## Draft Report: November 6, 2011



# Input Rate of Pilot Burners on Gas Fireplaces

Prepared for:
Alex Lekov Lawrence Berkeley National Laboratories

By
Jim Mullen EER Consulting, LLCGeneral

The following ignition system discussion is relevan t to Hearth Products that are usually certified to ANSI Z21.50 Vented Gas Fireplaces (Decorative) and Z21.88 Vented Gas Fireplace Heaters. While it is not mandatory that this equipment be certified to these standards nearly all units are.
In comments filed with the Department of Energy (DO E) on March 21, 2011, the HPBA (Hearth, Patio and Barbecue) Trade association states that Decorat ive vented gas fireplaces are 70% of all vented gas fireplace sales.
Requirements
The respective certification standards for these ap pliances require a gas Ignition system which is designed to ignite and reignite the main burner. B ased on ANSI Standard Z21.20, Automatic Electrical Controls for Household and Similar Use, such system s are required to:

a. Ignite gas at the main burner or gas at the pilot b urner so the pilot can ignite the main burner b. Prove the presence of either the ignition source, t he main burner flame, or both

c. Automatically act to shut off the gas supply to the pilot and main burner, when the supervised flame or ignition source is not proved.

The ANSI Z21.50 and Z21.88 standards include both re quirements for construction of the ignition system and performance tests based on Standard Z21.20. The ignition system and its’ components generally must conform to the requirements of, or be certifie d to, the requirements of Z21.20 in order to obtain certification of the appliance to the Z21.50 or Z21 .88 Standards.



### Units Not Requiring a 120 Volt Power Source

The basic ignition/flame safety system is generally referred to as a Millivolt, Thermopile or standing pilot control. Under Z21.20, it meets the definition of a Continuous Pilot with a pilot. When placed in operation, it is intended to remain ignited continu ously until it is manually interrupted. The system generally consists of:

a. A suitable automatic gas valve b. a pilot burner assembly with pilot burner, spark e lectrode, thermocouple and thermopile components

c. a Piezo-electric electric generator d. a high temperature limit

e. an electrical control switch to turn the main burne r gas on or off.

The automatic gas valve performs several functions : It starts and stops the gas flow. It regulates the outlet pressure of the main burner gas. And it con tains a manual knob with three selectable positions

Off, On and Pilot.The pilot assembly generally includes a spark rod, pilot burner, thermocouple and thermopile. The

spark electrode is used to light the pilot flame. The thermocouple is used to monitor the presences o f adequate pilot flame. The Thermopile is a number o f electrically connected thermocouples in a common housing in the pilot flame. The heat on the thermopile generates a small amount of electricity , sufficient to power the operator in the gas valve. The voltage generated is small, around 750 MilliVo lts.



### Pilot Input Rates
The gas Input to the pilot is primarily a function of the pilot orifice, gas valve pressure drop and g as line pressure. With the move to conserve energy over th e past 10-20 years, pilot input has generally been reduced. The pilot input on fireplace units, parti cularly the decorative units, may be considerably h igher in order to provide proper operation of the thermoc ouple and thermopile under varying field conditions.
While no published literature documenting a large n umber of input rate measurements has been located, one field measurement indicates a nominal rate of 1500 Btuh. A range of inputs can be estimated from several sources.

Literature on the NRCan website 1 reports the following: “In many gas fireplaces, a pilot light ignites the main burner as the unit is turned on. A pilot light is a small gas flame that, on its own, can consume from 600 to 1500 Btu of gas per hour . . . “. The Duke Energy website 2 gives an estimate of approximately 900 Btuh.
One manufacturer’s literature for the pilot assembl ies recommended for use with thermopile gas valves indicates “nominal” rates of 500, 1000, and 1500 Bt uh as standard offer product. A second manufacturer indicates 716 Btuh is the “nominal” in put rate. However, the manufacturers do not define several variables that were used to determine “nomi nal” flow.
Examining the Flow equations for an orifice, the fl ow of gas in cubic feet per hour is proportional to the discharge coefficient of the orifice(Cd), the diame ter of the orifice (D), the specific volume of the gas(V’n) and the pressure drop(dp) across the orifi ce. Specifically, the flow is calculable as CFH=358.66*Cd*D^2*(V’n*dp)^.5.
Using nominal values of .7 for Cd, and V’n for natu ral gas at 7.5 inches water pressure drop, the flow equation becomes CFH=3236*D^2. Using this as the b asis for a standardized “normal” flow, the Two manufacturers supply an orifice of D=.020 inch for natural gas and the third manufacturer uses D=.018

1 http://oee.nrcan.gc.ca/publications/infosource/pub/ home/all_about_gas_fireplaces_chapter3.cfm?attr =4

2 http://www.duke-energy.com/kentucky/savings/gas-usa ge-faq.aspinch, resulting in inputs of 1449 and 1174 Btuh res pectively. The .018 diameter is an alternate for t he

two manufacturer’s with the .02 inch as standard. The smallest natural gas orifice offered is .012 in which would produce a nominal flow of 522 Btuh. Wh ile not exact proportional, the orifices offered fo r propane provide similar input rates to those for na tural gas.
Based on the above, it can be anticipated that the majority of units will have pilot inputs in the 100 0 to 1500 Btuh range when the pilot is burning. The mai n factor affecting annual energy consumption of these pilots is whether or not they are turned off between fireplace usages. Most installations will fall into one of three patterns: On continuously, on wh en the fireplace is in use, or on during the heatin g season, and off the remainder of the year.