Energy efficiency of storage water heaters and solar collectors, use of heat with low temperature (40 C) - problems and solutions.
Factors affecting energy efficiency:
1. Information for water temperature to the large water heaters.
Used very inaccurate thermometers, showing water temperature at the top of the tank.
Normal state of the water in the tank, into height, is many layers with different temperatures. Because of the low heat transfer coefficient, the  temperature of the layers is maintained for a long time if not subjected to external influences (heating or using hot water).
Example of most commonly used thermometers:
A typical example of the temperature of the water layers in height:
As a result of the unknown temperature of the water layers in the height of the tank, the user can not decide, there is enough hot water boiler. To be sure it will be enough hot water, must be  keep permanently turn on the electric heater.
The excess maintain a large amount of hot water and higher temperatures, will be bring to greater temperature losses.
Possible argument that the thermometer is one and is this kind, to avoid expensive price of the water heater, can not be accepted.
The price of the previous thermometer is about 50 euro cents.
Three copies from the thermometer show below, placed on the  height of the tank is a normal and inexpensive solution.
The price of the thermometer show below, into the market for single pieces is 2 to 3 euro.
What makes all manufacturers of water heaters in the world to placed just one, inaccurate thermometer (with a few exceptions), measures the temperature of the water only at the top of the tank?
Experiment with a tank, fitted with addtional three temperature sensors to water temperature recording:
Heating the whole tank to 75 degrees..
Without using water from the tank, after several hours the sensors register the water temperature of the tank, showed to right . Depending on the thickness and type of insulation, the air temperature around the tank and the passage of time, change in temperature will be different.
Main which can be seen in the right water heater is cold water that falls to the bottom and hot water rises up, and support of the high temperature at the top thermometer with minor modifications. Cold water is the result of heat losses.
Putting a single thermometer measuring the temperature of the water at the top of the tank, purposive conceal of heat losses.
Below I will be show technical solutions for large water heaters, resulting in significant energy losses.
Who can benefit (in monetary terms) from the potentially higher cost of electricity?
Can only be the participants into the energy band.
2. The insulation of large water heaters have insufficient thickness.
The losses of heat depends on the following factors:
- Coefficient of thermal conductivity (thermal conductivity) of insulation used.
- Thickness of insulation.

- The water temperature in the tank.
- The air temperature around the tank.
- Surface of the boiler walls (up to touch water).
What are the differences in heat losses in the residential building and the water heaters?
Mechanism of heat losses is equal. Important is the temperature difference between inside and outside temperature, thickness of insulation and its coefficient of thermal conductivity (at equal surface).
For our area (Bulgaria) will accept (I'm not looked to the  statistical  meteorologic data) average outdoor temperature in winter is 0 C. I accept the average air temperature into the house for winter 20 C.
Temperature difference for housing is 20 .
If the water heater maintain an internal temperature of 85 C.
The temperature difference for water heaters is 65 C.
Water heaters is used all year but homes heated is season.
The homes has a large surface, water heater substantially smaller.
Approximate annual heat losses at the water heaters and the houses are equal.
I found information indicates a program "SAVE" the European Commission.

As can be seen below European standards, scanned from brochure:
In this column for water heaters 'Atlantic', misleading recorded "Power Consumption", but it is heat loss in KWh for 24 hours at water temperature of 65 C.
Not specified air temperature around the water heater and the temperature difference is unknown.
Not specified, the thickness and type of insulation.
What information give for the thermal insulation and the heat losses, world and Bulgarian manufacturers of water heaters?
I will discuss only a few of these water heaters that offer on the Bulgarian market.
Not provide information for thickness, type of insulation and heat losses at different temperatures of water and ambient air:
Very easy, anyone can determine the amount of heat loss for their own water heater. For example, if the whole family will be absent several days from home. Should be performed the following sequence of actions:
- Turn off all other electrical consumers.
- Turn on the water heater to heating to desired temperature, without using hot water.
- Once the thermostat is turn off record:
  a. The date and time.
  b. The electric meter (both rates)
  c. Air temperature in the tank room.
- Several days after the return must wait to the selfsame hour and record new showing of the electric meter.
- You can now include other electrical consumers and to use hot water.
- KWh spent to maintain the water temperature in the water heater divided by the number of days, will give the heat losses in the boiler, at the
   temperature of the water in the tank and the ambient air.

In 99% the your water heater needs additional insulation and at least three thermometers, at the height of the tank. You can do this yourself.


Example 1 - the lowest price.

