HVAC systems are mechanical systems, which run more frequently than any other appliance in your home. It is probably on more than the vehicle that you drive – which is to say, a lot if you live in Northern Virginia. These long run times can take a toll on your system, even in the best environments, resulting in the largest consumption of your monthly utility expenses. Making sure your HVAC systems are well maintained is paramount for extending the life of the equipment and making every utility dollar count. The main systems we see in our area are heat pumps and gas furnaces, paired with an air conditioner. Below, I will break down the necessary items to be monitored.
The Importance of Maintaining your HVAC System
Gas furnaces paired with air conditioners are very popular and provide great comfort when configured properly. A gas furnace generally has an efficiency rating of 80%-98% (AFUE) and many factors go into making sure we are getting every bit of efficiency out of the equipment. A gas furnace operates by igniting the gas and allowing the bi-products of combustion pass through the inside of metal plates and coils called heat exchangers, while simultaneously passing the cooler air from your home, on the outside of the heat exchanger and distributing the transferred heat to the home or business. These heat exchangers play a vital role in the efficiency and safety of the system.
What’s the heat exchanger? The heat exchanger isolates the flue gasses, which can contain poisonous harmful by-products of combustion from the air distributed to the home. Routine inspection of these plates and coils is highly recommended, because, a crack in the heat exchanger could result in a dangerous environment and most importantly, CO poisoning which is odorless, colorless and tasteless. To protect these heat exchangers, KCS will not only inspect the system, but we will also make required adjustments to ensure they are performing as the manufacturer intended.
To create clean combustion, we need the appropriate amount of air and fuel mixture to provide a clean flame. If our gas pressure is too high, we run the risk of our flame being too big, and impinging the flame, or not enough oxygen to mix with the gas, causing incomplete combustion, both resulting in higher levels of CO creating an unsafe environment and reducing the life of the appliance.
Low Gas Pressure and Its Effect on HVAC Maintenance
Low gas pressure can also affect the efficiency of your equipment, and even worse, not provide adequate heating to the dwelling in extreme temperatures. Another major factor in maximizing your system’s capabilities is proper air flow. With technology making huge strides in the last 15-20 years, our blower motors have become more complex and allow us to dial in furnaces very precisely. Every system has a sweet spot, or range in temperature where it wants to run, and airflow is a major factor in finding this sweet spot. Not enough air flow results in systems running too hot, increasing the likelihood of a crack or failure of the heat exchanger. Running too cool can actually cause flue gasses to condense in the chimney on lower efficiency furnaces, rust spots on the plates or clogging the passages in the plates, resulting in improper and sometimes unsafe operation.
HVAC Blowers and What They Do
There are many different blowers that are installed in these systems, some require simple oiling and component tests to maintain. These are called PSC motors and are very common in basic systems. They turn on and off on demand and require a static pressure test to help select the correct airflow for each system. The next motor we typically see is a very efficient ECM motor or boost motor. It actually can be more efficient to run all day than a 100 watt light bulb. It uses A/C voltage and converts to a specific kind of DC voltage to provide maximum RPMs while consuming very little Amp draw. These fans are very specific and require a static pressure test and must be adjusted in a gas furnace, to provide proper flow across the heat exchanger. Our final fan is a variable speed fan, which is much like an ECM motor but requires an adjustment in the logic of the control board to make the adjustments. They have the ability to self-monitor and speed up or slow down with any adjustment made to the system i.e. filter getting dirty, damper adjustments.
Although every system is different, it is important to check each one regularly to make sure they are adjusted correctly, to optimize efficiency and extend the life of the system. Gas furnaces also have a myriad of controls and sequences that are required to be monitored and tested for proper operation. Most modern furnaces have an induced draft motor that assists in providing proper combustion air to the furnace, to provide the required oxygen to fuel ratio, resulting in complete combustion. When this fan turns on, a special set of hoses and a switch, called a pressure switch, need to be free and clear of contaminants to allow for the furnace to fire.
The motor switch and hoses must be cleaned and cleared regularly, or eventually, they can become obstructed and prevent the furnace from firing. Other safeties in the system must be monitored for proper operation. One is a high limit switch that will turn the gas valve off, causing the burners to shut down if the system overheats. This switch is to protect your system in extreme temperatures and frequent trips of the high limit mean that the heat exchanger is regularly operating in extreme temperatures and can shorten the life of the system.
We also monitor safeties called flame roll out switches. These switches must operate correctly because they are in charge of shutting down the gas flow if the flames from the burners come out the front of the system. They are extremely important to the safe operation of the system. A furnace can be deceiving because for the most part it will cycle on and off without any issue and probably keep the space it services warm however making sure that it is working to optimum performance is another story and various tests and adjustments need to be made in order to allow for safe and efficient operation for the long term.
