Installing A Solar Domestic Hot Water Heating System

Installation of a solar assisted water heating system

The system is designed to add in to a hot water heater to reduce the energy.

Butler Sun Solutions sell a complete “Solar Wand” installation kit. The kit is unique in the solar industry in many ways – click the image at left for a complete system diagram. Most innovative is the solar wand heat exchanger that was designed and patented by Barry Butler. This device allows the most simple retrofit to an existing hot water heater – it simply drops into the tank, replacing the existing hot water outlet plumbing! The wand has about 2 square feet of surface area that contributes heat to the tank.

NOTE: See this page – I decided to install the wand in a separate 40 gallon storage tank that then feeds into the propane water heater, since this will improve the system efficiency due to the greater temperature difference between the incoming well water and the heated collector fluid.

The 4 solar collectors mount to the south side of my house, along with the 20 Watt solar panel that will power the circulation pump. This pump will be mounted above the water heater tank in the basement and will circulate solar heated water from the collectors, through an insulated umbilical of 3/8″ copper pipes to the Solar Wand in the tank.

Most solar collectors are mounted to a sloped roof that faces south to optimize performance, but my roof faces east/west. So my only option was the vertical south wall which is a slight compromise, so I added one extra collector to ensure good heat in the winter months. Solar panels and collectors need direct sun to work but collectors are more forgiving of off-axis sun light than solar electric panels.

There are many things about the design of this solar heating package that I really like:

The Solar Wand simplifies the plumbing. It’s a “no sweat” plumbing job since no copper soldering is required. All connections are done with swage fittings and unions with nuts that tighten to make the connection.
The automatic over temperature and pressure system is unique in the industry.
The collector frames come in a variety of colors to match the building, the red/brown I selected matched our paint trim very closely.
The simple structure for mounting the collectors consists of vertical mounting rails. It only took an hour to mount them – with the help of 4 friends and staging.
The insulated umbilical that carries heated antifreeze fluid is made of flexible 3/8″ copper tubes. 2 additional wire cables are tied to that for signals and PV power.

House before

View of before and after showing the collectors and PV panel mounted to the south wall of my home.

The total purchase price of the kit was around $3000 ($3500 as of October 2007). However my net cost will be around $1500 after the Maine state refund and federal tax break.

After placing the order for the solar kit in early July, I filed an application with the Maine State Energy Program for the 25% refund that they offer on small scale solar installations. The refund incentive was just voted in to law in 2006 and it has encouraged many people to “take the plunge”! I received my 25% refund check on October 10th 2006. This system is SRCC certified and is eligible for the 30% solar federal tax credit too.

I used RetScreen software to calculate my Return on Investment, which works out at 4.6 years based on the design and site of my specific installation. Click the graph below to see a detailed report. Allowing for inflation and increasing propane prices it shows that after 25 years I will have saved over $11,000 in offset heating costs! Pretty impressive.

The first box of parts arrived yesterday, 4 solar collectors:

On opening up the boxes I was immediately impressed by the thoughtfulness of the packing. Aside from being packed well enough to survive Fedex ground, I noticed all these little baggies of parts that were attached to each sub-assembly. Then I noticed that they even provided electrical tape, Teflon plumbing tape and ABS cement. Wow, that’s thorough!

The installation Manual and Owner’s Manual are both thick and extremely detailed. I had already downloaded the Installation Manual weeks ago and read it through page by page. My impression then was that the installation job did not seem too daunting if taken carefully and slowly. But today looking at ALL these parts it feels overwhelming, but then that’s how I felt when I started on mysolar heating system for my workshop!

I called Barry Butler to get some clarification about some of the parts that I didn’t recognize and to get a better idea about how the collectors mount. He spent nearly an hour talking with me about the system design theory and how it all goes together. Since he is in the process of revising the manual, I will be a beta tester for some new hardware and design revisions.

I realize now that I will need several strong friends to help me get these collectors mounted on the wall, and Barry helped me figure out the best strategy for assembling and mounting the collectors. It’s not that they weigh that much – the 4 solar collectors and mounting brackets are under 90 pounds total, it’s just getting them hoisted up there that will be tough. Most folks would be mounting these to a roof, which has it’s own challenges. I also would guess that most homeowners will contract a professional installer to do the work, but I’m a do-it-yourself kinda Guy!

Jul 15-17, 2006. Time Invested today:
1:00 Painting, and modifying parts/
0:45 Hardware store run for stainless screws.
3:00 Studying manual, and assembling overflow to collector.

