FAQ

1. I need a new electric water heater with a storage volume of 125 l. Later I would also like to heat water with photovoltaics. What do I need to add or rebuild a regular water heater?

You won't need anything when you buy the Logitex water heater. Logitex water heaters are equipped with two separate circuits. One (the normal circuit) works with the mains power, the other is supplied with the power from the photovoltaic panels. The photovoltaic circuit is switched off simply by turning the thermostat knob. The water heater is then powered by the mains electricity and works like a normal water heater. You can connect two DC cables from the photovoltaic panels to the water heater. Then, by turning the knob of the thermostat, you activate the photovoltaic circuit, which allows the water to be heated with ecologically generated electricity. And the most important thing: this electricity is free. However, if you buy a regular water heater from another manufacturer now, you won't be able to convert it later.

2. What is the difference between regular solar panel water heating and Logitex photovoltaic water heating?

See comparison here

3. Isn't it better to use regular AC water heater to heat water and connect the panels to the inverter?

There are statistics that show that connecting the water heater to the electricity grid is more economical than connecting it to the DC power supply from photovoltaic panels. However, this only applies to solar radiation that is less than 70% of the specified output. With an irradiation of 70%, the balance is balanced and with an irradiation of more than 70%, the supply from photovoltaic direct current is significantly better. A condition for this is that the resistance of the heating coil must correspond to the resistance of the panels at maximum power. For this reason, we only recommend 250 W panels with 30 V. Modules with a lower connected load result in a correspondingly lower output power. Many of our own measurements and also measurements by independent institutions show that the supply of electricity from the public power grid or from the photovoltaic modules leads to the same consumption. However, the inverter has direct current conversion losses of 30 to 50 W per hour. When converting direct current to alternating current, manufacturers state a loss of 3 to 4%. So if all losses of the inverter are taken into account, then the annual balance is really 1:1. If the sky were cloudy throughout the year then the inverter would of course be better and vice versa. And one more important difference. A normal water heater is always heated with mains electricity when it needs electricity - for example in the morning after a shower. Later, when the water heater could have used the electricity generated by the sun, it may happen that electricity is no longer needed. The difference then is that you have to pay for the mains electricity. The electricity from the photovoltaic modules is free. If you connect the inverter to the photovoltaic modules instead of to the water heater, the inverter supplies the electricity to the home network free of charge.
A few practical tips: The heating and water heating using photovoltaic panels is an additional system to the main heating and is recommended especially for the transitional periods. In these cases it can work that from a 2 kW system, 1 kW is used for DC heating or underfloor heating and 1 kW for the water heater. If the heating has reached the desired temperature or if the room thermostat has switched over, 2 kW are automatically used for water heating. The system can also be connected in reverse.

4. Is it possible to connect the Logitex storage tank with the photovoltaic panels directly to a heat pump?

Connecting the Logitex water heater directly to a heat pump is possible, but we do not recommend it. In fact, heat pumps have a temperature limit that varies between 55 and 60 °C. The heat pump would heat the water in the hot water tank to such a temperature. The photovoltaic modules can then supply practically no more energy, since the water would have already been heated to over 60 °C, which would automatically lead to a fault in the heat pump. There are a few dozen installations where the Logitex system is connected to the heat pump as follows: at the cold water inlet to the heat pump tank, the DZD tank is installed, in which the cold water is either preheated or heated to the maximum temperature of 75 °C will. With the help of a mechanical mixing valve, the heated water is brought into the storage tank of the heat pump. This means that the heat pump does not switch on as often, which on the one hand allows you to save money on mains electricity, on the other hand also increases the service life of the heat pump by at least 30%. The increased service life of the heat pump then plays an important role in the calculation of the return on investment in the heat pump. It makes a big difference whether you have to replace the pump after 10 or more than 13 years.

5. Can I connect a normal water heater to photovoltaic panels?

No! In no case. If you were to connect a regular water heater to the photovoltaic panels, as some hobbyists have already done, the thermostat and thermal protection would burn out. There is a risk of fire! To ensure that the system can work safely and reliably, Logitex has developed and patented a solution that is unique in the world.

6. Can I connect photovoltaic panels to a coil already installed in the water heater and intended to be fed from the grid ?