Air Conditioner Maintenance
Air Conditioners in most cases are paired with a gas furnace and work in conjunction with an outdoor condenser and evaporator coil inside. The job of and any air conditioning system is very simple, absorb heat from somewhere that is objectionable and reject it to a place that is less objectionable. This is accomplished by passing the refrigerant from one coil to another and rapidly changing the state of the refrigerant from liquid to gas. Four major components are involved in this process the compressor the evaporator coil the condenser coil and the TXV or thermal expansion valve (or another metering device). We also use two major motors in this situation to pass air across each coil to change the state or refrigerant. To properly condition a dwelling all of these components need to be operating in harmony and functioning properly when one is lagging it is a domino effect and can cause unnecessary strain on other major components. The heart of your system as most know is the compressor and its responsibility is not only to move the refrigerant through the system it is to change the state of the refrigerant in its vapor state. The state of the refrigerant when entering and exiting the compressor is imperative to proper operation. During maintenance we routinely monitor the pressure and temperature of the gas that is entering the compressor, this is important because compressors cannot compress a liquid and if they try to we run the risk of washing the lubricant from the moving parts inside the compressor and causing it to seize and fail. On the outlet of the compressor we are feeding our outdoor coil called the condenser, this is where we utilize the fan on the outdoor unit to cool our refrigerant and turn it into a liquid. Clean coils and proper fan operation are required to accomplish this. If our outdoor coil is dirty we lose capacity and ability to effectively cool a space, especially in extreme weather. Systems do a poor job at keeping designed indoor temperatures when the proper amount of heat is not rejected in very hot weather. This is the same for the air passing through the unit, a condenser fan motor is designed to draw the proper amount of air through the coil to cool the refrigerant into a liquid and send it inside. There are many different kinds of condenser fan motors PSC motors come on and require a capacitor to assist in shifting phase on startup and increasing the efficiency of the motor. ECM motors are also used on high-efficiency equipment to reduce energy consumption and vary depending on how hard the system is operating. Either fan needs to be monitored and serviced regularly because improper operation can affect the refrigerant pressures in the system, in turn, causing unnecessary wear and tear on the heart of the system the compressor. The next major component that is monitored for operation is the metering device which is referred to commonly as the thermal expansion valve (TXV), or orifice. These devices are provided with liquid refrigerant coming from the condenser. They act as a nozzle that sprays the refrigerant into the evaporator or indoor coil. Making sure we are providing only liquid to the thermal expansion valve or orifice allows us to maximize the amount of heat our evaporator coil can absorb. If the device is clogged or not allowing the refrigerant to flow correctly we can detect that easily and address the problem as necessary. The evaporator coil is inside the dwelling and intended to absorb unwanted heat. This is the component that generally causes the most problems in the warmer months. It receives warm air from the house absorbs the heat from that air allowing the liquid refrigerant inside the coil to boil off and return to the compressor. If this coil becomes dirty many problems can occur. The most prevalent is freezing of the indoor coil which after a few hours of operation can cause the system to stop cooling entirely. When this happens the indoor unit becomes a big block of ice and when it melts not only can it make a mess it can also get water on important components in the furnace it is attached to causing costly repairs. During an inspection, the coil in inspected for proper operation and problems are addressed. The last major component that must be checked is the indoor blower. It serves the same purpose as the outdoor fan and it is important that we feed the evaporator the required air that is designed for the cooling load. If we are not passing the proper amount of air the system will have problems keeping up. Playing close attention to all of these variables to better maintain and increase the performance of a home.
Heat Pumps – What They Are
Heat pumps are a type of system that has the ability to reverse the refrigerant cycle and discharge heat inside or outside. In the cooling mode, the heat pump works exactly like a conventional air conditioner and details of operation are the same. The heating mode, however, is very interesting and uses a reverse flow of refrigerant to absorb heat from the outside air and bring it into the home. In this process, we reject heat from the high-pressure side of the compressor into your home. Although temperatures outside feel cool to us, to the refrigerant, it is rather warm. We are able to convert this energy through compression, to raise the temperature of the gas and put it into the dwelling.
This rather simple process does add to the complication of controls because the lower pressure refrigerant is now in the outdoor unit. This can cause freezing of the outdoor coils. This freezing requires a cycle to happen intermittently called the defrost cycle. Three major things happen during this cycle: the reversing valve shifts, putting the refrigeration circuit into the cooling mode. This allows the hot gas to circulate through the outdoor coil, melting any ice buildup from normal operation. The outdoor fan shuts off because it is not needed to cool the refrigerant in the outdoor coil. During this process, the system is actually in the air conditioning mode, so we need to make sure we are not blowing cold air into the conditioned space. To temper the air being distributed, we have to engage the auxiliary heating system built into the system. This is generally a set of electric heat strips in a conventional setup. The defrost cycle time varies on outdoor conditions and making sure we have the shortest defrost cycles possible is very important in reducing energy expenses. In general, running backup electric heaters (emergency heat) can be 3-4 times more costly than operating the heat pump alone. Proper refrigerant charge and clean coils can greatly reduce the time it takes to properly defrost a coil. In any heat pump application, it is our goal to reduce the usage of back up auxiliary heating. This is typically an inefficiency, and monitoring proper refrigerant levels is key to making sure we are producing the maximum number of BTUs in colder conditions. Another key factor is air flow, especially to the indoor coil. If air is not moving at a proper rate, it can cause pressures to be too high and the system could go off on a safety, called high pressure. Unfortunately, the owner or occupant of the building usually is unaware, and the auxiliary heaters engage without anyone’s knowledge, causing electrical consumption to skyrocket. This is generally noticed only when a utility bill is received and the cost of heating has doubled, if not tripled. Keeping a clean heat pump is extremely important and making sure all of the systems are working in the desired sequence is imperative for longevity and efficient operation.