Equipment Energy Efficiency Rating

Air Conditioning Efficiency Rating

Manufacturers have a method of rating equipment so the designer and the owner can tell high efficiency from low efficiency at a glance.This rating was originally called the EER (Energy Efficiency Ratio) rating.It measures by dividing the output in BTU/H by the input in watts of power used to produce the output. For Example a system with an output of 36,000 BTU/H with an input of 4,000 W has an EER rating of 9.

36,000 BTU/H ÷ 4,000 W = an EER of 9

The larger the EER rating the more efficient the equipment.When the consumer get the same capacity using less power,the equipments is more efficient.The larger the EER rating, the more efficient the equipment. The EER rating is a steady-state rating and does not account for the time the unit operates before reaching peak efficiency.This operating time has unknown efficiency.It also does not account for shutting the system down at the end of the cycle when the thermostat satisfies.,leaving a cold coil in the duct.The cold coil continues to absorb the heat from the surroundings,not the conditioned space. This picture is not complete using an EER rating system, so a rating of seasonal efficiency has  been developed,called Seasonal Energy Efficiency Ratio (SEER). This rating is tested and modified by a rating agency and includes the start-up and shut down cycles. The government has been encouraging industry to go for equipments 13 SEER and up. Some speculative home builders have a tendency to install the lower price and lower efficiency equipment for quicker sale of the home.The rating agency is the AHRI (Air Conditioning, Heating and Refrigeration Institute).Published ratings by AHRI are being listed by manufacturers in their catalogs. 

Furnace Efficiency Rating

Furnace effieicny ratings are determined by the amount of heat that is transfered to the air or water. The following factors determine the efficiency of the furnace:

• Type of draft ( Natural Draft or Induced Draft)
• Amount of excess air used in combustion chamber
• Delta T or tempreture difference of the air or water entring versus leaving the other side of heat exchanger
• Flue stack tempreture

The following are furnace classifications and approximate AFUE ratings:

Mid-Efficiency Furnace 78% to 85% AFUE

• Usually induced or forced draft
• No draft hoods
• 20% to 30% excess air
• Delta-T of 45° F ~ 75°F
• Stack tempreture of 275°F ~ 300°F
• Non-condensing
• One heat exchanger

High-Efficiency Furnace 87% to 98% AFUE

• Usually induced or forced draft
• No draft hoods
• 10% excess air
• Delta-T of 35°F ~ 65°F
• Stack tempreture of 110°F ~ 120°F 
• Two Heat Exchangers
• Condensing furnace
• Use PVC pipes to avoid corrosion 

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