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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

Abstract

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.

Keywords

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

Abbreviations

Alphabetic symbols

AR

Radiator surface (m2)

a

Air thermal diffusivity (m2/s)

cel

Specific cost of electricity (€/kWh)

cg

Specific cost of natural gas (€/m3)

cp

Hot water specific heat (J/(kgK))

CO2

Carbon dioxide emission (kg)

COP

Heat pump coefficient of performance

COPa

Annual performance coefficient

COPsyst

System coefficient of performance

cv

Coefficient of variation

De

External pipe diameter (m)

Eel

Consumed electrical energy (kWh)

Eg

Consumption of natural gas (kWh)

Et

Heating usable energy (kWh)

EU

European Union

g

Gravitational acceleration (m/s2)

GCHP

Ground-coupled heat pump

gel

CO2 emission factor for electricity (kg CO2/kWh)

gg

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

GHE

Ground heat exchanger

Gr

Grashoff number

h

Room height (m)

iM

Metabolic rate (met)

k

Correction coefficient of the natural gas consumption

L

Characteristic dimension of the element surface (m)

m

Mass flow rate of water (kg/s)

N

Number of measured data

Nu

Nusselt number

PMV

Predicted mean vote

PPD

Predicted percent dissatisfied (%)

Pr

Prandtl number

q

Heat flux (W/m2)

qr

Radiant flux (W/m2)

R

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

R2

Coefficient of multiple determinations

Rcl

Clothing thermal resistance (clo)

Ri

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

RMS

Root mean square

r

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

r’

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

s

Arrangement step of the radiant floor tubes (m)

T1

Absolute temperature of radiant floor (K)

T2

Weighted average absolute temperature of all room walls (K)

tag

Mean heat carrier temperature (K or °C)

tc

Operative (comfort) temperature (K or °C)

td

Supply hot water temperature (K or °C)

te

Outdoor air temperature (K or °C)

tf

Mean floor surface temperature (K or °C)

ths

Heat source temperature (K or °C)

ti

Indoor air temperature (K or °C)

tmr

Mean radiant temperature (K or °C)

tP

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

twi

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

two

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

TRNSYS

Transient Systems Simulation

U

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

wZ

Uncertainty in the result Z

ymea,m

Measured value of one data point m

ycom,m

Computed value

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

Mean value of all measured data points

Greek symbols

α

Radiator exponent

αc

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

αi

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

αr

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

β

Volumetric expansion coefficient of air (/K)

δj

Thickness of layer j (m)

Δt

Logarithmic mean temperature difference (K)

Δtw

Hot water temperature drop (K or °C)

Δtf-a

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

ε1

Floor surface emittance

ε2

Room wall emittance

ηiz

Thermal insulation efficiency

λ

Air thermal conductivity (W/(m K))

λj

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

ν

Air kinematic viscosity (m2/s)

ρ

Tube radius (m)

σ

Stefan-Boltzmann constant (W/(m2 K4))

