1. By hot water

In this case the system is similar to a hot water heating system, with a boiler "Boiler (heating)") or other heating means, and a distribution network, but with the floor as emitter (or as has been said, another surface, although in hot water systems it is rare to find it), under which a pipe runs making meanders, so that the tubes are at a relatively short distance (between 8 and 30 cm).

The water pipes (generally made of plastic material) are distributed over the floor (see image), interposing a thermal insulator to prevent heat from dissipating to the lower floor. A layer of mortar "Mortar (construction)") made of cement or anhydrite and sand with a minimum thickness of 4 cm and a maximum of 6 cm is placed on the pipes. Then the flooring, which is recommended to be made of a poorly insulating material from heat (stone, ceramic or hydraulic tile) and not wood or carpet.[note 1]​ The unpleasant contact of the sole of the foot with a cold material, which we normally want to avoid with these thermal insulating floors, is compensated by the temperature of the floor.

If the building is well insulated, it is not necessary to cover the entire surface of the floor and you can leave some narrow strips, close to the walls, without pipes, to place furniture (shelves, sideboards,...) because under them the floor will not emit heat that could damage them.

Given the limitation of the ground surface temperature, in this case only regulation can be made by the heat transfer temperature (proportional regulation) which normally should not exceed 50-55 °C.[note 2]​ The system consists of a control unit that receives information from two temperature probes. One of the probes informs the control unit of the outside temperature, and depending on it, the control unit moves a motorized multi-way valve, mixing the water from the boiler with cooled return water, until the appropriate temperature of the water supplied to the network is achieved, according to the corresponding heating curve, at each moment, a temperature of which the other probe, located right at the beginning of the delivery pipe, informs the control unit.

It must be taken into account that the maximum soil temperature (the 28 or 29 °C mentioned) will only be needed in the coldest times of the year; the rest of the time (with lower heat needs), the emission must be done at a lower temperature, then the heat transfer temperature will also be lower.

This heating system also has a kind of natural self-regulation: as the ambient temperature rises (due to occupancy of many people, for example), the emitter-ambient thermal jump decreases, so the heat emission decreases, the heat carrier cools less and returns to the boiler hotter, reducing its work and saving fuel. As the surface-environment thermal jump is low (of the order of about 10 °C in the coldest times), an increase of 1 °C in the environment represents a 10% decrease in the emission on those coldest days. The truth is that the same thing happens to water systems and radiators at higher temperatures, but, as the thermal jump is much greater (50-60 °C), the savings are negligible (1-2%).

2. By electricity

There are also radiant wall systems that work by electricity. There are basically two ways to do it:

The electrical resistances are distributed over the floor,[note 3]​ interposing a thermal insulator to prevent heat from dissipating to the lower floor. A layer of mortar "Mortar (construction)") of cement and sand is placed on the resistors, and then the screed. Regarding the material of the flooring, see above what was said for the system with water pipes.

The carbon fiber system consists of a kind of weaving of these fibers, which function as resistance, in bands of a certain length, which have two electrical conductors on the sides and all wrapped in a sheath of flexible plastic material (as an electrical insulator). As has been said, in many countries it is prohibited to use anything under electrical voltage under the flooring (unless they are armored electrical resistance), so in those countries it is used on the ceiling: on a false ceiling of plaster or plasterboard, the sheet is placed and on top of it a fiberglass blanket insulator, so that the heat is directed exclusively to the heated room.[note 4]​.

In this case the regulation cannot be done by temperature of the emitter, but by time. It is regulated by a thermostat that cuts off the current of the resistors when the desired temperature is reached in the room; The lower the needs (depending on the outside temperature), the shorter the ignition time. It has the advantage that the regulation is done local by local, so that in the unused ones you can set a lower temperature, or even turn them off. The disadvantage is that the soil can reach the maximum temperature all season, even for short periods of time.

A more economical possibility is to use a system of water tubes, heated by a heat pump using electricity. In this case it would be an air-water pump (or water-water, if there is a possibility of having a suitable cold source) and then the installation would be through pipes, as in the previous case.

It is an old idea that underfloor heating (through pipes) could also serve as cooling in summer,[2]​ but the possibility that increasing the relative humidity of the air could reach the dew point on the floor and form puddles has paralyzed research.

