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Jebco Air Conditioning And Heating

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Its the efficiency of your system that determines what your bills will be

OVERVIEW

Well before the Department of Energy (DOE) standards were established, heating and cooling efficiency ratings became an important issue. As manufacturers have competed for industry leadership, consumers have become more demanding in their expectations of energy-efficient products. As these consumers request more and more comparison information, the manufacturers who conduct ratings tests and HVAC (Heating, Venting and Air Conditioning) contractors who install the equipment are ultimately held responsible for insuring that the information is accurate.

Unfortunately, cases have been reported in which the manufacturers and/or contractors have misinterpreted ratings information, calling into question the integrity of the industry as a whole. This integrity is critical for developing the long-term, trusting relationships that result in ongoing success.

Our goal here at Jebco is to protect that trust our customers have in us by providing the following information necessary to correctly interpret HVAC efficiency ratings.

We will take a look at some of the most common rating proceedures for HVAC products. Specifically, we will consider heating efficiency for gas furnaces (AFUE) and heat pumps (COP and HSPF): and cooling efficiency for split systems (EER and SEER). In addition, there is information about other efficiency issues relating to add-on products such as air cleaners, zoning controls and heat/energy recovery ventilators.

HVAC efficiency ratings help consumers make informed decisions. Thats why it's important to understand them.

Below are the definitions for each rating to be discussed further in the sections that follow.

RATINGS AT A GLANCE


Gas Furnace Ratings

Annual Fuel Utilization Efficiency (AFUE): Does not factor in electrical use; does include steady-state operation, cyclic operation, infiltration losses and seasonal heating days in the calculation. Heating output (Btu) annually divided by Gas fuel input (Btu) annually.

Combustion Efficiency: Does not account for infiltration losses; strictly a steady-state ratio of heat output vs. fuel input.


Split System Ratings

Heating Seasonal Performance Factor (HSPF): Factors in seasonal use, temperature bin data, cyclic operation, frost/defrost degradation and supplemental heating; a measure of energy efficiency during heating mode for heat pumps. Total seasonal heating requirement (Btu) divided by (Heat pump watts + electric heat watts over entire season).

Coefficient Of Performance (COP): Does not include seasonal use or supplemental heating; strictly a measure of watts out vs. watts in for heat pump primary heating mode at steady-rate conditions. Heat output (watts) divided by Electricity input (watts).

Seasonal Energy Efficiency Ratio (SEER): Includes seasonal use, cyclic operation and part-load factors. Seasonal cooling output (Btu) divided by Seasonal electrical input (watts).

Energy Efficiency Ratio (EER): Considers operation only at steady-state, maximum load conditions; does not consider part load or seasonal variations. Cooling output (Btu) divided by Electrical input (watts).


Whats Your Batting Average?

So what does all this mean to you the consumer, who is trying to make sense of the ratings and use them for equipment comparisons? Well... it's exactly like batting averages for baseball players.

While a star player may get three hits in three at-bats in one game, batting 1000 during that game is not a meaningful way to judge his performance. In the next game, he may very well strike out in all his at-bats. To make a meaningful comparison of batters' abilities, we look at their averages for the entire season, or even at their lifetime batting averages-which may be significantly different than their performance in any single game. During any one game, a batter may be going up against a tougher pitcher, recovering from an injury, or hitting "cold" because of the outdoor temperature. These things affect his batting much like load conditions, climate and cycling affect heating and cooling ratings. So, to make meaningful comparisons on HVAC equipment, we need to consider its overall performance over a range of specified conditions.

This is why standardized efficiency ratings were developed.


Gas Heating Efficiency: AFUE

Annual Fuel Utilization Efficiency (AFUE) ratings are used to compare gas furnaces on how much fuel gas is used in a year to generate a specific amount of heat. Tests and calculations are based on The Department Of Energy (DOE) rating procedures and are verified by the Gas Appliance Manufacturers Association (GAMA). The test standard encompasses more than 70 pages of test procedures and conditions that must be met throughout the rating process.

These "rules" take into account everything from the grade of fuel used to jacket loss to the type of burners and draft equipment used. Specific pressures and temperatures must be maintained every step of the way, and measurements must be accurate within the most exacting tolerances.

All in all, nearly 140 different factors must be calculated and computed in complex mathmatical formulas to arrive at an AFUE rating. However, for our purposes, in its simplest form, AFUE equals: Heating output (Btu) annually divided by Fuel gas input (Btu) annually.

Among others, calculations used to arrive at these two final values incorporate the following:

On and off cycling as well as steady-state operation

A specified number of heating degree days

Input and output under well-defined load conditions

Efficiencies at high and low speeds when variable-speed blowers are used

In other words, by its very definition, AFUE is an average efficiency based on all factors that affect furnace performance throughout an entire year. If the furnace provides multi-speed operation, the AFUE is calculated with weighting factors for operations at different speeds.

