Indoor air pollution and inter-room pollutant transport due to unvented kerosene-fired space heaters

Environment International Vol. 13, pp. 159-166, 1987

0160-4120/8753.00 + .00 Copyright © 1987 Pergamon Journals Ltd.

Printed in the USA. All rights reserved.

INDOOR AIR POLLUTION AND INTER-ROOM POLLUTANT TRANSPORT DUE TO UNVENTED KEROSENE-FIRED SPACE HEATERS G. W. Traynor, M. G. Apte, A. R. Carruthers, J. F. Dillworth, D. T. Grimsrud, and W. T. Thompson* Building Ventilation and Indoor Air Quality Program, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720, USA (Received 3 September 1986; Accepted 6 October 1986) Two kerosene-fired space heaters, one white-flame convective and one blue-flame radiant, were operated in the master bedroom and living room of an unoccupied house (elevation: 1800 m) under several simulated use conditions. Tests were conducted in the master bedroom with the bedroom door and bedroom window open and closed. The heaters were operated until an 8 °C temperature rise was achieved in the room. Increases in bedroom concentrations of CO, CO2, NO, NO~, and 02 are reported. The increases in CO2 levels ranged from 2440 to 5440 mL/m 3 (ppm) while the increases in NO2 levels ranged from 0.12 to 0.60 mL/m 3 (ppm). The NO2 emission rate from the convective heater was reduced at the high altitude location as compared with previous emission rate measurements conducted near sea level with the same heater. In addition, inter-room pollutant transport rates are reported for bedroom tests conducted with the window closed. While inter-room pollutant transport rates were less than 10 m 3 with the bedroom door closed (opening area less than 100 cm2), they ranged from 16 mVh to 53 m3/h with the bedroom door open 2.5 cm (opening = 520 cm2), and ranged from 190 to 3400 m3/h with the door fully open (opening area = 15,000 cm2). Continuous emission rate data are reported for tests conducted with the heater in the living room.

Introduction

We investigated the impact of operating unvented radiant and convective kerosene-fired space heaters on indoor air quality in an unoccupied house under several realistic use conditions. Experiments were conducted (1) to test the impact of window and internal door openings on bedroom pollutant concentrations while operating a kerosene heater in the bedroom, (2) to measure the inter-room pollutant transport rate while operating a heater in the bedroom, and (3) to measure the temporal emission rate profile of the two types of heaters.

The indoor use of unvented kerosene-fired space heaters in the United States has increased dramatically over the past decade due, in part, to increased energy costs. Because these devices are not vented to the outside, the pollutants they emit can have a detrimental effect on the quality of indoor air. Several past studies have concentrated on the quantification of pollutant emission rates from unvented kerosene-fired space heaters (Yamanaka et aL, 1979; Leaderer, 1983; Traynor et ak, 1983). Results of these studies have shown that kerosene-fired space heaters can emit:CO, CO2, NO, NO2, SO2, formaldehyde, and respirable particles while consuming oxygen. Laboratory-derived emission rates coupled with indoor air quality modeling indicate that NO2, CO2, and SO2 concentrations could exceed outdoor or occupational guidelines under certain operating conditions (Leaderer, 1983; Ryan et al., 1983).

Experimental The house used to condect these experiments is located in Truckee, CA (elevation: 1800 m). It is asingle-floor ranch~type structure with a volume of 236 m 3. The house has a long straighthallway (5.4 m × 0.93 m x 2.4 m) that allows access to the bedrooms. The master bedroom door is at the end of the hallway furthest from the living room and kitchen. Figure 1 shows the floor plan of the house. Tests were conducted with radiant and convective heaters operated in either the master

*Current address: Applied Research Corporation, 8401 Corporate Drive, Landover, MD 20785. 159

