Portable ACs are the perfect portable cooling solution for areas where installing standard air conditioning systems may be cost-prohibitive, impractical, or impossible. This is especially true in settings such as apartment buildings or server rooms located within an interior of a building. Moreover, portable air conditioners are compact, easy to maneuver, do not require permanent installation, and because they're most often used to cool specific areas as opposed to entire homes or buildings, they are quite energy-efficient as well. With regards to design, portable air conditioners are simple cooling devices. The box-like housing of the unit holds the cold and hot sides of the air conditioner in one while an exhaust hose expels heat. Water is condensed out of the air which is then collected in an internal drain bucket or through a drain hose. Furthermore, some portable ACs even utilize advanced evaporative technology and thus produce very little or no water at all. In addition to the above benefits, portable air conditioners are also multi-functional and offer more than just cooling.

The refrigeration cycle utilized by these portable coolers dehumidify moisture from the air, and some units even come with built-in heaters and air purifiers. when should i replace my ac unitNonetheless, when it comes to choosing a portable AC , one of the most common mistakes consumers make is incorrectly sizing their unit. how much does a new ac unit cost 2014Portable air conditioners are sized according to BTUs, which stands for British Thermal Units. sale on window ac unitsA BTU is a unit of energy that is commonly used in the power, steam generation, and heating and air conditioning industries. Generally speaking, a portable air conditioner's BTU rating describes its power and cooling capacity. Naturally, the higher the BTUs, the stronger the portable AC. Portable air conditioners have cooling capacities that usually range from 5,000 BTUs to as high as 30,000 BTUs, and the size needed to cool a room will depend on the area being cooled. 

Thus, an incorrectly sized portable AC with insufficient or excess BTUs will result in inefficient cooling. After these have been verified, it is then time to determine your BTU requirements. Simply look to the chart below: Portable Air Conditioner Sizing ChartSquare FootageRequired BTUs Recommended Air Conditioner100 - 200 7,000 - 8,000 American Comfort ACW200C150 - 250 8,000 - 10,000 NewAir AC-10100H250 - 350 10,000 - 11,000 NewAir AC-12100E350 - 525 12,000 -16,000 Soleus LX-14020' x 20' = 400 square feet  400 square feet = at least 12,000 BTUs As such, if your room measures 400 square feet, you will need a portable air conditioner that offers 12,000 BTUs of cooling. However, please note that the figures in the chart above are estimates based on average room conditions in a moderate climate. Some exceptions may also apply, and these are listed below: For second story homes or especially sunny areas, add the BTU amount by 10% For shaded areas, reduce the BTUs by 10% For each additional person over two persons in a room, add 600 BTUsTo cool a kitchen, add 4,000 BTUs

A question I pose to the attendees of each mini split class I conduct is: Can you oversize an inverter ductless mini split system? Before you start writing your reply to what I’m sure you think is an obvious answer, let me save you the effort — yes — the answer is yes, of course you can! Gerry Wagner’s testing lab for Comfort-Aire mini split products.   Now, with that out of the way, let me address why I pose the question at all if it’s so obvious. We need to start with the anatomy of an inverter system. An inverter compressor can run at 3,600 RPM like every other compressor in HVACR equipment, but the difference is that it doesn’t have to. Let me digress a moment… I'm a “wet-head” by birth. Being from the New Jersey and New York area, hydronics is the first HVACR subject you learn about, and then air comes later. When I started in the boiler biz back in the 1970s, we made a lot of different boilers: 50,000 Btuh, 75,000 Btuh, 100,000 Btuh, 125,000 Btuh, 150,000 Btuh, and on and on.

Today boiler companies, for the most part, make one boiler, a modulating boiler that can down fire to as low as 50,000 Btuh and modulate up all the way to 150,000 Btuh. If you install this boiler in a home with a heat loss of 100,000 Btuh it doesn't short-cycle because it will never produce anything over 100,000 Btuh. Because it measures indoor and outdoor ambient air temperature and fires the boiler accordingly. Now you can take that old, oversized non-modulating 150,000 Btuh boiler, in a home with a heat loss of 75,000 Btuh, and stop it from short cycling by adding indoor/outdoor reset to the control system. Instead of heating the water up to 180°F even when the outdoor temp is 50°F and you just need to take the chill off, the control will fire the boiler only up to the temperature required to meet the heat loss of the home based on the outdoor air temperature. There would be some mechanical changes required, specifically a bypass from the boiler supply to the return to make sure a minimum return temp came back to the boiler to prevent thermal shock.

