The name 'PULSACOIL' is simply a name
invented by the manufacturer Gledhill. It is not entirely clear
where the name originated as there doesn't seem to be anything
pulsing within the unit. One thing is for sure though, when you
open the cupboard and discover a unit with such a grand name you can
be excused for feeling intimidated by it. In fact this can be the
problem when it comes to getting one fixed or replaced - very few
people fully understand quite how this product works! As such, you
are likely to fall prey to the unscrupulous who will often blind you
with 'science' and overcharge
because they can tell you anything they wish. After all, if you don't understand it on what grounds
will you object?
What is a PULSACOIL and how does it
Pulsacoil is a thermal store. To be
more precise, a Pulsacoil is a DIRECT thermal store. A thermal store
(as the name suggests) is a device that stores heat. It generates
thermal energy with electrical heaters that are immersed a store of
water. The store of water is open vented. This is to say it is under
no pressure - at atmospheric pressure (rather like a bucket of water). This is a key feature of a
thermal store. Being at atmospheric pressure it is entirely safe
(unlike unvented devices that can explode if they malfunction and go
'over temperature or pressure'). The clever yet simple thing with a
thermal store is the way it creates high performance hot water for
your domestic use whilst remaining open vented. It does this by
employing a heat exchanger. The heat exchanger enables stored heat
(in the thermal store) to be imparted to mains pressure
cold water as it passes through the unit. This simple process
enables a vented store of hot water to make mains pressure hot
Why bother with a thermal store?
In a nutshell, thermal stores give you
mains pressure hot water safely - because they're vented.
One of the biggest problems when
creating hot water within a dwelling is delivering it at an
acceptable pressure. A typical house with a gravity hot water system
relies on water stored in a header tank (often located in the loft
space) pushing down under the force of gravity to create the
pressure we perceive. The higher the loft tank the greater the
For those who like
a bit more tech info, a 33 foot (10 metre) head of water will
generate 1 bar of pressure.
So if you apply this equation to any
scenario where there is a gravity water system you can begin to
appreciate how poor the water pressure can be. Simply measure the
height differential from the header tank to the outlet
point to appreciate this.
One way to overcome this problem is to
install what is known as an 'unvented hot water cylinder'.
This product is exactly what is claims to be - unvented. It is a
pressure vessel which is directly fed and kept under pressure by the
incoming water main. The contents of the cylinder are heated (either
directly or indirectly) and when you open a tap the contents are
forced out by the pressure of the incoming water - hence, mains
pressure hot water.
Unvented cylinders do however carry
with them an element of risk - the risk of explosion. If an unvented
cylinder goes over temperature or over pressure (or both) the risk
of explosion exists.
This might all sound great, but what
does it actually mean? Have a look at the following clips to
appreciate what an unvented cylinder can do if it goes wrong...
For this reason unvented cylinders are equipped
with pressure release equipment which activates when the internal
pressure exceeds a safe level. The problem is when the PR valve
activates it can release scalding hot steam, so this needs to be
piped to the outside of the building to vent safely into the
atmosphere. The dangers associated with unvented hot water cylinders
are addressed by Building Regulations - Section G3 (In England). A
cylinder that contains in excess of 15 litres of hot water under
pressure is subject to these regulations.
You might begin to appreciate why a
thermal store offers an attractive alternative to an unvented
system. As mentioned, a thermal store is open vented and as such
cannot explode. Therefore, being inherently safe it is not governed
by G3 Regulations as the only hot water under pressure is that
contained within the heat exchanger. This is viewed as a huge
advantage. Mains pressure hot water without any of the liabilities.
Thermal stores do not require an annual service (unlike their
unvented counterpart) making them doubly popular especially with
landlords and do not require a vent pipe as the potential for high
pressure steam simply does not exist (making them a favourite in
buildings with multiple occupation).
Replacing a Pulsacoil
Simple? This rather depends on what
you are replacing. Although Pulsacoil remains simple in principle
the way the unit does its job has changed over the years. This
affects installation requirements if you are replacing an older
The origins of Pulsacoil
Pulsacoil used to be made by the Water
Storage division of Gledhill. A few years ago this division went
into liquidation. Although Gledhill continue to make Pulsacoil they
do so now through their Building Products division. While they have
retained the name and the look the product has changed internally.
The newer model is identified by a BP suffix.
