Déjà vu, all over again
Building Mechanical Electrical HVAC Systems
HVAC contractors in Canada know very well that the bulk of their time is spent preparing for, or dealing with winter. One of the most important requirements for any heating system is maintenance. Every device, and the distribution system it connects to must be inspected every year. The annual preventive maintenance (PM) service call provides an opportunity to sell new equipment, accessories and services.
Modern heating and cooling systems that are AHRI rated and matched combinations, when properly specified, installed (including commissioning) and maintained (PSIM), will provide reliable service for many years. Another benefit of PSIM is reduced greenhouse gas emissions, not only from the HVAC system, but from the fleet of service trucks running around making unnecessary service calls.
SAFETY AND PERFORMANCE
The primary reason for maintenance is to prevent failures. But, before a tool or gauge is connected to any heating appliance, there is a host of safety checks that must be performed to ensure fossil-fueled appliances are capable of working safely (see Steps 1 to 13). Code requirements, municipal by-laws, manufacturer’s instructions, insurance company rules and fuel distributor regulations can all make the modern PM task complicated. Each type of appliance will have its own set of rules and regulations. When an HVAC contractor maintains his or her own work, especially when it meets PSIM, maintenance should not be too difficult. However, it is the “other guy’s” job, encountered every day that needs a thorough maintenance inspection. Of course, technicians must be prepared to red tag unsafe appliances.
I’LL BE BACK
The Quebec singer-songwriter Gilles Vigneault wrote, “Mon pays ce n’est pas un pays, c’est l’hiver” (my country is not a country, it is winter). Winter is just around the corner, leaving just enough time for a couple of cooling system installations and a quick vacation. Otherwise, before Frankie MacDonald can say, ”Major blizzard to hit St. John’s,” HVAC maintenance will start all over again.
Ian McTeer is an HVAC consultant with 35 years experience in the industry. Most recently he was a field rep for Trane Canada DSO. McTeer is a refrigeration mechanic and Class 1 Gas technician.
Step-by-step guide to preventive maintenance
Let us take a look at what a maintenance call to a residential high efficiency gas furnace might look like. We are going to look at the appliance and its accessories. Apart from all the necessary tools and instruments, the maintenance technician needs to have three things: knowledge, experience and a bright flashlight. Do not go near the appliance until its external infrastructure has been examined.
Step 1: Upon arrival at the jobsite, ask the customer for permission to enter the yard in order to examine the vent terminal. Note the configuration of the terminal. Does it meet the gas code and manufacturers’ specifications for clearance to grade/windows/doors/inside corners/air intakes/gas regulator vents? Check for blockages or customer installed screening. Ask the customer why the screen was necessary. Check any other accessory vent termination, such as from a gas fireplace or HRV. Vertical chimneys used with older draft hood equipped or 80 per cent AFUE appliances must be visually inspected for deterioration, missing wind caps or blockages.
Step 2: Interview the customer. Ask about unusual sounds, odours, filter maintenance, poor heat distribution, too much or too little humidity, or furnace failures. Listen carefully for clues to system performance problems. Get permission to do a room-by-room check looking for open floor registers and blocked return air grilles. Ask if the appliance installation instructions are available for reference, if necessary.
Step 3: Locate the thermostat. Depending on the existing thermostat, this would be an ideal time to offer the customer an upgraded thermostat. Get the old mercury bulb or battery operated control out of there – no more batteries to the landfill. Several manufacturers offer WiFi thermostats that communicate with a relay panel capable of operating just about any type of heating device. Most of these controllers have a test mode, a diagnostic screen with a history of events, a cycle rate screen showing burner or AC runtimes, and improved continuous fan control. Check the diagnostic log for a history of events if such a device is already installed. Ask the customer how any indicated failures were resolved.
Step 4: Move to the appliance location. On the way, inspect the horizontal venting (looking for sags, leaks, vent pipe running level, homeowner caused damage) and the gas piping. Typically, plastic vent pipe must have support every three or four feet and be continuously sloped toward the furnace at 0.25 in. per foot.
Step 5: The furnace room is where things get busy. Look at the number of appliances in the room. Determine where they are getting their combustion air. Many gas and oil-fired appliances continue to use indoor air for combustion. The gas code spells out specifically how much air is necessary, although some manufacturers’ instructions may be more “stringent” and must be followed in lieu of the code. Even though most sealed combustion appliances are approved to take air for combustion from within the building envelope, the tech must decide if there is enough air. Does the furnace room qualify as a “confined space” or not? Many homeowners have inadvertently put themselves at risk by enclosing the furnace room and restricting combustion air to the furnace or boiler and water heater.
Step 6: Check vent connections at the appliance(s). Inspect the vertical chimney and its vent connectors. Inspect condensate drain piping – it must be connected to an open/vented drain or condensate pump.
Step 7: Move to the appliance(s). With the visual safety checks mostly done, maintenance of performance is the next most important item. Maintenance means CLEAN: Start at the evaporator coil. It must be clean. After the coil inspection/cleaning, examine the heat exchanger for cracks or deterioration. Then, check the combustion chamber: burners must be clean, no rust, no dirt/lint in the cross-lighters. This is especially important for appliances taking indoor air for combustion near laundry rooms. When using outdoor air, check the burner air inlet screen for blockage. Replacing the flame rod does not necessarily put flame signal problems to rest. Ohm-out the hot surface igniter remembering it must be at room temperature for a proper reading.
Step 8: Check pressure switch tubing for cracks/moisture. Some furnaces allow vent condensate to run through the ventor assembly, other route condensate around ventor assembly. This tubing must be clean, also check for and repair any leaks. Are component wiring connections tight? Is there any sign of wire abrasion or discoloured insulation?
Step 9: Remove air filter, open the blower door and inspect the blower wheel. Remove the entire blower assembly if the wheel is dirty. Clean the blower wheel and the secondary heat exchanger. This is an ideal time to upgrade the homeowner to (at least) a MERV 11 air filter cabinet. Apart from the improved indoor air quality benefits, it is going to keep the important air handling components much cleaner. Low voltage wiring connections at the control board must be tight – look for signs of moisture in the blower compartment. Determine how it got there. Blow out the trap and drains and clean the condensate pump.
Step 10: To do performance testing start the unit and listen for unusual sounds. Then, check gas pressure by performing supply side static and working pressure tests. Do a manifold test (remember to check both stages on a two-stage model). Then, connect a dual input manometer to a sealed combustion furnace in order to verify pressure switch operation – if the start-up deep negative pressure is correct, then the venting system is clear. Then, check flame signal. After unit has run 10 minutes, do a temperature rise test. Check limit control operation by blocking off return air at the air filter.
Step 11: Accessories. Clean the humidifier components and check operation. If customer has complained about humidifier operation, a more detailed inspection will be needed. Perhaps a bypass humidifier is not the right one for this particular application.
Step 12: More Accessories. Remove and clean the HRV core. Clean the HRV filters and blow out the drain. Test operation.
Step 13: Remind the customer to replace batteries in smoke alarms and CO detectors. ‹‹
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