Day 2
Looking at all the exposed sheet metal screws, I recalled how the

mounting screws I used on my other solar collectors (at left) have

rusted, so I decided to replace them with stainless steel. A box of

100 screws was only about $6.00 – there are over 50 screws involved

in the collector mounts and brackets and it only took a few minutes

to replace them all.

I also decided that since the collector frames come in a nice brown color that I would

paint all the other exposed shiny metal parts. This includes the mounting rails and

PV frame. I used Krylon brown primer which matches exactly.

Day 3
I had considered making the PV panel mounts from wood, but

decided against it as it would make installation difficult. So I

made up some aluminum angle brackets that will support the

panel at an angle. All the bolts and screws are stainless. I

masked off the PV sprayed the whole frame with brown

primer to visually integrate it.

Day 4
After measuring the distance between the window frames on the house, I realized

that I needed to cut down the mounting rail by 1.5″. I hadn’t noticed this issue until

my neighbor John Rogers came by to asses the installation strategy. I’m grateful

for his considerable experience as a home builder. It was at this point that he

suggested that we install his staging rather than try and use 2 ladders

That evening I pre-assembled the top right panel to it’s mounting

rails in my workshop, and installed the overflow tank and plumbing

along the top. This is a very impressive part of the system design

which allows the water in the panels to boil over into the expansion

tank in the same way that an automobile radiator does. In fact there

is a standard radiator cap used for this purpose! This crucial piece

of the design is what makes it maintenance free and very unlikely to fail due to excess temperature or

pressure. I have come to really appreciate all the considerable thought that has gone into this design.

I decided to run the wire that goes to the PV panel through the mounting rails to keep

it out of sight and reduce the weather exposure. This 50 foot wire will follow the

plumbing umbilical run all the way to the solar powered pump above the water heater.

There is also a small sensor mounted to the end of the expansion tank that responds

to a float in the tank. If the tank level falls too low, this sensor lights a small red light

n the home. I ran this wire through holes in the rails too.

I spent over an hour looking at the manual to get it clear in my head how the Solar Wand

plumbing will assemble together after it is installed on the hot water tank. It is like a

puzzle with a number of options for connecting the parts. Again I am impressed by

the considerable attention to detail and the unique and unorthodox plumbing design.

This system has the “fingerprints” of an inventor who thinks outside the box and reminds

me of my own design methodology!

The day before installing the collectors, my neighbor John Rogers (in the red shirt)

came by to look over the equipment and discuss installation strategy. He is an

experienced home builder, and he helped convince me that using ladders would

be trouble. So we went over to his place and got his fancy aluminum staging

equipment and put it up in preparation for the next day. This is very cool

equipment and will definitely make the job much simpler!

John quickly mounted the support

brackets to my window frames with

1/4″ lag screws while I steadied the

ladder and handed him tools. That’s

me in the white shirt! Since the

platform remains several inches

from the wall we will be able to lift the collectors up between the staging and the wall. This will really make the job easier,

and having a work platform while attaching the mounts and finalizing the plumbing will be very helpful!

Day 6 – installing collectors

Jul 20, 2006. Time Invested today:
0:15 Site and tool preparation.
0:45 Installing collectors.
0:10 Installing PV panel.

At 4:30pm my neighbors all showed up for the “Solar Barn Raising”. We spent some time discussing the assembly and mounting sequence and strategy.

It seemed best to mount the top 2 collectors to the 3 vertical support rails first.

The assembly sequence required some thought because there is an

interaction on the center support rail between the plumbing connection

and the way the angle brackets on the solar collectors have to slip on

over the bolts sticking out from the rails (see right). It was simplest

to connect the pipe, then insert the bolts and secure them with a washer and nut.

Handing the collectors up to the scaffold

It was a relatively simple matter to pick up the whole rig and carry it

up to the staging. We were a bit concerned about stressing the

plumbing so we paid close attention to keeping everything lined up.

Our first problem arose when the center rail would not go flat

to the wall. We found that the black bracket at the left end of

the expansion tank was hitting the window sill. I marked it

with a pencil, and cut a notch in the sill and a corner off the

bracket. Lucky I had just bought a cordless reciprocating

saw last week!

Next we drilled starter holes for the 5/16″ stainless steel lag screws, and screwed them in tight with cordless drills

that I had set up with all the right bits and sockets. We put

all 6 screws in — one at the top and bottom of each rail.

That’s all that holds the solar collectors to the wall – 6 lag

screws! They are only supporting about 90 lbs. (the kit

provided galvanized 5/16 lag screws, but I chose to use

/8″ stainless ones).

Tightening the union between the collectors

I thought I would demonstrate how

light these 20lb collectors are as I brought

out the 4th one from my workshop.

