10,516 posts, read 22,544,338 times I'm going to be replacing my 15 year old heat pump soon and I'm thinking about getting a larger one. My house is 1200 sqft and the current unit is 2.5 tons, which I think is typical. It heats fine during the winter, but during the summer it just doesn't cool very good. On a typical 98 degree summer day (I live on the gulf coast) it will be 81 degrees inside even though the thermostat is set at 78, and this is even with one bedroom closed off. From about June till Sept the a/c comes on around noon and doesn't shut off until the sun goes down. I put in solar screens last year and they helped only slightly. I have a big oak tree that shades the west end of the house in the evening, but it may need to be cut down soon which may make the house even hotter. So, I'm thinking of bumping up to a 3 ton. Anyone think a 3 ton would be oversized for 1200 sqft? I heard that if they're too big that they will be cycling on and off all the time which is not good.

8,923 posts, read 33,173,370 times 172 posts, read 342,863 times Air Handler mismatch with compressor I have a situation where the air handler is 5 ton and the compressor is 3.5 ton (both 2009 models) The HVAC guy says that this was done in order to meet the SEER requirements or something to that effect..... Does this make sense? Can the system be really more efficient under this scenario? Thanks for you input! Need a home inspection in Nevada? listing of Nevada certified home inspectors. Re: Air Handler mismatch with compressorThis is how you obtain a higher SEER rating. The air handler will be oversized to meet the SEER rating. And yes it will be more efficient. Why did you not believe the AC contractor? Originally Posted by rmurphy1 I smell smoke when you say ahu does that mean refrigerant coil or blower or both. Standard protocol worst case is to never mismatch more than 1/2 ton over or under between the compressor and the refrigerant coil The CFM of the blower is also calculated to match

As the Master HVAC Mechanic (retired) states - Protocols are such that the mismatch shouldn't be more than 1/2 ton... Why didn't I believe the HVAC contractor? Because I have known them to be wrong and the above stated protocols have been in our toolbox. small air conditioning and heating unitI haven't disagreed with the man, I am merely finding out if what he is saying is correct.ac unit runs but no cold air If the systems are so much more efficient this way - Why aren't all systems installed in such a manner?water from ac indoor unit I am NOT an HVAC professional. I am trying to improve my knowledge base here. Is it not right to call out the mismatch and refer it to a professional? Sure if you want to use engineering formulas like this one

The polynomial equation that shall be used to represent the tabular data is a third degree equation of ten coefficients in the form of: X = C1 +C2 � (S) + C3 � D +C4 � (S2 ) + C5 � (S�D) + C6 � (D2 ) + C7 � (S3 ) + C8 � (D�S2 ) +C9 � (S�D2 ) + C10 � (D3 C = Equation coefficient, represents compressor performance S = Suction dew point temperature, F [C] D = Discharge dew point temperature, F [C] Originally Posted by wsiegel Back in the late 70's and early 80's that's how Coleman was achieving their high SEER rating. They were selling them as a package deal. We installed a lot of 3 ton condensing units matched with 5 ton A coils plus a liquid line shut off solenoid valve and an indoor blower time delay relay in those days. I had one in my own house until 3 or 4 years ago. As I recall the SEER was 12.4 or so then. Of course you can't (shouldn't) go the other way and use a smaller A coil.

Originally Posted by sparksnmore We installed a lot of 3 ton condensing units matched with 5 ton A coils What was the sweat line on the coil I have a hard time believing that a 3 ton condensing unit can hold enough liquid in its condenser to prevent a 5 ton coil from being starved. I was taught in two different A/C schools that you never over size the A-coil by more than 1/2 ton. To be honest I have never seen a MFG increase the size of the indoor coil to achieve a higher Seer rating but I am not a mechanical Engineer either. My observation has always been to increase the size of the outdoor condenser on the high seer units. Carrier was very famous for this when seer rating became a issue. They increased the size of the outdoor condenser X3 over a standard 12 seer unit, and had this little compressor wrapped in a blanket could barely see it. BTW Trane also did the same thing monster condensing unit same size coilGetting a new A/C and looking at different air conditioners?

You already know that a higher SEER air conditioner is more efficient. But by how much? And is the difference worth it in the Phoenix area?In this article, we’ll show you how to estimate the energy savings between any 2 air conditioners with different SEER ratings (assuming all else is equal). And, for example purposes, we’ll be using 3-ton, 16-SEER and 14-SEER air conditioners because they are popular sizes and choices in the Phoenix area. Determine each air conditioner’s estimated annual energy use with this equation: [(Size of A/C system x 12,000) / SEER] x 2100 = amount of Watt-hours used annually To better understand what’s happening here, let’s breakdown each step of this equation: Size of A/C system x 12,000 The first part of the equation is calculating the amount of cooling your air conditioner provides. 1 ton of cooling = 12,000 BTUs. (There’s a lot of history here if you’re curious). This is the capacity of your A/C system, much the same way the horsepower of a car tells you the capacity of the engine.

Next, we need to calculate how efficiently your A/C system provides that capacity... Dividing the capacity by the air conditioner’s SEER gives you the approximate number of Watts the air conditioner uses per hour. You’ll now have the amount of energy your A/C uses per hour, which is similar to how the MPG of your car tells you how many miles you can go on one gallon of gas. Now we simply multiply by the number of hours you’ll use your A/C... According to Energy.gov’s calculator the average Phoenix-area home uses their air conditioner for about 2100 hours per year. = amount of Watt-hours used annually You’ll now have the estimated amount of energy (measured in Watt-hours) that the A/C will use in a year. So for our 3-ton example air conditioners, we get: [(3x12,000)/14]x2100=5,400,000 Watt-hours (rounded to nearest thousand) Now that we know approximately how much energy each of our air conditioners will use, we need to find the difference between them.

This is simple subtraction: Energy use of 14-SEER - Energy use of 16-SEER = Energy savings of higher unit In our example, the difference is 675,000 Watt-hours, annually. Now we simply need to calculate the actual amount of money this number equates to. Your electric company (either APS or SRP) charges you per kWh, or kilowatt-hour. To convert the Watt-hours to kWh, you divide by 1000. So our example is 675,000 Watts/hour / 1000 = 675 kWh. Now to get the estimated annual energy savings, you just multiply by the rate your utility company charges. The average electrical rate in the Phoenix area is around 12 cents per kWh. So a 3-ton, 16-SEER unit in Phoenix saves you about $81/year (675 x $0.12) in electricity costs over a 14-SEER unit. Well, it will depend on 2 things: So, if in our example the 16-SEER air conditioner was going to cost $900 more and you only planned on being in your home 5 more years, you likely won’t see the payoff ($81 x 5 years = $405).