Why the
Xcel beats all Competition...
1. Xcel uses a
Plate Heat Exchanger for Hot Water rather than a Coil.
This gives a huge
performance benefit to the Xcel. The following graph shows the
output of a Heat Bank compared to a a well known make of coil type
thermal store. The graph details the temperature of water provided over
time, with taps running at 18 litres per minute (a good bath tap).
The graph demonstrated two
key differences between plate heat exchangers and coils.
The first is how the output temperature from a coil type thermal store
drops with time as the thermal store cools down. From the graph,
within 5 minutes draw off the temperature of water produced becomes too
cold to drive hot taps. Given that the draw off rate is 18 litres
per minute, the coil delivers approximately 90 litres before
performance drops off.
By comparison, the Heat Bank
draws water from the top of the store, returning it cold to the bottom,
and hot water temperatures are maintained until nearly all the stored
heat is used up. The result is 200 litres of hot water - over
twice as much - from the same size 180 litre store.
The performance of hot water
coils is usually quoted for the initial draw off, when the store is at
full temperature, and it is important to know that this is not the
whole picture.
The situation gets even
worst when the store is only partially heated. For example, if
only the top half of the store is heated, then with a coil type store
only some of the coil is sitting is hot water and performance will be
much lower than quoted. The Heat Bank however will give full
performance with only the very top of the store heated, and as such
allows it to operate in an economy mode with only smaller volumes
heated up. This is very noticeable when starting a system from
cold. The Heat Bank will generate hot water to taps in only a few
minutes from cold start, where a coil type store will take some time
while the majority of the store is heated up.
Coils also have another
disadvantage - they scale up. We pioneered coil type thermal
stores some 30 years ago, and have a great deal of experience with
them. One thing we found was that in hard water areas the coils scaled
up rapidly, becoming unusable within a year in some instances.
This is a result of the fact that the coil is sitting in hot water and
the mains water inside the coil heats up to store temperatures. At
these temperature limescale rapidly deposits and if not serviced in
time will result in the coil becoming unusable and the cylinder may
need changing (there are a few sites where coil type stores have failed
this way and the entire site has had units changes to Heat Banks).
On a Heat Bank the heat
exchanger sits externally to the store and is not submerged in hot
water. It is still possible for a plate heat exchanger to scale
up, but it is far more gradual and easy to service. There have only
ever been a handful of instances where plate heat exchangers have been
left to the point where limescale became a real issue. Most were solved
with a powerflush, and in the couple of occasions where this did not
work the heat exchanger was replaced.
Another advantage of plate
heat exchangers over coils is the power of them to generate hot water.
The standard heat exchanger on the Xcel is capable of generating over
100kW of mains hot water, or over 40 litres per minute, and at
pressures up to 10 bar. In order to get anywhere near the
performance of a plate heat exchanger, a coil size needs to be so large
that the cylinder itself usually needs reinforcing to carry the weight
of the coil. There are also options for over 300kW plate heat
exchangers, achieving levels of performance beyond the reach of any
coil.
This leads onto one more
disadvantages of coils - decent performance coils are sometimes easily
damaged in transit due to their sheer weight,
In summary therefore:
- Plate heat
exchangers can produce approximately twice as much hot water from the
same size store fitted with a hot water coil.
- Plate heat
exchangers can generate higher flow rates at higher pressures,
- Plate heat
exchangers function to full performance with only small volumes of the
store heated, allowing the use of an economy mode, and providing hot
water within minutes of a cold startup.
- Coil type stores
suffer badly from limescale depositing within the coil.
2. Patented
Top-Down Reheating of Stored Water.
When using a boiler to
reheat stored water, Xcel Heat Banks offer advantages that NO other
thermal store provides. We spend a number of years perfecting our
patented top-down reheat system that uses a return temperature control
to ensure that the water fed to the boiler for heating is always at the
perfect temperature to ensure optimum efficiency, and in turn
guarantee that the water fed into the top of the Heat Bank is at a
temperature that can be used immediately.
Other makes of thermal store
use a simple flow and return pipework to boiler, where water is pumped
from the bottom of the thermal store to the boiler and back. The
problem with this system is that the temperature of water in the bottom
of the thermal store varies greatly, from 25°C up to 70°C, and a boiler
will only lift water temperature 20°C in a single pass, typically
15°C. If the water in the store is at 55°C, then the boiler will
heat it to 70°C - fine. The problems start happening when the
bottom of the store drops to say 35°C. At this point the boiler will
heat the water up to 50°C, and this is too cold for achieve decent
performance. This 50°C water is fed back into the thermal store,
and can adversely affect the performance of hot water outlets currently
running, as upper store temperature start dropping.
To look at the problem with
other stores from another angle, look at a thermal store as it is
heated from cold (25°). On the first pass the boiler raises the
store temperature from 25 to 40°C. It has to heat up the whole
store so this takes some time (15 minutes for a 300 litre store running
of a 20kW boiler). The boiler then has to heat the store from 40
to 55°C, and again this takes another 15 minutes. Once the store
is at 55°C it should be possible to achieve low flow rates to taps,
although to achieve stated performance you still need to wait even
longer as the boiler heats the store from 55 to 70°C.