Currently, it has been concluded that, although true cooling cannot be achieved, it is possible to cool the air by circulating cold water through the pipes, so that the ground temperature is always above the dew point; With this, at least the high temperatures in the hot season are mitigated. This is called cooling soil and works best in dry climates, naturally.

Contenido

Es interesante hablar de las energías que se utilizan para calentar, cuestión que tiene dos aspectos distintos: coste de la energía y posibilidad de que la energía sea ecológica.

Energy saving

As has been said, this system allows energy savings due to the possibility of lowering the dry temperature of the ambient air, thanks to the fact that there is a hot face, whose radiation serves to increase the average radiant temperature. The savings produced by this drop in the temperature of the indoor environment depends on the average outdoor temperatures throughout the heating season. In most of the peninsular territory of Spain, with normal average outdoor temperatures, the savings of this system, throughout the heating season, can be estimated between 15% and 20%, compared to a radiator heating system.

Residual or free energies

When it is a hot water system, these energies can be used, be it geothermal or the use of residual energy, although all of them require urban or neighborhood infrastructure (heat distribution network), an issue that is difficult to resolve when it comes directly to a building. Another possibility that can be applied to a building is cogeneration, although very difficult in a residential building.

Despite the title, none of these energies would be free, even if the source is free (geothermal) or produced as waste, since it requires infrastructure that must be built, cared for and maintained. In any case they are much cheaper and more ecological.

solar thermal energy

Solar thermal energy could be used for underfloor heating. The advantage is that the hot water system uses the heat transfer medium at a low temperature, less than or equal to about 50 °C, which facilitates good performance of the collectors. The fundamental disadvantage is that their performance drops significantly with low outside temperatures, which means that precisely the more heat is needed, the colder days, the performance is lower and they also coincide with the shortest days of the year, which means that there is less sunshine. Technically it is possible to achieve this, at the cost of a large collector surface, but then, in warmer times, the collectors will continue to produce heat and will have to be disposed of.

A possible solution to this problem is to accumulate heat in large water tanks during the warm season, for use in the cold seasons. But this also requires the use of district heating techniques, given the significant investment that must be made in collectors and accumulators.[3]​.

Electrical energy

Electricity has a high efficiency in heat production (approximately 98%) but in exchange it is the most expensive per unit of energy (kWh). And there are important reasons for this. The production of electricity by fuel has a fairly low efficiency: with diesel, fuel oil or coal, it is difficult to reach a efficiency of 40% on the primary energy.[4]​ The conversion of these primary energies into heat directly, in a boiler, is difficult to drop below a efficiency of 75-80%, so the same amount of fuel can give twice as much heat in a hot water heating system. There is also the production of electricity with natural gas in the combined cycle, which can provide up to 50% efficiency, but there are also natural gas boilers, condensing boilers, which can provide up to 98% seasonal efficiency.

Once the electricity is produced, it must be transported and to do this, it must also be transformed first into high voltage and then again into low voltage. In the transportation process, including transformations, it is estimated that another 50% of the electrical energy produced is lost, so 25% of the primary energy reaches the user's meter. This explains the difference in prices between combustion energy and electric energy.

Contrary to what many say, it is not true that electrical energy is "ecological." It is true that it does not pollute at the point of consumption, but it does so at the point of production. According to the Annual Report of the Observatory of Energy and Sustainable Development in Spain,[5] electricity production in this country, in 2003, was: nuclear 24%; fuels, 40%; hydraulics, 16%; renewable energies, 16%; others, 2%, that is, non-polluting ones only accounted for 32% this year.[6]​ In any case, renewable energies (wind and solar) will have greater importance every day in the national balance, so that the problem of greenhouse gas pollution will decrease.

However, electricity can serve as energy in underfloor heating systems through pipes and water, heating the water using a heat pump powered by electrical energy.

In Iceland, where there are abundant hot springs, underfloor heating is used to thaw ice on the streets of the capital, Reykjavík, on cold days.

Also at the Copahue Thermal Tourist Center in the province of Neuquén, Argentina, it was inaugurated

in 1999 a radiant floor street heating system, taking advantage of natural hot springs.

