Liquid Thermal Mass

We saw in the previous page about Thermal Mass that water has a volumetric heat capacity more than twice that of concrete, three times that of bricks and readily absorbs and releases its heat to the surrounding atmosphere. So we can absorb either twice as much heat as in the same volume of concrete or the same amount in only half the volume.

There are a number of examples of water tanks being built into interiors of homes to act as a buffer to the daily swings in temperature and this is certainly an easy way to create varying quantities of thermal mass into houses without the need to transport large quantities of heavy weight materials to site and pay for placement and installation.

Add to this the fact that it can be easily moved around in systems that are well understood and readily available and that, due to the thermosiphon effect of hot liquids rising, it can even provide/remove heat from our interior environment without the use of electrical energy.

We already see this type of system in solar hot water collectors with linked tanks. Where space is available on sloping sites collector panels can be mounted at low level with insulated pipe work supplying hot water to a system inside the house for overnight warmth.

In summer, simply reversing the flow at night will cause flushing of the heat through the radiant panels open to the night sky, cooling the liquid thermal mass ready for the next day’s heat build up and reducing the temperature in the interior.

This can be improved where a below ground water source (Bore or well) is available to provide a heat sink and simply cycling the thermal mass water through a closed loop pipe system immersed in the ground water in a similar but more effective way as is used in ground source heat pumps. With thermal mass in large quantities high temperature differences are not required when linked to efficient levels of insulation in the exterior envelope of the home.