With the Xcel, as soon as
the system is started water is recirculated around the boiler until it
reaches 70°C. This usually takes less than a minute, and then the
system feeds the 70°C into the very top of the Heat Bank where it can
be used immediately for hot water. Most customers have great
pleasure in pointing out how they manage to obtain showers within
minutes of starting the system up - a big difference from their
previous systems where they had to wait over half an hour for any hot
water.
The benefits of this type of
reheating are multiple. If, for example, the aim of reheating is
to run a shower or wash up some dishes, then there is no need to reheat
anything more than the very top of the thermal store. As just
described, when using other thermal stores one will need to heat up the
entire store just to obtain a few litres of hot water. This is
very inefficient, especially where there are renewable heat sources
such as solar in the picture. The Xcel top-down reheating allows the
user to only heat up the water they need, and no more. This saves
time and money, and also ensures that there is enough cold water in the
store for the solar panels or wood burner to work with.
These benefits make it
possible to fit quite a large store into a property to allow for a
'full house' without loosing efficiency when there is only one or two
people living there. The amount of water heated can be adjusted to
match the occupancy level of the property, and this is a benefit unique
to the Xcel Heat Bank.
- Rapid reheating
using the full output of the boiler.
- The ability to
easily set how much stored water is heated, and how much water is left
unheated for use with renewables such as solar.
- Lower standing
heat losses as minimal volumes of water are heated.
- Maintains
condensing mode on condensing boilers, while stopping boiler rot in oil
and pellet boilers.
- Maintains
temperature differential across boiler.
- Automated
control of economy/full store modes using programmer and two or more
cylinder thermostats.
- Patented
technology.
3. Patented
Overheat Protection
 Another
unique aspect of the Xcel Heat Bank (again, patented by us so
unavailable anywhere else) is its ability to protect from overheating,
even during a power cut.
This system was designed
primarily for systems connected to a wood burner. It is needed
because wood burners provide a large amount of energy, and they don't
turn off, even when there is a power cut. As such they easily
have the ability to boil the water in a thermal store if there is no
other form of protection.
The standard approach is to
use a heat leak radiator - located higher than the wood burner so that
heat generated in the wood burner circulates naturally (thermo-syphon)
to the radiator where heat is dissipated and the cooled water drops
back into the wood burner. This is fine providing:
- The wood burner is
thermostatic, and slows its burn rate down when it gets hot.
- The heat leak radiator is
large enough to dump the output of the wood burner.
- A location can be found
above the wood burner for a dedicated heat leak radiator.
The problems start occurring
when not all of these criteria can be met, and given that most wood
burners are not thermostatic and have an output of approx 9kW to water,
the chances of dedicating 9kW of radiators (three large double
convectors) to this function becomes impossible.
The protection system on the
Xcel works on the basis that the heat can circulate from the wood
burner to the Heat Bank naturally using thermo-syphon (gravity)
circulation. The Xcel is fitted with a heat exchanger in the top, and
if the temperature of the water in the store ever goes over 95°C then a
mechanical valve opens up to allow cold mains water to pass through the
heat exchanger and out to drain, cooling down the stored water as it
does so. The heat exchanger can extract over 12kW of heat and as
such is suitable for all types of wood burner, and in many instances is
the only way that the latest building regulations (now covering vented
systems) can me met when using a wood burner.
When someone is designing a
system for you to run with a wood burner, ask them to guarantee that
the system will not boil if there is a power cut and the wood burner is
kept going at full output. Some installers may state that it is
ok to get away with a fairly small heat leak radiators, but they are
often not taking into account changes in building regulations that now
cover vented systems.
There is a reason why the
Xcel Heat Bank is the only system that all well known wood burner
manufacturers approve is that we know how to ensure systems are
safe. Again this is a patented system we have developed ourselves
and is available no where else.
It is also worth pointing
out that there are two other forms of overheat protection built into
Xcel Heat Bank systems. The first is an overheat thermostat that
turns on the central heating when the store reaches 90°C. This
protection is the normal day-to-day protection and requires power
supplies to be on, and pumps to be functional. The other form of
protection is the system is open vented. Whatever happens and if
ever the system does boil, you have peace of mind that the vent pipe
will protect the system from catastrophic failure.
- Protects against
system boiling even during a power cut.
- Often the only
way to comply to latest building regulations.
- Approved by most
wood burner manufacturers.
- Patented
technology.
4. Future Proofed
When we designed the Xcel,
the whole intention was to come up with a Heat Bank design that was
suitable for 95% of the enquiries we received. Before the Xcel
everything was custom made to order, and quite often customers would
come back at a later date asking how they could retro-fit another heat
source - a wood burner for example. The Xcel was given enough
connection points to allow almost any combination of heat sources and
loads to be connected, as well as a solar coil.
