heaer.

Some people have worked out ways to join small risers to big header without using T's -- one example is Ken's system:
Homemade Tee-Extractor for Solar Collectors

Gary

strider3700 · 07-15-11, 10:43 PM

fin making is slowly continuing when both kids are awake and happy and outside and there is nothing ultra dangerous around forcing me to watch them every second.

For the rest of the time we started digging the hole to put the tank in. I decided the easiest way to go was to sit the lid in place add some space for insulation and just remove the grass. myself the 1 and 3 year old then started digging. They are actually pretty good at softening an area up. We only got maybe 6" down across the entire thing before rain called a halt to the fun.

Since the lid was off the tank I took some internal measurements and worked out 164.57 gallons if I leave the water level 2" below the lid joint.

Having put this much work into everything I do have to admit I felt a small twinge of concern reading in the flyers tonight that $1700+tax buys a brand new certified 20 evacuated tube collector, pump, 60 gallon storage tank, flat plate heat exchanger, and controller from a local hardware store so it should be no shipping.

It would need to be installed by a pro to qualify for tax credits which would probably make it break even but It looks a lot like $2000 would get you a warrantied approved system.

What I don't know is how 20 evacuated tubes will compare to a 136"x76" fin and tube flat plate collector. And I have more then double the storage and data logging as well as far more advanced control of the pumps. The add also said starting at so who knows what they hammer you with.

we'll see. No going back now

randen · 07-16-11, 05:12 AM

Strider 3700

I had built my own panels 6 pcs Copper fins 3/8 tube risers aluminum box tempered glass. Materials about $1200.00 cnd. What I think I save in labour I spend in better materials. Do they work better than evacuated tubes, don't really know. I had found a couple sites where it seamed Flat Plate offered up more BTUs but at a lower temp than EV's. What I can tell you that here in southwestern Ontario we have enough domestic hot water for everything. We have the electric back-up disabled except when we have more than 2 days no sun we will flip it on. Almost completely 2 months solely solar. In the winter when the sun is low hitting the panels more direct as they are on vertical walls and we get a full day of sun we can actually heat the house for 24 hrs. Be persistant the reward is there.

Randen

strider3700 · 07-16-11, 04:49 PM

Doing a bit or research a 20 tube system typically has 20 sqft of actual tube coverage collecting energy. my system will have closer to 72 sqft. evacuated tube isn't anywhere near 4 times as efficient so I should be well ahead on heat collected and have 100 gallons more to store that in.

that makes me feel a little better

Daox · 07-16-11, 09:26 PM

Evacuated tube is only more efficient if there is a very large difference in collector temperature vs ambient. The crossover point on the image below shows the flat plat is vastly better until the delta T hits 100F.

Gary has this info on builditsolar:

GaryGary · 07-16-11, 09:47 PM

Quote:

Originally Posted by Daox

Evacuated tube is only more efficient if there is a very large difference in collector temperature vs ambient. The crossover point on the image below shows the flat plat is vastly better until the delta T hits 100F.

Gary has this info on builditsolar:

The SRCC site has the tested efficiency curve intercept and slope values for all the collectors they certify, including lots of flats and lots of evacs:
SRCC Ratings

One interesting thing is that the evac tube collector efficiency curves vary a lot for each other, but as Tim says they all tend to start with fairly low maximum efficiencies, but the their efficiency curves are very flat, and at some high temperature they tend to intersect with the flat colelctor efficiency curves.

Gary

Solaris · 07-17-11, 09:26 PM

It is true that flat plate collectors are generally more efficient for heating domestic hot water, which is a moderate temperature application. Vacuum tubes can be better when small quantities of hotter water are needed closer to boiling point, but at those temperatures the Glycol breaks down into an acid and can destroy a presurrized system in a short time. Too much heat is the biggest design problem with some solar (unless it is drainback), high heat cuts the life of the sytem in half.

Here is a good list from Heatspring Magazine's 2011 review:
Top 50 Most Efficient Solar Thermal Collectors on the Market
Top 50 Most Efficient Solar Thermal Collectors on the Market | HeatSpring Magazine
48/50 are flat panel collectors, only Sunda in spots 21 and 24 are vacuum tube.

