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Energy Efficiency Improvements of Tumble Dryers: -Technical Development, Laundry Habits and Energy Labelling
Karlstad University, Faculty of Technology and Science.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tumble dryers are becoming more and more common in ordinary households as a complement to the washing machine. Tumble dryers offer a fast drying cycle independent on weather conditions and require small space. They do, however, considering the large number of units use a large amount of electricity. The main objective in this thesis is to identify possibilities in order to reach a reduced electricity use for domestic tumble-drying of clothes. This involves an investigation of the condensing tumble dryer in order to point out possible energy efficiency improvements. The purpose of the energy label, which indicates the energy efficiency of the tumble dryer, is also studied, whether it matches the actual laundry habits. Finally, suggestions for technical development of the tumble dryer are made in line with today’s consumer behaviour.

The performance of the condensing tumble dryer has been studied using a design of experiments to create a statistical model in Paper I. This model was used to find the best settings for the power supply to the heater, the internal airflow and the external airflow in order to reach a high specific moisture extraction rate (SMER) and a low leakage ratio. A low external airflow and high power supply to the heater gives the highest SMER. To reach the lowest values for the leakage ratio, a low internal airflow should be applied together with a high external airflow. The use of a statistical model gave valuable information of the performance of the existing tumble dryer. For further improving the energy efficiency of the dryer, the amount of leakage and its location was investigated in Paper IV. By studying energy and mass balances from experiments, pressure measurements and modelling, the effects of leakage on the process were evaluated. As the location of the leakage is so important for the energy efficiency, the worst-case scenario where leakage is located between the heater and the drum is used as a start point in the study. It was determined that there is a large leakage of air between the heater and the drum leading to a significant loss in energy recovery.

The drying loads used by consumers are getting smaller, often less than 3 kg dry load, while the maximum capacity of the dryers are increasing, up to 7 or 8 kg. In Paper II, tests were made with different loads in order to investigate if the energy label serves its purpose as today’s standard is set at the dryers’ maximum capacity. The results from this study show that the energy efficiency when drying a small load is significantly lower than for a large load. In order to encourage a production of tumble dryers with higher energy efficiency for small loads, where the dryer is most frequently used, the standards for the energy label should be revised. Today, manufacturers do not gain any benefits by improving the performance for partial loads.

A mathematical model over a venting tumble dryer was established in Paper III with the aim of testing different control strategies in order to improve the energy efficiency of the tumble dryer for partial loads. The ideas behind the different strategies were to minimize the heat losses during the drying process and to increase the residence time for the air in the drum and thereby increase the moisture content of the air leaving the drum. Using such a control strategy it is possible to reach an improvement of SMER by approximately 4% when drying small loads. In order to reach larger improvements, however, a more extensive product development will be necessary.

Finally, the results in this thesis points at the necessity of including not only the technical development of the tumble dryer, but also the policy tools involved and the consumers’ habits in order to reach a reduced electricity use for drying clothes in households. 

Place, publisher, year, edition, pages
Karlstad: Karlstad University , 2011. , 56 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2011:43
Keyword [en]
drying, domestic, energy efficiency, textile, energy labelling standard
National Category
Energy Systems
Research subject
Environmental and Energy Systems
Identifiers
URN: urn:nbn:se:kau:diva-8109ISBN: 978-91-7063-378-2 (print)OAI: oai:DiVA.org:kau-8109DiVA: diva2:436372
Public defence
2011-10-04, 11D 257 (Agardhsalen), Universitetsgatan 1, Karlstad, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2011-09-14 Created: 2011-08-23 Last updated: 2017-12-07Bibliographically approved
List of papers
1. Modelling of Specific Moisture Extraction Rate and Leakage Ratio in a Condensing Tumble Dryer
Open this publication in new window or tab >>Modelling of Specific Moisture Extraction Rate and Leakage Ratio in a Condensing Tumble Dryer
2010 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, 2173-2179 p.Article in journal (Refereed) Published
National Category
Energy Systems
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-8242 (URN)10.1016/j.applthermaleng.2010.05.030 (DOI)000280892400035 ()
Available from: 2011-09-14 Created: 2011-09-14 Last updated: 2017-12-08Bibliographically approved
2. Does the energy labelling system for domestic tumble dryers serve its purpose?
Open this publication in new window or tab >>Does the energy labelling system for domestic tumble dryers serve its purpose?
2011 (English)In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 19, 1300-1305 p.Article in journal (Refereed) Published
National Category
Energy Systems
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-8243 (URN)10.1016/j.jclepro.2011.03.016 (DOI)000292716800003 ()
Available from: 2011-09-14 Created: 2011-09-14 Last updated: 2017-12-08Bibliographically approved
3. Potential Energy Savings Made by Using a Specific Control Strategy when Tumble Drying Small Loads
Open this publication in new window or tab >>Potential Energy Savings Made by Using a Specific Control Strategy when Tumble Drying Small Loads
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 102, 484-491 p.Article in journal (Refereed) Published
Abstract [en]

Tumble dryers manufactured today are optimised for their maximum capacity, i.e., 6–8 kg of dry load. An average washing load in ordinary households lands at between 2 and 3.5 kg dry load, which implies that the drying load is even smaller. The energy efficiency decreases with reduced drying load. The aim of this study is to establish a mathematical model for studying alternative control strategies for the venting tumble dryer in order to increase the energy efficiency of drying small loads. Two series of test runs were performed: the first series with three different drying loads was used as reference tests for validation of the mathematical model, and the second series was performed with airflow reduction. The model shows good agreement with the test runs. Two control strategies were tested using the model on the smallest drying load. By lowering the heat supply to the heater and by reducing the airflow, the energy efficiency increases by 6% in a small load drying cycle. It was not possible, however, for the investigated dryer, to reach the same energy efficiency for small loads as for the maximum drying load by using a control strategy.

National Category
Energy Systems
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-8245 (URN)10.1016/j.apenergy.2012.07.045 (DOI)000314190800054 ()
Available from: 2011-09-14 Created: 2011-09-14 Last updated: 2017-12-08Bibliographically approved
4. Energy Losses by Air Leakage in Condensing Tumble Dryers
Open this publication in new window or tab >>Energy Losses by Air Leakage in Condensing Tumble Dryers
2012 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 37, no May, 373-379 p.Article in journal (Refereed) Published
Abstract [en]

Tumble dryers, used for the drying of textiles, consume a considerable amount of electricity due to the large number of dryers in use. A large amount of this electricity is produced from coal, making it important to reduce the electricity use and, hence, the carbon dioxide emissions. Earlier studies made on the condensing tumble dryer have pointed out that leakage is one of the parameters affecting the electricity use for the drying process. With a view to reducing the energy use, leakage was estimated through measurements and modelling. Energy balances were used in order to verify the leakage. The energy balance showed good agreement with the results from the model and confirms that the leakage out from the dryer arises mainly between the heater and the drum where the air is hot and has low relative humidity. Large leakage at this location is detrimental for the energy efficiency of the dryer, meaning that the leakage must be reduced in order to obtain a reduced energy use. Results from the model also point out that even small changes in the size of gaps, or changes to the pressure in the internal system, result in a significant change in leakage from the dryer

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Energy balance, Tumble dryer, Leakage, Textile, Domestic
National Category
Energy Systems
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-8246 (URN)10.1016/j.applthermaleng.2011.11.051 (DOI)000301026600045 ()
Available from: 2011-09-14 Created: 2011-09-14 Last updated: 2017-12-08Bibliographically approved

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