We connected the plumbing as before

to make installation easier.

Lifting it up and lining it up was relatively easy,

except that the holes in the middle didn’t line

up with the bolts in the middle rail. So we

removed the lag screw at the bottom of that

rail and moved it over until everything lined up.

The left and right ends attach to brackets on

the rails with sheet metal screws into the

side of the collector casing (see below right). I used stainless steel screws throughout.

So far it has taken the 4 of us about 45 minutes and the job looks

really neat. The plumbing will connect at the right end and go

through the wall into the house at the bottom corner of the collectors.

From there the umbilical will drop down the corner and into the

basement. From there it’s another 12 feet across the ceiling to

the water heater.

The last thing to install is the PV panel that will power the

circulation pump. I was able to hand it out the bedroom

window and hold it in place while John and Tom secured

it to the wall with long stainless steel screws. I decided

on a low tilt angle that will optimize the winter sun.

4 collectors and PV panel all neatly mounted

Thanks to the use of John’s staging the job was complete in an hour and no humans were hurt

in the process! It’s great to have so many experienced and helpful friends and neighbors!

The final appearance is even more pleasing that we expected. The design integrates

architecturally very nicely! The angled surfaces the black absorber plates inside the collectors

even line up with the siding and look like a continued line.

For the curious – here’s how the collectors interconnect. The clever patented plumbing scheme allows them to interconnect

in a variety of ways and locate the inlet/outlet on one end.

After the guys left, I stapled the PV wire down and also

added a ground wire to connect the frame of the PV to

the collectors. I used a star washer under the

electrical terminal to ensure good electrical connection.

Someone has since pointed out that I should secure

the ground to the actual frame of the PV with a bolt

that threads right into the frame – not just the mounting

bracket. I’ll probably change that next time I’m up there. Since the copper pipe in the collectors

will all be grounded to the house plumbing I was thinking that grounding the frames was

secondary for the collectors anyway.

I will run a ground wire down to a ground rod below the PV later. I have learned the hard way

that grounding is essential. I will also splice the PV wire to the orange power cable later.

That wire will run all the way to the pump above the water heater.

Day 7 – planning plumbing

Jul 22, 2006. Time Invested today:
0:35 Walking through the job and considering options
0:45 Researching electric water heaters
2:00 Buying the wrong heater, going back and getting the right one

My neighbor John Rogers (the building contractor) and I took some time to plan the

plumbing strategy. We decided that the plumbing penetration through the exterior

wall could go right behind the collector inlet. When we measured inside, we found

that the hole would come through right at the top corner of the dining room

wall – perfect! The hole in the floor needs to come out along the wall a bit to line up

with the drywall downstairs.

My wife approved this concept, so long as I box in the plumbing in wood to match

the window frames. A simple job for me as an experienced woodcrafter.

Down in the basement the hole penetrates behind a joist above the

electrical panel. By opening up the gap above the drywall a bit we can

pull the umbilical up without too much trouble. Then the umbilical

can be attached to the joists along the exposed ceiling about 12

feet to the water heater closet.

We decided not to try running holes through the joists for the

umbilical, since it would stress the copper pipe too much and

probably damage the insulation too much to pull it through all those holes. It can be strapped up

with U brackets, and boxed in if we ever finish the ceiling in the basement.

Pressure tank and water heater in closet

Looking at the location of the 40 gallon water heater John observed that it

looked small. It suddenly occurred to me that it might be much more

efficient to install another 40 gallon tank (electric water heater) to the right

of the propane heater and use the Solar Wand to pre-heat cold water

entering this tank that would then feed the water heater. The higher

Delta-T between the cold water and the collector would dramatically

improve the Wand’s efficiency! A new tank would only cost about $200

or so and be very simple to install. I emailed Barry Butler asking his thoughts on this idea.

I took a drive down to Lowe’s and Sears to look at water heaters. I learned that 40 gallon units do sell for just under

$200, and Lowe’s also have a 50 gal. unit for about $250, both are 20″ wide which will just fit in the closet. I have

emailed Barry Butler at Butler Sun Solutions to see if he concurs with this plan before I go and buy a tank. It sure

would simplify the plumbing layout and make for a neat system.

John also observed that I was lucky to have my (blue) well pressure tank in my heated basement where it pre-heats

he incoming water somewhat. This had never occurred to me before, apparently many such tanks here in Maine

are in the unheated basement where temperatures approach freezing in the winter.

CHANGE OF PLAN!

