Room Chamber Assessment of Pollutant Emission Properties of Low-Emission Unflued Gas Heaters

Proceedings: Indoor Air 2002 ROOM CHAMBER ASSESSMENT OF POLLUTANT EMISSION PROPERTIES OF LOW-EMISSION UNFLUED GAS HEATERS SK Brown*, M Cheng and KJ Mahoney CSIRO Building, Construction and Engineering, Melbourne, Victoria, Australia ABSTRACT Pollutant emissions from unflued gas heaters were assessed in CSIRO’s Room Dynamic Environmental Chamber. This paper describes the assessment procedure and findings for major commercial “low-emission” heaters. The chamber was operated at controlled conditions of temperature, humidity, ventilation and air mixing, representative of those encountered in indoor environments. A fixed rate of heat removal from the chamber air ensured that the heaters operated at constant heating rates, typically ~6 MJ/h, simulating operation after warm-up in South-East Australian insulated dwellings. Pollutants assessed were nitrogen dioxide, carbon monoxide, formaldehyde, VOCs and respirable particulates. One heater was lower emitting for nitrogen dioxide, but emitted greater amounts of carbon monoxide and formaldehyde (the latter becoming significant to indoor air quality). When operated with low line pressure or slight misalignment of the gas burner, this heater became a hazardous source of these pollutants. Emissions from one heater changed little after continuous operation for three months. INDEX TERMS Gas heater, Unflued, Unvented, Pollutant emission, Indoor air, Nitrogen dioxide, Formaldehyde, Carbon monoxide. INTRODUCTION Unflued gas heaters have been used for many years in most Australian States as primary residential heaters, sometimes with restricted heater sizes or installation of fixed wall vents in the heated room. It is estimated that approximately 600,000 unflued gas heaters (natural gas or LPG) have been installed across Australia, about two-thirds of these in SE Australia. Health concerns over pollutant emissions from unflued gas heaters in dwellings and schools were raised in the 1980s, particularly in relation to nitrogen dioxide (NO2) and carbon monoxide (CO) emissions (Brown, 1997). Industry response to these concerns led to the development of low-NOx heaters and specification of pollutant emission levels (Gas Installation Standards Committee, 1998), as follows: (a) “The amount of nitrogen dioxide produced by an indoor flueless heater per hour, when divided by the nominal gas consumption, shall not exceed 5 ng/J.” (b) “The CO/CO2 ratio for indoor flueless space heaters shall not exceed 0.004 when operating on available gas at the manufacturer’s specified test point pressure.” The industry determined these emission levels according to “Method of Test 5.115/6–96 Emission Tests”, in which new heaters were operated at full capacity for a set period (approximately 15 minutes), after which exhaust gases were sampled. However, this is not how heaters typically operate in buildings, where they operate in an on–off mode with thermostat * Contact author email: [email protected] 637 Proceedings: Indoor Air 2002 control. Also, there are other toxic air pollutants that are potentially emitted from unflued gas heaters, such as formaldehyde, volatile organic compounds (VOCs) and respirable suspended particulates. CSIRO investigated the emissions of the above pollutants from several new and used unflued natural gas heaters using a Room Dynamic Environmental Chamber designed to simulate the physical conditions found in buildings. Pollutant emission rates from the heaters were determined at conditions considered “typical” of residences in SE Australia. This report will present the chamber and pollutant sampling procedures used, and results for the performance of heaters. METHODS Heaters Heaters were placed in the centre of the room chamber and were plumbed to the natural gas line (Victorian gas: ~90% methane, ~8% ethane) through a port in the chamber wall. Gas supply was regulated to provide a minimum gas inlet pressure (at heater bayonet connection) of 1.13 kPa with the heater operating at maximum gas consumption, as required by the Gas Installation Code AG601 (Gas Installation Standards Committee, 1998). The heaters were natural gas unflued heaters of 17–18 MJ/h capacity, with thermostat operation and piezoelectric ignition. Note that the maximum input rate (heat capacity per room volume) for these experiments was 0.51 MJ/h/m3, which exceeds the AG Code limit for thermostat heaters of 0.4 MJ/h/m3. However, heater operation was limited in the experiments to 5–7 MJ/h heat input, equivalent to ~0.2 MJ/h/m3, which is much below the above limit. Also, this rate of heat input is that expected for a well-insulated dwelling in SE Australia after the heat-up stage (Delsante, 1999). Gas consumption was measured using a gas meter (American Meter Co. DTM-200A) which was logged several times during each experiment. A line of best fit was fitted to the gas usage data to determine the gas consumption rate; alternatively, the latter was determined from the carbon dioxide emission rate of the heater. Room dynamic