There is also a lot to be said about durability and longevity of flat panel collectors working in the field for more than 30 years. Chinese tubes that I have seen turn cloudy after just a few years, and are disposable after 10 years.

Strider, I am guessing the add you saw was from Slegg, I know they are blowing Chinese tube crap out to upgrade to better Austrian flat panels.

Solar Mike · 07-17-11, 11:50 PM

Many of the newer design evac tube collectors use a heat pipe to collect the heat from the fin and move it to the water in the header condenser section. This mechanism isnt as efficient st collecting heat as a flat panel with the same area at lower temperatures, because the heat pipe, which typically contains a few cc of water inside an evacuated tube doesn't contain enough water vapor to convey much heat until the pipes warm up to > 50 Celsius.

Sales people will try to tell you they are more efficient, which they are, but only at much higher temperatures than you really require.

From my experience, if you use the evac tubes systems, then for a family of 4 and a 300 liter water cylinder you require 50 tubes. The quality of some of the cheaper tubes are unknown and possibly suspect. The failure normally being loss of vacuum in the glass envelope or the evacuated heat pipe loosing its vacuum and thus failing to move any heat. Quality components should last the distance. The same can be said for flat plate collectors, here in NZ many commercial systems over the past 10 years have failed completely, see Solar Water Heating - Corrosion and Performance Issues in New Zealand

At least DIY flat panels can be easily built from quality components that you have control over, this cannot be said for cheaper commercial systems.

07-16-11, 09:26 PM	#57
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Evacuated tube is only more efficient if there is a very large difference in collector temperature vs ambient. The crossover point on the image below shows the flat plat is vastly better until the delta T hits 100F. Gary has this info on builditsolar: __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

07-17-11, 09:26 PM	#59
Solaris Uber Effecient Join Date: Feb 2011 Location: Vancouver Island Posts: 18 Thanks: 0 Thanked 2 Times in 2 Posts	Flat Plate Collectors It is true that flat plate collectors are generally more efficient for heating domestic hot water, which is a moderate temperature application. Vacuum tubes can be better when small quantities of hotter water are needed closer to boiling point, but at those temperatures the Glycol breaks down into an acid and can destroy a presurrized system in a short time. Too much heat is the biggest design problem with some solar (unless it is drainback), high heat cuts the life of the sytem in half. Here is a good list from Heatspring Magazine's 2011 review: Top 50 Most Efficient Solar Thermal Collectors on the Market Top 50 Most Efficient Solar Thermal Collectors on the Market \| HeatSpring Magazine 48/50 are flat panel collectors, only Sunda in spots 21 and 24 are vacuum tube. There is also a lot to be said about durability and longevity of flat panel collectors working in the field for more than 30 years. Chinese tubes that I have seen turn cloudy after just a few years, and are disposable after 10 years. Strider, I am guessing the add you saw was from Slegg, I know they are blowing Chinese tube crap out to upgrade to better Austrian flat panels. __________________ Solaris To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

06-19-11, 07:20 PM	#51
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	I was doing a little research and I'm thinking about going with a conventional 60 gallon water heater rather then one of those lifetime plastic heaters I had originally planned on. I can get a 60 6 year which will need some basic upgrades and better insulation for $370. upgrades will be about 100 with superinsulated box. a 12 year is $550 and will still need some more upgrades and more insulation. plastic lifetime tank is $1400... I need to decide if a bottom inlet is better then top for the cold. I'm thinking it makes the plumbing a bit easier but this is without drawing it out.

06-29-11, 11:34 PM	#52
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	I'm getting ready to make some fins for my water heating collectors and was hoping to use a bunch of "old" aluminum I have lying around. I have some 12" roll flashing. some 18" valley flashing, some 12" L flashing, some 8" L flashing and a Bunch of 7.5" step flashings. I was thinking just go with 6" cut the big stuff down to 6" and leave the 8" and 7.5" stuff big with some overlap but after forming it for my 1/2" pipe that means the width is going to be somewhere between 4 and 4.5" which seems tight. my glass which sets the collector size is 34"x76" so that's 8x76"(minus frame/gap/header) risers or 18x 34" risers depending on if I go vertical or horizontal for the glass. Horizontal is more stealth for my location(guerilla install) but it's a bunch more 1/2" 3/4" T's. Any thoughts or suggestions?

