Indirect Hot Water Cylinders ~ these cylinders are a form of heat
exchanger where the primary circuit of hot water from the boiler
flows through a coil or annulus within the storage vessel and
transfers the heat to the water stored within. An alternative hot
water cylinder for small installations is the single feed or `Primatic'
cylinder which is self venting and relies on two air locks to
separate the primary water from the secondary water. This form
of cylinder is connected to pipework in the same manner as for a
direct system (see page 771) and therefore gives savings in both
pipework and fittings. Indirect cylinders usually conform to the
recommendations of BS 417-2 (galvanised mild steel) or BS 1566-1
(copper). Primatic or single feed cylinders to BS 1566-2 (copper).Primatic Cylinders ~
1. Cylinder is filled in the normal way and the primary system is
filled via the heat exchanger, as the initial filling continues air
locks are formed in the upper and lower chambers of the
heat exchanger and in the vent pipe.- The two air locks in the heat exchanger are permanently
maintained and are self-recuperating in operation. These air
locks isolate the primary water from the secondary water
almost as effectively as a mechanical barrier. - The expansion volume of total primary water at a flow
temperature of 82 °C is approximately 1/25 and is
accommodated in the upper expansion chamber by displacing
air into the lower chamber; upon contraction reverse occurs.
Indirect Hot Water Cylinders