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Low-temperature baseboard heaters with integrated air supply - An analytical and numerical investigation
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.ORCID iD: 0000-0001-5902-2886
KTH, School of Technology and Health (STH), Centres, Centre for Technology in Medicine and Health, CTMH.ORCID iD: 0000-0003-1882-3833
2011 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 46, no 1, 176-186 p.Article in journal (Refereed) Published
Abstract [en]

The functioning of a hydronic baseboard heating system with integrated air supply was analyzed. The aim was to investigate thermal performance of the system when cold outdoor (ventilation) airflow was forced through the baseboard heater. The performance of the system was evaluated for different ventilation rates at typical outdoor temperatures during the Swedish winter season. Three different analytical models and Computational Fluid Dynamics (CFD) were used to predict the temperature rise of the airflow inside the baseboard heater. Good agreement between numerical (CFD) and analytical calculations was obtained. Calculations showed that it was fully possible to pre-heat the incoming airflow to the indoor temperature and to cover transmission losses, using 45 degrees C supply water flow. The analytical calculations also showed that the airflow per supply opening in the baseboard heater needed to be limited to 7.0 l/s due to pressure losses inside the channel. At this ventilation rate, the integrated system with one air supply gave about 2.1 more heat output than a conventional baseboard heating system. CFD simulations also showed that the integrated system was capable of countering downdraught created by 2.0 m high glazed areas and a cold outdoor environment. Draught discomfort in the case with the conventional system was slightly above the recommended upper limit, but heat distribution across whole analyzed office space was uniform for both heating systems. It was concluded that low-temperature baseboard heating systems with integrated air supply can meet both international comfort requirements, and lead to energy savings in cold climates.

Place, publisher, year, edition, pages
2011. Vol. 46, no 1, 176-186 p.
Keyword [en]
Baseboard (skirting) heating, Low-temperature hydronic heating, Forced convective heat transfer, Channel airflow, Thermal comfort, CFD
URN: urn:nbn:se:kth:diva-25720DOI: 10.1016/j.buildenv.2010.07.011ISI: 000282407600019ScopusID: 2-s2.0-77956226184OAI: diva2:359571
QC 20101028Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2013-10-29Bibliographically approved
In thesis
1. Low - Temperature Basedboard Heaters in Built Environments
Open this publication in new window or tab >>Low - Temperature Basedboard Heaters in Built Environments
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The European Union has adopted a plan to decrease 20 % of total energy consumption through improved energy efficiency by 2020. One way of achieving this challenging goal may be to use efficient water-based heating systems supplied by heat pumps or othersustainable systems. The goal of this research was to analyze and improve the thermalperformance of water-based baseboard heaters at low-temperature water supply. Both numerical (CFD) and analytical simulations were used to investigate the heat efficiency of the system. An additional objective of this work was to ensure that the indoor thermal comfort was satisfied in spaces served by such a low-temperature heating system.

Analyses showed that it was fully possible to cover both transmission and ventilation heatl osses using baseboard heaters supplied by 45 °C water flow. The conventional baseboards, however, showed problems in suppressing the cold air down-flow created by 2.0 m high glazing and an outdoor temperature of – 12 °C. The draught discomfort at ankle level was slightly above the upper limit recommended by international and national standards. On the other hand, thermal baseboards with integrated ventilation air supply showed better ability to neutralize cold downdraught at the same height and conditions. Calculations also showed that the heat output from the integrated system with one ventilation inlet was approximately twiceas high as that of the conventional one. The general conclusion from this work was that low-temperature baseboards, especially with integrated ventilation air supply, are an efficient heating system and able to be combined with devices that utilize the low-quality sustainable energy sources such as heat pumps.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 18 p.
Trita-STH : report, ISSN 1653-3836 ; 2010:4
Baseboard (skirting) heating, Low-temperature heating, Thermal comfort, Heat transfer, CFD
National Category
Chemical Engineering
urn:nbn:se:kth:diva-25725 (URN)978-91-7415-744-4 (ISBN)
2010-10-29, Sal V2, Teknikringen 76, KTH, Stockholm, 13:00 (English)
QC 20101029Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2010-10-29Bibliographically approved
2. Technical solutions for low-temperature heat emission in buildings
Open this publication in new window or tab >>Technical solutions for low-temperature heat emission in buildings
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The European Union is planning to greatly decrease energy consumption during the coming decades. The ultimate goal is to create sustainable communities that are energy neutral. One way of achieving this challenging goal may be to use efficient hydronic (water-based) heating systems supported by heat pumps.

The main objective of the research reported in this work was to improve the thermal performance of wall-mounted hydronic space heaters (radiators). By improving the thermal efficiency of the radiators, their operating temperatures can be lowered without decreasing their thermal outputs. This would significantly improve efficiency of the heat pumps, and thereby most probably also reduce the emissions of greenhouse gases. Thus, by improving the efficiency of radiators, energy sustainability of our society would also increase. The objective was also to investigate how much the temperature of the supply water to the radiators could be lowered without decreasing human thermal comfort.

Both numerical and analytical modeling was used to map and improve the thermal efficiency of the analyzed radiator system. Analyses have shown that it is possible to cover space heat losses at low outdoor temperatures with the proposed heating-ventilation systems using low-temperature supplies. The proposed systems were able to give the same heat output as conventional radiator systems but at considerably lower supply water temperature. Accordingly, the heat pump efficiency in the proposed systems was in the same proportion higher than in conventional radiator systems.

The human thermal comfort could also be maintained at acceptable level at low-temperature supplies with the proposed systems. In order to avoid possible draught discomfort in spaces served by these systems, it was suggested to direct the pre-heated ventilation air towards cold glazed areas. By doing so the draught discomfort could be efficiently neutralized.    

Results presented in this work clearly highlight the advantage of forced convection and high temperature gradients inside and alongside radiators - especially for low-temperature supplies. Thus by a proper combination of incoming air supply and existing radiators a significant decrease in supply water temperature could be achieved without decreasing the thermal output from the system. This was confirmed in several studies in this work. It was also shown that existing radiator systems could successfully be combined with efficient air heaters. This also allowed a considerable reduction in supply water temperature without lowering the heat output of the systems. Thus, by employing the proposed methods, a significant improvement of thermal efficiency of existing radiator systems could be accomplished. A wider use of such combined systems in our society would reduce the distribution heat losses from district heating networks, improve heat pump efficiency and thereby most probably also lower carbon dioxide emissions.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 34 p.
Analytical and numerical modeling, baseboard (skirting) heating, building energy performance, computational fluid dynamics (CFD), heat transfer, low-temperature heating, space heating, thermal comfort
National Category
Energy Engineering
Research subject
Järnvägsgruppen - Effektiva tågsystem för godstrafik
urn:nbn:se:kth:diva-133221 (URN)978-91-7501-940-6 (ISBN)
Public defence
2013-11-15, Sal: Q2, Osquldasväg 10, KTH, Stockholm, 13:00 (English)
Swedish Energy Agency

QC 20131029

Available from: 2013-10-29 Created: 2013-10-29 Last updated: 2013-11-19Bibliographically approved

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