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bedroom or the living room. The heat of combustion o f the kerosene was 43.5 kJ/g. The convective and radiant heaters were operated in the master bedroom until the bedroom air temperature increased at least 8 °C. This procedure was followed under several operating conditions: first, the hinged bedroom door (to the rest of the house) was closed and the sliding window (to the outside) was closed; second, the bedroom door was opened 2.5 cm and the window was closed; third, the bedroom door was fully opened (74 cm) and the window was closed; and fourth, the bedroom door was closed and the window was opened 2.5 cm. The bedroom door opening is 204 cm high and the bedroom window opening is 101 cm high. All other interior doors, except closet and bathroom doors, were open for all tests while other exterior doors and windows were closed. Tests conducted with the heaters in the living room lasted several hours because the 8 °C temperature rise was not reached in any of the tests. The instrumentation used in this study has been described previously (Girman e t a l . , 1983). Pollutant concentrations at three indoor locations (living room, kitchen, and bedroom) and one outdoor location were monitored on a rotating basis every 24 mins (6 mins at each location). Temperature was monitored at each sample location. The bedroom temperature and air sampling probes were 1.5 m above the floor and were not in the direct path o f the heater plume. Inter-room pollutant transport rates were calculated

for tests with the bedroom window closed using CO2 concentration data and a two-compartment mass-balance model with several simplifying assumptions. The bedroom was treated as one compartment with a volume of 31 m 3 while the rest of the house was the second compartment having a volume of 205 m 3. House and room volumes were measured by injection of a tracer gas under well-mixed conditions. These volumes were confirmed by direct measurement. The primary simplying assumption used to calculated inter-room pollutant rates was that the flows out o f each compartment to the outside are equal to the flows into each compartment from the outside. This was plausible because the large ind o o r / o u t d o o r temperature differences, the low local wind speeds, and the wind-protected location of the house allowed us to assume that the stack effect, as opposed to the wind effect, was the primary driving force of infiltration in this house. In addition, the flows through the building shell were generally small compared to the inter-room flows. Thus, we were able to assign a portion of the total house infiltration air flow rate; measured by CO2 decay, to the bedroom and to the rest of the house using the length of wall exposed to the outside. The mass balance equation used to estimate the interroom floor rates are shown below: V1

dC1 dt

= q,(Co

-

C,)

+ q,~(C2

-

Cx) + S, (1)

Unvented Kerosene-fired space heaters

dC2

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-

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(2)

outside pollutant concentration (mL/m3); bedroom pollutant concentration (mL/m 3); C~= non-bedroom pollutant concentration (mL/m3); flow rate between bedroom and outside ql (m3/h); flow rate between rest of house and outq2 side (m3/h); flow rate between bedroom and rest of q12 house (m3/h); pollutant source strength (mL/h); S t = time (h); ~ = bedroom volume (m3); and ~ = house volume excluding bedroom (m3).

where CO C1

=

Rearranging Eqs. (I) and (2), we can estimate the interroom transport rate by two different but related equations: q12 ~

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-fit

-

S1 (3)

- q2(Co - col

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(4)

The carbon dioxide emitted from the heaters was used as the tracer for inter-room transport measurements. The derivatives, dC,/dt and dC2/dt, were determined by calculating the slope of the line between the two adjacent data points. Since Eqs. (3) and (4) yield two separate but not independent estimates of q,~, the average of the two values is reported here. Relative standard deviations of q,2 estimates ranged from 0.030/0 to 83°/o and averaged 37°7o. R e s u l t s and D i s c u s s i o n

Table 1 summarizes some of the test results including air exchange rate estimates, temperature data, and peak increase in bedroom pollutant concentrations for all tests where the heaters were operated in the master bedroom. CO2 was the only pollutant with a significant indoor background concentration, ranging from 360 to 990 m L / m 3 (ppm) with a mean of 580 m L / m 3 and a standard deviation of 4- 90 mL/mL The average fuel consumption rates were 7300 4- 1200 kJ/h for the convective heater and 6400 ± 300 k J / h for the radiant heater. Increases in bedroom CO2 concentrations ranged from 2440 and 5440 m L / m 3, excluding Test 1A which had a temperature increase greater than 10 °C. Actual peak bedroom CO2 concentrations ranged from 2870 to 5970 m L / m 3 excluding Test 1A. These numbers can be compared to the short-term (8-h average) U.S. occupa-

