Realistic operation of two residential cordwood-fired outdoor hydronic heater appliances—Part 1: Particulate and gaseous emissions

Figures & data

Table 1. Hydronic heater descriptions.

Parameter	Hydronic Heater A (HH A)	Hydronic Heater B (HH B)
Firebox Volume	354 L (12.5 ft^3)	186 L (measured)164 L (published in manual) (6.6 ft^3, measured; 5.8 ft^3, published)
Emission Factor (based on energy output)	30.09 mg/MJ (0.07 lb/MMBtu)	31.81 mg/MJ (0.074 lb/MMBtu)
Emission Rate	1.04 g/hr	1.04 g/hr
Maximum Rated Output	30 kW (102,400 Btu/hr)	35 kW (120,000 Btu/hr)
Delivered Annual Efficiency (based on HHV)	67.0%	67.5%
Water Jacket Volume	227.3 L (55 gal)	378.5 L (100 gal)
Number of Combustion Stages	2	2
Combustion Type	Two-stage, single zone	Downdraft gasification
Catalytic	Yes	No
Features	Lambda sensor, primary and secondary dampers, draft inducer	Primary damper, draft inducer

Figure 1. Schematic diagram of wood-fired hydronic heater experiment. Boiler device schematic adapted with permission from (Siegenthaler 2017).

Table 2. Multi-Phase testing protocol.

Phase	Description	Milestone to Signify End of Phase
Cold Start Fuel charge -kindling + starter fuel
1	Cold Start: Includes kindling (10% of fuel charge weight) made up of 50% small pieces and 50% larger kindling pieces	Once 80% of kindling fuel has been consumed
1^st fuel charge
2	Ramp-up to full load	Once 20% of 1^st fuel charge has been consumed during this phase
3	Maximum burn rate	Once 20% of 1^st fuel charge has been consumed during this phase
4	Steady state – less than 25% load, but greater than 15% load (This phase is similar to M28 WHH Category II heat load output)	1.25 hours
5	Steady state – less than 50% load, but greater than 25% load (This phase is similar to M28 WHH Category III heat load output)	Once 20% of 1^st fuel charge has been consumed
6	End phase – burn out	Once 85% of the 1^st fuel charge has been consumed, establishing a coal bed of 15% of the 1^st fuel charge
2^nd fuel charge
7	Reload – equivalent of a hot start	Only 10% of 2^nd fuel charge has been consumed during this phase
8	Steady state – less than 15% load (This phase is similar to M28 WHH Category I heat load output)	Greater of 2.0 hours or time required for 1 reheat firing cycles
9	Steady state 100% load (This phase is similar to M28 WHH Category IV heat load output)	Only 20% of 2^nd fuel charge has been consumed during this phase
10	Cyclic operation (10 minutes off, 5 minutes on)	One the HH temperature has returned back to its starting point of temperature set-point reached
End of sampling		Let remainder of fuel burn out at maximum load – no sampling

Table 3. Fuel charge description with size and fuel charge mass specification used for each appliance during each fuel loading event within the test method.

Fuel Charge	Description	Hydronic Heater A	Hydronic Heater B
-	Length of individual fuel piece (cm)	55.9	55.9
First	Total weight of fuel using a loading density of 160 kg/m^3 (kg)	56.7	29.9
Second	Total weight of fuel when filling the combustion chamber to within 2.5 cm of top of door (kg)	72.6–81.6	38.6

Table 4. Phase Weighting Factor.

Phase	Weighting Factor
1	0.1
2	0.1
3	0.0
4	0.25
5	0.05
6	0.05
7	0.1
8	0.25
9	0.05
10	0.05

Figure 2. Coefficient of variation heat map for burn rate, particulate matter (PM) emission factor, and efficiency for Hydronic Heater A and B.

Figure 3. Heat map with average particulate matter (PM) emission factor, emission rate, and emission index for each phase of the operating protocol for both hydronic heaters.

Figure 4. Bar chart showing the particulate matter (PM) emission factor (EF), in units of milligrams of particulate matter per megajoule of energy output (mg/mj), calculated for each experiment during triplicate testing of Hydronic Heater A (HH A).

Figure 5. Bar chart showing the particulate matter (PM) emission factor (EF), in units of milligrams of particulate matter per megajoule of energy output (mg/mj), calculated for each experiment during triplicate testing of Hydronic Heater B (HH B).

Figure 6. Heat map with average carbon monoxide (CO) emission factor, emission rate, and emission index for each phase of the operating protocol for both hydronic heaters.

Figure 7. Bar chart showing the carbon monoxide (CO) emission factor (EF), in units of milligrams of CO per megajoule of energy output (mg/mj), calculated for each experiment during triplicate testing of Hydronic Heater A (HH A).

Figure 8. Bar chart showing the carbon monoxide (CO) emission factor (EF), in units of milligrams of CO per megajoule of energy output (mg/mj), calculated for each experiment during triplicate testing of Hydronic Heater B (HH B).

Figure 9. Heat map of average methane (Ch₄) emission factor, emission rate, and emission index) for each phase of the operating protocol for both hydronic heaters.

Figure 10. Bar chart showing the methane (Ch₄) emission factor, in units of milligrams of CH₄ per megajoule of energy output (mg/mj), calculated for each experiment during triplicate testing of Hydronic Heater A (HH A).

Figure 11. Bar chart showing the methane (Ch₄) emission factor, in units of milligrams of CH₄ per megajoule of energy output (mg/mj), calculated for each experiment during triplicate testing of Hydronic Heater B (HH B).

Figure 12. Heat map of Appliance A and B average black carbon (BC) emission factor, emission rate, and emission index for each test phase of the operating protocol.

Figure 13. Heat map of Appliance A and B calculated efficiency for each phase of the operating protocol.

Table 5. Annual average emissions and efficiency from both hydronic heaters.

		EF_PM	ER_PM	EI_PM	EF_CO	ER_CO	EI_CO	EF_CH4	ER_CH4	EI_CH4	Efficiency
		mg/MJ	g/hr	g/kg fuel	mg/MJ	g/hr	g/kg fuel	mg/MJ	g/hr	g/kg fuel	%
HH A	Test 1	558.0	76.4	7.50	2017	257	34.1	54.6	5.65	0.92	83.2
	Test 2	376.8	47.8	5.03	3646	366	60.9	83.6	9.67	1.40	80.6
	Test 3	321.8	56.0	4.31	1867	176	31.1	54.1	4.81	0.90	82.6
	Average of three tests	418.9	60.1	5.61	2510	266	42.0	64.1	6.71	1.07	82.1
	COV	30%	25%	30%	39%	36%	39%	26%	39%	26%	2%
HH B	Test 1	91.4	12.3	1.23	2047	138	34.1	81.6	3.92	1.36	76.1
	Test 2	87.7	9.9	1.17	2043	156	33.8	137.6	5.42	1.38	77.9
	Test 3	111.3	12.2	1.44	2813	231	46.5	89.7	6.57	1.49	75.8
	Average of three tests	96.8	11.5	1.28	2301	175	38.2	102.9	5.30	1.41	76.6
	COV	13%	12%	11%	19%	28%	19%	29%	25%	5%	1%

Figure 14. Bar chart comparing the PM EF (mg/mj) calculated for each experiment during triplicate testing for hydronic heating Appliances A and B.

Siegenthaler, J. 2017. Hydronics for High Efficiency Biomass Boilers. NYSERDA.

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Data availability statement

The data that support the findings of this study are available from the corresponding author, R. Trojanowski, upon reasonable request.