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5 Efficiency Standards, Certification and Labelling
360 Refrigeration and Air-Conditioning
chiller, with the load rate and the variation of air or water inlet condenser temperature. It is becoming widely adopted as a criterion for chiller performance
and details can be found on the Eurovent website.
Enhanced capital allowances (ECA) are available for the purchase of products that meet defined efficiency criteria and these are published by the Carbon
Trust on the Energy Technology List (ETL). Refrigeration products include
compressors, condensing units, chillers and cellar cooling equipment. A full
list can be found on the ECA website. A European Eco-Labelling scheme is
being developed for heat pumps, and certain heat pump types are eligible for
purchase grants in the United Kingdom. This is a rapidly changing situation.
30.6 COMMITMENT TO ENERGY SAVINGS
A positive energy policy needs to be a company decision, taken at boardroom
level and backed by boardroom authority, since it cuts across departmental boundaries and may conflict with departmental financial targets. Typical issues are
The capital, operating, maintenance and fuel costs come from four
separate budgets, possibly accounted for by four different managers, so
these budgets need to be coordinated.
Documented system analysis and/or energy metering may be needed to
prove the savings.
There may be some disruption to normal working whilst energy
investment schemes are being investigated and implemented.
Staff may need to be released for training schemes.
The improvements may require changes in operating methods
previously considered as adequate.
It is important to be able to quantify the results of an energy conservation
programme. It is an ongoing process with all concerned alert to the possibilities of further improvements.
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Chapter | Thirty One
Many components used in refrigeration systems are major sources of sound and
these are often located in occupied buildings and offices. Unwanted sound is
noise, and awareness of the potential noise nuisance of equipment is vital, both in
the indoor and outdoor environment. Treatment of the theory of sound is beyond
the scope of this book, but some essential points concerning refrigeration and airconditioning equipment noise and attenuation are provided in this chapter.
31.2 PUBLISHED INFORMATION
All manufacturers publish sound levels for their products and such figures
should be scrutinized and compared as part of a purchasing decision. When
comparing noise levels it is essential to check that the figures are on a likefor-like basis. The main considerations are given below:
Is the noise level a sound power level or sound pressure level?
If sound pressure levels are quoted, what is the distance from the
Are the quoted levels ‘A’ weighted?
Sound power is the rate of sound energy output of a source and its units
are watts. Sound power is an inherent property of the source while sound pressure is also dependent on the surroundings (distance, reflection, absorption,
transmission). Sound pressure is measured directly by a pressure sensitive
microphone sensor; sound power is found from sound intensity measurements –
sound intensity is the amount and direction of flow of acoustic energy per unit
area at a particular location. ‘A’ weighted data is adjusted so that the individual
frequency levels match the sensitivity of the human ear.
31.3 SOME SIMPLE RULES
1. For each doubling of distance from the source there is a 6 dB decrease
of the sound pressure level.
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362 Refrigeration and Air-Conditioning
2. Addition and subtraction of sound levels is logarithmic. The total
combined the sound level (either power or pressure) of two separate
machines having sound levels L1 and L2, when they are working
together is given by:
10 Log(100.1*L1 ϩ 100.1* L 2 ) dB
For the case of two identical machines, the addition of the second
machine increases the sound level by 3 dB and addition of a third
machine would increase the sound level by a total of 4.8 dB.
3. If the source is mounted on a smooth surface, the sound level will be
equivalent to the free field level ϩ 3 dB (see Figure 31.1). In the case
where the source is also close to a wall there will be a 9 dB increase in
the sound level radiated in comparison with the free field case.
L ϩ 3 dB
Figure 31.1 Effect of placing a sound source on a reflective surface (Emerson Climate
31.4 COMPRESSOR NOISE
Each compressor type produces a different type of sound, mainly due to its
operating principle (reciprocating, centrifugal, scroll, etc.) and it will also depend
on its design and manufacturing process. In general:
1. Reciprocating compressors produce more noise in the low frequency
bands than the rotary types.
2. The noise produced by compressor motors is located in the midfrequency bands.
3. The noise in the high frequency bands is due to the gas compression
4. The noise level will be dependent on operating conditions.
In Figure 31.2 the frequency banded noise levels for a typical scroll and semihermetic reciprocating compressor are shown. These are general trends only and
manufacturer’s data should always be consulted for specific information.
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Noise of the motor
Noise of gas
Contact of scroll and mech. noise
Figure 31.2 Comparative sound power levels, dBA, for a typical scroll and semi-hermetic
reciprocating compressor type (Emerson Climate Technologies)
31.5 FAN NOISE
Centrifugal fans produce most of their noise at low frequencies, whereas axial
types generate higher frequency noise. Fans with high tip speeds will generate
noise levels that may require attenuation. The normal treatment of this problem is to fit a lined section of ductwork lined with an absorptive material on
the outlet or on both sides of the fan. Such treatment needs to be selected for
the particular application regarding frequency of the generated noise and the
degree of attenuation required.
31.6 AIR SYSTEM NOISE
All air systems have a noise level made up of the following:
1. Noise of central station machinery transmitted by air, building
conduction, and duct-borne
2. Noise from air flow within ducts
3. Grille outlet noise
The first of these can be reduced by suitable siting of the plantroom, antivibration mounting and possible enclosure of the machinery. Air flow noise is
a function of velocity and smooth flow. High-velocity ducts usually need some
Grille noise will only be serious if long throws are used, or if poor duct
design requires severe throttling on outlet dampers.
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364 Refrigeration and Air-Conditioning
Apart from machinery noise, these noises are mostly ‘white’, i.e. with no
discrete frequencies, and they are comparatively easy to attenuate.