1. By hot water

In this case the system is similar to a hot water heating system, with a boiler "Boiler (heating)") or other heating means, and a distribution network, but with the floor as emitter (or as has been said, another surface, although in hot water systems it is rare to find it), under which a pipe runs making meanders, so that the tubes are at a relatively short distance (between 8 and 30 cm).

The water pipes (generally made of plastic material) are distributed over the floor (see image), interposing a thermal insulator to prevent heat from dissipating to the lower floor. A layer of mortar "Mortar (construction)") made of cement or anhydrite and sand with a minimum thickness of 4 cm and a maximum of 6 cm is placed on the pipes. Then the flooring, which is recommended to be made of a poorly insulating material from heat (stone, ceramic or hydraulic tile) and not wood or carpet.[note 1]​ The unpleasant contact of the sole of the foot with a cold material, which we normally want to avoid with these thermal insulating floors, is compensated by the temperature of the floor.

If the building is well insulated, it is not necessary to cover the entire surface of the floor and you can leave some narrow strips, close to the walls, without pipes, to place furniture (shelves, sideboards,...) because under them the floor will not emit heat that could damage them.

Given the limitation of the ground surface temperature, in this case only regulation can be made by the heat transfer temperature (proportional regulation) which normally should not exceed 50-55 °C.[note 2]​ The system consists of a control unit that receives information from two temperature probes. One of the probes informs the control unit of the outside temperature, and depending on it, the control unit moves a motorized multi-way valve, mixing the water from the boiler with cooled return water, until the appropriate temperature of the water supplied to the network is achieved, according to the corresponding heating curve, at each moment, a temperature of which the other probe, located right at the beginning of the delivery pipe, informs the control unit.

It must be taken into account that the maximum soil temperature (the 28 or 29 °C mentioned) will only be needed in the coldest times of the year; the rest of the time (with lower heat needs), the emission must be done at a lower temperature, then the heat transfer temperature will also be lower.

This heating system also has a kind of natural self-regulation: as the ambient temperature rises (due to occupancy of many people, for example), the emitter-ambient thermal jump decreases, so the heat emission decreases, the heat carrier cools less and returns to the boiler hotter, reducing its work and saving fuel. As the surface-environment thermal jump is low (of the order of about 10 °C in the coldest times), an increase of 1 °C in the environment represents a 10% decrease in the emission on those coldest days. The truth is that the same thing happens to water systems and radiators at higher temperatures, but, as the thermal jump is much greater (50-60 °C), the savings are negligible (1-2%).

2. By electricity

There are also radiant wall systems that work by electricity. There are basically two ways to do it:

The electrical resistances are distributed over the floor,[note 3]​ interposing a thermal insulator to prevent heat from dissipating to the lower floor. A layer of mortar "Mortar (construction)") of cement and sand is placed on the resistors, and then the screed. Regarding the material of the flooring, see above what was said for the system with water pipes.

The carbon fiber system consists of a kind of weaving of these fibers, which function as resistance, in bands of a certain length, which have two electrical conductors on the sides and all wrapped in a sheath of flexible plastic material (as an electrical insulator). As has been said, in many countries it is prohibited to use anything under electrical voltage under the flooring (unless they are armored electrical resistance), so in those countries it is used on the ceiling: on a false ceiling of plaster or plasterboard, the sheet is placed and on top of it a fiberglass blanket insulator, so that the heat is directed exclusively to the heated room.[note 4]​.

In this case the regulation cannot be done by temperature of the emitter, but by time. It is regulated by a thermostat that cuts off the current of the resistors when the desired temperature is reached in the room; The lower the needs (depending on the outside temperature), the shorter the ignition time. It has the advantage that the regulation is done local by local, so that in the unused ones you can set a lower temperature, or even turn them off. The disadvantage is that the soil can reach the maximum temperature all season, even for short periods of time.

A more economical possibility is to use a system of water tubes, heated by a heat pump using electricity. In this case it would be an air-water pump (or water-water, if there is a possibility of having a suitable cold source) and then the installation would be through pipes, as in the previous case.

It is an old idea that underfloor heating (through pipes) could also serve as cooling in summer,[2]​ but the possibility that increasing the relative humidity of the air could reach the dew point on the floor and form puddles has paralyzed research.

