Investigation of user behavior and operating ...

Investigation of user behavior and operating conditions of residential wood combustion (RWC) appliances and their impact on emissions and efficiency DI (FH) Gabriel Reichert BIOENERGY 2020+ GmbH Inffeldgasse 21b A-8010 Graz [email protected] www.bioenergy2020.eu Co-Authors: DI (FH) Dr. Christoph Schmidl, DI Dr. Walter Haslinger, DI Dr. Wilhelm Moser, DI (FH) Stefan Aigenbauer, Ing. Mag. (FH) Franz Figl, Marius Wöhler M.Sc.,

1

Background & Objectives

Residential wood combustion (RWC) appliances have been identified as major source of air pollution in Europe [1], [2]. As the thresholds for ambient levels of harmful particulate matter (PM10 and PM2.5) are exceeded in many regions, public authorities are forced to implement effective emission reduction measures. But it seems that especially in real life operation RWC appliances are far away from test stand results regarding emissions and efficiency [3]. Prohibition as the most effective measure, however, is clearly in conflict with Europe’s renewable energy targets. Therefore it is essential to understand the reasons for high emissions of RWC appliances in real life operation to be able to improve the situation. Beside technological reasons (e.g. long lifetime of old technologies which are not state-of-the-art) it is claimed that important reasons for high emission and low efficiency in compare to standard type testing results are the user behavior as well as specific operating conditions in real life operation. Therefore the study aimed at the following objectives:  Investigation of user behavior of RWC appliances by a survey  Assessment of operating conditions of RWC appliances in real life operation  Investigation of impact of user behavior and operating conditions on emissions and efficiency

2

Materials & Methods

Survey for investigation of user behavior In order to get basis information about user behavior a survey based on a questionnaire was performed. The survey was conducted at the tradeshow “Bau und Energie” at Wieselburg in Lower Austria during the 28.09.2012 till 30.09.2012 by two students of the Austrian Marketing University of Applied Sciences of Wiener Neustadt. The questions of the survey aimed basically for evaluation the share of used technologies as well as the technological specific user behavior during operation. The questionnaire consisted of 15 questions. All questions were asked as closed questions with specific predetermined options for answers. All respondents were over 18 years old and users of RWC appliances - chimney stoves, tiled stoves or residential biomass cookers. The questionnaire as well as the interviews were done in German language. Field tests for investigation of real life operating conditions and performance For assessment of operating conditions in real life operation three RWC appliances were installed in field at different households with different installation infrastructures. All three appliances were commercial chimney stoves tested according to EN 13240:2001 + A2:2004 standard. Table 1 presents an overview of the used appliances and the specific infrastructure of the field sites.

Table 1: Overview of used RWC appliances and their infrastructure in field A B C Type EN 13240 EN 13240 EN 13240 Nominal heat output 4 kW 8 kW 8 kW Heat output range 2.5 – 6 kW 4 – 8 kW 4 – 8 kW Emissions and efficiency performance of standard type test (STP;13 vol.-% O2) CO 1250 mg/m³ 875 mg/m³ 793 mg/m³ OGC 98 mg/m³ 48 mg/m³ 36 mg/m³ TSP 20 mg/m³ 21 mg/m³ 25 mg/m³ Efficiency 80.9 % 88.3 % 83.2 % Infrastructure in field Chimney system Ceramic; insulated & Ceramic; masoned Ceramic; rear rear ventilated ventilated Absolute high of chimney 10.8 m 4.8 m 12.0 m Effective high of chimney 6.0 m 3.4 m 7.9 m For investigation of operating conditions as well as to evaluate the frequency of operation in a specific period long term measurements of flue gas temperature as well as draught conditions were performed. Therefore data loggers equipped with thermocouples of type K and pressure gauges for static pressure measurement (Thermokon DPT2500-R8; 0 - 100 Pa) were used (Figure 1). For assessment of emissions and efficiency of real life operation two test series were conducted with each appliance. One test was performed according to the mode of operation of the respective user. The second test was conducted according to the mode of operation recommended in manufacturers manual. Five batches per test series were performed and emissions of CO, OGC and TSP emissions were measured. The efficiency was calculated from the flue gas temperature measured in the main stream of flue gas (Figure 1). The gas components and temperatures were measured continuously. The gaseous emissions of CO and OGC were measured in ppm with a measuring cycle of 1 second. Averages of each batch were calculated and then transformed to mg per m³ (STP – 0 °C, 1013 hPa). All results were calculated based on 13 vol.-% of oxygen level in flue gas. Following table shows the measurement equipment as well as the used measurements methods. Table 2: Overview of used measurement equipment and measurement methods Device/ Measurement principle component PLUS rbr-ecom SG O2 potentiometric CO potentiometric CO potentiometric T-gas seebeck-effect T-room resistance temperature detector (PTC) FID M&A Thermo-FID PT63LT OGC flame ionization

