Installation manual
144
5
5 Noise Emissions from Heat Pumps
5.1 Solid-Borne Sound
Indoor installation
Like any boiler, heat pumps should be connected with isolating
fixings. The heat pump should be connected to the heating flow
and return flow with pressure-resistant-, temperature-resistant,
non-ageing, flexible hoses to prevent vibrations being
transmitted.
For reducing the transmission of solid-borne sound, the heat
pump should be set upon the SYL 250 sylomer strips (available
as accessory).
Outdoor installation
Solid-borne sound insulation is only necessary if the heat pump's
foundation is in direct contact with the building. Flexible hoses
facilitate the connection of the heat pump to the heat system and
simultaneously prevent any vibrations from being transmitted.
Fig. 5.1: Example of how a heat pump is integrated when installed outdoors
5.2 Airborne Sound
Every noise source - be it a heat pump, a car or an airplane -
emits a certain amount of sound. Thus, the air surrounding the
source of noise is turned into vibrations and the pressure
spreads out in waves. Once it reaches the human ear, this
pressure wave vibrates the ear drum, which then triggers the act
of hearing.
The sound field dimension serves as a description of this so-
called airborne sound. Two of these are the sound pressure and
the sound power.
Sound power is a theoretical dimension typical for a sound
source. It can be mathematically calculated from measurements.
The sound power consists of the total sound energy radiated in
all directions.
Sound pressure refers to the change in air pressure caused by
the air vibrated by the source of noise. The greater the change in
the air pressure, the louder the noise will be perceived.
Physically speaking, sound is caused by the propagation of
pressure and density fluctuations in a gas, liquid or solid.
Generally, sound is absorbed (i.e. heard) by human beings in the
form of airborne sound as a noise, tone or bang. Pressure
changes in the range between 2*10
-5
Pa to 20 Pa can be
detected by human hearing. These pressure changes
correspond to vibrations with frequencies between 20 Hz and
20kHz and represent the human audible sound or the range of
audibility. The frequencies result in individual tones. Frequencies
that are above of the range of audibility are referred to as
ultrasonic sound, those below as infrasonic sound.
The sound transmissions from noise or other sources of sound
are given or measured in decibels (dB). This is referred to here
as a reference value, in which the value 0dB generally
represents the auditory threshold. A doubling of the sound level,
i.e. by a second source of sound with equal sound transmission,
corresponds to an increase of +3dB. For the average human
sense of hearing, an increase of +10dB is necessary so that a
noise is perceived as twice as loud.
5.2.1 Sound Pressure Level and Sound Power Level
The terms, sound pressure level and sound power level, are
frequently confused and compared with each other. In acoustics,
sound pressure refers to the metrologically calculated level that
is triggered by a sound source at a certain distance. The closer
the sound source, the greater the measured sound pressure
level and vice versa. Thus, the sound pressure level is a
measurable dimension, that is dependent upon distance and
direction; it is, for example a decisive factor for adherence to the
immission standards according to the German government's
Technical Instructions for Noise.
The total air pressure, given off in all directions by a sound
source, is denoted as sound power or as sound power level.
Increasing distance from the sound source causes the sound
power to spread out upon an ever-increasing surface. The value
will remain unchanged as long as the total emitted sound power
is taken into consideration with reference to the enveloping
surface at a specified distance. Because the sound power
emitted in all directions cannot be precisely calculated
metrologically, the sound power must be determined from a
measured sound pressure at a specified distance. Thus, the
sound power level is specific to the source of sound, independent
of distance and direction, and can only be only be determined via
mathematical calculation. Based on the emitted sound power
level, sound sources can be compared with each other.
5.2.2 Emission and Immission
The total sound emitted from a sound source (sound event) is
referred to as acoustic emission. Sound source emissions are
generally denoted as sound power level. The effect of sound
upon a specified location is referred to as acoustic immission.
Acoustic immissions can be measured as the sound pressure
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