Water heat storage for solar hot air system.

menaus2 · 09-14-11, 01:40 PM

I have an idea for coupling my planned 150 sqft solar hot air collector to a EDPM lined water tank for thermal mass storage. I'm wondering if the heat exchange method I'm thinking of will be effective.

The hot air panels will be connected to 3 or 4 in pvc tubing powered by a 500 cfm blower. Im wondering if it would be realistic to plumb this tubing in a zig-zag pattern at the bottom of a 500 gal. or so EDPM rubber lined water storage tank and have maybe aluminum fins siliconed to the pvc pipes underwater to aid in heat transfer. Could heat be absorbed into the water fast enough in this setup? How many linear feet of pvc pipe (or similar material) in the bottom of the tank would be necessary to get a decent temperature drop for the air returning to the panels?

I just hope there's a way to make this work as the design is pretty elegant IMO. You could simply raise or lower the water level in the tank to tune the thermal mass amount, and put in a coil of PEX tubing floating just below the surface for hot water preheating.

Daox · 09-14-11, 02:30 PM

Unfortunately, PVC has too low a melting temperature to use it with a hot air panel.

Also, if you want to store the heat energy, I'd recommend just going with hot water panels, not air.

strider3700 · 09-14-11, 04:31 PM

if you're going through the trouble of having a water tank why not make the collectors water based?

Ryland · 09-14-11, 08:36 PM

If you really really need to do this, use a short stack of car radiators, but even then, I and everyone else has to ask why you are bothering with heating air if you want to heat water? air holds so little heat that it makes a really lousy transfer fluid.

AC_Hacker · 09-15-11, 12:53 PM

Well, menaus2 is planning to use air for his transfer medium. It does have certain advantages, one of which is that if it leaks, it doesn't wreck everything.

So, he could store heat in a rock bin. It would take more space, but it has been shown to work, and it is highly reliable.

Something that may not be obvious is that if a rock bin is used, the preferred method is to circulate the air DOWN through the bin rather than up, because if circulating up, warm paths will become the channels of least resistance and the hot air will self-select those warm channels, thus reducing efficiency & capacity. If circulated down, the bin will self-select cooler paths through the rock bin and thus self-select even warming.

As I recall, fist-sized rocks are the preferred size for maximum capacity of daily heat storage and heat release.

Good luck, menaus2!

-AC_Hacker

Daox · 09-15-11, 02:28 PM

I've heard of problems with rock heat storage and mold growth. Hot and humid air make a pretty good place for that stuff to grow.

GaryGary · 09-15-11, 08:38 PM

Hi,
This is a good writeup on using air collectors to heat water:
http://www.builditsolar.com/Projects...aterHeater.pdf

While I like the EPDM lined tanks, maybe a metal tank is better for air heating collectors.

Al did a hybrid air and water heating collector:
DIY Solar Air Heating Collector with Water Heating

I think that the car radiator scheme that was mentioned above would also work.

Gary

menaus2 · 09-20-11, 11:50 AM

Wow some really great ideas here! After doing some thinking, I don't think that seasonal air heat storage makes as much sense as I first thought it would. Water is by far the superior transfer fluid and will work best at cooling the panels in the summer. Due to the huge storage requirements for space heating, it makes the most sense imo just to use the heat when it's produced. In the long run, it's gonna save me a lot of headaches and frustration to go with something already proven, so I'm gonna go with Al's hybrid air and water heating setup. My lower panel is only maybe 8ft from where the pump will go so that will work nicely. The upper panel is about 2 stories up, so I'll just push the air directly into the apartments and just vent them during the summer. I don't think pumping that high is worth the cost. Now to plan it up for the city permit :P I'll keep everyone updated on the project's progress!

menaus2 · 11-08-11, 11:23 AM

Hey everyone its been a long time, but I want to bring everyone up to speed on the state of the apartment solar project.

I've broken the project into 3 large panels (roughly 3ft wide by 2 stories high each) on the southern exposure of the building.

I've finished work on the first panel. Its an aluminum screen type hot air collector that feeds directly into one of the lower apartment units.

Here is the unit before any work was done. The panels will go the tall spaces between the windows on the far left, right middle and far right.

I decided to build the panel directly on the side of the building as I had no means to hoist up a completed panel. The sides are 2"x8"s that i screwed into the wood siding. The lower air intake part was built over the stone foundation.