Barry emailed me back and agreed that the extra tank will be a good idea. He sent me a new

diagram (at left) and reminded me that the tempering valve will be on the existing hot water

heater to prevent scalding.

So I’m off to Lowe’s today to pick up a 50 gallon tank. It will be much easier to pre-install the

wand and all plumbing before sliding the tank into place in the closet. Then I can just re-plumb

the feed lines once it is in place. This will make for a very neat installation.

When I returned from Lowe’s with the 50 gallon tank that I found for $209.00 I Immediately opened up the box to check the outlet port to be sure that it would

fit the Solar Wand. Oops! It has a male thread (see left). Back to Lowe’s again

to find a tank with a female opening. I took a short length of 3/4″ copper pipe

which has the same OD and the Wand so I could check the openings. I found a 40 Gallon Whirlpool tank with only one heating element in it for $199.00. It has 3/4″ female connections, but it comes sealed with plugs (at right) that require a 1/2″

ratchet tool to remove. I’ll have to borrow a tool from a neighbor to open this up and see if the Wand will fit.

When I removed the plugs at the top of the tank, I still had the tank in it’s box, and did not

notice the connection on the side. I also noticed that this tank does not have a dip tube

for the top cold inlet so I called Whirlpool to ask about this. The helpful person explained

that this tank is designed for a mobile home and that the cold inlet should be connected

to the bottom inlet. This will make the plumbing a bit more annoying, but I’m committed

to this tank at this point.

When I opened up the box in my workshop I found that the

Wand would not fit past the indented ring right below the

threads on the hot outlet. In the Solar Wand Installation

Instructions it is noted that some tanks have this issue,

and one can use a Dremel or round file to open up the

hole. I used a diamond coated cutter, and it only took

a few minutes. I vacuumed out the hole, and used a

wire brush to clean out any debris from the threads.

After studying Barry’s revised layout, I set to work building up some of

the plumbing sub-assemblies. I had some parts laying around, and will

go to the hardware store to get other parts once I have planned out all

the plumbing. It will help to have the tank in place before I finalize the

plumbing layout

Day 8 – pulling the umbilical

July 29, 2006. Time Invested:
0:45 Drilling holes
0:40 Pulling the umbilicalJuly 30, 2006.
0:30 Connecting to the collectors
0:20 Strapping up the umbilical in the basement
0:15 Adding new outlet behind new tank

Today I began by drilling a hole through the outside siding,

and then in the drywall inside. I got a surprise when I opened

up the drywall as there was an active ant nest in there. I use

an environmentally friendly bug spray to kill them all off

before proceeding. I didn’t want to harm “Phil” our giant

philodendron that wraps around the top of all the windows

in the dining/living room!

I had previously painted the provided weather seal to match and had to cut it down a bit, then

tucked it up under a shingle.

I then drilled a hole through the interior floor to access the basement.

My friend John Grill came by to help with the pulling. Before we pulled the pipe, we pulled the 2 cables

through from the outside and down to the basement. The orange one brings PV power down to the

pump, and the gray one carries signals from the thermistor mounted to the collector outlet pipe and

the float sensor in the overflow tank. Down in the basement John and I carefully unrolled a length of t

he umbilical being very careful not to stress the copper. We removed 4 feet or so of the prepared

insulation from the end. This un-insulated section will be pulled through the 1.25″ hole in the exterior

wall and then bent to meet the collector outlet.

Here’s John preparing to feed the pipe up to me above on the first floor.

Once we got the pipe pulled through into the first floor, I bent an “L” so that

we could feed that 4 ft. length through the wall. Then on the outside I bent

another “L” for the line that feeds up to the collector outlet. The collector

inlet shoots straight into an “L” on the collector. I happened to have a nifty

tubing bender from a previous project, I got it from Harbor Freight Tools

for about $7.00. You can’t bend small diameter copper pipe to this tight a

radius without the proper tool or the wall will collapse. It was getting

dark so the shot at right was taken with a flash.

Next day I completed the connections by cutting the pipe to

length with a pipe cutter, and deburring the inner edge, then

the pipe just slips into the swage fitting and I tightened down

the nuts with adjustable wrenches. I really like the simplicity

of these connections! I hope they hold up to the extreme

temperature variations in Maine though.

I wrapped the exposed pipe with lengths of boiler insulation that came with the

kit for this purpose, and tucked some of it firmly into the hole to form a gasket

seal. Then I covered all the plumbing with a nicely prepared and painted section

of downspout that is split so that it can go around the pipe and then screw

down to the collector frame at top and bottom. I had to cut and modify this a

bit at top and bottom to accommodate the weather seal at the bottom. They

even provided a little weather cap formed from another piece of matching

downspout, this screws onto the top of the downspout with sheet metal screws.

