How to Build a Solar
Hot Water System

by

John Canivan

 

 

Printing January, 2004   
Sunny Future Press, Wantagh, NY
Copyright John Canivan 2002
ISBN 0-975498-0-2   $35   

All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means electronic or mechanical without the express permission of the publisher. How to Build a Solar Hot Water System is an easy to follow, step-by-step 87-page book with clarified theory and dozens of illustrations. It was written for anyone concerned about saving money, and saving our little blue-green planet. For more information log onto: www.JC-SolarHomes.com  

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MATERIALS    for collectors

1.                 Two rolls of 50-foot 20” aluminum flashing

2.                 Four .060-inch thick 4X8 sheets of Kalwall from:                       www.solar-components.com  

3.                 Twenty 1X4X8 pine with few or no knots

4.                 Four ½X4X8 CDX plywood

5.                 Four 1X4X8 sheet insulation R value 5 or better

6.                 Clear silicon caulking

7.                 Aluminum foil and some felt paper

8.                 One gallon of roofing tar

9.                 One gallon of oil base paint

10.             Angle iron for mounting

11.             Sixteen ¼ X 3 lag bolts, sixteen ¼ X 1½ inch machine bolts with nuts and washers

12.              1 ¼ inch and 2 inch drywall screws

13.             One pound of 1½ inch galvanized nails with small heads

14.             PLUMBING SUPPLIES

a.      Eight 3/8 to ½ adaptors

b.     Four ½ inch T’s

c.     Two ½ X ½ X ¾ T’s

d.     One ¾ inch T

e.      Four ½ inch unions

f.       Eight ½ inch elbows

g.     One ¾ inch street elbow

h.     One ¾ sweat to ¾ female pipe

i.        One pressure relief valve

j.        Four sixty foot rolls of 3/8 ID copper tubing

k.     ½ - inch rigid copper tubing type L

l.        ¾ - inch rigid copper tubing type L or M

m.   Solder and flux

 

 

Table of Contents

 

Chapter I      SOLAR HOT WATER SYSTEMS

        Passive Hot Water                                                9
       Active Hot Water                                                 10
       Heat Transfer                                                       11
       Parallel Flow                                                        13
       Serpentine Flow                                                   14

  Chapter II    ABSORBER PLATE CONSTRUCTION

        Theory                                                                                       20
        Materials
                                                                                    21
        Pounding jig construction instructions                                     22
        Absorber plate construction instructions                               23-27

  Chapter III   COLLECTOR BUILDING INSTRUCTIONS

                    Step 1.   Cut framing boards                                          28
                    Step 2.   Assemble frame                                              29
                    Step 3.   Fasten collector bottom and sides                 30
                    Step 4.   Construct tube bending jig                              31
                    Step 5.   Bend copper tubing                                         32
                    Step 6.   Install insulation                                                33
                    Step 7.   Drill inlet, outlet and vent holes                        34
                    Step 8.   Install absorber plate                                        35
                    Step 9.   Install serpentine tubing                                   35
                    Step 10. Install sweat union                                            38
                        Step 11. Cut serpentine tube supports                      40
                    Step 12. Install tube supports                                         41
                    Step 13. Touch up                                                           42
                    Step 14. Install Kalwall                                                     42

 

 

Chapter IV   COLLECTOR MOUNTING

                       Theory of orientation and pitch                                       44
                        Assembly of horizontal and vertical supports               45

                  

Chapter V    HOT WATER STORAGE

                      Thermodynamic theory                                                    46
                       Multi tank theory                                                              48
                       Heat exchange coil theory                                              49

 

Chapter VI   HEAT STORAGE VAULT CONSTRUCTION

                         Step 1.   Tank preparation                                              51
                          Step 2.   4X4 supports                                                  51
                          Step 3.   Bottom platform                                              51
                          Step 4.   Placing tanks on platform                               52
                          Step 5.   Framing the storage vault                              53
                          Step 6.   Insulating the storage vault                            54
                          Step 7.   Installing sides                                                54
                          Step 8.   Installing sheet insulation                               55
                          Step 9.   Making and installing the inner lid                  55

