WATER HEATING THERMAL STORAGE
The amount of heat that can be exchanged from the store into the potable water will be limited by the heat transfer effectiveness of the coil running through the centre
year, but systems that attracted a RHPP will be eligible for continuing payments based on the measured heat produced when the RHI is introduced this autumn as part of the expected rollout of the government’s Green Deal.
Whatever the motivation for using a
low carbon source for heating hot water – financial or environmental – the success of the systems will be dependent on being able to efficiently utilise the hot water. As testifed by the plethora of exhibits at last month’s Ecobuild exhibition in London, many of the major manufacturers who have previously been recognised for traditional water heating have developed integrated systems that can accept other heat sources (frequently solar thermal). An effective store should: lHave a high thermal capacity – as water has a reasonably high specific heat capacity and is the most common storage medium;
l Effectively transfer heat between the primary and secondary systems – this will often include enhanced heat transfer surfaces on coils and externally attached high efficiency plate heat exchangers;
Baxi_CIBSE_BCDRange_half DPS_April2012 14/3/12 09:12 Page 1
lMaintain stratified temperatures – allowing proper discrimination in the
temperature differences between the store and the primary and secondary thermal loops. In practical terms, this leads to taller, narrower storage vessels. Some vessels incorporate devices to assist in the stratification process. The high temperature water is drawn off at the top of the vessel to supply the hot water load, and the cold feed water enters at the bottom;
l Be able to operate safely at system pressures – whether vented or unvented the vessel must withstand the pressure exerted by the head of water above the vessel or the mains/pumped inlet pressure; and
lMinimise losses – this will be both thermal losses (requiring effective insulation and smallest external surface area) and loss of water pressure in the primary and secondary circuits. The requirements of stratification mean that there is a compromise between minimising heat loss surface and having a tall narrow vessel.
Stores may be used with bivalent (two energy source) systems such as in Figure 1 and Figure 2. These typically employ a hot water cylinder that, through the primary
A single The UK’s most comprehensive range of Condensing Boil Sirius FS SiriusWH range Eurocondense three Paramount three Baxi Commercial Division.
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