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Noiseless household refrigeration in the eighties?
3
of thawing medium (°C), and H is the surface heat transfer coefficient (W m -2 °C-1),
4
The use of the above expression for calculating thawing times will introduce an error of between + 4 % in addition to the prediction error of 4-5% previously mentioned. The formula can be used only for block thicknesses between 13 and 16 cm, thawing medium temperatures between 5 ° and 30°C and surface heat transfer coefficients from 5 to 1000 W m -2 °C -1
5
6 7 8
References 1 2
9
Bialod, D., Jolion, M., LeGoff, R. Microwave thawing of food products using associated surface cooling J Microwave Power 13 3 (1978) 269-274 James,S. J., Bailey, C. Air and vacuum thawing of unwrapped boneless meat blocks Proc Inst Refrig (Session 1979-1980)
Noiseless househ eighties?
10 11
refri
Vanichseni, S. Thawing time of frozen lamb shoulders, Meat Industry ResearchInstitute of New Zealand Report No 233 (1971) Perry, J. H. Chemical Engineers' Handbook 4th Ed McGraw-Hill. New York (1963) Miki, H., Nishimoto J.-I. Fundamental studies on the thawing of frozen fish - 1, Thawing rate of vacuum thawing Mem Fac Fish Kagoshima Un/v 24 (1975) 161-171 Earle, R. L. Physical aspects of the freezing of cartoned meat. Meat Industry ResearchInstitute of New Zealand Bulletin No 2 (1959) Mott, L. F. The prediction of product freezing time Aus Refrig Air Cond H[g 18 2 (1964) 16-18 Dusinberre, G. M. Numerical analysis of heat flow, 1st Ed McGraw-Hill, New York (1949) James, S. J., Creed, P. G., Roberts, T. A. Air thawing of beef quarters J Sci Fd Agric 28 (1977) 1109-1119 Cherneeva, L. I. Study of thermal properties of food. Report of VNIKHI (Scientific Research Institute of the Refrigeration Industry) Moscow (1956) Riedel, L Calorimetric investigations of the meat freezing process. K#ltetechnik9 2 (1957) 38-40. DKV Arbeitsblatt 8-11
ration in the
K. Kjeldsen
Froid m nager sans bruit dans les ann6es 1 980? Le bruit est I'un des probl#mes des r#frig#rateurs
m#nagers. On examine une nouvelle g#n#ration de compresseurs herm#tiques p o u r r#frig#rateurs et /'on #value/'importance des am#liorations du niveau sonore.
Noise is one of t h e problems associated w i t h household refrigerators. A n e w g e n e r a t i o n of h e r m e t i c compressors for refrigerators are
discussed, and t h e significance of i m p r o v e m e n t s in noise levels assessed.
In looking at commonly-used household appliances, one thing which has to be acknowledged is that they can become a daily burden because of the noise they make. In published studies of the noise of domestic appliances, refrigerators normally register the lowest levels in dB(A) and one is tempted to believe that the noise problems associated with these appliances were solved long ago.
through the years, many of the refrigerators and freezers on the market today would undoubtedly have difficulty in meeting even the Danish requirements. For example, a German test report from 1 979 states that only t w o out of fifteen tested refrigerators and freezers had a noise level lower than 35 dB(A).
In Denmark, the authorities permit a maximum of 40 dB(A) in kitchens and 35 dB(A) in living rooms and open kitchens. In Sweden, the corresponding levels are 5 dB(A) lower. Despite improvements The author is from Danfoss Ltd. DK 6430 Nordborg, Denmark. Paper presented at lOth International Congress on Acoustics, Sydney 1980. Paper received 1 June 1981.
358
Noiseless household refrigeration is within reach by using absorption refrigerators, However, the energy crisis renders this solution uneconomical, and we must therefore assume that household refrigeration in the eighties (and even longer) will still be based on compressor-driven refrigerators.
A new compressor generation While much is published, in detail, on noise reduction in hermetic compressors, there is
Revue Internationale du Froid
dB(A)
£^
~
dB(A)
60
50
40
"o . . . . .
