Underfloor heating is a reliable and efficient form of heating which combines thermal comfort conditions and economic operation. In this system, hot water of 35-45oC temperature flows through a circuit of pipes which is embedded into the floor of every room/space, turning the floor itself to become a heating radiator. The maximum surface temperature reaches 29oC in ordinary living areas. The heat from the floor to the heated space is transfered from the lower to higher layers across the surface area without strong currents, achieving in this way almost the desired stratification of temperature, i.e. at head height about 18 - 20oC. This fact, combined with the reduced heat transfer from the ends of the human body to warm floors, make an underfloor heating system ideal for thermal comfort.

The referred system is the most advanced solution not only for housing and business premises, but also for schools, churches, kindergartens, gymnasiums, science labs, restored houses. It operates in a simple way : Under the final floor lays the castellated panel over on which the tubes creating the corresponding circuits are placed. This achieves a harmonious flow of water across the floor and produces uniform heating. The floor works so long as a radiator for the space.
Before installing an underfloor heating system, it is necessary to study the installation (by an engineer), and after that comes the careful selection of the necessary materials and skilled installation crew.
A typical installation of underfloor heating, starting from the floor plate, requires the following materials: insulation material that meets the thermal insulation rules, vapour barrier, pipe supports, pipe, the screed (called thermobeton) and finally the topcoat. It is also necessary to place a pair of hydraulic collectors (for inlet and return circuits) on a wall inside the house and in such position that satisfies the symmetric loading of the system (similar as possible circuits). The maximum length of the circuits is about 80-120m for PE-X tubes Φ16x2.
By adding a chiller, the system itself becomes a cooling system during summer. The water supply temperature is about 16-18oC in the floor pipes, turning the floor into a heat absorber. When there is balance in the area, the body eliminates significant amounts of heat, so feeling a pleasant coolness. The underfloor cooling advantages because it is achieved without strong air currents into the living area and also because of the reduced power consumption.
Significant difference in the functioning of the system is that the underfloor cooling system controls in place both temperature and relative humidity values, finaly creating conditions close to ideal. For example, in an area with an indoor temperature of 20oC and relative humidity of 70%, the human body feels discomfort, while with an indoor temperature of 24oC and relative humidity of 50-55%, it receives a sense of the ideal feeling. The above example refers to outdoor temperature of 37oC.
Regarding the type of final floor coating, it should be mentioned that the tile and marble have the best coefficient of thermal conductivity, while using wood we reduce the cooling efficiency of about 5%.
The abundant solar energy in combination with the reduced requirements of underfloor heating, invite us to use the solar power not only for the production of domestic hot water (DHW), but also for heating the house.
The combined operation of solar thermal systems for DHW and space heating can meet on an annual basis by 10%-50% needs a home in heating and hot water, depending on the size of the collector surface to be installed, the volume of buffer tank, meteorological data of the region and the characteristics of the home (size, quality of insulation, thermal requirements). The ideal application of the system is in houses with good insulation and heating at low temperatures (underfloor type).
Generally these systems comprise the circuit of solar panels (energy production), the buffer tank (energy storage), an auxiliary power system (heat pump, oil or gas or electric boiler), a heating system (underfloor circuit) and a control system (PLC).
The solar energy collected in solar panels is converted into heat and transferred to a specially designed buffer tank, which heats the water for the heating and the domestic hot water circuits.
If solar energy is not enough, the auxiliary power source is automatically turned on and completes the required action. With this method high fuel economy is achieved. Space heating and hot water heating is achieved in a manner which is environmentally friendly, particularly in a country like Greece, where the need for saving energy and reducing greenhouse gas emissions becomes increasingly urgent.

Underfloor heating and cooling procedure can be powered by the stored energy on earth. The geothermal air conditioning is based on a simple principle whereby a few meters below the surface of the earth the ground temperature is constant. So if we take advantage of the ground/surface temperature difference, we can heat spaces in winter and cool them in summer. This can be done by installing a heat pump and a piping network.
The methods of installing a geothermal system vary depending on terrain, the available area of land, the existence or not of a groundwater flow, the requirements of space air conditioning and other factors. Therefore each case should be defined and designed independently. We have 2 types of geothermal systems : Closed circuit geothermal systems - either horizontal shallow depth system, or vertical system using blind boreholes. Open circuit geothermal systems - pumping and rejection of groundwater by means of drilling in an open borehole.

* Written by Dimitris Tsiatsios, Chemical Engineer NTUA, and owner of Technical and Construction Company YDROENERGIA, located in Corfu.

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