Heating devices for low temperature systems. Energy Efficiency of Steel Panel Radiators in Low Temperature Heating Systems Recommended Insulation for Low Temperature Heating Systems
Low-temperature heating systems today still have not yet become widespread in Russia, but they are successfully practiced in Europe, including in countries with not the mildest climate, but where renewable energy resources (RES) are actively used for heat supply and air conditioning of buildings ...
G The main and obvious advantages of such systems are energy savings based on fossil hydrocarbons in combination with minimizing environmental harm. In addition, low-temperature systems provide the user with additional opportunities to achieve thermal comfort in the house and control the indoor climate.
In Russia, the scope of application of low-temperature heating systems is limited not only by climatic features in many of its regions, but also by regulations. In particular, this factor acts during mass development, at objects such as apartment buildings, for which standards have been developed for other modes of heat supply to buildings. Therefore, low-temperature heating systems, if they are used, then in social institutions such as clinics and kindergartens, as well as more widely in the private cottage sector. In addition, they are usually designed and installed for heat supply and air conditioning of energy-efficient houses, primarily "active" ones, which have also begun to be built in Russia in recent years. Minimizing heat loss through the limiting structures and ventilation of the building is generally one of the main conditions for the successful use of low-temperature heating systems there.
Low-temperature heating systems are being created on the basis of highly efficient heat generators and RES energy transformers, as well as using modern models of heating devices and electronic automation, which are combined into intelligent control systems.
Generation with accumulation
According to the existing regulatory documents, the temperature regime of the heating system is characterized by three parameters: the temperature of the coolant at the exit from the heat generator, at the entrance to it and the air temperature in the room. A mode where at the outlet of the heat generator the temperature of the coolant does not exceed 55 ° C, and at the inlet is up to 45 ° C, is considered inherent in low-temperature systems. The air temperature in the room is usually taken equal to 20 ° C. The most common temperature conditions in such systems are 55/45/20 ° С, 45/40/20 ° С or even 35/30/20 ° С.
Low-temperature heating systems can be monovalent, where heat is generated by one heat generator, or, more often, polyvalent, in which the work of several heat generators or transformers is combined into heat of renewable energy ( rice. one). Such polyvalent systems are also called hybrid systems.
Fig. 1
For both mono- and polyvalent systems (as a peak heat generator) a condensing boiler is well suited. Its operating mode is the closest to that indicated above and largely depends on the temperature parameters of the heating system. The lower the temperature of the heat carrier in the return boiler circuit, the more complete steam condensation occurs, more heat will be utilized, and the higher the efficiency of the condensing boiler. For gas boilers, the threshold temperature for condensing is 57 ° C. Therefore, the heating system must also be designed to use a heating medium with a lower return temperature.
At average temperatures for the winter period, according to the design calculation, taking into account the maximum efficiency of the condensation regime, it should not exceed 45 ° C. Such parameters are provided by low-temperature heating systems, in which condensing boilers operate mainly in their "normal" mode.
Of course, not only condensing boiler technology can and is being used in low-temperature systems. A heat generator in such a system, including a peak one, can be any highly efficient boiler operating on any fuel and, in particular, an electric one. In hybrid systems, the boiler is turned on only at peak loads, when the rest of the heat generators (renewable energy transformers - solar collectors, heat pumps) cannot cope with ensuring thermal comfort in heated rooms and the needs of hot water supply.
When using renewable energy energy, low-temperature water heating systems usually include heat accumulators, which can be with liquid and solid fillers, phase (using the heat of phase transformations) and thermochemical (heat is accumulated due to endothermic reactions and is released during exothermic).
In heat accumulators with liquid and solid fillers (water, low-freezing liquids (ethylene glycol solution), gravel, etc.), heat is accumulated due to the heat capacity of the filler material. In phase heat accumulators, the accumulation of heat occurs when the filler melts or changes the crystal structure, and the release occurs when it hardens.
The most widespread in hybrid low-temperature water heating systems installed in cottages are water storage tanks that successfully dampen peak DHW loads, store heat from the operation of a solar collector, a heat pump or (in winter) a peak heat generator. By accumulating heat energy from various sources, such a heat storage unit allows them to optimize their work in terms of maximum economic efficiency at a particular moment, by reserving “cheap” heat. The surplus of the generated heat can then be used for DHW. Their use is also justified when using heat pumps to optimize the operation of the compressors and hydraulic decoupling of the heat pump circuits and the load.
