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Thermal performance of combined solar and pellet heating systems
Högskolan i Dalarna.
Högskolan i Dalarna.
Högskolan i Dalarna.
Högskolan i Dalarna.
2006 (English)In: Renewable energy, ISSN 0960-1481, Renewable energy, Vol. 31, 73-88 p.Article in journal (Refereed) Published
Abstract [en]

Various pellet heating systems are marketed in Sweden, some of them in combination with a solar heating system. Several types of pellet heating units are available and can be used for a combined system. This article compares four typical combined solar and pellet heating systems. System 1 and 2 with a pellet stove, system 3 with a store integrated pellet burner and system 4 with a pellet boiler. The often lower efficiency of pellet heaters compared to oil or gas heaters increases the final energy demand. Consequently, heat losses of the various systems have been studied. The systems have been modeled in TRNSYS and simulated with parameters identified from measurements. For almost all systems the flue gas losses are the main heat losses except for system 3 where store heat losses prevail. Relevant are also the heat losses of the burner and the boiler to the ambient. Significant leakage losses are noticed for system 3 and 4. For buildings with an open internal design system I is the most efficient solution. Other buildings should preferably apply system 2 or 3. The right choice of the system depends also on whether the heater is placed inside or outside of the heated area. Unlike the expectations and results from other studies, the operation of the pellet heaters with modulating combustion power is not necessarily improving the performance. A large potential for system optimisation exists for all studied systems, which when applied could alter the relative merits of the different system types

Place, publisher, year, edition, pages
2006. Vol. 31, 73-88 p.
Keyword [en]
pellet heating systems, heat losses, flue gas losses, leakage losses
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6489DOI: 10.1016/j.renene.2005.03.007ISI: 000232741200006OAI: oai:DiVA.org:kth-6489DiVA: diva2:11216
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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