Discussion on the utility of implementing home appliance identification

The current test process for evaluating the air conditioning characteristics of a home is a steady state test that determines the energy efficiency ratio (EER) of the air conditioner being tested (US Federal Bookkeeping Office 1995a). Dividing the cooling capacity of the air conditioner by its full input current. EER. The outdoor ambient temperature during the test should be maintained at 95 F ( 35 ). Due to the cyclical effect (air conditioning self-shutdown and start-up to achieve a fixed temperature) is negligible, there is no seasonal evaluation process for residential air conditioners. It can be seen that the weighted EER value of residential air-conditioning freight has continued to increase over the past 20 years.

First, the classification standard of room air conditioning

In the National Household Appliances Energy Conservation Act (NAECA), the minimum energy efficiency standards for 12 residential air conditioners are regulated. The types of these 12 air conditioners are classified according to the following criteria: refrigeration capacity.

Whether the outdoor part of the air conditioner has a louvered side (if the outdoor part of the air conditioner has a louvered side, the air flow in the outdoor condenser cooling area can be improved, so the performance of the air conditioner will be improved).

Whether there is a directional valve (that is, whether the air conditioner can function as a heat pump).

In the NOPR proposed by the DOE, two types of room air conditioners are additionally specified. These two types of air conditioners are specifically designed to install air conditioners on door windows and rail windows. These two types of air conditioners have been added because of the performance-related characteristics of window air conditioners (suitable for the door type and the corresponding proportions).

The top 500 energy-using units have an annual comprehensive energy consumption of 243.35 million tce of quasi-coal, involving 21 industries, with a total energy consumption of 503.44 million tons of standard coal, accounting for the total energy consumption of 7283 key energy-using units. 65. 4%, accounting for 37.1% of the total energy consumption in the country.

Through analysis, it can be seen that by focusing on 7283 key energy-using units, we can grasp the key points of energy management. Among the 7283 units, it is also possible to prioritize the top 500 households. It is necessary to formulate incentive policies, encourage these enterprises to do a good job in energy management, save energy and reduce consumption, improve energy efficiency, promote environmental improvement, and lay a solid foundation for achieving sustainable economic development in China.

Product Energy Efficiency Standard AHAM is a business association that represents the majority of US home air conditioner manufacturers.

Windows), while other types of air conditioners do not have such features. In DOE and NOPR, the minimum energy efficiency values ​​of 12 air conditioners (as specified by NAECA) have been newly proposed (the relevant standards have not been proposed for door and window air conditioners and sliding window air conditioners). The above 14 air conditioners and their current minimum are given. The minimum energy efficiency standard proposed in the energy efficiency standards and DOE's NOPR.

Second, the design choice of room air conditioning

The improvement measures described below can be used to improve energy efficiency when designing a room air conditioner. An improved version of the American Oak Ridge National Laboratory (ORNL) Heat Pump Design Model (HPDM), Mark % (Fischer and Rice, 1983; Fischer et al., 1988), can be used to determine the most significant increase in energy efficiency after improvements. The Association of Home Appliances provides an estimate of manufacturing costs after design improvements, which are in line with DOE requirements (AHAM, 1994a).

Increasing the front heat exchange area The use of a heat exchange tube with a large front area is one of the most versatile methods for increasing the heat exchange surface area. As the frontal area of ​​the tube is increased, the heat exchange performance of the tube is also increased. Enhancing the heat exchange performance of the evaporator or condenser tube can increase the efficiency of the air conditioning system. In the current design of most living room air conditioners, if the frontal area of ​​the pipe is to be increased, the air conditioning case needs to be enlarged. Because of the higher cost of increasing the cabinet, manufacturers will consider other methods to improve heat exchange performance before taking this approach.

Under the premise that the increase in volume of the tank is unavoidable, AHAM gives an estimate of the manufacturing cost of increasing the frontal area of ​​the evaporator and condenser tubes (AHAM, 1994a). The increase in cost and the volume of the tank Large and related to the refrigeration capacity of air conditioning products. Based on the design data, AHAM gives the actual increase in the area of ​​the front tube area. The resulting increased system efficiency is estimated from the modified ORNL heat pump model.

Increasing the depth of the heat exchanger and increasing the number of turns of the tube can also increase the surface area of ​​the heat exchanger. Most residential air conditioners are designed to allow the evaporator and condenser with maximum depth to be installed in the cabinet. Vertically increasing the number of turns in the duct will result in a further increase in the depth of the design. Under the premise of not increasing the size of the box, there are strict regulations on the number of turns of the pipe. Therefore, most manufacturers use other methods to improve the efficiency of the system before they have to increase the depth of the pipe. Furthermore, the efficiency of the new pipe is only 70% of the efficiency of the previous cycle. Therefore, for the overall efficiency of the system, the method of increasing the efficiency of the system by increasing the number of turns is not very effective.

