Before we dive into the details of a residential HVAC system, there is one simple concept you must know:
Home comfort is about one thing: moving heat energy.
That’s it! When your home is being cooling during a hot and humid Houston summer, cold air isn’t blow inside from the air conditioner. Instead, heat energy is removed from your indoor air, and dissipated outside, thus cooling indoor air. And there’s more that goes on, which you can read about below. The numbers correspond to the system layout graphic above. Call us today at 713.474.5853 with any questions you have about home comfort.
1. Air Conditioner / Heat Pump
The outside unit of a split heating and air system is either an air conditioner or a heat pump. Sometimes you’ll hear us HVAC guys call it a compressor or a condenser. We’re referring to the same thing. So does the air conditioner/heat pump blow cold air inside your home? Actually, it doesn’t do that at all, but instead has one primary job: compressing refrigerant.
Refrigerant is a gas that when compressed, condenses down to a chilled liquid. R-22 is refrigerant used in older air conditioners that is now illegal for manufacturers to use due to environmental issues. R-410A is the new version, and some manufacturers like Carrier (and Bryant) have their own version of R-410A called Puron. It’s essentially the same stuff. So back to what an air conditioner does: An air conditioner compresses refrigerant which dissipates the heat energy in the gas into the outside air. This causes the gas to condense down to a chilled liquid. Once compressed, the ice cold refrigerant is then pumped inside the home through small copper tubing, to the indoor coil.
Air conditioner and heat pump cooling efficiency is measured with a Seasonal Energy Efficiency Ratio (SEER) rating. A heat pump’s heating efficiency is measured with a Heating Seasonal Performance Factor (HSPF) rating.
2. Gas Furnace
A gas furnace is typically run off natural gas, but they can also be powered by propane when outside city gas areas. Modern furnaces have made some significant advancements in the form of fully modulating flames (as opposed to just two-stage flames), condensing technology (which uses heat energy lost in older furnaces), and variable speed fan motors which offer not just better comfort and increased efficiency, but whisper quiet operation. No more turning the TV up when the heating and air kicks on.
For Houston, paying for a furnace with a fully modulating flame is a waste of money. However, a furnace with a decent efficiency and a variable speed fan motor is definitely the ticket. Remember, the furnace is used year round when the AC is running too. So that quiet, variable speed fan will be greatly enjoyed.
A gas furnace’s efficiency is measured with an Annual Fuel Utilization Efficiency (AFUE) percentage. This essentially shows the amount of fossil fuel that is actually converted into heat energy. So a furnace with an 80% AFUE is converting 80% of the natural gas used into actual heat energy for your home.
3. Evaporator Coil
Above we talked about an indoor coil. It’s where an air conditioner pumps refrigerant. The most common location for the indoor coil is the Evaporator Coil. That’s a geeky name that really only us contractors understand. All you need to know is that your indoor coil is key in overall cooling performance and efficiency. A dirty coil means higher utility bills. How do they get dirty? Mold and bacteria are two big culprits. You see, when warm air is pulled from the home during a hot Houston summer, it is forced through the indoor coil (which contains chilled refrigerant). The heat energy transfer that takes place causes water to condensate on the coil. Mold is all too happy to grow in this dark, damp environment. A UV lamp will nuke airborne and surface mold, keeping your coil nice and clean.
4. Whole House Air Cleaner
Even the cleanest Houston homes can suffer from indoor air pollution. Why? Because it’s not a clean issue. In fact, the more you clean with store bought cleaning products, the more polluted your air can become with VOCs released from many major brands of cleaners and detergents. Other airborne contaminants include allergens, mold spores, dander and viruses. A whole house air cleaner traps and destroys micro-sized contaminants as air is cycled in your home during air conditioning and/or heating.
5. Heat Recovery (HRV) & Energy Recovery (ERV) Ventilators
These bad boys are magic workers. When dealing with indoor air quality, UV lamps and whole house air cleaners do a great job. But what about stale air inside your home? When the windows and doors are shut tightly during our humid summer weather, indoor air can suffer. A ventilator exchanges fresh air from outside with stale air from inside. The magic part? It transfers heat energy and humidity (ERV model) during the process. That means the incoming, hot and humid air is dehumidified and cooled as it enters your home, and the heat and humidity is added to the stale air being pumped outside. It’s like opening a window for fresh air without a hit on your comfort or utility bill!
6. Whole House Humidification
Pictured in the image above is a fan powered, whole house humidifier. Whether we’re in the middle of a hot and humid summer, or a drier winter season, humidifiers and dehumidifiers can do a lot for indoor comfort. You see, humid air in the summer feels hotter than it really is. That means you run your AC more. That means higher electric bills. Likewise, dry air in the winter feels colder than it actually is. You get the idea. Maintaining proper humidity is not only more comfort, but it will save you money.
7. UV Lamps
Above when talking about evaporator coils, we mentioned the benefits of a UV lamp. UV lamps can be used in the indoor coil and in ducting to kill airborne and surface bacteria and mold. They’re excellent additions to any home comfort system, and part of our indoor air quality offerings.
20 years ago, thermostats didn’t do more than manually adjust the temperature. Eventually digital thermostats came along with sexy features like 7-day programming. Cool! But… SNORE. Modern stats (that’s short for thermostat) offer so much more than they used to. From smart phone access to voice control to auto learning to weather forecasts. Upgrading to the right thermostat typically pays for itself rapidly.
