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Next to heating/air-conditioning, fridge freezer appliances account for the highest energy consumption of domestic appliances.
This is not surprising since these appliances are normally in operation 24 hours a day and are rarely turned off. It is therefore
worthwhile to become familiar with the key properties of these appliances. In this way an informed choice can be made to determine
which fridge freezer will best meet particular needs and maximise energy savings. The key properties are sumarised in the following tables:
PROPERTIES
FRIDGE FREEZERS
| Energy Rating |
Letters A++,A+,A,B,C,D,E,F,G provide a scale of relative energy efficiency. The letter A++ environmental rating
indicates the most energy efficient and consequently the lowest level of damage to the environment. At the other end of the scale the letter G environmental
rating indicates the least energy efficient and consequently the highest level of damage to the environment.
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| Energy Consumption |
The energy consumed by the appliance (kWh) over a defined period of time measured in kWh/24h or kWh/year.
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| Capacity |
Capacity is normally measured in litres(L) or cubic feet(cu ft). For fridge freezers, it is important to
distinguish between fridge capacity and freezer capacity. Net capacities refer more closely to to actual usable capacity or space and
gross capacities refer to total volumes including both usable and non usable space. For daily use, the net capacities are critical.
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| Frost-free |
Frost free models rely upon air circualation to prevent frost occurring and is primarily a convenience.
In the case of long term storage in a frost free freezer, the defrost cycle of thawing and freezing may cause
deterioration of foodstuffs containing high fats and some meats. Also if protective wrapping is not used, foodstuffs
tend to dry out more readily than in a coventional freezer.
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| Super-cooling |
A fridge compartment which can be regulated for rapid continuous cooling for a preset period of time usually about 6 hours but depends on load.
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| Fast-freeze |
A fast freezing facility or setting (regulated by a thermostat) that helps foodstuffs retain more of its nutrients and reduces deteroration in the texture.
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| Thermostats/Compressors |
Fridge-freezer models are supplied with one to two thermostats to regulate the temperature. A separate thermostat for each section of
fridge and freezer provides dual control and is more flexible than the the single thermostat system. For example: switch off fridge
and leave freezer on; or leave fridge on and defrost freezer at same time. Some of the higher specification fridge freezers are fitted
with two separate compressors each with their own thermostat - one for the freezer section and one for the fridge section.
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| Freezer star ratings |
The star-rating system for freezers indicates the temparature freezing scale, the type of foodstuffs suitable for freezing and the period of time.
4 stars (****): -18°C or colder. Freeze fresh food, and store food for three to 12 months
3 stars (***): -18°C. Store pre-frozen food for three to 12 months
2 stars (**): -12°C. Store pre-frozen food for up to a month
1 star (*): -6°C . Store pre-frozen food for up to a week
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| Freezing Capacity |
The time taken to freeze a given weight of foodstuffs in 24 hours (kg/24h).
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| Thaw Time |
The time taken in hours for foodstuffs to thaw (h).
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| Power Cut Safe Time |
The time in hours following a sustained power cut that the foodstuffs may be considered safe to use providing that the freezer door remains closed (h).
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| Climate class |
'Climate Class' defines the range of valid operating room temperatures for fridge freezers.
In the UK, N class and SN class are common. Both work effectively in room temperatures up to 32°C.
N models should be used be used in room temperatures below 16°C. SN models should not be used at
room temperatures below 10°C.
ST classes: ST models work best at between 18°C and 38°
C and T classes: these models work best between 18°C and 43°C.
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| Noise |
The maximum noise level in decibels [dB(A)]
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| Chill compartment |
The Chill fridge compartment is colder than the rest of the fridge and is maintained at a temperature around 0°C. It's good for storing
meat, fish and poultry.
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| Humidity controlled compartment |
This facility permits the maintenance of a controlled humidity compartment in the fridge. Increasing the humidity
can prolong the nutrient quality of fruit/vegetables and prevent drying out and shrivelling; lowering the
humidity can prolong the nutrient quality of meat, fish and dairy foods.
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| Water filters |
Most side-by-side fridge-freezers have a dispenser plumbed into the mains that provides chilled water, ice cubes and crushed ice.
Dispensers include replaceable water filters to reduce the build up of scale within the internal pipes.
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| Security |
Security consists of additional functions such as:
Sound Alarms - e.g., High-temperature warning indicating that food stuff is not sufficiently cold and that the temperature needs to be lowered;
Separate control of fridge and freezer sections;
Vacation Mode (energy savings);
Child Lock;
Self closing door hinges;
Save settings on power failure; etc.