 

Chapter VII   HEAT EXCHANGE COILS

                    Theory                                                                              56-62
                    Assembly                                                                               61
                    Inner lid construction and installation                               63-64

 

Chapter VIII   CIRCULATION AND VAULT PLUMBING

                    Mounting platform                                                                  66
                    Plumbing overview                                                                 67
                    Details of plumbing                                                                68
                    Assembly                                                                               69                                                

 

Chapter IX   COLLECTOR PLUMBING

              Overview                                                                                     70
                    Union T assembly                                                                 71
                    Main output junction assembly                                              72
                    Main input junction assembly                                                73

 

Chapter X    THE SENSOR SYSTEM                                                      74

Chapter XI    FILLING AND DRAINING THE SYSTEM                       75-76

Chapter XII   OTHER SOLAR APPLICATIONS                                        77

GLOSSARY                                                                                         78-79

Author’s Note                                                                                          80

Experimental Heat Storage Vault                                                          81-87    

If you have $2000 (in 2002) and a few weeks of labor to invest this book could save you $50,000 or more in hot water and home heating costs. You folks with carpentry and plumbing skills have a definate advantage but anyone with a grasp of the English language, capable of or willing to learn can install a solar hot water system and there are qualified carpenters and plumbers available who can help you anytime. A good solar heating system is not free. It seems like it should be; after all heat from the sun is free why isn’t a solar heating system?  Fossil fuel contractors throw in oil burners for free when they sign you sign up for a five-year contract. Why doesn’t Mr. Sunshine give us the same deal? I guess Mr. Sunshine is just a mean old man.

We are all part of a vast, interdependent universe. Energy for life is our birthright like the air we breathe or the water we drink. Our sun is enough to sustain us, and still we burn the fluid remains of our ancestors to stay warm. Buckminster Fuller, who coined the saying  “Doing more with less,” compared fossil fuel with the starter motor of an automobile.  He believed that the modern technological world we live in was started with a little boost from fossil fuel consumption. Once started technology should free us from dependence on non-renewable energy. Our starter motors are growing weary. It’s time to start the motor of social harmony, get back to our roots and welcome in the “Solar Age”.

 

SOLAR ELECTRICITY  The photovoltaic power industry has a long way to go before becoming a practical investment for the average consumer although some remote locations miles from the power grid find that it is more practical to install solar than have power lines run to their house.  Government incentives and technological production breakthroughs are necessary before the photovoltaic industry blossoms. $5.00/watt is too much. When the price comes down to $1.00/ watt give me a call. A typical $40,000 residential investment would take about 40 years to reach payback. This is of course assuming that $40,000 has the same value today as it would have forty years from now.  Solar Electricity is a beautiful thing, but for most of us the time is not right. We’ll have to wait a little longer until this growing technology becomes feasible.

 

SOLAR HEATING Solar heating is feasible today. The average American household consumes between 1000 and 2000 gallons of number two fuel oil per year.  Efficient use of the sun’s energy could easily cut this consumption in half or eliminate it entirely. The heating of water is perhaps the easiest, most cost effective solar project a person can get involved with.

 

 

  SOLAR HOT WATER SYSTEMS

 

What once was a luxury is now a necessity. Over 500,000,000 households have or would like to have running hot water. In 1970 a friend of mine left the civilized comforts of a New Jersey home to seek out and experience the free, wild wilderness of an Adirondack hilltop in upstate New York. Jake loved the country life and swore that he’d never leave his mountain retreat. He endured the cold winters without electricity and baseboard heating, but Jake still missed running hot water. When spring came he took a 300-foot coil of black plastic tubing and connected one end to a spring high up on the mountain. He draped the remainder of the 300-foot coil on his roof and spread it out to cover as much surface area as possible. For a $50 investment and one hour’s worth of labor Jake had himself a bona fide hot water shower. He made good use of it whenever the sun was high on the mountain. I used it a few times myself. It works. The roof might look a little funny and the hot water would sometimes run out sooner than you’d like, but it did work when the sun was shining. When the sun disappeared the shower would get very cold. Toward the end of summer water would freeze inside the plastic pipe when the spigot was turned off. 

