Since 1979 TACL A537C Doctor COOL & P rofessor HEA T The Team For All Seasons TM A Glossary of HVAC Terms: Confused by the many terms and acronyms surrounding your indoor comfort system? Don t be! This handy glossary of terms will tell you what you need to know when discussing your HVAC system with a professional contractor. HVAC: Heating, Ventilating, Air Conditioning Ton of air conditioning: This is not how much the box weighs. A ton of A/C is defined as 12,000 btuh (see BTU). Example: 3 ton = 36,000 btuh, 4 ton = 48,000 btuh. This is a nominal number ie: 34,800 would be referred to as 3 ton 46,640 would be 4 ton etc. In residential A/C the max tonnage is 5 ton or 60,000 btuh, anything larger is considered commercial. By the way the term: ton of A/C did originate from tons of ice piled in front of a fan in an effort to cool the air. Similar to what was done to comfort U.S. President Mc Kinley as he lay dying from an assassin s bullet. BTU: British Thermal Unit, the measurement of heating and air conditioning capacity. A BTU is the amount of heat that must be added to one pound of water to raise its temperature one degree Fahrenheit. Usually referred to as btuh, btu per hour. Did you know? The first air cooling system was in medieval times. Picture this: A still and hot day. A large hanging sheet of loose woven burlap type material that has cool stream water running down it. Nearby is a large air bellows powered by manual labor. As the air is pushed thru the material it is cooled. On the cold side the air is channeled into a stone block chamber (a duct) where it takes a 90 degree turn upward. As the air goes up some of the moisture gathers on the vertical stone blocks and runs down. The air then makes another 90 degree turn where it flows into the sleeping chambers of a very influential man of the times.
What very influential man of the time did the sleeping chamber belong to? Who designed this first cooling system? Keep reading, the answers are within the yellow folder. Efficiency Ratings: Just like cars AC efficiencies and capacities decrease from when new as they are used. Approximately 2 to 3% loss per year. Gas Furnaces: are rated by percent of heat produced that goes into the home. Eighty percent furnace means twenty percent of heat goes in to the atmosphere with the products of combustion (up the stack.) Electric Heat: is rated @ 100% efficient. No vent. But it is still more costly than gas heat. Air Conditioners: (2 methods of rating efficiency) Method #1 EER: The original method of calculating efficiency. The steady state of energy removal (cooling capacity) by the equipment in btuh divided by the steadystate energy input to the equipment in watts. To simplify 13 EER = 13 pieces of heat (btu) removed for each watt of electricity you pay for. To calculate eer: BTU s out divided by power (watts) in. FYI: Some manufacturers believe that EER is a more accurate measurement of efficiency than the new method SEER is. The Fed has now tied EER s to SEER s to qualify for their current (expires in Dec. 2010) tax credit. Method #2 SEER: 13 SEER this is the new minimum efficiency standard (effective January 2006) for an air conditioner or heat pump. All new units must now meet this standard. Previously manufactured equipment may be used, sold and installed. A note to you: Doctor Cool & Professor Heat thinks basing your buying / purchasing / investment decision on SEER vs. dollars can be a costly mistake especially in the humid gulf coast. SEER / EER numbers can be tweaked upward by simply using a 5 ton coil on a 4 ton system. This match up will be more efficient at removing temperature but less efficient at removing moisture. Moisture removal is not a part of the SEER / EER calculation but is critically important to comfort and air quality in your home.
Heat Pump: Uses the same air conditioning equipment that removes heat from your home in the summer to provide heat inside in the winter. It is surprisingly more efficient than gas heat or electric heat. Heat pumps however are more complicated and require a higher level of expertise to install and service. Look for NATE certified technicians. Heat pump efficiencies are rated in COP. (COP): Coefficient of Performance Used to compare efficiencies of Heat Pump brands. Similar to SEER/EER comparing AC s. COP is a good number when your trying to get a comparison of cost and efficiency of a heat pump compared to electric heating. COP ratings usually range from 2.5 to 3.5 +. This means a 3.25 cop heat pump will provide 3.25 times the heat as compared to electric heat for the same electricity (energy) paid for. The higher the cop the more efficient. Calculating AC system actual output in tons AC. Performance Test Sensible formula: cfmx delta t or (temp difference) x 1.08 = sensible btu s di vided by 8,400 = Tons sensible output. Total formula: cfm x delta h (or enthalpy difference) x4.5 = total btu s divided by 12,000 = total tons output. Note: Both capacity formulas require cfm. If you don t measure your just guessing. CFM: (cubic foot per minute): a cubic foot is a box of air 1 +1 +1 (about the size of a square basketball). A 3 ton AC needs to circulate 1,200 cubic foot per minute, a 4 ton 1,600 cubic foot per minute, 5 ton 2,000 cfm through the duct system / house to produce 3, 4, or 5 tons respectively or 400 cfm per ton. How do you measure cfm? Use an air flow hood is best. There are other more complicated but less reliable methods to determine cfm. Note both capacity formulas require cfm.. Delta t: temperature difference through the AC duct system. Minimum is 15 degrees maximum is 20 degrees: Take the entering temperature at the filter grill ie: 77 degrees, and also the leaving temperature at the cold air supply grill ie: 58 degrees and that equals a 19 degree delta t.