Other measures of Gas Furnace Efficiency: Combustion Efficiency and Electrical Power Consumption

Remember that AFUE measures a furnace's gas use only. Combustion efficiency is a measure of how well a furnace converts gas input into heat output. However, combustion efficiency is not enough to accurately compare furnaces because it does not account for any infiltration or cyclic losses. It is simply a ratio of how much heat is put out and how much gas is taken in by the furnace at steady-state conditions. The air/fuel mixture burned must remain within strict limits to avoid incomplete combustion and the possibility of carbon monoxide build-up. For safety reasons, more air is added than what is needed for complete combustion, so combustion is always less than 100%.

Induced draft furnaces and improved blower motors (e.g., ICM motors), also make consideration of a furnace's electrical power consumption much more important.


Consumers are mostly interested in energy efficiency as it translates to their month utility costs. Therefore, you need to understand that a furnace requires electricity as well as gas, and it is a combination of both energy sources that determines overall operating costs. Currently there is no certified rating that allows a consumer to compare overall combined energy usage in the same way that he or she can compare one AFUE rating to another. However, in actual operation, this is the most meaningful comparison for consumers.

Most consumers don't understand that a fixed-speed condensing furnace may have a higher AFUE than a variable-speed model, but may cost more to operate because of the electrical expense.

The difficulty in producing an accurate, meaningful energy cost rating stems from the widely varying fuel costs around the country. While it is possible to be informed of how much electrical input a particular unit requires, this only has meaning when added to how much gas is required. Adding the two together requires that we come up with a common denominator---operating cost. This can be done from the worksheet in the front of the GAMA directory, but you must factor in local fuel costs. While it is possible to use national averages for fuel costs to come up with and arbitrary standard, this goes back to the baseball analogy: if you are served by an electric utility whose rates are exceptionally high, the national average for electricity will mislead you in your decision making process, much like quoting a batting average for one game doesn't really speak to a player's overall ability.


Heat Pump Heating Efficiency: HSPF

American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) and The Department Of Energy (DOE) test proceedures to determine heating efficiency for heat pumps are used by the Air Conditioning & Refrigeration Institute (ARI). Much like those for determining AFUE, these test proceedures are very extensive and specific. Heating Seasonal Performance Factor (HSPF) is basically a ratio of the total seasonal heating requirements (Btu), including supplemental electric heat, during its annual usage period for heating, divided by the total electric power consumption in watts during the same period. The calculations used to arrive at this number incorporate:

Performance variations due to on-off cycling

Lost heat from defrost operation

Average annual fractional hours in temperature bins for regional climates

Variations in capacity and electrical use that occur at these temperatures when the system operates at multiple speeds

Just as it is in furnaces, it is impossible to develope an HSPF rating for a multi-speed unit based soley on one of its speeds. By its very definition, HSPF includes weighted factors for operation at its various speeds. While a rating could be approximated at a specific speed, the number would be meaningless for efficiency comparisons, since in "real life," the heat pump will not operate at any single, given speed.

Some manufacturers and contractors also seem to be confusing matters by stating Coefficient Of Performance (COP) ratings. By their very nature, COPs seem impressive, as they are always greater than 1.0. This implies that a heat pump is putting out a lot more heating capacity than it is using in electricity. Unlike electric resistance heat--which produces one watt of heat output for each watt of electricity purchased from the electric utility-- a heat pump uses a watt of electricity during the compression cycle, absorbing heat from the outside air and pumping it into the structure. So, while electric resistance heat achieves a COP of 1 (1 watt output divided by one watt input), a heat pump may furnish 3 to 9 wattts of usable heat per 1 watt of electricity used, so it is 300% to 900% efficient. Or has a COP of 3 to 9.

However, a high COP only occurs during higher outdoor temperatures. As the outdoor temperature falls, The COP falls, because there is less heat to pull from the out door air. Most important, a COP rating does not factor in supplemental heat. While even at 0 degrees F. the typical heat pump will achieve COPs between 1 and 3, it does not keep the homeowners warm without the use of back-up heat. The HSPF takes into account the use of back-up heat to create a realistic rating that provides an accurate comparison considering the unit's use of supplemental heat in conditions at or below the balance point for the structure. Higher capacities may reduce the supplemental heat requirements, but this will be reflected only in the unit's HSPF, not its COP.


Cooling Efficiency: EER and SEER Ratings

For both heat pumps and air conditioners, published cooling ratings are Seasonal Energy Efficiency Ratios (SEERs). SEERs use data based on a full cooling season, whereas an EER (Energy Efficiency Ratio) uses only one specific set of conditions (operation at 95 degrees F outside temperature, 75 degree indoor drybulb with a 55% relative humidity). As in our baseball anology, an EER is the batting average in one game only, whereas the SEER is the batting average for one entire season. Like HSPF, SEER also factors in operation at multiple operating speeds when applicable. A SEER rating includes factors for:

Steady-state operation

Cyclic operation

Changes in input and/or output that occur during normal operation if the unit provides multi-speed operation

Load conditions


Other System Influences

As a wider array of products become marketed by HVAC companies, other ratings are also becomming important. A few of these are described briefly in the sections that follow.

