With the split system, the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspended from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity, so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms.
The most recognized standards for HVAC design are based on ASHRAE data. The most general of four volumes of the ASHRAE Handbook is Fundamentals; it includes heating and cooling calculations. Each volume of the ASHRAE Handbook is updated every four years. The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices; codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.
An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which have thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[17]
DIY: We don’t recommend a DIY approach. Depending on the system, working with gas, electricity and refrigerant create dangers. Beyond that, it is essential that split system components be selected for compatibility. DIY installation of an HVAC system will void the warranty of most brands. The manufacturers won’t stand behind the warranty when anyone other than a certified installer does the work. This is true since improper installation is the main cause of poor system performance and mechanical breakdowns.
Indoor Fan Motor -- Indoor fans circulate the air from your house and through the system. Age and dust buildup are the two biggest contributing factors to their failure. When they are starting to fail they will often make noise. Failure of the fan will result in no heating or cooling, and if it is not repaired soon, it can cause other components to fail.
Roof-mounted systems have the heating and cooling systems in one cabinet. Sometimes called "gas packs" (if the heater uses natural gas), they typically cost less than a comparable split system. In dry regions, most homes originally had "swamp-coolers" installed. When replacing them with HVAC systems, it's often cheaper to use existing mounts and ducting.
SEER is useful for comparing one model to another much in the same way that a car's calculate MPG is useful. It's not an accurate prediction of exactly how efficient the system is, but it can tell you which one is more efficient. Also, since SEER is based on a "cooling season", what region you live in will determine how long or short your cooling season is.
A little simple math can help determine the size system you need. A rule of thumb is 20 BTUs per square foot. So, a 500 square foot room would need 10,000 BTUs to cool or warm it efficiently. This assumes that you live in a temperate region and have adequate insulation with no energy loss. In the real world, all units have some degree of energy loss. This is reflected in an HVAC system's SEER rating for cooling and AFUE rating for heating.
Having the most energy-efficient system ever built won't matter much if it's not maintained. Lack of maintenance is the number one killer of HVAC systems. Before each cooling season, it's recommended that your system get a professional tune-up. However, there are things you can do in the meantime to make sure your system runs efficiently throughout the year.
Pro HVAC company Southern Comfort Mechanical says on its blog, “If there’s mold growth inside the handler due to excess moisture, algae in the condenser drain line or a dirty evaporator coil, it can negatively impact your AC unit’s efficiency. The filters inside may also build up excess dirt and become clogged, which will also make your AC [or heat pump] waste energy trying to sustain the cool climate inside your home.” These issues are easy to solve. They don’t require replacing the air handler.
If you’re anything like most of our readers, you’ve spent hours online researching HVAC information in preparation for replacing your old heater or air conditioner. I’m the same way; it’s a big investment! You may want to consider saving yourself some time and money by getting an HVAC-Facts Report from this online HVAC installation cost calculator.  Take a look:
In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.
Clean air delivery rate is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 100 cfm (cubic feet per minute) and an efficiency of 50% has a CADR of 50 cfm. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. Filter performance depends on the size of the particle or fiber, the filter packing density and depth and also the air flow rate.[30]
You can adjust for seasons: During the summer, you can have the air conditioner stay off during the cooler morning hours and start cooling the house as everyone gets up and starts moving around. During the winter, you can have your heater stay off while you are away at work and turn on about a half hour or so before you get home so that you are coming home to a nice, warm house.
An EER certifies the cooling efficiency of HVAC units. It's calculated by the rate of the cooling in British thermal units (Btus) per hour and divided by the rate of energy input in watts at a specific temperature. The calculation goes as BtuH/WATT at dry bulb (db) versus wet bulb (wb) temperatures. The optimal rating for a cooling unit is about 80db/67wb inside and 95db/75wb outside.
The belt should slip right into place. If it seems to be too tight or difficult to set in place, it may be necessary to adjust the motor mount to provide more slack. Then you can re-tighten the tension once the belt is in place. Check the manufacturer’s specifications for proper tension—in most cases, the belt should deflect about an inch when you press down on it.
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