You might be interested in a simple system like this if you enjoy taking showers when the sun shines. If you desire a more sophisticated hot water system you’ll need to invest more time and more money. I will be discussing several solar hot water designs. If you live in a very warm sunny area a simple passive batch heater is probably all you’ll need. If you’re interested in an automatic system that works well in cold climates with a minimum amount of sunlight you’ll need an active array of flat plate collectors with a massive heat storage system. Parabolic-trough heat concentrating collectors work, however they are usually inefficient, expensive and impractical.

 

PASSIVE HOT WATER

 

 

BATCH HEATERS In gentle climates like coastal California or almost any place in Florida where freezing is a rare occurrence a simple passive batch heating system is all that’s necessary.  The batch heater could be as simple as a water tank painted black. A more efficient system would enclose this black tank in an insulated box. Glass or some form of glazing would be installed at an angle perpendicular to the sun’s rays.  This is a practical, cost effective passive solar hot water system, ideal for gentle climates. For more information about this system check out www.solarnet.org 

 

 

 

 

 

 

 

 

 

ACTIVE HOT WATER

Active solar hot water systems are designed for those less gentle climates. Although they are a bit more complicated and require electricity to run a circulator pump, active solar hot water systems harvest a lot of energy and save you money. 

How much money will they save me on my fuel bill?

Good question. The answer to this question will of course depend on:

        1.     Your location.
    2.     The orientation of your roof.
    3.     The angle that you position your collectors
    4.     The number of collectors used
    5.     How well you insulate the ¾” heat transfer pipes
    6.     The size of your heat storage vault
    7.     The amount of insulation used on the heat storage vault
    8.     The amount of hot water used

 

You are avoiding my question.

OK It’s a fair question and I’m going to give you the best answer I can from data on my collector performance and other environmental data. For my four-collector system with a storage vault of four 55-gallon drums I estimate a $500 savings per year on Long Island.

 

How much will the electricity cost to harvest all this heat?

Between $10 and $20 per year.

 

 

 HEAT TRANSFER THEORY

Before diving into the building plans for an active solar hot water system I’d like to discuss a few basic concepts regarding light, heat and heat transfer.

 

How does light make heat?

Most of the sun’s energy that makes the 93,000,000-mile journey is in the form of visible and ultraviolet light. Heat is produced when high frequency light is converted into low frequency infrared radiation. Ultraviolet and visible light easily passes through glass, however when they strike a darkened surface they are converted into long wave infrared radiation. The glass or special solar glazing traps these long waves. This is known as the greenhouse effect. CO2 is also capable of trapping long wave radiation. Small amounts of CO2 keep our planet nice and warm. Too much CO2 in the atmosphere may transform our forest into deserts. Is it not ironic that we are using the same effect to save the planet that is destroying the planet?

 

Now I understand the Greenhouse effect. Could you explain what heat is?

With pleasure. Heat is a measure of the average motion of molecules. When light strikes an object it causes the molecules to vibrate faster. Intense light can ignite a log or melt steel. The faster an object vibrates the hotter it becomes. It’s as simple as that.

 

OK I get it. Light causes molecules to move faster. So how do these fast moving light excited molecules get into my hot water system?

They don’t. If they did you would have a contaminated system and you’d get sick and die, because collector fluid usually contains antifreeze. The molecules that are excited by the sun never enter your domestic hot water. Only molecular movement is transferred in the double insulated flat plat plate collector system that I am proposing.

 

Wouldn’t it be easier to use plain old ground water for collector fluid than you wouldn’t need antifreeze?