tional CO2 standard of 5000 m L / m 3 (U.S. Government, 1979). As expected, CO concentrations were highest when the radiant heater was used and NOt (NO + NO2) concentrations were highest when the convective heater was used. However, NO2 concentrations, although widely varying, were similar for both the convective and radiant heaters. This was surprising since earlier work by Traynor et al. (1983) showed NO2 emissions for convective heaters were higher than for radiant heaters. The range of increase in NO2 concentrations was from 0.12 to 0.60 m L / m 3 for the convective heater tests and was from 0.12 to 0.52 m L / m 3 for the radiant heater tests. These numbers can be compared to the short-term (1-h average) California outdoor NO2 standard of 0.25 m L / m 3 (State of California, 1977). An important observation from the results of these tests is that moderate increase in ventilation rates, a result of opening a windor or door 2.5 cm, did not reduce the short-term peak pollutant concentrations because the heater operated longer to achieve the same temperature rise. The peak CO2 concentration (less indoor background) averaged 4080 4-870 m L / m 3 when the window and door were closed, 4370 4- 700 m L / m 3 when the door was open 2.5 cm, and 3830 ± 1100 m L / m 3 when the window was open 2.5 cm. However, opening the bedroom door fully did dilute the pollutants enough to lower the peak CO2 concentration to 2560 ± 160 m L / m 3 above the background. Table 2 summarizes the test data collected when the kerosene heaters were operated in the living room. It is interesting to note the high CO2 concentrations while achieving only a few degree Celsius increase in the indoor temperature. The first-order indoor, NO2 reactivity rate was 0.20 ±0.12 h -3 for convective heater tests and was 0.56 4-0.13 h-' for radiant heater tests. The difference may be a result of higher particulate emissions from the radiant heater (Traynor et al., 1983). Semi-continuous emission rates were determined for CO, NO~, and N (of NOx) and are shown in Figs. 2, 3, and 4, respectively, using a technique previously published (Trayner et al., 1985). The technique allows calculation of an emission value between every two wholehouse average concentration data points- every 24 m i n and then applies a mixing correction factor using the ratio of the calculated CO2 emission rate to the theoretical CO2 emission rate of 71,400 #g/kJ. The CO emission rate from the convective heater falls rapidly during the first hour of operation. After the first hour, the CO emissions from the radiant heater were stable while the CO emissions from the convective heater were below detection. The CO emission rates from the radiant heater compare well with the emission rates measured with the same heater near sea level which ranged from 60 to 140 /zg/kJ (Traynor et al., 1983). The N (of NOx) emission rates in this study were slightly below those of the near sea level tests of the same heater (Traynor et al., 1983). The near sea level N (of NOx)

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Table 2. Peak pollutant concentration (less background) in a house from using an unvented kerosene-fired space heater. House Air Exchange Rate (h-')

Mean Outdoor Temp. (°C)

Initial House Temp. (°C)

House Temp. Increase (°C)

Peak Pollutant Concentration Increases (mL/m 3) CO

CO2

NO

NO:

02

Heater Type

Combustion Timea (h)

During Burn b

After Burn

Convective heater Test 9A Test 9B Test 9C

3.02 9.43 8.70

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0.26 0.28 0.32

2.4 0.9 1.1

12.3 13.2 13.9

3.2 4.3 4.1

0.5 0.0 0.2

4330 4670 4880

2.10 2.17 2.55

0.19 0.11 0.16

-5400 -6400 -6400

11.38 8.02

0.39 0.33

0.31 0.24

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15.4 13.8

1.0 3.4

6.3 8.9

3070 3640

0.08 0.11

0.07 0.07

-4300 - 4700

Radiant heater Test 10A Test 10B

aAverage fuel consumption rates were 7300 ± 1200 k J / h for the convective heater and 6400 ± 300 k J / h for the radiant heater. Kerosene heat of combustion is 43.5 kJ/g. bEstimation procedure for house air exchange rate during burn gives more weight to data at the end of the burn than at the beginning of the burn.

