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External DHW units for solar combisystems
Högskolan i Dalarna.
Högskolan i Dalarna.
2003 (English)In: Solar energy, ISSN 0038-092X, Vol. 74, 193-204 p.Article in journal (Refereed) Published
Abstract [en]

This article compares seven different external DHW units, comprising flat plate heat exchanger and flow control, with a reference method for preparing hot water. These DHW units use different control methods. The objective of the study was to determine which methods are most effective in solar combisystems and to identify other factors that strongly influence the energy savings of the system. Five of the DHW units were judged to be of interest for the study because of their measured performance or the simplicity of their design. Of these, measurement data showed that two had the same control function although of different physical construction. Thus four DHW units were modelled in the simulation environment PRESIM/TRNSYS, parameters were identified from measured data, and annual simulations were performed with a number of parametric variations. Three of the DHW units performed significantly better than the reference system provided that they were sized correctly: microprocessor control with variable-speed pump; proportional controller with regulating valve; and a turbine pump. The most important design factors identified by the study were: the maximum possible primary flow, which needs to be suitable for the design hot water load profile; and ensuring a low temperature is returned to the store. The hot water load profile was also shown to strongly influence the energy savings, assuming that auxiliary heater's thermostat is set so that the system just meets the worst-case discharge.

Place, publisher, year, edition, pages
2003. Vol. 74, 193-204 p.
Keyword [en]
solar heating, DHW preparation, solar combisystem
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6491DOI: 10.1016/S0038-092X(03)00158-0ISI: 000184888500002OAI: oai:DiVA.org:kth-6491DiVA: diva2:11218
Note
QC 20100916Available from: 2006-12-04 Created: 2006-12-04 Last updated: 2010-09-16Bibliographically approved
In thesis
1. Combined solar and pellet heating systems for single-family houses: how to achieve decreased electricity usage, increased system efficiency and increased solar gains
Open this publication in new window or tab >>Combined solar and pellet heating systems for single-family houses: how to achieve decreased electricity usage, increased system efficiency and increased solar gains
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In Sweden, there are about 0.5 million single-family houses that are heated by electricity alone, and rising electricity costs force the conversion to other heating sources such as heat pumps and wood pellet heating systems. Pellet heating systems for single-family houses are currently a strongly growing market. Future lack of wood fuels is possible even in Sweden, and combining wood pellet heating with solar heating will help to save the bio-fuel resources.

The objectives of this thesis are to investigate how the electrically heated single-family houses can be converted to pellet and solar heating systems, and how the annual efficiency and solar gains can be increased in such systems. The possible reduction of CO-emissions by combining pellet heating with solar heating has also been investigated.

Systems with pellet stoves (both with and without a water jacket), pellet boilers and solar heating have been simulated. Different system concepts have been compared in order to investigate the most promising solutions. Modifications in system design and control strategies have been carried out in order to increase the system efficiency and the solar gains. Possibilities for increasing the solar gains have been limited to investigation of DHW-units for hot water production and the use of hot water for heating of dishwashers and washing machines via a heat exchanger instead of electricity (heat-fed appliances).

Computer models of pellet stoves, boilers, DHW-units and heat-fed appliances have been developed and the parameters for the models have been identified from measurements on real components. The conformity between the models and the measurements has been checked. The systems with wood pellet stoves have been simulated in three different multi-zone buildings, simulated in detail with heat distribution through door openings between the zones. For the other simulations, either a single-zone house model or a load file has been used. Simulations were carried out for Stockholm, Sweden, but for the simulations with heat-fed machines also for Miami, USA.

The foremost result of this thesis is the increased understanding of the dynamic operation of combined pellet and solar heating systems for single-family houses. The results show that electricity savings and annual system efficiency is strongly affected by the system design and the control strategy. Large reductions in pellet consumption are possible by combining pellet boilers with solar heating (a reduction larger than the solar gains if the system is properly designed). In addition, large reductions in carbon monoxide emissions are possible. To achieve these reductions it is required that the hot water production and the connection of the radiator circuit is moved to a well insulated, solar heated buffer store so that the boiler can be turned off during the periods when the solar collectors cover the heating demand. The amount of electricity replaced using systems with pellet stoves is very dependant on the house plan, the system design, if internal doors are open or closed and the comfort requirements. Proper system design and control strategies are crucial to obtain high electricity savings and high comfort with pellet stove systems.

The investigated technologies for increasing the solar gains (DHW-units and heat-fed appliances) significantly increase the solar gains, but for the heat-fed appliances the market introduction is difficult due to the limited financial savings and the need for a new heat distribution system. The applications closest to market introduction could be for communal laundries and for use in sunny climates where the dominating part of the heat can be covered by solar heating. The DHW-unit is economical but competes with the internal finned-tube heat exchanger which is the totally dominating technology for hot water preparation in solar combisystems for single-family houses.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 143 p.
Series
TRITA-FPT-Report, ISSN 1652-2443 ; 06:56
Keyword
Pellets, stove, boiler, solar heating, DHW preparation, system design, single-family house, electricity savings
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-4204 (URN)978-91-7178-538-1 (ISBN)
Public defence
2006-12-13, Sal M3, KTH, Brinellvägen 64, Stockholm, 10:00
Opponent
Supervisors
Note

QC 20100916

Available from: 2006-12-04 Created: 2006-12-04 Last updated: 2017-02-23Bibliographically approved

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Publisher's full texthttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V50-48SBMC4-1&_user=4478132&_coverDate=03%2F31%2F2003&_alid=501063127&_rdoc=1&_fmt=summary&_orig=search&_cdi=5772&_sort=d&_docanchor=&view=c&_acct=C000034958&_version=1&_urlVersion=0&_userid=4478132&md5=c5194c6a518a3ca2a5fc876b264206fe

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