Measurement range

Reproducibility/accuracy (rel. / abs.)

0 – 25 % 0 - 4000 ppm 0 - 10 % 0 - 999 °C 0 - 99 °C

0.5 % of ultimate value 5 % of ultimate value / 200 ppm 5 % of ultimate value / 0,5 % 2 % / 20 °C 2 % / 2 °C

0 - 100 ppm  10000 ppm

< 4 % of reading

The TSP measurement was performed discontinuously in batch 1 (lighting batch), batch three and batch five. The TSP measurements were done according to the VDI-Guideline 2066-1. The TSP sampling was done during the complete batch in two samples. First sampling was done in the first 10 minutes of batch, then the filter was exchanged within 5 minutes. Second sampling was done from th 16 minute till the end of respective batch For retention a stuffed quartz wool cartridge was used. The stuffed quartz wool cartridge was placed in a filter head device which was located outside of the flue gas tract (“out-stack” method). The sampling system outside of the flue gas was heated to 130 °C. Downstream the filter the partial gas flow was conveyed into a gas drying unit and the volume flow was determined. Dust was determined gravimetrically after conditioning of used filter media. For conditioning before and after measurement performance all samples were dried in a drying oven at 130 °C for at least 4 hours. Subsequently the samples cooled down in a desiccator equipped with

silica gel for at least 8 hours. Finally, the conditioned unloaded and loaded filters were weighed on a precision balance (Type: Satorius ME 235P, Range: 0 - 230 g, accuracy: 0.01/ 0.02/ 0.05 mg). The combustion test facility was adapted to field conditions according following test scheme:

Figure 1: Scheme of combustion test facility for field measurements

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Results & Discussion

In the following section essential results of the survey as well as results of the field tests are presented. User behavior based on the survey – fuel specifications and lighting procedure

Figure 2: Kind and length of common used fuels in real life operating As illustrated in Figure 2 the interviewed users of RWC appliances generally prefer hardwood for operating of their appliances. Hence 65 %of respondent specified to use hardwood, 23 % to use softwood and 11 % to use briquettes as mainly used fuel. Only 1 % of respondent declared to use other fuels than the predefined options. The average length of used firewood is mainly 33 cm or

25 cm. However, 8 %of respondents specified to use firewood of 50 cm length. But zero percent of respondents declared to use firewood over 50 cm length. The results of the survey correlate with latest results of other studies indicating also hardwood as predominant fuel used in batch-wise fired RWC appliances [4]. Table 3 presents the results of survey respecting the common used placement of lighting batch. Table 3: Results of the survey respecting the mode of lighting of RWC appliances Lighting mode of RWC appliances – placement of lighting batch Option for answer

Cross joint, on top shavings

Firewood, at the bottom shavings

Cross joint, without shavings

Campfire

8%

58 %

15 %

19 %

Example picture

Frequency of answers

The most frequent mode of placement the fuel of lighting batch is firewood above shavings at the bottom of combustion chamber. 58 % of respondents specified this procedure as commonly used for the lighting batch. 19 % of respondents declared the placement of firewood like the traditional campfire as general procedure. 15 % of respondents RWC users placed the firewood as cross joint, but without using any shavings. Only 8 % of users indicated to use cross joint assembled firewood at the bottom of combustion chamber together with shavings placed on top of the firewood which is the ignition mode where lowest emissions are expected [5][6]. Figure 3 illustrates the results about commonly used starting aids as well as the position of ignition the first batch.