I had to break a hole through the foundation (an ordeal in itself) and ran 4" metal ducting into the basement where the blower will be situated. The hole in the foundation and gap between plywood backing and the foundation was filled in with spray foam. The inside of the panel was covered with 3/4" polyiso insulation. It was sealed with silicone caulk and painted with flat black primer spray paint.

Intake closeup. Not pretty, but it will be painted black and covered by the baffle anyways :P

menaus2 · 11-08-11, 11:59 AM

Baffle in place.

Baffle insulated on inside and painted. You can see the 3/4" metal conduit support bar as well. The side 2x8s are painted with several coats of primer and gaps with the siding are being caulked in.

One side of the two layer screen absorber. because of the height of the panel the absorbers are placed in a "sideways V" arrangement. Heres what it looks like from the right side view:
|\|
|/|

Closeup of the screen absorber. This is just the first layer above the baffle.

Detailing the sides. The clear suntuff type polycarbonate will go over this so i want it to look nice

Another shot of the support bar. You can also vaguely see the 2 layers of screen in place.

Polycarbonate starting to go up. Its sealed with silicone caulk and secured with rubber washer roofing screws. There is a vertical wood bar up the middle to secure the 2 polycarb sheets together.

filling in the top.

Top done. The top is insulated on the inside with 2 layers of polyiso. The exhaust wraps around the side of the house into the units kitchen. the ducting is currently insulated with a polyiso box filled with sprayfoam (i like sprayfoam

) The very top is also insulated with spray foam. The exhaust boxing and angled top detailing will wait till spring.

The blower is a Suncourt TF104. It's controled by a plug-in thermostat (commonly used in greenhouses). It has an electronic sensor so i simply extended it from the furnace room into the panel with some thermostat wiring. The exhaust has a hinged dryer vent to prevent backflow.

09-14-11, 01:40 PM	#1
menaus2 Apprentice EcoRenovator Join Date: Feb 2011 Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster Posts: 116 Thanks: 13 Thanked 35 Times in 25 Posts	Water heat storage for solar hot air system. I have an idea for coupling my planned 150 sqft solar hot air collector to a EDPM lined water tank for thermal mass storage. I'm wondering if the heat exchange method I'm thinking of will be effective. The hot air panels will be connected to 3 or 4 in pvc tubing powered by a 500 cfm blower. Im wondering if it would be realistic to plumb this tubing in a zig-zag pattern at the bottom of a 500 gal. or so EDPM rubber lined water storage tank and have maybe aluminum fins siliconed to the pvc pipes underwater to aid in heat transfer. Could heat be absorbed into the water fast enough in this setup? How many linear feet of pvc pipe (or similar material) in the bottom of the tank would be necessary to get a decent temperature drop for the air returning to the panels? I just hope there's a way to make this work as the design is pretty elegant IMO. You could simply raise or lower the water level in the tank to tune the thermal mass amount, and put in a coil of PEX tubing floating just below the surface for hot water preheating.

09-14-11, 02:30 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Unfortunately, PVC has too low a melting temperature to use it with a hot air panel. Also, if you want to store the heat energy, I'd recommend just going with hot water panels, not air. __________________ 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.

09-15-11, 12:53 PM	#5
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 724 Times in 534 Posts	Well, menaus2 is planning to use air for his transfer medium. It does have certain advantages, one of which is that if it leaks, it doesn't wreck everything. So, he could store heat in a rock bin. It would take more space, but it has been shown to work, and it is highly reliable. Something that may not be obvious is that if a rock bin is used, the preferred method is to circulate the air DOWN through the bin rather than up, because if circulating up, warm paths will become the channels of least resistance and the hot air will self-select those warm channels, thus reducing efficiency & capacity. If circulated down, the bin will self-select cooler paths through the rock bin and thus self-select even warming. As I recall, fist-sized rocks are the preferred size for maximum capacity of daily heat storage and heat release. Good luck, menaus2! -AC_Hacker __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker...

09-15-11, 02:28 PM	#6
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I've heard of problems with rock heat storage and mold growth. Hot and humid air make a pretty good place for that stuff to grow. __________________ 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.

09-14-11, 04:31 PM	#3
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	if you're going through the trouble of having a water tank why not make the collectors water based?

