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Published: 07/05/2021
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Modern heating systems require many parameters to be adjusted, and hysteresis is one of the most important of them. This affects not only the thermal comfort of the home, but also heating costs. Check what this setting refers to and how to configure it correctly!
- 1 What is temperature hysteresis? 1.1 What does hysteresis mean for a central heating boiler?
- 1.2 What does DHW hysteresis mean?
What is temperature hysteresis?
When choosing a home design, most people pay attention not only to its architecture, but also to the possible costs of maintaining it. Without a doubt, the most important factor in this regard is heating, because in our climate the heating season often lasts more than six months.
These costs are greatly influenced by the volume of the building and the technology used to construct it - definitely by choosing an energy efficient home you can limit heat loss, resulting in lower bills. The cost of heating a home also depends on the correct choice of heating system, and then on its correct operation. Modern controllers used to determine the operating parameters of the heating boiler help with this. One such parameter that affects energy consumption (but also thermal comfort) is hysteresis.
The hysteresis adjustment function allows you to determine the temperature at which the heating device turns on and off. The hysteresis itself - oven or domestic hot water - means the difference between the set temperature in the installation and the actual temperature at which the device will be activated to achieve the set temperature.
Using hysteresis, you can regulate the operation of the heating device according to your needs, i.e. prevent it from being switched on too often, which leads to higher energy consumption, or switched on too infrequently, which in turn negatively affects the efficiency of the installation.
What does hysteresis mean in a central heating boiler?
According to the definition described above, the hysteresis of a central heating boiler is nothing more than the difference between the set temperature and the temperature at which the device returns to operating mode. Suppose you set the boiler set temperature to 55 o C and the hysteresis to 3 o C.
When the temperature reaches 55 o C, the boiler will automatically switch to maintenance mode. The device will only start when the actual temperature drops to 52 o C, that is, by 3 o C, because this is how the hysteresis was determined.
What does DHW hysteresis mean?
In the same way, we can explain what DHW hysteresis is, i.e. boiler that heats process water. In this case, the device will also turn on only when the sensor shows that the temperature has dropped from the set value to a certain value. If the hysteresis is set to 5 o C and the set temperature is 55 o C, the DHW pump will start when the actual water temperature drops to 50 o C.
However, it is worth noting that the effectiveness of DHW hysteresis depends on the location of the temperature sensor in the boiler. The water cools down from below, so it is better if the sensor collects data from this part of the device. Then it is easier to decide how to establish DHW hysteresis, because with a certain temperature difference in the lower part of the boiler, warmer water from its upper part will continue to flow into the taps for some time.
In this case, the hysteresis may be slightly larger. In turn, when setting up the sensor, a lower value for this parameter is indicated - otherwise the water will cool down too much and require much longer operation of the device.
Varieties
Modern heating devices can be equipped with an adjustable or fixed temperature controller. The cyclic switching behavior of the element depends on this characteristic.
- Fixed. These regulators already have preset closing/opening settings, with a fixed hysteresis. The advantage of such an element is that there is no need to independently set the trigger moment.
- Adjustable. The most common. They are of the electromechanical type. The adjustment is made by increasing or decreasing the mechanical pressure on the bimetallic plate. Adjustment is made by rotating the screw. The greater the pressure on the plate, the higher the response threshold during heating. Such devices are cheaper than fixed ones and are more dependent on the state of the power circuit contact.
When purchasing a heating device, it is important to know about the cyclical nature of its operation. This will help you set up and maintain the required mode.
Optimal boiler hysteresis
You already know what boiler hysteresis is, now it’s time to explain what its optimal value should be. Let's start with the fact that many furnaces have a factory setting for this parameter and it cannot be changed.
If possible, follow the general rules:
- greater hysteresis means longer interruptions in the operation of the device and, therefore, the risk of excessive cooling of the premises, heating, which will require a correspondingly longer operation of the boiler;
- lower hysteresis - allows you to maintain thermal comfort at an optimal level and requires more frequent, but also shorter operation of the furnace.
Frequently starting a device with low hysteresis contributes to its faster operation, as well as consuming a fairly large amount of energy for the startup itself. In turn, maintaining high hysteresis causes large temperature fluctuations, but on the other hand, this method of heating a house is considered more economical.