The water tank of the heat accumulator is a container well insulated, for example, with a layer of polyurethane foam 80-100 mm thick, into which several heat exchangers are built. A heat accumulator with a volume of 0.25-2 m 3 can accumulate 14-116 kWh of thermal energy.
Low temperature heating devices
The low temperature of the coolant determines the choice of devices for low-temperature heating systems, which must efficiently transfer heat in heated rooms, working in a flexible mode. If these devices are installed in a cottage, where the pressure of the coolant in the pipelines is obviously low, then their strength characteristics go into the background.
Fig. 2
According to experts, wall-mounted, parapet or floor convectors with forced ventilation are most successfully used in low-temperature systems ( rice. 2) and steel panel radiators ( rice. 3). In such systems, convectors should be used, equipped with a heat exchanger with a large surface - multilayer with frequent fins and a fan that provides high heat removal. In addition to convectors, wall-mounted wall and ceiling fan coil units (fan coil units) also satisfy these conditions.
Fig. 3
In forced convection systems without a fan, induction coils can be used. Due to effective heat removal and high power, these devices will have small dimensions compared to other types of equipment.
The advantage of such devices is the possibility of their use in combined systems that heat the premises in the cold season, and in the summer are used to cool the air.
If convectors without a fan are used in low-temperature systems, their height must be at least 400 mm.
The heating medium panel of the steel panel radiator is located outside the heater. The lamellas of the convective element are heated from it. The farther from the panel, the colder the lamellas. Convection at low temperatures of the radiator is hampered by the viscosity of the air trapped between the fins. But nothing interferes with the thermal radiation from the panel.
Steel panel radiators are successfully used in low-temperature heating systems also because their model lines include a wide range of standard sizes, and this is important for optimal placement of heating devices in such systems, in particular, they should be equipped with heating devices that cover the entire length of the window opening.
Fig. 4
The operation of convectors with forced ventilation and steel panel radiators will be successfully combined with a warm water floor ( rice. 4), which is literally designed to work with a coolant characterized by a low temperature. According to SNiP 41-01-2003 "Heating, Ventilation and Air Conditioning", p. 6.5.12, the average surface temperature of floors with built-in heating elements should be taken no higher than 26 ° С - for rooms with constant presence of people; and not higher than 31 ° С - for premises with temporary stay of people. The temperature of the floor surface along the axis of the heating element in childcare facilities, residential buildings and swimming pools should not exceed 35 ° C. In real conditions, with existing technologies for installing a warm floor, such temperatures of its surface are achieved at temperatures of the coolant at the entrance to the underfloor heating pipeline not higher than 45 ° C.
Underfloor heating significantly increases the efficiency of low-temperature heating systems. So, when equipping a warm floor, the energy reserve of a water heat accumulator with a capacity of 1.2 m 3 is sufficient to heat a house with an area of 130-140 m 2 due to electricity received at a low night rate.
All hot water heating devices in low-temperature heating systems are equipped with thermostatic automation.
Intelligent control
Since most of the low-temperature systems are hybrid, and it is also possible to combine the functions of heating and air conditioning in one such system, their greatest efficiency and economy can be achieved with the rational management of all components of the system. Today, smart control systems are used for this.
Without intelligent control, it is impossible to effectively and at the same time flexibly regulate the system based on real readings of sensors, and not on built-in graphs that do not take into account the conditions of a particular heat supply facility. When smart-control is used in the project, it is only necessary to set the initial settings, and then the intelligent automation will automatically support them.
The smart controller is responsible for switching the system from one heat source to another. By processing several inputs every second, the controller selects the most economical heat source at the moment. According to the given logic, heat energy from the cheapest source is used first.
The use of such intelligent control systems allows you to differentially set the temperatures in controlled rooms, thereby achieving, in addition to being economical, also the highest level of thermal comfort.
Article from ... Heading "Heating and DHW"
Surely all of you have repeatedly heard from manufacturers of steel panel radiators (Purmo, Dianorm, Kermi, etc.) about the unprecedented efficiency of their equipment in modern high-efficiency low-temperature heating systems. But no one bothered to explain - where does this efficiency come from?