09-14-11, 08:36 PM	#4
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	If you really really need to do this, use a short stack of car radiators, but even then, I and everyone else has to ask why you are bothering with heating air if you want to heat water? air holds so little heat that it makes a really lousy transfer fluid.

09-15-11, 08:38 PM	#7
GaryGary Apprentice EcoRenovator Join Date: Nov 2008 Location: SW Montana Posts: 139 Thanks: 1 Thanked 21 Times in 15 Posts	Hi, This is a good writeup on using air collectors to heat water: http://www.builditsolar.com/Projects...aterHeater.pdf While I like the EPDM lined tanks, maybe a metal tank is better for air heating collectors. Al did a hybrid air and water heating collector: DIY Solar Air Heating Collector with Water Heating I think that the car radiator scheme that was mentioned above would also work. Gary

09-20-11, 11:50 AM	#8
menaus2 Apprentice EcoRenovator Join Date: Feb 2011 Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster Posts: 116 Thanks: 13 Thanked 35 Times in 25 Posts	Wow some really great ideas here! After doing some thinking, I don't think that seasonal air heat storage makes as much sense as I first thought it would. Water is by far the superior transfer fluid and will work best at cooling the panels in the summer. Due to the huge storage requirements for space heating, it makes the most sense imo just to use the heat when it's produced. In the long run, it's gonna save me a lot of headaches and frustration to go with something already proven, so I'm gonna go with Al's hybrid air and water heating setup. My lower panel is only maybe 8ft from where the pump will go so that will work nicely. The upper panel is about 2 stories up, so I'll just push the air directly into the apartments and just vent them during the summer. I don't think pumping that high is worth the cost. Now to plan it up for the city permit :P I'll keep everyone updated on the project's progress!

11-08-11, 11:23 AM	#9
menaus2 Apprentice EcoRenovator Join Date: Feb 2011 Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster Posts: 116 Thanks: 13 Thanked 35 Times in 25 Posts	Hey everyone its been a long time, but I want to bring everyone up to speed on the state of the apartment solar project. I've broken the project into 3 large panels (roughly 3ft wide by 2 stories high each) on the southern exposure of the building. I've finished work on the first panel. Its an aluminum screen type hot air collector that feeds directly into one of the lower apartment units. Here is the unit before any work was done. The panels will go the tall spaces between the windows on the far left, right middle and far right. I decided to build the panel directly on the side of the building as I had no means to hoist up a completed panel. The sides are 2"x8"s that i screwed into the wood siding. The lower air intake part was built over the stone foundation. I had to break a hole through the foundation (an ordeal in itself) and ran 4" metal ducting into the basement where the blower will be situated. The hole in the foundation and gap between plywood backing and the foundation was filled in with spray foam. The inside of the panel was covered with 3/4" polyiso insulation. It was sealed with silicone caulk and painted with flat black primer spray paint. Intake closeup. Not pretty, but it will be painted black and covered by the baffle anyways :P

11-08-11, 11:59 AM	#10
menaus2 Apprentice EcoRenovator Join Date: Feb 2011 Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster Posts: 116 Thanks: 13 Thanked 35 Times in 25 Posts	Baffle in place. Baffle insulated on inside and painted. You can see the 3/4" metal conduit support bar as well. The side 2x8s are painted with several coats of primer and gaps with the siding are being caulked in. One side of the two layer screen absorber. because of the height of the panel the absorbers are placed in a "sideways V" arrangement. Heres what it looks like from the right side view: \|\\| \|/\| Closeup of the screen absorber. This is just the first layer above the baffle. Detailing the sides. The clear suntuff type polycarbonate will go over this so i want it to look nice Another shot of the support bar. You can also vaguely see the 2 layers of screen in place. Polycarbonate starting to go up. Its sealed with silicone caulk and secured with rubber washer roofing screws. There is a vertical wood bar up the middle to secure the 2 polycarb sheets together. filling in the top. Top done. The top is insulated on the inside with 2 layers of polyiso. The exhaust wraps around the side of the house into the units kitchen. the ducting is currently insulated with a polyiso box filled with sprayfoam (i like sprayfoam ) The very top is also insulated with spray foam. The exhaust boxing and angled top detailing will wait till spring. The blower is a Suncourt TF104. It's controled by a plug-in thermostat (commonly used in greenhouses). It has an electronic sensor so i simply extended it from the furnace room into the panel with some thermostat wiring. The exhaust has a hinged dryer vent to prevent backflow.