Error (measurement accuracy) of the thermostat.
When converting the measured temperature to a digital value, decimal places are discarded and the accuracy is reduced.
An accuracy of more than 0.1 is obviously not needed.
An accuracy of 0.5 is often selected in room thermostats.
But precision 1 seems too rough.
However, there are thermostats that do not display decimal places at all.
I also noticed that for some thermostats the accuracy of the temperature value involved in the calculations and the accuracy of the displayed value differ.
Optimal hysteresis of a pellet stove
Pellets are solid fuel in the form of pressed chips, which ignite fairly quickly and then burn just as quickly. This should be taken into account when determining the optimal level of hysteresis for a pellet boiler. So what is the best hysteresis on the boiler? In this case, it should have a fairly low value - about 2-3 o C. Thanks to this, you can maintain the desired temperature and at the same time save on heating costs. Too much variation in temperature will cause the boiler to consume a lot more fuel to even it out to the expected level.
Room thermostat for gas boiler from Aliexpress from China
Choosing a programmable room thermostat for a gas boiler on Aliexpress
Why do you need a room thermostat?
Installing a room thermostat in the house and connecting it to the gas boiler solves two problems:
In rarely visited areas of the house, it is beneficial to keep the temperature lower. Building regulations recommend maintaining the air temperature in different rooms of the house during the heating period in the range from +12 to +26 o C.
Standards for air temperature in residential areas of the house
A room regulator allows you to maintain a constant temperature in a heated room with high accuracy. With manual control, the range of temperature fluctuations is larger and deviations are more often towards higher temperatures. Every extra degree in the room leads to an increase in gas consumption for heating. In addition, using a thermostat, you can program an automatic decrease in the temperature in the house during certain periods (at night...).
In rich EU countries, the room temperature set at night usually does not exceed 16-17 degrees. This is evidenced by a report presented by the German thermostat manufacturer Tado for 2014.
Room thermostat saves energy
When the boiler operates without a room thermostat, the circulation pump runs constantly, consuming electricity. The circulation pump, controlled by a two-position room thermostat, operates intermittently, which saves energy and the life of the pump.
Which room thermostat should you choose?
We select a room thermostat based on the following basic and mandatory requirements for the thermostat:
Don't go wrong with your choice. Don't buy a powered thermostat. The relay contacts of such a thermostat will most likely be under mains voltage. They are intended for other purposes.
The thermostat relay contacts can be in one of two positions: closed or open. Connected to the boiler, closed thermostat contacts switch on the boiler heating mode. When the contacts open, the heating mode is switched off. The boiler operates in cycles - on/off. There are no changes in the heating mode settings on the boiler itself.
Another important parameter to choose is the temperature control algorithm. Thermostats available:
Thermostats with PI control have advantages. They provide more accurate maintenance of the air temperature in the room +/- 0.5 o C. The temperature of the heating water, and therefore the radiators, changes to a lesser extent during the regulation process.
The choice in favor of a room thermostat with hysteresis control was made due to their lower cost and availability on the AliExpress trading platform.
Choosing a room thermostat on Aliexpress from China
At first glance, the AliExpress trading platform offers many models of room thermostats for a gas boiler. But, after careful study, you understand that most models are analogues under different brands.
I considered two options: a model with control buttons on the body and with touch buttons on the screen. The choice was made in favor of the buttons on the case. You won't have to use the buttons often. It's more convenient and cheaper.
Room thermostat from Aliexpress from China, model BGL02-5BB, is an electronic two-position programmable controller that allows you to adjust the temperature according to one weekly program with the possibility of combinations of six different time intervals.
The thermostat, model BGL02-5BB, supports the function of protecting the heating system from freezing when the room temperature drops to 5 °C.
The amount of hysteresis can be set in the settings. The minimum hysteresis value is +/- 0.5 o C.
The body of the device is made of high-quality plastic with a glossy surface. The printed circuit board looks neat, covered with protective transparent plastic on top.
The parcel was delivered by Chinese and Russian mail 18 days after payment for the order.
Cons, disadvantages of a thermostat with Aliexpress
When you manipulate the buttons, the screen backlight turns on. If the screen is located above eye level, the image on the screen becomes difficult to see. Place the device on the wall as expected, at a height of 1.5 m. If you look at the illuminated screen from top to bottom, then everything is clearly visible.