3C
O4
= i g
20
O0" - - J Hz
I0:31.5
6.'3
125
?.50
500
I000
200040008000
Hz
Fig. 1 a - S o u n d e m i s s i o n f r o m refrigerators, in a k i t c h e n , u s i n g s t a n d a r d c o m p r e s s o r s ; b - t h e s a m e r e f r i g e r a t o r s as Fig. l a w i t h n e w T L compressors. - a - 1 4 0 I R / F C P W 3 K 6 , b - T L 2.5 A , . a - 140 IR/FC competitor, b - TL3A, --.-- a - 1 60 IR/FC competitor, b - T L 3 A ; - - - a - 2 1 0 IR P W 3 . 5 K 7 b - T L 3 A ; - - - - - a - 210 IR/FC PW 4.5K7. b - TL4A; ...... a - 385 IR/CC, b - TL4A, R - refrigerator, FC - freezer c o m p a r t m e n t , C C - c h i l l e r c o m p a r t m e n t Fig. I a - E m i s s i o n d e b r u i t d e s r # f r i g ~ r a t e u r s clans u n e c u i s i n e , a v e c des c o m p r e s s e u r s h a b i t u e l s , b - les m # m e s r # f r i g # r a t e u r s a v e c d e n o u v e a u x c o m p r e s s e u r s TL. a - 140 IR/FC PW3K6, b - TL2.5A, a - 1 4 0 I R / F C c o m p e t i t o r , b - TL3,4; - - . - - a - 1 6 0 I R / F C competitor, b - TL3A; --- a - 210 IR PW3.5K7 b - TL3A; -----a - 210 IR/FC PW4.5K7. b - TP4A; ...... a - 385 IR/CC, b - TL4A R - r#frig#rateur, FC - c o m p a r t i m e n t cong~lation, CC - c o m p a r t i m e n t r#frig~ration
surprisingly little written about what significance the separate noise reduction steps have had on the final product, ie the refrigerator installed at its point of use.
Some years ago, experiments were carried out to investigate how factors like compressor vibration, gas pulsation and airborne noise affects the noise level of a refrigerator. These investigations showed that it is important to hold airborne noise from the compressor at a low level, but with modern lightweight refrigerator and freezer construction it is also vital to reduce gas pulsation in the discharge tube and reduce compressor vibration. The results were combined with existing knowledge to form the basis for a new generation of hermetic compressors. In tests involving ten medium-size compressors, the airborne noise (measured in accordance with ISO 3742) showed a relatively modest reduction in the A-weighted sound power level, but a marked decrease in the 2 kHz area. This decrease is due to several factors, the main one being a change in the design of the compressor pot.
Volume 4 Num6ro 6 Novembre 1981
A noticeable reduction of gas pulsation has been achieved by altering the filter characteristic of the discharge muffler. Of special interest here is the frequency range 1 0 0 - 8 0 0 Hz which is the resonance range for tube runs and condenser. The reduction in vibration is a technical milestone in our compressor design and it has been achieved by the simple but especially effective modification and matching of the internal suspension system. In order to assess the significance of the improvements, as regards finished refrigerators and freezers, we carried out noise measurements in our laboratory on six different sizes of refrigerators. Three of the cabinets were tested for customers, while the other three, fitted with older Danfoss compressors type PW, were bought direct from retailers. After noise measurements had been taken, the compressors were replaced with the new TL compressors and noise measurements were taken again. For a 'standard' kitchen it w o u l d probably be realistic to estimate a room absorption (7,A) of
359
about 1 0 ITI2. As far as the directivity factor (Q) of the refrigerator is concerned (installation against a wall, built-in, or in a corner), or from where noise radiation is greatest, ie, the distance to the "source', a slight problem arises. Since a significant part of the radiation will come from the rear of the cabinet and from its motor conqpartment, measurement in accorda'nce with Danish building regulations (1 m from the cabinet) more or less corresponds, in practice, to a distance from the 'source' of 1.5-2 m. Taking these factors into consideration, we can estimate a noise emission at the point of use of approximately 4 dB lower than the sound power level of the refrigerator. Figs l a and l b show the results for the six cabinets.
Conclusion The result from the use of the new generation of hermetic compressors was a marked reduction of the noise level in household refrigerators and freezers, and thus in the beginning of the eighties it already becomes possible to satisfy even the most strict legislation on noise. Published investigations on new appliances with lower A-weighted sound levels are hard to find. This may indicate that the question concerning noiseless household refrigeration in the eighties can be answered with a yes, and that the last remnants of noise cannot be eliminated by hunting sound levels below 30 dB(A), but rather by looking at the sound character. A fuller version of the article is published in the Danfoss Journal available on request from Danfoss Ltd.