emission rates ranged from 15 to 16 #g/kJ for the convective heater and ranged from 1.7 to 2.2 #g/kJ for the radiant heater. However, the NO2 emission rate for the convective heater was dramatically lower in these high elevation tests than the earlier lower elevation tests. The low elevation tests showed an NOx emission rate that ranged from 12 to 25/tg/kJ whereas these high elevation tests show long-term emission rates between approxi-

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mately 2 to 6 gg/kJ. The facts that the low-elevation tests were conducted for only 1 h , as compared with several hours for these high-elevation tests, and the high-elevation NO2 emission rates are greatest during the initial burn period do not explain the entire difference observed. Inter-room pollutant transport rates were calculated for all bedroom tests with the bedroom window closed.

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Fig. 2. CO emission rates versus time for tests conducted with a kerosene heater in the living room of an unoccupied house,

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Fig. 3. NO2 emission rates versus time for tests conducted with a kerosene heater in the living room of an unoccupied house.

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only be calculated while the heater was operating and an inter-room pollutant concentration gradient existed. Figure 6 shows the time-dependent inter-room flow rates and inter-room temperature differences for the convective and radiant heater tests. These rates are considerably higher than those with the door closed and the

'

When the bedroom door was closed the inter-room flow rate averaged 6 ± 3 mVh. This corresponds to an interroom air exchange rate (relative to the bedroom volume) of 0.2 h-'. This number can be compared with the values of 0.35 to 0.50 h-' in the third column of Table 1, which represent the total flow o f air out o f the bedroom for these cases. The inter-room temperature difference peaked at approximately 8 °C. Pollutants continued to be transported at a relatively constant rate, from the bedroom to the rest o f the house for several hours after the heater was shut off. The small area opening between rooms, estimated to be less than 100 cm ~, may have been responsible for the flow pattern that mimicked capillary flow. The average inter-room temperature differences over the measurement period were in the range of 3 to 5 °C. When the bedroom door was partially open 2.5 cm and the opening area between rooms was approximately 520 cm =, the inter-room flow rates ranged from 16 to 53 m~/h, which corresponds to an inter-room air exchange rate range o f 0.5 to 1.7 h-L Inter-room temperature differences and inter-room pollutant transport rates are shown on Fig. 5. When the bedroom door was wide open and the opening area between rooms was approximately 15,000 cm =, the inter-room flow rates were so high that they could

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Unvented Kerosene-fired space heaters

! 65

door open 2.5 cm. At the end of the convective heater test, the bedroom CO2 concentration was almost identical to the living room and kitchen values. The interroom transport rate was higher for the convective heater test than for the radiant heater test. We hypothesize that this difference may be due to the greater heat output of the convective heater and/or to the larger vertical temperature gradiant in the bedroom caused by the convective heater. The latter explanation is plausible since virtually all of the heat from the convective heater is contained in its plume while the radiant heater's output has both convective and radiant components. Previous research by Weber and Kearney (1980) resulted in the development of an empirical model that describes inter-room heat transfer due to natural convection caused by inter-room temperature differences. The model, also used by Balcomb and Yamaguchi (1983), has been converted to standard international units and is as follows: Q = 0.0023w (h AT) 3/2, where Q w h AT

= -= =

(5)

convective heat flow (k J/h); door opening width (cm); door height (cm); and inter-room temperature difference (°C).

The inter-room flow rate can then be described as follows:

q~2 =

Q

sdAT'

(6)

where q12 = inter-room flow rate (m3/h); s = specific heat of dry air (1.0 kJ/kg/°C); and d = room temperature density of air (0.96 kg/m 3 at 0.8 atm). Combining Eqs. (5) and (6) yields the following: q,2 = 0.0024 w(h) 3'2 (AT) ''2.

