Heat Pump Design Principles & Sound Levels

Carlyle Environmental Ltd
System Principles

The decentralised approach
Nearly all central HVAC systems have poor part-load efficiencies.

At design load conditions, the best central systems operate magnificently, but during most of the annual operating hours, they consume a disproportionate amount of energy, maintaining a holding pattern, contributing very little energy to actual building heating or cooling.

The desirability of having heating or cooling available in any room, at any time, is obvious, but most central systems fill this need with “energy bucking” approaches, which divide the air conditioning medium (air or water) in two; part is overheated and part is overcooled.

The medium is delivered to the space, mixing the hot and cold quantities as required to maintain the desired space temperatures.

A terminal unit in each zone or room provides inherent energy conservation. Each unit heats or cools as required, whenever desired, only to the extent necessary, thus allowing the realisation of diversity in heating, cooling and electrical use.

The second major step is to make the terminal units water source heat pumps, and interconnect them with a closed water loop. This allows transfer of energy from satisfied spaces in the building to areas lacking sufficient energy.

The closed water loop permits efficient energy transfer (there is probably no less efficient method of transferring energy over long distances than using air as a heat transfer medium).

System Description
This decentralised, year-round heating and cooling system consists of a two-pipe closed loop water circuit, through which non-refrigerated water circulates continuously throughout the building.

A supplemental central heat source adding heat to the loop at the lower end of the range and heat rejecter equipment capable of removing heat at the high end of the range maintains the loop water temperature throughout the year in an approximate range of (20º to 45ºC).

Filled with water, this circuit provides both a “sink” and “source” of energy.

These systems achieve energy conservation by pumping heat from warm to cold spaces whenever they coexist anywhere within the building.

Since the temperature of the water circulating is close to the room ambient temperature, all the internal pipework does not require thermal insulation.

On demand for heating a space, the conditioner will absorb heat from the loop circuit, whereas on demand for cooling a space, the conditioner will reject heat to the loop circuit.

The system provides the essential benefit of decentralised and individual choice of heating or cooling. The occupant may select heating or cooling or may shut off the conditioner serving an individual space without affecting conditions maintained in other spaces. The occupant may realise this freedom at any time of the day or year.

Sound Levels
A very important issue in the design of air conditioning systems is the sound levels that can be achieved in the treated areas. The Carlyle Environmental range of Heat Pumps have very low sound levels and for the wall/floor mounted models up to and including 2.5kW total cooling these are probably the lowest of all available W.S.H.P.s.

The Sound Power spectra for ARO wall/floor models are reproduced below:-

The importance of low sound levels for hotel applications is paramount. The Hotel Series of W.S.H.P.s are specially treated to achieve even lower sound levels as shown in the table opposite:-

Sound Power Levels
Console Models (reference 10-12 Watt).

The values indicated are levels of acoustic power generated by the machine.
 


Water Source Heat Pumps [WSHP] are not manufactured as calibrated sources. Variations will occur within manufacturing tolerances. The level of acoustic power is the preferred criterion, if measurements are taken in ideal conditions.

Conversion from power level to pressure level. [SWL to SPL]

The difference between Sound Power Level and Sound Pressure level is a function of the sound absorption in the room and the distance from the sound source.

SWL - Room Effect = SPL



Sound Power Levels
Hotel Series

Sound Power Levels calculated from Sound Pressure Levels measured in situ in the Bedroom, with the microphone in the centre of the room at the head of the bed.




Further Information
Further information and technical assistance may be obtained from the sales/technical team at Carlyle Environmental, see details below.




Carlyle Environmental Ltd
15 Little Orchard
Carlton Road
Headley Down
Hampshire
GU35 8JW

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