First, let's look at the question: "What are low-temperature heating systems for?" They are needed in order to be able to use modern, highly efficient heat sources such as condensing boilers and heat pumps. Due to the specifics of this equipment, the temperature of the coolant in these systems ranges from 45-55 ° C. Heat pumps are physically unable to raise the temperature of the heat carrier higher. And condensing boilers are economically impractical to heat above the steam condensation temperature of 55 ° C due to the fact that when this temperature is exceeded, they cease to be condensing boilers and work like traditional boilers with a traditional efficiency of about 90%. In addition, the lower the temperature of the coolant, the longer the polymer pipes will work, because at a temperature of 55 ° C they degrade for 50 years, at a temperature of 75 ° C - 10 years, and at 90 ° C - only three years. In the process of degradation, pipes become brittle and break in loaded places.
We decided on the temperature of the coolant. The lower it is (within acceptable limits), the more efficiently energy carriers (gas, electricity) are consumed, and the longer the pipe works. So, the heat from the energy carriers was released, the heat carrier was transferred, it was delivered to the heater, now the heat must be transferred from the heater to the room.
As we all know, heat from heating devices enters the room in two ways. The first is thermal radiation. The second is heat conduction, which turns into convection.
Let's take a closer look at each method.
Everyone knows that thermal radiation is the process of transferring heat from a warmer body to a less heated body by means of electromagnetic waves, that is, in fact, it is heat transfer by ordinary light, only in the infrared range. This is how the heat from the Sun reaches the Earth. Because thermal radiation is essentially light, the same physical laws apply to it as to light. Namely: solids and steam practically do not transmit radiation, and vacuum and air, on the contrary, are transparent to heat rays. And only the presence of concentrated water vapor or dust in the air reduces the transparency of the air for radiation, and part of the radiant energy is absorbed by the environment. Since the air in our houses contains neither steam nor dense dust, it is obvious that it can be considered absolutely transparent for heat rays. That is, the radiation is not delayed or absorbed by the air. The air is not heated by radiation.
Radiant heat transfer continues as long as there is a difference between the temperatures of the emitting and absorbing surfaces.
Now let's talk about heat conduction with convection. Thermal conductivity is the transfer of thermal energy from a heated body to a cold body during their direct contact. Convection is a type of heat transfer from heated surfaces due to the movement of air created by Archimedean force. That is, the heated air, becoming lighter, tends upward under the action of the Archimedean force, and cold air takes its place near the heat source. The higher the difference between the temperatures of hot and cold air, the greater the lifting force that pushes the heated air upward.
In turn, convection is interfered with by various obstacles, such as window sills, curtains. But the most important thing is that the air itself, or rather, its viscosity, interferes with air convection. And if, on a room scale, the air practically does not interfere with convective flows, then, being "sandwiched" between surfaces, it creates significant resistance to mixing. Remember the glass unit. The layer of air between the glasses slows down itself, and we get protection from the outside cold.
Well, now that we have figured out the methods of heat transfer and their features, let's look at what processes take place in heating devices under different conditions. At a high temperature of the coolant, all heating devices heat equally well - powerful convection, powerful radiation. However, with a decrease in the temperature of the coolant, everything changes.
Convector. The hottest part of it - the coolant pipe - is located inside the heater. The lamellas are heated from it, and the farther from the pipe, the colder the lamellas. The lamella temperature is practically the same as the ambient temperature. There is no radiation from cold lamellas. Convection at low temperatures interferes with the viscosity of the air. There is very little heat from the convector. To make it warm, you need to either increase the temperature of the coolant, which will immediately reduce the efficiency of the system, or artificially blow warm air out of it, for example, with special fans.
Aluminum (sectional bimetallic) radiator structurally very similar to a convector. The hottest part of it - a collector pipe with a coolant - is located inside the sections of the heater. The lamellas are heated from it, and the farther from the pipe, the colder the lamellas. There is no radiation from cold lamellas. Convection at a temperature of 45-55 ° C interferes with the viscosity of the air. As a result, the heat from such a "radiator" under normal operating conditions is extremely small. To make it warm, you need to increase the temperature of the coolant, but is this justified? Thus, almost everywhere we are faced with an erroneous calculation of the number of sections in aluminum and bimetallic devices, which are based on the selection "according to the nominal temperature flow", and not on the basis of the actual temperature operating conditions.
The hottest part of a steel panel radiator - the external heat carrier panel - is located outside the heater. The lamellas are heated from it, and the closer to the center of the radiator, the colder the lamellas. And the radiation from the outer panel is always
Steel panel radiator. The hottest part of it - the outer panel with the coolant - is located outside the heater. The lamellas are heated from it, and the closer to the center of the radiator, the colder the lamellas. Convection at low temperatures interferes with the viscosity of the air. What about radiation?