Back down in the basement I used the provided wire ties to

strap the cables to the insulation. It’s about a 10 foot run

across the ceiling to the closet.I then strapped it to the

joists with 1 1/2″ conduit clamps that I had previously

bought for this section.

In the closet I noticed that the outlet where the power vent for my existing

propane water heater would be permanently blocked by the new 40 gallon

pre-heat tank that will totally fill that space. So I installed another outlet above

it – using a GFCI outlet that I had laying around. Note the umbilical and cables

entering from the upper right. I’ll bring in the new tank tomorrow.

Day 9 – plumbing the pre-heat tank

July 31, 2006. Time Invested:
3:40 Plumbing in the new tank
1:00 Finding the leaky pressure relief valve and cleaning upAugust 1, 2006. Time invested:
1:00 Get replacement valve and installing it

I really should have started in the day time so I could have made a run to the hardware store if I needed something. Murphy rules when you are plumbing… I started at 8:00pm. It was pretty easy to get the pre-heat tank in place, it sits right up against the propane fired water heater. I set it on some lengths of treated 2X4s to keep it off the damp cement floor.

I used the revised layout that I got from Butler Sun Solutions that shows how to plumb in a solar pre-heat tank. I began by shutting off the water main and draining the plumbing from the bottom of the hot water heater. Oh, yes, before that I had shut off the gas and power to the water heater and I took a long shower to cool off the tank. I attached a garden hose to the heater tank drain, and ran it outside.

Note the unusual connections to this tank. I accidentally bought an electric water heater designed for mobile homes. It has connections on the side as well as the top, and no dip tube for the cold inlet at the top, so I had to use the lower inlet on the side for the cold feed.

It wasn’t too hard to plumb in the cold line. There need to be 3 shut off valves so that the tanks can be configured as a normal hot water heater, or fed through the pre-heat tank. The pre-heat tank also needs its own shut-off.I moved on to plumbing the wand outlet into the cold side of the propane tank using a T that allows that original water heater to be fed from cold, or solar heated water.

Then I plumbed in the tempering valve on the hot outlet of the water heater (upper left in the image at right). It is hidden by the white combustion exhaust pipe at the upper left of the image to the right. 3.5 hours – not bad!

Then the trouble began. I turned on the cold main and filled each tank — watching for leaks. I stopped twice to tighten unions and swage fittings. Once the system was holding pressure I noticed this dripping sound. “This can’t be good” I thought. Sure enough the over pressure valve next to the main pressure tank had sprung a leak. (For those without wells, you need a pressure tank to store pressure so the well pump doesn’t run every time you run water.) This little valve had rusted out, and I noticed that the pressure gauge was sticking too. Darn! There was a lot of water to mop up — and more importantly no chance of taking another shower tonight. Did I mention it has been 85F and humid as a sauna all day?I had to shut off the main again and attach the garden hose to the inlet drain to relieve the pressure. Shown below are the new pressure gauge and below it the new pressure relief valve.

August 1, 2006 After an early morning run to the plumbing supply, I was able to replace the defective relief valve and install a new pressure gauge. Now I could pressurize the whole house and fire up the water heater. It’s another hot, humid day and much to be done.

I decided to install the thermal cutoff switch next. According to the well written Installation Manual, this needs to be at the top of the tank and touching the metal of the tank wall. I opened up the electrical panel at the top of the tank and removed the inner metal wiring box to expose the insulation. I cut away the wires that feed the electric element — I won’t be needing those! Then I cut out a square of insulation for the thermal switch so it could fit down against the tank wall.I pulled the wire out through the electrical fitting and secured the wire. This is a great spot for this important switch. If the tank gets over heated from a really good solar day, this switch turns off the collector circulation pump so no more heat can be added.

Day 10 – plumbing the Solar Wand

August 1, 2006. Time Invested:
4:00 plumbing in the Solar Wand and installing wiring and control panel

Here’s a shot of me test fitting the Solar Wand in my workshop a few days ago. I had to whittle the hole out in the tank a bit more because the upper section of the Wand had some thick places. I had been using just the bottom end to check the hole size back when I was opening up the hole. I’m glad I double checked since it is easier to ream out the hole in my workshop than down in the basement.

I made one small mistake when connecting the plumbing parts to the Wand. I saw that I had 2 parts transposed after I had really tightened down the swage fitting and deformed the ring. There was nothing for it but to go back to the hardware store for a replacement part ($4.80).This part was pretty easy, and if I had not elected to install the pre-heat tank I think a “normal” installation would go very quickly. One must really pay attention to the details and plan out the assembly sequence so that all the parts are rotated so that they clear each other. I particularly wanted to be able to see the red lights on the El-Sid circulation pump. I know from experience that these pumps are so quiet that you need the lights to be able to tell they are running!