No! Almost all heating coils are submerged in water. If you connect them to direct current, electrolysis occurs and the hot water tank gradually breaks down. To prevent this phenomenon, Logitex uses dry heating coils specially designed to be powered by direct current from the photovoltaic panels.

7. What care and maintenance does the Logitex system require throughout the year?

None. Two weeks after installation you will be curious about the temperature in the hot water storage tank. After that, once you are satisfied that the system is working properly, you will only stop at the water heater when you walk past it, and then again you will only check the water temperature.

8. Can I order a 1kW photovoltaic system from you and install it myself?

How about the guarantee then?

Basically yes, if you are a certified electrician and a plumber at the same time. The guarantee runs from the day of sale. The warranty is 2 years for the electrical parts and 5 years for the memory. If, in the event of a complaint, it turns out that the system was not connected correctly, the complaint cannot be accepted. We recommend having the system installed by a certified company. A list of certified companies can be found on the Logitex website.

9. Where is the best place to place the photovoltaic modules?

Anywhere where the sun shines and where there is no shadow. For example, if shadows from a chimney or tree overshadow one of the panels, all panels will perform poorly because they are connected in series. The south orientation is always best ± 20°. If you decide between the south-east and the south-west, then the south-east is always better, although it is usually colder in the morning. The sky is clearer in summer and clouds form around noon. During the rest of the year fog can form in the morning, often lasting into the later hours of the morning. For this reason, the south-west orientation is less favourable. Photovoltaic panels don't like heat, they work much better when it's cold. Because of this, the performance can be much higher at -30°C and on a sunny day than on a hot summer day. So, the panels work all year round, which is an undeniable advantage of the panels. The panels do not only have to be installed on the roof.

10. How is the consumption of hot water in the household calculated?

In the past, when calculating the volume of domestic hot water, it was assumed that an adult human consumed 50 liters of hot water heated to 42°C. Nowadays people are more economical and in the calculation 36 liters are taken into account. Another big difference is whether you bathe in the tub or just shower. If bathing in the tub is preferred, the volume of the tank must be increased by at least 50%. A larger storage volume is not necessary when heating water with gas, because this type of water heating is much faster than with electricity.

11. What do the photovoltaic modules do when the water in the tank is heated to the desired temperature and the panels are switched off?

In such a case, the photovoltaic modules do not supply any electricity. But the tension remains. However, it would be a pity not to fully utilize the full capacity of the modules. It is precisely for this reason that the Logitex company has developed a new model "M", which, after heating the water in the tank, transfers the energy. This energy can then be used to heat water in the nearest Logitex water heater. However, the model can also be connected to the inverter and the electricity consumed in the home network.

12. Can the Logitex products also be used in a prefabricated building that has its own gas boiler room?

Yes, Logitex products can be used anywhere there is a need for hot water. In prefabricated buildings, apartments, schools, authorities, workshops, houses, simply everywhere. But in prefabricated buildings, the area of the roof without shade is a limiting factor. The photovoltaic modules are connected to the Logitex water heaters using only DC cables that can be run in a duct. In your case, the water heaters would preheat the cold water that is fed into the central storage tank.

13. When heating water using LX ACDC 125 using mains power, recommend setting a heating limit in case of persistent bad weather. In the operating instructions, you also recommend heating the water to 75 °C or more using the photovoltaic modules. However, they also recommend installing a mixing valve. But how to calculate the volume of water that can flow through the mixing valve if it is set at say 40°C and the water in the water heater is at 75°C ?

The calculation is based on the formula below:
x ÷ yxz = k
x - volume of the accumulator in liters
y - temperature set on the mixing valve in °C
z - temperature of the water in the tank in °C
k - available amount of water, temperature according to y
So in your case it is:
125L ÷ 40°C x 75°C = 234L
So, from the above calculation, you can get 234 liters of water at 40°C.

14. I bought your hybrid water heater with photovoltaic panels. The water heater works very well, but why does the water occasionally drip out of the pressure relief valve?