Radiation from the outer panel lasts as long as there is a difference between the temperatures of the surfaces of the heater and the surrounding objects. That is, always.
In addition to the radiator, this useful property is also inherent in radiator convectors, such as, for example, Purmo Narbonne. In them, the coolant also flows from the outside through rectangular pipes, and the lamellas of the convective element are located inside the device.
The use of modern energy efficient heating devices helps to reduce heating costs, and a wide range of standard sizes of panel radiators from leading manufacturers will easily help to implement projects of any complexity.
Low-temperature heating is called heating, in which the heating of the coolant is 55-45 degrees. This means that the temperature of the water leaving the boiler should not exceed 55 degrees, and the temperature of the return water should not be lower than 45 degrees. In this case, the surface of the heating radiator will be heated by about 38-40 degrees in the upper part of the device.
Hot, in the generally accepted sense of the word, you cannot call it. You should not count on intense heat radiation from radiators at such a coolant temperature, just as convectors should not be installed in low-temperature heating systems - they are effective only at a water temperature of at least 70C and are used in high-temperature (traditional) heating systems.
Heat sources for low temperature heating
In a conventional heating system, the temperature of the water leaving the boiler is much higher and is approximately 70-80 degrees, while the return temperature is 20 degrees lower.
It should be noted that low-temperature heating systems are used not because they are better and more efficient, but because only with their help you can heat a house, using heat pumps, geothermal heat sources or condensing heating boilers for this.
The so-called traditional heating boilers in low-temperature systems can only be used in combination with an elevator unit that mixes cold heat carrier with hot water from the boiler and brings the heat carrier temperatures to the required (55-45) parameters.
Long-term operation of a conventional boiler for heating the return flow with a low temperature can lead to excessive formation of condensate in the chimney and its premature failure. Therefore, in low-temperature heating systems operating on conventional heating boilers, the coolant from the return pipeline must be heated before being fed into the boiler, using part of the heat generated by the boiler for this.
All this complicates the design of the heating system and leads not only to an increase in its cost, but also greatly complicates the process of operation and maintenance.
Only condensing heating boilers can operate on a coolant with a low temperature.
Low temperature sources
As already mentioned, low-temperature heating is focused on the consumption of heat energy generated by heat pumps, as well as heat from the sun and geothermal heat. It is these sources that are optimal for low-temperature systems. If it is decided to use low-temperature heating without the use of renewable energy sources, then it is easier and more economical to install a condensing boiler.
But the system of obtaining "soft heat", as low-temperature heating is often called, will work only with the right choice of heating devices.
Heating devices for low temperature systems
Conventional radiators are not suitable for low temperature heating systems. They simply will not be able to operate at full capacity, and it will be cold in the house. You will have to heat the house with a low-temperature heating system using heating surfaces. It can be warm floors or warm walls. The ratio is simple: the larger the heating surface, the warmer it will be in the house.
It should be noted that low-temperature heating systems have a number of advantages:
- Heating surfaces with a temperature of about 35-40C emit heat in the most comfortable wavelength range for humans
- Warm floors allow you to redistribute heat in the room. If, when installing conventional radiators, the warmest air in the room (and with it the warmest zone) is under the ceiling, then when using a warm floor it is located under the feet, which is more natural and comfortable for a person.
- The use of geothermal heat and solar energy reduces heating costs and has a positive impact on the environment.
What is more expensive?
Unfortunately, today it is premature to talk about real savings when using low-temperature heating.
In our country, it is cheaper to heat with gas, using traditional boilers complete with convectors and heating radiators.
For those who want to enjoy the mild warmth from heating surfaces, it is best to install a condensing boiler. It is more expensive, but it can reduce gas consumption by 15-20%.
They are considered attributes of heating systems with a high temperature parameter. But the foundations on which such views were built are outdated. Saving metal and thermal insulation is not a priority today to save energy resources. And the characteristics of current radiators allow us to talk not only about the likelihood of their use in low-temperature communications, but also about the advantages of such a conclusion. This is substantiated by scientific research carried out for a couple of years at the suggestion of Rettig ICC, the owner of the brands Purmo, Radson, Vogel, Finimetal, Myson. A decrease in the temperature of the coolant is the basic trend in the progress of heating technology in the past years. European countries. This was implemented as the thermal insulation of buildings was improved, and heating equipment was improved. In the 1980s, the usual parameters were reduced to 75/65 ºC (flow / return). The main advantage of this was the reduction of losses during the formation, transportation and distribution of heat, as well as safety for consumers. Progress regarding water supply is not standing still. In order to protect the internal surfaces of pipes from corrosion and high levels of wear, the avk valve is used. This is a certain element of pipeline fittings, the main parts of which are in the form of a disk. High performance avk valve is provided by carbon nickel steel from which it is made, as well as epoxy coating. The avk valve is used for water and neutral liquids.
