Two-Stage Air Conditioning
Humid Climates such as the US Gulf Coast
- For hot, humid climates, two-stage air conditioners can increase your comfort and reduce your electricity bill.
- Two-stage air conditioners are made by MAYTAG, LENNOX, and CARRIER.
- Engineering knowhow is important in getting good results with two-stage air conditioners. Be sure that your service company is competent.
- Two-stage air conditioners run at 67% and 100% of capacity. The thermostat controls which speed is used based on the home temperature.
- Comfort is increased because cool air circulates almost all of the time between noon and 8 pm. This reduces room "heatup" that occurs during the "off cycle" of conventional, single-speed air conditioners. Also, moving air gives one a cooler feeling.
- To ensure that dehumidification is adequate or that it is as desired, the evaporator (cooling) coil may be chosen smaller than normal. Choose a smaller evaporator coil because the air conditioner will run at 67% of capacity for 80 to 100% of the run time depending on the size of the air conditioner compared to the load. That is, often best results will be achieved by selecting an evaporator coil suitable for the 67% of capacity operation.
- The furnace blower circulates air in the home for the cooling system. Therefore, the blower speed is switched between a high speed and a lower speed to coincide with the compressor high and low stage.
- LENNOX has published a pamphlet titled "Selection of Equipment for High-Humidity Environments." Discussed are the need to adjust blower speeds and coil size to achieve good results for dehumidification and cooling.
- To allow "normal mortals" to get good results with two-stage systems, manufacturers have introduced complicated control systems that measure the Relative Humidity (%RH) and then adjust the speed of a variable-speed blower motor to achieve comfortable conditions in the home. With experience and adequate knowhow, this complication with its attendant higher repair costs can be avoided by proper design.
- Most recent thermostats measure the Relative Humidity (%RH) and have options to continue running the cooling until either the requested %RH is reached are until the home cools a prescribed amount below the setpoint (3F maximum).
- Savings are substantial with weather conditions like those in Houston, Texas. A two-stage air conditioner can save 15 to 30% on your cooling bill.
- Economic evaluations of two-stage air conditioners have shown that the incremental price (investment) has a greater than 10% Return-on-Investment (ROI) and a 4 to 5 year payout.
- Only two-stage air conditioners have gotten the compliments: (1) My house is so comfortable that I turned off all six of my ceiling fans and (2) My bills really are as low as you said that they would be and I did not really believe you, but you are right!
- Homes have many design deficiencies. The Two-stage air conditioner can overcome deficiencies such as inadequate air ducts, air filters, air balance, and refrigerant lines. Overcoming the deficiencies is achieved by low-stage operation. Low-stage operation has 60% of the capacity of high stage. Therefore, 80+ or 90+ percent of the time, from 10 am to 8 pm during hot weather, the A/C is running in low stage. At 60% of capacity in low-stage operation, the air ducts, air filters, air balance, and refrigerant are generally aadequate. The deficiencies that are so expensive to correct and which lead to much discomfort and extra electricity consumption are thus finessed. This is one of the characteristics of two-stage air conditioners that makes them so useful and practical.