In order to properly evaluate this improved design, AHAM gives the maximum number of pipe turns allowed for each set of rings without enlarging the air conditioning cabinet. AHAM also provides energy efficiency standards and markings for manufacturing cost estimates in the form of additional pipe and fin material costs (AHAM, 1994a). The increased system efficiency by increasing the number of pipe turns is estimated by the modified heat pump model. .

Increasing the fin density and increasing the fin density can also increase the surface area, thereby improving the heat exchange performance of the tube. However, the blade density has a direct impact on the fan's energy consumption, displacement, and dust accumulation. Therefore, there is a limit to the increased fin density without compromising performance. Arranging overly dense blades will generally result in an increase in pressure drop in the loop of the coil airflow, which will increase the energy consumption of the fan.

Obviously, all the consequences resulting from the optimization of the fin density must be taken into account, for example, the burden on the system cannot be increased. To determine the practical maximum fin density, manufacturers specify different blade density values ​​for different pipe rings, depending on the type of pipe (ie, evaporator or condenser), blade type (ie, Depending on the wavy, louvered or narrow groove shape, pipe diameter and number of pipe turns. AHAM gives an estimate of manufacturing costs in the form of additional blade material costs (AHAM, 1994a). The increased system efficiency by increasing blade density is estimated from the modified heat pump model.

Adding a subcooler subcooler to the condenser tube can further cool the refrigerant coming out of the condenser, so, in essence, it will increase the size of the condenser tube. Typically, the subcooler is placed at a location between the outlet of the condenser and the inlet of the capillary channel and is flooded by condensate produced by the evaporator. The size of this space determines whether a subcooler can be installed in the system without expanding the space of the air conditioning base of the living room.

Improved fin design fin design improves the heat exchange coefficient of the air circulation portion of the tube. By improving the design of the fins, the turbulence of the air on the tube can be increased, and the increase in air turbulence on the tube is part of the improvement in heat exchange performance. In the design of the tube ring, almost all manufacturers use some form of blade reinforcement design measures, such as the shape of the fins to be wrinkled, wavy, louvered or narrow.

According to the method proposed by the heat pump model, the heat exchange coefficient of the air circulation portion after the fin design is improved can be obtained by multiplying the calculation formula of the heat exchange coefficient under the smooth blade condition by an improvement factor. The manufacturer provides improvement factors for the wavy and narrow-slit blades to calculate the heat exchange coefficient of the room air conditioner using this improvement measure by the heat pump model. AHAM gives an estimate of the manufacturing cost of improved fin design in the form of a growth in the cost of smooth fin manufacturing (AHAM, 1994a).

Improving the design of the refrigerant pipe The method of raising the groove of the pipe ring to change the smoothness of the inner surface of the refrigerant pipe can improve the heat exchange coefficient on the refrigerant side. This type of refrigerant pipe is often referred to as a split or trough pipe. Although the double pipe can improve the heat exchange performance of the pipe ring, it must be pointed out that this method has a side effect of increasing the pressure drop on the refrigerant side of the pipe ring.

Spraying condensate onto the condenser coils to spray condensate onto the condenser increases the heat exchange coefficient of the condenser air circulation portion. These condensed materials are first formed on the evaporator, then dripped from the evaporator, and collected in a condensate collection tray located below the condenser fan. If a lifting eye is attached to the top of the condenser fan blade, it can bring a small amount of cooling material up and spray it toward the condenser as the fan rotates.

This method is more practical, and most of the indoor air conditioners have adopted this method.

Improve the efficiency of the fan motor In a room air conditioner, only one fan motor can drive the fan of the evaporator fan and the condenser. Typically, the evaporator fan is a blower wheel (centrifugal forward arc), while the blades of the condenser fan are helically propelled and have a sling on top that condenses the condensate to the condenser. Most manufacturers are now using inefficient negative (inductive) asynchronous motors with efficiencies of 30% and 40%, and efficient split-phase capacitive (PSC) motors with 50% and 70% efficiency. The efficiency of an electronically commutated motor (ECM, also known as a brushless constant magnet motor) is between 70% and 80%. The use of this motor further increases the efficiency of the fan motor. The ECM's motor weighs about twice as much as a standard PSC motor. If the air conditioner uses an ECM motor, it will increase the overall weight of the air conditioner.