Thermometers and insulation, has in almost all building materials stores. You can use instead of those thermometers, wireless thermometers 3 pieces (in this case the price will be no lowest).
So far I calculated, heat losses of water heaters. I will try to determine, what Approximate losses across Europe.
Population in 2009 - European Union (27 countries) = 499,723,520.
Assume that a household consists of 4 people.
Then the number of households 499 723 520 / 4 = 124 930 880.
Assume that 50% of households use 150 liters (average volume) electric water heaters.
And the number of water heaters is 124 930 880 / 2 = 62 465 440.
Assume that the annual savings of electricity for a heater, as a result of additional thermal insulation of 200 mm, 85 C water and 15 C air is:
- loss (at L = 16 mm) = 1295 KWh
- loss (at L = 16 +200 mm) = 96 KWh
- saving = 1295-96 = 1199 KWh
All water heaters for one year will allow saving 62 465 440 * 1199 = 74 896 062 560 KWh.

How many nuclear energy units (from 1000 MW) can produce this energy?
- 1 000 MW=1 000*1 000 000 W=1000*1000 KW = 1 000 000 KW
electrical power.
- for 1 year production is 24*1000000*365 = 8 760 000 000 KWh
Saving for 1 year e  74 896 062 560 / 8 760 000 000  =   8.5 .
For the other countries in Europe will add another 1.5 atomic energy units.
For the rest of the world will add 40 more nuclear energy units and the total becomes 50.
50 *  8 760 000 000 = 438 000 000 000 KWh  is the amount of heat that is emitted into the atmosphere through the thermal insulation of water heaters per year worldwide. If polyurethane (used for thermal insulation of water heaters)  is an expensive material, I could understand his savings. Is it on all home improvement stores and anyone can check the price.
Example 2 - average price.
Example 3 - the highest price.

Much more appropriate would be the European Commission to change the program name from the "SAVE" to "LOSS".
Most manufacturers do not provide data on heat losses. Below is shown a typical case of deliberate deception of the consumer.
If someone decides to produce additional thermal insulation with various size for water heater will probably be well received by all users. 
Another way to reduce heat loss is the use of timers. Heating the water should so to ended shortly before its use. It is desirable mostly at the water heaters with small thermal insulation thickness.
Perhaps the energy band to justify the large heat losses, would say use instantaneous water heaters with a capacity of 7 to 10 KW and will be no heat loss.
This is true, but:
- You can not fill the tub with warm water for a reasonably short time.
- You can not use the tank to accumulate heat energy from alternative heat sources.
- With widespread instantaneous water heaters will be required costly new electricity power plantsand and electric transmission facilities.  
   Likelihood of overloading will always be there.

3. The water heaters with a coil heated by hot water priority in the boiler.
    Need a new type a water heaters, warming the cold water with priority.
One of the main factors for the heat losses was the temperature difference between the water into tank and the ambient temperature.
In the same extent that applies to the heat gains (absorption of heat from heat sources alternative).
The greater temperature difference between heat source and heat receiver, the amount of heat absorbed per unit time will be greater.
The below shows diagram, the warming of the hot water heater.
Below the diagram shows, how warming with advantage of the hot water into the tank.
The water into tank is almost cold.
If the sensor on the solar collector reaches a maximum temperature of 85 C and the tank sensor shows 45 C will have a temperature difference of 40 C. The transfer of heat will start at S1 = 50 C and S2 = 45 C. Maximum possible, temperature difference at heating with the advantage of the warm water is 85-45 = 40 C.
The cold water enters the tank at a temperature of 12 C and remains at the bottom. If it is possible to warm with advantage the cold water will have the maximum possible temperature difference of  85-12 = 73 C.
As a result of heating with the advantage of the hot water loses temperature difference of 35 .
Estimated loss of heat is between 25% and 50%.

