• Air Conditioners / Heat Pumps
• Gas Furnaces

Residential Design Issues

• Heat Loss and Gain Calculation - Load
• Equipment Selection
• Duct System Design

HOW DOES IT WORK?
 

Air Conditioners and Heat Pumps

Both a central air conditioner and a heat pump have two basic parts: the condenser unit and the evaporator coil. Refrigerant gas is compressed and cooled inside the condenser and pumped through refrigerant lines to the evaporator coil. A blower circulates air through the evaporator coil, cooling the air, and then blows it through the duct system into your home.

In the winter, a heat pump reverses this process, absorbing heat from outside and releasing it inside your home. A heat pump can even absorb heat at temperatures below zero degrees Fahrenheit.

Gas Furnaces

A heating system uses a blower to draw in cool air, passes it over a heat exchanger where it is warmed, and blows it out through air ducts to heat your home. There are essentially three types of furnaces: Upflow furnaces draw cool air from the bottom and send warmed air out the top; Counterflow furnaces draw cool air from the top and send warmed air out the bottom; Horizontal furnaces are suspended beneath the floor or in a crawlspace, drawing cool air from one side and sending warmed air out the other.

EFFICIENCY

Just as new cars get much higher gas milage than older models, currently available heating and cooling systems can heat and cool your home using a lot less energy than older units. Efficiency is an important feature for you to consider in making a decision to buy a new home comfort system.

But what exactly is meant by efficiency? How is a unit's efficiency determined? To determine the efficiencies one can expect, the federal government has established numerical rating systems for cooling (SEER ratings), heat pump heating efficiency (HSPF ratings) and gas furnace efficiency (AFUE ratings).

Cooling Efficiency = SEER
 

SEER stands for Seasonal Energy Efficiency Ratio. A SEER rating is determined as follows:
 

The higher the SEER rating number, the more energy efficient the unit. Specifically, SEER is the total cooling output in BTUs (British Thermal Units) during a normal annual usage period for cooling divided by the total electric power input in watt-hours during the same period. It also indicates the amount of heat absorbed in BTU's per watt of energy consumed. For example, a 10 SEER system will absorb 10 BTU's per watt of energy consumed.

Heat Pump Heating Efficiency = HSPF

Measuring a heat pump's heating efficiency is very similar to measuring an air conditioner's cooling efficiency in that they both use electric power. The term used here is Heating Seasonal Performance Factor, or HSPF. HSPF compares the quantity of heat produced in a heating season to the quantity of electricity consumed. The higher the HSPF rating, the more efficient a heat pump is at heating your home. HSPF determination is essentially the same as for SEER:

You will see the following tag on your unit, indicating its SEER (cooling) or its HSPF (heat pump):

 

What these efficiency ratings come down to is this: A unit with a higher SEER and/or HSPF rating is more efficient than one with a lower rating. It will deliver the same quantity of cooling or heating while using less electricity. This means lower electric bills for you, and lower operating costs in the long run.

This is especially true if you are replacing an older unit with a new high efficiency system, particularly when it comes to air conditioning. For example, many older units have SEER ratings as low as 5 or 6. So a new unit could be twice as efficient and reduce your electric bills for cooling by as much as 50%. Use the table below to get an estimate of what your savings could be with a new high efficiency system.

The table above lists approximate annual operating costs for units with various SEER Ratings. For example, if you current air conditioner has a SEER of 6.0 and your annual operating cost is $600, the cost to operate a new 14 SEER system will be approximately $260, giving you an annual savings of about $340, or 57%!

If you don't know the SEER rating for your current system, use the table below to estimate an average SEER rating for your system, based on when it was manufactured:

 

New units have a minimum SEER rating of 10. Some manufacturers are expected to release 20 SEER models in 2005. The higher the SEER rating, the more expensive the system and the lower the operating cost. Let Air Wave explore all the possibilities with you.



Gas Furnace Heating Efficiency = AFUE
 

When discussing a furnace's heating efficiency, the term used is AFUE. AFUE stands for Annual Fuel Utilization Efficiency and represents the percentage of heat delivered from the quantity of fuel used during a heating season. The higher the AFUE%, the more efficient the product. Calculated as follows:
 

When you replace an older furnace with a new gas furnace, your heating costs could be substantially reduced. In the past when energy was inexpensive, much of the heat generated by an older furnace was sent up the flue pipe and wasted. Today's modern furnaces are design to capture most of the heat they generate. Some models are rated as high as almost 95% AFUE, meaning they convert virtually all of the fuel they consume into heat to warm your home.

The following tag attached to your furnace indicates its AFUE rating:

 
Use the table below to get an estimated cost savings by replacing an old furnace with a high efficiency model:

 

If your current furnace is more than 10 years old the efficiency is likely to be about 60%. For example, if your current furnace is 60% efficient and your annual operating cost is $700, the cost to operate a new 93% AFUE system will be between $425 and $450, giving you an annual savings of approximately $250, or about 36%! Air Wave is ready to help you get the most from your energy dollar.

Equipment Selection

After the load calculation of your home comes equipment selection. Many factors are evaluated in selecting the proper equipment for your home. The calculated load, projected usage, geographic location and more are all weighed in selecting the proper equipment for your individual application. Additional options will also be considered, such as the cost of a heat pump as opposed to a natural gas furnace. We will explore everything with you so that you may make a fully informed decision.

Duct System Design
 

After the load calculation and equipment selection, the final issue is the design of the duct system. The size and location of air ducting will depend upon the materials used, the load, and the type of duct system. There are three principle types of air distribution systems available today. Each differs in performance based on the ability to closely follow the design.

Trunkline systems offer the most flexibility in maintaining equal air pressure, while flex and wye branch systems must follow the design carefully but are generally less expensive to install. Regardless of the system used, actual duct size will vary based on the type of material used (sheet metal, flexible duct, fiberglass), the load, and the layout of the system. The outcome of this design process is an air distribution pattern that matches the load (heat loss and gain) of your house.

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