How It All Works Together
The Split System Air Conditioning Process:
- Refrigerant is compressed and chilled: Once the thermostat registers indoor air is too warm, the air conditioner (or heat pump) kicks on and compresses refrigerant. The chilled refrigerant is pumped inside to the indoor coil, typically called an evaporator coil. The efficiency of an air conditioner or heat pump (cooling mode) is measured with a Seasonal Energy Efficiency Ratio (SEER).
- Fan pulls air from the home: The furnace fan or fan coil (air handler) pulls air from the home through the return air duct. Yes, even in the cooling season, your furnace is used. As mentioned above, a variable speed fan offers quieter, more efficient operation.
- Air is filtered: Return air is filtered before entering the air conditioning system. Advanced air cleaners can filter microscopic particles and viruses out of the air keeping your home healthy and your system very clean which helps with efficiency and reliability.
- Air is cooled: The filtered air is then pushed through the indoor coil by the fan motor. The cold refrigerant in the evaporator coil absorbs heat energy from the warm air. This transfer causes moisture to condensate on the coil (hence the need for a UV lamp). The conditioned air is pushed on by the fan while the heated refrigerant is sent back outside to the air conditioner (or heat pump). The heated refrigerant is pressurized again to remove the heat energy.
- Mold is killed & coil efficiency kept high: In the damp interior of an evaporator coil, mold will grow which affects not only the health of your family (mold spores in the air), but the efficiency of your system. UV light kills airborne and surface mold keeping your system efficient and healthy.
- Cooled air sent back into the home: After leaving the evaporator coil, the cool, dehumidified air is pushed back into the home. In Houston’s high humidity climate, a separate whole house dehumidifier can be installed to further remove humidity from the conditioned air.
- Air is exchanged: If an HRV or ERV ventilator is installed, this is the last step. Ventilators are part of complete indoor air quality solutions. They exchange fresh outdoor air for stale indoor air. A ventilator is able to do this with minimal loss of energy, retaining the cooled and dehumidifed air your HVAC system worked hard to produce!
The Split System Heating Process:
- Heat exchanger is heated: A heat exchanger is a type of metal tubing that holds heat and combustion from the gas furnace flame. When the thermostat registers air in the home is tool cold, the flame ignites and begins heating up the heat exchanger.
- Fan pulls air from the home: The furnace fan motor pulls air from the home through the return air duct(s). A variable speed fan is quieter, more efficient and provides a more comfortable climate as opposed to single speed fan motors.
- Air is filtered: As with air conditioning, the return air is filtered before entering the system. Advanced air cleaners can filter microscopic particles and viruses from the air, keeping your home healthier and your HVAC system very clean, which helps with system life and efficiency.
- Air is heated: The air is then pushed through and around the hot heat exchanger tubing by the fan motor.
- Humidity is added back: A heat exchanger dries out winter air even more. A whole home humidifier replenishes needed moisture for a healthier home. Restored humidity also helps the air feel warmer, thus decreasing the energy needed during the winter to feel cozy and comfortable.
- Heated air sent back into the home: The fan forces the heated air back into the home via installed ductwork.
- Air is exchanged: At the top left of the above system layout sits a ventilator. Ventilators are part of complete indoor air quality solutions as they exchange fresh outdoor air for stale indoor air. A ventilator is able to do this with minimal loss of energy, retaining the warm, humidified air your system worked hard to produce!
- Heat Pump is engaged: When the thermostat registers the need for warm air, the heat pump turns on and begins extracting heat energy from the outside air. Even when it is cold outside, air contains a certain amount of heat energy. A heat pump absorbs this energy into the refrigerant, and then sends the heated refrigerant back inside.
- Fan pulls air from the home: The fan motor in your fan coil (air handler) pulls air from the home through the return air duct(s).
- The air is filtered: As with a furnace based system, an advanced air cleaner filters out microscopic dust, mold and organisms.
- *Coil difference: When using a furnace and an air conditioner, the indoor coil is separate, and housed in what’s called an evaporator coil. When using a heat pump only, the indoor coil is contained in a fan coil. A fan coil is basically a combination of the furnace fan motor and the coil from the evaporator coil.
- Air is heated: The air is then pushed through the coil system by the fan motor. The heated refrigerant adds heat energy to the passing air.
- Mold is killed & coil efficiency kept high: In the damp interior of an evaporator coil and/or a fan coil, mold will grow which affects not only the health of your family (mold spores in the air), but the efficiency of your system. In the example layout above, a UV lamp is mounted within the coils to prevent this. UV lights kill airborne and surface mold.
- Heated air sent back into the home: After leaving the indoor coil, warm air is pushed back into the home. In dry winter climates, a separate whole house humidifier can be installed to replenish the humidity in indoor air.
- Air is exchanged: At the top left of the above system layout sits a ventilator. Ventilators are part of complete indoor air quality solutions. They exchange fresh outdoor air for stale indoor air. A ventilator is able to do this with minimal loss of energy, retaining the cooled and dehumidifed air your system worked hard to produce!
Hybrid Heating System:
- A hybrid system uses both a furnace and a heat pump. Heat pumps can be more efficient than a gas furnace at certain temperatures in areas where fuel prices are high. Heat pumps cannot provide adequate heat however in extreme cold, and their efficiency drops substantially at that point. For Houston winter climates, a heat pump is definitely a viable option.
- A smart thermostat is used to control a hybrid heating setup. It intelligently switches between units for the highest energy efficiency available depending on the outside temperature.