Where machinery of any type is mounted within or close to the conditioned
area, discrete frequencies will be set up and some knowledge of their pattern will
be required before acoustic treatment can be specified. Manufacturers should be
able to supply this basic data and offer technical assistance towards a solution.
Where several units of the same type are mounted within a space, discrete
frequencies will be amplified and ‘beat’ notes may be apparent. Special treatment
is usually called for, in the way of indirect air paths and mass-loaded panels.
Airborne sound is transmitted by way of the air and can be attenuated by the
use of barriers and walls placed physically between the noise and the receiver.
Structure borne sound is generated by vibrations induced in the ground and/or
structure. These vibrations excite walls and slabs in buildings and cause them
to radiate noise. This type of noise cannot be attenuated by barriers, or walls
but requires the interposition of a resilient break between the source and the
receiver. Large pipes, for example, suspended by springs from a ceiling can
considerably reduce structure borne sound and vibration in adjacent rooms.
When airborne noise is generated in a room, by a compressor or another
machine, it can be transferred to adjacent rooms via a number of transmission
paths – walls, floors, doors and the general building structure. The sound insulation performance of a material structure is termed Sound Reduction Index
(SRI) (sometimes called Sound Transmission Loss [dB]). The larger the SRI
is for a partition, the better is the sound insulation. Because the SRI is dependent on frequency, the averaged SRI over a band of frequencies is often used
for evaluating the performance of different materials. In simple one-leaf panels, where both exposed surfaces are rigidly connected, when the weight per
unit area is increased, the SRI is increased. This dependence between the mass
and the SRI is the Mass Law and it is noted that theoretically there is approximately 6 dB SRI increase for each doubling of the panel mass or for each doubling of the frequency. In practice the actual increase rate is about 4 dB. Higher
values of sound insulation can be achieved through the use of double (or more)
leaf panels with a cavity between. To achieve significant low-frequency benefits the cavity width should be at least 150 mm. In the cavity, porous materials
should be hung, for example mineral wool or glass fiber mats. It is noted that
for achieving high efficiency of the total structure, good sealing between the
panel connections is required.
Some compressors can be fitted with sound jackets that considerably reduce
the airborne sound leaving the source.
Sound attenuation is a specialist field, and expert advice may be required in
the case of specific problems.
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Units of Measurement
The SI system is used in this book and numerous reference sources for definitions and conversions are available. Visual conversion illustrations can provide a quick way of relating quantities, and the pressure and energy flow rate
examples shown in Figures A1 and A2 give relationships between commonly
encountered units – the arrow points towards the larger quantity.
Imperial units, previously used in the UK, have now been superceded by
international SI units, but are still used in the USA. These together with some
other idiosyncrasies deserve special mention:
Btu and Btu/h – British Thermal Units are very deeply rooted in the world
of heating and cooling. Data originating in the USA and some parts of Asia
is likely to be expressed in terms of Btu. The rate of thermal energy is Btu/h,
commonly abbreviated verbally as simply ‘Btu’. The Fahrenheit temperature
scale is likely to be used in these situations.
Tons Refrigeration (TR) – Defined as 12 000 Btu/h. Originally one ton-day
was the amount of heat removed to make on US ton (2000 lb) of ice in one day.
12 ϫ 103
Figure A1 Energy flow rate conversion
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Figure A2 Pressure conversion
366 Appendix Units of Measurement
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Units of Measurement 367
HP – Horse Power is a defined rate of thermal energy (746 Watts).
Refrigeration equipment of a specific size can deliver cooling and absorb power
at very different rates depending on refrigerant and operating conditions. This
makes it very difficult to differentiate equipment physical size by, for example,
wattage. Commonly a piece of equipment will be described in terms of HP, for
example, ‘5 hp condensing unit’. This has no quantitative meaning except that
at one time a nominal 5 hp motor would be necessary to drive it, so it gives an
idea of the size.
COP – Coefficient of Performance is the dimensionless ratio of thermal
energy rate and power input rate (mechanical or electrical). The same units are
used for both, normally W or kW. COP may apply to cooling or to heating,
depending on whether a system is delivering useful heat or useful cooling. For
a simple system:
COP (heating) ϭ COP (cooling) ϩ1
Normally it is quite clear from the context which COP is intended, and occasionally suffixes are used, e.g. COPR, COPH.
EER – Energy Efficiency Ratio is the Imperial Units version of COP. It has
the dimensions of Btu/h/W, and is found in US documentation and standards.
Seasonal efficiency (SEER) is a benchmark rating for air conditioners in the
USA. To convert EER to COP it is necessary to divide by 3.412. Somewhat
confusingly, EER is used instead of COP in Europe for some air conditioning units including chillers. Instead of using the normal Btu/h/W definition,
EER for a chiller is defined as kW cooling capacity/kW power input (including fans). Thus the chiller ‘EER’ value is the dimensionless ratio normally
expressed as COP.
Pressure drop, K – Compressor capacity data is given with reference to
evaporating and condensing temperatures (see Section 10.4) and refrigeration
pressure gauges are provided with temperature scales for various refrigerants
(Figure 9.5). Pressure drops in suction and discharge lines are therefore frequently referred to in terms of temperature differences, for example ‘2°C pressure drop’, or more correctly, ‘2 K pressure drop’.
Pressure, bar – Pressure is shown in absolute values unless otherwise stated.
Traditional pressure gauges measure the difference between system pressure
and atmospheric pressure, and it is normal to refer to this reading as bar gauge,
or bar g. The gauge pressure will vary slightly depending on atmospheric conditions and altitude but this is normally ignored and the absolute pressure is
obtained by adding 1.103.
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