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Technical solutions for low-temperature heat emission in buildings
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.ORCID iD: 0000-0001-5902-2886
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.
Keyword [en]
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
Identifiers
URN: urn:nbn:se:kth:diva-133221ISBN: 978-91-7501-940-6 (print)OAI: oai:DiVA.org:kth-133221DiVA: diva2:660277
Public defence
2013-11-15, Sal: Q2, Osquldasväg 10, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QC 20131029

Available from: 2013-10-29 Created: 2013-10-29 Last updated: 2013-11-19Bibliographically approved
List of papers
1. Heat emission from thermal skirting boards
Open this publication in new window or tab >>Heat emission from thermal skirting boards
2010 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 45, no 5, 1123-1133 p.Article in journal (Refereed) Published
Abstract [en]

The performance of three hydronic skirting heating systems was investigated. The main focus of this study was to ascertain whether thermal skirting boards served by low-temperature supply flow were able to suppress strong downdraught. The evaluation was made for a two-person office room with mechanical ventilation. Computational Fluid Dynamics (CFD) simulations and three different draught rating models were employed to predict the level of thermal discomfort inside the room. CFD results were validated against several analytical calculations and four sets of experimental data presented in previous studies. Numerical simulations showed that all three skirting heating arrangements were able to cover transmission and ventilation thermal losses of the office room. Horizontal and vertical heat distribution inside the room was uniform for all heating systems. CFD simulations also showed that thermal skirting boards served by 40 and 45 degrees C supply flow had difficulty in reducing the velocity of the downdraught at ankle level. Consequently the draught rating in this region was around or slightly above 15% for these cases. In contrast, heat-emitting skirting boards supplied by 55 degrees C hot water showed a better ability to suppress downdraught, and the proportion of people sensing draught at 0.1 m above the floor was low. The conclusion of this study was that thermal performance of hydronic skirting heaters with low-temperature water supply must be improved in order to counter strong downdraughts, in particular where such systems may be combined with heat pumps of other low-valued sustainable energy sources.

Keyword
CFD simulations, Draught (draft) sensation, Low-temperature heating, Skirting (baseboard) heating, Thermal comfort, air, draft
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-19243 (URN)10.1016/j.buildenv.2009.10.016 (DOI)000274835800004 ()2-s2.0-74149086415 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2013-11-19Bibliographically approved
2. Low-temperature baseboard heaters with integrated air supply - An analytical and numerical investigation
Open this publication in new window or tab >>Low-temperature baseboard heaters with integrated air supply - An analytical and numerical investigation
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.

Keyword
Baseboard (skirting) heating, Low-temperature hydronic heating, Forced convective heat transfer, Channel airflow, Thermal comfort, CFD
Identifiers
urn:nbn:se:kth:diva-25720 (URN)10.1016/j.buildenv.2010.07.011 (DOI)000282407600019 ()2-s2.0-77956226184 (Scopus ID)
Note
QC 20101028Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2013-10-29Bibliographically approved
3. Low-temperature ventilation pre-heater in combination with conventional room heaters
Open this publication in new window or tab >>Low-temperature ventilation pre-heater in combination with conventional room heaters
2013 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 65, 248-259 p.Article in journal (Refereed) Published
Abstract [en]

The main focus of the present study was to find design requirements for an air-heater that would be able to operate at low pressure loss and low-temperature water supply. The idea was to combine this low-temperature air-heater with existing radiator systems so that they can operate at similar low-temperature supply as used in floor heating systems. Results indicated that the proposed air-heater was able to lift the temperature of supply air at 10 l/s from -15 degrees C to 18.7 degrees C using 40 degrees C water supply. In addition, a thermal performance analysis showed that radiator systems equipped with the proposed air-heater could meet a space heat loss of 35.6 W per square meter floor area, using supply water of 40 degrees C. It was also shown that the heat pump efficiency in the hydronic system with proposed air-heater was 8-18% higher than in system without air-heater. All results in the present study were obtained by analytical (semi-empirical) and numerical (Computational Fluid Dynamics - CFD) calculations.

