The Gledhill Pulsacoil BP is the simplest form of Thermal Store and the easiest for a layman to understand. Thermal stores are also known as Heatbanks or Energy Stores.

The cylinder is filled with water through the expansion tank. The body of water in the cylinder never changes.

The water in the cylinder is electrically

heated by one or both of the elements.

 

On demand (when a tap is opened), water passes through the coil (surrounded by hot water) and is heated on its way to the tap.

Water in the cylinder is stored at a higher temperature than normal.

A blending valve is used to regulate the

water temperature from the Pulsacoil.

The problem with this early system was limescale deposits in the coil (heat exchanger) in hard water areas e.g.London.

This led to a series of design changes from the Original Pulsacoil.......

Pulsacoil BP,  Pulsacoil 3,  Pulsacoil 2000,  Pulsacoil A Class through to the current Pulscoil Eco.

This diagram is the simplest illustration of the thermal store principle.

Pulsacoil IIIs were fitted with  float valves. This was supposed to eradicate the need for manual top up.

Bad idea, especially when the copper expansion tank was attached to the hot cylinder below.

Float valves on toilets etc are exercised/used every day during normal use. As the Pulsacoil cylinder only loses water due to evaporation the float valve never moved and when it as called upon to work it was stuck.

You can always put a float valve on a remote fill/expansion tank but then you need an overflow.

Gledhill now market this as an advantage with the Pulsacoil, to architects and developers.

You do not need an overflow or relief pipework. Hence cylinder location is more flexible.

The clear alternative to the Pulsacoil for a an electrically heated, mains pressure, hot water system, is a pressurised unvented system, generically known as the Megaflo, who are the brand leaders.

From a developers point of view a, Megflo requires relief pipework, more consideration is required as to location of the cylinder and the installers need  G3 certification..

When we are called upon to replace a Pulsacoil with a newer or larger version, we are often asked if there is an alternative. Because the Pulsacoil is usually centrally located and there is no relief pipework another thermal store is the only realistic choice. The Gledhill Pulsacoil is the leading model of thermal stores.

As above, the problem with the internal coil/heat exchanger was internal scaling of the pipework.

Limescale deposits out of cold water around 60 deg C. Which is why it is always the hot tap which 

scales and starts dripping first in a hard water area.

With the Pulsacoil the internal water is stored at 73 degs C.

Every time hot water is used, at the tap or shower, newly introduced cold water (with dissolved calcium carbonate) sits in the coil at 73 degs C, just depositing more scale.

This only applies to hard water areas but, realistically, this model was never fit for use in London.

The Gledhill Pulsacoil III looked a bit odd. Customers used to describe it as looking like a Dalek. Last made in the 1990s there are very few left in operation now. To overcome the scaling problem, the Pulsacoil became much more complicated. A laminated stainless steel plate heat exchanger was fitted externally to the stored hot water. 

For a plate heat exchanger to transfer heat quickly enough, to the incoming cold water, a circulation pump is required. As you need a pump anyway, for a decent heat transfer rate, perhaps you could regulate the water temperature by varying the speed of the pump. Indeed you can but apparently Gledhill were not sure so they left a blender valve and flow switch in as well.

To vary the pump speed, a PCB and series of sensors was required. A trigger sensor (and flow switch) first recognised hot water demand and kicked the pump in at full speed. A further sensor monitored the temperature of hot water to the taps and adjusted the pump speed, and water temperature, by varying the voltage to the pump.

The Gledhill Pulsacoil 2000 was the next Pusacoil model. Introduced around 1999/2000. By now Gledhill were confident that that pump speed regulation system worked and could be used to control the hot water outlet temperature alone. The blender valve and flow switch of the Pulsacoil III were removed from the system. They were a bit slow off the mark and the original models used element thermostats which did not have integral overheat stats. A separate overheat stat was used to prevent boiling in the event of element stat failure. Gledhill later introduced a thermostat upgrade kit for the Pulsacoil 2000.

The cylinder itself had bonded foam insulation instead of the fibreglass used on the Pulsacoil III. The external cabinet was redesigned to a cuboid shape 

Better insulation. Different pump speed control board and the introduction of a true modulating pump. The sensors used on both the Pulsacoil III and Pulscoil 2000 were replaced with a newer more sensitive versions.

Power switching relays system was upgraded

And Pulsacoil Eco Stainless were introduced in 2014/2015.  Stainless steel cylinders instead of copper. Higher efficiency components. The elements are always 3 kilowatts so control component cost savings are negligible. These models

can be heated from a normal heating boiler source if so required. The latest Pulsacoil Stainless model has a different appearance as Gledhill have abandoned the cuboid cabinet and reverted to a cylindrical design.

We can diagnose and repair all Pulsacoil Faults

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