The box with the thermostat contains one sheet of instructions in English. The instructions do not contain any indication of the model or brand of thermostat. The contents of the instructions in some points do not correspond to the thermostat model.
Complaints about the instructions not matching the device model are often found in customer reviews on AliExpress.
Connecting a room thermostat to a Protherm gas boiler
The wires from the room thermostat - thermostat are connected to the terminal block marked as X17 (black in the figure on the left) in the 24 V compartment of the control panel of the Protherm Gepard (Panther) gas boiler.
The wires from the contacts of the on-off thermostat relay are connected on the block to the RT terminals. The terminals will be shorted with a jumper wire that must be removed.
Terminal block for room thermostat from Aliexpress. The two-core wire from the gas boiler is connected to the terminals designated COM and NO. It does not matter which wire core is connected to which terminal.
Connecting a room thermostat to other models of gas boilers is done in the same way. You just need to find the location of the corresponding terminal block on the boiler.
Products for construction and repair
How does a gas boiler room thermostat work?
A room thermostat installed in the room, with temperature control by hysteresis, measures the current air temperature and, if the temperature drops from the value set in the settings, turns the boiler on. For example, if the temperature is set to 22 o C in the thermostat setting, then the boiler will turn on, taking into account hysteresis +/- 0.5 o C, when the air temperature drops to 21.5 o C. The heating water heated by the boiler will begin to flow into the radiators and heat their. The radiators, in turn, will heat the air in the room.
The problem is that the process of heat transfer from radiators to the room air is very slow. After turning on the boiler, the air temperature in the room, at the place where the thermostat is installed, will continue to decrease for some time, to 21 o C, and only after that it will begin to increase. When the air temperature increases to 22.5 o C, the thermostat will turn off the boiler. But from the heated radiators, the air temperature in the room will continue to increase for some time, up to 23 o C.
Due to the presence of a large time delay in the feedback loop, fluctuations in the air temperature in the room will be noticeably greater than the value of the thermostat hysteresis. Fluctuations in the air temperature in the room will be +/- 1 o C from the specified 22 o C.
Often the temperature of the heating water manages to increase to the maximum at which the boiler will disconnect from the boiler temperature sensor. Although the thermostat will still command the boiler to turn on.
Setting the boiler thermostat
Since the instructions for the thermostat purchased on Aliexpress are in English and do not correspond to the device, I had to find a video on setting up a room thermostat. The device in the video and its functions are exactly the same, although the model is called differently.
I recommend that you set the hysteresis value in the settings, function dIF = 0.5.
To save gas, I highly recommend setting the thermostat to weekly temperature programming.
Previously, the gas boiler operated under the control of a room thermostat with PI control. Air temperature fluctuations were two times less.
Setting up the heating system under the control of a room thermostat
On a gas boiler controlled by a two-position thermostat, the heating water temperature setting must be set to maximum. The same as it was installed in winter in the coldest weather (65 o C).
It is advantageous to install a room thermostat that controls the operation of the boiler in the largest room of the house. Radiators in the room in which the thermostat is installed should not have automatic valves that regulate coolant flow.
In other rooms, I recommend installing a thermostatic valve on each radiator, which regulates the coolant flow through the radiator depending on the temperature in the room. This will avoid overheating and keep the air temperature in the house lower but comfortable.
Optimal oven hysteresis for eco-peas
Eco-peas are a fuel made from hard coal or lignite that ignites slowly but retains heat for a long time. The hysteresis of a coal furnace is typically set at approximately 2 of C, although this value depends on many additional factors, e.g. Fan settings and stop time and tray. Incorrect configuration can cause, for example, the oven to turn off. For this reason, it is best to follow the manufacturer's instructions or ask a specialist for the optimal boiler setting.
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If control panels are used, for normal operation of the heating system it is necessary to set the system temperature at the entrance to the boiler (return), at the exit from the boiler (supply) and hysteresis (hysteresis setting) for each channel.
Hysteresis (hysteresis setting) is the difference between the temperature of switching off and subsequent switching on, set for each channel in the range from 1 to 9°C. We recommend setting this parameter within:
- on the return line 2 - 6°C;
Features of the physical phenomenon
We will focus specifically on hysteresis in electronic technology associated with magnetic processes in various substances. It shows how this or that material behaves in an electromagnetic field, and this thereby allows one to build dependence graphs and take some readings of the environments in which these same materials are located. For example, this effect is used in the operation of a thermostat.