Manufacturing cost estimates to improve motor efficiency should be based on information provided by the motor manufacturer. When using an ECM motor, the air conditioning cabinet should be adjusted to suit the weight of the motor, however, neither AHAM nor the motor manufacturer gives the corresponding manufacturing cost.

Increase compressor efficiency Most air conditioner manufacturers use rotor compressors. Although the maximum efficiency of the compressor has now reached 10. 7 11. 1EER (The EER value of the rotary compressor is measured under the following ASRE T conditions: evaporation temperature, 45 F < 7. 2 > ; condensation temperature, 130 F < 54. 4 > ; reflux gas temperature, 95 F < 35 > ; liquid temperature, 115 F < 46. 1 > ; ambient temperature, 95 F < 35 > .), but by 1994, there has been more than one manufacturing plan development Rotary compressors with an efficiency of 12.0EER (SA, 1990). But these development plans have to be terminated because it is difficult to find the materials needed to make efficient compressors. Other manufacturers want to develop rotary compressors with efficiency between 11.1 11. 3EER, but this requires efficient motors, advanced compressor materials, and new compressor manufacturing methods and equipment. High-power air conditioners can use high efficiency scroll compressors and reciprocating compressors. The efficiency of the scroll compressor is 11. 0EER or more, and the efficiency of the reciprocating compressor with the new technology is close to 12. 0EER (Duffy, 1991). However, due to the volume of the scroll compressor and the reciprocating compressor Both the weight and the weight exceed the rotary compressor, so the use of these two compressors will give the air conditioner manufacturer higher manufacturing costs.

AHAM provides an estimated manufacturing cost after using high efficiency rotary compressors and scroll compressors (AHAM, 1994a).

Design Improvements to Improve Seasonal Efficiency The use of variable speed compressors, temperature control valves, electronic expansion valves, and temperature control devices can increase the seasonal efficiency of air conditioning equipment. However, it is generally believed that the impact of the cycle is small, so improvement measures aimed at improving seasonal efficiency do not save much air-conditioning energy. In addition, the room air conditioning efficiency (ie EER value) is measured under steady state conditions, so only the improvement measures used to improve the seasonal efficiency have no effect on the energy efficiency design value of the air conditioner.

Replacing refrigerants All residential air conditioners are now using R 22. Because it is a chlorofluorocarbon (HCFC) and has ozone depletion potential (ODP), the US Environmental Protection Agency (EPA) has ordered 2020 Production and use of this refrigerant ceased on January 1 (United States Federal Bookkeeping Office, 1995b). As a result, the air-conditioning industry is now developing new refrigerants. There have been satisfactory results in the development of two refrigerants: (1) R 407C, a mixture of three fluorocarbon mixtures R 32, R 125, R 134a in specific gravity 23%, 25%, 52%; ( 2 ) R 401A, a mixture of fluorocarbons R 32 and R 125 in azeotrope (dot) at specific gravity 50% and 50%. However, compared with R 22, they still have significant shortcomings. Air conditioners using the R 407C are 5% less efficient than air conditioners using the R 22, while air compressors using the R 401A have higher discharge pressures than those using the R 22 (Godwin, 1994).

Third, the reference model

As mentioned earlier, engineering data from different manufacturers (unconfirmed) describes the structural complement of the actual reference model and their performance (ie, the model under the current minimum energy efficiency standard). AHAM is nine of the 14 air conditioners. A reference model is available and a representative reference model is available for each of the nine air conditioners. Refrigeration capacity and efficiency are two selection criteria when determining the baseline model. A HAM lists the most representative cooling capacity values ​​for this type, and the EER value should be very close to the minimum allowable value specified in NAECA, which came into effect in 1990.

Fourth, model simulation

The simulation process was implemented using the modified March 00% version of the ORN L heat pump design model. The model has a comprehensive program for simulating an electrically driven air heat pump. The model is a steady-state model that calculates the EER value of the simulated equipment under various specific environmental conditions.

The calibration and calibration results of the simulation model are discussed here.

V. Cost-effectiveness data

In this section we analyze the manufacturing costs and energy efficiency data for four of the nine air conditioners. These four air conditioners (without reverse circulation, with louvered sides and cooling capacity below 20,000 Btu/h < 5860W>) accounted for 85% of the air conditioning market in 1994 (AHAM, 1994b).

In addition to manufacturing costs and energy efficiency, data on cooling capacity, annual energy consumption, retail price, life cycle cost, and payback period are also listed.