I will try to estimate of the losses in the European Union.
According to the European Solar Thermal Industry Federation ESTIF, installed in 2009 have solar power in KW and surface in square meters:
Installed capacity in Europe (27 countries + Switzerland) is 22 137 251 KW.
If this power is used for six months a year (there is sunlight).
For a year we get energy 22137251 * 10 hours * 182 days = 40 289 796 820 KWh.
Assume that the losses represent 25%, then we have (40 289 796 820 / 100) * 25 = 10 072 449 205 KWh losses mainly due to warming of the hot water with priority.
These are losses for 2009. With each passing year to install new solar power and the losses increase.
Is there an easy way to prove the amount of losses as a result of heating of hot water advantage, by making measurements with heat meters and comparing analyse for efficiency.
Below are shown schemes of measurement:
- Figure 15 traditional water heater with a coil, warming to hot water advantage.
- In Figure 16 with a many-column coil for warming with priority of cold water in the tank.
- In Figure 18 with a many-column coil for warming with priority of cold water in the tank and the added ability to absorb heat with low temperature (40 C) from air.
4. Using air as a massive heat source with low temperature.
Warming with advantage of cold water in the tank, allows widespread use of the new, alternative heat source - the air.
When air temperature reaches 35 C to 40 C and the cold water is 12 C, there is the temperature difference of 28 C. The air temperature does not always depend on solar radiation and often she is high late into the evening. Can be absorb large amounts of heat from the air.
For extracting heat from the air can be used, air-water exchangers with ventilator, used to heating of living quarters. They have the opportunity to work in cooling mode, which allows for heating the boiler water and can cool your home. Figure 18 is an example to use of air-water exchangers with ventilator to absorb heat from the air. The scheme provides and heat amount valuation and intake amount  of heat from each source. Measurement is the best way for proving-efficiency.
Below see into Figure 1 and 2, two models tanks to warming the cold water with advantage.
You can see more details (of Bulgarian language) about this type of water heaters (this is an application for registration to the Patent Office).
5. Conflict by co-absorption of heat from heat of sources  alternative and thermostatically maintain the hot water by electric heater.
If the electric heater is included, with entry of cold water in the tank (this will happen if you use hot water), will include a thermostat and warming water will start until the water reaches the set temperature.
This means not can absorb heat from the alternative heat source if use the thermostat.
In turn off the thermostat off in cloudy weather will lead to a lack of hot water.
This problem is solved if on the height of the tank have located several temperature sensors. Each of them can be used to control the thermostat and the electric heater. For example, if control to the thermostat is used the sensor S2b (see Figure 18) and the thermostat is set to include 60 C, the heater will begin to heat only when the water reaches under 60 C to that sensor. Using of hot water from tank, do not turn on immediately the thermostat. This will only happen when using hot water in large amounts and missing (or insufficient) of sunshine.
By choosing different sensors (on the tank height) to control of the thermostat, may be deferred turn on the heater and provides different amounts of water, where to accumulate alternative energy.
If your heater is situated at the bottom of the tank will heat the water out along its entire height, regardless of what height is used sensor to the thermostat , as shown in the figure below:
On figure 19 the thermostat will turn on to heating at 54 C.
If used sensor and electric heater located to middle of the tank, warming is shown in Figure 20 (it is the thermostat set to 54 C).
In Figure 20 we see that under the heater, the water is not warming.
The higher is placed the thermostat sensor, the latest will to turn on electric heating of the water. This gives the larger amount of water which can accumulate heat.
Choice of electric heater located in the middle as the tank gives the opportunity to ensure hot water in the upper half of the tank and the bottom half to keep the accumulation of alternative heat.
TS-42Rbox thermostat lets you manually select one of three sensors to control a heater.
TS56+ controller allows automatic selection of one of the 6 sensor and a heater 4 at different hours and days of the week.

If you work during the day, it is desirable to programming:
- At the beginning of the day use of the above sensors to control of thermostat for heating and the upper heater.
  So provide greater volume of water to accumulate alternative heat.
- In the afternoon of the day using the lower sensors to thermostat control for heating, and the lower heaters.
  This will ensure availability of hot water (no matter what it was like sunshine) when you returning from work.
  You can change automatically into the time and temperature for the thermostat.
The possibility of using heat with low temperature provides the following advantages:
- Increases the temperature difference between heat source and heat receiver.
- Increases the time to use of the solar collectors, see Figure 21.
- Virtually the entire summer day, will be absorbed heat from the air, even if there is no sunshine, see Figure 22.
9. Mobile phone to control of water heaters.
It is not hard to do. TS56+ controller superior to all known controllers for water heaters and has very good reliability.  Comparative analysis of the ability of TS56+ to other controllers, see here (Application for registration with the Patent Office of Bulgarian language).
Currently is not included function, management of the mobile phone.
Dialogue will be by following scheme:
It is necessary to establish a protocol for exchanging and adding necessary software to the controller.
From your mobile phone user can:
- To see the water temperature into the water heater.
- To turn on or  turn off electrically heater if necessary.
- Programming to the controller.
- Receive all possible information.
This avoids the heat losses to maintain the water temperature, at absence of people in the dwelling. 