environmental chamber This was a 4.0 × 3.0 × 2.7 m high room constructed of inert materials, such as stainless steel, glass and Teflon®, which has been shown to exhibit very low sink effects for VOCs (Mason et al., 1999). Air supplied to the room chamber was cleaned to reduce background pollutants to 3 3 3 levels of NO2 <5 µg/m , formaldehyde <10 µg/m , respirable particles <3µg/m , CO <1 ppm, total VOC (TVOC) 40–80 µg/m3. Supply air was temperature- and humidity-controlled to 23°C and 50% RH and supplied to a nominal ventilation rate of 2.0 air changers per hour (ACH). The actual ventilation rate in the room chamber was determined by dosing the chamber with the tracer gas sulfur hexafluoride (SF6) and monitoring its decay by gas infra- red spectrophotometer (ASTM, 1995). The chamber was operated at a positive pressure, initially 0.2 kPa, but this counteracted the gas supply pressure to the heaters, and subsequently a pressure compensation device was added to limit chamber positive pressure to 0.01 kPa for all measurements presented here, unless specified otherwise. Air within the chamber was well mixed by recirculating air from floor level to ceiling level at a rate of 18 chamber volumes per hour. This caused air currents of approximately 0.3 m/sec adjacent to the heaters, which are typical of those found in buildings (Christianson et al., 1989). The air recirculation system was equipped with a chiller coil through which water at 638 Proceedings: Indoor Air 2002 16°C was circulated while the heater operated. Water condensation on the coil was prevented at this temperature, so that loss of water-soluble pollutants was prevented. Under these conditions, the chiller coil was capable of removing approximately 6 MJ/h of heat and, since the room was well insulated, this was the major means for removing heat in a controlled manner from the chamber and for regulating the operation of the heater. Under well-mixed conditions, a pollutant source with a constant emission rate will lead to pollutant concentrations in the room chamber over time of: –Nt Ct = C∞ (1 – e ) (1) where Ct is pollutant concentration at time t; C∞ is pollutant concentration at t = ∞; and N is the chamber ventilation rate. At a ventilation rate of 2 ACH, it can be shown that at t = 2 hours, Ct = 0.98 C∞; and at t = 6 hours, Ct = 1.00 C∞. Thus, the chamber concentrations of pollutants are expected to reach 98% of steady-state levels after 2 hours of operation of a source with a constant emission rate. This assumes that no “sink” losses of the pollutants occur to chamber internal surfaces. If such losses occurred, then a steady state would not occur by 2 hours. Pollutant concentrations in initial experiments were measured at both 2 and 6 hours as a check for potential sink effects by reactive pollutants such as NO2 and formaldehyde. These were not found to differ, and so sampling only at 4 hours is considered to be acceptable in future emission experiments. Pollutant sampling and analysis NO2 concentration was measured using the standard method ASTM D1607–91 “Standard Test Method for Nitrogen Dioxide Content of the Atmosphere (Greiss–Saltzman Reaction)”, using three fritted glass bubblers in series capturing chamber air, generally as 25 L samples. Duplicate measurements were made at each sampling time. CO and CO2 were monitored using a Q-Trak™ Model 8550/8551 IAQ Monitor (TSI Inc., USA). This instrument logged CO, CO2, temperature and RH at one-minute intervals using a probe positioned inside the room chamber. Data was averaged for one-hour periods at each sampling time. Formaldehyde concentration was measured using the Australian Standard method AS 2364.6– 1995 ‘Determination of Formaldehyde-Impinger Sampling in Chromotropic Acid Method’, using two fritted glass bubblers in series to capture room chamber air, generally as 60 L samples collected over a one-hour period. Duplicate samples were collected at each sampling time. VOCs were sampled from chamber air onto Envirochem multisorbent tubes (containing Tenax TA/Ambersorb/Activated Charcoal), generally as 3–4 L samples collected over periods of 20–30 minutes. Duplicate samples were collected at each sampling time. These were analysed by thermal desorption/gas chromatography (GC)/flame ionisation detector (FID)/mass spectrometry (MS) under conditions described previously (Brown, 1999). The major 15–20 VOCs in each sample were quantified. The TVOC concentration was also estimated from the total GC peak area from 5 to 35 minutes (approximately C5-alkanes onwards and including ethanol but not methanol), expressed as toluene-equivalent concentration. Since very volatile organic compounds were observed in analyses up to 5 minutes of the GC program, these were also estimated by summing peak areas and expressing this measure as ΣVVOC. Respirable suspended particles were logged at one-minute intervals using a Dustrak Model 8520 Aerosol Monitor (TSI Inc., USA) fitted with a nylon cyclone that provided a 4.0 µm cut- 639 Proceedings: Indoor Air 2002 point for particle sampling within the room chamber.

Load more