(7)

At sea level, the coefficient in Eq. (7) would be 0.0019. In order to calculate expected inter-room flow rates, the opening width, opening height, and average A T were determined for the three types of bedroom tests with the bedroom window closed. The door opening height was measured to be 204 cm for all tests. The door opening width was estimated to be 0.2 cm for the closed door test and measured to be 2.5 cm and 74 cm for the partiallyopen-door and wide-open-door tests, respectively. Average inter-room temperature differences were approximately 4 °C for all tests. Using the above, sometimes rather rough, estimates of input parameters for Eq. (7) we obtain predicted average inter-room flow rates of 3, 35, and 1000 m3/h for the closed-door, partially-open-door, and wide-open-

door tests, respectively. These numbers can be compared with the earlier results of 6 ± 3 m3/h for the closed-door test, a range of 16 to 53 m3/h for the partially-opendoor tests, and a range of 190 to 3400 m3/h for the wideopen-door tests. This rough analysis shows reasonably good agreement between measured and predicted results.

Conclusions The use of a kerosene heater in a bedroom under a wide variety of ventilation conditions can result in NO2 and CO2 concentrations that are a significant fraction of or in excess of U.S. state or federal air quality guidelines. Moderate increases in ventilation rates obtained by slightly opening a window or door do not necessarily reduce peak pollutant concentrations since the heaters must be operated longer to obtain the same increase in room temperature. Inter-room pollutant transport rates, however, can be sufficiently high to be an important mechanism for the dilution of pollutants generated in a single room. Good agreement was obtained between inter-room flow rates measured in this study and the empirically modeled results of previous work. Finally, the NO2 emission rates for the convective heater were significantly lower at the high elevation site than previous measurements conducted near sea level. The reasons for the difference should be investigated further because of the implications for controlling NO2 emissions from unvented combustion space heaters. Acknowledgment-This work was supported by the Director, Office of Energy Research, Office of Health and Environmental Research, Human Health and Assessments Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

References Balcomb, J. D. and Yamaguchi, K. (1983). Heat distribution by natural convection, Proceedings o f the Eighth Passive Solar Conference, pp. 289-294. Sante Fe, NM, 7-9 September; American Solar Energy Society, New York, NY. Girman, J. R., Allen, J. R., Apte, M. G., Martin, V. M., and Traynor, G. W. (1983) Pollutant emission rates for unrented gas-fired space heaters: A laboratory study. LBL-14502, Lawrence Berkeley Laboratory, Berkeley, CA. Leaderer, B. P. (1983) Air pollutant emissions from kerosene space heaters, Science 218, 1113-1115. Ryan, P. B., Spengler, J. D., and Letz, R. (1983) The effects of kerosene heaters on indoor pollutant concentrations: A monitoring and modeling study, Atmos. Environ. 17, 1339-1345. State of California (1977) California Administrative Code, Title 17, Subchapter 1.5, Section 70100. Traynor, G. W., Allen, J. R., Apte, M. G., Girman, J. R., and Hollowell, C. D. (1983). Pollutant emissions from portable kerosenefired space heaters. Environ. Sci. Technol. 17, 369-371; Addendum (1985) Environ. Sci. Technol. 19, 200. Traynor, G. W., Girman, J. R., Apte, M. G., Dillworth, J. F., and White, P. D. (1985) Indoor air pollution due to emissions from unvented gas-fired space heaters. J. Air Pollut. Control Assoc. 35, 231-237. U.S. Government (1979) Code of Federal Regulations, Title 29, Section 1910.1000.

166 Weber, D. D. and Kearney, R. J. (1980) National convective heat transfer through an aperture in passive solar heated buildings, pp. 1037-1041. Proceedings of the Fifth National Passive Solar Conference, Amherst, MA, 19-26 October, American Section of the

G.W. Traynor et al. International Solar Energy Society, Newark, DE. Yamanaka, S., Hirose, H., and Takada, S. (1979) Nitrogen oxide emissions from domestic kerosene-fired and gas-fired appliances, Atmos. Environ. 13, 407-412.