Presentation Transcript

1. Mingledorff’s – Atlanta Heat Exchanger Inspection Seminar

2. Safety Review Good safety practices will prevent many injures Safety must be first on your mind at all times Always remove loose items when working around equipment with moving or rotating parts Be cautious of sharp objects
3. Safety Review Always lift with your legs and not with your back Wear a back support belt when lifting heavy objects When working with electrical equipment always verify that the power is off Do not rely on a shut-off switch or disconnect being off -- always check yourself
4. Safety Review Be cautious of hot surfaces or work areas Be cautious of any gas or oil leaks Always check for carbon monoxide Always follow proper safety practices when working with ladders Be cautious of confined spaces - provide proper ventilation when required
5. Safety Review Use Safety Equipment
6. Safety Review
7. Safety Review Lock out/tag out equipment disconnect switch Gas pipe leak testing
8. Safety Review BE CAREFUL! High voltage is always dangerous. Even 40 volts can be lethal if skin is wet or damaged.
9. Safety Review Do not wear rings or jewelry when working on electrical circuits. Never use screwdrivers or other conductive tools in an electrical panel when the power is on.
10. Ask Yourself This Question How is the carbon monoxide supposed to get through the hole or crack in the heat exchanger if the blower is pushing air around and over the heat exchanger?
11. The Answer To That Question It can’t, the same blower pressure that pushes air through the duct work and out the registers also pushes against the OUTSIDE of the heat exchanger and forces air into it!
12. Myths About Cracked Heat Exchangers That you can test for carbon monoxide at the register if there is a crack in the heat exchanger.
13. Myths About Cracked Heat Exchangers This is a total waste of time in most cases because the blower motor of a residential furnace is positive and the combustion side of the heat exchanger is a negative, the much more powerful positive pressure is going to infiltrate this negative pressure and keep carbon monoxide from escaping into the air stream to the conditioned space except in severely open heat exchangers. Where carbon monoxide is more likely to show up is at the burner port of the cracked cells because the blower pressure is infiltrating the exchanger and pushing it out of the cell or tube openings or in the flue gasses going out of the vent.
14. Myths About Cracked Heat Exchangers 2. A crack is open at all times. This is not true and a crack may only open up when the metal of the exchanger is hot.
15. Myths About Cracked Heat Exchangers 3. Heat exchanger failures are usually manufacturer defects. Factory testing of heat exchangers has shown that most field failures of cracking, burn-through and warping were not manufacturing quality or design related but the direct result of not following installation instructions or application related issues such as:
16. Myths About Cracked Heat Exchangers Excessive temperature rise due to restricted airflow (blocked or restrictive filters). Poor duct design causing excessive static pressure and low airflow. High manifold gas pressures resulting in over-firing. Chemicals in the combustion air zone that cause corrosion when burned in the heat exchanger.
17. CO Facts At A Glance CO poisoning kills more than 200 people per year CO poisoning sends more than 10,000 people to the hospital emergency rooms for treat every year *Information from the Consumer Product Safety Commission
18. Common Sources of CO Unvented cooking appliances Wood burning fireplace Blocked chimney Water heat Gas clothes drier Gas refrigerator BBQ grill Pool/spa heaters Tobacco smoke Ceiling mounted unit heater Fuel burning space heater Attached garage
19. How Is Carbon Monoxide Formed? A gas furnace that is set up correctly and burning clean will produce as little as 20 ppm of carbon monoxide directly out of the flue. Air/Fuel Mixture – If an insufficient amount of combustion air is supplied to the furnace, incomplete combustion occurs. Usually the flame is yellow and waving. Soot would also be forming inside the heat exchanger and vent pipe.
20. How Is Carbon Monoxide Formed? Dirty and or Rusty Burners – With dirty or rusty burners, this impedes the flow gas from reacting properly with the combustion air, causing carbon monoxide to form. Clogged vents, improper sized vents, chimneys clogged can cause a properly working furnace to spill carbon monoxide into the living space.