It is not just enough to put
on lots of connection points. They must be of the right size and
in the right position, and thankfully our 25 years experience in
designing multifuel thermal stores has allowed us to perfect the
connection arrangement to make everything work as it should. For
example, how many makes of thermal store provide two 1.1/2" connections
for wood burners to ensure thermo-syphon works even on larger wood
burner?
 It is safe to
say that by fitting an Xcel Heat Bank you will never need to change the
system ever again, whatever heat sources to wish to connect in
future. We know from experience that having a future proofed Xcel
system adds value to a property, although difficult to put a value on.
In summary the Xcel Heat
Bank can connect to all the following - at the same time !
- Gas, Oil, or
Wood Pellet Boilers
- Solar Panels
- Wood Burners
- Heat Pump
- Immersion
Heaters (up to three)
- Radiators
- Underfloor
Heating
- Multiple Hot
Water Outlets
5. Build Quality
When we say the Xcel Heat
Bank should never need changing, whatever you decide to do in future,
this is really only valid if the quality of the system is good enough
to last a long time.
The Xcel is manufactured for
us from Duplex Stainless Steel, and connections are manufactured
in-house without skimping on metal. The welding on the Xcel is
performed in the same factory that manufactures nuclear waste
containers for BNFL and as such the quality is second to none.
Although we put a guarantee
of 25 years on the store, the fact that it is also protected by
corrosion inhibitor should result in a system life far longer. We
are unsure how long because none have ever failed or had a single
problem
- Duplex Stainless
Steel Construction
- 25 year Guarantee
6. Prefabricated
Controls
One of the key differences
between the Xcel Heat Bank and other thermal stores is the option to
have the system supplied with all the heating and hot water controls
factory fitted and wired. We have developed over 50 different
assemblies to allow for all the different types and sizes of boilers
out there, as well as the different types of central heating and hot
water controls. These assemblies are selected during the design
process, and are then fitted to the Xcel in such a way that saves a
great deal of space and time during the final installation. We
make sure pumps and valves are specified to the correct sizes to work
with the selected equipment, and setup to work as intended.
Standardised control
assemblies also ensures that service engineers are faced with a known
layout of components, with set documentation and spares. If an
engineer needs to fault find a system years down the line, he can
obtain the correct drawings and documents he needs, and can discuss the
system over the phone with someone who is familiar with the relevant
assemblies and controls. Where controls are put together on site,
the only line of technical backup is usually from the installer that
put the system together and know how it works. If he is unavailable
then it can be very difficult for another engineer to get their head
around the system in order to locate a problem.
The specific design of each
Xcel is stored on the internet for future reference. Any relevant
documentation can also be uploaded to the web site, providing a very
valuable resource for both householders and service engineers in years
to come.
It is worth noting that
after manufacturing and providing on-site backup when things go wrong
for many years, we know what components provide the best
reliability. Xcel Heat Banks are always fitted with the best
there is - not the cheapest.
- Assemblies to
match different types of boilers and heat loads
- Standardised
control layout with supporting documentation
- Reliable
components selected with 25 years experience
6. Over 25 years
Experience, offering the Best Design Service and the Best Backup in the
Industry
Xcel Heat Banks are supplied
with a guarantee that the system will work as intended, along with one
year of on-site backup to correct any issues. The only way this
is possible is by taking customers through a rigorous design process
that identifies potential problems prior to supply of any equipment,
and ensures we have all the data we need to select the type of Xcel and
assemblies with confidence.
Our Online System Designer
has been evolved over many years to help speed up this process, as well
as provide the design tools necessary to take out the guess work.
If there is ever a problem
with an Xcel, we want to know about it, and we want to help fix
it. This is a unique level of service not offered by other
manufacturers, and one that keeps customers coming back as they know
they are in safe hands.
- Systems
guaranteed to work as intended
- One year on-site
backup
- Technical backup
(by phone) for the life of the system
- Over 45
showrooms nationwide, each providing design and service assistance in
addition to our own manufacturers backup
7. The Most
Advanced Renewables Training Facilities in the UK
We do our utmost to ensure that installers have all the tools they need
to perform succesful installations, conforming to the latest
regulations.
- Free Xcel
Installer Courses
- Hetas Training
- MCS Training for
Biomass, Solar and Heat Pumps
8. Continuous
Research and Development
We never stand still. For
the past 25 years we have been at the forefront of thermal storage
design. Just type 'thermal store' into Google to see proof of
this.
At the moment we are working
on the next generation of intelligent control systems that will allow
customers to control their systems from their phone or computer.
Systems will be able to send text messages if ever a fault occurs, and
allow engineers to view graphs of the temperatures around the system
along with the amounts of energy generated by the various heat sources
and where this is used.
We intend for this to tie
into our online design system so that customers designing their own
multifuel systems can look at real data from live systems already
installed, and see how effective they are.
Such advances in technology
will always be made available for existing customers to retro-fit to
their systems, should they wish to take advantage of them.
|