Water is not compressible and therefore any system in which water is heated must be fitted with a pressure relief valve. The drops from the pressure relief valve are to be discharged into the next sewage pipe. Another option would be to have an expansion tank installed to equalize the pressure in the system. The volume of an expansion tank suitable for water heaters with a volume of 100 and 125 liters is 5 liters. For water heaters with a volume of 160 and 200 liters, the expansion tank should have a volume of 8 liters. However, air pressure in the expansion tank must be taken into account. The air pressure must be higher than the water pressure in the pipes and lower than the value set on the pressure relief valve (0.6 MPa).

15. How much hot water does an adult person use per year?

That is very individual. It is generally assumed that an adult person uses an average of 15 liters per shower. It is estimated that 36 liters of hot water per person per day. This means 13,140 liters of hot water per person per year. In terms of energy, we are talking about 870 kWh per person per year. If the 2 kW Logitex system produces about 2,400 kWh per year, then it should be sufficient for 2.76 people (2,400 ÷ 870).

16. What is the output in kW of a tubular heat exchanger in the M+K water heater?

24 kW at 80 °C and flow rate of 720 liters per hour.

17. What is the difference between connecting photovoltaic panels directly to the Logitex water heater and connecting photovoltaic panels directly to an inverter, which converts the direct current into alternating current, which can then be used to power the home grid to which a normal water heater can be connected ?

The difference is big. A classic water heater draws mains power when it needs it and not when the sun is shining. The Logitex water heater uses the free electricity from the photovoltaic modules when the sun is shining and only when this energy is not sufficient is the difference drawn from the grid. This achieves a significant saving in mains electricity. If you were to deliver power from your small power source directly to the grid, you would be getting three times less from the utility compared to the price you buy grid power at. So, if we come back to your question, then connecting photovoltaic panels directly to our water heater is three times more economical.

18. How are the panels attached to the tin roof?

Very easy. Special screws are screwed into the roof truss, which are sealed with a rubber seal. Guide rails are fastened to the screws via plates and the panels are then mounted on the guide rails.

19. After a year of operation, I only have cold water flowing, even though the photovoltaic panels have heated the water in the Logitex water heater to 70°C. I installed a mixing valve at the outlet of the water heater and set it to 49 °C. We have very hard water. What can be the cause of the problem ?

If there is a problem with the thermostatic mixing valves, limescale is always the cause. The formation of limescale on the mixing valve sensor causes its isolation, which leads to improper mixing. For safety reasons, the mixing valves are built in such a way that in the event of an inaccurate function of the sensor, the hot water is blocked so as not to endanger human health. An immediate solution is to turn on the hot water, lift the mixer valve cover, turn the tap left and right as far as it will go at least three times, and then close the cover.

20. I have a condensing boiler with a solar heating system, of course with the appropriate pipes. I would now like to move on to your system. Is it possible ?

It would be ideal to separate the solar heating system from the condensing boiler and run it as a stand alone system. The boiler could then be connected to the Logitex memory M+K or M+KW (special variant for gas boilers). The pre-heated water from the solar heating system would supply the Logitex storage tank and there the water would then be further heated by photovoltaics. If the sunshine were too weak, the gas heating would switch on. Of course, there will be an overproduction of electricity in the Logitex memory. However, this does not cause any problems for the Logitex system (in contrast to ordinary solar heating systems). The house network is supplied with the excess electricity via inverters. In such a case, the gas consumption for water heating would be minimal. You can generate a sufficient amount of electricity for self-consumption and actually don't have to throw away and replace anything.

21. I have a 1,000 l storage tank connected to a solid fuel boiler, in which heat for heating and water heating is accumulated. In order to have hot water outside of the heating season, I always have to heat up the boiler in the morning. How could I install your hybrid water heating system so that I don't have to heat it up every day?

Very easy. The Logitex LX ACDC/M water heater is connected to the hot water outlet from your large storage tank and this in turn is connected to the photovoltaic modules. The Logitex heater will accumulate solar energy. If the weather is unfavorable for a long time, the water can be additionally heated with mains electricity. During the heating season, the pre-heated water from your large storage tank enters the Logitex water heater. Here it is either further heated or - if it is sufficiently warm - it just flows through. If the system is connected as described above, you do not need to heat the boiler every day and you will heat only during the heating season.

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