A major consideration when it comes to domestic or commercial heat pump technology is the noise level. As with many domestic or commercial heating and hot water installations, regional noise limitations and regulations can be a key design consideration.
In this blog, we will investigate the sound levels or decibel (Db) levels of modern heat pump technology whether used for central heating or hot water and how their inherent technology and performance affects the overall sound output of your commercial heating project.
We will explore the common factors that impact noise levels, these include the size or kW of the air source heat pump, ground source heat pump, or water source heat pump, the compressor technology used inside the different types of heat pump, and other environmental factors affecting the level of noise.
Understanding noise levels in heat pumps
An increasingly important area of renewable energy system design is the noise levels of heat pumps. There are multiple noise control regulations across the UK including the Environmental Protection Act 1990, and The Noise Act 1996, all of which can result in domestic or commercial noisy heat pumps being investigated or requiring planning permission. There are also multiple localised noise level control regulations run by local government that are designed to limit noise and ensure the installation of the quietest heat pumps.
This means that many air source or ground source heat pump installation projects are required to meet permissible noise levels to be considered. The noise performance of ground source or air source outdoor units can vary significantly. For instance, a quiet external unit such as a low kW modern domestic air source outdoor unit will operate around 50 dB, which is similar to a refrigerator. In contrast, an older outdoor unit can exceed 70 dB, similar to a vacuum cleaner whirring sound.
Air source heat pump sound is measured in decibels. This is a scale that is logarithmic, which means that every rise of 10 dB signifies a tenfold raise in sound intensity. Therefore, an outdoor unit that can operate at around 60 dB produces ten times more sound energy than an air source heat pump operating at 50 dB.
It is also important to understand the difference between sound pressure and sound power, as manufacturers' noise limit declarations can often refer to one or the other.
So, sound power (SWL): the official definition of sound power is the total acoustic energy discharged by a source of noise per unit of time. Importantly, sound power is an inherent property of the source of the sound – it doesn't vary with the constant of distance.
The measurement method for sound power is in watts (W) expressed in decibels (dB) relative to a reference power level. This means that a good way to think about sound power is like the power of a warm air heater. The warm air heater's power output is constant, regardless of where you are in the room.
Sound pressure on the other hand, the official definition is the deviation in air pressure triggered by a sound wave at a specific location. Therefore, sound pressure factors in environmental details such as distance from the sound source, room size, and sound reflections.
The measurement methodology is somewhat different to sound power as it is measured in pascals (Pa) and stated in decibels (dB) relative to a reference pressure level. An explanatory example of sound pressure could be described as similar to the temperature you feel from the previously discussed warm air heater i.e. the nearer you are to the heat source, the warmer you feel. Conversely, sound pressure also reduces the further the source is from you.
To summarise, sound power is basically a fixed property of the sound generating source, sound pressure differs with environmental aspects such as distance and sound reflection surfaces such as a wall. The decibel level you hear is established by the SPL (sound pressure level) at your given location.
At Rinnai, we have a team of dedicated engineers ready to answer any of your questions regarding heat pump design and features. Simply drop us an email or ask us a question today.
Factors contributing heat pump noise
Numerous factors contribute to the noise levels created by domestic or commercial heat pumps. One significant reason is the compressor technology used within these greener heating systems.
There are two main designs of heat pump compressors: the scroll type and the reciprocating type. Scroll compressors minimise vibration which tends to make them inherently quieter – these differ from reciprocating compressors which can make more noise because of their mechanical action.
Another factor is the size in terms of kW and the chosen location of the heat pump installation. For example, a commercial heat pump that is incorrectly specified for a project in terms of the kW rating being too large or too small for the load requirement may find itself working harder than necessary and therefore subsequently making more noise.
Other factors such as how the heat pump technology is installed can affect sound levels; for instance, a heat pump can vibrate against the surface, which subsequently amplifies the noise.
Misconceptions about heat pump noise
Advancements in heat pump technology have led to the development of quieter options including ultra-quiet heat pumps. As mentioned previously, many modern heat pumps are designed with noise-reduction features like noise insulated compressor compartments, in-built or ancillary vibration-dampening mounts, or advanced blades for the unit fans which minimise sound output on these quieter units.
Another misconception is that heat pumps are only noisy when they are in operation. In reality, noise levels can vary depending on the mode of operation. An example of this is when the defrost cycle is running, heat pumps may produce more sound as they work to remove ice build-up.
Finally, it is a common misconception that the size of the unit directly correlates with its noise output. Larger units can create noise due to their increased capacity and power, but the statement is not universally correct. The technology deployed and system specification and design of the heat pump is a significant contributor in determining sound levels.
Measuring and comparing heat pump sound levels
Most - if not all - manufacturers will provide the sound ratings of their heat pumps in decibels (dB). These can usually be found within the manuals or on product specification sheets, and technical submittal documents. It is important when evaluating the declared noise levels that close attention is paid to the operating conditions at which the noise level has been measured. The reason for this is because sound measurements can differ between various operational modes like heating or cooling.
Silent heat pump models and their features
In recent years, manufacturers have invested in the development of silent or super silenced heat pump models. To find out more about the Rinnai super silence models, ask us a question at help me choose a product.
The silenced heat pumps use design features that significantly reduce sound levels. For instance, the use of variable-speed compressors is common; this technology adjusts the operation based on heating or even cooling demand, this results in quieter performance compared to more traditional fixed-speed models.
A common feature that contributes to reduced noise is sound insulation. Many modern heat pumps come equipped with or have optional extras of sound-dampening materials within their casing, this absorbs the sound vibrations and support minimising external noise.
Advances in fan design and the housing also plays a significant role in noise level reduction. Blades engineered for efficiency can operate at lower speeds while still moving the required volume of air. The fan design consideration means efficiencies and are maintained whilst noise is reduced.
It is paramount when considering silent heat pump models to pay attention to the decibel ratings provided in manufacturers' specification sheets and technical submittal documentation.
Conclusion and final thoughts on heat pump sound levels
In conclusion, understanding heat pump sound levels is a crucial aspect for designers and specifiers. A vital part of any project will be paying close attention to localised noise restriction regulations and designing the heat pump system to suit these requirements. The advancements in commercial and domestic heat pump technology have led to the development of quieter, silenced and super silenced models that can support even the most restrictive local or nation noise reduction policy. Vital factors to be considered include features such as compressor type, size, installation and heat pump placement, and environmental conditions and sound reflection.
For design support with your next heat pump project, email us today at our contact us page.
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