A monthly journal to keep you in touch with developments in the low temperature field. Cryogenics is the international journal of low temperature research and engineering. The subject matter covers the complete field of science below --100°C. This includes low temperature plant technology, cryosurgery, tram suspensions and superconducting motors. Each issue contains specially commissioned review articles and original papers. Complimentary to these are research and technical notes describing preliminary results and details of work in progress, and letters to the editor on areas of discussion and controversy. Other features include reports on conferences, book reviews and a lively news section covering the cryogenics industry. The quality of the editorial is ensured by a distinguished board of international editors. For further details and sample copy contact: Geraldine Hills, IPC Science and Technology Press Ltd, PC) Box 63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH. Tel: 0483 31261
360
International Journal of Refrigeration
of thawing medium (°C), and H is the surface heat transfer coefficient (W m -2 °C-1),
4
The use of the above expression for calculating thawing times will introduce an error of between + 4 % in addition to the prediction error of 4-5% previously mentioned. The formula can be used only for block thicknesses between 13 and 16 cm, thawing medium temperatures between 5 ° and 30°C and surface heat transfer coefficients from 5 to 1000 W m -2 °C -1
5
6 7 8
References 1 2
9
Bialod, D., Jolion, M., LeGoff, R. Microwave thawing of food products using associated surface cooling J Microwave Power 13 3 (1978) 269-274 James,S. J., Bailey, C. Air and vacuum thawing of unwrapped boneless meat blocks Proc Inst Refrig (Session 1979-1980)
Noiseless househ eighties?
10 11
refri
Vanichseni, S. Thawing time of frozen lamb shoulders, Meat Industry ResearchInstitute of New Zealand Report No 233 (1971) Perry, J. H. Chemical Engineers' Handbook 4th Ed McGraw-Hill. New York (1963) Miki, H., Nishimoto J.-I. Fundamental studies on the thawing of frozen fish - 1, Thawing rate of vacuum thawing Mem Fac Fish Kagoshima Un/v 24 (1975) 161-171 Earle, R. L. Physical aspects of the freezing of cartoned meat. Meat Industry ResearchInstitute of New Zealand Bulletin No 2 (1959) Mott, L. F. The prediction of product freezing time Aus Refrig Air Cond H[g 18 2 (1964) 16-18 Dusinberre, G. M. Numerical analysis of heat flow, 1st Ed McGraw-Hill, New York (1949) James, S. J., Creed, P. G., Roberts, T. A. Air thawing of beef quarters J Sci Fd Agric 28 (1977) 1109-1119 Cherneeva, L. I. Study of thermal properties of food. Report of VNIKHI (Scientific Research Institute of the Refrigeration Industry) Moscow (1956) Riedel, L Calorimetric investigations of the meat freezing process. K#ltetechnik9 2 (1957) 38-40. DKV Arbeitsblatt 8-11
ration in the
K. Kjeldsen
Froid m nager sans bruit dans les ann6es 1 980? Le bruit est I'un des probl#mes des r#frig#rateurs
m#nagers. On examine une nouvelle g#n#ration de compresseurs herm#tiques p o u r r#frig#rateurs et /'on #value/'importance des am#liorations du niveau sonore.
Noise is one of t h e problems associated w i t h household refrigerators. A n e w g e n e r a t i o n of h e r m e t i c compressors for refrigerators are
discussed, and t h e significance of i m p r o v e m e n t s in noise levels assessed.
In looking at commonly-used household appliances, one thing which has to be acknowledged is that they can become a daily burden because of the noise they make. In published studies of the noise of domestic appliances, refrigerators normally register the lowest levels in dB(A) and one is tempted to believe that the noise problems associated with these appliances were solved long ago.
through the years, many of the refrigerators and freezers on the market today would undoubtedly have difficulty in meeting even the Danish requirements. For example, a German test report from 1 979 states that only t w o out of fifteen tested refrigerators and freezers had a noise level lower than 35 dB(A).
In Denmark, the authorities permit a maximum of 40 dB(A) in kitchens and 35 dB(A) in living rooms and open kitchens. In Sweden, the corresponding levels are 5 dB(A) lower. Despite improvements The author is from Danfoss Ltd. DK 6430 Nordborg, Denmark. Paper presented at lOth International Congress on Acoustics, Sydney 1980. Paper received 1 June 1981.
358
Noiseless household refrigeration is within reach by using absorption refrigerators, However, the energy crisis renders this solution uneconomical, and we must therefore assume that household refrigeration in the eighties (and even longer) will still be based on compressor-driven refrigerators.
A new compressor generation While much is published, in detail, on noise reduction in hermetic compressors, there is
Revue Internationale du Froid
dB(A)
£^
~
dB(A)
60
50
40
"o . . . . .