It was relatively simple to finalize the umbilical connections. Per the instructions I had identified which tube was which and labeled them with arrows on each one. Cutting them to length and bending them into place was quite simple. One thing I was unclear about with all the swage fittings was how much to tighten them, so I erred on the loose side at first.

I stopped to make a control panel from a scrap of 1/4″ Cherry veneer plywood I had laying around. I mounted this at a convenient angle to the right of the tank. I mounted the provided terminal strip for the signals and hooked up the red LED that indicates low fluid in the overflow tank – it lit up from the power in the PV panel! Then I added my own second terminal strip for the PV wire and mounted one of my own solar powered Differential Temperature Controllers, and connected the sensors and pump to it. Finally I installed the provided temperature gauge. I admire the simplicity and cleverness of using a standard automobile gauge for this. They had even opened up the package it came in and taped a hose clamp to the end of the sensor to make it obvious that the sensor should be clamped to the tube coming from the collector. Very thoughtful!

Note that the red light is on indicating a low reservoir level in the overflow tank above the collectors. This is because I have not yet filled the system with glycol anti-freeze mix, so the tank has only a little fluid in it.

Once again the Installation Manual was quite clear about the filling process. It begins by identifying and naming the 4 valves. I stopped to make up little plastic tags that I tied onto each valve to identify them so I would not get confused. It also makes it easier to follow the steps in manual.There are 2 hoses provided with the kit. One that allows a garden hose to be used to fill and flush the collectors, and a fill drain hose that allows the water to exit the plumbing into a bucket. (This same hose is also used later to siphon anti-freeze mix into the system.) I connected the garden hose to the drain valve on the pre-heat tank and cautiously opened the valve. There were ominous hissing sounds and drips right away. I identified the loose fittings and tightened them down. After 2 more tries I had them all tight and drip free.

Then I left the fill hose open and waited a minute or so for the collectors to fill and to see water come back out. Finally warm water! Another minute or so to purge all the crud from the system.

Again, following the instructions carefully, I shut off the drain valve and let the house pressure push some water out of the radiator cap into the overflow tank above the collectors. I went up and opened my bedroom window to check for the presence of water in the tank and yes there it was! I noted that the little float sensor was just beginning to lift up in the water.

Since it was late in the afternoon there was only glancing sun on the collectors so the water was only slightly warm, but there was enough PV power to run the pump. I was able to use the ON/AUTO/OFF switch on my differential temperature controller to operate the pump.

Test Results

August 6, 2006I attached a HOBO data logger to the system so I could monitor the performance of the system. I made up my own sensor probes to monitor the temperature coming into the Wand and out, the temperature at the top of the tank, and the PV voltage (to track the solar exposure). The HOBOware software allows me to produce a very clear graph of my first full day. The outdoor temperatures peaked in the mid ’70’s and there were no clouds. We used hot water in a normal way, and the graph clearly shows a significant solar contribution (green line). I will add more graphs as I tweak the system.

Aside from all these detailed statistics, we are noticing a distinct change in the pattern of the water heater’s operating time. Our heater uses a forced air vent driven by a loud blower and typically we used to hear it kick on very soon after using hot water. In the last day or so we have barely noticed it running at all! This is a blessing for my wife who uses the daylight basement for her business as it is much quieter now.

One thing I learned was that the sensor that reads tank temperature for the Differential Temperature Controller should not be at the bottom of the tank. That is where it was in the morning on the day of this graph. The other sensor is right at the top of the collectors. The pump turned on before there was enough sun to run the pump, since the PV was not getting direct sun at that point. The bottom of the tank has 60F water coming from our well that keeps the sensor too cool, and when the collectors got above 60F or so the DTC turned on the pump before the water was hotter than the average tank temperature. When I moved the sensor to near the top of the tank later in the day, the pump turned off at a more appropriate time.

Average tank temperature 87.329F

August 16, 2006We just returned from a vacation and I had left the data logger running to monitor the system, taking readings every 60 seconds — the interval for all these plots.

The plot showed a surprising loss of heat each evening, I would have expected to see a continuous gain in stored temperature in the tank, and a much higher temperature overall. I assume that the collectors are reverse thermosiphoning (cold water in the collectors flowing down) in the cool night air which is dropping to the low 60’s and upper 50’s.