New condensing boilers don't require a bypass as the lower the return temperature the more efficient they run. So why am I giving you the Hydronics 101 lesson? Well, because the same principle applies to an inverter compressor. Wagner conducts a course sponsored by Comfort-Aire and Heat Controller Inc.   The inverter compressor does not start at 3,600 RPM and then ramp down as the system finds the set point programmed by the homeowner. It starts at the lowest RPM and ramps up. If the actual room temp and the setpoint are only a few degrees apart, then the compressor will never come anywhere near full capacity. Like the modulating boiler, the inverter system senses both indoor and outdoor temperatures and applies power to the compressor accordingly, (the compressor is the burner, if you will).   The test lab I can prove it very easily. My test lab here in New York is a 10-ft. x 20-ft. prefabricated garage where Itest mini split products on a consistent basis with multi zone and single zone inverter systems, both cooling and heating.

. . This building contains radiant floor heating, (slab on the first floor, joists on the second), with a Pulse condensing boiler and a small duct high velocity air conditioning throughout. [Wagner’s home is also heated via radiant flooring, a thermal solar system for domestic hot water, and an oil fired boiler is used as the heat source, plus, small duct high velocity for air conditioning.] A recent equipment test had me install a single 12,000 Btuh inverter ductless system in the lab. Rather than short cycle as you would expect, what happens is the system rarely shuts off. The compressor will initially, (over a three minute period, if needed), ramp up to full capacity and get the room to the programmed set point and then you will see the compressor ramp down to a minimum running RPM. If the fan is on auto, it will do the same. The compressor may shut down completely and the controls programmed into the equipment will keep the compressor off for a minimum of three minutes and then it takes another three minutes for the compressor to come back up to full capacity.

A minimum cycle (if it existed) could be no shorter than three minutes. Inside the lab two 9K evaporators are tested. You can further increase the run cycles by placing the evaporator fan in the manual mode and operating it at the lowest speed. What always has to be considered when dealing with inverter ductless mini splits is the range of operation that the system will provide. Unlike a conventional system that only knows two performance points, on and off, the inverter offers a range of performance. A 9,000 Btuh inverter evaporator will give you an operating performance range of approximately 2,000 Btuh to 11,000 Btuh of cooling. A 12,000 Btuh inverter evaporator will give you an operating performance range of approximately 3,000 Btuh to 13,000 Btuh of cooling. An 18,000 Btuh inverter evaporator will give you an operating performance range of approximately 7,000 Btuh to 23,000 Btuh of cooling. Two ways to oversize Let’s look at an example. If you install a 9,000 Btuh inverter evaporator in a room that has a heat gain of 5,000 Btuh, will it ever produce 9,000 Btuh?

It will ramp up to 5,000 Btuh and satisfy the set point programmed by the homeowner and then maintain that set point thereafter. So, with this in mind, back to my original question: can you oversize an inverter ductless mini split system? Well, I believe there are two ways to oversize utilizing an inverter mini split. The first is the obvious capacity oversize. Let’s use the same example of a room with a 5,000 Btuh heat gain. If you install an 18,000 Btuh inverter evaporator in that room, are you oversized? The low end of the performance range of an 18,000 Btuh inverter evaporator is 7,000 Btuh — more than the total heat gain of the room. Where I see installers make a less obvious mistake in sizing inverter mini splits is with this scenario.  Again, the room with the 5,000 Btuh heat gain, but now we have an installer who decides to install a 12,000 Btuh evaporator in the room saying to himself, “It’s an inverter, it won’t ever go up to 12,000 Btuh because the room only needs 5,000 Btuh … so what’s the harm?”