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On the Design of Residential Condensing Gas Boilers

Näslund, Mikael LU (1997)
Abstract
Two main topics are dealt with in this thesis. Firstly, the performance of condensing boilers with finned tube heat exchangers and premix burners is evaluated. Secondly, ways of avoiding condensate formation in the flue system are evaluated.



In the first investigation, a transient heat transfer approach is used to predict performance of different boiler configurations connected to different heating systems. The smallest efficiency difference between heat loads and heating systems is obtained when the heat exchanger gives a small temperature difference between flue gases and return water, the heat transfer coefficient is low and the thermostat hysteresis is large. Taking into account heat exchanger size, the best boiler... (More)
Two main topics are dealt with in this thesis. Firstly, the performance of condensing boilers with finned tube heat exchangers and premix burners is evaluated. Secondly, ways of avoiding condensate formation in the flue system are evaluated.



In the first investigation, a transient heat transfer approach is used to predict performance of different boiler configurations connected to different heating systems. The smallest efficiency difference between heat loads and heating systems is obtained when the heat exchanger gives a small temperature difference between flue gases and return water, the heat transfer coefficient is low and the thermostat hysteresis is large. Taking into account heat exchanger size, the best boiler is one with higher heat transfer per unit area which only causes a small efficiency loss. The total heating cost at part load, including gas and electricity, has a maximum at the lowest simulated heat load. The heat supplied by the circulation heat pump is responsible for this.



The second investigation evaluates methods of drying the flue gases. Reheating the flue gases in different ways and water removal in an adsorbent bed are evaluated. Reheating is tested in two specially designed boilers. The necessary reheating is calculated to approximately 100-150C if an uninsulated masonry chimney is used. The tested boilers show that it is possible to design a proper boiler. The losses, stand-by and convective/radiative, must be kept at a minimum in order to obtain a high efficiency. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Dr Hendriks, Theo, the Netherlands
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Energy research, flue systems, modelling, efficiency, condensing boilers, space heating, natural gas, Energiforskning
pages
169 pages
publisher
Division of Energy Economics and Planning, Department of Heat and Power Engineering, Lund University
defense location
School of Mech. Engineering, Hall M:B
defense date
1997-02-28 10:15
external identifiers
  • other:ISRN: LUTMDN/TMVK--1011--SE
ISSN
0282-1990
language
English
LU publication?
yes
id
2fccfe84-9142-4e84-9f65-84675e7501a1 (old id 18178)
date added to LUP
2007-05-24 10:43:05
date last changed
2016-09-19 08:44:53
@phdthesis{2fccfe84-9142-4e84-9f65-84675e7501a1,
  abstract     = {Two main topics are dealt with in this thesis. Firstly, the performance of condensing boilers with finned tube heat exchangers and premix burners is evaluated. Secondly, ways of avoiding condensate formation in the flue system are evaluated.<br/><br>
<br/><br>
In the first investigation, a transient heat transfer approach is used to predict performance of different boiler configurations connected to different heating systems. The smallest efficiency difference between heat loads and heating systems is obtained when the heat exchanger gives a small temperature difference between flue gases and return water, the heat transfer coefficient is low and the thermostat hysteresis is large. Taking into account heat exchanger size, the best boiler is one with higher heat transfer per unit area which only causes a small efficiency loss. The total heating cost at part load, including gas and electricity, has a maximum at the lowest simulated heat load. The heat supplied by the circulation heat pump is responsible for this.<br/><br>
<br/><br>
The second investigation evaluates methods of drying the flue gases. Reheating the flue gases in different ways and water removal in an adsorbent bed are evaluated. Reheating is tested in two specially designed boilers. The necessary reheating is calculated to approximately 100-150C if an uninsulated masonry chimney is used. The tested boilers show that it is possible to design a proper boiler. The losses, stand-by and convective/radiative, must be kept at a minimum in order to obtain a high efficiency.},
  author       = {Näslund, Mikael},
  issn         = {0282-1990},
  keyword      = {Energy research,flue systems,modelling,efficiency,condensing boilers,space heating,natural gas,Energiforskning},
  language     = {eng},
  pages        = {169},
  publisher    = {Division of Energy Economics and Planning, Department of Heat and Power Engineering, Lund University},
  school       = {Lund University},
  title        = {On the Design of Residential Condensing Gas Boilers},
  year         = {1997},
}