References

  1. Ali, A. H., & Morsy, M. G. (2010). Energy efficiency and indoor thermal perception: a comparative study between radiant panel and portable convective heaters. Energy Efficiency, 3, 283–301.CrossRefGoogle Scholar
  2. Allard, F., & Seppänen, O. (2008). European actions to improve energy efficiency of buildings. Rehva Journal, 45(1), 10–20.Google Scholar
  3. Andersen, N. (1999). End users dictate the potential for low temperature district heating. Energy and Environment Journal, 4, 30–31.Google Scholar
  4. Anisimova, N. (2011). The capability to reduce primary energy demand in EU housing. Energy and Buildings, 43, 2747–2751.CrossRefGoogle Scholar
  5. Ardehali, M. M., Panah, N. G., & Smith, T. F. (2004). Proof of concept modeling of energy transfer mechanisms for radiant conditioning panels. Energy Conversion and Management, 45, 2005–2017.CrossRefGoogle Scholar
  6. ASHRAE Handbook. (2011). HVAC applications. Atlanta: American Society of Heating, Refrigerating and Air Conditioning Engineers.Google Scholar
  7. ASHRAE Handbook. (2012). HVAC systems and equipment. Atlanta: American Society of Heating, Refrigerating and Air Conditioning Engineers.Google Scholar
  8. ASHRAE Handbook. (2013). Fundamentals. Atlanta: American Society of Heating, Refrigerating and Air Conditioning Engineers.Google Scholar
  9. ASHRAE Standard 55. (2010). Thermal environmental conditions for human occupancy. Atlanta: American Society of Heating, Refrigerating and Air-conditioning Engineers.Google Scholar
  10. Bechthler, H., Browne, M. W., Bansal, P. K., & Kecman, V. (2001). New approach to dynamic modelling of vapour-compression liquid chillers: artificial neural networks. Applied Thermal Engineering, 21(9), 941–953.CrossRefGoogle Scholar
  11. Berglund, L. G., & Fobelets, A. (1987). A subjective human response to low level air currents and asymmetric radiation. ASHRAE Transactions, 93(1), 497–523.Google Scholar
  12. Bojic, M., Cvetkovic, D., Miletic, M., Malesevic, J., & Boyer, H. (2012). Energy, cost, and CO2 emission comparison between radiant wall panel systems and radiator systems. Energy and Buildings, 54, 496–502.CrossRefGoogle Scholar
  13. BUDERUS. (1994). Handbuch fur Heizung-stechnik. Berlin: Beuth Verlag.Google Scholar
  14. Chen, Q. (1990). Comfort and energy consumption analysis in buildings with radiant panels. Energy and Buildings, 14, 287–297.CrossRefGoogle Scholar
  15. Demidovitch, B., & Maron, I. (1979). Elements of numerical computation. Moscow: Mir.Google Scholar
  16. Hanibuchi, H., & Hokoi, S. (2000). Simplified method of estimating efficiency of radiant and convective heating systems. ASHRAE Transactions, 106(1), 487–494.Google Scholar
  17. Hasan, A., Kurnitski, J., & Jokiranta, K. (2009). A combined low temperature water heating system consisting of radiators and floor heating. Energy and Buildings, 41(5), 470–479.CrossRefGoogle Scholar
  18. Henze, G. P., Felsmann, C., Kalz, D., & Herkel, S. (2008). Primary energy and comfort performance of ventilation assisted thermo-active building system in continental climates. Energy and Buildings, 40(2), 99–111.CrossRefGoogle Scholar
  19. Hesaraki, A., & Holmberg, S. (2013). Energy performance of low temperature heating systems in five new-built Swedish dwellings: A case study using simulations and on-site measurements. Building and Environment, 64, 85–93.Google Scholar
  20. Holman, J. P. (2001). Experimental method for engineers. Singapore: McGraw Hill.Google Scholar
  21. IEE. (2013). Intelligent Energy Europe. http://ec.europa.eu/energy/environment.
  22. Iivonen, M. (2009). Energy efficiency of radiator heating. Rehva Journal, 46(3), 32–34.Google Scholar
  23. Ilina, M., & Burchiu, S. (1996). Influence of heating systems on microclimate from living rooms. Fitter, Romania, 6, 24–29.Google Scholar
  24. Imanari, T., Omori, T., & Bogaki, K. (1999). Thermal comfort and energy consumption of the radiant ceiling panel system comparison with the conventional all-air system. Energy and Buildings, 30, 167–175.CrossRefGoogle Scholar
  25. ISO 7730. (2005). Moderate thermal environment—determination of the PMV and PPD indices and specification of the conditions for thermal comfort. Geneva: International Organization for Standardization.Google Scholar