21. The Heat Exchanger The heat exchanger is designed to be heated by the burner flames while the furnace blower moves room air across it. Under normal conditions, when the furnace is running, the air coming into blower from the house (return air) is generally 68 to 72 degrees F. As the air passes through the furnace, the heat exchanger warms the air. The discharge air coming out of the furnace and moving through the duct work will be somewhere between 35 and 65 degrees hotter than the return air. (refer to data plate for proper rise)
22. The Heat Exchanger
23. The Heat Exchanger The heat exchanger is what separates air flow of the fuel burning process from the blower-driven air that moves through your house. This is a box-in-a-box arrangement, when the furnace blower is running, it pushes air through inside of the outer cabinet across the outside of the heat exchanger. The force of the blower-driven air is much greater than the air pressures inside the heat exchanger. As a result, any crack or hole or split results in air being pushed INTO the heat exchanger.
24. The Heat Exchanger
25. The Heat Exchanger
26. Symptoms of a Cracked Heat Exchanger A heat exchanger crack that can cause trouble usually cause the burner flames to roll out the front of the burner openings. This can cause fire, burned wiring and should trip the "rollout switches", which are temperature sensors located near the front and above the burners.
27. Symptoms of a Cracked Heat Exchanger If the crack or split is really big, it will keep a burner from lighting correctly and cause a delayed ignition (if the blower is running continuously). On older furnaces with standing pilots, a big crack might cause the pilot flame to be blown out, which turns into a no-heat situation.
28. Temperature Rise – Why Should You Care? The increase in temperature between the return air and discharge air is called "temperature rise". This number is printed on the ratings tag (where the model and serial numbers are) and is used by technicians to make sure that the proper amount of air is moving through the furnace. If the furnace blower is moving too slow, the temperature rise will be higher than the rating. If the blower is moving air too quickly through the furnace, the discharge temperature will be too low.
29. Temperature Rise – Why Should You Care? The temperature rise rating dictates the "recommended" and safe range of discharge temperatures for your furnace. A high temperature rise puts additional stress on the heat exchanger, results in higher energy losses through the duct work and can cause a lot of other problems. If the temperature rise is too low, the discharge air might feel cool when coming out of a register, areas of the house may be hard to heat or problems with condensation in the flue or on the inside of the heat exchanger may occur.
30. Temperature Rise – Why Should You Care? Follow the information on the furnace or RTU name plate!!
31. Recommended Yearly Inspections Check chimneys, flues, and vents for leakage and blockages Check vents to furnaces, hot water heaters, boilers, and other fuel-burning appliances for proper connection to the appliance Confirm proper combustion air
32. Recommended Yearly Inspections What Not To Use For Heat Exchanger Inspections DO NOT use salt spray solutions. DO NOT use smoke bombs (sulfur style). * Both of the above methods can cause damage to the heat exchangers. They will create acids which in turn will deteriorate the heat exchangers. This will cause premature failure of the heat exchangers.
33. Recommended Yearly Inspections Tools Needed For Heat Exchanger Inspections Good flashlight Bore Scopes Inspection mirror CO test instrument Common sense Spray Dyes Magnehelic Gauge
34. Recommended Yearly Inspections Methods For Heat Exchanger Testing Visual inspection Observing flame pattern during operation Using the methane (CH4) tracer procedure CO electronic test instruments
35. Recommended Yearly Inspections Methods For Heat Exchanger Testing Smoke Candles Pressure Test Change Chemical Smoke Tests (very corrosive)
36. Recommended Yearly Inspections Visual Inspection Use mirror and flashlight to inspect internal sections for signs of split seams, open cracks, and severe deteriorations. Since cooling coils block the inspection of the heat exchanger pulling the blower section and viewing the heat exchanger via the air side can be done.