Figure 3: Results of survey about the use of starting aids and the position of lighting the first fuel batch 62 % of respondent users indicate small firewood pieces together with paper for lighting their appliances. Consequently these are the common used starting aids. 15 % of respondent RWC users light their appliances with small firewood pieces together with specific starting aids. 10 % of respondent users specified paper as exclusively used starting aid. 8 % of respondent users declared to use specific RWC starting aids. However, 5 % of respondent users light their appliances with other starting aids (e.g. straw) than the given options of the survey. The position of lighting RWC appliances is predominantly done at the bottom or at the bottom third of fuel batch placed on the grate of combustion chamber. Only 13 % of users light their appliance in the middle of the first fuel batch, whereas only a minority group of 4 % lights the appliance from the top or top third of ignition fuel batch. This corresponds with the results of the question about lighting modes (Table 3). Generally the outcome of the survey indicates the lighting procedure far away of the state-ofknowledge respecting emission and efficiency optimized lighting procedure [5]. In the recommended

procedure the first fuel batch should be placed cross joint on the grate of combustion chamber - first small firewood pieces then small shavings should be used. The fuel batch should be lighted with specific starting aids placed on top or top third of the fuel batch [5]. The common procedure indicated by the survey leads to the conclusion that predominantly shavings or small firewood pieces are placed direct on the grate of combustion chamber under the rest of firewood. Subsequently the shavings or small firewood pieces together with paper are ignited at the bottom or bottom third of fuel batch. As its shown in several studies this procedure of lighting RWC appliances causes high gaseous and particulate emissions and low efficiency [5][6]. Real life operating conditions, emissions and efficiency – Field measurements Table 4 presents the operation frequency investigated by long term measurements of all three chimney stoves in real life operation. The period of review was in winter 2012/2013. Table 4: Results of operation frequency of three chimney stoves Stove Period of review Number of days Frequency of operation cycles Number of batches Average of batches per operation cycle Complete hours of operation Average duration of one batch Average operation hours per day

A 17.01.2013 – 24.01.2013 8 days 3 10 3 (min. 3 batches; max. 4 batches) 7h 0.70 h 0.9 h/d

B 18.01.2013 – 22.01.2013 5 days 7 23 3 (min. 2 batches; max. 5 batches) 26.5 h 1.15 h 5.2 h/d

C 17.01.2013 – 12.02.2013 27 days 38 213 6 (min. 2 batches; max. 16 batches) 189 h 0.89 h 7.0 h/d

The frequency of operation cycles differs significantly between the three monitored chimney stoves. Whereas stove A was operated only around 0.9 hours per day stove B and C were operated considerably more. The calculated average operating time of stove B was 5.2 and of stove C 7.0 hours per day. The determined average duration of one batch was 0.70 hours for stove A, 1.15 hours for stove B and 0.9 hours for stove C. The number of batches performed during one heating operation cycle ranged from two batches (stove B) up to maximum of 16 batches (stove C). The data lead to the assumption that stove A is only occasional used, assumable for esthetic reasons, whereas stove B and C are regularly used mainly for room heating purposes. For investigation of operating conditions induced by the infrastructure of stove and chimney the static pressure of flue gas (draught) as well as flue gas temperature were measured during real life operation (Figure 1). Figure 4 - Figure 6 presents examples of draught conditions of respective chimney stoves during operation at field tests.

