Energy Efficiency

, Volume 8, Issue 3, pp 609–627 | Cite as

A study of the performances of low-temperature heating systems

  • Ioan SarbuEmail author
  • Calin Sebarchievici
Original Article


In Europe, high energy consumption in the building environment has raised the need for developing low-temperature heating systems both in new buildings and in retrofitting buildings. This paper addressed many different topics related to energy saving in central heating systems with reduced supply temperature and radiant panel heating including floor heating, ceiling heating and wall heating. The paper investigated the performance of these different types of low-temperature heating system using numerical modelling, simulation tools and also site measurements. Thus, energy performance of radiator and radiant floor heating systems connected to a ground-coupled heat pump (GCHP) is compared, as obtained with experimental measurements in an office room. Furthermore, the thermal comfort of these systems is compared and a mathematical model for numerical modelling of thermal emission from radiant floors is developed and experimentally validated. Additionally, a comparative analysis of the energy, environmental and economic performances of floor, wall, ceiling and floor-ceiling heating using numerical simulation is performed. Finally, the energy efficiency of a heat pump in conjunction with a radiator or radiant floor heating system is calculated for different supply, return, and air design temperatures. This study showed that floor-ceiling heating works better than other low-temperature heating systems regarding providing better thermal comfort, lower energy consumption, lower CO2 emission and lower operating cost.


Heating system Low temperature Radiator heating Radiant panel heating Heat pump Mathematical model Performances analysis 


Alphabetic symbols


Radiator surface (m2)


Air thermal diffusivity (m2/s)


Specific cost of electricity (€/kWh)


Specific cost of natural gas (€/m3)


Hot water specific heat (J/(kgK))


Carbon dioxide emission (kg)


Heat pump coefficient of performance


Annual performance coefficient


System coefficient of performance


Coefficient of variation


External pipe diameter (m)


Consumed electrical energy (kWh)


Consumption of natural gas (kWh)


Heating usable energy (kWh)


European Union


Gravitational acceleration (m/s2)


Ground-coupled heat pump


CO2 emission factor for electricity (kg CO2/kWh)


CO2 emission factor for natural gas (kg CO2/kWh)


Ground heat exchanger


Grashoff number


Room height (m)


Metabolic rate (met)


Correction coefficient of the natural gas consumption


Characteristic dimension of the element surface (m)


Mass flow rate of water (kg/s)


Number of measured data


Nusselt number


Predicted mean vote


Predicted percent dissatisfied (%)


Prandtl number


Heat flux (W/m2)


Radiant flux (W/m2)


Thermal diffusion resistance of compound floor layers above the tube (m2 K/W)


Coefficient of multiple determinations


Clothing thermal resistance (clo)


Heat transfer resistance at the internal surface (m2 K/W)


Root mean square


Distance from point P to the centre of the tube cross section (m)


Distance from point P to the centre of the virtual tube cross section (m)


Arrangement step of the radiant floor tubes (m)


Absolute temperature of radiant floor (K)


Weighted average absolute temperature of all room walls (K)


Mean heat carrier temperature (K or °C)


Operative (comfort) temperature (K or °C)


Supply hot water temperature (K or °C)


Outdoor air temperature (K or °C)


Mean floor surface temperature (K or °C)


Heat source temperature (K or °C)


Indoor air temperature (K or °C)


Mean radiant temperature (K or °C)


Temperature at floor surface point P (K or °C)


Hot water temperature in the inlet section of pipe (K or °C)


Hot water temperature in the outlet section of pipe (K or °C)


Transient Systems Simulation


Coefficient of heat transfer (W/(m2 K))


Uncertainty in the result Z


Measured value of one data point m


Computed value

\( {\overline{y}}_{mea,m} \)

Mean value of all measured data points

Greek symbols


Radiator exponent


Convective heat transfer coefficient (W/(m2 K))


Superficial heat transfer coefficient of the floor surface (W/(m2⋅K))


Radiative heat transfer coefficient (W/(m2 K))


Volumetric expansion coefficient of air (/K)


Thickness of layer j (m)


Logarithmic mean temperature difference (K)


Hot water temperature drop (K or °C)


Temperature difference between the floor surface and air (K or °C)


Floor surface emittance


Room wall emittance


Thermal insulation efficiency


Air thermal conductivity (W/(m K))


Thermal conductivity of layer j (W/(m K)


Air kinematic viscosity (m2/s)


Tube radius (m)


Stefan-Boltzmann constant (W/(m2 K4))


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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Department of Building Services EngineeringPolytechnic University TimisoaraTimisoaraRomania

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