I emailed the plot below to Barry Butler, and he suggested that I shut off the Solar Wand flow at the valve right above it overnight, and turn it back on in the am. This would prevent any reverse thermo-siphon from the collectors. I will also turn off the pump using the ON-AUTO-OFF switch on my Differential Temperature Controller. Barry said that they can send me a one-way check valve if this test prevents heat loss.

Average tank temperature 102.097F

Today’s plot (below) shows a cloudy day that shows only moderate solar gain that does not fully offset the water usage for the day. (Each drop in the blue line is a cloud blocking the sun). Keep in mind that the water entering this pre-heat tank comes from my well which is about 60F. Any temperature exiting this tank that is significantly above 60 is a net solar gain that reduces the need for propane to heat the regular water tank up to 100F.

Note that the pump now turns on exactly when the collector becomes hotter than the tank top. I moved the sensor that runs to the Differential Temperature Controller so that it can respond appropriately to the tank temperature rather than turning on (as above) based on the temperature of the lower part of the tank.

Average tank temperature 89.365F

August 19, 2006Below is a plot that shows my test as suggested by Barry (see above) to see if a reverse thermo-siphon effect in the collectors at night was causing heat loss in the tank.

I shut off the Wand circulation using the valve right above the Solar Wand at 7:00pm and opened it at midnight. What happened at midnight clearly shows a thermo-siphon, but the flow is in the normal direction which is peculiar. I would expect to see the red line bump up from a reverse thermo-siphon that would result from the larger cold mass in the collectors falling down through the plumbing. Barry Butler is just as perplexed, since a check valve will not prevent this effect.

Also notice the drop in tank temperature from the cooler water that is now circulating through the Wand from the collectors.

I had not gotten around to filling the system with glycol mixture, so you can see a dip in temperature at 7:45 as I filled in fresh 50% glycol mix.

Average tank temperature 85.462F

August 21, 2006The last few days have been progressively cloudier, with yesterday being fully overcast and rainy all day. The plot below clearly shows that you can’t get solar heat without direct sunlight. Even on days when clouds pass over the heat gain is compromised significantly. The tank temperature is returning to the default 60F from the well.

September 3, 2006Below is an 8 day plot that compares propane consumption to solar gain. You can see s slight decrease in the frequency of the propane heater’s run time when the solar storage tank is hottest on 8/31. It is interesting to see the sudden drop in the temperature of the bottom of the tank (red line) when water is used and cold water is drawn in. The biggest drops are from showers which consume 10-20 gallons, and the propane kicks in right away for 5 to 10 minutes. The hotter the solar heated water is the less time the propane runs . Smaller drops are from the clothes washer and dishwasher etc.

A “dashboard” in the kitchen

August 22, 2006

I have been so obsessed with documenting the system performance that my wife has started teasing me about my “affair” with the water heater. To which I reply “Yeah, once you’ve had a water heater baby, you never go back. They’re hot!”.

But seriously, when I tire of logging data I will need a conveniently located basic system monitor, or a “dashboard” if you will. So I put a dual display up next to the kitchen sink which is right above the water heater in the basement. This unit displays the collector temperature (from the pipe as it enters the Solar Wand just above the tank) and the temperature at the top of the tank. There are 2 lights, a green one indicates the pump circulation, and a flashing red one that warns of low fluid in the overflow reservoir above the collectors.

August 2009 update:
I have found that the low fluid warning has activated about every 14 months or so. It is great to have this warning in a highly visible location rather than hidden in the basement utility closet (where I have a duplicate light). I checked the tank each time the warning came on and it was about 1/2 full and I added 2-3 quarts of 50% glycol solution. I am able to simply reach out the bedroom window to fill the tank – a nice feature of a wall mounted system.

A note to anyone with electronics experience. The displays are digital voltmeters that are connected to LM34CZ temperature to voltage sensors. The sensors produce a signal with 1mV/degree F. So .85 Volts represents 85F. Neat! Check the page 7 of the data sheet LM34CZ to learn how to attach it to a long inductive wire (I used microphone cable).

Click the image at left to see a schematic for the whole dashboard.

I tucked the collector sensor under a piece of insulation wrapped around the tube that enters the Solar Wand, and the tank sensor I poked deep under the tank insulation at the top of the tank. All the wires connect to a terminal strip on the back wall. The sensors and meters are powered by a wall transformer that provides 12 Volts at 100mA.At some point in the future I might even build a graphical display that shows the readings for the last 24 hours.

Installing a check valve

October 21, 2006. Time Invested today:
0:45 Drain system, install valve, re-fill system.