In order to determine the payback period and life cycle costs of different improvement measures, they must first determine their annual energy consumption. After testing, DOE proposed the annual energy consumption of indoor air conditioning (US Federal Bookkeeping Office, 1995c) Expression: AEC = (cooling capacity / EER) hours 0. 001 type AEC annual energy consumption (kWh / year); refrigeration Capacity unit is Btu/h; EER energy efficiency ((Btu/h) / W); hours compressor working time (750h/a); 0. 001 conversion factor (kW/W).

In order to determine the annual energy consumption of each improvement measure, it is assumed that the cooling capacity of the air conditioning equipment is constant, that is, the impact of different improvement measures on the air conditioning refrigeration capacity is not considered. The annual cooling capacity can be obtained by multiplying the basic cooling capacity of the air conditioner by 750 hours. 750h is a national average and is determined by AHAM through probability statistics (1982). The annual cooling capacity of a basic model divided by the cooling capacity of an improved measure is the annual working time for this improvement. The annual working hours of the improvement measures are multiplied by their total power (the cooling capacity is divided by the EER value) to obtain the annual energy consumption of this improvement.

Although the test methods provided by DOE have been widely used to calculate the annual energy consumption, there are also field data indicating that the actual annual energy consumption of air conditioners is much lower than 750h (the calculated annual energy consumption. Relatively, using test data) The calculated freight-weighted annual energy consumption is 930 kWh/year (US DOE, 1996a), while the field (on-site) benefits, and when this best cost-effectiveness is obtained, there is no need to increase the volume of the air-conditioning cabinet. The following improvements have been made: high-efficiency rotary compressors, PSC fan motors, improved heat exchangers (narrow grooved vanes/slot cooling ducts), and subcoolers, etc. Compared to current minimum efficiency designs, EER values ​​are 10 (Btu / h) / W ( 2. 93W / W) Air conditioning has a lower life cycle cost and a payback period of no more than half of the product life.

According to 71% of the test data, this can be simply understood as the actual working time is 71% of the estimated time of 750h, which is 553h. Therefore, based on the calculation (the annual energy consumption multiplied by 71% can be obtained based on the field The amount of energy consumed.

For comparison purposes, the efficiency, cooling capacity, energy consumption, manufacturing costs, retail price, investment recovery time, and life cycle cost of the four most common air conditioners are now compared. Among them, the improvement measures are sorted according to a single payback period (PBP). Mathematically, PBP is equal to the increase in retail price (additional improvements to the base model) divided by the decrease in annual energy expenditure, and the value of PBP is expressed in years. For example, a three-year PBP means: The electricity bill saved by an energy-efficient air conditioner for three years can make up for the extra expenses when purchasing an energy-efficient air conditioner. If the PBP value is higher than the effective service life of the product, it means that the extra money paid at the time of purchase cannot be compensated for during the effective use time of the product. Among the four most common types of residential air conditioning, there are only air conditioning types with EER values ​​around 10. 0 (Btu/h) / W ( 2. 93W/W), and their PBP values ​​are half or less of the product life. It is particularly worth mentioning that the air conditioning type with an EER value of 10. 0 (Btu/h) / W ( 2. 93W/ W) does not require modification of the cabinet design.

Life Cycle Cost (LCC) is the sum of the retail price and the discount rate spent on its useful life. In general, the service life of a residential air conditioner is approximately 12.5 years (US DOE, 1996a). If 1999 is used, the LCC value of a common type of air conditioner can be calculated at a discount rate of 6%. Among the 4 most common types of residential air conditioning, only air conditioning types with EER values ​​around 10. 0 (Btu/h) / W ( 2. 93W/ W) have the lowest LCC values ​​and do not require modification of the cabinet design. .

It can be seen that the energy efficiency of air conditioners after adopting the corresponding technical improvement measures is decreasing continuously, the production cost is increasing, and the payback period is also increasing. Among them, the seventh technology choice has the longest payback period, reaching 44.8 years. From the curve of product life cycle cost after adopting different technical measures, it is a valley curve from high to low and then low to high. Among the various technology options, the third measure is optimal, with a lifetime cost of only $678, which is $24 less than the energy efficiency benchmark model and $369 less than the seventh most efficient measure; Less than 1/4 of the product life

For the four most common types of residential air conditioning (occupying more than 85% of the air conditioning categories sold in the US market in 1994), air conditioners with EER values ​​around 10 (Btu/h) / W ( 2. 93W/W) are optimal. Product energy efficiency standards and identification

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