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FRIDGES
| Climate class |
Climate Class defined exactly as in FRIDGE FREEZER table above.
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| Icebox stars |
Ice Box stars defined exactly as 'Freezer star ratings' in FRIDGE FREEZER table above.
No stars - Suitable only for making ice. In principle 4-star ice boxes should be able to
freeze 2kg of fresh food without adversely affecting the temperature in the fridge.
However, in practice this condition is not always met. If large quantities of
food require freezing, then a fridge freezer or standalone freezer may be better suited.
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| Antibacterial coatings |
The jury is out on the scientific evidence determining the efficacy of these antibacterial coatings.
The increased use of antimicrobial products increases the risk that bacteria may become further
resistant to antibiotics. Moreover, the development of a healthy immune system requires some level
of microbial exposure. It would seem prudent to avoid these coatings or at least investigate the
extent of the coatings, their type and activity before purchase. Of course for those with already
specifically compromised immune systems, the use of antibacterial coatings may prove beneficial in
certain instances.
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ANALYSIS (Skip this section: Go to Comparison Table or Go to Conclusions)
Energy Consumption
To compare the annual energy consumption of fridge freezer models with different net capacities, we need to relate the total average energy consumption
per year (E)(kWh/year) to the total net capacity of the appliance (CT)(L).
In practice we may assume that the total average energy consumption per year (E) may be represented as linear combination of the average energy annual
consumption contributed by the freezer component and of the average energy annual consumption contributed by the fridge component.
- (E1): average energy annual consumption contributed by the freezer component
- (E2): average energy annual consumption contributed by the fridge component
- Thus E = E1 + E2
To account for the individual freezer and fridge specific capacities we define the following:
- e1 = E1/c1; Here e1 is the freezer specific average energy consumption per net freezer capacity c1
- e2 = E2/c2; Here e2 is the fridge specific average energy consumption per net fridge capacity c2
Solving for E1 & E2 in lines 4. & 5. respecively and then substituting E1 & E2 into line 3. gives:
- E = e1c1 + e2c2
But clearly, the sum of the net capacities for the freezer and fridge is equal the total net capacity CT of the fridge freezer appliance
- CT = c1 + c2
Dividing equation in line 6. by equation in line 7. gives the desired result:
- E/CT = (c1/CT)e1 + (c2/CT)e2
E/CT is an energy consumption factor (ECF) that provides a relative method of comparing the total average energy consumption per year of appliances
per unit total net capacity for different models.
The signifigance of the energy consumption factor is that it enables a comparison of fridge freezer models with different energy consumption values and net capacities over
a period of one year. The larger the ECF factor, the greater the environmental impact per unit net capacity. The smaller the ECF factor,
the less environmental impact per unit net capacity.
Environmental Impact
To get a single numerical measure of the overall environmental impact score(OEI), we introduce an environmental impact index by assigning a numerical weighting
to each letter of the erergy efficiency rating: A+=1/2, A=1, B=2, C=3, D=4, E=5, F=6, G=7 and thus define the OEI as follows:
- OEI = (Energy Rating Index) x E
This enables appliances with different energy ratings and the same energy consumption values (E) to be distinguished and provides a measure of not only how much energy
is consumed by the appliance over one year, but how efficiently that energy is used. For example, the same amount of energy consumed by two appliances may be used by
one appliance more efficiently thus keeping the temperature cooler or used to provide more functionality. The higher the OEI score, the greater the environmental impact.
The lower the OEI score, the less the environmental impact.
A Method of Choice
By combining the energy consumption factor (ECF) with the Energy Rating Index a method of choice (moc) may be deifined:
- moc = (Energy Rating Index) x ECF = (Energy Rating Index) x E/CT = OEI/CT
The moc value provides a rational measure of the annual energy performance of a fridge freezer per total net capacity scaled to the energy efficiency rating.
Here is how it works in practice. You determine what total net capacity (actual usable space) you or your family require in litres (L). Then look at the table below and see which
models have a total net capacity closest to your needs. Then choose the model with the lowest moc value. This choice represents the optimum use of energy
and minimum impact to the environment. Clearly, the moc represents choice based on energy considerations only.
COMPARISON TABLE (Skip this section: Go to Conclusions)
In the comparison matrix shown below, the brands and models selected have been chosen as typical fridge freszer products available in the marketplace today. The purpose
of the comparison is to suggest a method to help choose a product using the moc method of choice with the lowest overall environmental impact (OEI) and meet practical needs. This
requires achieving a balance between cost and application requirements. The salient properties for each model are included.
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