What does the nuclear phase-out have to do with heating costs?
Gross electricity generation in Germany in 2006
Source: German Association of Energy and Water Industries (BDEW)
Dear Sir or Madam,
Our federal government has just passed a resolution:
- The seven oldest nuclear power plants in Germany, which were initially shut down temporarily after the Japanese nuclear disaster, will never be reconnected to the grid.
- The remaining operating lives of the other ten nuclear power plants will be limited to a fixed date.
- Nuclear power will finally be phased out at the end of 2022, but the nuclear fuel rod tax will remain in place.
- The search for a final repository is being intensified and expanded.
- The electricity grids are to be expanded rapidly in order to transport wind power from northern Germany to the south, for example. More expensive underground cables are also to be used.
- Offshore wind farms, hydropower and geothermal energy are to be subsidised more, while subsidies for solar plants and onshore wind turbines are to be reduced. At the same time, older wind turbines are to be replaced by new, more powerful ones.
- In addition to the new coal and gas-fired power plants already under construction, a further 10 gigawatts of fossil-fuelled power plant capacity is to be added. However, these power plants are to be as efficient and flexible as possible. However, the national targets for reducing CO2 emissions are to be maintained.
- Funding for the energy-efficient refurbishment of buildings will initially be increased to 1.5 billion euros per year for the years 2012 to 2014. In addition, measures to reduce energy consumption will be more easily tax-deductible. In this way, the government aims to ensure that two per cent of the building stock is renovated each year in order to save energy and reduce CO2 emissions.
Source: AFP, WELT ONLINE, WIKIPEDIA
What does that mean for us?
With immediate effect, we are doing without seven of the last 17 or 41% of our nuclear power plants, which still accounted for 23% of gross electricity production in 2009 according to the German Association of Energy and Water Industries (BDEW). This means that we are now lacking a good 91TP3 tonnes of our electricity generation capacity, which we can obviously still cover from existing reserves without any problems. As there is currently no more wind, hydro, waste or photovoltaic capacity available, this gap will probably have to be covered by fossil fuels (2009: 57% of electricity production) or biomass (2009: 4% of electricity production). It should be noted here that reserve capacities at power plants can nevertheless only be utilised through the increased use of fuel! In view of the distribution, it can be assumed that currently over 90% of the switched-off nuclear capacity is covered by the additional use of fossil fuels. If fossil-fuelled power plant capacity is to be expanded as "efficiently and flexibly" as possible in the future, this can only mean that the share of natural gas (2009: 13% of electricity production) in particular must increase, as gas turbines are extremely flexible and highly efficient in conjunction with downstream steam turbines. In addition, gas is the fossil fuel with the lowest CO2 emissions. At the same time, it is also the most important energy source for heating buildings in Germany, especially for private households.
Conclusion: Not only heating with electric heat pumps will become more expensive; prepare yourself for rising heating costs overall - even for gas and oil. Invest in your heating system this summer so that you can benefit from the cost savings as early as next year.
Why do you actually need both: two-zone loading and two-zone unloading?
Which by now word has got around ...
is that the best possible layering is the be-all and end-all of efficient buffer cylinder utilisation. This is because only a storage tank that is as well stratified as possible can still absorb heat when it is already relatively full and release heat when it is already relatively empty. The secret of this benefit lies in the fact that, with good stratification, the cylinder is always hot at the top and always cold at the bottom (image, buffer 2-4), while the mixed cylinder is warm from top to bottom (image, buffer 1). The boundary between hot and cold should be as abrupt as possible. The fuller the cylinder is, the lower (image, buffer 3), the emptier it is, the higher (image, buffer 4) this limit is.
Charging states of buffer storage tanks
In any case, a well stratified storage tank contains as little hot water as possible.
A misconception that many still succumb to
Many of our customers have found that they have been able to improve the stratification of their buffer tanks so significantly by using the two-zone unloading assemblies rendeMIX 3×2 (for one heating circuit) or rendeMIX 3×4 (for two heating circuits) that the overall efficiency of solar systems has increased noticeably and operators are highly satisfied. Others have found that the two-zone charging assembly rendeMIX 2×3 (with return boost for a wood boiler or CHP) also brings them noticeable benefits. What few have realised, however, is that it is precisely the combination of both processes, i.e. the simultaneous use of two-zone charging and two-zone discharging, that first inspires the buffer storage tank to absolute peak performance. To do without one of the two just because you are doing the other is simply to settle for a significantly worse result.
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Why is the combination of both methods so successful?