Airflow

Although the old "rule of thumb" tells us that 400 CFM per ton of capacity is necessary to achieve optimum heating or cooling performance, this rule of thumb no longer holds true. This number originally came about as a way to compensate for installation variables such as duct sizing and configuration (which affects static pressure), as well as the floor plan. It allowed a "fudge factor" to ensure that the rooms furthest from the unit's fan received adequate heating or cooling. Today, however, our new variable speed fan coils and gas furnaces can achieve optimum heating and cooling at airflows below 400CFM per ton. This is possible because of ICM (Integrally Contrlled Motor) motor technology. By monitoring blower motor torque and speed at a given airflow, the motor automatically compensates for static pressure, using built-in algorithms. Though you may rarely need to know this, it does become important as you evaluate HVAC equipment. In some cases, these "smart" motors help to compensate for oversized latent loads allowing the installation of a unit with nominal capacity that will still provide optimum heating and cooling-- even if the home has ductwork or airflow restriction problems.

Air Cleaners

The most troublesome part of air cleaner ratings is understanding how particle size affects efficiency. Click here for more on filtration.


Heat Recovery Ventilators And Energy Recovery Ventilators

Recent concerns over radon and carbon monoxide levels in homes has prompted a growing demand for HRVs and ERVs. Be sure to understand that efficiency ratings for these units are based on how well they capture and reuse heat in the circulated air--not how well they "filter" gases. Though most ERVs and HRVs incorporate some type of filtering system to eliminate particles from the outside air, their primary purpose is to eliminate gases by exchanging the inside air that contains these gases for outside air in which these gases are either non-existent or present in much lower concentrations. In the process, heat is transferred (remember, heat is transferred even in cooling). How well the heating energy is transferred determines the recovery efficiency.


Zoning Systems

To date, there is no published or certified rating system for zoning. Zoning controls have no efficiency of their own, beyond how accurately they can measure room temperature and setpoint. Yet, zoning systems do increase overall energy efficiency of the system, by controlling operation times and heated/cooled areas. You should know that zoning enhances energy savings like a photoelectric sensor reduces electrical costs on a dusk til dawn lighting system. If you have an outdoor security light, it requires a bulb. If that bulb is a 60 watt bulb, it will require 60 watts of electricity for every hour of operation. The sensor doesn't make the bulb more efficient. It still uses 60 watts per hour whenever it is on. What it does do is change the amount of time that the bulb is on. Zoning can also save energy by playing a role similar to individual room light switches. When a room is in use, zoning will control how much heating or cooling needs to be added to suit your preferences and usage patterns. When the room is not in use, heating or cooling can be shut off or reduced to that area the way a light switch lets a person turn off the lights in an unused room.

System Efficiency

Much like zoning, other parts of a total system affect overall performance. While these things are nearly impossible to compare because of how each part affects the others, system efficiency should be very important to the consumer. Regardless of ratings, these factors do affect your monthly heating and cooling costs. Proper coil and system matching and supplemental heat are just two examples of how overall system efficiency can be affected by the interaction among components. Click here for information on how efficiencies can help a unit pay for itself


Coil and System Matching

To achieve optimum cooling capacity and efficiency, the indoor coil and blower system must be properly matched to the outdoor unit. If a new heat pump or air conditioning condenser is matched with an existing older coil, the coil would most likely be too small, especially if there is an upgrade in efficiency. Even the existing refrigerant line set size should be addressed. Undersized coils and refrigerant lines can result in overcharging the system in the summer to maintain correct system pressures. The coil may not be able to absorb the heat necessary to keep suction pressures up, so coil freeze-up could occur. In the winter, the tendency would be to undercharge the system due to high pressures. This can cause excessive temperature rise and head pressures, which can negatively affect compressor reliability. It may also reduce efficiency as the high pressure switch is repeatedly tripped or the thermal overload shuts the system down on milder days. Consumer literature is available to explain this issue to customers based on individual manufacturers information.


Heat Pump Supplemental Heat

In many areas of the country, supplemental heat must be available to keep homeowners comfortable when the outdoor temperatures drop to or below the balance point for the structure. Because electric resistance heat requires one watt of electrical input for each watt of heating output, a heat pump system that relies on a great deal of supplemental heat will be much less efficient. (This makes proper sizing for low temperature conditions critical, since it will reduce the need for supplemental heat). Click here for a free system analysis and cost comparison report

While the ratio of output to input will always be equal for any supplemental resistance heat system, some supplemental heating systems require less power because they can be activated in stages (produce less output and more even temperatures) according to heating demand.

Just ask us for literature on our Smart Heat for more information


The issues that surround HVAC equipment performance ratings are increasing every day. Our best choice here at Jebco is to provide real answers. In doing so, we hope we have demonstrated ourselves, to you the consumer, as knowledgeable leaders in our industry and will continue to do so as the authority for all your home comfort and energy needs.

We realize that no web site can provide all answers so we have included this form page to allow you to ask any questions that come to mind about the efficiency or anything else concerning your system and we will make every effort to get you the information you need. We will email your answer as quickly as time permits.

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