Figure 4: Trend of flue gas draught during one heating operation cycle of stove A

Figure 5: Trend of flue gas draught during one heating operation cycle of stove B

Figure 6: Trend of flue gas draught during one heating operation cycle of stove C The measurements of draught conditions indicated a strong correlation of average draught level and effective height of chimney. Therefore stove C connected to a chimney of 7.4 m effective height lead to an average draught level of operation cycle of 32 Pa. In contrast, stove B was connected to a chimney with 3.4 m effective height. Hence an average draught level of operation cycle of 13 Pa was measured. Stove A was connected to a chimney of 6.4 m high. The average draught level of operation cycle was 24 Pa. Consequently no linear correlation of effective chimney height and average draught levels were indicated due to several other factors influencing draught level, for example material and heat storage capacity of chimney system, damper settings of RWC appliance as well as weather conditions. However, the average draught levels of operation cycles of all three stoves generally were above 12 Pa used at standard type testing. Beside average draught level of operation cycles also similar trends of all three stoves respecting draught curves during operation were obvious. At the beginning of operation an efficient increase of draught was determined for all stoves. After the lighting batch only slight increase of average draught levels of batches were indicated. The deviations of absolute draught values recorded with a measuring cycle of 10 seconds were induced by combustion conditions, measurement precision, current weather conditions and in case of stove C by automatically controlled damper settings. Emissions and efficiency of field measurements – operation according manual and specific user behavior For investigation of gaseous and particulate emissions as well as efficiency performance in real life operation comprehensive field tests were conducted. Exemplary the results of field measurements of stove C which was operated according specific user behavior as well as according to manufacturers manual are illustrated. Following manufacturers manual beech firewood with 14 % water content of was used. The placement of lighting batch was done cross joint with small firewood pieces and shavings on top of firewood. The lighting batch was ignited at the top of fuel batch with specific starting aids. In contrast to the manufacturers manual three pieces instead of two pieces of firewood were used for recharging a new

fuel batch. The firewood pieces were placed direct into the fire bed on the grate. The total mass of one fuel batch was about 2.2 kg. The operation according to user behavior was done with squared timber of spruce with a water content of 14 percent. For lighting of the stove small shavings were placed on the grate. On top of the shavings three pieces of squared timber were placed. The lighting batch was ignited with specific starting aids at the bottom of combustion chamber. For recharging a new fuel batch three pieces of squared timber (spruce) were used. Two pieces were placed on the grate whereas the third piece was placed on top of the other two pieces. The total mass of batches varied between 1.4 kg and 1.8 kg. For both modes of operating damper settings for controlling combustion air were done by an automatically air control system of the stove. Table 5 presents the photo documentation of placement the lighting fuel batch as well as the fuel batches for recharging. Table 5: Photo documentation of lighting mode as well as recharging a new fuel batch – Field measurements Operation according to user behavior

Operation according to manufacturers manual

Lighting of stove

Recharging a new fuel batch (Example)

Table 6 presents the results of emissions and efficiency according the different modes of operation. Table 6: Results of field measurements respecting emissions (STP; 13 vol.-% O2) and efficiency (indirect calculated) of batch 1, 3 and 5 Stove C: Field measurements - Specific user behavior Batch

Duration

CO

OGC

TSP

η

1

43 min.

7556 mg/m³

1096 mg/m³

318 mg/m³

51.5 %

3

39 min.

9491 mg/m³

1351 mg/m³

141 mg/m³

29.1 %

5

39 min.

8059 mg/m³

1320 mg/m³

125 mg/m³

42.5 %

Stove C: Field measurements – Manufacturers manual 1

32 min.

2546 mg/m³

151 mg/m³

150 mg/m³

61.0 %

3

58 min.

3661 mg/m³

239 mg/m³

63 mg/m³

42.0 %

5

45 min.

1993 mg/m³

272 mg/m³

79 mg/m³

45.7 %

Stove C: Results of standard type test (STP; 13 vol.-% O2) 55 min

793 mg/m³

36 mg/m³

25 mg/m³

83.2 %

The operation according to user behavior caused significant higher CO, OGC and TSP emissions compared to the operation according to manufacturers manual. The gaseous emissions of CO varied from 7600 mg/m³ up to 9500 mg/m³, for OGC emissions from 1.100 mg/m³ up to 1300 mg/m³. In contrast CO and OGC emissions were significant lower when operating according to the manufacturers manual. In this case the CO emissions ranged from about 2000 mg/m³ to 3700 mg/m³, for OGC emissions from 150 mg/m³ to 270 mg/m³. The particulate emissions for the user operation varied from 125 mg/m³ up to 318 mg/m³ whereas the operation according to manufacturers manual lead to explicit lower TSP emissions between 63 mg/m³ and 150 mg/m³. Also significant differences between the calculated efficiencies were evident. The mode of operation by the user leads to efficiencies of respective batches between 29.1 % and 51.5 %. The operation followed manufacturers manual in contrast resulted in higher efficiencies of 42.0 % to 61.0 %. However, the measured