I noticed that as the weather started to drop down around freezing at night that the reverse thermosiphon issue became more of a problem. The fluid in the collectors cools so much that it causes a reverse flow that removes heat from the tank. See the plot below for an example where the night low was 30F. By 8:00pm there is over 8 degrees difference between the 2 pipes above the solar wand. The temperature loss is most visible in the lower part of the tank (red line).

I had talked with Barry Butler about this issue. While it is common in most solar heating applications to use a check valve to prevent this, there is no standard part made for 3/8″ copper pipe. So Barry, being the brilliant inventor that he is, designed his own low flow check valve. He sent me one to beta test and I installed it — see below.

I drained the collector fluid into a bucket at around 8:00pm and cut the tube that exits the Solar Wand and inserted the new check valve. Using a pump, I then re-filled the system, and as you can see in the plot above, once the temperatures equalized the reverse flow was blocked. I am sure that this will prevent significant heat loss in the very cold months to come here in Maine.

An interesting footnote. The next morning I saw that the red light was showing on my control panel (and on my custom dashboard in the kitchen) that indicates that the fluid in the reservoir above the collectors was low. I am able to access this from the bedroom window and verified it was dry — and it was 3/4 full the night before. On thinking about this I realized that I had filled the collectors with 68F fluid and over night it had cooled to 30F causing the system to draw fluid from the tank as it reduced in volume. So I topped up the reservoir with more 50% glycol mixture and the level remained normal afterwards.

System upgrade: adding a heat exchanger and pump

August 21, 2008. Time Invested today:
1:45 Add an external heat exchanger and pump

After 2 years of watching my dashboard display in the kitchen I have decided that the system could be improved. The maximum temperatures I would see at the top of the storage tank on a clear sunny day would be 90F and often in the low 80’s. I decided that the weakest link in the system is the Solar Wand itself since it only has about 2 sq. ft. of surface area to transfer heat.

I decided to add an external heat exchanger with nearly 3 times the surface area. I researched heat exchangers and found a really good deal on eBay ($89.00) for a 20 plate, flat plate heat exchanger.

This unit has stacked plates that allow the 2 fluids to interleave within. I built an insulating box for it out of 2 inch blue foam board wrapped in aluminum tape. I figured the foam might melt if it got too hot, so the tape should reflect the heat back. Also it just looks kinda NASA tech cool!

I also found a good price on a 3 Watt El-Sid pump. This low wattage pump would not require that I add another solar panel to power it as I already have a 20 Watt panel running the original 10 Watt pump. The extra 10 Watts in the original design accounts for my northern latitude and gives a bit of headroom. Theoretically I should add another 5 Watt panel, but adding a mere 3 Watt load to the 20 Watt panel has not compromised performance as far as I can tell. In fact performance of the system is way up!

My plumbing strategy was to disconnect the tube coming from the collectors as it enters the Wand and move it over to the input of the new heat exchanger. Then come out of the new unit and back into the Wand. This makes the flat plate HX the primary unit and the Wand now operates from the remaining heat.

I installed a “T” in the cold water line that feeds down into the bottom of the tank from the outside and put the new (red body) pump there so that it can pull water from the bottom of the tank and pump it through a flexible hose to the heat exchanger. I used a flex hose because the whole addition is really tight and I wanted the option of flexibility. I then plumbed the output from the heat exchanger right into the top of the tank. This particular tank has 2 ports on the sides and 2 on the top. So I had an unused cold inlet at the top that I could use. Strangely this port does not have a dip tube inside, which is actually ideal for my retrofit as I want the hot water to remain at the top.

I also added a second solar powered differential temperature controller that reads the temperature of the tube just before it enters the new heat exchanger and compares that to a sensor about 14″ from the top of the tank. Since I manufacture these controllers I get them for free! Click here to purchase one.

I am very pleased with the performance of this upgrade. Now I am seeing temperatures over 110F at the end of a good sunny day, often over 116F. This is an average of 20 more degrees. Since our well water is about 65F at this time of year that is a 45-50F improvement for the water entering our propane water heater which is set at 115F. It is running much less often now for sure.

Documentation

I have documented the increased performance of the new external Heat Exchanger.

Below are 2 graphs, one from October 25, 2006 right after I had gotten the system dialed in, and the other from September 11, 2008. The biggest difference is the heat gain as measured at the top of the tank:
2006 went from 82 to 105 = 23F temp rise
2008 went from 68 to 112 = 44F temp rise. A 21F improvement!

The difference is that I have gone from 2sq.ft. of heat exchanger surface area to more than 8 sq.ft. Clearly this improves heat transfer efficiency.