3C
O4
= i g
20
O0" - - J Hz
I0:31.5
6.'3
125
?.50
500
I000
200040008000
Hz
Fig. 1 a - S o u n d e m i s s i o n f r o m refrigerators, in a k i t c h e n , u s i n g s t a n d a r d c o m p r e s s o r s ; b - t h e s a m e r e f r i g e r a t o r s as Fig. l a w i t h n e w T L compressors. - a - 1 4 0 I R / F C P W 3 K 6 , b - T L 2.5 A , . a - 140 IR/FC competitor, b - TL3A, --.-- a - 1 60 IR/FC competitor, b - T L 3 A ; - - - a - 2 1 0 IR P W 3 . 5 K 7 b - T L 3 A ; - - - - - a - 210 IR/FC PW 4.5K7. b - TL4A; ...... a - 385 IR/CC, b - TL4A, R - refrigerator, FC - freezer c o m p a r t m e n t , C C - c h i l l e r c o m p a r t m e n t Fig. I a - E m i s s i o n d e b r u i t d e s r # f r i g ~ r a t e u r s clans u n e c u i s i n e , a v e c des c o m p r e s s e u r s h a b i t u e l s , b - les m # m e s r # f r i g # r a t e u r s a v e c d e n o u v e a u x c o m p r e s s e u r s TL. a - 140 IR/FC PW3K6, b - TL2.5A, a - 1 4 0 I R / F C c o m p e t i t o r , b - TL3,4; - - . - - a - 1 6 0 I R / F C competitor, b - TL3A; --- a - 210 IR PW3.5K7 b - TL3A; -----a - 210 IR/FC PW4.5K7. b - TP4A; ...... a - 385 IR/CC, b - TL4A R - r#frig#rateur, FC - c o m p a r t i m e n t cong~lation, CC - c o m p a r t i m e n t r#frig~ration
surprisingly little written about what significance the separate noise reduction steps have had on the final product, ie the refrigerator installed at its point of use.
Some years ago, experiments were carried out to investigate how factors like compressor vibration, gas pulsation and airborne noise affects the noise level of a refrigerator. These investigations showed that it is important to hold airborne noise from the compressor at a low level, but with modern lightweight refrigerator and freezer construction it is also vital to reduce gas pulsation in the discharge tube and reduce compressor vibration. The results were combined with existing knowledge to form the basis for a new generation of hermetic compressors. In tests involving ten medium-size compressors, the airborne noise (measured in accordance with ISO 3742) showed a relatively modest reduction in the A-weighted sound power level, but a marked decrease in the 2 kHz area. This decrease is due to several factors, the main one being a change in the design of the compressor pot.
Volume 4 Num6ro 6 Novembre 1981
A noticeable reduction of gas pulsation has been achieved by altering the filter characteristic of the discharge muffler. Of special interest here is the frequency range 1 0 0 - 8 0 0 Hz which is the resonance range for tube runs and condenser. The reduction in vibration is a technical milestone in our compressor design and it has been achieved by the simple but especially effective modification and matching of the internal suspension system. In order to assess the significance of the improvements, as regards finished refrigerators and freezers, we carried out noise measurements in our laboratory on six different sizes of refrigerators. Three of the cabinets were tested for customers, while the other three, fitted with older Danfoss compressors type PW, were bought direct from retailers. After noise measurements had been taken, the compressors were replaced with the new TL compressors and noise measurements were taken again. For a 'standard' kitchen it w o u l d probably be realistic to estimate a room absorption (7,A) of
359
about 1 0 ITI2. As far as the directivity factor (Q) of the refrigerator is concerned (installation against a wall, built-in, or in a corner), or from where noise radiation is greatest, ie, the distance to the "source', a slight problem arises. Since a significant part of the radiation will come from the rear of the cabinet and from its motor conqpartment, measurement in accorda'nce with Danish building regulations (1 m from the cabinet) more or less corresponds, in practice, to a distance from the 'source' of 1.5-2 m. Taking these factors into consideration, we can estimate a noise emission at the point of use of approximately 4 dB lower than the sound power level of the refrigerator. Figs l a and l b show the results for the six cabinets.
Conclusion The result from the use of the new generation of hermetic compressors was a marked reduction of the noise level in household refrigerators and freezers, and thus in the beginning of the eighties it already becomes possible to satisfy even the most strict legislation on noise. Published investigations on new appliances with lower A-weighted sound levels are hard to find. This may indicate that the question concerning noiseless household refrigeration in the eighties can be answered with a yes, and that the last remnants of noise cannot be eliminated by hunting sound levels below 30 dB(A), but rather by looking at the sound character. A fuller version of the article is published in the Danfoss Journal available on request from Danfoss Ltd.
A monthly journal to keep you in touch with developments in the low temperature field. Cryogenics is the international journal of low temperature research and engineering. The subject matter covers the complete field of science below --100°C. This includes low temperature plant technology, cryosurgery, tram suspensions and superconducting motors. Each issue contains specially commissioned review articles and original papers. Complimentary to these are research and technical notes describing preliminary results and details of work in progress, and letters to the editor on areas of discussion and controversy. Other features include reports on conferences, book reviews and a lively news section covering the cryogenics industry. The quality of the editorial is ensured by a distinguished board of international editors. For further details and sample copy contact: Geraldine Hills, IPC Science and Technology Press Ltd, PC) Box 63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH. Tel: 0483 31261
360
International Journal of Refrigeration