Using a conventional chiller to cool a tank is an expensive business. If you have a good quality and convenient supply of water it is much cheaper to let nature help out via evaporation.

Evaporating water takes a lot of energy. The amount of energy required is called latent heat of evaporation, this figure changes with atmospheric pressure (the higher the pressure the harder it is for a molecule of water to break free as vapour). At sea level it takes a whopping 2257 Kj to evaporate one Kg of water, or 970.4 BTU's to evaporate 1lb of water.

The down side is that air can only hold a limited amount of water vapour, so you need a supply of fresh air. You also need a way of removing the warm moisture-laden air out of the house. 

With our system the amount of cooling achieved means the chiller unit only works in very hot and humid weather, when the scope for cooling by evaporation is greatly reduced. To prevent condensation we duct the humid air out under the floor.

Click below for a better quality image

Although using evaporation to achieve the majority of cooling is efficient, the fans required to achieve it are also noisy.  Admittedly no noisier than a chiller unit but still enough to compromise the enjoyment of the surround sound in your favourite film.

To achieve the desired peace and quiet , I looked towards a British company specialising in soundproofing and vibration reduction.  One of their engineers kindly used some of his own time to advice me on producing a quiet tank -  on a budget

Very roughly, sound waves are rapid changes in pressure, transmitted through the air. The rapid variation between high and low pressure causing backward and forward movement i.e vibration of the 'air' molecules.  Other materials in contact with the air will be buffeted by this vibration.  They, in turn, vibrate, transmitting the noise through the material.  Therefore to prevent noise escaping an area you need to provide a very dense barrier in which the molecules are hard to vibrate. In doing so, the noise is not transmitted from one side of the material to the other. A slight complication is that sound also reflects off very dense materials.  To efficiently soundproof you need not only to block the propagation of the sound wave but also absorb it.

I was advised to use a combination of double plasterboard walls, lined inside with rock wool (loft insulation) see cross section diagram below left.  NOTE It is very important to carefully contain the rock wool as it is a nasty irritant, also be careful to wear suitable protective clothing etc when handling it.

 On any sections of soundproofing that  I needed to be able to remove regularly,  I used a tight fitting wooden frame sandwiched with plasterboard with a healthy filling of rock wool,

Click on the diagram below for a better quality image.