Both methods primarily focus on the weak point of every cylinder, the hot water at medium temperature. Unfortunately, this is created again and again by unavoidable turbulence in the cylinder, which can never be completely avoided, even with the most sophisticated inner workings. However, the systematic and prioritised use of this warm, mixed water ultimately makes it possible to "dynamically tidy up" the cylinder. This means that the stratification is improved while the heat is transported through the cylinder. The assumption that the buffer cylinder is first charged by the heat source and only then discharged by the consumers is unrealistic. In fact, both processes always take place more or less simultaneously.
Example 1
If a 20 kW wood boiler supplies a 20 kW system via a buffer, the heat content of the cylinder remains constant. Nevertheless, the simultaneous charging and discharging of the cylinder using the two-zone method means that all the mixed hot water is removed and the stratification of the cylinder is completely rebuilt.
Example 2
If the power consumption increases to over 20 kW, the buffer cylinder is slowly but surely emptied, as the missing power is taken from its heat supply.
Example 3
If the power consumption falls below 20 kW, the buffer storage tank is slowly but surely filled, as the excess power is added to its heat reserve.
Pro tip: Feeling good is half the battle
What is the quality of a control loop?
Sensor on CHP
A controller constantly compares a specified SET value with a measured ACTUAL value and determines a reaction (manipulated variable) from the difference (deviation) with the aim of making the deviation between the SET and ACTUAL values as small as possible. If, for example, a constant return temperature of 60°C is required for a CHP unit, this is the SET value, while the ACTUAL value is determined by a temperature sensor. A possible reaction would be a three-point signal that opens, stops or closes a mixing valve via an electric drive so that the return temperature is raised, maintained or lowered.
Control behaviour through sensor
The quality of the control loop is primarily understood as how precisely and how quickly the controller brings the ACTUAL value closer to the TARGET value, for example after a sudden change in the TARGET value at time T. Ideally, the ACTUAL value only overshoots the target slightly once and then approaches the TARGET value from this side. If the controller is too slow, too much time passes until the target is reached. If the controller is too fast, it swings several times over the target. Since in our example the servomotor is also part of the control loop and thus influences its quality, its running time should be set correctly on the controller, if this option exists.
What is a dead time?
Long distance of the sensor to the mixer
The dead time of the controlled system is the time that elapses before the effect of a change in the controller is detected by the sensor. If, for example, the sensor of our above-mentioned return lift is located at the return inlet of the CHP, while the mixer has been installed 5m away, the dead time is at least as long as the running time (t) that the water needs to flow the distance (s) at the speed (v) from the mixer to the sensor.
t = s / v
v = Q / A = Q / ¼πDN²
For a CHP unit with a thermal output of 12.5kW, which supplies 80°C in the flow and receives 60°C in the return, the delta-T is 20K and the flow rate (Q) is therefore 0.54m³/h. This results in the following flow velocities (v) for the following nominal diameters and the following running times (t) for a 5m section, for example:
| DN [mm] | v [m/s] | t [s] | |
| 15 | ½“ | 0,84 | 5,9 |
| 20 | ¾" | 0,47 | 10,6 |
| 25 | 1″ | 0,30 | 16,5 |
| 32 | 1¼" | 0,19 | 27,0 |
First of all, it can be seen from this that a greatly oversized nominal size leads to a significant increase in dead time. And this certainly gets in the way of a high controller quality.
Why is the correct sensor installation so important?
Furthermore, it is clear that the distance between the sensor and the mixer must be as small as possible in order not to increase the dead time unnecessarily. This makes the location of the sensor the first parameter to be considered.
Short distance of the sensor to the mixer
But the heat transfer from the heating water to the sensor is also a hurdle with time relevance: the better the heat transfer, the faster the sensor reacts. Contact sensors that are mounted from the outside on the pipe through which the heating water to be measured flows are particularly common. Three main factors come into play here:
Contact surface
The contact area should be as large as possible. For example, if a probe is placed lengthwise on a corrugated tube, only several small points are available for heat transfer.
With a smooth tube, the contact between sensor and tube still consists of a line. Only through the use of thermal paste or another thermal bridge does the line become the required contact surface that guarantees rapid heat transfer.
Sensor without thermal paste and sensor with thermal paste
Thermal conductivity of the transition materials
Metals are the best heat conductors in contrast to plastics, oxides (rust) or other impurities. Therefore, the pipe should be made of metal and carefully cleaned before sensor installation.
Contact pressure
The tension of the contact force should be permanently maintained elastically, which must be taken into account when selecting the tensioning strap. In this respect, a spiral spring wire is certainly better than a cable tie and a cable tie is certainly better than adhesive tape.
Contact pressure due to tensioning strap
In any case, the installer's expertise and care are required to avoid unnecessary errors at this point, which in the worst case can deteriorate the control loop quality to such an extent that permanent temperature fluctuations occur in the return of the CHP unit.
Poor heat transfer leads to longer dead time