37. Recommended Yearly Inspections Tools Needed For Heat Exchanger Inspections Flexible lights are good for getting a light right on a suspected area. Having a light almost on the crack will highlight the defect.
38. Recommended Yearly Inspections Tools Needed For Heat Exchanger Inspections Small round and oval mirrors that have long telescoping reach are available at most welding supply stores.
39. Recommended Yearly Inspections Visual Inspection Disassemble the Furnace until you can visually inspect all heat exchanger exterior surfaces. Any crack or hole that is big enough to affect combustion will be easily visible to the naked eye. Do not use wateron crimped style heat exchangers.
40. Example of Failures
41. Example of Failures
42. Flame Pattern Inspection Ignite the main burner Observe the flame pattern prior to the blower/fan coming on Watch for floating flames, flame roll-out, or flame distortion If the above conditions exist: *Possible split seam, open crack, or severe deterioration of the heat exchanger. Replacement of the heat exchanger or the entire furnace is needed.
43. Smoke Candle Test Inspection The use of smoke bombs is common practice of determining if there is a cracked heat exchanger. Place the fan in the “on” position. With the flue outlet and burner access opening blocked a smoke bomb or candle is ignited in the heat exchanger. Observations for smoke turbulence is then made inside the heat exchanger while the air is circulating around the heat exchanger.
44. Recommended Yearly Inspections Tools Needed For Heat Exchanger Inspections Using a smoke candle or puffer you can fill the burner chamber with smoke. Then turn the blower on. If the smoke sprays out and away from the burner opening you have a good indication of a leak in the heat exchanger.
45. Tracer Gas Method *This method is not accepted to detect CO for the crimped seam heat exchanger and should not be used to evaluate the heat exchangers integrity. Used this method for the welded seam heat exchanger installed in the typical natural draft furnaces.
46. Tracer Gas Method Welded Seam Heat Exchanger
47. Tracer Gas Method Warm the heat exchanger up Inject the tracer gas (carbon monoxide) into the heat exchanger area *heat exchanger may have to be plugged to contain gas A gas detector is then passed above and around the proximity of the heat exchanger In some tests, the detection device is used to check for the tracer gas at the supply grills within the home or office
48. Tracer Gas Method The methane/nitrogen gas injection method.
49. Tracer Gas Method Freon has been used as a tracer gas with a halogen leak detector. (no longer allowed) Freon gas is released in the combustion side of the heat exchanger and if the halogen leak detector senses halogens in the circulating air stream a leak is present. A problem with this method is phosgene gas (a deadly poison) can be generated if the Freon passes through a flame. Also, Freon is heavier than air.
50. The Magnehelic Pressure Test Tape shut burner chamber openings or combustion air box and the flue outlet. Connect magnehelic gauge to inducer pressure sensing port. Operate the blower. Movement of the gauge needle indicates leakage into the heat exchanger either from cracks, rust perforations or leaking seals or gaskets.
51. The Magnehelic Pressure Test If a crack is allowing distribution air to blow into the heat exchanger (through a crack or hole) then you will increase pressure onto your heat exchanger. Be aware of the normal leakage rate of the heat exchanger.
52. CO Tester Method
53. CO Tester Method After the Furnace has run for at least five minutes, measure the CO level in the return airstream near the furnace and record the value. Then measure the CO level in the supply airstream at a location in the system where the air is well mixed. Generally, a location downstream of one or more bends in the ductwork is a good place to take the sample for this measurement. Record this value.
54. CO Tester Method If there is no measurable difference in the CO in the return and supply air, it is likely the furnace is not leaking CO into the air stream.
55. CO Tester Method If there is no difference in the CO concentration between the return and supply air, but there is CO detected in the air stream above 9 ppm, there may be another source of CO in the home such as other gas-fired appliances, an automobile operating in a garage, or a fireplace in operation.
