Noise protection and heat recovery in one concept

At a small hospital in France, we installed a sound bonnet for a recooler used to cool the operating theatre and computer tomographs.

The acoustic bonnet was required to reduce the noise emissions from the recooler to the bed wing. The recooler moves 28,000 m3/h at full load. The recooler was installed directly adjacent to the plant room on the ground floor. Among other things, 6 heat pump boilers, each with a capacity of 500 litres, are installed in the plant room. The plant room is not heated.
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The idea quickly arose to use some of the warm exhaust air from the recooler to raise the temperature in the plant room and thus supply the 3,000 litres of service water.

As the heat pump boilers use the ambient air, a thermally insulated duct with adjustable louvres was installed directly on the exhaust air side of the acoustic bonnet in order to channel some of the warm exhaust air into the plant room.

The free cross-section, which is 1.94 m2 when the louvres are fully open, is designed for full-load operation of the refrigeration system of 28,000 m3/h at an air speed of 4 metres/sec. The position of the louvres is controlled by a pressure and temperature sensor. The louvre position can thus be positioned between 0° and 90°.

This reduces the Delta-T for the domestic hot water treatment and achieves a temperature lift of the domestic hot water. Around 1,000 m3/h of air volume is required per heat pump boiler at full load. At full load, the 6 heat pump boilers that provide the service water for the overhead laundry room, sterilisation and kitchen have a total air volume of 6,000 m3/h.

To remove the cold exhaust air from the room, a thermally insulated duct with a cross-section of 0.417 m2 was installed, which was connected directly to the exhaust air outlets of the heat pump boilers. This means that all the exhaust air is discharged to the outside. At full load of the 6 heat pump boilers, we have a maximum air velocity of 4 metres/sec in the duct.

A load profile measurement, which we will now carry out over the next 12 months, shows how much electricity can be saved in the domestic hot water treatment with this concept.

In addition to the noise reduction of the recooler, it has already been achieved that negative pressure and room cooling no longer occur in the plant room when the heat pump boilers are in operation.

The following advantages were utilised in this project. Installation of the recooler directly at the smallest possible distance from the plant room and the fact that the heat pump boilers were already in place. 

Image Legend
1) Heat pump boiler 2) Air inlet duct 3) Water pipe 4) Exhaust air duct 5) Consumer (washing machine etc...) 6) Recooler acoustic bonnet 7) Cold air inlet 8) Hot air recooler 9) Service access in the acoustic bonnet to the recooler