Considering in more detail the concept of hysteresis and the effect associated with it, one can notice such a feature. A substance with this feature is capable of becoming saturated. That is, this is a state in which it is no longer able to accumulate energy in itself. And when considering the process using the example of ferromagnetic materials, energy is expressed by magnetization, which arises due to the existing magnetic connection between the molecules of the substance. And they create magnetic moments - dipoles, which in the normal state are directed chaotically.
Magnetization in this case is the adoption of a certain direction by magnetic moments. If they are directed chaotically, then the ferromagnet is considered demagnetized. But when the dipoles are directed in one direction, the material is magnetized. By the degree of magnetization of the coil core, one can judge the magnitude of the magnetic field created by the current flowing through it.
Handymen will be interested in this article on how to connect running lights yourself.
Types of thermal relays for on/off
A conventional on/off thermostat is a compact electronic unit that is mounted on the wall in a suitable location and connected to the equipment being controlled. The simplest, and therefore the most affordable temperature controller has a mechanical control.
In addition, all thermal relays are divided into:
- Programmable control devices. Such regulators are connected to equipment both wired and wireless. The relay is configured through a special program or LCD display. Thanks to the software, you can configure the relay to operate at certain times of the day and year.
- Thermal relay with GSM wireless programming module. Such devices can have either one or two temperature sensors.
- Autonomous regulators powered by batteries. Such installations are most often used to control the operation of household appliances (for example, a refrigerator) and incubators.
Wireless devices with an external sensor are separately distinguished. Such devices are considered the most effective. They are distinguished by their speed, because the temperature sensor responds to temperature changes even before they have time to affect the temperature inside the room.
The principle of dii
When the set boiler temperature is reached, the temperature controller vibrates the fan. When the boiler temperature drops below the set value for the boiler hysteresis, the temperature regulator turns on the fan again.
Boiler temperature hysteresis is a value that shows the difference between the set boiler temperature and the boiler temperature, when the temperature controller has cooled down to a certain level, turn on the fan again
Hysteresis of the pump switch-on temperature is a value that shows the difference between the set switch-on temperature of the central combustion pump and the temperature of the boiler, when cooled down to that temperature, the temperature controller is connected to the central combustion pump.
The hysteresis value is initially set by the factory settings of the transmitter, i.e. 3-5 ° C.
In this way, until the boiler goes out, the coolant temperature is maintained within the specified value.
The use of a fan with a temperature controller allows you to maintain a constant temperature in the cabin and save up to 35% of heating costs.
How to make a thermostat with your own hands
A thermal relay suitable for its method of operation can be ordered in an online store, or you can assemble it yourself. Most often, homemade air temperature regulators are powered by a 12 V battery. You can also power the thermostat to the electrical wiring through a power cable.
In order to assemble a reliable thermostat with a sensor, you should:
- Prepare the device body. For these purposes, you can choose a housing from an old electric meter or circuit breaker.
- Connect a potentiometer to the comparator input (marked with a “+” sign), and LM335 type temperature sensors to the negative inverse input. The operation of the device is quite simple. When the voltage at the direct input increases, the transistor supplies power to the relay, which, in turn, supplies power to the heater. As soon as the voltage at the reverse input becomes higher than at the forward input, the level at the output of the comparator will approach zero and the relay will turn off.
- Create a negative connection between direct input and output. This will create limits for turning the thermostat on and off.
To power the thermostat, you can take a coil from an old electromechanical electric meter. To obtain the required voltage of 12 V, you will need to wind 540 turns on the coil. For this, it is best to use copper wire with a diameter of at least 0.4 mm.
Other properties
In addition to magnetic hysteresis, galvo-magnetic and magnetostrictive effects are also distinguished. In these processes, a change in electrical resistance is observed due to mechanical deformation of the material. Ferroelectrics, under the influence of deformation forces, are capable of generating electric current, which is explained by piezoelectric hysteresis. There is also the concept of electro-optical and double dielectric hysteresis. The last process is usually of the greatest interest, since it is accompanied by a double graph in zones approaching saturation points.