56. CO Tester Method If the CO in the supply air is less than the CO in the return air, it is possible that there is an error in the measurement or that the measurement is being diluted by a ventilation or fresh air intake.
57. CO Tester Method If the CO in the supply air is greater than the CO in the return air, it is possible that the furnace is generating the CO that is leaking into the airstream.
58. Borescope Method Optical borescopes can also get you access to some narrow openings. VIDEO
59. Water Test Method Not a preferred method on crimped heat exchangers. If using this method on tube heat exchangers, be cautious of the amount of water or level of water that is being used. Furnace heat exchangers joints are not hermetically sealed, so a small amount of leakage is normal.
60. Water Test Method
61. Spray Dyes for Heat Exchanger Tests A spray of fluorescent solution is marketed which is sprayed into the heat exchanger with a suspected leak and penetrates even the finest crack. Then the crack is detected using an ultraviolet light; however the heat exchanger must be accessible for close examination of all surfaces.
62. Spray Dyes for Heat Exchanger Tests The Nu-Calgon Visible Defects Heat Exchanger Inspection System
63. Heat Exchanger Design It is almost impossible to construct a heat exchanger that is entirely air tight. Therefore any test method developed to detect flue gas leakage needs to have quantitative aspects.
64. Heat Exchanger Design Heat exchanger design has evolved from a welded seam to the current design utilizing the crimped clam shell design. The crimped design heat exchanger does not form a 100% leak-proof seal as it does not need to be.
65. Heat Exchanger Design
66. Heat Exchanger Design Furnace Heat Exchanger Gas Leak Standards The standards for Gravity and Fan Type Direct Vent Wall Furnaces is Z21.44.1981, and for Direct Vent Central Furnaces Z21.64-1978. Requirement for tight joints in heat exchangers is met if the combustion chamber-vent section does not leak more than 2% of the flue gases. This test is conducted with the internal pressure of the heat exchanger raised to 0.1 w.c. static pressure.
67. Negative Pressure Induced draft furnaces are design to operate with a negative pressure heat exchanger. *The negative pressure within the heat exchanger imposed by the inducer motor is verified by the pressure switch. *The pressure switch will shut down the burners if the heat exchanger pressure were to rise above the negative setting.
68. Negative Pressure
69. Negative Pressure Airflow-Positive Pressure
70. Negative Pressure Airflow-Positive Pressure
71. Can A Inducer Motor Change Cause High C0? Yes!!!! When changing from a 4-wire to a 3-wire inducer motor, if wired incorrectly will cause high C0. If wired incorrectly, the motor will run at a lower speed, however, fast enough to keep the hall effect engaged.
72. Can A Inducer Motor Change Cause High C0? 48SS400 606 Capacitor IGC control board Brown L2 CM Yellow This wire needs to be field supplied Purple The 3 wire sensor plugs into the board the same as the original motor. This diagram will help you wire a replacement motor for the original that had 2 brown wires to the capacitor and 2 power wires. There a few wiring changes in the different models. Some of the older motors picked up line 2 at the line side of the compressor contactor. Other models share a capacitor with the blower motor.
73. Can A Inducer Motor Change Cause High C0? 48GS Unit Seals Seals Wire Seal Seals
74. Cracked Heat Exchangers Needs To Be Addressed It is usually an indicator of more trouble in the future, and should NOT be taken lightly. If it is a small hole or crack, then it is a minor issue that needs to be corrected - generally by replacing the furnace or heat exchanger.
75. Conclusion Ultimately ANY crack in a heat exchanger that was caused by wear and tear or some event like improper operation is potentially dangerous. For that last reason we'd be surprised if any HVAC contractor would risk the lives of the occupants (nor a lawsuit) by saying leaving the unit in place is OK.
76. Conclusion Ultimately, there is no silver bullet when it comes to finding cracks in heat exchangers. Experience and knowledge of particular equipment will help you know where the flaws typically occur.
77. Thank You For Your Business & Attending The Seminar