In gentle climates perhaps, however if you travel north of Georgia the batch tank would loose too much heat in the evening to be practical. Under extreme conditions the water in the tank might even freeze. For cold climates it is always best to separate the heat collection area from the heat storage area.  

 

How about that drain away system?

Good point. There is another type of system called the DRAIN BACK or DRAIN DOWN system that allows heated water to drain back into a holding tank when sensors indicate that no heat gain is possible. Some of these systems employ heat exchange tanks and some use the solar heated water directly. These systems do save that hot water in the pipes with a system of automatic valves and relays, but it is more complicated, more expensive and more prone to problems than the double insulated heat exchange system.

 

OK! You convinced me. Should I get my tools? I feel like hammering and drilling and sawing and screwing.

That’s good, but hold onto these feelings a bit longer. I want to be sure you understand a few things about fluid mechanics.

 

Forget it. I have a friend who is still baffled by the concept of fluid mechanics and he spent four years of intense study at R.P.I..

Come on, it will be fun. Think of it as plumbing 101.

 

That sounds less threatening. I’ll give it a try.

That’s the spirit.  I’ll make this as painless as possible and even throw in a few pictures to liven things up a bit. On the following pages I wish to compare and contrast two types of flat plate collectors, the parallel and the serpentine.  Since the parallel collector is the most popular commercially available system I’ll discuss this one first. Here is an example of a flat plate parallel pipe collector system:

 

FLOW RATE THEORY

 

PARALLEL FLOW  DYNAMICS

 

This parallel collector is designed to transport collector fluid from the bottom of the collector to the top via a network of parallel pipes. Notice that the top and bottom pipes are larger than the vertical pipes. There is a reason for this.

Fluid mechanics favors an increased flow rate for the end pipes. This is because incoming fluid pressure is greatest at the base of the first pipe and outgoing fluid pressure is smallest at the top of last pipe.  If the top and bottom pipes are large the pressure difference is moderated and the flow rate in each of the parallel pipes is more uniform. These collectors may be connected in series because the top and bottom distribution tubes are so large. It is unfortunate that the flow rate is minimal at the center of the collector where most of the heat is concentrated. Other problems associated with the parallel flow with collector include cost and leaks. Half inch and two inch copper tubing is expensive, not to mention the dozens of special T fittings and all that solder. One small, undetected leak on one of those T fittings could become catastrophic mess.

SERPENTINE FLOW  DYNAMICS

 

 

The serpentine collector consists of one long continuous flexible tube so there is no problem with uniform flow rate. The size of this flexible tubing is an important consideration. Quarter inch copper tubing is inexpensive, however it restricts the flow rate too much. Half inch flexible tubing is difficult to bend and fairly expensive. 3/8 inch tubing is just right for the money. It has a reasonable flow capacity, low cost, and ease of fabrication. What more could one ask for?  

The main problem with a serpentine collector is flow rate restriction. Even the larger half inch copper tubing restricts flow rate too much and puts an unnecessary burden on the circulator pump. Connecting the serpentine collectors in parallel alleviates this problem. A two-collector system works fine. A four-collector system works even better. It is very important to bend this 3/8 copper tubing carefully to avoid kinks. This will insure that the flow rate is uniform throughout the serpentine collector array hooked in parallel.

                                    

If you want to learn how to assemble and install this serpentine ,closed loop solar hot water system you'll need to purchase the book. My easy to understand, 87 page, fully illustrated book,  How to Build a Solar Hot Water System  has a retail price of $40, but is now available for $35. "SUN HEAT " an auto run Multi Media CD-ROM is included at no additional cost. 

How to Build a Solar Hot Water System                                                              $35

How to Build a Solar Hot Water System ebook version  $15

This book has helped thousands of people in countries all over the world build their first solar hot water system, but there are still other books about other solar thermal projects that you may find usefull. These books may be found in my  Strawberry Fields Solar Book Store

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