With the increasing popularity of underfloor and other types of panel heating in systems where they are used, the supply temperature is lowered to 55 ºC, which is taken into account by the creators of heat generators, balancing fittings, etc. Now the supply temperature in ultra-technological heating systems can be 45 and 35 ºC ... The impetus to achieve such parameters is the ability to more efficiently operate sources such as heat pumps and condensing boilers. At a secondary circuit medium temperature of 55/45 ºC, the COP efficiency element for a ground-to-water heat pump is 3.6, and at 35/28 ºC it is already 4.6 (during heating operation). And the use of boilers in a condensation state, requiring cooling of flue gases with water from the return flow below the "dew mark" (when fuel is fired - 47 ºC), gives a bonus in efficiency of about 15% and more. Thus, a decrease in the temperature of the carrier gives a significant saving in resources and a reduction in the release of carbon dioxide into the air. Until now, the basic solution for supplying heat to a room at a low temperature of the carrier was a "warm floor" and convectors with copper-aluminum exchangers.
Studies initiated by Rettig ICC allowed steel panel radiators to be added to this category. With the assistance of several scientific institutions, including those in Helsinki and Dresden, they were tested in various investigated conditions. The results of other works on the functioning of modern heating communications have been added to the "evidence base". At the end of January last year, the research results were transmitted to the journalists of the leading European publications at an event held at the "Purmo-Radson" center in Erpfendorf.
Radiators are traditionally considered attributes of heating systems with high temperature parameters (in the literature, the terms "high-temperature" and "radiator" are often even used interchangeably, in particular when it comes to heating circuits). But the postulates on which this point of view was based are outdated. Saving metal and building thermal insulation is not considered higher today than saving energy resources. And the technical characteristics of modern radiators allow us to speak not only about the possibility of their use in low-temperature systems, but also about the advantages of such a solution. This is proved by scientific research carried out for two years at the initiative of Rettig ICC, the owner of the brands Purmo, Radson, Vogel & Noot, Finimetal, Myson.
If you want to buy heating equipment, then you can go to the corresponding section:
Reducing the temperature of the coolant is the main trend in the development of heating technology in recent decades in European countries. This became possible with the improvement of the thermal insulation of buildings, the improvement of heating devices. In the 1980s, the standard was reduced to 75/65 ºC (flow / return). The main benefit from this was the reduction of losses in the generation, transportation and distribution of heat, as well as greater safety for users.
With the growing popularity of underfloor and other types of panel heating in systems where they are used, the supply temperature is reduced to 55 ºC, which was taken into account by the designers of heat generators, control valves, etc.
Today, the supply temperature in high-tech heating systems can be 45 or even 35 ºC. The incentive to achieve these parameters is the ability to most effectively use heat sources such as heat pumps and condensing boilers. At a secondary circuit temperature of 55/45 ºC, the COP efficiency coefficient for a ground-to-water heat pump is 3.6, and at 35/28 ºC it is already 4.6 (when operating only for heating). And the operation of boilers in condensation mode, requiring cooling of flue gases with return line water below the "dew point" (when burning liquid fuel - 47 ºC), gives a gain in efficiency of about 15% or more. Thus, a decrease in the temperature of the coolant provides significant savings in energy resources, and, accordingly, a reduction in carbon dioxide emissions into the atmosphere.
Until now, the "warm floor" and convectors with copper-aluminum heat exchangers were considered the main solution providing heating of premises at a low temperature of the heat carrier. Research initiated by Rettig ICC allowed steel panel radiators to be added to this range. (However, practice in this case goes ahead of theory, and such heating devices have been used for a long time as part of low-temperature systems in Sweden .
With the participation of several scientific organizations, including the universities of Helsinki and Dresden, the radiators have been tested under various controlled conditions. The results of other studies on the functioning of modern heating systems are also included in the "evidence base".