1) Example: the air flow hood measures a total cfm of 1120 cfm x 19 degree delta t x 1.08 constant = 22,982 then divide by 8,400 = 2.73 ton output. Within 10% of 3 ton is acceptable. 2) Example of low air flow: 815 cfm x 19 degree x 1.08 = 16,724 divided by 8,400 = 1.99 ton. A full ton short. FYI: Air flow (CFM) is just as important to performance as the temperature drop but is never measured! Air flow hood aka Air balance or air capture hood: Held up to each supply grill it will do many calculations and then average them to produce a digital readout of actual cfm s. If you don t measure your just guessing. FYI: The USDOE says typical duct systems lose 25 to 40% of the energy consumed by the air conditioner. Some types of systems such as attic ducts in hot humid climates lose more. Do you agree that measuring air flow is the key to delivering an AC system that is performing at full capacity? Freon: the chemical medium used to move heat from one place (the home) to another (outside). An air conditioner doesn t provide, or make, cold air it removes heat from the air, thereby cooling it. The heat from your home is absorbed by the freon and brought through the pipes where it is discharged to outdoor air. Feel the heat coming off your outdoor section. Old: R 22 known as Freon 22 New: R 410 known as Freon 410 Influential man------ Pope Julius II The designer: Michelangelo Filtration: Hundreds of choices. At first, filters were meant to protect the equipment from large dirt particles (bug stoppers). Now they are used to clean the air in your home. Very important! Most homes have undersized filters. The minimum filter area should be 200 sq in per ton. 3 ton = 600 sq in minimum. 5 ton = 1,000 sq in minimum.
This is total filter area ie: a 3 ton AC with @ 20x25 filter = 500 sq in is undersized. If you add a second grill 20x14 = 280 sq in for total 780 it would be more than 600 sq in minimum. Good. Filter ratings: MERV (minimum efficiency reporting value) is the accepted industry standard for filters. The higher the MERV isn t necessarily better, as it can restrict air flow and make your ac system work harder. Ask your AC pro for the right filter for your system. Some filters do not list their MERV rating on their product. Hmmmmmmm Duct: The large pipes in the attic that circulate the air throughout your home. There are two types of residential duct. Hard or metal pipe. The original type material insulated on the inside or out side. Flexible duct: Currently in use on 95% + of homes. Cheaper material cost and labor cost and if designed properly and then performance measured, flex duct systems are the equal or better of the two. FYI: The USDOE states that typical duct systems in the US lose 25 to 40% of the energy being used by A/C and heat. If you look at the data tag info on most heaters you will see a line. Max external static pressure:.5. This is like your blood circulating pressure..5 or lower would be like 120/60 blood pressure, Good! Higher ESP s like.8 would be like a blood pressure of 210 over 140, Bad! Most ESP s on furnaces in the field exceed.5,.8 is the average. When you go to the doctor he always checks your blood pressure, its very important. At Doctor Cool we check your AC s pressure also, then we can prescribe a cure. Higher static pressure means low air flow through the duct system. Very low static pressures usually mean duct leakage. Load Calculation: the method used to calculate the correct tonnage to keep your home at design conditions. Design conditions for the Houston Galveston area: The tons required to maintain 75 degrees inside when its 95 degrees outside. Too large a system will cool the home quickly, not allowing enough run time to remove humidity. Too small a system, is better than too big, but may allow the home to get to a higher than desired temperature. If you don t measure your just guessing!
The actual load is determined by: Windows, single pane? double pane? Doors: wood? insulated metal? Walls, insulation r factor? Ceilings: insulation r factor? Ventilation, infiltration, Direction house faces: N.S.E.W. and other factors. There is no reliable or useful rule of thumb. Bigger is not Better. It is important that you remember, and then inform your advisor. Since your home was built have you made changes that may affect the load? Upgraded windows? Added or enclosed a room? Added insulation Has the older system cooled / heated satisfactorily? Anything else? Regulating State Authority: TDLR phone #800-803-9202. Local AC contractors organization: ACCGH 713-781-4822. Your local permitting authority: call your city. BBB: #281-809-7076