Currently, it has been concluded that, although true cooling cannot be achieved, it is possible to cool the air by circulating cold water through the pipes, so that the ground temperature is always above the dew point; With this, at least the high temperatures in the hot season are mitigated. This is called cooling soil and works best in dry climates, naturally.

Contenido

Es interesante hablar de las energías que se utilizan para calentar, cuestión que tiene dos aspectos distintos: coste de la energía y posibilidad de que la energía sea ecológica.

Energy saving

As has been said, this system allows energy savings due to the possibility of lowering the dry temperature of the ambient air, thanks to the fact that there is a hot face, whose radiation serves to increase the average radiant temperature. The savings produced by this drop in the temperature of the indoor environment depends on the average outdoor temperatures throughout the heating season. In most of the peninsular territory of Spain, with normal average outdoor temperatures, the savings of this system, throughout the heating season, can be estimated between 15% and 20%, compared to a radiator heating system.

Residual or free energies

When it is a hot water system, these energies can be used, be it geothermal or the use of residual energy, although all of them require urban or neighborhood infrastructure (heat distribution network), an issue that is difficult to resolve when it comes directly to a building. Another possibility that can be applied to a building is cogeneration, although very difficult in a residential building.

Despite the title, none of these energies would be free, even if the source is free (geothermal) or produced as waste, since it requires infrastructure that must be built, cared for and maintained. In any case they are much cheaper and more ecological.

solar thermal energy

Solar thermal energy could be used for underfloor heating. The advantage is that the hot water system uses the heat transfer medium at a low temperature, less than or equal to about 50 °C, which facilitates good performance of the collectors. The fundamental disadvantage is that their performance drops significantly with low outside temperatures, which means that precisely the more heat is needed, the colder days, the performance is lower and they also coincide with the shortest days of the year, which means that there is less sunshine. Technically it is possible to achieve this, at the cost of a large collector surface, but then, in warmer times, the collectors will continue to produce heat and will have to be disposed of.

A possible solution to this problem is to accumulate heat in large water tanks during the warm season, for use in the cold seasons. But this also requires the use of district heating techniques, given the significant investment that must be made in collectors and accumulators.[3]​.

Electrical energy

Electricity has a high efficiency in heat production (approximately 98%) but in exchange it is the most expensive per unit of energy (kWh). And there are important reasons for this. The production of electricity by fuel has a fairly low efficiency: with diesel, fuel oil or coal, it is difficult to reach a efficiency of 40% on the primary energy.[4]​ The conversion of these primary energies into heat directly, in a boiler, is difficult to drop below a efficiency of 75-80%, so the same amount of fuel can give twice as much heat in a hot water heating system. There is also the production of electricity with natural gas in the combined cycle, which can provide up to 50% efficiency, but there are also natural gas boilers, condensing boilers, which can provide up to 98% seasonal efficiency.

Once the electricity is produced, it must be transported and to do this, it must also be transformed first into high voltage and then again into low voltage. In the transportation process, including transformations, it is estimated that another 50% of the electrical energy produced is lost, so 25% of the primary energy reaches the user's meter. This explains the difference in prices between combustion energy and electric energy.

Contrary to what many say, it is not true that electrical energy is "ecological." It is true that it does not pollute at the point of consumption, but it does so at the point of production. According to the Annual Report of the Observatory of Energy and Sustainable Development in Spain,[5] electricity production in this country, in 2003, was: nuclear 24%; fuels, 40%; hydraulics, 16%; renewable energies, 16%; others, 2%, that is, non-polluting ones only accounted for 32% this year.[6]​ In any case, renewable energies (wind and solar) will have greater importance every day in the national balance, so that the problem of greenhouse gas pollution will decrease.

However, electricity can serve as energy in underfloor heating systems through pipes and water, heating the water using a heat pump powered by electrical energy.

In Iceland, where there are abundant hot springs, underfloor heating is used to thaw ice on the streets of the capital, Reykjavík, on cold days.

Also at the Copahue Thermal Tourist Center in the province of Neuquén, Argentina, it was inaugurated

in 1999 a radiant floor street heating system, taking advantage of natural hot springs.