At the end of January 2011, research materials were presented to journalists from leading specialized publications in Europe at a seminar held at the Purmo-Radson training center in Erpfendorf (Austria). Presentations were made by Professor of the University of Brussels (Vrije Universitet Brussels, VUB) Lin Peters and the head of the Department of Energy Systems of the Institute of Building Physics. Fraunhofer-Institute for Building Physics (IBP) Dietrich Schmidt.
The report by Lin Peters considered the issues of thermal comfort, accuracy and responsiveness of the heating system to changing conditions, heat losses.
In particular, it was noted that the causes of local thermal discomfort are: radiation temperature asymmetry (depends on the heat-transfer surface and the orientation of the heat flow); the temperature of the floor surface (when it is outside the range of 19 to 27 ºC); vertical temperature difference (air temperature difference - from the ankle to the head of a standing person - should not exceed 4 ºC).
At the same time, the most comfortable for a person is not static, but "moving" temperature conditions (conclusion of the University of California, 2003). The interior space with areas with low temperature differences increases the feeling of comfort. But large temperature changes are the cause of the discomfort.
According to L. Peters, it is the radiators that transfer heat both by convection and radiation that are most suitable for ensuring thermal comfort.
Modern buildings are increasingly becoming thermally sensitive - thanks to improved thermal insulation. External and internal thermal disturbances (from sunlight, household appliances, the presence of people) can strongly affect the indoor climate. And radiators respond to these thermal changes more accurately than panel heating systems.
As you know, a "warm floor", especially located in a concrete screed, is a system with a high heat capacity, slowly reacting to regulatory influences.
Even if the "warm floor" is controlled by thermostats, a quick reaction to the supply of external heat is not possible. When laying heating pipes in a concrete screed, the response time of underfloor heating to changes in the amount of incoming heat is about two hours.
The room thermostat, which quickly reacted to the incoming heat, turns off the underfloor heating, which continues to give off heat for about two more hours. When the supply of external heat stops and the thermostatic valve is opened, the floor is completely heated only after the same time. Under these conditions, only the effect of self-regulation is effective.
Self-regulation is a complex dynamic process. In practice, it means that the supply of heat from the heater is regulated in a natural way due to the following two regularities: 1) heat always spreads from a hotter zone to a colder one; 2) the magnitude of the heat flux is determined by the temperature difference. The well-known (it is widely used when choosing heating devices) equation allows you to understand the essence of this:
Q = Qnom. ∙ (ΔT / ΔTnom.) N,
where Q is the heat transfer from the heater; ΔT is the difference between the temperature of the heater and the air in the room; Qnom. - heat transfer under nominal conditions; ΔTnom. - the difference between the temperature of the heater and the air in the room under nominal conditions; n is the exponent of the heater.
Self-regulation is common for both underfloor heating and radiators. In this case, for the "warm floor" the value of n is 1.1, and for the radiator - about 1.3 (exact values are given in the catalogs). That is, the response to the change in ΔT in the second case will be more "pronounced", and the restoration of the set temperature regime will occur faster.
From the point of view of regulation, it is also important that the surface temperature of the radiator is approximately equal to the temperature of the coolant, and in the case of underfloor heating this is not at all the case.
In case of short-term intensive influx of external heat, the control system of the "warm floor" cannot cope with the work, as a result of which there are fluctuations in the temperature of the room and floor. Some technical solutions allow them to be reduced, but not eliminated.
On the rice. one shows the graphs of changes in the operating temperature in the simulated conditions of an individual house when it is heated by adjustable high- and low-temperature radiators and a "warm floor" (research work by L. Peters and J. Van der Vecken).
The house can accommodate four people and is equipped with natural ventilation. Sources of third-party heat inputs are people and household appliances. The operating temperature is set as the comfort temperature.
21 ºC. The graphs consider two options for maintaining it: without switching to energy-saving (night) mode and with it.
Note: the operating temperature is an indicator characterizing the combined effect on a person of air temperature, radiation temperature and the speed of movement of the surrounding air.
Experiments have confirmed that radiators are clearly faster than a "warm floor" to respond to temperature fluctuations, providing smaller deviations.
The next reason for radiators, given in the workshop, is a more comfortable and energy efficient indoor temperature profile.
In 2008, John R. Meichren and Stur Holmberg published in the international journal Energy and Buildings F low patterns and thermal comfort in a room with panel, floor and wall heating). It, in particular, compares the vertical temperature distribution in rooms of the same area and layout (without furniture and people), heated by a radiator and a "warm floor" ( rice. 2). The outdoor temperature was -5 ºC. The air exchange rate is 0.8.
