Air Conditioner Capacity Is Measured in Tons — Know the Reason? Why is air conditioner capacity measured in tons? You may have wondered this, especially since you know your 4-ton capacity air conditioner doesn’t actually weigh 4 tons. Here’s what that 4 ton designation really means and why air conditioner capacity is measured this way. We know that the air conditioner’s number of tons doesn’t refer to its weight. In fact, this number refers to the amount of heat the air conditioner can remove from a house within one hour. For example, a 4-ton air conditioner is able to remove 48,000 British thermal units (or BTUs) from the house per hour. One BTU is roughly equivalent to the heat that would be produced if you lit one match and burnt it all the way. One ton of A/C capacity is equivalent to 12,000 BTU per hour. Now we know what a ton means, but we still haven’t answered the question of why the ton is the unit of measure for air conditioner capacity. Before the invention of the air conditioner, people who could afford it used large blocks of ice to cool their homes in the summer and refrigerate food.

The ice was harvested during the winter from frozen lakes and rivers.york ac & heating unit But how did the use of ice to cool buildings lead to the term “ton”? carrier ac units sizesBasically, it takes 143 BTUs to melt a one-pound block of ice at 32 degrees. outdoor ac unit not coolingAccordingly, if you have a one-ton (2000 pound) block of ice, it takes 286,000 BTUs to melt it completely. If that block of ice melts evenly over the course of the day, it absorbs heat at the rate of 11,917 BTU/hour. Rounded up, we get 12,000 BTU/hour, or one ton of AC capacity. Today most people know that a ton is used to measure A/C capacity, but not everyone knows that the term originally referred to blocks of ice! For more information on air conditioner capacity or any other home comfort issues, contact the pros at Climactic Conditioning Co., Inc.

We’re proud to serve homeowners in and around Sarasota, Bradenton and Lakewood Ranch. We provide useful tips and information for homeowners, facility managers and contractors looking to improve their current HVAC system. Since the minimum efficiency regulation changed to 13 SEER in January 2006, most OEM systems now incorporate a thermostatic expansion valve (TXV) style metering device as the standard for air conditioning systems. It is now extremely important for the HVAC technician to understand the design and operation of this type of valve. The thermostatic expansion valve (TXV) is a precision device, which is designed to regulate the rate at which liquid refrigerant flows into the evaporator. This controlled flow is necessary to maximize the efficiency of the evaporator while preventing excess liquid refrigerant from returning to the compressor (floodback). One of the design features of the TXV is to separate the high pressure and low pressure sides of an air conditioning system.

Liquid refrigerant enters the valve under high pressure via the system’s liquid line, but its pressure is reduced when the TXV limits the amount of this liquid refrigerant entering the evaporator. The TXV – What It Does Do The thermostatic expansion valve controls one thing only:  the rate of flow of liquid refrigerant into the evaporator. Contrary to what you may have heard, the TXV is designed to control: Trying to use the TXV to control any of these system variables will lead to poor system performance – and possible compressor failure. How the TXV Controls the System As the thermostatic expansion valve regulates the rate at which liquid refrigerant flows into the evaporator, it maintains a proper supply of refrigerant by matching this flow rate against how quickly the refrigerant evaporates (boils off) in the evaporator coil. To do this, the TXV responds to two variables: the temperature of the refrigerant vapor as it leaves the evaporator (P1) and the pressure in the evaporator itself (P2).

It does this by using a movable valve pin against the spring pressure (P3) to precisely control the flow of liquid refrigerant into the evaporator (P4): TXV Pressure Balance Equation P1 = Bulb Pressure (Opening Force) P2 = Evaporator Pressure (Closing Force) P3 = Superheat Spring Pressure (Closing Force) P4 = Liquid Pressure (Opening Force) Energy Transfer in the TXV Here is a closer view of the TXV in operation. The flow of the liquid refrigerant is restricted by the valve pin. As the flow is restricted, several things happen: The pressure on the liquid refrigerant drops A small amount of the liquid refrigerant is converted to gas, in response to the drop in pressure This “flash gas” represents a high degree of energy transfer, as the sensible heat of the refrigerant is converted to latent heat The low pressure liquid and vapor combination moves into the evaporator, where the rest of the liquid refrigerant “boils off” into its gaseous state as it absorbs heat from its surroundings.

The pressure drop that occurs in the thermostatic expansion valve is critical to the operation of the refrigeration system. As it moves through the evaporator, the low pressure liquid and gas combination continues to vaporize, absorbing heat from the system load. In order for the system to operate properly, the TXV must precisely control the flow of liquid refrigerant, in response to system conditions. 1,531 posts, read 2,369,379 times I will be purchasing a new AC and furnace to take advantage of rebates. But I don't know the difference between 4 and 5 ton. I live in Texas and it gets hot for three months out of the year but I will also have sprayed insulation in the attic with the possibility of radiant barrier also installed depending on the price of the barrier. Thxs in advance for your input. 26,349 posts, read 68,900,480 times 635 posts, read 2,279,224 times Originally Posted by eyewrist Not to belabor the point, but did someone spec the 4 ton based on an actual cooling load/heat loss calculation?

I really do see some old timers say things like, "well, you have 2200sqft and all my years tell me you need 4 ton", but don't take into account the new tech, insulation, etc. I'd get a couple/three calculations done and hopefully they'll all be close. If not, I'd ask questions why. I'd also suggest doing some individual research into pricing and rebates for higher SEER units. When we installed our 15ish SEER unit a couple years back, it was not significantly more expensive than the 13 SEER option. Any pro worth their salt will be happy to do heat loss/cooling load calc for free or a small fee as part of the estimating process. If they refuse, I'd think about sending them on their way. While the SEER 16 may be more expensive than a SEER 14 for example, depending on you electricity rates, the breakeven point might not be that long. In Huntsville, our electricity is cheap, like $0.09/kwhr. Back where I lived in Los Angeles it was between $0.15 and $0.25 so a high SEER AC would be a good idea in LA.