10. Estimate global impact.

Will assume that 100% of all boilers in the world, have:
- Insulation thickness of not less than 100 mm.
- At least 3 thermometers on the height of the tank with accuracy 2 C.
- Several number of timers.
- Heat exchangers for alternative heat, always warming first the coldest water.
- Embedded controllers operating with extras mentioned above.
- Using heat from the air.
Annual impact will be equivalent to the electricity produced from 80 to 100 atomic energy units of 1000 MW.
See TS-41Rbox
See TS-42Rbox
See TS-55T
See TS56+
To make the calculation formulas, used books:
- "PHYSICAL QUANTITIES AND measuring UNIT" by N. Mindova Publishing "Technique" 1985
- "INTERNATIONAL SYSTEM measuring UNIT SI", author G. Bordun Publishing "Technique" 1966
Here you can see the basic sheets, used from the first book.
Below show the method to calculate of the diagrams:
Used for calculation formulas are the international system units SI:
Coefficient of thermal conductivity
      J = Q / S * grad t 
where  Q  is the heat flow in W / (m. C)
(small Greek letter 'lamda'  is not into the font, used the letter 'J')
                                                       grad t is the temperature gradient grad t = (Tin-Tout) / L
                                                       Tin is the temperature inside the tank in C
is the temperature of air around the tank in C
                                                       L is the thickness of the insulation in m

                                                       S is the area of ??the walls of the boiler, to which contact with water in square meters.
                                                       S=2*(3.14*D*D/4)+3.14*D*H  .
                               D is the inside diameter of the tank in meters.
                               H is the height of the tank in meters.
                               J=0.020 for polyurethane.
                               To determine the D and H of the tank will use the formula for a cylinder:
                               V is the volume of the tank in cubic meters
                               H=V/((3.14*D*D)/4)  in meters

The actual heat loss will probably be larger by several percent, because it is not taken into account the heat losses through the pipes for hot and cold water. The pipes are metal and have a high coefficient of thermal conductivity.
Below show the heat losses of 80 liters water heaters, with  insulation 16 mm, 32 mm, 43 mm, 116 mm and 216 mm:
Author by dipl. eng. Decho Georgiev
Below show the heat losses of 150 liters water heaters, with  insulation 16 mm, 32 mm, 43 mm, 116 mm and 216 mm:
Heat regulators
TS-42Rbox or
consistently showing
data of 4 sensors
Method for installation of sensors
Water tank
thermal contact paste
heat sensor
heat sensor
heat sensor
Additional insulation
Additional insulation
Additional insulation
Heat controller
TS-55T or
TS56 +
Method for installation of sensors
Water tank
heat sensor
heat sensor
heat sensor
Indication of
sensor 1
Indication of
sensor 2
Indication of
sensor 3
Indication of sensor 5
ambient air temperature)
Indication of sensor 6
outdoor air temperature)
sensor 4 is not installed
1. Information provision of the large water heaters.
2. The insulation of the large water heaters is insufficient thickness.
3. The water heaters with a coil heated by hot water priority in the boiler.
4. Using air as a massive heat source with low temperature.
5. Conflict by co-absorption of heat from heat of sources  alternative and thermostatically maintain the hot water by electric heater.
6. Have Need by-pass.
7. Return valve is indispensable.
8. Other tricks of the energy band, that make us to using more electricity.
9. Mobile phone to control of water heaters.
10. Estimate global impact.
11. Throwing from us heat into the air.
8. Other tricks of the energy band, that make us to using more electricity:
- Missing sockets for temperature sensors on the water heaters with heat exchanger. This causes the installation of sensors in an incorrect position and hence further reduce the absorbed solar energy.
- The water heaters with heat exchanger is not equipped with appropriate management, water pump, return valves, three way solenoid valves, etc.. which is up-expensive and thus reduces the number of installed solar collectors. If for example factory producing 100,000 water heaters of year, you must purchase and appropriate number of controllers and pumps. Such quantity will likely cost twice as low. Now these controllers and water pumps, will buy of high price from the user (after passes through several merchants).
- Installation of timers temperature is rather the exception. Maintaining the same high temperature throughout the day, increases heat losses, because have high temperature difference between water and ambient air.
6. Have Need by-pass.
Aside during summer into another time the water in a pipe cools rapidly. When you turn on the water pump, water passes through the coil and cooling the tank water.
If not used a three-way solenoid valve, the temperature losses depend on the following factors:
- The amount of water which is located in tube 1.
- The thickness and type of the pipe insulation.
- Ambient temperature.
Below on the left figure shows the action of the solar installation with cooling before heating.
Below on the right figure shows the action of the solar installation with by-pass.
7. Return valve is indispensable.
In the absence of non-return valve, evening (and at any other time when there is no sunshine), the hot water from the tank will rise to the collector. There will be cooling and will come back into the tank. The turbine blades in the water pump can not stop the movement of water.
11. Throwing from us heat into the air.
Below shows where it goes the discarded heat from the appliances in each home.
People discovered the hot water. But they do not know how to warming the cold water.
Energy boss and company
The reasonable and entirely possible solution is shown below:
Energy boss
and company