  26. ISO/TS 13732–2. (2001). Ergonomics of the thermal environment. Methods for the assessment of human responses to contact with surface, Part 2: Human contact with surfaces at moderate temperature. Geneva: International Organization for Standardization.Google Scholar
  27. Kalmar, F. (2004). Adjustment of central heating systems to reduce energy needs of retrofitted buildings. Doctoral thesis, University of Technology and Economics of Budapest, Hungary.Google Scholar
  28. Kilkis, I., Sager, S., & Uludag, M. (1994). A simplified model for radiant heating and cooling panels. Simulation Practice and Theory, 2, 61–76.CrossRefGoogle Scholar
  29. Kilkis, I., Eltez, M., & Sager, S. (1995). A simplified model for the design of radiant in slab heating panels. ASHRAE Transactions, 99, 210–216.Google Scholar
  30. Laouadi, A. (2004). Development of a radiant heating and cooling model for building energy simulation software. Building and Environment, 39, 421–431.CrossRefGoogle Scholar
  31. Miriel, J., Serres, L., & Trombe, A. (2002). Radiant ceiling panel heating-cooling systems: experimental and simulated study of the performances, thermal comfort and energy consumptions. Applied Thermal Engineering, 22(16), 1861–1873.CrossRefGoogle Scholar
  32. Roumajon, J. (1996). Modélisation numerique des émissions thermiques. Chaud, Froid and Plomberie, 579(4), 55–58.Google Scholar
  33. Sarbu, I. (2010a). Energetically analysis of unbalanced central heating systems: In Recent Advances in Energy & Environment, Proceedings of the 5th IASME/WSEAS Int. Conference on Energy and Environment. Cambridge, UK.Google Scholar
  34. Sarbu, I. (2010b). Energy efficiency of low temperature central heating systems. In Advances in Energy Planning, Environmental Education and Renewable Energy Sources, Proc. of the 4th WSEAS Int. Conference on Energy Panning, Energy Saving and, Environmental Education. Kantaoui, Sousse, Tunisia.Google Scholar
  35. Sarbu, I. (2013). Influence of heating systems on indoor environment in buildings. In Ecology, Economics, Education and Legislation, Proc. of the 13th Int. Multidisciplinary Scientific GeoConference SGEM2013. Albena, Bulgaria, vol. 1, 583–590.Google Scholar
  36. Sarbu, I., & Sebarchievici, C. (2013). Aspects of indoor environmental quality assessment in buildings. Energy and Buildings, 60, 410–419.CrossRefGoogle Scholar
  37. Sarbu, I., & Sebarchievici, C. (2014). General review of ground-source heat pump systems for heating and cooling of buildings. Energy and Buildings, 70(2), 441–454.CrossRefGoogle Scholar
  38. Sarbu, I., Bancea, O., & Cinca, M. (2009). Influence of forward temperature on energy consumption in central heating systems. WSEAS Transaction on Heat and Mass Transfer, 4(3), 45–54.Google Scholar
  39. Stetiu, C. (1999). Energy and peak power potential of radiant cooling systems in US commercial buildings. Energy and Buildings, 30, 127–138.CrossRefGoogle Scholar
  40. Strand, R. K., & Baumgartner, K. T. (2005). Modeling radiant heating and cooling systems: integration with a whole-building simulation program. Energy and Buildings, 37, 389–397.CrossRefGoogle Scholar
  41. Strand, K., & Pederson, O. (2002). Modelling radiant systems in an integrated heat balance based energy simulation program. ASHRAE Transactions, 108, 1–9.Google Scholar
  42. THERMAL COMFORT tool. (2011). Version 2, ASHRAE. Berkeley: Centre for the Built Environment.Google Scholar
  43. TRNSYS 17 Manual. (2012). Getting started, vol. 1, 5. Madison: Solar Energy Laboratory, University of Wisconsin.Google Scholar
  44. Yost, A., Barbour, E., & Watson, R. (1995). An evaluation of thermal comfort and energy consumption for a surface mounted ceiling radiant panel heating system. ASHRAE Transactions, 101, 1221–1235.Google Scholar
  45. Zhang, Z., & Pate, B. (1987). A semi analytical formulation of heat transfer from structures with embedded tubes. Heat Transfer in Buildings and Structures, 78, 17–25.Google Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Department of Building Services EngineeringPolytechnic University TimisoaraTimisoaraRomania

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