Keyword
Low-temperature heating, Forced convective heat transfer, Transitional flow regime, Energy efficiency, Heat exchangers, Radiator heating, Ventilation, CFD
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-131710 (URN)10.1016/j.enbuild.2013.04.011 (DOI)000324449800027 ()2-s2.0-84880058681 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20131018

Available from: 2013-10-18 Created: 2013-10-17 Last updated: 2017-12-06Bibliographically approved
4. Performance evaluation of radiant baseboards (skirtings) for room heating - An analytical and experimental approach
Open this publication in new window or tab >>Performance evaluation of radiant baseboards (skirtings) for room heating - An analytical and experimental approach
2014 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 62, no 2, 382-389 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate the thermal performance of the hydronic radiant baseboards currently used for space heating in built environments. The presently available equations for determination of heat outputs from these room heaters are valid for a certain height at a specific temperature range. This limitation needed to be addressed as radiant baseboards may be both energy and cost efficient option for space heating in the future. The main goal of this study was therefore to design an equation valid for all baseboard heights (100-200 mm) and excess temperatures (9-60 C) usually used in built environments. The proposed equation was created by curve fitting using the standard method of least squares together with data from previous laboratory measurements. It was shown that the predictions by the proposed equation were in close agreement with reported experimental data. Besides, it was also revealed that the mean heat transfer coefficient of the investigated radiant baseboards was about 50% higher than the mean heat transfer coefficient of five conventional panel radiators of different types. The proposed equation can easily be used or programed in energy simulation codes. Hopefully this will help engineers to quantify more accurately the energy consumption for space heating in buildings served by radiant baseboards.

Keyword
Baseboard (skirting) heating, Radiator heating, Space heating, Energy efficiency, Measurements, Curve fitting
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-133220 (URN)10.1016/j.applthermaleng.2013.09.053 (DOI)000330910700009 ()2-s2.0-84886681164 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20131029

Available from: 2013-10-29 Created: 2013-10-29 Last updated: 2017-12-06Bibliographically approved
5. Low-temperature heat emission with integrated ventilation air supply
Open this publication in new window or tab >>Low-temperature heat emission with integrated ventilation air supply
2010 (English)In: Proceedings of International Conference Clima 2010, 2010Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:kth:diva-25724 (URN)
Conference
10th Rehva World Congress on Sustainable Energy Use in Buildings, Antalya – Turkey
Note
QC 20101029Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2013-10-29Bibliographically approved
6. Heat emission from thermal skirting boards: An analytical investigation
Open this publication in new window or tab >>Heat emission from thermal skirting boards: An analytical investigation
2009 (English)In: FIFTH INTERNATIONAL WORKSHOP ON ENERGY AND ENVIRONMENT OF RESIDENTIAL BUILDINGS AND THIRD INTERNATIONAL CONFERENCE ON BUILT ENVIRONMENT AND PUBLIC HEALTH, VOL I AND II, PROCEEDINGS / [ed] Zhang Q; Leung M; Wang XK; Liu YJ; Mo JH, HUNAN: HUNAN UNIV, COLLEGE CIVIL ENGINEERING , 2009, 1354-1361 p.Conference paper, Published paper (Refereed)
Abstract [en]

Thermal insulation of buildings has greatly improved over past decades and thermal power needed to cover heat losses through the building envelope has markedly decreased. This means that powerful heating appliances are not always needed in modern buildings. Low-temperature thermal emitters can often replace conventional heating devices. Different studies have shown that people living in buildings with low-temperature heating systems were very satisfied with ambient indoor conditions. In particular; thermal comfort levels were considered to be higher than in buildings with a traditional heating system. Low-temperature heating systems distribute mainly radiant heat with small temperature differences and minimal air movement. This means less spread of allergens and pollutants in the room air and a healthier indoor environment. The general conclusion from this research is that low-temperature heating systems give not just energy savings but may also improve indoor conditions. A combination of low-temperature heating systems and low-valued energy sources, such as heat pumps, give a higher coefficient of performance (COP). This means an environmentally friendly alternative.

Place, publisher, year, edition, pages
HUNAN: HUNAN UNIV, COLLEGE CIVIL ENGINEERING, 2009
Keyword
Heat requirement, Heat transfer, Low-temperature heating, Skirting heating, Thermal power
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-30682 (URN)000270107401009 ()
Conference
5th International Workshop on Energy and Environment of Residential Buildings/3rd International Conference on Built Environment and Public Health, Guilin, PEOPLES R CHINA, MAY 29-31, 2009
Note

QC 20110310

Available from: 2011-03-10 Created: 2011-03-04 Last updated: 2013-11-19Bibliographically approved

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Citation style
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  • ieee
  • modern-language-association-8th-edition
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  • nn-NO
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