07-15-11, 10:43 PM	#54
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	fin making is slowly continuing when both kids are awake and happy and outside and there is nothing ultra dangerous around forcing me to watch them every second. For the rest of the time we started digging the hole to put the tank in. I decided the easiest way to go was to sit the lid in place add some space for insulation and just remove the grass. myself the 1 and 3 year old then started digging. They are actually pretty good at softening an area up. We only got maybe 6" down across the entire thing before rain called a halt to the fun. Since the lid was off the tank I took some internal measurements and worked out 164.57 gallons if I leave the water level 2" below the lid joint. Having put this much work into everything I do have to admit I felt a small twinge of concern reading in the flyers tonight that $1700+tax buys a brand new certified 20 evacuated tube collector, pump, 60 gallon storage tank, flat plate heat exchanger, and controller from a local hardware store so it should be no shipping. It would need to be installed by a pro to qualify for tax credits which would probably make it break even but It looks a lot like $2000 would get you a warrantied approved system. What I don't know is how 20 evacuated tubes will compare to a 136"x76" fin and tube flat plate collector. And I have more then double the storage and data logging as well as far more advanced control of the pumps. The add also said starting at so who knows what they hammer you with. we'll see. No going back now

07-16-11, 05:12 AM	#55
randen Uber EcoRenovator Join Date: Apr 2011 Location: Strathroy Ontario Canada Posts: 657 Thanks: 9 Thanked 191 Times in 129 Posts	Strider 3700 I had built my own panels 6 pcs Copper fins 3/8 tube risers aluminum box tempered glass. Materials about $1200.00 cnd. What I think I save in labour I spend in better materials. Do they work better than evacuated tubes, don't really know. I had found a couple sites where it seamed Flat Plate offered up more BTUs but at a lower temp than EV's. What I can tell you that here in southwestern Ontario we have enough domestic hot water for everything. We have the electric back-up disabled except when we have more than 2 days no sun we will flip it on. Almost completely 2 months solely solar. In the winter when the sun is low hitting the panels more direct as they are on vertical walls and we get a full day of sun we can actually heat the house for 24 hrs. Be persistant the reward is there. Randen

07-16-11, 04:49 PM	#56
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	Doing a bit or research a 20 tube system typically has 20 sqft of actual tube coverage collecting energy. my system will have closer to 72 sqft. evacuated tube isn't anywhere near 4 times as efficient so I should be well ahead on heat collected and have 100 gallons more to store that in. that makes me feel a little better

07-17-11, 11:50 PM	#60
Solar Mike Helper EcoRenovator Join Date: Apr 2010 Location: Wellington, New Zealand Posts: 61 Thanks: 0 Thanked 6 Times in 5 Posts	Many of the newer design evac tube collectors use a heat pipe to collect the heat from the fin and move it to the water in the header condenser section. This mechanism isnt as efficient st collecting heat as a flat panel with the same area at lower temperatures, because the heat pipe, which typically contains a few cc of water inside an evacuated tube doesn't contain enough water vapor to convey much heat until the pipes warm up to > 50 Celsius. Sales people will try to tell you they are more efficient, which they are, but only at much higher temperatures than you really require. From my experience, if you use the evac tubes systems, then for a family of 4 and a 300 liter water cylinder you require 50 tubes. The quality of some of the cheaper tubes are unknown and possibly suspect. The failure normally being loss of vacuum in the glass envelope or the evacuated heat pipe loosing its vacuum and thus failing to move any heat. Quality components should last the distance. The same can be said for flat plate collectors, here in NZ many commercial systems over the past 10 years have failed completely, see Solar Water Heating - Corrosion and Performance Issues in New Zealand At least DIY flat panels can be easily built from quality components that you have control over, this cannot be said for cheaper commercial systems.