efficiencies for both modes of operation are quite low due to high draught level of the chimney system. This was indicated by parallel field tests series with stove A and B where higher efficiencies were measured. The highest efficiencies of about 72 % were measured for stove B where the average draught level of operation cycle was about 13 Pa. As it is illustrated by Table 6 the mode of lighting, kind and mass of used fuel batches as well as the mode of recharging a new fuel batch have a strong impact on emissions as well as on efficiency. The user operation caused approximately three times higher emissions of CO, six times more OGC emissions and double TSP emissions. Interestingly gaseous emissions of lighting batches for both modes of operation were not significant different to the other batches. In contrast the TSP emissions of lighting batch were at least two times higher than the other batches. Due to there seems to be a tendency of significant higher TSP emissions during the lighting batch.

4

Summary & Conclusions

The results of the survey about user behavior as well as the field tests lead to following conclusions:  For batch-wise fired RWC appliances predominantly hardwood is used.  The length of used firewood is either 25 cm or 33 cm.  The mode of lighting is predominantly firewood placed on top of shavings at the bottom of combustion chamber.  Small shavings together with paper are common starting aids for lighting RWC appliances.  Predominantly ignition is done at the bottom or bottom third of combustion chamber.  Frequency and duration of operation of RWC appliances varies significantly.  Draught conditions in real life operation are significantly higher than the 12 Pa used for standard type testing.  Draught conditions increase strongly during the first batch. After the first batch only little increase of draught levels was observed.  Draught level depends strongly of the effective high of chimney system.  Operation in real life seems to cause higher emissions and lower efficiencies due to maloperation by the user. But also operation according manufacturers manual causes significantly higher emissions compared with by standard type tests results due to following reasons: o Different operating conditions - mainly draught levels - lead to lower efficiencies. o Significant impact of lighting batch respecting TSP emissions. o Strong impact of used fuel as well as placement of fuel batch in the combustion chamber respecting emissions and efficiency. o Only optimal operation performance is illustrated by the standard type test. The results of the survey as well as the results of the field tests confirmed the assumption of significant influence and effect of operating conditions as well as user behavior regarding emissions and efficiency in real life operation. Further the field tests confirmed that results of standard type tests for RWC appliances are hardly realizable in real life operation even when the appliance is operated according to manufacturers manual. Acknowledgements The study was done in the project “Stove Testing 2020” that was financial supported by the Austrian Climate and Energy Fund in the frame of the “New Energy Projects” of the Austrian Research Promotion Agency (FFG project 834 639) Literature [1] Kappos A. et al.; Health effects of particles in ambient air, Int. J. Hyg. Environ. Health 207(4):399–407, 2004 [2] Directive on Ambient Air Quality and Cleaner Air For Europe, (http://ec.europa.eu/environment/archives/cafe/general/keydocs.htm), EU CAFÉ Program; 2005. [3] Hartmann H.; Status on emissions, regulation and technical improvements and future developments for residential wood burning appliances in Germany, Presentation at Seminar th on wood combustion and air quality in Aahus/Denmark, March 15 ,2012 [4] Technologie und Förderzentrum; Rationelle Scheitholzbereitstellungsverfahren, Reports of TFZ 11, Straubing, July 2006 [5] Hartmann H. et al.; Low emission operation manual for chimney stove users, Report within the scope of ERA-NET Bioenergy Project „FutureBioTec“, October 2012 [6] Nussbaumer T. et al.; Particulate Emissions from Biomass Combustion in IEA Countries – Survey on Measurements and Emission Factors, Zürich, Jannuary 2008