The early model Pulsacoil
(picture right) used to use plate heat
exchanger technology to create mains pressure hot water. This
required a pump to circulate hot water from the store through the
exchanger. Water temperature was regulated by modulating the pump
speed according to feedback from temperature sensors. This function
and others of switching and timing needed control, so a micro
processor circuit board became necessary. On the newer BP model heat
exchange is performed by a different method, one that does not rely
on such complicated control.
The new PULSACOIL BP
The Pulsacoil BP utilises an immersed heat
exchanger (unlike the plate heat exchanger on the earlier type that
was situated within the cabinet but outside the store). This is to say the heat exchanger is immersed within the
hot water in the thermal storage compartment.
How Pulsacoil BP works
Mains pressure cold
water is passed through the immersed heat exchanger, is rapidly heated and exits as hot mains pressure water.
Temperature control is achieved using a thermostatic mixing
valve (TMV) on the outlet that limits the
maximum temperature water can emerge (usually set to approx 55oC).
Simplicity at it's best
Hopefully you can appreciate how simplicity in method requires a
much less complex control. The Pulsacoil BP has been
stripped of all control functions (an important point to consider if
you are replacing an older unit). When you purchase a Pulsacoil
BP your installer must add all necessary controls (such as
Economy 7 and boost switching) externally.
Conclusions about Pulsacoil
A safe vented unit producing mains
pressure hot water must be considered a good thing. Pulsacoil is
presented in a smart little cabinet (looking a bit like a filing
cabinet) which is pleasant in appearance. No requirement for a high
pressure vent pipe to atmosphere makes them simpler to install and
less obtrusive. However, since it's conception it has been
substantially simplified placing the newest 'BP' model in direct
competition with other 'Thermal Stores'.
Pulsacoil is now just a thermal store
in a steel cabinet. The cabinet only performs an aesthetic function
and the internals only do what all other direct thermal stores do
(vented, 2 heaters, cold in, hot out). All the
clever more useful bits such as switching, timing and the higher
performance plate heat exchanger technology have gone (see picture
right). Keeping something simple is however arguably better as the more complex something is the more prone to
breakdown it becomes. The loss of complicated electronics and
controls that can be costly to repair is no great shame.
The bare truth remains that the Pulsacoil is
now nothing out of the ordinary - just a thermal store. Whether you
are replacing an older unit or installing new, you will need to add
external control gear - just like with any other thermal store.
You might also consider maintenance
before making your decision. For example, immersion heaters for the
Pulsacoil cost in excess of £50 each to buy. The equivalent
replacement heater for other makes costs £44 (prices at Summer 2012)
and they perform exactly the same function. Hummm!
Lastly, there is a matter of
availability. Pulsacoil can be difficult to obtain quickly. Lead
times frequently range up to 3 or 4 weeks. When you or your tenants
have no hot water this borders on ridiculous. 3 to 4 weeks without
hot water is not only mind blowing to contemplate in this day and age
but might meet with an angry response!
Alternatives to Pulsacoil
As mentioned, the new Pulsacoil BP is
just a thermal store in a metal box. Hopefully the above information
will have helped to dispel the mystique surrounding the product
which in effect leaves you free to make your own choice.
Thermal stores are readily available
from numerous manufacturers. Indeed, Gledhill are prolific in the
manufacture of thermal stores but they attach wonderful names to
their products which serves to protect the true function of a unit
unless you're 'in the know', such as
Torrent Multifuel - both
However, now you have been enlightened
your new found understanding means you are no longer shackled to a product name
simply because you or your plumber didn't know what it did.
If you need an alternative to
Pulsacoil (for whatever reason) you can
begin your search here.
Pictured right you will see what a thermal store looks like without
a cabinet. The one in the image is a 'combination' version (meaning
the F&E tank [needed for all thermal stores to work] is incorporated on the top but there are
normal 'cylinder types' available too (that require a remote F&E tank). These
are quality thermal
stores configured in the same way as a Pulsacoil BP, they just
So, when it comes to making a decision
check out the lead time first. A sudden lack of hot water
and a lead time of many days can often be unacceptable.
It has been our objective to explain:
what a Pulsacoil is
what function it performs
how it performs said function
the advantage of a thermal store
the difference between new and
older models of Pulsacoil
considerations when installing or
alternative product advice
We sincerely hope we have succeeded by
providing you with clear and objective information. This document
has been produced to help you (the end user or installer) make an
educated decision based on understanding.
You are always welcome to call our office for
more advice if you would rather discuss your requirement further.
If PULSACOIL BP is the product
for you please click here to
go straight to the appropriate product section.
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